Lifes Edge

CARL ZIMMER

INTRODUCTION

THE BORDERLAND

In the fall of 1904, the Cavendish Laboratory was full of curious

experiments. Clouds of mercury shuddered with flashes of blue light. Lead cylinders pirouetted on copper disks. The ivy-covered building on

Free School Lane, nestled in the heart of Cambridge, was the most exciting

place for physicists to be, not just in England but in the entire world, a place where they could toy with the fundamental pieces of the universe. Amidst

this forest of magnets and vacuums and batteries, it would have been easy

to overlook one small experiment sitting forlornly by itself. It consisted of

little more than a glass tube capped with cotton, half-filled with a few

spoonfuls of brown broth. But something was coming into being in that tube. In a few months the

world would collectively gasp at it. Newspapers would celebrate the

experiment as one of the most remarkable achievements in the history of

science. One reporter would describe what lurked in the tube as “the most

primitive form of life—the ‘missing link’ between the inorganic and

organic worlds.”

This most primitive life was the creation of a thirty-one-year-old

physicist named John Butler Burke. In photographs from around the time of

the experiment, Burke’s boyish face has a melancholy cast. He was born in

Manila to a Filipino mother and an Irish father. As a boy he traveled to

Dublin for schooling and ended up at Trinity College, where he studied X-

rays, dynamos, and the mysterious sparks released by sugar. Trinity

awarded Burke a gold medal in physics and chemistry. One professor described him as “a man who is gifted with the power of exciting in others

the enthusiasm which he brings to bear upon his own lines of

investigation.” After finishing his studies, Burke moved from Dublin to

England to teach at a series of universities. His father soon died and his

mother—“an old lady of very large means,” as Burke later called her—

supported him with a generous allowance. In 1898, Burke joined the

Cavendish. Nowhere on Earth had physicists learned so much in so little time about

matter and energy. Their most recent triumph, courtesy of the lab’s director,

Joseph John Thomson, was the discovery of the electron. In his first few

years at the Cavendish, Burke followed up on Thomson’s work by running

experiments of his own on the mysterious charged particles, investigating

how electrons could light up clouds of gas. But then a new mystery lured

him away. Like many other young physicists at the Cavendish, Burke

started experimenting with a glowing new element called radium. A few years beforehand, in 1896, a French physicist named Henri

Becquerel had discovered the first evidence that ordinary matter could cast

off a strange form of energy. When he wrapped uranium salts in a black

cloth, they created a ghostly image on a photographic plate nearby. It soon

became clear that the uranium was steadily releasing some kind of potent

particle. To follow up on Becquerel’s work, Marie and Pierre Curie

extracted uranium from an ore called pitchblende. In the process, they

discovered that some of the energy was coming from a second element. They named it radium and christened its new form of energy

“radioactivity.”

Radium unleashed so much energy that it could keep itself warm. If

scientists set a piece atop a block of ice, it could melt its own weight in

water. When the Curies mixed radium with phosphorus, the particles

unleashed by the radium made the phosphorus glow in the dark. As news of

this rare, exotic substance spread, it became a sensation. In New York,

dancers put on radium-coated outfits to perform in darkened casinos. People

wondered if radium would become a mainstay of civilization. “Are we

about to realize the chimerical dream of the alchemists—lamps giving light

perpetually without the consumption of oil?” one chemist mused. Radium

also seemed to have a vitalizing power. Gardeners sprinkled it on their

flowers, convinced it could make them grow bigger. Some people drank

“liquid sunshine” to cure all manner of ills, including even cancer. It was cancer that would eventually claim Marie Curie’s life in 1934,

probably because of the radium and other radioactive elements she worked

with on a daily basis. Now that we understand the deadly risk posed by

radioactivity, it’s hard to imagine how anyone could think that radium could

have vitalizing powers. But in the early 1900s scientists knew surprisingly

little about the nature of life. The best they could say was that its essence

lurked in the jellylike substance in cells, a material they called protoplasm. It somehow organized cells into living things and was passed down from

one generation to the next. Beyond that, little was certain and all manner of

ideas were viable. To Burke, life and radioactivity displayed a profound similarity. Like a

caterpillar becoming a moth, a radium atom could undergo a transformation

that seemed to come from within. “It changes its substance—in a limited

sense it lives—and yet it is ever the same,” Burke declared in a 1903

magazine article. “The distinction, apparently insuperable, that the biologist

holds to exist between living and so-called dead matter, should thus pass

away as a false distinction...

All matter is alive—that is my thesis.”

Burke said all this as a scientist, not a mystic. “We must be careful lest

our imagination should carry us away, and lead us into regions of pure

fancy, to a height beyond the support of experimental facts,” he warned. To

prove his thesis, Burke designed an experiment: he would use radium to

create life from lifeless matter. To carry out this act of creation, Burke prepared some bouillon, cooking

chunks of beef in water and sprinkling in salt and gelatine. Once the

ingredients had turned to a broth, he poured some into a test tube and put it

over a flame. The heat destroyed any cow cells or microbes that might be

lurking in the liquid. All that was left was a sterile bouillon made up of

loose, lifeless molecules. Burke put a pinch of radium salt in a tiny sealed vial, which was

suspended over the broth. A platinum wire wrapped around the vial and

snaked out a side port. To launch the experiment, Burke pulled the free end

of the wire until the vial cracked. The radium tumbled into the broth below. After he let the radioactive broth stew overnight, Burke saw that it had

changed: a cloudy layer had formed on its surface. Burke drew off a little to

see if it was made of contaminating bacteria. He spread it over a petri dish

loaded with food for microbes. If the cloudy layer had any bacteria in it, they would feast until they grew into visible colonies. But no colonies formed. Burke concluded the layer must have been

formed by something else. Taking another sample of the cloudy layer, he

spread it on a glass slide and put it under a microscope. Now he could see

that it contained a scattering of specks far smaller than bacteria. A few

hours later, when he checked again, the specks had vanished. But the next

day they returned, and Burke began drawing them, documenting how they

grew in size and changed in shape. Over the course of the next few days

they turned into spheres, with inner cores and outer rinds. They stretched

into dumbbells. They bulged and pinched into miniature flowers. They

divided. And then, after two weeks, they fell apart. Some might say they

died. As Burke sketched these changing shapes, he could tell they were not

bacteria. It wasn’t just that they were too small. When Burke put some of

them in water, they dissolved away—a fate that bacteria did not suffer. Yet

Burke was convinced these radium-laced blobs were not crystals or any

other familiar forms of lifeless matter. “They are entitled to be classed

among living things,” Burke concluded. He had created “artificial life,” as

he called it—creatures that existed at the far edges of life’s territory. And to these things he gave a name that commemorated the element that gave birth

to them: radiobes. Burke could only guess at how he had created his radiobes. When he

dropped the radium into the broth, the element must have given the

molecules the powers of growth, organization, and reproduction. “The

constituents of protoplasm are in the bouillon,” he later wrote, “but the vital flux is in the radium.”

That December the scientists of the Cavendish Laboratory celebrated

Burke’s discovery at their annual dinner in a back room at a Cambridge

restaurant. Dressed in black tie, they read lyrics written by a physicist

named Frank Horton. They belted out “The Radium Atom” to the tune of an

old music hall song:

Oh, I am a radium atom,

In pitchblende I first saw the day,

But soon I shall turn into helium:

My energy’s wasting away. The physicists sang about the gamma rays and beta rays that radium unleashed, and then they turned to Burke’s experiment:

Through me they say life was created

And animals formed out of clay,

With bouillon I’m told I was mated

And started the life of today. Five months later, on May 25, 1905, Burke published his first report on

radiobes in the journal Nature. He adorned his account of his experiment with three blurry sketches of “highly organized bodies.” Burke ended his

report by christening the bodies as radiobes, thus “indicating their

resemblance to microbes, as well as their distinct nature and origin,” he

said. When the reporters came calling, Burke at first shied away from

claiming too much for his discovery. But they gnawed at his resolve like

termites in old wood. Pointing out that radioactive minerals were turning

out to be surprisingly widespread, Burke speculated that radiobes existed

across the entire planet. “Life may have originated on earth in that way,” he

told one reporter. The public lapped it up. “Has Radium Revealed the Secret of Life?” the

New York Times asked. Burke’s radiobes, they marveled, seem to “tremble between the inertia of inanimate existence and the strange throb of incipient

vitality.”

The news made Burke as famous as his radiobes. “John Butler Burke

has suddenly become the most talked about man of science in the United

Kingdom,” the New York Tribune reported. The Times of London anointed him “one of the most brilliant of our younger physicists,” who had carried

out “one of the supremely great achievements of all time.” Another British

writer judged that “Mr. Burke attained suddenly to a notoriety which, in this

country, is usually reserved for prominent athletes.” Letters full of questions about the radiobes arrived “from the remotest corners of the Earth,” Burke

later recalled. Burke enjoyed his fame. Instead of running more experiments at the

Cavendish, he traveled from lecture hall to lecture hall showing off his

lantern slides. Magazines paid him handsomely for his words. The World’s

Work went so far as to compare Burke to Darwin. Radiobes “provoked

more discussion, perhaps, than any event in the history of science since the

publication of the Origin of Species,” they declared. In 1859, Charles Darwin had laid out a theory of how life evolved. Now, almost a half

century later, Burke was wrestling with an even greater mystery: life itself. Chapman and Hall, one of London’s leading publishers, gave Burke a

contract to write a book about his theory. The Origin of Life: Its Physical Basis and Definition came out in 1906.

Whatever caution Burke originally had was now gone. In his book, he

held forth on the properties of living matter, on the “borderland between

mineral and vegetable kingdoms,” on enzymes and nuclei, on his own

electric theory of matter, and on something he called “mind-stuff.” Burke

unhelpfully described mind-stuff as “perception in the universal mind

which constitutes the ‘great ocean of thought’ in which we live and move

and have our being.”

And with those words Burke reached his Icarus peak. Soon a wave of

brutal reviews of The Origin of Life came out, scoffing at Burke’s hubris. Here was a physicist holding forth on the nature of life when he didn’t even

know the difference between chlorophyll and chromatin. “Biology is

decidedly not his forte,” one reviewer sniffed. An even more devastating verdict soon came from a fellow scientist. W. A. Douglas Rudge, who had also worked at the Cavendish for a few years,

decided to run Burke’s radiobe experiments for himself. He recognized

ways to make them more rigorous—running separate trials with tap water

and distilled water, for example. Instead of Burke’s “mere drawing,” as

Rudge called it, he documented his results with photographs. When Rudge

cooked his broth with distilled water, he discovered, the radium produced

nothing. In tap water, Rudge found some odd shapes, but no sign of the

lifelike radiobes Burke had drawn. Burke tried to smear Rudge as an amateur, but other scientists saw his

report to the Royal Society as the final word on radiobes. “Mr. Rudge has

carried out the experiments that Mr. Burke should have made long ago,”

declared Norman Robert Campbell, a physicist at the Cavendish. “Mr. Rudge has produced convincing evidence that the ‘cells,’ or radiobes, are

nothing but little bubbles of water produced in the gelatin by the action of

the salts upon it.”

In September 1906, Campbell published a vicious attack on Burke. It

was ostensibly a review of The Origin of Life, but it read more like a

character assassination. “Mr. Burke was not educated at Cambridge; he had

been at two universities before he came thither as an advanced student,”

Campbell scoffed. “It is misleading to say, in connection with his recent

publications, that Mr. Burke is ‘of the Cavendish Laboratory.’ He did some

physical research there a few years ago: during his investigations of the

biological properties of his radiobes he merely stored in the room in which

he had done his former work some of the test-tubes in which those bodies

were ‘incubating.’”

It was around this time that Burke stopped working at the Cavendish. Whether he quit or was barred, no one can say. In December 1906 the lab

gathered again for another end-of-the-year dinner. They had cause to

celebrate: Thomson had just won the Nobel Prize. But the song for 1906

was not an ode to the electron. Instead, the mathematician Alfred Arthur

Robb wrote a song set to the tune of “The Amorous Goldfish” from the

1896 musical The Geisha. It was entitled “The Radiobe.”

A radiobe swam in a bowl of soup

As dear little radiobes do,

And Butler Burke gave a wild war whoop

As he over his microscope did stoop,

And it came in the field of view. He said: “This radiobe clearly shows

How all the forms of life arose;

And further plainly shows,” said he,

“What a very great man is J. B.B.!”

In the years that followed, Burke took a long fall—one that only ended

with his death forty years later in 1946.

After he left the Cavendish, no one

offered him a plum professorship. Magazines lost interest in his ideas. He

wrote two sprawling manuscripts but struggled for years to find a publisher. His income from lectures and writing dried up at the same time that his

mother slashed his allowance. During World War I, Burke managed to

support himself with a job inspecting airplanes, but after a few months poor

health forced him to quit. In 1916 he begged the Royal Literary Fund for a

loan to save him from “the dreaded event of bankruptcy.” They turned him

down. As a young man, Burke had seemed on the verge of defining life, of

charting its borders. But life got the better of him. In 1931, a quarter century after his brief fame, he published a dubious magnum opus, The Emergence

of Life. It was a rambling mess. “Burke had gone right off the deep end,”

the historian Luis Campos later wrote. In the book, Burke flirted with

levitation and other psychic phenomena. He remained fiercely loyal to his

radiobes, which the world had long forgotten. He argued that life emerged

from what he called “time-waves” that flowed between units of mind that

make up the universe. The more Burke thought about life, the less he understood it. At one

point in The Emergence of Life, he offered a definition of life, but it sounded more like a cry for help: “Life is what IS.”

—

I never learned about Burke when I was growing up. I was taught the

standard pantheon of biologists, which is mostly made up of scientists with

ideas that turned out to be right: Darwin and his tree of life, Mendel and his

genetic peas, Louis Pasteur and his disease-causing germs. It’s easier that

way: to leapfrog from one designated hero to the next—to ignore the

mirages along the way, the failures, the fame that curdled. When I started writing about biology, I still didn’t learn about Burke. I

have had the good fortune to get to know many forms of life and many of

the scientists who study them. I’ve hauled hagfish out of the North Atlantic,

hiked into North Carolina longleaf pine forests to find Venus flytraps in the

wild, and spotted orangutans lounging high in the canopies of Sumatran

jungles. Scientists have shared with me what they’ve learned about the

marvelous slime that hagfish make, the insect-destroying enzymes in

carnivorous plants, the tools orangutans fashion out of sticks. The beams of their scientific flashlights are bright, but only because

they are narrow. Someone who spends her life tracking orangutans doesn’t

have enough time to become an expert on Venus flytraps. Venus flytraps

and orangutans have something profoundly important in common—they are

alive—and yet asking biologists about what it means for something to be

alive makes for an awkward conversation. They’ll demur, stammer, or offer

a flimsy notion that crumbles under even a little scrutiny. It’s just not

something that most biologists give much thought to in their day-to-day

work. This reluctance has long mystified me, because the question of what it

means to be alive has flowed through four centuries of scientific history like

an underground river. When natural philosophers began contemplating a

world made of matter in motion, they asked what set life apart from the rest of the universe. The question led scientists to many discoveries but also

many blunders. Burke was hardly alone. For a brief time in the 1870s, for

example, many scientists came to believe that the entire ocean floor was

carpeted with a layer of throbbing protoplasm. More than 150 years later,

despite all that biologists have learned about living things, they still cannot agree on the definition of life. Puzzled, I set out on a trip. I started out in the heart of life’s territory: in the confidence that each of us has that we are alive, that we have a life that

is bounded by birth on one side and by death on the other. Yet we feel our

own life more strongly than we understand it. We know that other things are

alive, too, like snakes and trees, even if we can’t ask them. Instead, we rely

on the hallmarks that all living things seem to have. I took a tour of these

hallmarks, getting to know creatures that display them in their most

impressive, most extreme forms. Eventually my travels took me out to life’s

edge, to the foggy borderland between the living and the nonliving, where I

encountered peculiar things with some of life’s hallmarks but not others. It

was here, at last, that I first encountered John Butler Burke and came to

appreciate that he deserves a place in our memory. It was here that I met his

scientific descendants who still grope their way around life’s edge, trying to

figure out how life began or how weird it might get on other worlds. Someday humanity may draw a map that will make this journey easier. In a few centuries, people may look back at our understanding of life and

wonder how we could have been so blinkered. Life today is like the night

sky four centuries ago. People gazed up at mysterious lights that wandered,

streaked, and flared across the dark. Some astronomers at the time were

getting the first inklings of why the lights traced their particular paths, but many of the explanations of the day would turn out to be wrong. Later

generations would look up and instead see planets, comets, and red giant

stars, all governed by the same laws of physics, all manifestations of the

same underlying theory. We don’t know when a theory of life might arrive,

but we can hope, at least, that our own lives last long enough to let us see it. PART ONE

THE QUICKENING

THE WAY THE SPIRIT

COMES TO THE BONES

As I made my way down the hairpin road, a sage brush–studded wall

of sand to my right, I felt keenly aware of my own life. I could feel

the steep slope in my legs. After a series of tight turns, the wall

swung away, revealing a long, desolate beach. It ran northward, a sash of

coast between high, slumping cliffs and the Pacific. Out over the sea, the

sun hid behind clouds, a sky-wide bank of white. Earlier that day, in my

hotel room, my phone had informed me the sky was cloudy and the

temperature was in the low seventies. My brain responded to that

information by choosing a light, long-sleeved shirt for my walk to the

beach. And now my brain was updating its decision without cc’ing my

conscious self. Nerves sprinkled throughout my skin sensed the humidity and

temperature of the layer of air encasing my body. Voltage spikes traveled

from the nerve endings along long branches known as dendrites until they

reached the cores of the nerves, called the somas. From there, new signals

raced onward along long, cable-shaped extensions called axons. The axons

reached my spine and traveled up toward my head. From neuron to neuron,

the signals from the outside world made their way into my brain and finally

to a nub of neurons deep inside my skull. Those neurons combined the Morse code readout from across my body

to generate new, different signals. They carried commands instead of

sensations. The new voltage spikes left my brain along outward-bound

axons, through my brain stem and down my spinal cord, until they reached

millions of glands in my skin. There, they created electric charges in twisted

tubes that wrung water out of the surrounding cells. Sweat ran down my back. My conscious self was annoyed with the brain that generated it. One of

the few shirts I had brought with me was now drenched in salt water. I

could not actually sense the trill of voltage spikes that shuttled information

from skin to brain. I didn’t feel a surge of blood in the center of my head as

the heat-regulating part of my brain swung into action. In the moment, by

the sea, I simply felt myself sweating. I felt annoyed. I felt alive. As I felt aware of my own life, I also recognized other lives on the

beach. A man walked lazily south, carrying a white-and-blue surfboard. Far

to the north, a paraglider launched off from the top of the cliffs. The

corkscrewing of the yellow paraglider wing spoke of intentions that arose in

some human’s brain and produced signals to hands gripping brake handles. Along with human life, I could see feathered life as well. Sandpipers

skittered along the surf. Their seed-sized brains sensed the flash of

incoming waves and the cold foam around their legs, contracting muscles to

keep their bodies upright, to scuttle to higher ground, to poke the sand for

buried snails. The snails didn’t quite have brains but rather fretworks of

nerves that produced signals of their own for slowly, relentlessly burying

their bodies into the earth. I contemplated the thousands of other

subterranean nervous systems inside the mud dragons and the Pismo clams

and other creatures buried below my feet. Out in the ocean, down the

underwater canyon, other brains were swimming, carried along inside the

buoyant bodies of leopard sharks and stingrays while the nerve nets of

jellyfish drifted by. After a few minutes of walking along the water, I stopped and looked

down. A gigantic neuron, six feet long, lay on the sand. Most of it was

made up of a glistening, caramel-colored axon. It curved gently like a

heavily insulated electric cable. At one end it swelled into a bulb-shaped

soma, which was crowned in turn by branches of dendrites. It could have

been all that survived from a kraken that died in a battle with a pod of killer whales somewhere between here and Hawaii. This fantastical neuron was, in fact, a stalk of elk kelp. It had washed up

from an underwater forest a mile out to sea. What I had imagined to be an

axon was the kelp’s stipe, a trunk that not long ago anchored the organism

to the ocean floor. What looked like a neuron’s soma was in reality a gas-

bloated bladder that kept the kelp upright in the ocean currents. The

branching dendrites were the elk kelp’s antlers, on which long blades had once grown. And the blades acted like the leaves of plants, catching what

little sunlight filtered down through the seawater and fueling the growth of

the elk kelp to heights that rivaled the palm trees that crowned the cliffs

behind me. The kelp had the kind of complexity that marks living things. But as I

looked down at it, I could not say whether this particular kelp was still

alive. I couldn’t ask it how its day was going. It had no heartbeat I could

check, no lungs to lift and lower a chest. But the kelp still glistened, its

surfaces intact. Even if it could no longer capture sunlight, its cells might

still be carrying on, using up its remaining fuel to repair its genes and

membranes. At some point, maybe today or next week, its death would

become certain. But along the way, it would also become a part of life on land. Microbes

would feast on its tough cuticles. Beach hoppers and kelp flies would

follow, nibbling on its tender tissues. These wrack-feasting creatures would

themselves become food for the sandpipers and terns. Plants would be

fertilized by the kelp’s nitrogen soaking into the ground. And a sweaty

human being, his brain packed with thoughts of brains on this beach, would

carry away in his neurons a memory of the kelp’s neuron-like body. —

The next morning I walked along the tops of the cliffs. North Torrey Pines

Road cut north through La Jolla, California, alongside groves of looming

tower cranes. With a stream of rush-hour traffic flowing by me, it was hard

to remember the ribbon of wild coast tucked away close by. I crossed a

eucalyptus-lined parking lot to get to the Sanford Consortium for

Regenerative Medicine, a complex of glassed-in labs and offices. Once

inside, I found my way to a third-floor laboratory, and there I met a scientist named Cleber Trujillo—Brazilian-born, with a close-cropped beard. Together we suited up in blue gloves and smocks. Trujillo led me to a windowless room banked with refrigerators,

incubators, and microscopes. He extended his blue hands to either side and

nearly touched the walls. “This is where we spend half our day,” he said. In that room Trujillo and a team of graduate students raised a special

kind of life. He opened an incubator and picked out a clear plastic box. Raising it above his head, he had me look up at it through its base. Inside

the box were six circular wells, each the width of a cookie and filled with what looked like watered-down grape juice. In each well a hundred pale

globes floated, each the size of a housefly head. Every globe was made up of hundreds of thousands of human neurons. Each had developed from a single progenitor cell. Now these globes did

many of the things that our own brains do. They took up nutrients in the

grape-juice-colored medium to generate fuel. They kept their molecules in

good repair. They fired electrical signals in wavelike unison, keeping in

sync by exchanging neurotransmitters. Each of the globes—which scientists

call organoids—was a distinct living thing, its cells woven together into a

collective. “They like to stay close to each other,” Trujillo said as he looked at the

undersides of the wells. He sounded fond of his creations. The lab where Trujillo worked was led by another scientist from Brazil

named Alysson Muotri. After Muotri immigrated to the United States and

became a professor at the University of California at San Diego, he learned

how to grow neurons. He took bits of skin from people and gave them

chemicals that transformed them into embryo-like cells. Dousing them with

another set of chemicals, he steered them to develop into full-blown

neurons. They could form flat sheets covering the bottom of petri dishes,

where they could crackle with voltage spikes and trade neurotransmitters. Muotri realized that he could use these neurons to study brain disorders

that arose from mutations. Instead of carving out a piece of gray matter

from people’s heads, he could take skin samples and reprogram them into

neurons. For his first study, he grew neurons from people with a hereditary

form of autism called Rett syndrome. Its symptoms include intellectual

disability and the loss of motor control. Muotri’s neurons spread their kelp-

like branches across petri dishes and made contact with each other. He

compared them to the neurons he grew from skin samples taken from

people without Rett syndrome. Some differences leaped out. Most

noticeably, the Rett neurons grew fewer connections. It’s possible that the

key to Rett syndrome is a sparse neural network, which changes the way

signals travel around the brain. But Muotri knew very well that a flat sheet of neurons is a far cry from a

brain. The three pounds of thinking matter in our heads are a kind of living

cathedral, if a cathedral were built by its own stones. Brains arise from a

few progenitor cells that crawl into what will become an embryo’s head. They gather together to form a pocket-shaped mass and then multiply. As the mass grows, it extends long, cable-like growths out in all directions,

toward the forming walls of the skull. Other cells emerge from the

progenitor mass and climb up these cables. Different cells stop at different

points along the way and begin growing outward. They become organized

into a stack of layers, known as the cerebral cortex. This outer rind of the human brain is where we carry out much of the

thinking that makes us uniquely human—where we make sense of words,

read inner lives on people’s faces, draw on the past, and plan for the distant

future. All the cells that we use for these thoughts arise in a particular three-dimensional space in our heads, awash in a complex sea of signals. Fortunately for Muotri, scientists came up with new recipes to coax

reprogrammed cells to multiply into miniature organs. They made lung

organoids, liver organoids, heart organoids, and—in 2013—brain

organoids. Researchers coaxed reprogrammed cells to become the

progenitor cells for brains. Provided with the right signals, those cells then

multiplied into thousands of neurons. Muotri recognized that brain

organoids would profoundly change his research. A disease like Rett

syndrome starts reworking the cerebral cortex from the earliest stages in the

brain’s development. For scientists like Muotri, those changes happened

inside a black box. Now he could grow brain organoids in plain view. Together, Muotri and Trujillo followed the recipes that other scientists

laid down for making organoids. Then they began creating recipes of their

own to make a cerebral cortex. It was a struggle to find the blend of

chemicals that could coax the brain cells onto the right developmental path. The cells often died along the way, tearing open and spilling out their

molecular guts. Eventually the scientists found the correct balance. They

discovered to their surprise that once the cells set off in the right direction, they took over their own development. No longer did the researchers have to patiently coax the organoids to

grow. The clumps of cells spontaneously pulled away from each other to

form a hollow tube. They sprouted cables that branched out from the tube,

and other cells traveled along the cables to form layers. The organoids even

grew folds on their outer surface, an echo of our own wrinkled brains. Muotri and Trujillo could now make cortex organoids that would grow to

hundreds of thousands of cells. Their creations stayed alive for weeks, then

months, then years. “The most incredible thing is that they build themselves,” Muotri told me. On the day I visited Muotri’s lab, he was checking in on some organoids

he had sent into space. He sat in his office, a glass box perched out on a

balcony next to the lab. Muotri had a gentle, relaxed manner, as if he might

at any moment take off early from work, scoop up the scarred surfboard

leaning against the wall by his desk, and head for the water. But today he

was focused on the most extravagant of his many experiments. Outside his

window, the paragliders were taking flight in the distance. He paid them no

mind. Aboard the International Space Station, 250 miles above Muotri’s

head, hundreds of his brain organoids were sitting inside a metal box. He

wanted to know how they were faring. For years astronauts aboard the space station had run experiments to see

how cells grow in low Earth orbit. As they free-fell around the planet, the

cells no longer experienced the same tug of gravity that has pulled on all

life on Earth for the past 4 billion years. Strange things happen in

microgravity, it turned out. In some experiments, the cells grew faster than

they would on the ground. They sometimes became bigger. Muotri was

curious to see if his organoids would grow into larger clusters in space and

perhaps become more like our own brains. When they won approval from NASA, Muotri, Trujillo, and their

colleagues began collaborating with engineers to build a home for

organoids in space. They designed an incubator that could nurture the

organoids, keeping the conditions right for their development. A few weeks

before I visited the lab, Muotri had poured a fresh batch of miniature brains

into a vial, which he put in a backpack. Standing in the security line at San

Diego International Airport, he had no idea what he’d say if anyone asked

what was in the tube. These are a thousand miniature brains I’ve grown in

my lab, and I’m about to send them into space. Apparently, organoids don’t grab that kind of attention. Muotri managed

to board his flight without getting questioned. When he got to Florida, he

handed the tube over to the engineers for a flight aboard a supply rocket. A

few days later Muotri watched the SpaceX Falcon 9 rise from the earth. When the payload arrived at the space station, the astronauts grabbed

the box loaded with organoids and plugged it into a bay. There it sat for a

month. When the experiment was over, the astronauts would dunk the

organoids in alcohol. They would die, but their lives would be frozen at the

moment of death. Once they fell back into the Pacific, were fished out, and were delivered to Muotri’s lab, he’d be able to inspect their cells and see

which genes they had used in space. The entire effort depended on the organoids surviving till their

appointed end, and Muotri didn’t know whether they’d make it. To keep

track of the organoids during their month in space, he had arranged for

miniature cameras to spy on them, taking pictures every thirty minutes. The

space station transmitted the photos down to Earth, and eventually Muotri

could log into a remote server to grab them. When he downloaded the first batch of images from early in the

mission, they turned out to be a mess. Air bubbles blocked his view. For

three weeks he had no idea how his organoids were doing. Now I watched

Muotri connect to the server once more. He found a new image from the

space station to download. The massive file decompressed and the picture

appeared, stripe by stripe, on his screen. “Oh!” Muotri called out. He laughed in disbelief. “I can actually see

them!”

He moved his face close to the screen to inspect the image. Half a dozen

gray spheres floated on a beige background. “Yeah, they all look quite good,” he said. “They’re rounded, and they

more or less have the same size. You don’t see them fusing or clustering

together.” He rolled his chair back from his computer. “So this is all good

news. I’m happy. This is fantastic.”

Even in space, Muotri could tell his organoids were alive. In late 2015, Muotri and Trujillo got their first chance to use their

organoids to learn something about brains. In Brazil, doctors were

struggling to understand why the brains of thousands of babies were

drastically deformed. Their cerebral cortices were practically missing. It

turned out that their mothers had been infected by a mosquito-borne virus

called Zika, which had never before been found in the Americas. Muotri

and Trujillo got a supply of Zika viruses and began infecting brain

organoids. They wondered if they’d see a change. “It was night and day,” Muotri told me. The Zika viruses immediately destroyed progenitor cells in young

organoids. Without those cells, an organoid could not sprout cables to build

a cortex. The experiments revealed that Zika viruses do not kill the cerebral

cortex, so much as prevent it from growing in the first place. Once the

scientists figured out how Zika viruses wreak their havoc, they were able to discover drugs that could block them. Those drugs then went into tests on

animals to see if they could help prevent brain damage. Word spread that Muotri was growing brain mimics by the thousands. Graduate students and postdoctoral researchers wanted in. When they

joined his lab, they first had to train with Trujillo for months, learning the

fine art of making organoids. I asked a graduate student named Cedric

Snethlage to describe his education. Making a brain organoid wasn’t just a

matter of reading temperatures and pH levels off a protocol, he explained. Snethlage had to learn how to carry out each step by intuition—how far, for

example, to tilt the wells to keep the organoids from sticking to the bottom. I told Snethlage that he sounded like he had just gone through cooking

school. “It’s more like making a soufflé than making chili,” he said. Snethlage wanted to learn how to grow organoids to study neurological

disorders. Other graduate students had come to Muotri’s lab to discover

how to make organoids more brain-like. Brain cells need nutrients and lots

of oxygen to thrive, and the ones at the center of an organoid can starve. So

some of Muotri’s students were adding new cells to organoids that could

develop into artery-like tubes. Others were adding immune cells to see if

they might sculpt the branches of the neurons into more natural shapes. Meanwhile, Cleber Trujillo’s wife, Priscilla Negraes, began listening to

the chatter going on between the organoid cells. When a brain organoid reaches a few weeks in age, its neurons become

mature enough to generate spikes of voltage. Those spikes can travel down

an axon and trigger neighboring neurons to fire as well. Negraes and her

colleagues created an eavesdropping device that could pick up the crackle. At the bottom of miniature wells, they placed eight-by-eight grids of

electrodes. They filled the wells with broth and rested an organoid atop

each array. On her computer, the readout from the electrodes formed a grid of sixty-

four circles. Whenever one of the electrodes detected a firing neuron, its

circle swelled, turning from yellow to red. Week after week the circles

reddened and swelled more often, but there was no pattern Negraes could

see to the bursts. The cells in the organoids spontaneously fired on their

own from time to time, creating neurological static. But as the organoids got more mature, Negraes thought she saw some order emerge. Sometimes a few of the circles would all suddenly swell red

together. Eventually all sixty-four electrodes registered signals at once. And

then Negraes began to see them turn on and off in what looked like waves. Was Negraes seeing actual brain waves developing in the organoids?

She wished that she could compare the patterns she was seeing in her wells

with the developing brains of human fetuses. But scientists had yet to figure

out how to detect their electrical activity in the womb. The closest that

anyone had managed was to study babies born premature, putting miniature

EEG caps on their orange-sized heads. Negraes and her colleagues enlisted a University of California, San

Diego, neuroscientist named Bradley Voytek and his graduate student

Richard Gao to compare organoids to premature babies. The earliest-born

babies, with the least developed brains, produced sparse bursts of brain

waves separated by long spells of disorganized firing. The babies that were

born closer to term had shorter lulls, their bursts of brain waves growing

longer and more organized. Organoids displayed some of the same trends as

they got older. When a young organoid first began making waves, they

came in sparse bursts. But as the organoid developed over months, they

grew longer and better organized, their lulls growing smaller. This unsettling discovery did not mean that Negraes and her colleagues

had created baby brains. For one thing, a human infant’s brain is a hundred

thousand times bigger than the biggest organoids. For another, the scientists

only mimicked one part of the brain—the cerebral cortex. A working

human brain has many other parts: a cerebellum, a thalamus, a substantia

nigra, and on and on. Some of its parts take in smells. Others handle sight. Still others make sense of different kinds of input. Some parts of the brain

encode memories; some jolt it with fear or joy. Still, the scientists were unsettled. And they had every reason to suspect

that, with more research, brain organoids might become more brain-like. A

blood supply might let them grow bigger. Researchers might connect a

cerebral cortex organoid to a retinal organoid that could sense light. They

might link it to motor neurons that could send signals to muscle cells. Muotri even dabbled with the idea of linking an organoid to a robot. What might happen then?

When Muotri started growing organoids, he

assumed they could never become conscious. “Now I’m more unsure,” he

confessed. So were bioethicists and philosophers. They began gathering to talk about brain organoids and how to think about them. I called one—a

Harvard researcher named Jeantine Lunshof—to get her opinion. Lunshof wasn’t too worried about Muotri accidentally creating

conscious creatures in a dish. Brain organoids were so small and simple that

they still fell far below that threshold. What concerned her was a simple

question: What on earth are these things?

“In order to say what you should do with it, you first have to say, ‘What

is it?’” Lunshof explained to me. “We’re making things that were not

known ten years ago. They were not in the catalog of philosophers.”

In La Jolla, Lunshof’s question came to my mind as Trujillo showed me

his latest batch of organoids. “This is just a mass of cells,” he said, pointing to one of his wells. “It

does not get close to a human brain. But we have the tools to make a more

complex mini-brain.”

“So you feel okay with this,” I said, groping for the right words,

“because obviously it’s not a human brain—”

“Human cells!” Trujillo clarified. “So they’re alive,” I half said, half asked. “Yes,” Trujillo replied. “And they’re human.”

“But they’re not a human being?”

“Yes,” he said. “But where would you start to approach that line?” I asked. Trujillo had me imagine an organoid rigged up to an electrode. “You can

do a pattern of electrical shocks,” he said. Trujillo was sitting in front of a microscope as we talked. He extended

two of his fingers and rapped them on the counter, producing galloping

beats. Ba-bap, ba-bap, ba-bap. He suspended his hand over the counter. “And then we stop.”

After a few seconds Trujillo brought down his fingers again. Ba-bap,

ba-bap, ba-bap. “And then the thing fires,” he said. In response to the incoming signal,

the organoid uses its neurons to create a matching signal of its own. “That’s

a bit more concerning. It’s learning something.”

We are badly equipped to make sense of these crackling spheres. Our

problem is not simply that brain organoids are new. If you get a new

smartphone for your birthday, it may take you a little while to figure out how to unlock it, but it doesn’t cause a philosophical crisis. Brain organoids

are troubling because we feel in our bones that making sense of life should

be easy. These clusters of neurons prove that it’s not. To decide whether brain organoids are alive or not, we compare them to

the life we know best, the benchmark against which we judge all other

possible kinds of life: our own. If someone asks you if you’re alive, you

don’t need to check your pulse or prove to yourself that your cells are

breaking down carbohydrates before answering yes. It’s just a deeply

experienced fact. “We know what it feels like to be alive,” the biologist J. B. S. Haldane

observed in 1947, “just as we know what redness, or pain, or effort are.”

These chunks of knowledge seem powerfully obvious. And yet, Haldane

observed, “we cannot describe them in terms of anything else.”

People can lose this sense of what it feels like to be alive without

actually dying. To the contrary, they insist they are dead. The condition is

rare, but people suffer from it often enough that it has earned a name:

Cotard’s syndrome. In 1874 the French physician Jules Cotard examined a woman who had

been admitted to a hospital after becoming suicidal. He wrote in his note

that she “affirms she has no brain, no nerves, no chest, no stomach, no

intestines; there’s only skin and bones of a decomposing body.” The fact

that she could express this conviction in fully formed sentences did not

sway her from it. In the generations since, more accounts of Cotard’s syndrome have

surfaced. In Belgium a woman became convinced her whole body was a

translucent husk. She refused to bathe for fear that she would dissolve and

vanish down the drain. A man in Germany informed his doctors that he had

drowned in a lake the year before. The only reason he could explain his

condition to them was that radiation from cell phones had turned him into a

zombie. Because Cotard’s syndrome is so rare, neuroscientists have managed to

study only a few of the brains of people who experience it. In 2015, Indian

doctors described the case of a woman who told her family that cancer had

rotted her brain and then claimed her life. An MRI revealed that her skull

still contained a working brain. But the doctors noticed that a region a few

inches behind her eyes was damaged. This region, known as the insular cortex, receives signals from across our body. It then generates a conscious awareness of our internal sensations. The insular cortex becomes active when we’re thirsty, experience an

orgasm, or have an uncomfortably full bladder. The signals that flow into the insular cortex may be crucial to our

intuitive sense of being alive. If it gets damaged, that intuition may abruptly vanish, producing Cotard’s syndrome. Our brains constantly update their

picture of reality to suit the signals they process. When people no longer get

information about their internal state, they update reality to make sense of

the change. The only explanation that makes sense is that they’re dead. We don’t just know what it feels like to be alive, however; we also

recognize life beyond our own skin. For our brains, recognizing other living

things is a bigger challenge, since our nerves don’t reach into their bodies. We have to bridge the gap with the signals we take in with our sensory

neurons—in other words, what we see, hear, smell, taste, and touch. To speed up this recognition, we use unconscious shortcuts. We take

advantage of the fact that living things can direct their own motion toward

their own goals. As wolves run down a hillside in pursuit of a moose, they

dodge trees and look for ways to cut off their prey. A boulder tumbling

down that same hill falls predictably and passively. Our brains are tuned to

these differences, recognizing whether an object is showing biological or

physical motion in a fraction of a second. Scientists have found that we can perceive living things so quickly

because we only need a tiny amount of information to trigger biological

circuits in our brains. In one series of experiments, psychologists filmed

people walking, running, and dancing and marked their joints in each video

frame with ten dots. They showed movies of these moving dots to people,

interspersed with movies of ten dots moving independently of each other. People could quickly tell the difference. Our perceptions are not the only feature of our brain tuned to life. Our

memories are as well. As we build up information about things, we file it in

our brains according to whether they are alive or not. Brain damage can

expose our filing system. People with damage to certain regions struggle to

name living things such as insects and fruits. And yet they have no trouble

with toys or tools. Psychologists have long wondered to what extent we’re born making

these distinctions and how much we learn them as we grow up. After all,

you can immediately recognize the words in this sentence, but that doesn’t mean you were born with that skill. Experiments on children suggest that

their intuitions about life are present from the start. Infants prefer to look at dots that move in biological patterns rather than random ones. They will

look longer at geometrical shapes that seem to be self-propelled than ones

that seem to move passively. Children also have a bias toward life in the

way they learn: they can learn about animals faster than inanimate objects,

and they hold on to the memories of what they learn longer. Our knowledge

of life, in other words, arises long before we can tell ourselves what we

know. “If we carve the human mind at its joints,” the psychologist James

Nairne and his colleagues have written, “the distinction between living and

nonliving things forms a natural place to cut.”

Our sense of living things is far older than our species. Experiments on

animals have revealed they can make some of the same distinctions

between the living and the nonliving that we do. In 2006, Giorgio

Vallortigara and Lucia Regolin, two Italian psychologists, made a dot movie

of their own, but they filmed chickens rather than humans and then showed

their movies to newly hatched chicks. If the hen-shaped dots faced the left,

the chicks tended to turn that way as well; they tended to turn right if the

hen was facing that way. Vallortigara and Regolin didn’t observe this

behavior when they showed the chicks movies of random dots or if they

turned the hen-shaped dots upside down. Studies such as these suggest that animals have used visual shortcuts for

millions of years to recognize other living things. This strategy allowed

predators to quickly spot prey. It was good for the prey, too, because it

provided crucial information for making a safe escape. Evading a wolf and

evading a falling boulder call for two very different—and very quick—

reactions. About 70 million years ago our earliest primate ancestors inherited this

ancient instinct for life. But in their subsequent evolution they gained new

ways to recognize living things. Their descendants evolved powerful eyes

and big brains, with complex networks of neurons that merged their vision

with other senses. Along the way, some species of primates became

intensely social, often living in large groups. To thrive in a society, they had to become keenly sensitive to the faces of other primates, reading

expressions and tracking gazes. Our ape ancestors arose about 30 million years ago. They evolved even bigger brains, along with a deeper understanding of their fellow apes. Our

closest living ape relatives, the chimpanzees and bonobos, can use subtle

cues in faces and voices to infer what others are feeling and what they

know. They do not have a language to put these inferences into words. Ask

a chimpanzee to define life, and you’ll be sorely disappointed. Yet an ape

still has a deep sense of its fellow apes as living things—the same sense we

inherited when our ancestors split off into their own lineage 7 million years

ago. The brain continued to grow in the human lineage; our species has the

biggest brain in the animal kingdom relative to our body size. Our ancestors

also evolved the capacity for language and an even more powerful ability to

get into the heads of other humans. But all these features evolved on top of

the foundation we inherited from earlier primates. And that deep foundation

may account for our overweening confidence that we know what it means

to be alive, even when we don’t. —

When a new member of our species was born, our ancestors could use their

biology-sensing brain circuits to recognize another living human. But they

had not evolved any intuition about how that new human life had come

about. Instead, people came up with explanations. In Ecclesiastes, for example, we read about “how the spirit comes to the

bones in the womb of a woman with child.” Jewish scholars would later

teach that the embryo is “mere water” until the fortieth day. Christian

theologians combined the Bible with Greek philosophy to create a different

explanation. In the thirteenth century, Thomas Aquinas described a process

of “ensoulment.” He argued that human embryos first gained a vegetative

soul, with the same faculties for growth as plants. The vegetative soul was

later replaced by a sentient soul like that of an animal. And later the sentient soul was finally replaced in turn by a rational soul. Other cultures created their own explanations. The Beng, a group of

rural villagers in the Ivory Coast, see the beginning of life as the journey

from another world. Babies are spirits from wrugbe, a settlement occupied by the dead. Only a few days after birth, when the umbilical cord stump

falls off, does a newborn truly belong to this world. If it should die before

then, the Beng give it no funeral. There is no death to observe. Beliefs about how living things get their start gave rise to customs and laws around pregnancy. For ancient Romans a human life began with its

first breath. Roman doctors and healers regularly induced abortions in

pregnant women by giving them herbs. But a woman had no say in whether

she could get an abortion; the decision lay entirely with the patriarch of her

family. In medieval Europe, Christian theologians held that fetuses had

souls, which meant that abortion was a crime. Yet they debated about

exactly what that rule meant for actual pregnancies. Aquinas’s followers

argued that a distinction had to be made between the early and late stages of

pregnancy. In 1315 a theologian named John of Naples gave physicians

guidance for cases in which a pregnancy threatened a woman’s life. If the

fetus was not yet ensouled, the physician should provide the abortion. “Although he impedes the ensoulment of a future fetus, he will not be the

cause of death of any man,” John declared. If a fetus had already gained a rational soul, on the other hand, a

physician should not try to save the mother’s life with an abortion. When

“one cannot help one without hurting the other,” John wrote, “it is more

appropriate to help neither.”

The trouble with this kind of guidance was that no one had any idea of

exactly when a fetus became ensouled. Some theologians believed the best

way for physicians to deal with this uncertainty was to never perform an

abortion. Others left the matter up to a physician’s conscience. In the

sixteenth century, judges in Italy set the threshold for ensoulment at forty

days after conception. And in 1765 the British judge William Blackstone

came up with a new standard: the quickening. “Life is the immediate gift of God, a right inherent by nature in every

individual,” Blackstone wrote, “and it begins in the contemplation of law as

soon as an infant is able to stir in the mother’s womb.”

The American colonies adopted quickening as their standard, too. And

for generations abortions were a quiet fact of American life. Pregnant

women who sought out abortions suffered little penalty. Housewives

medicated themselves with abortion-inducing plants they grew in their

gardens. Later, in the industrial revolution, women flocked from farms to

cities, where they tried to induce abortions with “female monthly pills”

advertised in newspapers. These crude abortion-inducing drugs often failed,

forcing the women to find doctors who would surgically carry out the

procedure in secret. Over the course of the nineteenth century, the opposition to abortion grew more organized. Pope Pius IX declared abortion a mortal sin—even

before the quickening. In the United States, anti-vice crusaders warned that

access to abortions tempted women into sinful lives. The American Medical

Association agreed, and prominent doctors gave speeches about the dangers

that abortions posed to fetuses and to pregnant women alike. In 1882 a

Massachusetts doctor named Charles A. Peabody delivered one such attack,

calling on his fellow physicians to resist the pleas of pregnant women for

abortions. “It is a sin against God—a crime of the deepest dye,” Peabody warned. For a doctor like Peabody, educated in late nineteenth-century medicine,

the terms of battle over pregnancy were profoundly different from those in

earlier centuries. Medieval scholars had little idea of what happened inside

a uterus. They relied on the Bible, Aristotle, and a few fetal kicks. Peabody

lived at a time when scientists studied sperm, eggs, and fertilization. They

tracked the development of embryos. In the late 1800s many scientists still

thought of life in terms of a mysterious vital force, the fundamental role of

genes and chromosomes still decades away from discovery. Those vital

forces were unleashed at the moment of conception. “When does life begin?” Peabody asked. “Science returns but one

answer: no other is possible. Life begins at the beginning, with the first

moving of the vital principle, with the first co-ordination of its forces.”

According to this line of reasoning, the law could not use quickening as

a line for legal abortions. “No!” Peabody thundered. “Life begins at the

beginning, and along the way of his natural journey a human being has a

right to his life.”

By the time Peabody delivered this attack in 1882, many American

states had already passed strict laws banning abortions. Yet loopholes

allowed doctors to keep carrying out the procedure as they saw fit. Sometimes they performed abortions for the health of the mothers. Depression, suicide, or extreme poverty could be justification enough. Many doctors were willing to perform abortions for victims of rape. Only

rarely did these abortions come to light. And rarer still did a doctor get

arrested. This invisible, semilegal system lumbered along for decades in the

United States until a new push against abortions in the 1940s suddenly

eliminated many of the safer avenues pregnant women could take. Many

got botched abortions, often self-administered, and showed up in hospitals in droves. Hundreds died every year. Reformers called for a change to the laws. A massive outbreak of

measles in the early 1960s produced a wave of devastating birth defects,

leading to demands from women for access to safe abortions. States

responded by making abortions legal under certain circumstances. In the

1973 case Roe v. Wade, the Supreme Court ruled that criminalizing abortion violated a woman’s right to privacy. States could restrict abortions only

after the first trimester, they ruled, once a fetus became viable to survive

outside of the womb. In their decision, the court addressed the start of life—only to say they

did not have to address it. “We need not resolve the difficult question of

when life begins,” the court declared. “When those trained in the respective

disciplines of medicine, philosophy and theology are unable to arrive at any

consensus, the judiciary, at this point in the development of man’s

knowledge, is not in a position to speculate as to the answer.”

Antiabortion groups responded to the court’s ruling by searching for a

way to block abortions that didn’t clash with the decision. They boycotted

companies that did research into abortion drugs. They lobbied for laws

making it hard for abortion clinics to do their work. To win over voters,

they invoked new scientific research—or at least a carefully selected

version of it. They claimed that studies on fetuses pushed back the time at which they

began to feel pain. Some antiabortion legislators introduced “fetal

heartbeat” bills. They skipped over the fact that hearts do not yet exist when

cardiac cells start to contract. The bills didn’t have anything to do with

actual hearts anyway, since their purpose was to effectively ban most

abortions after just six weeks. Beyond these half measures, many antiabortion groups wanted to

overturn Roe altogether. The only way to do that was to address the

question of when life begins—or, to be legally precise, to decide when an

embryo becomes a person, with all the rights that come with personhood. A

so-called personhood movement arose, claiming that these rights extend

back to fertilized eggs. If they did, those rights would make any abortion

illegal. Some leaders of the personhood movement acknowledged that certain

forms of contraception would also have to be banned, because they blocked

pregnancies by preventing newly formed embryos from implanting in the uterus. And to justify this legal case, they invoked science in much the same

way Charles Peabody had over a century earlier. “Life begins at conception,” the conservative pundit Ben Shapiro

declared in 2017.

“That’s not religious belief. That’s science.”

Shapiro, it should be pointed out, was not a scientist. He had a law

degree and a podcast. And when he made this claim, he did not offer

scientific evidence to back it. Scientists, on the other hand, have been

pushing against these sharp, all-or-nothing claims about life ever since the

molecular underpinnings of life became clear. In 1967, in the pre- Roe

battles over abortion, the Nobel Prize–winning biologist Joshua Lederberg

addressed the controversy with a piece called “The Legal Start of Life” in

the Washington Post. “There is no single, simple answer to ‘When does life begin?’”

Lederberg wrote. “In contemporary experience, life in fact never begins.”

A fertilized egg is alive, Lederberg explained, but in the way cells are

alive, not people. Some organisms, like bacteria, spend their entire

existence as single cells, thriving happily in the ocean or the soil, but the

cells that make up our bodies are not so rugged. If you prick your finger and

dab a drop of blood on a table, your cells will not crawl off to seek their

fortune. They will dry out and die. For cells, death means that their proteins

malfunction, their interiors are thrown off chemical balance, and their

membranes tear open. Inside a body, a cell can thrive. It can feed on the

nutrients that wash over it, keep its proteins in good working order, and get

rid of its waste. If it gets the right signals, it can grow and divide. One cell becomes two, as the so-called mother cell splits up all its molecular legacy

between a pair of new daughter cells. At no point during cell division does

the mother cell die. At no point do the daughter cells come to life. What

gives life flows from the former to the latter. Some types of cells can run this movie backwards. Instead of dividing,

they fuse together. When we exercise, for instance, we stimulate muscle

cells to multiply and then merge in order to create new fibers. In our bones,

immune cells fuse into giant blobs called osteoclasts, which nibble away at

old bone so that it can be replaced with new tissue. Each muscle cell and

osteoclast can hold many nuclei, each packed with its own DNA. The

independent cells that came together to form them did not die. They simply

mixed their molecules together into a new form of life. This is the cellular universe in which a fertilized egg exists. It is certainly alive, but it does not snap into life thanks to the assembly of

lifeless molecules. Instead, it emerges from the fusion of two living cells. But the mother’s egg and the father’s sperm from which it arose did not

jump into existence, either. The egg arose from cells that divided when the

mother was still an embryo. A man makes hundreds of millions of sperm

each day, but ultimately they all descend from the fertilized egg that gave

rise to his entire body. The flow of life arrives unbroken from the previous

generation, and from generations back through the ages. You’d have to

canoe up life’s river for billions of years before reaching its headwaters. “Life begins at conception” is a simple slogan, easy to remember, easy

to shout. Taken literally, though, it’s false on its face. The personhood

movement’s politics have always made it plain that the slogan wasn’t

supposed to be taken literally anyway. It’s not life that they’re talking about starting at conception but a life. And not just any life—not the life of an armadillo or a petunia—but a human life, with all the legal protections it is

due, including—to close the circle—the right to life. “A distinct, living human individual comes to be with the fertilization of

the oocyte by the spermatozoan,” Patrick Lee and Robert George, two

abortion opponents, wrote in 2001.

What makes it distinct, they argued, is

that it has a unique set of DNA, combined from its two parents, that can

guide its development. It might be invisible to the naked eye, but Lee and

George argued that the fertilized egg already has the potential for reasoning

and all the other capacities that make us human. The actual course of human development makes it impossible to pin one

instant as marking the origin of a new human individual. It certainly can’t

be the moment that a sperm fuses with an egg. Cells typically carry forty-

six chromosomes—twenty-three from our mother and twenty-three from

our father. But at the moment of fertilization, the combination of a father’s

and mother’s DNA actually produces sixty-nine chromosomes. That’s

because an unfertilized egg is a cell like any other cell in a woman’s body,

with forty-six chromosomes arranged in twenty-three pairs. A cell with sixty-nine chromosomes could never give rise to a healthy

human being. Its genes would be wildly out of balance. To avoid this

catastrophe, an egg responds to the arrival of a sperm by pinching off a tiny

bubble. Inside that bubble, the egg stows away twenty-three of its

chromosomes. The egg is now left with the other twenty-three—a perfect counterpart to the father’s DNA. Even now, however, the fertilized egg has not gained a single new

genome we can call its own. Its mother’s and father’s chromosomes still

remain separate, swaddled in their own membranes, in which they undergo

separate changes. It’s better to think of the early fertilized egg as a

coworking space, a place in which the male and female genomes busy

themselves on their own. The fertilized egg then divides into two cells, each of which inherits the

chromosomes of both the father and the mother. It takes a day after

fertilization to reach this milestone. And only then do the chromosomes

abandon their separate containers. Only in the two-cell embryo do the two

sets of DNA join together. And yet even at this point the new embryo does not have its molecular

independence. Virtually all the proteins in the cells come from the mother,

encoded by her genes. In this important respect, the embryo still behaves as

if it were a cluster of the mother’s cells. A distinct, human individual is not yet taking hold of its own fate. Before the father’s chromosomes can wake

up—before the new genome can take charge—there’s a lot of work yet to

be done. Inside the egg are a special set of assassin proteins, made from the

mother’s own genes. They roam the embryo’s cells, annihilating her other

proteins. Another set of her proteins grabs hold of both her and the father’s

chromosomes and prepares them for their new job. Now the cells make a

fresh batch of proteins, rebuilt from the shredded remains of the mother’s

molecules. As these changes take place within an embryo, it floats out of the

mother’s oviduct and down into her uterus. Along the way it may break in

two. The two clusters of cells continue to divide, each becoming an

ordinary embryo. Ultimately, these two sets of cells can develop into

identical twins. If we must believe that a fertilized egg immediately

becomes a person, then we’re left to wonder where that person went when it

became two people. Fraternal twins develop in a different way. The mother releases two eggs

at once, each of which is fertilized by a different sperm cell. Sometimes,

when these twins are still tiny clumps of cells, they bump into each other

and merge. Thanks to their flexibility, the cells reorganize themselves into a

single embryo that continues to develop normally, even though some cells contain one genome and the other cells contain another. Scientists call these mergings chimeras. Chimeras can grow into healthy

adults who go through life made up of two populations of cells, each with

their distinct genome. If every fertilized egg is a single person with all the

rights that a single person is entitled to, does a chimera get to have two

votes?

When we living humans look back at the development of an embryo, it’s

tempting to see it as a gorgeously precise clockwork of chemistry that

transforms a single cell into a 37-trillion-cell body. Textbooks illustrate

every stage proceeding without a glitch. But development often ends in

failure, with many pregnancies lost along the way. The biggest risk to the

survival of an embryo is if it doesn’t end up with twenty-three pairs of

chromosomes. Sometimes it ends up with a third copy of a chromosome. With three copies of each gene instead of two, an embryo may make too

many proteins, poisoning itself. Embryos may end up with just one copy of

a chromosome, leaving them unable to make all the proteins they need to

survive. Sometimes the imbalance arises in the egg. When the egg tries to get rid

of its extra chromosomes in a bubble, one of them accidentally stays

behind. Other times the trouble comes after fertilization, when the embryo

starts to divide. As the cells split, they may fail to divide their chromosomes equally between their daughter cells. One cell may end up with too many

chromosomes and the other with too few. As they divide, they pass down

that imbalance to their descendants. Biologists call this imbalance aneuploidy. It doesn’t necessarily spell

doom for an embryo. If it contains balanced and unbalanced cells, the

unbalanced ones may stop growing, while the balanced ones go on to make

up the vast majority of the body. Even if an embryo is made up entirely of

aneuploid cells, it may still have a chance of surviving. It depends on the

nature of the imbalance. An embryo with an extra copy of chromosome 21

may be born as a child with Down syndrome. In most cases, however,

aneuploid embryos fail. Sometimes they simply stop growing. Sometimes

they fail to implant in the uterus and get flushed out. Aneuploidy is not the only cause of lost pregnancies. Some women

can’t make enough hormones needed to prepare their uterus to take in a new

embryo. A badly timed infection may overcharge a woman’s immune

system, which then treats embryos and placentas as foreign enemies to be attacked. Scientists have come up with estimates for how many pregnancies are

lost naturally, and they’re enormous. One study published in 2016

concluded that between 10 and 40 percent of embryos are lost before they

can implant in the uterus. All told, from conception to birth, the researchers

found that the figure may rise to 40 to 60 percent. If a country were to

declare that life begins at conception, and that fertilized eggs have the legal rights that all persons are due, it would have to treat these losses as a

medical catastrophe. Worldwide, it would mean the deaths of perhaps more

than 100 million human beings every year, dwarfing the deaths from heart

disease, cancer, and every other leading cause. Yet this crisis hasn’t become an urgent priority for opponents of

abortion. Just the opposite: some of them have questioned these estimates,

suggesting the losses are somewhat smaller—as if tens of millions of deaths

would somehow be easier to live with. Some claim that the causes of these

lost pregnancies, such as aneuploidy, are unstoppable, so these lives

couldn’t be saved anyway. But that’s not true. A great deal of research has

gone into reducing pregnancy losses—not because researchers subscribe to

the idea that life begins at conception, but because they want to help

couples struggling to have children. Some women who have recurrent

pregnancy losses can improve their odds of a successful birth by getting

hormone injections. Other researchers are exploring new possibilities for

saving embryos, from managing a mother’s immune system to editing the

DNA of fetal cells. Abortion opponents also undermine their own sweeping claims with

illogical exceptions. In 2019, Alabama legislators introduced a bill that

would charge doctors who carried out abortions with a felony. They would

face a punishment of up to ninety-nine years in jail. But the bill’s authors

made an exception for women who faced serious health risks from their

pregnancy. When the bill attracted controversy, the Alabama Senate

Judiciary Committee tacked on additional exceptions, for rape and incest. One of the bill’s sponsors, state senator Clyde Chambliss, objected. “In

the situations of rape and incest it is a very difficult, difficult situation

following a horrendous act,” Chambliss told reporters. “But if we believe

that life begins at conception, and I do, then life is lost.”

But Chambliss couldn’t follow his own rule to its logical end. When couples use in vitro fertilization to have children, fertility doctors routinely make a batch of embryos, not just one. They may pluck one cell from the

embryo to closely examine its DNA to see how viable the embryo will be. Since all the cells in early embryos can become embryos of their own, this

test should, by Chambliss’s logic, cause the loss of life. Once fertility

doctors choose the best embryos for implantation, they may freeze or

discard the others. If abortions are unjustifiable because embryos are

persons, then it is unjustifiable to let embryos die as a result of in vitro

fertilization. It doesn’t matter whether they are actively or passively killed. Yet, during the debates over the Alabama bill, Chambliss declared his

ban did not stop in vitro fertilization. When a fellow lawmaker challenged

him on this inconsistency, he gave an inscrutable response. “The egg in the lab doesn’t apply,” he declared. “It’s not in a woman. She’s not pregnant.”

The Alabama legislature went on to vote down the amendment to allow

abortions in the case of rape and incest. The governor signed the bill. —

In vitro fertilization complicated the question of life’s beginning, and now

reprogrammed cells promise to complicate it even more. With the right

combination of chemicals, a reprogrammed cell can start developing into an

embryo. Scientists have turned the skin cells of adult mice into mouse

embryos, which can grow into mouse pups. It may soon be possible to do

the same with humans. When that happens, trillions of cells in each of our

bodies will gain the potential to become a human being. According to the

logic of the personhood movement, they will all be due the rights of a

person. The dust in our homes is largely made up of the dead skin cells we

slough off by the millions every day. Is each one a potential life lost?

None of these complications means that we can walk away from our

moral obligations to our fellow humans. It just means there’s no easy way

to figure them out. And as organoids become more complex, it may get

especially hard to decide what our moral obligations are to them. Today’s

brain organoids are alive, yes, and they are human, but they don’t

experience the life that human beings do. That life has something to do with

Haldane’s feeling of being alive. It’s conceivable that a bigger, more

complicated organoid might make intricate brain waves, might even learn. Perhaps it might even gain a rudimentary sense of life. How could we find out if it gained that sense?

Christof Koch, the

director of the Allen Institute for Brain Science in Seattle, has an idea. He

thinks scientists could measure the complexity of an organoid’s experiences

by eavesdropping on its signals. Koch’s proposal emerges out of work that

he and other scientists have done on the nature of consciousness. They

argue that consciousness is the integration of information across the brain. When we are conscious, information flows across our whole brain, giving

us a coherent feeling of reality. When we fall asleep or go into a coma, the

flow dwindles down. The regions of the brain remain active, but their

information no longer adds up to a single, unified experience. Koch and his colleagues believe that we can measure this integration by

disturbing it, like tossing a rock into a pond to look for ripples. They’ve put magnets on the heads of volunteers and delivered harmless pulses. The

pulses briefly disturb their brain waves. In people who are awake, the

pulses produce flows of information traveling along complex paths through

the brain. The same pattern arises when people dream. But when people go

under anesthesia, the pulses trigger simple responses—like the ringing of a

bell instead of a fugue played on a pipe organ. Koch has suggested that scientists could apply the same magnetic pulses

to brain organoids and see how they respond. What makes his proposal

particularly intriguing is that he and his colleagues have invented a way to

measure the integration in a brain with a single number. It’s like a

thermometer for consciousness. We might agree that brain organoids should

never rise above a certain number. And if we discovered that a particular

batch of organoids managed to sneak past the threshold, we’d know that we

have to decide how we’ll care for their lives. “What would it mean for a cerebral organoid to suffer?” Koch asked at

the end of a lecture he gave in 2019.

“That’s not an obvious question to

answer.”

In 1967, long before the dream of organoids even existed, Joshua

Lederberg could see the trouble that lay ahead. “The biologist, then, is not really very helpful to the law,” Lederberg

said. “The question of when life begins is answered according to the

purposes for which we ask it.”

DEATH IS RESISTED

In 1765 a fifteen-year-old boy named James Forbes boarded a ship in

England and sailed for Bombay. There he joined the East India

Company, and over the next nineteen years his job took him back and

forth across the subcontinent. Along the way, Forbes turned himself into a

naturalist and artist, painting portraits of bulbul birds and Parsee families. By the time Forbes left India to return to Europe, he had produced 52,000

pages of writing and art. Back home he combed through his work, and in 1813 he published a

four-volume book called Oriental Memoirs offering a sumptuous tour of

India for his British fireside readers. The Monthly Magazine praised “the TRULY SPLENDID work before us.” With his encyclopedic scope, the

editors believed, Forbes made a visit to India pointless. “He has left little of novelty to be discovered by future travelers.”

Along Forbes’s journeys, he stopped off at a great banyan tree on the

banks of the Narmada River. It sent hundreds of trunks into the sky, creating

a canopy big enough to shelter an army of seven thousand soldiers. A local

chief sometimes visited the tree to host giant parties. He set up lavish tents

that served as a dining room, a drawing room, a saloon, a kitchen, and

bathrooms. He had enough free space left over to fit his camels, horses,

carriages, guards, and attendants—along with his friends and their herds of

cattle. The Narmada banyan was also home to birds, snakes, and langur

monkeys. Forbes observed the monkeys teaching their young how to leap

from tree to tree and kill dangerous snakes. “When convinced that the

venomous fangs are destroyed, they toss the reptile to their young ones to

play with, and seem to rejoice in the destruction of a common enemy,”

Forbes said. A friend of Forbes once paid a visit to the Narmada banyan as part of a shooting party. He shot a female monkey with his fowling piece and took

the corpse to his tent. A cacophony of screeching began outside the tent

walls, and when he looked out, the hunter saw dozens of monkeys “who

made a great noise, and in a menacing posture advanced towards it,” Forbes

said. Forbes’s friend brandished his fowling piece. The animals fell back,

with the exception of one male, who seemed to be the leader of the troop. The monkey approached the hunter, chattering aggressively. But eventually

his calls changed to what Forbes described as “a lamentable moaning.”

It seemed to the hunter that the monkey was begging for the dead

female’s body. He gave it back. “With tender sorrow he took it up in his arms, embraced it with conjugal

affection, and carried it off with a sort of triumph to his expecting

comrades,” Forbes wrote. After the monkeys departed, the entire shooting

party was left shaken. “They resolved never more to level a gun at one of

the monkey race.”

Forbes’s story of the lamentably moaning monkey was so remarkable

that people in England repeated it for decades. It seemed to fly in the face

of what Victorians thought about the animal brain. Humans could make

sense of life, thanks to their rational minds. And through understanding life,

they could also see its limit in death. But here were brutes that acted

remarkably like humans in mourning, that seemed to know that the life in

their fellow monkey had gone. One might conclude that monkeys had more

sophisticated minds than we gave them credit for. Or perhaps we humans

flatter ourselves too much about what we know about life and death. —

Forbes’s story of the mourning monkey was joined by other stories of

grieving primates, and no one was more fascinated by them than Charles

Darwin. Once he conceived of his theory of evolution in his late twenties,

Darwin recognized that it explained the origins of humans just as it did any

other species. He could see the legacy of evolution in our anatomy, with its

striking similarity to chimpanzees and other apes. He paid visits to an

orangutan at the London Zoo and could see the legacy in her humanlike

facial expressions. And he could see it in the stories of primates displaying

emotions that were once thought unique to our own species. Among them

were tales of grief. “So intense is the grief of female monkeys for the loss of their young, that it invariably caused the death of certain kinds,” Darwin

wrote in his 1871 book The Descent of Man. Nearly a century would pass before scientists regularly traveled to the

wild habitats of monkeys and apes to make detailed observations of their

behavior. But once they got there, they began accumulating their own

firsthand stories of the striking ways that primates responded to death. Researchers came to see these stories as a scientific question in its own

right, which they called primate thanatology. The first modern record of

primates facing death came in the 1960s from Jane Goodall, a young British

naturalist who traveled to Tanzania to live with chimpanzees. One day

Goodall dedicated her observations to a female she called Olly. Olly had

recently given birth, but Goodall could tell the baby was not well. “All his

four limbs hung limply down,” she later recalled, “and he screamed almost

every time his mother took a step.”

Since the baby was too weak to grip Olly’s hair, she had to carefully

cradle him. She took him up a tree, where she sat on a branch and carefully

placed him in her lap. A blinding rainstorm swept in and drenched

chimpanzees and primatologist alike for half an hour. When it cleared away,

Goodall watched Olly climb down to the ground again. The baby now made

no sound. His head hung as lifelessly from his body as his limbs. And now

Goodall noticed that Olly treated her baby differently. “It was as though she knew he was dead,” Goodall said. Rather than cradling the infant, Olly now held him by a leg or an arm. Sometimes she slung his body around her neck. In a seeming daze, she

carried her baby for the next two days. Other chimpanzees gawked at her

and her dead infant, but Olly simply stared off into space. Eventually,

Goodall lost track of her as she traveled through a dense thicket. She did not

catch up with Olly until the following day. The baby was gone. In the decades since, other primatologists have seen other mothers

respond to the loss of their infants much as Olly did. They have observed

young gorillas sitting vigil with their dead mothers. While working in the

forests of the Ivory Coast, Christophe Boesch once came across the body of

a chimpanzee on the ground. It looked as if it had just died after falling out

of a tree. He then saw five other chimpanzees arrive and spot the body, too. They swiftly climbed into the surrounding canopy, where they hooted and

screamed for hours. Our sense of what it means to be alive emerges partly from our

awareness of our own life, and partly from our intuitive ability to tell living things apart from inanimate objects. But it also grows out of our

understanding of the difference between life and death. To be alive is to not

be dead, in other words. Humanity did not come to this realization through

logic and deduction. Our understanding of death is not like Darwin’s theory

of evolution or Thomson’s discovery of the electron. It has its origins in

ancient intuitions. Animals probably first evolved to behave differently toward living and

dead things hundreds of millions of years ago. Today, mammals, birds, and

even fish can be put off by the smell of rotting bodies. The disgusting smell

of death is the result of certain airborne molecules with evocative names

like cadaverine and putrescine. These molecules are not produced by death, however, but by life growing on death. After an animal dies, its cells self-destruct and become food for the body’s resident bacteria. They chew

through the walls of the gut and spread through the body. They release

cadaverine and putrescine merely as byproducts of their metabolism. These

molecules are not actually dangerous to us. They won’t kill us like a whiff

of sarin or cyanide. Yet our ancestors evolved a keen sensitivity to these

molecules, along with an instinctive response to recoil at the merest whiff. That’s because they are reliable signals of the dangers of the dead, even if

they’re not dangerous themselves. Thanks to primate thanatology, we now know that our monkey-like

ancestors 70 million years ago did not have to wait for their dead

compatriots to start rotting to sense that something important had happened

to them. This keener sense of death, some scientists have argued, resulted

from a keener sense of life. When a primate died, living primates around it

would still see features like the eyes and mouth that triggered their

biological detection circuits. But the circuits dedicated to biological

motions would register nothing—not even a blink. These contradicting

signals may explain why primates so often sit vigil with their dead. They

may need time to make sense of this cognitive clash, to move a primate that

they’ve lived with for years to the category of the lifeless. —

By about 30 million years ago, the lineage of apes—the evolutionary

branch that would produce orangutans, gorillas, chimpanzees, and us—split

off from other primates. Studies on chimpanzees suggest that our common ape ancestors evolved an even deeper sense of death, perhaps as a result of

evolving bigger, more powerful brains. Chimpanzees not only react

differently to fellow chimpanzees when they die: they also show some signs

of recognizing the cause and effect of life and death. Their behavior

suggests that they comprehend that a fall out of a tree or the attack of a

leopard can bring the life of an ape to an end. Our own lineage split off from that of chimpanzees roughly seven

million years ago. Early hominins gradually evolved to walk upright in

woodlands; aside from that they didn’t look much different from other apes. Nor is there a sign in the fossil record that they treated their dead any

differently than apes do. Only in the past few hundred thousand years do the

first hints of a modern sense of death appear. And the oldest of these hints,

not surprisingly, are the most ambiguous. In a few caves in Africa and Europe, paleoanthropologists have found

caches of early human skeletons. These humans belonged to our own genus,

Homo, but to two different species: Homo heidelbergensis and Homo naledi. It’s conceivable that the skeletons of these early humans were

ceremoniously carried to their resting places and then dropped down

fissures. But for now the evidence is still too patchy to be sure. It’s also

possible that predators dragged these early humans into caves or roaring

floodwaters washed them in. The oldest indisputable evidence of a new concept of death dates back

about 100,000 years. Members of our species, Homo sapiens, began

carrying out funerals. In caves in Israel, archaeologists have found

skeletons that were carefully laid out and surrounded with deer antlers,

chunks of ochre, and shells from distant shores. In Australia, Aboriginals

were digging graves for their dead by about 40,000 years ago. These rituals

tell us something about the minds of the people who practiced them. They

were understanding death in a way that other primates did not: that diseases

and injuries were its cause, that there was no going back. They honored the

memory of the dead by carefully interring their bodies. By the time people were performing these first funerals, they were

capable of full-blown language. The echoes of the songs they may have

sung or the stories they may have told dispersed long ago. To trace the

origin of our concept of death, we have to content ourselves with written

accounts and the spoken words of people recorded from across the world. It’s clear that humans have come up with many explanations of death, but they share some things in common. People don’t simply think about it as a

physical change. They also see death as a social transformation. Some

cultures conceive death as a separation, as the deceased travel to another

world. Others see death as a transformation that enables their ancestors to

be always with them. Buddhists, meanwhile, think of it as the

disappearance of the self, like the dewdrop on a blade of grass evaporating

into the air at dawn. Western science was slow to create a detailed account of death. It was

mostly left to physicians, who were too busy trying to save lives to explain

what they were trying to stave off. “Medical men have rarely discussed the

so-called sense and essence of death; they had to leave this to philosophers

and theologians,” the historian Erwin Ackerknecht once wrote. The first physician to investigate the nature of death in a scientific

manner was arguably the French doctor Xavier Bichat. In the late 1700s, he

studied both humans and animals in the moments after death. After

criminals were executed at the guillotine, Bichat examined their severed

heads and headless bodies. He slit open the chests of living dogs to fit

stopcocks on their windpipes. With a twist, he could close the flow of air

into a dog’s lungs. After the dog’s blood turned from red to black, he

discovered, death was not far off. This grisly work let Bichat see an intimate connection between the

heart, the lungs, and the brain—a vital tripod, as it came to be known. If the

lungs failed, they could not transform dark blood to red, the life-sustaining

form that the brain needed to keep working. If the heart failed, it could not

deliver blood to the other two organs. When Bichat damaged the brains of

animals, he discovered that a crucial connection to the heart and lungs was

lost, causing the animals to die. No one part of the body had a monopoly on

the forces of life, Bichat could see. Those forces were distributed across the

body in an interconnected system. “Life,” Bichat concluded, “consists in the sum of the functions, by

which death is resisted.”

Bichat saw a gleaming line dividing life and death, but its brightness

was the result of the kinds of life he studied. Decapitated criminals and

exsanguinated dogs left little doubt which side of the line they were on. If

Bichat had studied other animals, however, he would have encountered a

blurry boundary. In the late 1600s a Dutch trader named Antonie van Leeuwenhoek

crafted the first microscopes powerful enough to open up the microscopic

world. A single drop of water from a pond might contain a swarm of

strange shapes. They looked unlike anything in the macroscopic world, but

they moved, and their movements touched Van Leeuwenhoek’s instinctive

sense of what makes things alive. He thought of them as little animals. When his reports appeared in the Philosophical Transactions of the Royal

Society, his English translators used the word animalcules. “The motion of most of these animalcules in the water was so swift, and so various,

upwards, downwards, and round about, that ’twas wonderful to see,” he

reported. Van Leeuwenhoek went on to discover red blood cells, sperm cells,

bacteria, protozoans, and a host of miniature animal species. And then, on a

summer day in 1701, he noticed that the lead gutter hanging off the front of

his house was full of reddish water. He scooped up some of it and put a

drop in his microscope. He now saw a new kind of animalcule. These

creatures were shaped like pears, with what looked like two wheels atop

their heads. (Today they’re known as rotifers, meaning “wheel-bearers” in

Latin.)

Van Leeuwenhoek then let some of the gutter water evaporate. He had

tried this experiment on other animalcules before, and usually they burst as

they dried. But this time was weirdly different. As a rotifer dried out, it

shrank into a smaller version of itself and became motionless. “It preserved

its oval and round shape unhurt,” Van Leeuwenhoek observed. As the summer grew hot and dry, the red water in Van Leeuwenhoek’s

gutter turned to dust. He decided to search the dust for rotifers, dousing it

with water and looking at the drops with his microscope. He spotted more

shrunken rotifers, lying in a motionless heap as if they were dead. But after

they soaked for a while, they expanded, and then they started to move. “In a short time afterwards they began to extend their bodies, and in half

an hour at least a hundred of them were swimming about the glass,” he later

wrote. Van Leeuwenhoek stored away the rest of the gutter dust. Months later

he took it out again and mixed it with water. The rotifers unfolded their

bodies and came alive even after all the time that had passed. “I confess I never thought that there could be any living creature in a

substance so dried as this was,” he said. Four decades later, in 1743, a British naturalist named John Needham discovered another creature capable of resurrection. Needham had been

studying stalks of wheat that were sick with earcockle disease, which

caused their grains to swell and turn black. Farmers called these sickened

grains peppercorns. When Needham cut open a peppercorn, he found a

clump of dry white fibers inside. He added a drop of water to them, hoping

it would become easier to pull them apart. The Philosophical Transactions of the Royal Society of London

described what happened next. “To his great surprise, these imaginary

fibres, as it were, instantly separated from each other, took life, moved

irregularly, not with a progressive, but twisting motion; and so continued

for the space of 9 or 10 hours, when he threw them away.”

Needham had discovered the larvae of a nematode worm, today known

as Anguina tritici. But at the time, many naturalists refused to believe him. The Royal Society handed Needham’s wheat over to another naturalist

named Henry Baker to judge. Baker tried out Needham’s instructions and

brought the worms to life. His curiosity now aroused, Baker carried out

more experiments of his own. In one study he stored some peppercorns for

four years. The worms survived over that long stretch of time; when he

added water to their white fibers, he saw more writhing life. “We find an Instance here, that Life may be suspended and seemingly

destroyed,” Baker announced in his 1753 book, Employment for the

Microscope. How the worms could hold on to their “living Power,” as Baker called it, he would not dare guess. “What Life really is, seems as much too subtile for our Understanding to conceive or define, as for our

Senses to discern and examine.”

Soon a third animal joined the undead ranks of the nematodes and

rotifers. Tardigrades, which look like headless eight-legged bears, only get

to be as big as the period at the end of this sentence. Naturalists first

discovered tardigrades crawling over mats of moss and later found them

lurking in damp soil, in lakes, and even in the ocean. When researchers let

tardigrades dry out, the animals retracted their legs and their bodies took on

the appearance of sesame seeds. A few minutes of water was enough to

sprout their legs again. Many naturalists refused to believe life could survive this desiccated

limbo. They believed something simpler must be happening. Perhaps the

desiccated animals died, and when scientists applied water, they awoke

hidden eggs that hatched. The battle raged for decades, the two sides coming to be known as the resurrectionists and the anti-resurrectionists. The

debate became so dire that France’s leading organization of biologists, la

Société de Biologie, appointed a special commission in 1859 to settle the

matter. After spending a year running experiments, the august scientists

issued a 140-page report that came down in favor of the resurrectionists. Yet

the anti-resurrectionists kept battling against their conclusion for decades. Today all biologists are resurrectionists. There is no doubt that

tardigrades, nematodes, and rotifers can dry up and then come back to life. The more that researchers study these animals, the longer it seems that they

can survive in limbo and still be able to return to the world of the living. In the 1950s a team of researchers collected dried tardigrades in Antarctica. They put the animals in cold storage for thirty years, after which water and

warmth brought them back as healthy as ever. The nematodes that occupy

peppercorns have lasted even longer, returning from lifeless fibers after

thirty-two years. In recent decades, scientists have added flies, fungi, bacteria, and other

species to the ranks of the resurrectable. In Antarctica, glaciers retreated to reveal moss that had been dried out and frozen for at least six hundred

years. With some tender gardening, it produced new green sprouts. In

Siberia, scientists came across burrows dug by Ice Age squirrels 30,000

years ago that contained dried-out bits of a flower called narrow-leafed

campion. The scientists nurtured the fragments, which grew into healthy

new plants that produced seeds of their own. What today’s resurrectionists have yet to figure out is how these

creatures survive this transformation. In ordinary species, water is essential

to a flurry of chemical reactions that take place in every cell every second. Water also helps keep membranes in their proper oily consistency, and it

cradles proteins so that their arms and sheets stay in their proper

arrangement. When a cell loses water, chemical reactions grind to a halt. Its

proteins stick to each other and form toxic clumps, while its membranes

turn to sticky jelly. Our bodies can endure the temporary loss of a little

water—the kidneys make less urine; the heart beats faster to increase the

delivery of oxygen to cells—but once we lose more than a few percent of

our body weight in water, our organs start to fail and death soon follows. Tardigrades and their ilk, on the other hand, can lose all their water. You

could argue that they are no longer alive, since they cannot carry out the

chemical reactions required for life. Yet neither are they dead. If you pour water on someone who has just died from dehydration, they will not sit up. You are left with a damp corpse. But if you pour water on a dried-out

tardigrade, in a matter of minutes it becomes a moving, feeding,

reproducing animal. This gray zone of existence has earned a name of its

own: cryptobiosis—what one team of scientists has described as “a third state between life and death.”

When a cryptobiotic species starts to dry out, it eases its own passage

into limbo. Some species respond to dehydration by making a sugar known

as trehalose. Thanks to its chemical structure, trehalose can help proteins

keep their proper shape, much like water does. But unlike water, it doesn’t

evaporate in dry conditions. This supply of fake water buys the drying

creature extra time to make preparation for a long spell of cryptobiosis. Many species make a new batch of proteins that link together to form a kind

of biological glass. It entombs the cell’s DNA and other molecules in their

three-dimensional form, so that they’re ready to revive when water returns. This third state is so durable that it doesn’t just give organisms the

power to resist dehydration. They can also survive in outer space. In 2007 a team of scientists collected tardigrades in Germany and

Sweden, dried them out, and loaded them into a canister. The canister was

placed in a Russian rocket that went into orbit around Earth. For ten days

the animals were exposed directly to the vacuum of space. Back on Earth, a

splash of water resurrected them. In 2019 humans delivered tardigrades far deeper into space. An

organization called the Arch Mission Foundation set out to create what its

founder described to Wired as “the hard backup of this planet.” They

created a miniature “lunar library” in which they stored 30 million pages of

information, along with samples of human DNA and thousands of dried-out

tardigrades. A private Israeli aerospace company put the library on the

Beresheet lunar lander, which they launched to the moon. The engine failed just before landing, and the Israeli engineers lost track

of the probe. It almost certainly crashed into the moon. It’s possible that the library sits at the impact site unharmed. The earth rises and sets over the

tardigrades as they wait, their cells locked in a glass tomb between life and

death, for water that will never come. —

As Van Leeuwenhoek put his little animals into a deathlike state, people across Europe were worrying that they might slip into one of their own. They read pamphlets full of terrifying tales of seizures that left their victims without breath or heartbeat. Mistaken for dead, they were lowered into

graves, waking up in their coffins when it was too late to be saved. The fear of this Gothic terror gained strength throughout the eighteenth

century and only grew more terrifying in the nineteenth. Edgar Allan Poe

mined the nightmare for his story “The Premature Burial,” which he

published in 1844.

“The boundaries which divide Life from Death are at

best shadowy and vague,” Poe wrote. “Who shall say where the one ends,

and where the other begins?”

Families made frantic by these stories bought coffins equipped with a

string and a bell, so that their not-quite-departed loved ones could sound the

alarm. In the 1800s, many German cities built ornate “waiting mortuaries”

where the apparently dead could be housed until they began to rot. Mark

Twain visited one of these establishments on a trip to Munich in the early

1880s. “It was a grisly place,” he later wrote. “Along the sides of the room

were deep alcoves, like bay windows, and in each of these lay several

marble-visaged babes, utterly hidden and buried under banks of fresh

flowers, all but their faces and crossed hands. Around a finger of each of

these fifty still forms, both great and small, was a ring; and from the ring a

wire led to the ceiling, and thence to a bell in a watch-room.”

It was all an elaborate waste of time: the fears of premature burial were

fueled by rumor rather than evidence. But without a quick, foolproof way to

determine death, doctors couldn’t calm uncertain next of kin. One physician

recommended giving patients an enema of tobacco smoke. If they didn’t

react, they could be safely declared dead. By the mid-1800s a number of

doctors were adopting the newly invented stethoscope. Even a faint lub-dub

meant patients were still alive. Only a long silence came to be the reliable

sign that people were truly gone. Bichat had recognized why a stopped heart is a good sign of death. It

belongs to the vital tripod, along with the brain and lungs. If the heart fails, the other two will fail as well. In the twentieth century, scientists mapped

these failures in cellular detail. The heart may fail if it can’t get enough

oxygen from lungs that are scarred or filled with fluid. The cells of the heart need oxygen and sugar to make fuel, and without fuel they cannot contract. If they cannot contract, then the heart cannot send blood to the brain. Brain cells are even hungrier for oxygen than heart cells, and within minutes they

will start dying. A blow to the head can also stop the heart. The impact causes the brain

to crash into the interior wall of the skull, ripping apart delicate blood

vessels. As the blood gushes in, the brain swells and squeezes its way to the

back of the head and then down to the opening at the base of the skull. The

pressure shuts off blood vessels throughout the brain, cutting off the supply

of oxygen to wide swaths of tissue. The brain stem—the region of the brain

that sends out signals required by the heart to beat as well as the lungs to

breathe—is often the first part to die. Bichat was right to believe that, by understanding death, doctors would

be better able to protect life. They learned how to treat the loss of blood

with transfusions. They learned how to block poisons and fight pathogens. In the early 1900s, American doctors faced a wave of polio outbreaks that

left thousands of children paralyzed and slowly suffocating to death. Engineers developed iron lungs to breathe for those young patients. The

iron lungs used pumps to create negative pressure around the bodies of the

children, drawing air into their lungs. In effect, they were propping up the

vital tripod long enough for the children to fight off the virus and regain

their ability to breathe on their own. By the 1950s, iron lungs had given way to tubes that could push air

directly into a patient’s airway. The advent of polio vaccines made

epidemics of paralysis a thing of the past, but doctors still used artificial

ventilation on other patients: on victims of drug overdoses, people who had

fallen into icy lakes, premature babies—anyone who needed help breathing

as they regained good health. The French neurologists Pierre Mollaret and Maurice Goulon came to

see ventilators as a mixed blessing. They saved many lives but dragged out

the ends of others. When people suffered massive brain damage, ventilators

could keep their hearts and lungs working, but their brains would never

recover. Mollaret and Goulon took careful notes on the outcomes of these

patients and found that even with the help of ventilators they didn’t wake up

again. Instead, they usually died within hours or days. All the ventilators

seemed to do was draw out the pain of their families. This futile condition was, Goulon once said, “a new, previously

undescribed, state.” At a conference in 1959, he and Mollaret gave it a

name: coma dépassé, beyond a coma. Modern medicine was now challenging the familiar boundaries of death,

just as it has changed how we think about birth. The beginning of life was

once out of our control, until stem cell biologists learned how to turn an

ordinary skin cell into an embryo, one that might potentially become a

human being or something new like a brain organoid. There was a time

when death was likewise inevitable if Bichat’s vital tripod lost one of its

three legs. Now artificial ventilation undermined Bichat’s law, giving rise to

a new kind of life. Other doctors agreed with Mollaret and Goulon’s worries about coma

dépassé.

“The developments in resuscitative and supportive therapy have led to many desperate efforts to save the dying patient,” the Harvard

anesthesiologist Henry Beecher said in 1967.

“Sometimes all that is rescued

is a decerebrated individual. These individuals are increasing in numbers

over the land and there are a number of problems which should be faced up

to.”

There was a grim irony in the timing of coma dépassé.

As ventilators

were trapping patients in futility, transplant surgeons were learning how to

save lives by moving organs from donors to recipients. In 1954 the Boston

surgeon Joseph Murray replaced a man’s damaged kidney with one from his

twin brother. Finding people willing to give up a kidney was hard, and a

donor’s organ might not even be the right match for a patient. When it came

to the heart or the pancreas, people didn’t have an extra to spare. Murray and other doctors turned to cadavers for more organs, but this

method had its own drawbacks. Transplant surgeons had to make the

arrangements to remove an organ while a dying patient was still alive. Then

they had to wait until the patient’s heart stopped and a doctor made an

official declaration of death before rushing into surgery. The more time that

passed between dying and transplantation, the more the organs deteriorated,

and the worse the prospects became for the patients who received them. Meanwhile, the transplant surgeons could see more and more patients

lying in coma dépassé, awaiting death with their organs intact. “Patients are being brought in dead to emergency wards and potentially useful kidneys

are being discarded,” Murray complained. Some doctors quietly took matters into their own hands. They would

prepare a patient to receive a transplanted organ, and then they would wheel

in another patient in coma dépassé.

The doctors turned off the ventilator

and waited for the sure sign of death: the ceasing of the heart. Then they immediately removed an organ from the donor and moved it to the living

patient. This procedure cut down on the time required to carry out the

transplant, but even in that short period the organs could still deteriorate. In Belgium, a surgeon named Guy Alexandre decided he would no

longer wait so long. Preparing for a kidney transplant, Alexandre picked out

a patient who had suffered catastrophic brain injuries and showed no sign of

brain activity. Without turning off the ventilator, he removed a kidney,

which he immediately transplanted into its new host. The donor soon died,

while the transplanted kidney went to work right away. It kept on working

for the next three months, until Alexandre’s patient died of sepsis. In 1966, Alexandre described what he had done at a surgical conference. The other doctors in the audience balked. “I feel that if a patient has a heart beat, he cannot be regarded as a cadaver,” said the British surgeon Roy

Calne. The president of the meeting asked for a show of hands from surgeons

who agreed with Alexandre’s definitions of life and death and would follow

his example. Only one hand shot up: Alexandre’s. In 1967, Beecher organized a committee at Harvard to figure out how to

define this mysterious new state. Murray and other doctors joined him, as

did a lawyer and a theologian. They immediately launched into fierce

debates for months, but eventually they agreed on a report that they

published in 1968 in the Journal of the American Medical Association. It offered a new standard for declaring a patient dead: the death of the brain. The committee argued that medicine had to free itself from obsolete

notions of life and death. A stopped heartbeat had once been a reliable way

to rule someone dead, since it led to the lungs and brain failing, too. Now

doctors had the means to keep a heart beating even when the brain was

damaged beyond hope. “These improved activities can now restore ‘life’ as

judged by the ancient standards of persistent respiration and continuing

heart beat,” the committee wrote. Beecher and his committee spoke of “life,” rather than life. Massive

brain damage often left patients without the remotest possibility of

recovering consciousness, the committee declared. If doctors determined

that their patients had “brain death syndrome,” as the committee called it,

the time had come to declare their patients dead. The committee recommended that doctors carry out a series of tests before making the declaration. A patient’s EEG reading should be flat. The

pupils should be fixed and dilated. The doctors should shut off the

ventilator for a few minutes to make sure a patient could not breathe

without it. Some members of the committee thought doctors should repeat

these tests for three days in a row. But the transplant surgeons found this

delay too long with desperate patients waiting for organs. They persuaded

their colleagues to knock the recommendation down to just one day. A

doctor could then declare a patient dead and shut down the ventilator. The

committee advised doctors never to reverse that order. “Otherwise, the

physicians would be turning off the respirator on a person who is, under the

present strict, technical application of law, still alive,” they warned. The committee’s report was loaded with helpful guidance, but it was

sorely lacking in argument. Beecher and his colleagues simply asserted that

patients with brain death syndrome should be declared dead, rather than

making a case for it. They raised huge questions, which they left hanging. When the committee claimed people with brain death syndrome had no

hope of regaining consciousness, for example, did they mean that

consciousness was the essence of life?

These gaps went overlooked when the report came out. The New York

Times put it on their front page with the headline “Harvard Panel Asks

Definition of Death Be Based on Brain.” Doctors in the United States and

other countries swiftly fell in line. A decade later a Harvard surgeon named

William Sweet looked back at the 1967 meeting and judged it an

unquestionable success. “The inescapable logic of the concept that death of

the brain is equivalent to death of the person has now achieved widespread

acceptance,” he wrote. That acceptance gradually became law. States began

adopting what came to be known as the “whole-brain standard”: people

with “irreversible cessation of all functions of the entire brain, including the brain stem,” as the law put it, are dead. —

On December 9, 2013, a girl named Jahi McMath was admitted to

Children’s Hospital in Oakland, California, for a minor procedure to treat

her snoring. A surgeon removed her tonsils and part of her palate, and a few

hours later she was awake and enjoying a Popsicle. But an hour later Jahi

was spitting up blood. Less than five hours after that, her heart stopped. Jahi’s medical team rushed to her aid and got her heart beating again, but they had to put her on a ventilator. The following morning, when

doctors examined her, they determined she had suffered a devastating lack

of oxygen. No brain waves appeared on her EEG. Her pupils didn’t react to

light. Forty-five years had passed since Beecher’s committee had mapped

out the concept of brain death, and Jahi’s doctors now decided she clearly

met its standards. Three days after her disastrous surgery, Jahi McMath was

declared dead. Thanks to the ventilator, her lungs still inflated with air and her heart

still beat. A social worker met with Jahi’s stunned and devastated family to

talk about shutting it off. But their experience with the medical staff had left them embittered. When Jahi started spitting up blood, her family had

begged for help, and it only came slowly. Later, it emerged that the doctor

in charge had made a note that her carotid artery was unusually close to her

tonsils, which the hospital staff apparently overlooked. Now the social

worker left Jahi’s family feeling as if the hospital was leaning on them to

kill her. They refused to agree to turning off the ventilator and instead asked for it to be kept running. And they also asked for a feeding tube so that Jahi

would not starve to death. The hospital refused to give care to someone who had just been declared

dead. So the family went to court with their demand. “Plaintiffs are

Christians with firm religious beliefs that as long as the heart is beating,

Jahi is alive,” their lawyer, Christopher Dolan, told the judge. The judge ordered that an independent neurologist review the case. He

came to the same conclusion as the hospital’s doctors: Jahi was dead. Her

beating heart was irrelevant; all that mattered was the state of her brain. After more negotiations, the family and the hospital reached an agreement. A coroner would issue a death certificate, and then the hospital would

release Jahi to her family still hooked to a ventilator. Using funds raised online, Jahi’s mother, Nailah Winkfield, put her on a

plane and flew with her across the continent. They landed in New Jersey, a

state that allows families to reject brain death on religious grounds. Most doctors and bioethicists found this turn in Jahi’s case deeply

frustrating. Brain death was death. Some experts hinted that moving Jahi’s body to New Jersey was just a ploy cooked up by Dolan in order to squeeze

money out of the hospital in a lawsuit. “She is going to start to decompose,”

the bioethicist Arthur Caplan told USA Today. By the time Jahi was settled in at her new hospital, she hadn’t eaten for three weeks. When doctors gave her a feeding tube, she began to improve. Most patients declared brain-dead died within hours or days, but Jahi

remained alive week after week, month after month. Her teenage body was

growing. She began to menstruate. In August 2014, Nailah moved Jahi out of the hospital and into an

apartment. Nurses cared for Jahi round the clock, and Nailah helped them

turn Jahi every four hours to protect her from bedsores. Meanwhile, Jahi’s family launched a lawsuit against Children’s Hospital

Oakland for malpractice. A nonprofit foundation paid for a doctor to give

her a new battery of neurological tests. Dolan later announced that the test

revealed that some regions of her brain were still intact, with blood flowing

through them. He asked a California court to have Jahi declared alive. Once

again they turned his request down. Three years later a staff writer for the New Yorker named Rachel Aviv

paid a visit to the apartment. Nailah showed Aviv videos she had taken on

her cell phone. In the jumpy movies, Jahi moved her fingers or toes,

seemingly in response to her family and her nurses. When Nailah asked Jahi

to move a finger, Aviv saw it move with what looked like a flicker of

agency. “I could also be investing undue meaning in gestures nearly too subtle to

discern,” she later wrote. The case of Jahi McMath opened up a debate about the meaning of brain

death. The more it unfolded, the more it became clear that the debate ran in

striking parallel to the one over abortion. It came down to what we think it

means to be alive—and, more particularly, what it means for us humans to

live. Ever since the Harvard meeting in 1967, some critics had questioned the

logic of brain death, and Jahi’s case now threw their questions in high relief. How could someone diagnosed with brain death have a heart that continued

beating for years?

How could she enter puberty, and possibly even respond

to commands?

Alan Shewmon, a California neurologist and a longtime

critic of the brain death diagnosis, was invited by the McMath family to

look over their videos and tests. “I am convinced that, from early 2014, Jahi

McMath was in a ‘minimally conscious state,’” he later declared. Shewmon speculated that when Jahi had stopped breathing, her brain

stem had been badly damaged, but parts of her cerebral cortex remained

intact. That would mean she did not meet the whole-brain standard for brain death, even though her exams indicated she did. Shewmon speculated that

the physicians who examined Jahi missed the fleeting moments when she

could respond to the outside world. Robert Truog, a Harvard pediatric intensive care physician, favored

another possibility. Jahi really had met the criteria for brain death after her surgery in 2014.

But she no longer did, Truog suggested. “Perhaps McMath actually improved somewhat, rising a little on the

spectrum of brain injury,” Truog wrote in 2018.

“This would not seem to be

surprising in itself. But what makes this conceptually important would be

that, in so doing, she would have crossed the bright legal line we have

drawn between the living and the dead.”

Other doctors were more skeptical. They were not impressed by the

secondhand accounts of the cell phone videos. Still, no one denied that Jahi

had gone through puberty. That transition is governed by the hypothalamus

in the brain. Among its many tasks, the hypothalamus is responsible for

releasing the hormones that trigger a child’s body to mature. The fact that

Jahi experienced puberty meant that at least this one small part of her brain

was still intact. The hypothalamus may be more resilient than the rest of the brain,

thanks to its peculiar anatomy. It sits at the base of the brain, where it is

nourished by a dedicated set of arteries. No one knows for sure how many

other people who have been diagnosed as brain-dead had an intact

hypothalamus. But there are hints that many did. Among its other jobs, the hypothalamus manages the body’s salt

balance. It does so by squirting a hormone called vasopressin into the

bloodstream. The hormone is exquisitely fragile, surviving only minutes

after its release. To keep a body’s level of salt steady, the hypothalamus has

to monitor it and provide a steady supply of vasopressin. If a stroke or a

tumor destroys the hypothalamus, it throws off the body’s salt balance,

leading to a condition called diabetes insipidus that can damage the

kidneys. In 2016 a team of researchers reviewed medical information on 1,800

patients who were diagnosed as brain-dead. Some of them suffered from

diabetes insipidus, suggesting that their hypothalamuses were no longer

working. But some did not have the condition. The researchers concluded

that roughly half of the patients showed signs that their hypothalamus was still regulating their salt. One of the authors of that study was Michael Nair-Collins, a bioethicist

at Florida State University. He went on to publish a series of attacks on the

whole-brain standard for brain death. He argued that a patient simply can’t

be in whole-brain failure if part of their brain—in this case the

hypothalamus—is still working. If doctors come to that conclusion after an

exam, Nair-Collins said, the problem does not lie in the patient’s brain but

in the exam, or perhaps with the concepts of life and death that the doctors

rely on. The hypothalamus is one of many parts of the body that are essential to

keeping our body balanced. A proper balance of salt is important, but so is a

proper blood pressure, which is regulated by hormones released by the

kidneys. The body also needs a stable supply of red blood cells. The spleen

destroys old cells as the bone marrow produces new ones. The immune

system needs to fight off pathogens while brokering a peaceful relationship

with the trillions of bacteria that live in our bodies. The food that comes

into the body—whether through our mouths or through a feeding tube—has

to be converted to sugar and other nutrients. The liver and other organs have

to store extra sugar and then release it to keep its level steady in the blood. In fact, the only reason that ventilators can work at all is that they pump

air into bodies that are actively maintaining their inner balance. The air that they pump into the lungs has to reach the delicate ends of their branches,

where their oxygen can get absorbed into blood vessels. The cells at those

ends keep the lungs open by making a greasy film to coat the branched

endings of the airway. “The ventilator is capable of blowing air in and out of the bronchial

tree,” said Nair-Collins. “The organism must do the rest.”

These facts apply not only to Jahi McMath, he argued, but to every

patient diagnosed with brain death who can still breathe on a ventilator. In

every case, the patient’s body remains alive in a fundamental sense. “The

implications for brain death are obvious,” Nair-Collins said. “The patient

meeting brain death criteria, supported with mechanical ventilation, is

clearly biologically living.”

While Nair-Collins called for abandoning brain death, its champions

continued to fight for it. James Bernat, a neurologist at Dartmouth Medical

School, published his first defense of brain death in 1981.

When Jahi

McMath’s case drew national attention thirty-three years later, Bernat did not see it as a reason to give up the concept. The trouble lay not in the

concept but in the tests. Jahi’s diagnosis, Bernat said in 2019, “may

represent a false-positive determination of brain death.”

But one false positive didn’t mean that the whole concept of brain death

was wrong, Bernat argued. The cells in our bodies are alive, but our human

life is not defined by its parts alone. What matters to a human life is how its parts are integrated, creating new levels of complexity. The human brain

integrates signals from across the body and sends out commands to manage

it. From that integration emerge our reasoning, our self-awareness, and all

the other things that we call the human mind. “Death is a biological and irreversible event that all organisms share in

common,” says Bernat. For all of them, death is the loss of their wholeness. A microbe dies if it loses the integration inside a single cell. For humans,

Bernat argued, there’s much more to lose: “Although both a living bacterial

cell and a human being eventually die, the events of death markedly differ.”

In humans, the essential functions of the organism as a whole are carried

out by the brain. So brain death—the permanent loss of those functions—is

the criterion of death for our species. As these arguments unfolded, Jahi began to falter. After three years of

health, her liver failed and she developed internal bleeding. Exploratory

surgery did not discover the source of her trouble, and she continued to

decline. Jahi’s doctors suggested another operation, but Nailah Winkfield

decided Jahi had suffered enough. “I told her, ‘I just want you to know, don’t stay here for me. If you want

to go, you can go,’” she later said. Jahi died on June 22, 2018, at age seventeen. Her mother brought her

home at last to California for a funeral. The state of New Jersey, which had

considered her alive until then, issued another death certificate. In the

purblind eyes of the law, Jahi McMath died twice. PART TWO

THE HALLMARKS

DINNER

One afternoon in Tuscaloosa, I met a python named Haydee. At the

age of three, she had already grown over six feet long, her muscular

cross-section thicker than a bodybuilder’s biceps. She lay coiled in a

fiberglass box, and under its lights her scales gleamed like a dark diamond

sleeve. As I admired Haydee, her owner, a man named David Nelson, tossed

her a live rat. The rodent froze in a corner of the box, but at first Haydee

seemed indifferent to it. She gazed toward Nelson instead. It had been two

weeks since she had eaten her last meal, so perhaps she wanted to see just

how many rats were on the menu today. Nelson moved on to tend his other snakes, and after a while Haydee

lazily turned back to her visitor. She flicked her branched tongue. And then,

in the middle of one of my blinks, she lunged. Her languid body turned into

a missile. On the roof of Haydee’s mouth were a pair of long curved teeth. As her

head crashed into the rat’s body, she dug them into her prey. She coiled her

trunk, wrapping herself twice around the rat. Above the coils, I could see

pink legs and a hairless tail sticking up in the air. Between them I could see

the rat’s white midriff still taking in breaths. It looked as if Haydee was suffocating the rat, but scientists suspect

that’s not actually how pythons kill. Their prey simply die too fast. It’s

possible that the snakes extinguish the life of their victims by pushing extra

blood into their brains. Instead of a blackout, they experience a red-out. Haydee’s rat grew still in under a minute. She unspooled herself and slithered away as if she had forgotten the

dead animal in her midst. Later she sidled languidly back. When she came

face-to-face with the dead rat, she opened her mouth again. Now she used

the small teeth on the sides of her mouth to grab its head. She did not swallow the rat so much as ratchet her own head over it. Saliva oozed from

glands in her mouth to lubricate the rat’s body, making it easier for her to

slip her jaws over its shoulders and front legs. Her jaws stretched apart to

either side so she could widen the passageway for her meal. Haydee pushed

the rat down her esophagus by curving her body from side to side. After a

few minutes of these contortions, she arched her head up, looking toward

the glass door of the box again. She offered her human audience a chance to

say farewell to the rat as its hind legs and tail glided out of view. —

Barring a case of Cotard’s syndrome, each of us knows that we are alive. Thanks to our socially tuned brains, we have a swift intuition about the

lives of our fellow humans. It’s harder to recognize life in other species,

because we cannot talk to them or interpret a smile flashing over their faces. But from infancy onward we use mental shortcuts to sense the lives of

others, like recognizing movements generated from within. At a young age

children recognize that animals, like humans, are alive, but it takes longer

for them to learn that plants are alive, too. As children get older, they don’t lose these intuitions, but they do develop the ability to shroud them in

words. If they’re asked why they know a snake or a fern is alive, they will

point to one of life’s hallmarks—the things that seem to be shared in

common by all living things. Children, in other words, are underage

biologists. And biologists, in turn, are overgrown children. I met Haydee on a series of trips I took to meet with overgrown children

who explore life’s hallmarks. Depending on the biologist you ask, you’ll get

a different set of hallmarks. But a few come up again and again:

metabolism, information gathering, homeostasis, reproduction, and

evolution. From species to species, each hallmark may take on an

unimaginable diversity of forms. But underneath even the most extreme

variations there’s a unity. I would not be able to swallow a rat whole like Haydee, for example,

but I do need to eat in order to live. Hummingbirds need to drink nectar, and

giraffes must browse treetops. A sequoia does not eat other living things,

but it still eats after a fashion, its meals little more than air and sunshine. This food then undergoes a transformation into work and flesh. Haydee

turned much of her rodent meals into muscle, gut, brain, and bone. Sequoias

turn their own meals into wood and bark. This transformation is known as metabolism, from the Greek word metabolē, meaning change. I was introduced to Haydee by the person who understood the

metabolism of pythons better than anyone: a biologist at the University of

Alabama named Stephen Secor. I found Secor at his lab, and we took a

drive from campus to the east side of town, past the Zion Hope Baptist

Church and Moon Winx Lodge, until we reached the home of David Nelson

and his wife, Amber. Secor pulled his RAV4 into the Nelsons’ driveway just

as David was heading toward his converted basement, hauling a blue cooler. He was a towering, bald man with a network of tattooed stripes that

snooped out from the sleeves of his green T-shirt. The cooler was full of

dead rats. Secor and I followed Nelson inside. The basement’s concrete floor was

covered by black spongy squares. Half the space was given over to weight-

lifting equipment and signs on the wall like U. S.M. C. and TONY STEWART

FANS ONLY. The other half of the basement was full of stacked fiberglass boxes that looked like refrigerators tipped on their sides. Each box was

fronted by a glass door, through which I could see a massive snake. Nelson and Secor began taking snakes out of their boxes, letting them

glide over their arms and necks. “How’s my sweetheart?” Secor asked a

python named Monty. “Monty’s a good snake, aren’t you?” he said. “Oh, yeah,” Nelson said gently, as if he were talking about his toy

Pomeranian upstairs. Yet Nelson never let his guard down around his

snakes. He was always aware of their movements, even as he let them flick

their tongues across his eyebrow. “Any of these could kill you if you let it,”

Nelson said, somehow cheerfully. Secor stood a few inches shorter than Nelson, but he could still handle

powerful animals. He grew up working on a horse farm, thinking he would

become a veterinarian. In college, one of his jobs was to help horses recover

from surgery. Horses have a bad habit of leaping back up before their anesthesia has

fully worn off, only to stumble and break a leg. Secor had to keep them

from rising before they were ready. He’d wrap his legs around their necks

and use his arms to pin down their heads. At first the horses would be too

groggy to resist him. Eventually they became strong enough to hurl him

away. “When they could throw me off, they had enough strength to stand up,”

Secor explained to me. It was during those horse-wrestling days that Secor

decided to scrap plans of becoming a vet and go to graduate school instead,

to study snakes. Nelson was a product manager at a local car parts factory during

working hours. The rest of the time, he was a snaker. He grew up catching

snakes in the Alabama woods, and once he bought a house of his own, he

started raising them indoors. He learned how to give a python a bath. He

perfected a way to swiftly kill rats without suffering, by mixing vinegar and

baking soda to flood a cooler with carbon dioxide. He learned how to

groom a shedding snake so that its skin came off in a smooth sheet. He

posted pictures of his pythons and boa constrictors on Instagram and

brought them to his church’s Bible school to teach children not to hate

snakes. “At night, this is what I do,” he said, looking across his serpentine

kingdom. Amber came down to the basement to watch the feeding. She had

frosted blond hair and rhinestone hoop earrings. At first, she told me, she

was not happy to be a snaker’s wife. But she changed her tune when one of

David’s snakes got sick. Amber, who is a nurse, helped him keep the

snake’s nostrils clear so it could breathe. As the snake recuperated, it would

coil contentedly in her lap as she watched television in the living room. “Momma mode came out, I guess,” she said. A friend in common introduced Nelson to Secor. At the time, Secor had

some snakes that had gotten too big for his research, and he wanted to find

them a good home. Nelson installed new stacks of boxes in his basement,

and Amber translated Secor’s soulless titles—AL1 and AQ6 and the like—

into names like Haydee and Samson. She was fond of all of Secor’s snakes, save one. She dubbed him

Lucifer. “You should have heard the first name,” she said. As Secor and Nelson let snakes glide around their necks, they rated the

personality of each animal. Monty was good with children. Some of the

other snakes were happiest in a dark corner. Others had figured out how to

slide open the box doors and liked to crawl up to the ceiling fan. Delilah, an

albino python, hadn’t eaten for months. “She has these spells every year,

and then she’ll pound food,” Nelson said. Nelson got back to work feeding the snakes. Today the menu was rats,

but on other days it was rabbits. “It’s easier for time management,” Nelson

said. “I give them a rabbit and I’m done.” Sometimes he managed to get weaned piglets for his biggest snakes. In the wild, pythons can readily eat

prey half their weight. They have been documented eating deer and

alligators. Out of deer and alligators, pythons create fuel. It is the same fuel that we

make, the same fuel that powers lichens growing on the tops of the Andes

and the crabs skittering in the depths of the Pacific. It consists of molecules made up of carbon, hydrogen, oxygen, nitrogen, and phosphorus, known as

ATP. Snakes and other animals make ATP inside their cells, using the sugar

in their food and the oxygen they breathe. Plants use photosynthesis to

make their sugar, which they can then use to build ATP. Some bacteria

make ATP from sunlight as they bob on the sunny surface of the ocean. Deep underground, other kinds of bacteria make ATP by harnessing the

energy stored in iron atoms. Once living things build up a sufficient supply of ATP, they can use it as

a fuel, breaking its bonds to unleash the energy inside. Haydee used it when

she slithered around her box, powering the contraction of muscle fibers. She

broke apart ATP molecules to power every beat of her heart. Her kidneys

needed ATP to pull toxins out of her bloodstream. And the biggest entry in

her fuel budget was the ATP she needed just to keep her cells intact. Cells need to keep a big supply of charged potassium atoms on hand to

carry out a lot of essential reactions. But with so much potassium inside a

cell, there’s a powerful force that pulls the atoms out into its surroundings. A cell would die if it just let its potassium bleed away. Instead, a cell uses

molecular pumps studding its surface, each made from three interlocking

proteins, to pull more potassium back inside. Just as a sump pump has to be

plugged into a generator, a molecular pump needs ATP for power. It will

use up one ATP molecule for every two potassium atoms it pulls in. These

pumps have to run day and night, consuming vast amounts of ATP along

the way. Haydee’s potassium pumps, like those in any organism, survive for only

a few days before they start wearing out. Her cells have to rip them apart as

they become defective and build new ones to take their place—a task that

requires using up even more ATP. The instructions for building new pumps are encoded in Haydee’s DNA. Deoxyribonucleic acid, as this molecule is properly called, is made of two

long strands that twist around each other. They’re like a miniature spiral

staircase with billions of steps. Pythons have 1.4 billion of these steps in their DNA, while we have over 3 billion. (Before you conclude that means

we are genetically superior to pythons, bear in mind that onions have 16

billion.) Every step is built from two parts that stretch out from each strand. Those parts, known as bases, spell out instructions for molecules in a four-

letter alphabet: adenine, cytosine, guanine, thymine; or A, C, G, and T for

short. Each of the three proteins in potassium pumps is encoded by its own

stretch of DNA: a gene. To make a new potassium channel, a snake cell will

bring enzymes and other molecules to the start of a potassium channel gene

and read it one base at a time. They will produce a shortened, single-

stranded readout, called messenger RNA. That molecule gets quickly

sucked up by a floating cellular factory, which reads its bases and builds a

corresponding protein. And at each stage of this creation, a cell must use

more of its ATP. Haydee was not just making new proteins to replace old ones. Her body

was also growing. She had already tripled in size since she had hatched

three years before, and she would keep growing throughout her life as long

as she got to eat every few weeks. And she would need more fuel to

expand. Just to create one new copy of its DNA, a cell has to break apart

billions of ATP molecules. Haydee even had to burn fuel to get fuel. She used up ATP to lunge at

rats and choke them to death. She needed more ATP to build digestive

enzymes, and those enzymes needed ATP of their own to break down the

molecules in the rat. All living things face this same quandary: they pay a

metabolic cost to keep their metabolism going. But snakes like Haydee take

this quandary to an extreme. Pythons, boas, rattlesnakes, and a number of

other species of snakes live through famines interrupted by feasts. They go

for weeks without eating, swallow animals whole, and then extract as much

ATP from them as possible in the days that follow. Stephen Secor became fascinated by this living alchemy in the early

1990s. At the time, scientists knew very little about how snakes digest their

prey. No one had even measured how much energy snakes used up in the

process. Secor decided to find out, starting off with sidewinder rattlesnakes

he caught in the Mojave Desert. He brought them to the University of

California, Los Angeles, where he worked as a postdoctoral researcher. He

fed them rats and then put them in a box. The box was designed to measure a snake’s metabolic rate: how much energy it used each hour. Secor took advantage of the fact that every time a

snake uses up some ATP, it needs to make some more. And to make ATP, an

animal needs oxygen. Every time a snake in Secor’s box took in a breath,

the level of oxygen around it dropped. From time to time Secor opened a

stopcock on the side of the box, inserted a syringe, and drew off some air. The level of oxygen in the syringe told Secor how much ATP the snake

inside was using up. “In two days I had these numbers that made no sense,” he told me. After we eat a meal, our metabolic rate climbs by as much as 50 percent

as we digest our food. The same is true for most other mammals. But

Secor’s rattlesnakes jumped by about sevenfold. With that observation

Secor broke the standing record for the metabolic rate of a digesting animal. He then promptly broke that record when he switched his rattlesnakes for

pythons. If he gave a python a quarter of its body weight in rats, its

metabolic rate rose tenfold. Secor kept feeding some of his pythons until

they ate their entire body weights in rats. Their metabolic rate increased

forty-five-fold. For comparison, when a horse goes from a standstill to a

full gallop, its metabolism increases by a factor of about thirty-five. But a

horse cannot run at a full gallop for very long before getting exhausted. When a python digests a meal, it can burn fuel like a racehorse for as long

as two weeks. Now Secor was left with an even bigger mystery: How were these

snakes ramping up their metabolism so dramatically, and what exactly were

they doing with all that energy?

The answer begins in the stomach, which

makes hydrochloric acid to start breaking down food. Our stomachs release

several squirts of hydrochloric acid a day, because we are adapted to regular

meals. But a fasting python makes none at all. The fluid in its stomach is

neutral, like water. As soon as Haydee swallowed her first rat on the day I

visited her, her stomach received a signal to make a flood of fresh acid. By

the time the rat’s head reached the end of her esophagus, her stomach was

ready to start dissolving it. This acid flood was only one of many changes that Haydee went

through once she caught the rat. Organs throughout her body began growing

in order to handle the sudden onslaught of food. Secor discovered that a

python’s small intestines double in mass overnight, and the fingerlike

projections on its cells extend their length sixfold. Once the partly digested

rat arrives in the intestines, they are ready to absorb glucose, amino acids, and other nutrients and deliver them into the bloodstream. The liver and

kidneys also double in weight in advance of the work they’ll have to do to

store the nutrients and expel the waste. The heart grows 40 percent in order

to push the extra load of sugar and other nutrients around the body. But this discovery only left Secor more baffled. He had no good answer

for how the snakes were transforming their bodies. They have the same

basic anatomy and biochemistry as other vertebrate animals. They have

livers, stomachs, and hearts that work much like ours do. Their cells come

in many of the same types as in our bodies, from neurons to pathogen-

killing immune cells. Many of their genes are nearly identical to our own,

encoding the same hormones, neurotransmitters, and enzymes. Secor

suspected that snakes are able to transform themselves so drastically not

because they have unusual genes, but because they use their genes in an

unusual way. Their genetic orchestra uses the same instruments as ours, but

they were reading different sheet music. When cells have to carry out a job—whether fighting a virus or

secreting bone—they begin reading certain genes and making proteins

based on their sequences. Some of these genes encode proteins that act like

master switches: they latch onto other genes and switch them on. Some of

those genes encode even more master switches. A regulating protein may

ultimately trigger hundreds of genes, which produce a swarm of proteins

that together carry out complex jobs. Secor formed a hypothesis that snakes

are using their regulating proteins in a peculiar way. But in order to test that hypothesis, he would have to track the activity of genes in his snakes. In the

early 2000s, when Secor started looking around for help, geneticists told

him he was on a fool’s errand. “I said, ‘What would it take to go after this?’” Secor recalled. “And

they’d say, ‘You couldn’t do it. It would take years and years and years,

because you’d have to pull each one out, and then you’d have to find out

what it was.’”

In 2010, Secor finally found someone who didn’t shut him down: a

geneticist named Todd Castoe. At the time, Castoe was sequencing small

chunks of DNA from reptiles at the University of Colorado School of

Medicine. Secor and Castoe became scientific partners, bringing together a

team of researchers to sequence the entire genome of the Burmese python. Once they had completed the job, they had both a catalog and a map to

guide their research. Now they could track the activity of genes as pythons changed their bodies for digesting. Castoe and Secor began collecting muscle and other tissues from

pythons, fishing out the messenger RNA the cells were making. They

looked at their catalog to match up the messenger RNA to the genes in the

python genome. Secor and his students compared the activity of genes in

snakes before and after eating to look for changes brought about by their

metabolism. The researchers expected that maybe twenty or thirty genes

would switch on. Instead, the snakes performed a far greater transformation. Within twelve hours of swallowing a rat, the scientists found, the

pythons switched on several thousand genes in organs across their bodies. Many of the genes worked together along ancient pathways, the same

pathways found in many other species of animals. Some of the pathways

that become active when a snake eats are used by many animals to make

their bodies grow. Others let them respond to stress. And still others create

the proteins necessary to fix damaged DNA. The growth pathway genes may enable snakes to swell their organs to

prepare to metabolize a massive meal. But making billions of new cells in a

matter of hours may also harm the snakes. Their cells grow so quickly that

they make deformed proteins, which create stress. Charged molecules may

fly around the cells, damaging their DNA. The snakes have to fix this

damage, a task that increases the metabolic cost of digestion even more. Haydee would spend the next week or two digesting today’s meal. All

told, she would burn up about a third of the energy in her rat simply to

digest it. She would burn so much fuel so fast that her body temperature

would rise. On an infrared nightscope, she would look as warm-blooded as

a live rat. It’s not a waste, though, since her metabolic fires still leave two-thirds of the rat for herself. Her blood would course with fatty acids, at a

concentration high enough to kill a human. Across her body, her cells

would take up the calcium, the amino acids, and the sugar she harvested

from her prey. She would grow some more muscle, add bone to her

skeleton, and store away new fat. And to survive until David Nelson gave her another rat, Haydee would

undo all the fleshy equipment she had swiftly created to digest her meal. Her strange, borrowed genetic networks would shut down. Her organs

would shrink down to their previous size. The cells in her intestines would

retract their tentacles. She would excrete all that was left of the rat, a pod of

hair, as she entered another long fast. There’s a simple logic to this extreme cycle, but it is so far from our own experiences that it can seem bizarre even

to trained scientists. Secor would sometimes show pictures of the intestines

of fasting snakes to pathologists. He’d point out the shrinking fingers and

ask their opinion of what was happening to his snakes. “Your animals are sick. They’re dying. They have parasites that are

ravaging their intestines,” they’d say. “No, they’re healthy,” Secor would insist. Secor never managed to persuade the pathologists that they were just

looking at a different kind of metabolism. “They just shook their heads and

sent me on my way,” Secor said. By the time Secor and I were ready to leave the Nelsons’ house, Haydee

had become still, a loosely coiled rope of glistening biomass. I could hardly

make out the bulges where the rats she had swallowed were gliding toward

digestive destruction. It was hard to believe she was the metabolic

equivalent of a racehorse. In a few days, when she had finished absorbing

their nutrients, her metabolic rate would slide down again. She would still

need to burn a little fuel to beat her heart, to pump charged atoms in and out

of her cells, to grow a little longer. Her basal metabolic rate would never

drop to zero. But she would get remarkably close. DECISIVE MATTER

Subash Ray pulled open a drawer and took out a smudged piece of

paper. It looked as if he had spilled his coffee on a Post-it note,

ignored it for a few days, and then tossed it in the drawer instead of

the trash. But now Ray was going to perform some magic on it. “We are going to bring spring to its life,” he said. Ray had a round face and rectangular glasses. He wore jeans and a polo

shirt decorated with a tiny dark eagle. He spoke softly, so softly that

sometimes I had to ask him to repeat himself as he described to me what he

was doing. I came to visit Ray and his colleagues in the city of Newark,

where he was earning his PhD at the New Jersey Institute of Technology by

studying these smudges and what they can become. Ray stretched his arm up to a high shelf and grabbed a jar of dried algae

extract, known as agar. He put it on the seat of a lab chair as if he were in a supermarket and it was his shopping cart. He added the smudged paper,

which he stored in a jewel glass for safekeeping. He found a pair of beakers

and a kitchen whisk. His chair fully loaded, Ray wheeled it into another room in the lab. I

trailed behind, along with Ray’s supervisor, a biologist named Simon

Garnier. Garnier was a red-bearded Frenchman who wore a hoodie and

played European handball—“like water polo on land,” he said, in an

unsuccessful attempt to explain it to a confused American. Ray rolled up to a sink, where he filled up an electric teakettle and

switched it on. He put his beaker on the counter and filled it with the water

after it had gotten hot. His whisk clanged as he stirred in some agar, and

then he poured the mixture into an empty petri dish. Once the agar cooled to a firm bed of goo, Ray picked up a pair of

tweezers, plucked the smudged paper out of its jewel glass, and transferred

it to the petri dish. He tamped it down on the agar and gave it a spritz of water. Now Ray steered the chair away from the sink, to a windowless room

that was overheated and sticky with humidity—the conditions in which

many living things like to grow. Against each wall there were large white

boxes sitting on tables. Ray turned a knob on the front of one box and

swung it up like a door. Inside I could see a pair of metal rails on which

rested three downward-pointed cameras, complete with flashes. Ray slid the

dish, with its smudge and goo, under one of the cameras. Garnier sat down at a laptop and began typing commands. After a few

moments the box lit up with a white glow, and then the camera flashed. As

the box turned dark again, we left the room, the camera set to snap a new

picture of the dish every five minutes. That evening Garnier took me out to dinner with some of his fellow

biologists. We walked down Raymond Boulevard, a street full of human life

and human construction—of little nail salons and massive warehouses, of

empty Art Deco buildings for lease and bus stops crowded with waiting

passengers. We reached a boutique restaurant where we sat around a

wooden table and shouted over the din about the living things around which

each of the biologists had built their working lives. They talked about the

nervous systems in worms the size of a comma, about the transparent

bodies of zebra fish. Meanwhile the camera back at Garnier’s lab popped

flashes through the night. The next morning I made my way back to the lab in the Central King

Building, and we reentered the humid camera room. We looked at the dish. The smudges were gone, and in their place was a lemon-colored blob. The

blob had spilled over the edges of the paper and spread across the dish,

growing to the size of a silver dollar. Garnier smiled as he looked over the

change. “Well, they’re alive,” he said. “They haven’t moved much, but they’re

alive.”

When I inspected the blob, I could see that it was actually a thicket of

tentacles that branched again and again as they radiated out from the center

of the dish. They were still splitting even as I looked down at them, but too

slowly for my short-attention brain to perceive. The creature Ray had brought to life was Physarum polycephalum,

otherwise known as the multiheaded slime mold. You can’t find slime

molds on the streets of Newark, but travel a few miles to a wooded preserve beyond the city—to the Eagle Rock Reservation or the Great Swamp—and

on a suitably warm, damp summer day you can spot its golden web on

decaying logs or the cap of a mushroom. Pretty much anywhere on Earth

where a forest grows, you can find Physarum or one of the hundreds of

other species of slime molds. Their bizarre appearance inspires visceral

names. Wolf’s milk. Dog vomit. After growing over the summer, Physarum prepares for winter by

making spores. The spores survive the cold as the rest of the slime mold

turns to a dead black crust, and in the spring they start growing again. But if this cycle is interrupted by a catastrophe—a drought or the crash of a tree

exposing the forest floor to harsh sunlight— Physarum takes emergency

measures. Its entire body dries up into a drab, brittle form, called a

sclerotium. The sclerotium flakes into fragments and blows away. If one of

those fragments lands on a damp patch of ground, it revives. Slime mold

researchers can make a sclerotium simply by putting a dollop of live

Physarum on a piece of filter paper and letting it dry out. They can store it away for weeks or months. If they then put a sclerotium in a dish of agar,

they can bring spring to its life. Flashing through the night, the camera had created a stop-action movie

of Ray’s slime mold. Sped up for human perception, it revealed the smudge

turning to gold before ballooning off the edge of the paper and expanding

across the agar. Later in the night, the tentacles on the opposite side of the

paper spread out as well. Now the slime mold became a spreading disk. Its movement was not the result of gravity acting on passive matter. The

slime mold did not spread like a drop of water. It was displaying a hallmark

of life: it was using its own stores of fuel, its own proteins, the logic

encoded in its own genes—the same combination found in all living things

—to make decisions about what to do next. It had agency. It was hunting. The graduate students and postdoctoral researchers who worked with

Garnier were an eclectic band. Some were off in Namibia, putting collars on

baboons to track their movements and record their grunts. They were

learning how the baboons stayed together as a group by exchanging

information about their locations. In Panama another student was studying

how millions of army ants used their bodies to create a living nest,

including chambers where their queen could live. The concept of decision-

making conjures up a human brain—plump, convoluted, generating word-

laced thoughts about the future. Our brains are tens of thousands of times bigger than the brains of ants, and yet ants can together create a house out

of their own bodies. Slime molds, without any brain at all, distill life’s

decision-making down to an even more exquisite essence. “What I really

like is that it gets back to the origin of intelligence,” Garnier told me. In the forest, a slime mold searches for bacteria and spores of fungi. It

extends its tentacles across logs and soil until it finds prey. As it crawls over its victims, it oozes out cell-slashing enzymes and drinks up the debris. “It’s a moving stomach,” Garnier said. When Ray brought his slime mold back to life for me, it started looking

for food, but he had not provided it any food to find. To let me see how a

slime mold discovers its next meal, Ray set up a new experiment. He placed

three pale chunks of cooked oatmeal on the agar, like the corners of a

triangle. “If you can cook porridge, you can grow slime molds,” Ray said. I

glanced up and noticed the rows of Quaker Oats canisters on the lab

shelves. They looked down at the scientists with cheerful colonial smiles. “They like the old-fashioned ones,” Garnier said— they being the slime

molds. To be more precise, they like the bacteria that grow on the old-

fashioned ones. No breakfast is sterile. Ray dropped a dollop of live Physarum in the center of the dish. It could not see the pucks of oatmeal. But it could taste the sugars and other

molecules that diffused away from the food and spread through the agar. As

the slime mold’s tentacles spread out from the center, proteins on their

surfaces picked up these signals. It then used a simple set of rules to seek

the food. As each tentacle moved, it compared the concentration of molecules at

different points in its path. If the concentration dropped, the slime mold

stopped extending tentacles in that direction. If the concentration went up, it continued to explore. Hours after Ray dropped the slime mold in the middle

of the dish, its tentacles had reached all three pucks. As they infiltrated the oatmeal, they turned it from gray to gold. With no brain to issue commands, slime molds allow scientists to see

how life’s powers of decision-making can emerge from nothing more than

biochemistry. They’ve discovered an entire playbook of elegant rules that

slime molds use to thrive. To show me one of their more impressive tricks,

Ray re-created an experiment that was first carried out in 2012 by another former student of Garnier’s. He created a slime mold cul-de-sac. It was simple enough to build. Ray used scissors to cut a sheet of acetate

into a sharp-cornered shape: |_|.

He set the acetate in a dish. Slime molds

can only crawl over damp surfaces, which meant that the dry acetate was as

impassable as a high brick wall. Ray then placed a scoop of Physarum near the open end of the cul-de-

sac. On the opposite side of the dish, he placed a drop of sugar. The wall of

the acetate cul-de-sac lay between them, but the sugar could sneak under it,

diffusing through the agar, teasing the slime mold with its fragrance, luring

it into the trap. The next day, when we came back to look in on the slime mold, it had

escaped its cul-de-sac. When I watched the overnight movie, I felt like a

guard reviewing a prison break. The slime mold followed the trail of sugar

into the cul-de-sac and hit the acetate wall. But it did not give up its search. It sprouted tentacles to either side. Its left-hand branches eventually reached the corner of the wall and then turned back, exiting the trap. They then

wheeled around and made their way along the outside of the wall, heading

toward the sugar. Slime molds manage this escape by using a brainless kind of memory. They continually send out probing tentacles, and the ones that don’t detect

increasing signals of food retract. As they pull back, the tentacles leave

behind a slimy coat. Physarum can sense its own trails and will steer its new tentacles away from them. This external memory lets a slime mold

override its attraction to sugar. Rather than banging its multiheaded head

against the acetate wall, it can move out of the cul-de-sac and explore new

paths toward food. We need a brain to remember things, but Physarum has no such organ. Instead, it stores a record of its experiences in the outside

world. Slime molds have solved far more complex problems. A scientist named

Toshiyuki Nakagaki, for example, found that slime molds can discover the

shortest path through a maze. He built a labyrinth by cutting pathways out

of a plastic sheet and setting it on a bed of agar. Nakagaki and his

colleagues placed an oat flake covered in slime mold at one opening of the

maze and put more oats at the other. The slime mold extended new tentacles

through the labyrinth, exploring every possible path. Once it found the

oatmeal at the end of the maze, it began feeding on both supplies of food at

once as it retracted the branches in the dead ends. Eventually the slime mold became a single streamlined tentacle mapping a route through the

maze. Nakagaki designed the maze so that the slime mold could take four

possible routes to the food. In the end, he found, it always traced the

shortest path. Some scientists have given slime molds other puzzles to solve that have

more bearing on their lives on the forest floor. In nature, slime molds don’t

find food at the two ends of a maze. Instead, they may encounter patches of

food scattered across a log. If they can feed on all the food at once, they

will grow faster. But, to reach all the food, they have to pay the metabolic

cost of building tentacles. If they overbuild, they will use up more energy

than they get from the food. It turns out that slime molds are very good at finding an efficient

solution to this problem: they work out the shortest path to several pieces of

food at once. Nakagaki and other slime mold experts have run experiments

to see how slime molds make these complex choices. They sprinkled oats

across a dish and watched Physarum work out a solution. Instead of

forming a single zigzag tube, it built a network that connected the oats in

close to the shortest possible distance. In one experiment, scientists created

a map of the United States, with oatmeal standing in for the biggest cities. The slime molds built what looked remarkably like the American interstate

highway system. They have mimicked Tokyo subways and Canada’s

transportation network. It’s unsettling to mathematicians that slime molds

can solve this kind of problem in a few days. It’s kept them busy for

centuries. Another puzzle that has kept generations of mathematicians busy is

known as the Knapsack Problem. Imagine you’re preparing for a hike, and

you have to decide what to put in your knapsack. You can choose from a lot

of different items that are more or less useful for the trip. But you also have to keep in mind the weight of your items, since you can’t pack an infinite

number of them. You might tuck a deck of cards in your backpack so that

you’d be able to pass the time on rainy mornings in the mountains playing

poker. But you wouldn’t fill your knapsack with a forty-pound chess set

made of carved soapstone merely to make sure you didn’t get bored. Mathematicians distill this choice into a pure abstract form. You have a set

of items, each with a value and a weight. Now you must find the

combination of items with the greatest value that is under a certain weight. Many businesses face practical versions of the Knapsack Problem. Airline companies want to figure out how to pack their planes so they can

deliver the most valuable cargo using the least amount of fuel. Financial

firms look for the best way to spread their funds across investments with

different potential returns. There’s no simple equation to solve the

Knapsack Problem, though. Researchers have filled books with strategies to

get us close to the best solution. Slime molds may not be able to write books, but they can solve the

Knapsack Problem. Audrey Dussutour, a scientist at Paul Sabatier

University in Toulouse, France, and her colleagues brought their skill to

light by translating the problem into the terms that matter to slime molds:

food. To grow as fast as possible, Physarum needs both protein and

carbohydrates. It turns out the optimal mix is two parts protein to one part

carbohydrates. Dussutour offered Physarum a choice between two lumps of food, both

far from ideal. One was nine parts protein to one part carbohydrates, and the

other was one part protein to three parts carbohydrates. If the slime mold

reached out to the first lump and only ate that, it wouldn’t get enough

carbohydrates. The second lump would leave it without enough protein. The slime mold managed to turn Dussutour’s two bad choices into one

good one. It grew tentacles out to find them both. Eventually its network

collapsed into a highway joining the two supplies of food. Simply mixing

them together would not give the slime mold its ideal diet. And so the slime

mold drew more food from the protein-rich supply than the carbohydrate-

rich one, balancing out its meal close to its ideal two-to-one ratio. In other

experiments, Dussutour tried out more combinations, and the slime molds

always figured out how to balance them. In other words, they learned how

to stuff their knapsack with the right blend of supplies. As slime mold researchers run more of these experiments, they better

understand how a web of Physarum makes its way in a forest. It takes in information about everything it touches, and as it encounters places rich in

bacteria and spores, it can shift to these feasts. If it creeps out into the

sunlight, it can pull back into the shade. It can adjust its network from day

to day with a mathematician’s precision so as to guzzle the biggest meal for

the least cost. It’s a strategy that works impressively well. Under the right

conditions, slime molds can get as big as a throw rug. When I asked Garnier how exactly slime molds solve all these

problems, he gave a Gallic shrug. “Welcome to the beautiful world of slime

molds, where nobody knows much,” he said. But one of his graduate students, Abid Haque, was willing to show me

where he and Garnier suspect that some answers lie: inside its golden

tentacles. Before coming to Newark, Haque had been studying to be a mechanical

engineer at the Indian Institute of Technology Guwahati. A summer

research project lured him to the kingdom of Physarum, and now he was

working toward a PhD in Garnier’s lab. The day we met, he was wearing a

black T-shirt covered with Victorian engravings of slime molds: filigreed

spore cages, tadpole-like sexual cells, and Physarum webs looking like

elastic trees. Haque carefully snipped an inch-long slime mold tentacle and took it to

a dim microscope room. He quietly twirled the knobs on the microscope for

a few seconds. “Oh, this is gorgeous,” he said. When I looked down at the slide, it took a while for my eyes to adjust

and for my brain to figure out what I should be seeing. And then, in an

instant, I was looking at a green river. The current carried along grains,

some dark and some light. As I watched, the river slowed down. The grains

coasted to a stop. After a moment of stillness the river reversed course and

pushed the grains back the other way. The lighter grains contained enzymes that the slime molds use to break

down food. The darker grains were nuclei, microscopic sacs in which they

hold their genes. We have nuclei in our cells, too, but typically each cell

contains just one. When it divides in two, it makes a new nucleus so that

each new cell inherits its own set of DNA. Slime molds can also make new

nuclei, but they don’t bother to divide their cells in two. Instead, every

slime mold—stretched out over a petri dish or across a forest floor—is a

single gigantic cell. “It’s mind-boggling that it’s just one thing,” Garnier said. Physarum comes from the Greek, meaning “small bellows.” It was

probably inspired by the pulsations that naturalists could see with their

naked eye in the slime mold’s golden web. The early generations of slime

mold scientists had no way to determine what made them throb. It was only

in the 1900s that biologists got their first glimpses of the molecules that

slime molds are made of. Each tentacle is enmeshed in a microscopic skeleton of wires. It’s not a rigid trusswork like the Eiffel Tower, though. A slime mold is perpetually

building new parts of its skeleton and taking down others. It can assemble

wires in a tight network that pinches a tentacle and pushes away the fluid

inside. If the wires slide away from each other, the walls of the tentacle

relax, letting the fluid flow back in. Squeezing and slacking, the slime mold beats like a web-shaped heart. The pulsations push the grains in waves, and these waves can ripple across

its entire network, crashing into each other to create even more complex

patterns. Haque and Garnier wondered if these waves might serve as a kind of

information relay for the single-celled slime mold, allowing it to learn about

its surroundings and merge its findings in a vast, wave-based computation. The slime mold could then reach decisions about what to do next. To decipher this language of waves, Haque began with a simple

experiment. He placed inch-long sections of slime mold tentacles in dishes. Inside each tentacle, waves traveled back and forth. Haque put a dollop of

food just out of reach of each end. One was rich with oatmeal, the other less

so—and thus less desirable. The slime mold sensed the food and stretched

out in both directions. And as it probed the two meals, Haque found, its

waves changed. Haque and his colleagues found that the waves moved more often

toward the good food than toward the bad. And as the waves changed, the

slime mold itself changed. The skeletal wires at the end that was feeding on

the good food fell away, causing the slime mold to swell. Meanwhile, some

researchers have theorized, the end of the tube feeding on the bad food

stiffened its walls. The result was that the slime mold crawled away from

the bad food and engulfed the good. “It would be like when you get to a good location, your muscles melt,”

Garnier told me. “But it’s okay, because you are in a good place.”

Melting your muscles once you reach a good place is, Garnier argued, a

kind of intelligence. To him, intelligence is not a score on an IQ test or the

ability to learn Dutch. It is a hallmark of life: the ability to respond to a

changing environment in a way that helps keep an organism alive. “If you compare any organism, they do better than random,” Garnier

said. We need an overstuffed brain to do better than random, but cellular

waves rolling across a network of tentacles may also suffice. “The slime mold,” Garnier said, “is the thing that has pushed this principle as far as possible.”

PRESERVING CONSTANT

THE CONDITIONS OF LIFE

On a snowy morning in the Adirondacks, I hiked up a hillside to an

abandoned graphite mine. I trailed a pair of biologists, Carl Herzog

and Katelyn Ritzko. They stopped at the maw of a mine, alongside a

frigid stream. Herzog and Ritzko began to change gear to go inside, and I followed

their example as best I could. I took off my hiking boots one at a time and

tried to get my socked feet into a pair of chest waders without tripping over

into a drift. We put on helmets with headlamps. We peeled off outer layers

of flannel and fleece. It was time to trade our defenses against the snow and

winter winds for defenses against cold water and sharp rocks. Herzog ran

down a list of risks we might encounter inside the mine. “Tripping and

falling is the biggest threat,” he said. “You don’t ever want to touch the

ceiling.”

As Herzog spoke, Ritzko was storing pencils and notebooks in her

wader pockets, checking batteries in an assortment of devices. “Ready to go?” Herzog asked her. “Tally-ho,” she replied. We stepped down into the frigid current and

waded into the mine. The snowy light dimmed as we splashed forward. The walls were sloped

and jagged. After a night of hard rain and a morning of snow, water was

pouring down from the overhanging hillside. As it streamed into the mine,

the water froze into icy versions of stalactites and stalagmites. The cave

grew dim as we waded farther in, and the stream gained a thick frozen lid,

as clear as a window. Ritzko climbed out of the stream and walked along a narrow strand of loose rocks running along the right-hand wall. But Herzog wanted to take a

closer look at the left side of the cave. He stepped up onto the transparent

ice, levitating one nervous step at a time. “If I break through, I have waders up to my chest, so it should be no

concern at all,” he said, hovering. “But it’s amazing how much anxiety it

conjures.”

Herzog scanned a flashlight across the wall and saw nothing. He

gingerly crossed back over the skin of ice to join us, and we moved into the

darkness. I had to remind myself I was not in a natural cave but a vast man-made

hole. In the mid-1800s, lumberjacks around Lake George noticed veins of

dark minerals in their log skids. They turned out to be deposits of graphite. The lumberjacks reinvented themselves as miners, digging into hillsides

and hauling out graphite to be turned into pencils and crucibles. The mine

that we were now entering, near the town of Hague on the banks of Lake

George, grew over the years into a network of rough-walled tunnels, tight

passageways, and side chambers. As the miners carted out rock, they

sometimes brought in tall timbers to prop up the ceilings, creating an

underground grove of undead trees. The New York graphite boom lasted a few decades before bigger,

cheaper mines opened up in Madagascar and other countries. In the early

1900s, miners pulled out some of the timbers from the Hague mine to sell

for lumber and then gave up on it completely. Over a century had passed,

and now I could see only a few traces of their presence. In the surrounding

woods, there were scattered hillocks of rock hauled out of the mine. A

string ran down the length of a deep tunnel, perhaps a guide back out for

men lost in the dark. After people abandoned the mine, the elements slowly reclaimed it. Water coated the hacked walls with a glossy coat of flowstones. It decorated

the ceilings with striped ribbons known as cave bacon. Some of the timbers

that the miners hadn’t pulled out had since tumbled into the stream. Herzog

pointed out parts of the ceilings and walls that had collapsed, dumping fresh

rock and erasing passageways. “I don’t expect it to happen while we’re here,” Herzog said, but he

warned me not to touch the timbers. “You can dislodge things if you touch

them.”

Herzog and Ritzko’s flashlight beams flicked over the walls and ceilings, up into alcoves, deep inside fissures. This cold, rocky labyrinth

seemed about as lifeless as a place could be. But after an hour of

spelunking, Ritzko’s beam froze. I made my way over the loose rock to

where she stood and followed her gaze. At eye level I saw what looked like

a furry pear dangling from sheer stone. “It’s a northern long-eared bat,” Ritzko whispered. The bat pressed its face against the cold mine wall. I could make out its

wedge-shaped ears poking out from its head and its miniature feet splayed

out as anchors. “How does it stay up?” I whispered. “Their ankles have a locking mechanism,” Ritzko said. “It expends

almost no energy to hang there.”

“Is it even breathing?” I wondered. “It is breathing,” Ritzko whispered. “But everything is much slower.”

The bat we observed had flown into this mine four or five months

before. It had found a place to hang from the walls of stone and had

survived through the winter without eating a morsel. Within a few weeks

the bat would fly out again, to enjoy months of glorious spring and muggy

summer. Even on the hottest days it would manage not to cook itself. It

might get infected with bacteria and fend them off. It might have a bad

night of hunting and manage to avoid starving to death. When it chased

after prey, its heart could pound without pushing so much blood into its

head to make its brain explode. And in the fall, it would return to another

mine like this one to endure another winter. As Ritzko and I examined the

northern long-eared bat hanging before us, I marveled at the fact that this

animal can withstand these unpredictable crises and drastic crises for

eighteen years or more. The bat and the mine in which it hibernated could

not be more different. The lifeless mine was gradually collapsing. Within a

few decades the eroding power of the seasons might erase it altogether. And

yet this little bat inside the decaying mine remained astonishingly stable. “All the vital mechanisms, however varied they may be, have only one

object, that of preserving constant the conditions of life in the internal

environment.” So wrote the French biologist Claude Bernard in 1865.

Bernard observed that our internal environment is mostly water. When our

body’s water supply starts running low, we get thirsty, causing us to

replenish it. In 1926 the Harvard physiologist Walter B. Cannon updated Bernard’s concept and gave it its modern name: homeostasis. Homeostasis is not a physical thing to be weighed or poked. It is not a

particular assembly of atoms forming a molecule like DNA or proteins. It’s

instead a principle that you can find throughout the living world, acting on

many levels at once. In a bat, it is present in its cells, in its organs, and even in its flight. While few people have seen a bat hibernating in a cave, many have seen

them on warm evenings, darting through the fading light after a mayfly or a

mosquito. Once the sky grows black, bats will go on flying, unseen in the

dark, traveling hundreds of miles in a single night. They stay aloft thanks to

an airborne form of homeostasis. To fly, bats flap their gargantuan, membranous hands. As they push

down, they set the surrounding air into swirls that circulate around their

wings, and with each upstroke they shed some of the air behind them as

spinning donuts of air. The physics of these swirls is so complicated that

scientists still barely grasp the fundamentals. But the outcome is clear: the

pressure above the wing drops as the pressure below increases, creating an

upward force. By adjusting the timing of its wingbeat, by spreading or closing its long,

spar-shaped fingers, by contracting some wing muscles and relaxing others,

by sculpting the invisible donuts of air that trail behind it, a bat can

precisely cancel out gravity. It hovers in place. And if a hovering bat tilts its wings, it can turn some of that lift into thrust, which shoots it forward. Northern long-eared bats and other insect-eating species chase their prey by

shrieking and listening to the echoes that bounce back. Many of the species

they hunt have evolved the ability to hear bat echolocation, and they try to

bank suddenly to escape. The bats can follow suit, folding a hand to make a

tight turn. As a bat flies, it perpetually runs the risk that the swirls of air will peel

away from its body, causing it to fall like a pebble. A homeostasis of air

keeps it aloft. One secret to this stability is a scattering of tiny hairs on the bat’s otherwise hairless wings. The hairs sway as the currents of air shift

around them, and their fluttering gets translated into electric signals that

travel to the bat’s brain. The bat can sense warning signals that swirls of air are going to peel away and adjust the shape and curve of its wings so they

will keep hugging its body. Bats regularly get buffeted by unexpected gusts of air. When swarms of them rush out of caves each evening, they often crash into each other. Because bats are so small—a northern long-eared bat weighs about as much

as an empty envelope—these disruptions can easily throw them off kilter. They may then stall and crash. The biologist Sharon Swartz got to wondering why bats aren’t

constantly dropping out of the sky. At her lab at Brown University, she and

her students filmed bats in flight, capturing a hundred images every second. To study how they handled gusts, they installed a tube that could deliver a

puff of air to bats flying past. It hit one of their wings, swinging their bodies about a quarter turn. In less than a tenth of a second, Swartz found, the bats righted

themselves. A close look at the films revealed their trick. If a puff of air

caused a bat to roll to the left, it stretched out its right wing, forcing its body to roll back. As the bat approached an even keel, the rotational forces of the

two wings perfectly canceled each other out. Its balance was restored. This strategy is familiar to engineers. It’s the same one built into cruise

control systems, for example. When a driver puts a car on cruise control,

the vehicle doesn’t simply spin its engine a fixed number of times a second. It continually adjusts the rate as it senses its acceleration. If the car heads down a hill, its sensors cause it to slow down. Once the car drops below the

desired speed, it gently accelerates again. Negative feedback loops, as

engineers refer to these designs, keep systems stable by pulling them back

to a set point each time they’re disturbed. Bats use negative feedback loops not only to stay in flight but to keep

their chemistry in balance. The sugar in their bloodstream remains

exquisitely stable even as they feast on insects, burn fuel in flight and then

fast during sleep. When bats sense that their blood sugar is rising, a blast of insulin triggers their cells to store away the extra supply. If the level of

sugar in the blood drops a little, the cells release enough to bring it back up without overshooting. Bats have other negative feedback loops for their salt, potassium, and

acidity. Like humans and other vertebrates, bats have a circulatory system

powered by a beating heart that demands a steady pressure to work. To stay

at that set point, bats use negative feedback to make their blood vessels

relax and tighten. Bats also keep their bodies at a constant temperature. If

they overheat, they can pump extra blood into their skin to dump excess heat into the air. Cold bats burn fat to stoke their metabolic fires. Bats evolved perhaps 60 million years ago, on a planet so warm that

Antarctica sprouted forests. Today most of the 1,300 species of living bats

are limited to the tropics. But some, like bats we were observing in the

Hague mine, have adapted to life closer to the poles, in places where they

have to endure long winters without any insects to catch, nectar to sip, or

fruits to nibble. Making matters worse, the cold temperatures in winter

demand extra energy to keep their bodies warm. Bats have evolved an extraordinary strategy to thrive in these

unwelcoming places, one that other species such as black bears and ground

squirrels have also hit on: they hibernate. In other words, the bats reset their homeostasis around a new set point. After a busy summer of hunting, northern long-eared bats search for

mates by visiting new caves or mines. Each evening they fly out into the

darkness again to find more food to store away in their bodies to get

through the winter. A six-gram northern long-eared bat may put on an extra

two grams of fat. Imagine surviving a five-month famine on half a teaspoon

of butter. The bats choose one last cave or mine where they will spend the

winter—a hibernaculum. They clamp their feet to the walls, hang upside

down, and slow their breathing. Within an hour their body temperature

plunges. They become as chilly as the cave air around them. As Ritzko and I inspected our northern long-eared bat, she jotted a few

notes down on her pad. When she was done, she cast her flashlight farther

down the mine and soon found more. I let her go, and clambered over to

Herzog, who was finding bats of his own. The mine was home not just to

northern long-eared bats, but to other species: little brown bats, big brown

bats, small-footed bats, even the rare tri-colored bat. They all looked alike to me, but Herzog pointed out subtle differences

between them: the shapes of their ears, the way some of them gripped the

stone with their thumbs as well as their feet. After a few rounds, he asked

me to ID a bat on my own. I shrugged a wrong guess. Herzog forgave me. When he went awhile without looking at bats, he

could get confused. “It’s a perishable skill, frankly,” he said. We were finding so many bats that we now could see patterns. This

mine was full of different set points. Some species clearly preferred to

hibernate closer to the mine’s opening, where the outside air made it cold

and dry. Farther back in the mine, the stagnant air was cool and damp enough to make my glasses fog. We found a little brown bat that had chosen

this set point, its fur turned from brown to silver by the beads of water

condensing on it. When these bats began hibernating a few months before, their torpor

freed them from the hard work of staying warm-blooded. Rather than

maintain a high body temperature, they could let themselves match the

temperature of the air around them. If they were hanging from a tree

outside, this strategy would have been suicide. The bitter cold of winter

would have frozen them solid, destroying their cells. But inside the cave,

insulated by rock and overhanging soil, they enjoyed a chilly but constant

temperature. They could, in effect, borrow the mine’s own homeostasis. The bats also had no need for fuel to fly, since they were forsaking

hunting till the spring. The females that had mated in the fall were not yet

pregnant. They were storing away their sperm till they roused again in the

spring, when they would finally fertilize their eggs. Then they could nourish

their hungry embryos with fresh food. Still, the bats hibernating here for the winter were very much alive. They went on inhaling oxygen to burn their ATP molecules. They needed to

breathe out carbon dioxide to keep their blood from turning too acidic. With

each exhalation, they also let out a tiny bit of water. More water evaporated

from their wings. The water they lost in a day wasn’t enough to put them in

danger. But after two or three weeks the bats felt the homeostatic pinch. Once they sensed they were running dangerously low on water, the bats

took a brief break from hibernation. They warmed back up to their

summertime temperature in a matter of minutes. Their reheated bodies

allowed them to flit around the hibernaculum and sip water. Now

replenished, they could return to a chilly roost to hibernate for another few

weeks. Every time the bats roused, they burned up more of their dwindling

supply of fuel. But in the spring, if all went well, they would emerge from

hibernation, their homeostatic ledgers still in the black. As I crouched in the mine, though, it was hard to imagine the bats ever coming back to life. They

remained weirdly still, hanging alone, in pairs, in a cluster of eleven. As our tally of bats grew, the mine seemed to me like a crowded zoo. In

reality, though, it was a ghost town compared to what I would have seen

had I visited in earlier years. When biologists surveyed the mine sixteen

years before, in 2004, they counted 1,102 little brown bats. Two years later, things changed. In hibernacula around Albany, biologists found dead bats

scattered around the entrances. Some had been scavenged by raccoons. Some had flown into snowbanks. Some had blooms of fungus in their

noses. Soon other bat populations around New York crashed, and then other

states followed the same steep decline. The dead bats all turned out to be

infected by a fungus from Europe called Pseudogymnoascus destructans. Its deadly bloom gave its disease the name “white-nose syndrome.”

The new disease took over Herzog’s life. “It immediately went to the top

of the list, and everything else fell far behind,” he told me. Herzog watched

some species plummet 90 percent in a few years. Others fell 99 percent. Thanks to the decades of records that he and other biologists had made of

bats in New York, they had an unrivaled view of the destruction white-nose

syndrome caused. “If the disease had arrived somewhere else, we wouldn’t

have known nearly as much as quickly as we did,” Herzog said. He was

mourning more than bragging. “I don’t know if ‘fortuitous’ is the right

word.”

In Europe, the fungus had been harmless to bats. It caused only minor

infections that the animals easily kept in check with their immune systems. Somehow the fungus had been transported from Europe to North America

—likely to some cave or mine not far from Albany. And somehow it proved

deadly to the bats in its new home. How it killed North American bats was a mystery at first. Pathologists

who looked at the dead animals didn’t see the kind of overwhelming

damage that a lethal fungal infection typically causes. “They were looking

at it through clouded lenses,” Herzog said. It gradually became clear that white-nose syndrome is a disease of

homeostasis. In the late summer and fall, the bats picked up fungal spores

as they visited caves and mines. The cold-loving fungus stayed dormant on

their bodies until the bats began to hibernate and their bodies cooled. Once

their body temperature fell below about 68 degrees, the spores opened and

the fungus pushed threads into their skin and muscle. Herzog and his fellow scientists discovered that sick bats roused

themselves out of hibernation more often than healthy ones. It’s possible

that they were losing extra water from the sores that formed on their wings. To keep their homeostasis, they had to drink more. It’s also possible that the

bats were fighting the fungus by warming up their bodies more often,

allowing their immune systems to wake up and engage their enemies in brief but intense battles. Some of the infected bats managed to keep their homeostasis intact until

spring, when they could warm up again and fend off the fungus. But others

suffered a homeostatic failure, running out of their winter stores. Some

became so desperate that they flew out of their hibernacula and into the

snowy daytime in a futile search for food. Many were picked off by hawks. We waded through hip-high water to count more bats, and then we

clambered up a loose heap of rocks and grit toward a sliver of light. We

crept out into the bright day, the snowstorm having departed off to the east. Ritzko and Herzog compared their numbers, which they would officially

log when they got back to their desks in Albany. The big brown bats turned out to be the most abundant, fifty-four all

told. Those numbers hadn’t changed in three decades, even after the arrival

of white-nose syndrome. For some reason big brown bats were among the

few species in New York that didn’t seem harmed by Pseudogymnoascus,

perhaps because they preferred parts of the cave that were too cold for the

fungus to grow. The little brown bats, on the other hand, preferred a warmer

perch. “They have the worst microclimate,” Herzog said. As a result, they

were also one of the hardest-hit species. On our 2020 survey, Herzog and

Ritzko found only six of them. It was puzzling that the little brown bats had fallen so far and yet were

avoiding outright oblivion. Herzog and his colleagues were exploring the

possibility that the few surviving little brown bats carried protective genes. They might have mutations in their DNA that caused them to behave

differently in the winter—perhaps preferring a colder perch—in a way that

could let them withstand the fungus. For now, Herzog and Ritzko couldn’t do much beyond bear witness. They couldn’t try saving the bats by scrubbing a few mines clean of fungus

to make them into sanctuaries. The bats themselves would contaminate

these refuges by bringing the fungus from the other places they visited. All

the scientists could do was observe whether the homeostasis of the bats

continued to fail or shifted instead to a new, safe set point. “We have failed largely to come up with anything we can do,” Herzog

admitted as we drove out of the woods. “The bats are going to have to

figure it out on their own.”

COPY/PASTE

One early spring day, I drove to New London, Connecticut, to watch a

tree prepare to make more trees. At the north end of the city, I

passed through a gate on Williams Street and entered a twenty-acre

spread of New England’s native trees and shrubs. Its official name was the

Connecticut College Arboretum, but everyone there just called it the Arbo. A botanist named Rachel Spicer was waiting for me at the Arbo gate, a

borer dangling from her backpack. Whenever she spent time among trees,

she brought it along just in case she came across one she wanted to drill. “It’s my favorite thing in the world to do,” she said. We wandered down the Laurel Walk, past a tree surgeon who was

desperately getting ready for an exam. He stared up at the crown of a

Washington hawthorn, checked the species identification app on his phone,

and then looked to us, shaking his head in desperation. We wandered farther

down the wood-chipped paths, passing American beech and eastern

shadbush. “Sometimes I feel like I was meant to study trees,” Spicer said. Her

father had taught her how to recognize different species in the forests of

Massachusetts where she grew up, and then she went to graduate school for

botany, studying the red maple trees of New England and the Douglas firs

of Oregon. After she became an assistant professor at Connecticut College

in 2010, she set up a lab in which she could study trees up close, growing

bits of poplar in petri dishes and inspecting the genes that switched on and

off in their cells. The work was fascinating, but Spicer would sometimes get

lab fever. When I asked if we could meet, she jumped at the excuse to grab

a borer, cross Williams Street, and spend an afternoon with trees in full. We made our way farther down the sloping gardens to a stretch of low-

lying swamp. There we stopped in front of a red maple. It stood like a

crooked telephone pole, its canopy high and narrow thanks to decades of competition for light with neighboring trees. A few errant branches shot off

the lower parts of the maple’s trunk, twisting and turning toward the

ground. The branches had been bare for six months, and now it was hard to

tell if the tree was even alive. I thought back to the previous summer and

tried to picture the maple vibrant with green chlorophyll, capturing sunlight

in its leaves to power a molecular machine for making fuel. I flipped

forward through the calendar in my mind to autumn, when the chlorophyll

in the leaves broke down, the green giving way to red. “It’s not just breaking down because it’s old and getting cold,” Spicer

said. “It’s being deliberately broken down. Because it is precious.”

Spicer explained that every molecule of chlorophyll contains four atoms

of nitrogen. If the maple tree in the Arbo simply dropped its leaves in the

fall, it would have to make a huge effort in the spring to gather a fresh

supply of nitrogen from the soil, which it would then have to pump up from

its roots to its branches. Instead, the tree spent the autumn carefully

dismantling its chlorophyll into molecular parts, which it moved down little

tunnels from the leaves into the branches. There the parts would spend the

winter in safekeeping, ready to be quickly moved into new leaves in the

spring and reassembled into fresh chlorophyll. It was a smart strategy but a tricky one. In the summer the thick layer of

chlorophyll in the maple’s leaves had two jobs: to make food and to serve

as a sunscreen. It protected proteins and genes from damage caused by

errant high-energy photons. Once the fall arrived and the leaves began

breaking apart their chlorophyll, they opened themselves up to attack. The maple tree defended itself in the most beautiful way possible: it

produced a red pigment in its leaves called anthocyanin. The autumn

pigment protected the leaves from sun damage for the few weeks they

needed to move their chlorophyll into winter storage. Only then did the

maple sever its leaves, letting them drop to the ground. Now in early spring the branches looked dead to me. But the future of

the tree was unfolding inside. Spicer grabbed one of the low-reaching

boughs and bent it close enough to show it to me at close range. She pointed to the reddish bulbs that swelled out along its length. After

the leaves had dropped in the fall, the branches had produced these bud

scales, each coated with a tough outer wall packed with anthocyanins to

shield against the winter sun. The bud scales built these defenses to protect

delicate new cells inside. These cells were filled with potential: they could become any of the structures that the tree would create in the spring. Spicer

used a fingernail to slit open a bud scale. I could see tiny curved streaks

inside, some of which might ultimately give this maple tree a chance at

eternity. “There are preformed flowers in there,” Spicer said. Driving home from the Arbo, I looked at the miles of maples flanking

the highway. In previous years I didn’t pay them much mind in March. But

now I was keenly aware of the faint haze of red that floated on their crowns:

thousands of bud scales hiding flowers that were coming into being. It

looked like a canopy of bloody smoke. Every one of these trees had come

into existence out of another red haze on another tree decades ago. They all

had ancestors, as do we all, along with every other living thing on Earth. As a hallmark of life, reproduction is as hard to miss as the screams of

childbirth. People make people, maples make maples, dog’s vomit makes

dog’s vomit. For all species, the core of reproduction is the same: the

generation of new organisms that carry copies of their forerunner’s genes. The details of human reproduction—how cells copy their DNA as they

divide, how eggs and sperm end up with only half a set, how they are

combined at fertilization, how embryos develop in the womb—is the

version we’re most familiar with. But it’s a mistake to generalize too far

from our own species. What’s true for humans is fairly true for another mammal, like the

northern long-eared bat. Both species have uteruses and produce live young

that suckle milk. But what’s true for us is less true for a python, which

hatches from an egg, and it’s far less true for slime molds like Physarum

polycephalum. One way for slime molds to reproduce is by making spores, which can

get carried away by wind or water. If the spores of Physarum land in a

promising spot, they tear open and cells crawl out. Slime mold experts refer

to these cells as amoebae. Like our eggs and sperm, each amoeba has only

half a set of chromosomes. But despite this shortfall they can live on their

own. They crawl across the forest floor, destroying and eating bacteria they

encounter. If they happen to bump into another Physarum cell, the two can merge together in an underground version of fertilization, to create a slime

mold version of an embryo. Slime mold amoebae are not male and female cells, but they do have their own bizarre version of sex. When two amoebae meet, they inspect the

proteins on each other’s surfaces. Depending on the versions of these

proteins that slime molds inherit, they may belong to one of hundreds of

different mating types. As long as two amoebae don’t belong to the same

mating type, they can merge. Their chromosomes join together into a full

set, whereupon the single fused cell becomes a kind of slime mold embryo. It now starts to grow tentacles, making new copies of its chromosomes that

populate the single, gigantic cell. Physarum has yet more strange ways to reproduce. It can, for example,

skip the sex and simply dry up into sclerotia. If these fragments blow away

in the wind and start growing elsewhere, that single network can turn into

many new ones. You can think of the new slime molds as genetically

identical offspring. Or you can think of them as just one giant network with

some big gaps in it. The slime mold does not care about these word games. It just keeps looking for food. The alien sex life of slime molds happens largely out of view,

decipherable only by the scientists who dedicate their lives to such things. Maple trees, on the other hand, mate across the sky. After my visit with

Spicer at the Arbo, I spent the following weeks closely observing the

maples in my life. A red maple looms in the far corner of our backyard, and

we have a scattering of smaller Norways and silvers. In the salt marshes

along the edges of my town, along the verges of the streets, on the flanks of

hills, in the empty lots—everywhere, new maples volunteer in endless

supply. Through the spring, I watched as one species of maple after another

split its buds, putting forward different versions of flowers, some pale green

and some crimson. The trees bloomed before leafing, building their flowers

solely from the ingredients they had stored away in their twigs the previous

autumn. Like many other plants, maples put forth flowers that botanists call male

and female. Those labels stick only lightly to the trees, though, because

plant reproduction is so different from ours. A red maple may put out male

flowers one year, switch to females the next, and then put out both male and

female flowers the year after that. The reason that botanists call a maple

tree’s flowers male and female is that each kind produces sex cells that

follow some of the same rules as eggs and sperm. Just as men produce

small sperm, male flowers produce small pollen grains; women make eggs, and female flowers make ovules, which will become seeds after pollination. Humans come together to have sex, but maple trees need the wind to

unite their sex cells. Although they can withstand hurricane winds, even a

slight breeze can whisk away their pollen. Most grains land on the ground

or the wrong kind of tree. Even if pollen alights on another red maple, it

will likely land on the bark or a bough. Only a minuscule fraction of pollen

grains have the good fortune to reach a female flower. The flower snags the pollen on sticky hairs, and a tunnel forms from its

surface to its core. The pollen gets pulled through it until it reaches the

female flower’s ovule. When they fuse, pollen and ovule form a new

genome, which gets stored away in a new seed. I couldn’t witness these invisible fertilizations, but I could watch the

result: the female maple flowers fell away, leaving behind fleshy red

structures that look like pairs of impala horns. These growths, called

samaras, held a pair of seeds at their base. The horns grew long and then

grew flat. They took on the shape of curved blades, their surfaces

resembling stiff paper. When they broke apart and dropped from their

stems, they didn’t fall so much as fly. A samara’s blade has the same overall geometry as a wing, which it uses

for the same purpose: to manipulate the air around it into flight. But while a

bat grows wings to catch prey and find a place to hibernate, maple trees

grow wings to spread their seeds. The seed at the base of the samara is

heavy enough to fall fast, creating a rush of air flowing up along the papery

blade. The samara spins like a helicopter, generating lift. The result is a

long glide that can carry a maple seed hundreds of feet from its parent tree

before it finally reaches the ground. It took only a few days for each of our maples to drop all its samaras. In

a good year a seed rain may bring down nearly a hundred thousand samaras

from a single tree. A one-acre stand may shower as many as 8 million. It is

a spectacular feat of reproduction. It is also a spectacular waste. As many as

half of a maple’s samaras are empty, lacking a seed. A sizable fraction of

the seeds in the remaining samaras commit suicide. Scientists don’t yet

understand the evolutionary logic behind these dead and empty vessels. Trees may make hollow samaras as decoys, tricking squirrels and birds into

wasting their time and thus giving their seeds a better chance to sprout. Seeds may commit suicide if they happen to carry bad combinations of genes that make it unlikely they’ll produce healthy trees. In the end, only a small fraction of the samaras in a seed rain manage to

sprout. Yet, even after this decimation, the trees are still left with an absurd number of progeny—sometimes dozens of viable seeds on every square

yard below them. They need little sunlight and not even much soil to sprout

roots and send up shoots. As the spring progressed, samaras carpeted the grass. I live on half an

acre of grass-covered pink granite, with plenty of bare patches where the

ancient volcanic rock pokes out. Volunteer maples unfurled fingernail-sized

leaves. I climbed a ladder to muck out fistfuls of samaras from the gutters. I

even found seedlings growing there, as if they could start an aerial forest. In the summer, my wife and I drove out into the forests that surround

our town to hike. One day we traveled through a maple stand where the

ground was covered in a great green shallow lake of foot-high saplings. Only a few pole-stage maples rose above them. Fewer mature maples were

growing toward the light. And even fewer ancient trees towered over them

all, spreading their branches out to form a canopy. Here we could see the dismal odds in the life of a maple tree laid out

before us. As a hallmark of life, reproduction is not as simple as the others. Every living thing metabolizes food, makes adaptive decisions, and keeps

itself in homeostasis. The alternative is death. Every living thing is the

result of reproduction, but it is not guaranteed to reproduce. If a maple tree

lives for its full life span—over a century for some species, three centuries

for others—it may rain millions of flying offspring. But only a few will ever

manage to rise to meet them crown to crown. The unconscious competition

continues on through the generations. A maple tree may succeed in passing

down its genes to a few progeny, only to have them all die of root rot. The maple trees that rain samaras on us today have a deep genealogy. Maples arose more than 60 million years ago, not long after an asteroid

crashed into the earth and wiped out the giant dinosaurs. They originated in

East Asia, where species like the Nippon maple and lime-leaved maple still

grow, and by about 30 million years ago, maples had spread their samaras

to North America. They continued to diversify into new forms. The red

maple and silver maple that grow side by side in backyards today are distant

cousins, having diverged from a common ancestor 10 million years ago. These looming trees are the product of a thin pedigree of success that has sliced through a vast field of reproductive failure. In fact, it is the intertwined failure and success of maple tree

reproduction that has produced all their impressive adaptations—their keen

sense of the calendar, their sunscreen, their living helicopters. It is

responsible for their diversity, too, having generated 152 species of maple

trees all told. Out of life’s success and failure at making copies of itself

emerges its most impressive hallmark of all: evolution. DARWIN’S LUNG

The petri dishes were stacked high, like a laboratory pillar. The top

dish had a cerulean coat, the color of the sky just after sunset. The

dishes below were blue as well, but the farther I scanned down, the

paler they became. By the time my eye reached the ground floor of the

tower, it had become transparent. I encountered this plastic monument in Osborn Memorial Laboratories,

a castle-like building on the campus of Yale University. It had been stacked

by a researcher named Isabel Ott. She had short jet hair; her earrings were

coaster-sized disks decorated with all the phases of the moon. Ott had

graduated the year before from the University of Georgia, where she had

studied all manner of diseases, both human and animal. She had come to

New Haven to work for an evolutionary biologist named Paul Turner. For

Ott, stacking the petri dishes was not a laboratory version of Jenga. It was

the start of a day’s work that might eventually save someone’s life. The dishes, Ott explained to me, got their blue cast from the bacteria

growing on them. And those bacteria had come from the lungs of

desperately ill people who were running out of hope. Some of the

volunteers sent Ott notes along with their samples, writing of their plight

and begging her for help. “They’re my age,” Ott said. “And I say, ‘Sorry. I

am trying everything.’”

The people who had provided Turner and Ott with these bacteria all had

a broken gene. Normally, lung cells use the gene to make a protein called

CFTR that helps keep the airway clear. But mutations in the CFTR gene

disable the protein. The lungs of people who inherit this mutation become

obstructed with a thick, sticky layer of mucus. The disease is known as cystic fibrosis. One of the most dangerous

results of this disease is that the lungs become an incubator for certain kinds

of bacteria. A species called Pseudomonas aeruginosa poses one of the biggest dangers. Normally it lives on the leaves of plants and on clumps of

soil. If healthy people happen to breathe in a snort of Pseudomonas

aeruginosa, their immune systems quickly wipe it out. But the congested airways created by cystic fibrosis give the bacteria refuge, a chance to take

hold. Half of people with cystic fibrosis are colonized by an infection of

Pseudomonas aeruginosa by age three, and 70 percent of adults will

develop a chronic infection. Antibiotics sometimes kill off the bacteria but

often fail. As the years pass, the bacteria cause inflammation and scarring

that make it harder to breathe. Ott was helping run an experiment that might offer a new way to attack

the bacteria. She and her colleagues were testing their idea on volunteers

with cystic fibrosis. To see how effective their attacks were, the participants periodically coughed mucus into tubes, which they sent to the scientists. The bacteria in their mucus were now growing in Ott’s dishes. If the idea proved valid, the scientists might be able to transform the

bacteria from potential killers into harmless nuisances. To carry out this

alchemy, they were taking advantage of life’s never-ending power to

evolve. Every living thing on Earth is the product of evolution, a process that

has unfolded for some 4 billion years. Bacteria and other microbes were the

first lineages to evolve, and about 2 billion years ago they were joined by a

new form of life. Amoeba-like single-celled organisms began hunting the

microbes. Their cells were far bigger, and they kept their DNA stuffed in a

sac called a nucleus. These new forms of life were known as eukaryotes. Today, slime molds and many other species of eukaryotes do very well

as single cells. But some lineages of eukaryotes evolved many-celled

bodies. Green algae moved ashore about half a billion years ago, becoming

mosses and ferns, with flowering plants arising hundreds of millions of

years later. Animals evolved from single-celled eukaryotes in the ocean

about 700 million years ago, and some of their descendants later crawled

ashore—first millipedes and primitive scorpions and other invertebrates,

then four-legged salamander-like creatures. Some of the four-legged

animals lost their limbs and became snakes. Some modified their legs and

began to fly, becoming birds and bats. One lineage of primates stood

upright about 7 million years ago and eventually spread from African

savannas across the planet, looked back through time, and recognized for the first time the crude outlines of evolution’s deep history. Life continues to evolve today. It can no more escape evolution than

water can escape being wet. When a maple tree showers the earth with

samaras, it spreads copies of its genes. But each new sapling is not a perfect

replica of its parents. It inherits shuffled samples of their chromosomes. Its

genes contain new variations. Charged atoms and high-energy photons

crash into genes and alter their sequence. When enzymes create new copies

of DNA, they sometimes accidentally put a G where there should be a C. Sometimes they accidentally duplicate thousands of bases in a row. Cells have special enzymes to proofread these mistakes, but some get

through. The egg and sperm that produced you carried mutations that your

parents were not born with. New mutations get passed down through the

generations along with old ones, building up genetic diversity over the

centuries. Many mutations have no effect one way or another. Some are

devastating, causing lethal disorders and deformities. Others are beneficial,

helping organisms survive and reproduce. As mutations get passed down,

some become more common, and some less. Chance can steer their fate, but

if a mutation has a strong effect on how many offspring an organism has, it

can meet that fate much faster. As beneficial mutations accumulate in a

lineage, they can give rise to new adaptations. The basic logic behind evolution is simple enough. It’s so simple, in

fact, that Charles Darwin worked it out in the mid-1800s, decades before

scientists recognized genes, let alone figured out what genes are made of. It

was enough for Darwin to observe that animals and plants had variations in

each generation and that some of those variations could be inherited. He

hypothesized that a process he called natural selection would favor the

variations that helped with surviving and having offspring. Darwin could see the results of evolution in living species. But he

believed that life evolved the way mountains grew—over millions of years,

on a scale that humans were not equipped to perceive. “We see nothing of these slow changes in progress, until the hand of

time has marked the long lapses of ages, and then so imperfect is our view

into the long past geological ages, that we only see that the forms of life are now different from what they were,” he declared. Darwin was wrong, but he can be forgiven. He had no way to appreciate that microbes could display evolution in action over a matter of weeks. They first began to reveal its secrets on the morning of February 15, 1988,

in Irvine, California. A microbiologist named Richard Lenski started an

experiment with bacteria that would last for decades. Bacteria can divide in as little as twenty minutes, which means that a

single microbe can give rise to a population of billions overnight. Some of

those descendants will carry new mutations, which affect how quickly the

microbes grow and reproduce. A billion birds require a continent. A billion

microbes need only a flask. Lenski came up with an experiment he hoped would lead to

evolutionary change he could measure. He began with a single Escherichia

coli, a species of gut bacteria that has become the workhorse of

microbiology labs. He grew a colony from that founder and divided its

descendants among twelve flasks. Each flask contained only enough sugar

to last the bacteria a few hours. After their supply ran out, they had to

survive till the next morning. Then Lenski and his students drew a little

liquid from each flask and squirted it into fresh ones. The bacteria that

managed to make the journey could feast on sugar and reproduce again. To track their history, Lenski created what he liked to call a frozen fossil

record. Every five hundred generations his team drew off some of the liquid

from each flask and put it in a freezer. Later he could revive them and see

how they measured up to their descendants. By the time Lenski moved his

flasks and freezers to a new job at Michigan State University in 1991, his

twelve colonies had passed through thousands of generations. And they had

clearly evolved. The descendants in all twelve flasks gained mutations that enabled them

to thrive in their new environment, taking up food quickly and then

surviving their daily fasts. They needed less time to get big enough to split

in two. As they gained more beneficial mutations, they kept improving until

they were growing 75 percent faster than their ancestors. The microbes

swelled along the way, evolving to be twice as big as their ancestors—for

reasons that Lenski and his students have yet to figure out. In later years

they identified many of the mutations that arose in each of the twelve lines. Different mutations were responsible for some of the changes. But natural

selection pushed all twelve lines in the same general direction. Scores of graduate students passed through Lenski’s lab over the years. They tended to his bacteria, became experimental evolutionists in their own

rights, and established labs across the United States. Paul Turner was one. Another was named Vaughn Cooper. At a scientific conference in New

Hampshire in 2019, I watched Cooper, lanky and eager, give a talk about

how high school students could also see evolution in action. He and his

colleagues at the University of Pittsburgh had put together a kit that the

teenagers could use to run a weeklong experiment. Thousands of students

had already gotten results, Cooper announced. Surely, I thought, a writer in

his fifties could follow in their wake. Cooper agreed to send me a kit, and one day a cardboard box showed up

outside my front door. I slit open the top to check the contents. I found petri dishes, sealed tubes, bottles of clear liquids, and a bag of black and white

beads. The dishes were pimpled with ghostly streaks and swipes. They gave

off an unpleasantly sweet odor, like what you might sniff from a jug of

cider forgotten for a few days on a picnic table. The dishes were seeded

with another species of Pseudomonas. Pseudomonas fluorescens, which also grows on plants and in the soil, does not attack the lungs of people with

cystic fibrosis. It’s harmless enough for high school students to safely

handle. I taped the box back shut and put it in my refrigerator, hoping the

bacteria’s odor wouldn’t penetrate the food nearby. I still needed a stand-in

for a teacher. I lived near Yale, where I taught a writing class, and Turner

and Ott kindly agreed to help me run an experiment. One day I brought my box to Turner’s high-ceilinged lab, where a flock

of grad students were centrifuging tubes, spreading microbes on plates, and

labeling lids. I set down my box on a space Ott had cleared next to hers. She had me don gray gloves and a white coat. When we took the dishes out

of my box, the odor leaped out, too. “Pseudomonas,” Ott groaned, like meeting an old nemesis. “If I’m in a

bad spot working on it, it can nearly give me a migraine. I have to go and sit

on a couch for a few minutes to have a cup of tea so I can get my brain to

cooperate.”

Before coming to the lab, I had taken an online class on basic lab safety:

flushing out eyes, cleaning up spills, and the like. But now, working with

Ott, I felt like I was in hygiene boot camp. She instructed me to wipe down

my lab bench with alcohol and then light my Bunsen burner. She put her hands around the flame as if she was holding a globe. “This is your zone of sterility,” she announced. As long as I worked in my zone, I would be safe from all the invisible

life that could throw off my experiment. The bacteria and the fungal spores

drifting through the air would get torched before they could drop into my

tubes and plates and outcompete my Pseudomonas. I labeled a set of plastic test tubes with letters and numbers. Taking up a

pipette, I squirted liquid into the tubes laced with nutrients that

Pseudomonas needs to grow. When I accidentally brushed the tip of my

pipette across the counter, Ott had me stop and replace it with a new one. It

might have picked up microbes that had rained down on the surface since I

had sterilized it, and they might run riot in my tubes. “There’s a spectrum of paranoia,” Ott said, “and I’m at one end.”

Once I had filled all the tubes, Ott had me douse a pair of forceps in

alcohol and then stick them in the Bunsen burner flame. The alcohol flared

blue and then died away. I slipped the sterile forceps into the bead pouch,

drew out beads one at a time, and dropped them into the tubes. Now it was time to add bacteria to the tubes. Ott handed me an

inoculation loop: a long, stiff wire that ended in a barely visible circle. I

scorched it in the flame, lifted the lid of one of the dishes, and scooped up a pinhead bump. The tip of my loop now carried millions of genetically

identical members of a strain called Pseudomonas fluorescens SBW25,

which scientists originally isolated from a sugar beet on an English farm. I dunked the bacteria into a tube, scorched the loop again, and seeded

another tube. When I had filled them all with bacteria, Ott slotted them all

in a tray, which she set on a platform in a refrigerator-sized incubator. She

turned a switch and the platform began to swivel, sloshing the liquid in the

tubes. The next day the tubes had turned from clear to cloudy, thanks to all the

billions of new bacteria that had grown overnight. Even more heartening

was the sight of the beads. Pseudomonas had covered them in a slimy coat. To microbiologists, this slime is an architectural marvel. When

Pseudomonas lands on a surface, proteins on its membrane register the

event. They change shape, and that transformation causes them to alter

proteins swimming around on the inside of the microbe. A rolling cascade

of molecular flips occurs, ultimately causing the microbe to switch on a set

of genes. It makes proteins from those genes that it then ferries up to its membrane and squirts out. These proteins weave together into a gooey,

sticky matrix. The microbe nuzzles itself into the goo to anchor itself to a

surface. It can then feed on the protein fragments passing by. When it grows

and divides, its daughter cells release their own goo, spreading their

collective slime. Every species of Pseudomonas builds biofilms as a way to colonize surfaces—a leaf, a grain of soil, the gut of a grasshopper, the lung

of a person with cystic fibrosis. I moved the slimy beads into new tubes into which I had placed fresh

beads. The next day I found that the new beads had become slimy with

bacteria, too, and these I moved onward to new tubes. With each transfer of

a bead I was playing the part of natural selection. Every time a Pseudomonas divides, there’s about a one-in-a-thousand

chance it will make a mistake, leaving behind a mutation in a daughter cell. With each cell able to produce a billion descendants in a day, my tubes

produced many millions of mutants. And by moving beads from one tube to

the next, I was favoring the mutants that were better at forming biofilms on

the beads. Any bacteria still left floating in the broth were doomed to

destruction when Ott and I sterilized the old tubes. A week after my first visit, I came into the lab to see if life had evolved

under my watch. Ott held up a pair of petri dishes. “So, basically, here is a normal,” she said, moving one dish forward. “And here’s your boy,” she said, indicating the other. “If you want to glove

on, I can take a picture of you and your evolved mutants.”

I put on my gloves and held up the dishes with a grin for the iPhone. In

one hand I held the normal boy, a petri dish of ordinary Pseudomonas

fluorescens. It contained bacteria that we had allowed to grow under

ordinary conditions for the week. When Ott spread them across a petri dish,

they grew into tiny pimple-sized colonies, just as their ancestors had. In the other hand, I held my boy: my collection of evolved mutants. After I had transferred slimy beads from tube to tube for a week, I put the

final tube on a shaker to pull the biofilm off its bead. I spread the bacteria

across a fresh petri dish and let it grow into colonies. Ott spied some weird-

looking ones, and she scooped one up to seed a fresh dish of its own. There

the mutant bacteria grew into dozens of big, fuzzy-edged blobs that looked

like ghostly petals on a flower. Later Ott sent some of my mutants back to Pittsburgh so that Cooper and his colleagues could take a look at them for themselves. They split

some of the bacteria open to read their DNA and search for the change that

had made them grow strangely. “It’s a new mutant for us,” Cooper later told me. The genome of

Pseudomonas fluorescens contains 6.7 million base pairs. Printed out, it would run about as long as the entire Harry Potter series. In all that DNA,

Cooper and his fellow scientists found two genetic typos new to my

bacteria. The researchers suspected that one of those mutations—a C

flipped to a T—was responsible for the strange flower-shaped colonies that

the bacteria formed. The mutation altered a gene that normally helps weave

a cotton-candy-like shroud of sugar around each microbe. The mutation in

my bacteria likely made that shroud stickier, making them better able to

cling to beads and to each other. Cooper and his graduate students have run high-powered versions of my

experiment, moving slimy beads from tube to tube for months. By letting

evolution work longer on their microbes, they’ve created an impressive

menagerie of mutants. Some grow into colonies that look like a splash of

ink. Others look like slices of kumquats. Some take on the color of

tangerines, others of blood. These colors and shapes are probably just side

effects of mutations that make the bacteria grow better in biofilms. The

diversity of the colors and shapes Cooper’s team has created may reflect the

jungle-like complexity of life in a biofilm, a place in which evolution can

fill many different niches with many different mutants. Over the week I had spent in the lab, Ott was conducting an experiment

of her own next to me. I could see she was handling a tremendous number

of tubes, flasks, and dishes, but I was so preoccupied with grabbing slimy

beads with tweezers without shooting them across the lab that I couldn’t ask

her much about it. Once I had successfully reared a mutant, I asked Ott to

tell me more about the cerulean tower. Her experiment was part of a project to understand how Pseudomonas

aeruginosa evolves in the lung. A human body is radically different from a leaf or a pond, meaning that when the bacteria first slip into a host, they are poorly suited to their new home. They divide slowly at first. When

mutations arise, some of them help the bacteria fare better in the human

lung, and they grow faster. Mutation after mutation accumulates. They

make biofilms well suited to the airways. If doctors douse them with

antibiotics, new mutations can arise that help them shut out the poison. For the bacteria, human lungs are like Lenski’s flasks. Ott was working on a study to find a way to seize control of this

evolution. Rather than try to kill the bacteria, the researchers wanted to

render them harmless. They would do so by running a version of the

experiment I had just carried out. They would alter the bacteria’s

environment, driving natural selection in a new direction. The blue color in Ott’s dishes came from a pigment produced by the

bacteria. Known as pyocyanin, it’s the hallmark of Pseudomonas

aeruginosa infections. Indeed, when doctors first isolated the bacteria from sick patients in the late 1800s, they called the microbes “bacteria of blue

pus.”

Many decades later, scientists began learning what pyocyanin actually

does. Among other things, it appears to ward off immune cells that would

otherwise attack the bacteria. But it also helps trigger the inflammation that

causes so much damage in the lungs of people with cystic fibrosis. If the

bacteria simply stopped making pyocyanin, they would become much less

of a threat. A researcher in Turner’s lab named Benjamin Chan found what

might be a tool to push the evolution of Pseudomonas aeruginosa in that direction: a virus. Viruses that infect bacteria are known as bacteriophages, or phages for

short. Each strain of phage has molecular hooks that can grab onto a

particular kind of protein on the surface of bacteria. Once they latch on,

they can invade the microbe and make new phages inside. Bacteria have evolved a number of defenses against phages, and they

can evolve new ones when they come up against a new enemy. One of the

simplest ways to protect themselves against a phage is to lose the protein it

grabs. If the phage uses a key to unlock its way into bacteria, the bacteria

can just get rid of the door. Of course, bacteria put proteins on their surface for a reason. They use some of them to pull in nutrients, others to send

signals to their fellow bacteria, and others to act as sensors to tell them

about their environment. But the cost of losing one of these proteins may be

smaller than the benefit that comes from a defense against phages. Searching for new species of phages, Chan found dozens that infect

Pseudomonas aeruginosa. When he and his colleagues unleashed one of the phages on the bacteria, natural selection favored mutants that stopped

making the protein the phages used to get in. But the mutation had another

effect: it also caused the bacteria to make less pyocyanin. It’s possible that the mutation shuts down a genetic switch in the bacteria’s DNA that

controls both the surface protein and the blue pigment. Chan and his colleagues wondered if they could use their newfound

phage to help people with cystic fibrosis. If they inhaled the phage, it would

be unlikely to harm them because phages only infect bacteria, not our own

cells. The bacteria might evolve resistance to the phage, but in the process,

they would sacrifice their ability to make their dangerous blue pigment. In a clinical trial, doctors sprayed Chan’s phages into the airways of

people with cystic fibrosis. As the phages began to attack their

Pseudomonas aeruginosa colonies, the volunteers coughed up sputum into

tubes from time to time. Those tubes made their way to Ott, who isolated

the Pseudomonas aeruginosa and spread them on petri dishes. After the

bacteria grew into a microbial lawn, she stacked them into a tower. The blue

dishes on the top came from patients before their phage therapy, and the

ones below came from samples taken afterward, week after week. As the

blue faded further down the tower, Ott and her colleagues could see that

their evolutionary hunch was right. The bacteria were steadily giving up

pyocyanin, perhaps becoming safer residents of people’s lungs. “If there’s less blue, there’s less inflammation,” Ott said, “which is a

good thing.”

Ott and her colleagues would need to take a close look at the bacteria—

and run their experiment many more times—before they could determine if

the phages were a safe and effective way to tame the microbes. What

government regulators might say to the idea of infusing viruses into sick

people was anyone’s guess. But sooner or later, with enough persistence,

this living medicine would probably work. Evolution made it hard to deny. —

Biology expands our vision of life, letting us see beyond our own

experiences of being alive, look back over billions of years of living history, and peer down into the microscopic confines of a cell. But every biologist

faces a harsh trade-off. No one can know everything about everything. To

become an expert on just one kind of life can demand an entire career. Isabel Ott could regale me with tales of disease-causing bacteria if I asked. If I were to quiz her on pythons instead, she would have little to say. I spent hours in conversation with Stephen Secor about pythons as we sampled

some of Tuscaloosa’s finest microbrews. But I would not go to him to understand the reproductive biology of maple trees. Yet maple trees and snakes and Pseudomonas and slime molds and bats

are all joined together by their hallmarks. They all reproduce and evolve;

they all make decisions, turn food into energy, and maintain an internal

balance. People knew a little about some of these hallmarks before the rise

of biology. They knew that trees produced seeds that became more trees. They knew that bats somehow managed to live through both the cold of

winter and the heat of summer. Now they know much more about why such

things are so. And they find that what is true for one species is, in a

fundamental sense, true for all. From time to time, researchers have

wondered what these different strands of unity together create. If all living

things share certain hallmarks, can they tell us what life is?

That question—

What is life?—may seem like it’s the first and foremost question biologists

should answer. And yet it remains unanswered and, perhaps, ultimately

unanswerable. PART THREE

A SERIES OF DARK QUESTIONS

THIS ASTONISHING

MULTIPLICATION

Waves crashed onto the beach, delivering fresh sand with each

break. The beach rose into lines of dunes, like waves of land. On

their lee side they surrendered to an orderly landscape of living

things: topiaries, parterres, and orangeries. The sprawling estate, known as

Sorghvliet, was the summer residence of Count William Bentinck of the

Netherlands. In the eighteenth century, it was considered one of the most

delightful gardens in Europe. Today little of Sorghvliet’s former glory

survives: gone is the giant artificial hill enclosed by a maze; gone are the

trees with doorways and windows cut out of their branches to make them

look like houses of leaves. To biologists, however, Sorghvliet remains a sacred place. For them its

glory does not lie in its once-magnificent grounds but in a tiny animal that

lurks in its fishponds and canals. It came to light in the summer of 1740,

when scholars across Europe were confidently making declarations about

what it means to be alive. And this mystifying creature revealed how deep

their ignorance of life truly was. That animal was discovered by a rootless young man named Abraham

Trembley. Trembley had officially come to Sorghvliet to serve as a tutor to

the count’s two young sons, but soon he was acting as a stand-in parent to

the boys. Their mother had left for Germany to live with her lover, and their

father spent most of his time at the Hague, either on matters of state or his

impending divorce. As isolated as the boys were at Sorghvliet, Trembley

was even more so. He had been born in Switzerland, training in

mathematics and theology as he prepared to join the church. But political

strife drove him to Holland; he scraped by on private lessons for a few years before the count gave him a stable position. A teacher both pious and curious, Trembley decided he would make it

his mission at Sorghvliet to teach the boys to see God’s omnipotence in

nature’s works. Trembley didn’t spend much time on formal lessons or

regurgitating Aristotle’s writings. He was a child of the Scientific

Revolution, which had ushered in new theories about life, and he wanted to

see how well they explained the natural world with his own eyes. “Nature must be explained by Nature,” Trembley later said, “and not by

our own views.”

At Sorghvliet, nature was happy to help. Trembley and the boys

wandered the grounds to observe animals and plants. They fished out

duckweed floating in the ponds. They scooped up insects in the ditches. They brought their hauls back to Trembley’s study, where they examined

the fine anatomical details of their specimens. Sometimes they used

magnifying glasses. Other times they used a custom microscope provided to

them by the count, its lens attached to the end of a jointed arm. Trembley carefully sketched what he and the boys saw in this miniature

world. Very often they were the first people ever to see it. Trembley wrote

to other scholars across Europe about what they were observing—the

strange complexities of caterpillars, bees, and aphids—and his

correspondents quickly recognized this teacher, alone on the Dutch coast, as

one of their own. The animals of Sorghvliet soon drew Trembley into a debate about the

nature of life itself that had been roiling Europe for almost a century. On

one side of the debate were the followers of the seventeenth-century

philosopher René Descartes. Descartes attacked traditional notions of nature

having goals, such as gravity carrying objects to the middle of the earth as if it knew where that was. Instead, Descartes offered a vision of matter in

motion. At first he filled that vision only with inanimate objects like

pendulums and planets. But eventually Descartes came to see living things

as matter in motion, too. They were made up of parts that worked together,

much like a clock. The parts of a clock were set in motion by springs and

weights. The parts of an animal’s body were likewise set in motion—

Descartes believed by tiny explosions inside their nerves. He expected that

someday life would be as well described by physicists as a rock dropped to

the ground or the moon orbiting the earth. Descartes inspired generations of followers, and they extended his machine-centered view of life from animals to humans. Aside from our

rational souls, they argued, our bodies were much like machines. Cartesian

doctors saw themselves in league with clock repairmen. “Like all of nature,

medicine must be mechanical,” the German physician Friedrich Hoffmann

declared in 1695.

But Descartes also inspired generations of opponents. Some were

simply appalled that he seemed to have no need of God to explain the

world. Others could not reconcile Descartes’s vision with their own

understanding of nature. The closer these anti-Cartesians looked at life, the

more complex it proved to be, both in anatomy and in behavior. And this

complexity served a greater purpose: it allowed living things to survive and

reproduce. No mechanical philosophy could encompass that complexity or

explain its purpose. That purpose, the anti-Cartesians firmly believed,

created a decisive difference between inorganic matter and living things. The physician Georg Ernst Stahl declared that the mission of science

was to understand the difference—to get to the bottom of what exactly set

life apart. “Above all else, consequently, it comes down to this: to know,

what is life?” Stahl said in 1708.

Stahl offered an answer to his own question: a definition that would be

followed by many others in the centuries that followed. Life was “not the

matter of the body—anatomy, chemistry, the ‘mix’ of fluids—but rather

their interdependence.” Stahl believed life’s interdependence served the

purpose of allowing living things to endure the assaults of a hostile world

and resist the forces of decay. There had to be an inner force—what Stahl

referred to as a soul—to sustain the interdependence of life. One of life’s most obvious hallmarks was reproduction, but naturalists

were fiercely divided over explaining how life managed this feat. Some

scholars argued that the parts of a living thing already existed in an egg or

sperm. A seed that could sprout into a tree also contained the future seeds of

that future tree, they believed, which contained their own seeds in turn. Other scholars found it absurd to imagine that life could exist in such an

infinity of boxes within boxes. They argued that the parts of living things

did not exist before the things themselves. The complex anatomies of

animals and plants must unfold gradually, in a mysterious process of

development. When Trembley began trading letters with other naturalists in 1740, they shared with him a startling discovery about how life can reproduce. From

Geneva, Charles Bonnet wrote that he had observed female aphids bearing

offspring without mating first. Both Bonnet and his mentor, the French

naturalist René Antoine Ferchault de Réaumur in Paris, relayed their

astonishment to Trembley, who decided to investigate the paradox for

himself. He and the boys reared some female aphids at Sorghvliet. Just as

Réaumur and Bonnet had promised, they eventually began laying eggs. If female aphids could produce ordinary offspring without sex, their

eggs must contain preformed aphids. That possibility hinted that animals

could have more autonomy than one would expect from divinely created

machines. Trembley wondered if the laws of nature that scholars were

claiming might actually be presumptions. His observations made him even

more humble in his work. He was content to observe patterns rather than

claim to have uncovered God’s laws. That humility allowed Trembley to notice something else that had gone

overlooked. One day in June 1740 he was inspecting a duckweed plant that

he had collected from a ditch. He noticed a tiny green trunk stuck to its side. Atop the trunk was a strange crown that looked like strands of silk. When

he looked at more duckweed, he found more trunks. Trembley didn’t know it, but other naturalists had observed this strange

form of life forty years before. They had classified it as a plant. Trembley

assumed it was a plant, too, as did visitors to whom he showed it. Some

thought he was looking at bits of grass or the tufts of dandelion seeds. But Trembley noticed something bizarre: their crowns moved. They

didn’t simply sway in the current of water in his jars. The threads of the

crown seemed to move with intention. “The more I followed the movements of these arms, however, the more

it seemed that it had to come from an internal cause,” Trembley later

recalled. He grabbed one of the jars containing these strange things and jogged it

a little. To his surprise, the threads suddenly pulled back inside the little

green trunks. Once he let the jar settle, the threads snaked their way back

out again. Their behavior, Trembley said, “roused sharply in my mind the

image of an animal.”

One day Trembley found that the crowned animals were now stuck to a

side of a jar where they had not been before. They were moving on their

own, he realized, uprooting themselves from the duckweed and crawling like underwater inchworms. These animals had a goal: over time, they made

their way to the light. If Trembley swiveled a jar to put them in the dark,

they crept back to the sun. The creatures were also eating. Trembley

watched them grab worms in their arms, pulling in their prey to stuff into a

mouth nestled at the center of their crown. He observed them eating water

fleas and even little fish. These animals were stranger than anything Trembley had ever seen or

read about. He thought up experiment after experiment to make sense of

them. He sliced one of the creatures in two, but instead of dying, the pieces

regenerated into two full-blown individuals, complete with trunk, head, and

tentacles. They even began walking again. “I did not know what to think,”

Trembley confessed to Réaumur. Neither did Réaumur. Trembley’s letters about the creatures were getting

more fantastical. When he told others what Trembley was seeing, they

simply refused to accept such a thing could exist. Réaumur asked for some

of the creatures to look at for himself. Trembley packed fifty of his creatures in a glass tube that he stopped

with Spanish wax. When Réaumur received the tube in France, the animals

were all dead, the wax having suffocated them. Trembley tried again with a

corked tube, and one day in March 1741, Réaumur received a live batch of

the animals. When he sliced them into pieces, the creatures regenerated just

as Trembley had promised. “This is a fact I cannot accustom myself to

seeing, after having seen and re-seen it hundreds of times,” Réaumur

confessed. If Trembley’s animal was an exquisite machine, snapping it in two

should have stopped its parts from working. But if animals developed from

some preformed seed, regenerating entire new creatures should have been

impossible. If every animal was endowed with an indivisible animal soul,

did cutting a single individual into pieces lead it to make new souls, without

God’s foresight and planning?

“Is the soul divisible?” Réaumur wondered. Réaumur suggested to Trembley that the animals needed a name. He

proposed “polyps,” adapting the Latin word for octopus. (Today they’re

known as Hydra, and their genes reveal a kinship to jellyfish and corals.) When Réaumur showed off Trembley’s polyps to the Academy of Sciences,

he inspired in his colleagues the same awe he had originally felt. The

official report on his demonstration sounded more like a circus barker’s spiel than a scientific paper: “The story of the Phoenix who is reborn from

its ashes, fabulous as it is, offers nothing more marvelous than the discovery

of which we are going to speak.”

With Réaumur’s endorsement, the polyp became famous across Europe. Naturalists begged Trembley for animals of their own to look at. “I am

entirely taken up with dispatching polyps to one place or another,” he

groused. When he sent his first batch of polyps to London, two hundred

people gathered at the Royal Society to look at them through microscopes. Henry Baker got hold of the Royal Society’s polyps, observed them, and

drew the animals in their acrobatics. He whipped off a book, An Attempt

Towards a Natural History of the Polype. While Trembley quietly continued to do experiments at Sorghvliet, Baker satisfied the public’s curiosity. The secondhand stories of the polyps, Baker explained, “have appeared

so extraordinary, so contrary to the common Course of Nature and our

received Opinions of Animal-Life; that many People have look’d upon them as ridiculous Whims and absurd Impossibilities.” Baker provided a lyrical

firsthand account of how the polyp moved, caught prey, and devoured it. Still, he knew that some skeptics would scoff at the fantastical idea that the

polyp was an animal because it happened to be “unsuitable to their

Hypothesis of Life in general.”

Their regeneration was most unsuitable of all. “If the Animal Soul or

Life, say they, be one indivisible Essence, all in all, and all in every Part,

how comes it, in this Creature, to endure being divided forty or fifty Times,

and still continue to exist and flourish?” Baker asked. While Baker sang the praises of polyps, Trembley discovered even more

extraordinary things about them. Their bodies were held together by a

gooey substance that reminded him of an egg white, tenaciously resisting

his efforts to pull it apart. Trembley wondered if he was handling the stuff

of life, a glue that not only held his animals together but also gave them the

power to move. It was the first time anyone had conceived of such a life-

giving substance—what scientists a century later would refer to as

protoplasm. In other experiments, Trembley turned single polyps into dozens. He

lopped off bits of animals so that they grew back as deformed monsters. He

fused two polyps together and found they could live comfortably as a single

animal. One day he held a polyp in a drop of water cupped in the palm of

his hand. With his other hand, he snaked a boar bristle into the trunk of the animal and drew it out. The animal’s body was reversed, like a glove

quickly shucked off at the end of a winter day. Its interior now its exterior,

the polyp lived on. When Trembley reported this feat, many naturalists

considered it impossible. He had to round up a group of prominent experts

to gather at Sorghvliet to watch him turn polyps inside out and serve as his

witnesses. In 1744, Trembley finally published a two-volume monograph about all

this work. But far from launching his new career as a zoologist, it marked

the end of his scientific research. The Bentinck boys were growing up and

no longer needed his services. During Trembley’s time at Sorghvliet, the

count had introduced him to a powerful network of acquaintances who

recognized his sharp intellect. He joined a secret diplomatic mission to

France to settle the War of the Austrian Succession. When that task was

finished, Trembley was hired to oversee the education of a young English

duke, traveling the continent with his student for years. Those two posts

earned Trembley a pair of lavish pensions, which he used to return to

Geneva, buy a mansion, raise five children of his own, and write a series of

books on teaching. Trembley’s most important student had been himself. Over the course of

only four years, he had taught himself how to run rigorous experiments on

animals. As he learned how to extract knowledge from his polyps, he

invented the science of experimental zoology. Long after he had finished his

work and left Sorghvliet, the discoveries he had made in his polyps haunted

the minds of naturalists and philosophers. The creatures—which some

incorrectly called insects—demonstrated that life was different from what

anyone had previously thought. “A miserable insect has just shown itself to the world and has changed

what up to now we have believed to be the immutable order of nature,” the

naturalist Gilles Bazin declared. “The philosophers have been frightened, a

poet told us that death itself has grown pale.”

IRRITATIONS

As Trembley and the Bentinck boys splashed in ditches, a young

doctor was building a more conventional sort of fame in the German

town of Göttingen. Albrecht von Haller had moved there in 1736,

lured by a local baron who was building a new university and needed the

best anatomist in Europe to staff it. At twenty-eight, Haller was already the

obvious choice. The baron wanted him so badly that he built Haller a

mansion, a botanical garden, and a Calvinist church for him to worship in. But that was not all the baron would give Haller. “Called to Göttingen, there

was nothing more important for me to do than to build an anatomical

theater,” Haller later wrote, “and to supply it with corpses.”

Like Trembley, Haller was a Swiss in exile. He was born near Bern into

a family with a reputation as nervous, secretive, and eccentric. At age five,

young Albrecht would sit on the kitchen stove and preach to the family’s

servants from the Bible. By the time he was nine, he read Greek fluently

and had written biographies of more than a thousand famous people. He

developed a curiosity about the insides of bodies, which he satisfied by

cutting open animals. When he left Switzerland for medical school—first in

Germany, then in Holland—he began to cut open humans. Haller’s fellow medical students found him annoying. He took opposing

opinions as personal attacks. “He was unable to bear another’s error in

silence,” one biographer wrote. When a famous professor announced he had

found a new salivary duct, the teenage Haller carried out an experiment to

see it for himself. Haller humiliated the professor by proving he had been

fooled by an ordinary blood vessel. After finishing medical school, Haller traveled to London and Paris to

continue his studies. Watching a horrific surgery to fix a bladder, he decided

he would not operate on living people. Now he spent even more time with

cadavers, and the closer he looked in them, the more things he found. “To go through everything, and to have fully seen all the regions of the human

body, is as difficult and as rare as a full account of all the immense districts, rivers, valleys, and hills,” Haller later said. His studies finished, Haller returned to Bern to work as a family doctor,

which mostly meant bleeding mothers and children. His meager practice

left him with a lot of free time, much of which he spent wandering in the

Alps. Still in his early twenties, Haller became famous for his alpine botany. In London he had developed a taste for English poetry, and now he wrote a

long, romantic poem, “Die Alpen,” in tribute to the mountains. It made

Haller the most-read German poet of his day, and it turned the Alps into an

eighteenth-century tourist magnet. When he wasn’t bleeding, writing, or hiking, Haller was dissecting—

mostly the cadavers of criminals and the poor. He found new muscles,

junctures, and vessels. In 1735, Haller carried out the first careful dissection of conjoined twin babies. The babies, who had died shortly after birth, had

separate brains but a shared heart. Haller concluded that the soul could not

travel in the blood, because that would mean that the two distinct souls of

the babies would have to mix together. Far from a deformity, Haller saw the

exquisitely merged anatomy of the twins as further evidence of God’s

design and omnipotence. The reputation Haller built in Bern brought him an invitation to the new

university in Göttingen, and there he immediately began working even

more furiously, publishing volumes on botany and anatomy despite the

deaths of two wives and two children over just a few years. In his theater

Haller oversaw an army of anatomists as well as artists who sketched

everything they revealed in the cadavers. Dead bodies helped Haller understand living ones. He liked to call the

science he was developing “anatomy in action.” On the first floor of the

theater, Haller ran experiments on human cadavers, and on the second he

carried out an even grislier sort of research. There he and his students

worked on live dogs, rabbits, and other animals. It was not enough to

observe how the domed sheet of the diaphragm was attached to the ribs in a

dead man’s chest. Haller needed to see living diaphragms in motion. Trembley carried out gruesome experiments of his own on polyps, but

no one was much concerned with the plight of the tiny creatures he cut in

half. Haller, by contrast, became notorious around Göttingen for the way he

made his animals suffer. “One needs a stock of dogs and rabbits, which have their difficulty in a small town where everything astonishes and

attracts gapers,” Haller complained. The pain he caused his animals took a toll on Haller as well. He once

described his research as “a species of cruelty for which I felt such a

reluctance, as could only be overcome by the desire of contributing to the

benefit of mankind, and excused by that motive which induces persons of

the most humane temper, to eat every day the flesh of harmless animals

without any scruple.”

At first Haller designed experiments to understand one organ at a time. Gradually, though, he came to see the diaphragm, the heart, and all the other

parts of the body as part of one great system. Haller’s mind moved to more

fundamental questions about life. For Haller, no question was more

important than how living things moved. We can see some of life’s motions

when we take a walk or blink our eyes. But inside, Haller knew, our bodies

are also in constant hidden motion. Our hearts thump. Our gallbladders

squeeze out bile. Our intestines ripple. Haller believed that movements came in just a few forms. Some arise

from our will. In other cases we respond automatically to sensations. Haller

reasoned that nerves must somehow bring about movements like these. Based on what scholars knew of nerves at the time, Haller believed that

they must also sense what happened in the parts of the body they moved. To see if this was true, Haller and his students probed the interiors of

hundreds of living animals with knives, heat, and scalding chemicals. Screams and struggles revealed to them which parts of the body were

sensible. The skin, not surprisingly, was exquisitely sensible. But the lungs,

hearts, and tendons were not. Probe them as much he might, Haller found

no response. Haller also recognized that nerves were not always required for the body

to move. After he removed hearts from animals, the organs sometimes

continued to beat long after being severed from the nervous system. After

the hearts grew still, Haller could sometimes reanimate them for a spell by

touching them with a knife or exposing them to a chemical. This second kind of movement—known in the eighteenth century as

irritability—intrigued Haller even more. He set out on another set of

experiments to map it across the body. He and his students probed organs

and tissues to see if they contracted in response to a stimulus. Some didn’t

respond, while others did so weakly. But every muscle proved strongly irritable, and the heart, Haller concluded, was “the most irritable organ of

all.”

Haller wondered what caused sensibility and irritability. In the 1700s,

physicians generally believed that nerves contained a mysterious substance

called animal spirits. By some accounts these spirits created chemical

explosions to move muscles. But irritability did not rely on the nerves, and

so the force driving it must come from elsewhere. That place, Haller

decided, was within the muscle fibers themselves, where it was generated

independent of the soul. The more Haller contemplated irritability, the more profound it became. He decided that it was the hallmark of life, providing a clear-cut definition

for death: the moment at which the heart lost its irritability. As a force,

irritability seemed to Haller as profound as gravity—and also as mysterious. Even a gentle poke to a muscle could trigger an outsized response, seeming

to defy standard physics. In 1752, Haller delivered a series of lectures about his experiments,

which he published as a book the following year. Coming out soon after

Trembley’s work on polyps, Haller’s research proved equally provocative. People had wanted to watch polyps regenerate with their own eyes. Now,

all over Europe, anatomists wanted to run Haller’s experiments for

themselves. One visitor to Florence in 1755 wrote, “I saw in all corners

limping dogs, on which experiments on the insensibility of the tendons had

been made.”

Some of the experiments confirmed Haller’s, but others failed. Critics

attacked him for claiming that so much of the body created its own force,

independent of a soul. “The enemies of Mr. Haller have everywhere been of

a very great number,” one of his students observed. But none of his critics

could match Haller’s scientific output. The sheer volume crushed his

opposition. One French physician simply shrugged in surrender, asking,

“What to answer to 1,200 experiments?”

Not long after Haller published his findings, he left Göttingen. He

abandoned his mansion, his church, his garden, his theater. Now forty-five,

Haller returned to Switzerland hoping to gain political power, but he

misjudged his chances, merely landing a job running a saltworks. This left

him with plenty of time to write about medicine and botany and to publish

9,000 book reviews. Haller would never dismantle another cadaver. He did

not flay another rabbit. The closest Haller came to that sort of research was experimenting on himself. By the time Haller returned to Switzerland, he had lost the energy that

had propelled him over mountains as a young man. He was now a victim of

fevers, indigestion, insomnia, and gout. Sensibility took its vengeance on

him. Haller began to observe it from within, with intense curiosity. When

his gout flared, he would flex the tendon in his big toe and record his

sensations. Not once did he feel discomfort—or at least not until he bent his

toe so far that his skin began to stretch, “at which point,” he later wrote,

“the pain became unbearable.” To Haller, his unbearable pain was a

personal proof that skin was sensible but joints were not—and thus must

not contain nerves. When Haller reached his sixties, he began suffering chronic infections in

his bladder that forced him to use opium. He was intimately familiar with

the drug. In Göttingen he had grown poppies in his botanic garden,

extracted opium from them, and given it to animals to observe its effects. Haller noted that opium made the animals less sensitive. A heavily drugged

dog would show no response in its pupils when he put a candle close to its

eyes. But when Haller checked the animals for irritability, he observed that

the opium had a much weaker effect. It only made the intestines somewhat

less irritable, while the heart kept on beating normally. Haller saw these

results as more evidence that sensibility and irritability were two

fundamentally different things. After Haller published his findings, a Scottish physician named Robert

Whytt declared he was wrong. Whytt had run experiments of his own and

found that opium slowed the pulses of his animals. Haller’s “candor and

love of truth,” Whytt said, should make him “readily acknowledge his

mistake, as soon as he shall discover it.” That was not Haller’s way, though. He waved off Whytt’s work as inferior science. Haller’s pain grew worse. He slept even less at night, and his joints

began to ache with arthritis. Despite his familiarity with opium, he was

reluctant to take it himself. He had heard rumors of eastern kingdoms where

rampant use of the drug caused “terrible weakness of mind,” he said. For a

leading figure of the Age of Reason, nothing could be more frightening than

unreason. Haller shared his anxieties in letters with an old friend, the British

physician John Pringle. As one of Britain’s leading doctors—he would later

become personal physician to King George III—Pringle soothed Haller’s concerns with medical authority. “The dose is not to be measured by drops

or grains, but by what can procure you nights free from pain and such

frequent irritations to make water,” he assured Haller in 1773.

The opium gave Haller immediate relief, he reported back to Pringle,

“with the hush of the winds that soothe the raging sea.” Along with poetry,

Haller also recorded the experience as a scientist, tracking his pulse, noting

his sweats and the quality of his sleep. He checked his pulse before and

after each dose. He recorded every urination. He noted his farts. As the

weeks passed, he grew addicted and the opium grew less effective. Haller

increased his dose to 50 drops, then 60, 70, and eventually 130.

The opium

now launched Haller into blissful hours that were “joyous and of the highest

zeal for activity,” he wrote. And they were always followed by a crash. “The already generally weak physical strength is exhausted even more

when the effect of opium subsides,” he wrote. “I noticed the very repulsive

odor of opium exhalation through the skin; in this odor lay something burnt

of unpleasant sensation for the nose.”

By 1777, Haller was housebound, obese, and partly blind. But he still

greeted a flow of visitors to his home, including Emperor Joseph II, who

asked if Haller was still writing poetry. “Indeed no,” he reportedly said. “That was the sin of my youth.”

Yet Haller still wrote, thanks to his steady supply of opium, including a

report on his experiences with the drug. To the end, he looked for evidence

that he was right and that Whytt was wrong. Haller found that his pulse rose

as the opium eased his pain, and it dropped when the drug wore off. Haller

used his addiction to tease apart the nature of irritability and sensibility. Soon after Haller’s report on opium was delivered in a public lecture, he

died. He had many biographers, and they all loved to tell the story of his

last moment of life. This one, from a 1915 biography, is obviously fake but

wonderfully apt:

The fingers of one hand rested upon the diminishing pulse in the other. At length he said, calmly: “It no longer beats—I die.”

THE SECT

What Haller and Trembley alike cared about most was observing

life. They had little desire to forge sweeping explanations of all

the things they observed. Haller believed he would never truly

understand irritability, because its true nature was, he said, “concealed

beyond the research of the knife and microscope.” Beyond that boundary,

Haller would not venture. “The vanity of attempting to guide others in paths

where we find ourselves in the dark, shows, in my humble opinion, the last

degree of arrogance and ignorance,” he wrote. God had mysteriously

invested muscles with irritability, just as He had lodged gravity inside the

earth and moon. But other naturalists dared to explain life for themselves. The leading

naturalist of the day, Georges-Louis Leclerc, Comte de Buffon, argued that

life was chemically different from lifeless matter because it was made up of

things he called “organic molecules.” Buffon had no idea of what any

molecule was made of, let alone what distinguished one organic molecule

from another. But he was convinced that all living things—be they polyps

or people—reproduced in the same way: they assembled organic molecules

into copies of themselves. A polyp and a person were both alive because they were made of these

organic molecules, and could faithfully reproduce themselves in new

combinations of them. The reason that a polyp and a person were different

was that every living species had a unique “internal mold,” as Buffon liked

to call it. A mold drew in some kinds of organic molecules but not others,

creating a distinctive body. Haller and Trembley didn’t enjoy watching others use their work to

fertilize their own theories. When Trembley read Buffon’s claims, he was

aghast. “I confess that I can only consider his system as a hazardous

hypothesis,” he wrote to Count Bentinck. “He makes the facts on which he builds it, prove too much.”

Haller was likewise appalled at how theorizers made sweeping claims

about his work on irritability. “Irritability is becoming a sect,” he groused. “That is not my fault.”

The sect was made up of philosophers, naturalists, and physicians who

believed that life contains some sort of vital force. These so-called vitalists carried on the fight against Descartes, despite the many victories that his

mechanical vision scored in the eighteenth century. Inventors built

steamboats, air compressors, power looms, and other devices that would

make the industrial revolution possible. Astronomers who treated nature as

matter in motion made new discoveries of their own, such as the planet

Uranus. But the vitalists pushed back, arguing that life was fundamentally

different from a planet or a steamboat. The vital force endowed matter with

self-directed motion and the power to generate new complex bodies. The

vitalists saw life infused with purpose: eyes were made for seeing, wings

for flying, bodies for reproducing. To them, Haller’s irritability and

Trembley’s regeneration were potent examples of what the vital force could

do—and what a mechanical view of nature could never explain. After Haller’s death, the vitalists rose to even greater influence. In 1781

the German naturalist Johann Friedrich Blumenbach declared that within all

living things “lies a special, innate effective drive, active lifelong, initially to infer their definite form, then to preserve it, and, if it is injured, where possible to reproduce it.” Some envisioned the force being passed down

from one generation to the next, changing over time to produce different

forms. A British doctor named Erasmus Darwin was the first to share this

private notion—what later came to be known as evolution—with the public

at large. Today Erasmus is best known as Charles’s grandfather, but in the

late eighteenth century he was a towering figure in his own right. He wrote

a two-volume book that classified every disease known at the time. He

made major advances in science as a hobby, developing the first good ideas

of how plants use sunlight and air to grow. Erasmus Darwin believed all his ideas held together in a unified vision

of life. He wanted the world to see it, but he knew that most people would

not read a dense monograph. And so he created a genre all his own:

scientific poetry. Darwin turned the finer points of botany into hugely

popular verse. In the age of Wordsworth, Byron, and Shelley, it was Darwin who in the 1790s was the most famous poet in Britain. Samuel Taylor

Coleridge called him “the most original-minded man.”

Not long before his death in 1802, Erasmus Darwin wrote a poem called

“The Temple of Nature.” He followed life from its beginnings to the present

day. Organic life beneath the shoreless waves

Was born and nurs’d in ocean’s pearly caves;

First forms minute, unseen by spheric glass,

Move on the mud, or pierce the watery mass;

These, as successive generations bloom,

New powers acquire and larger limbs assume;

Whence countless groups of vegetation spring,

And breathing realms of fin and feet and wing. When the poem appeared a year after Erasmus Darwin’s death, it

shocked pious readers. Darwin was rejecting the belief that God breathed

species into existence in their current form. The reviews of “The Temple of

Nature” were savage. One nameless critic sneered at Darwin’s “unreal and

unintelligible philosophy.” It was so appalling that he practically threw his

quill away: “We are full of horror, and will write no more.”

For Romantic writers like Percy Shelley, however, Darwin’s poetry was

kindling for literary fires. In the summer of 1816, Shelley and his eighteen-

year-old lover Mary Wollstonecraft Godwin—soon to become his wife,

Mary Shelley—paid a visit to Switzerland. They stayed with Lord Byron

for part of the summer, which was so cold and rainy that they remained

cooped up indoors for days at a stretch. To pass the time, they wrote ghost

stories for each other. “Have you thought of a story?

I was asked each morning, and each

morning I was forced to reply with a mortifying negative,” Mary Shelley

later wrote. One night the conversation wound its way into “the nature of the

principle of life,” she later recalled. She listened to her fiancé and Byron

discuss Erasmus Darwin’s claim that simple life-forms arose from organic

matter. They wondered if that meant a corpse could be reanimated. “Perhaps the component parts of a creature might be manufactured, brought

together, and endued with vital warmth,” Shelley wrote. Late at night the party ended. When Shelley fell asleep, her mind was flooded with images. She saw a man kneeling beside a stitched-together

corpse. He used “some powerful engine,” as she described it, to bring the

corpse to life, making it stir with “an uneasy, half vital motion.” The man

then went to bed, hoping the “slight spark of life” in the corpse would go

out. But he was then awakened. “Behold the horrid thing stands at his

bedside, opening his curtains, and looking on him with yellow, watery, but

speculative eyes,” Shelley wrote. She woke up herself. “I have found it!

What terrified me will terrify

others,” she wrote. Shelley eventually turned her ghost story into a full-

blown novel, which she published anonymously in 1818.

She called it

Frankenstein. Her hero, the young scientist Victor Frankenstein, grows obsessed with

a question: “Whence, I often asked myself, did the principle of life

proceed?” He echoes the language of vitalists, and he follows the example

of Xavier Bichat, studying death to understand life. “The dissecting room

and the slaughter-house furnished many of my materials,” he says. Before long, Frankenstein has solved the mystery. “After days and

nights of incredible labour and fatigue, I succeeded in discovering the cause

of generation and life; nay, more, I became myself capable of bestowing

animation upon lifeless matter,” he declares. Shelley is delightfully cryptic

about his success, but she hints that it somehow involves electricity. By the

early 1800s it was clear that electricity had something to do with life—a

shock could make the legs of dead frogs twitch. But it was still mysterious

enough that it could stand in for the vital force of life. Erasmus Darwin wrote of the vital force with lyrical poetry, describing

it like the blooming of a cosmic flower. But Shelley saw something

grotesque in science’s obsession with life, something that seemed more like

an urge to control and exploit. “When I found so astonishing a power placed

within my hands, I hesitated a long time concerning the manner in which I

should employ it,” Frankenstein says. He decides to create a living thing by

assembling parts from human cadavers. “I collected the instruments of life

around me, that I might infuse a spark of being into the lifeless thing that

lay at my feet.” What he creates might be called life, but only a monstrous

kind. —

Along with his experiments with electricity, Frankenstein also uses

“chemical instruments.” Shelley never described exactly what sort of

chemistry he carried out, but the very mention of that science would have

given a bracingly modern feel to the book. At the dawn of the nineteenth

century, chemists were sweeping away the occult mysteries of alchemy,

replacing them with elements and atoms. To appreciate just how revolutionary this change was, consider water. In

the 1500s, alchemists tried to define water by its qualities—its transparency,

its ability to dissolve substances, and so on—and they ended up in a

muddle. Their research revealed to them different kinds of water that shared

some qualities in common, but not others. Unlike ordinary water, strong

water ( aqua fortis) dissolved most metals. But only noble water ( aqua regia) could dissolve the noble metals of gold and platinum. In the late eighteenth century, the French chemist Antoine Lavoisier

demonstrated that water contains molecules made of two atoms of hydrogen

and one oxygen. Strong water proved to be no water at all, but instead a

combination of nitrogen, hydrogen, and oxygen. Today it’s known as nitric

acid. And noble water was something else entirely: a mix of nitric acid and

hydrochloric acid. Living things could be broken down into elements as well. But the

molecules into which these elements combined in life were hard to find in

lifeless matter. Many chemists came to see a vitalist gulf between the

organic and the inorganic. “In living Nature the elements seem to obey

entirely different laws than they do in the dead,” an 1827 chemistry

textbook declared. A chemist named Friedrich Wöhler soon showed that the textbook was

wrong, and he used his own urine to prove it. Wöhler experimented with a

poisonous acid called cyanogen, mixing it with ammonia. He ended up with

peculiar white crystals made from carbon, nitrogen, hydrogen, and oxygen. The proportion of the elements in Wöhler’s crystals was identical to those

in a molecule called urea, which had only been found up till then in urine. Our kidneys make urea as a way to pull extra nitrogen out of our blood

and flush it out of the body. Chemists in the 1700s first discovered the

compound when they let urine evaporate and form crystals. To make sense

of his artificial crystals, Wöhler collected his own urine and isolated urea

from it. He compared his natural urea crystals to the artificial ones he had

concocted from ammonia and cyanogen. Chemically they behaved the same way. “I can no longer, as it were, hold back my chemical urine,” he declared,

“and I have to let out that I can make urea without needing a kidney,

whether of man or dog.”

Wöhler hadn’t created a Frankenstein’s monster, but he had managed to

create an organic molecule without relying on life’s vital force. When he

published his experiment in 1828, many chemists refused to acknowledge

what Wöhler had accomplished. Creating urea from scratch was not all that

important, they argued, because it was just one of life’s waste products. They continued to argue that only a vital force could create life’s organic

molecules. But some researchers followed up on Wöhler’s experiment with ones of

their own. The German chemist Hermann Kolbe studied acetic acid, which

could only be found at the time in vinegar from fermenting fruit. Kolbe

discovered how to make acetic acid in his lab out of carbon disulfide, an

inorganic molecule produced from coal. In 1854, Kolbe looked back to

Wöhler’s experiment and sanctified him as a scientific prophet. “The

natural dividing wall that separated organic from inorganic compounds

came down,” Kolbe declared. Life relied on ordinary chemistry but

somehow managed to use it for extraordinary ends. THIS MUD WAS ACTUALLY

ALIVE

On the night of August 14, 1873, Lord George Granville Campbell

gazed out from his ship at an ocean on fire. Every wave flashed with

light. When Campbell made his way to the stern of HMS

Challenger and looked down at the keel cutting through the Atlantic, he saw a glowing band of blue and green trailed by rising yellow sparks. When

he walked up to the prow, the light coming up from the ocean was bright

enough to read by. It was, Campbell later said, as if the Milky Way “had dropped down on

the ocean, and we were sailing through it.” But this galaxy, it turned out,

was made not of stars but of life. A sublieutenant in the Royal Navy, Campbell was serving aboard the

Challenger on a three-year scientific voyage. The ship, originally built for war, had been refitted for research. The navy had installed a hundred miles

of ropes, as well as trawls, dredges, and sounding devices. They took out

the Challenger’s cannons and converted the bays into laboratories. The

crew’s mission was to learn about the chemistry and biology of the world’s

oceans. For thousands of years sailors had seen lights on the sea, but now

the Challenger crew studied the phenomenon scientifically. They first

spotted lights near the Cape Verde islands and immediately threw out fine-

meshed dredges to see what might be producing them. They hauled up all

manner of nocturnal marine creatures, which they brought to the ship’s labs

to analyze. As the ship sailed on, it encountered more lights. Sometimes they turned

out to be produced by microscopic algae illuminating themselves whenever

the water around them was stirred. Sometimes the crew discovered the glow

came from siphonophores, monstrous colonies of gelatinous animals stretching as long as sixty feet. Henry Moseley, the ship’s naturalist, used

his finger to trace out his name on one specimen curled up in a bucket. “The

name came out in a few seconds in letters of fire,” he said. The Challenger discovered living fire not just at the surface of the ocean but also thousands of feet down. The ship was equipped with new

technology to survey the deep ocean, a world almost entirely unknown until

then. The crew would periodically drop tethered brass tubes into the depths

as the Challenger’s engines held the ship motionless against the wind. The tubes fell two miles to the bottom of the ocean, where they measured the

temperature—often barely above freezing—and sometimes scooped mud to

bring back up. The crew sometimes dragged openmouthed dredges over the

seafloor to see what they could haul up. When the dredges were spilled out

across the deck, the crew picked through the deep-sea jetsam. Sometimes

they found ancient volcanic rocks. Sometimes they found the dust of

meteorites that had fallen from space and settled on the seabed. And

sometimes they found living things that gave off light: luminescent fish,

corals, starfish. The Challenger crew wrote long letters about their

adventures, which took months to get back to England. But when they

arrived, newspapers there and abroad reprinted them. To a Victorian reader,

they read like dispatches from an Apollo mission to our own planet. For the Challenger crew, some of the most exciting dredges spilled what seemed like nothing but pale mud on the ship’s deck. Rather than simply

washing it back overboard, they carefully shoveled the mud into filters and

preserved what passed through in sealed bottles. In that mud the crew was

searching for a primordial creature they called Bathybius. Many biologists were convinced that it covered almost the entire ocean floor around the

world. It was not an animal or a fungus but a primordial jelly—the same

stuff that made up our own cells. On earlier voyages some naturalists had

found hints of this mysterious form of life, but the Challenger was finally equipped to reveal Bathybius in full detail. No one looked forward to the Challenger finding Bathybius more than Thomas Huxley, the British scientist who had given it a name. By the time of the Challenger voyage, Huxley had become one of the

world’s most prominent scientists. He had reached those heights from a

childhood mired in filth, poverty, and occasional starvation. Despite his

hardships, Huxley’s genius still managed to shine. As a child, he taught

himself German, mathematics, engineering, and biology. He dreamed of joining an expedition to discover strange new forms of life. A scholarship

enabled Huxley to go to medical school, where he quickly proved a master

of anatomy. As a teenager, he made a close examination of hair and

discovered a hidden sleeve of cells in the sheath that surrounded each

strand. It’s known today as Huxley’s layer. Staggering debts forced Huxley to leave medical school and enlist in the

Royal Navy at age twenty-one as an assistant surgeon. To his delight, he

was assigned to HMS Rattlesnake, an aging frigate destined for the coasts of Australia and New Guinea, where its crew would search for safe

passages. The ship’s captain, Owen Stanley, wanted a doctor with the

expertise—or at least the curiosity—to study the animals and plants they’d

encounter along the way. “I need not say how gladly I accepted the

proffered appointment,” Huxley later recalled. The Rattlesnake left England in December 1846.

In the South Atlantic,

Huxley noticed a Portuguese man-of-war drifting close by, the wind

catching the animal’s bright blue bladders like a sail. Mindful of its deadly

sting, Huxley carefully plucked the man-of-war out of the water and

brought it to the ship’s chart room. Laying it on the table, he carefully examined its fragile, toxic body until the tropical heat destroyed it. He was

dazzled by its anatomy, which was profoundly different from any vertebrate

like ourselves. A few naturalists had studied men-of-war before, but Huxley

realized they had gotten the anatomy wildly wrong. As the Rattlesnake sailed on toward Australia, he caught more

specimens and made a careful study of them. His curiosity extended to

other gelatinous creatures such as moon jellies and sea rafts. As he

inspected their soft bodies, he found striking similarities between them. They all used the same microscopic harpoons to deliver their stings, for

example. All he could do was describe these animals as accurately as he

could and send his accounts back to friends in London, hoping they might

be read. When Huxley finally returned to England in 1850 at age twenty-five, his

letters had already created a sterling reputation for him. Within a few years

he became a professor at the Royal School of Mines and one of the most

powerful public champions for science. He wrote essays for magazines and

gave lectures intended for “working men.” Huxley also found time to keep

studying life, working through his collection from his days aboard the

Rattlesnake. While his expedition days were over, he was now powerful enough to get hold of new samples from Britain’s network of shipboard

naturalists. Huxley had launched his scientific career skimming the surface

of the ocean for strange forms of life, but in the late 1850s his attention

plunged down to its dark depths. A flotilla had begun surveying the ocean floor to prepare for laying the

first telegraph cables connecting England to Europe and then to the United

States. Like other biologists, Huxley wanted to know whether anything

lived down there. He arranged for the surveyors to save some of the mud

they brought up, sealing it in jars along with alcohol, in the hopes of

preserving any soft tissue that would otherwise rot on the voyage home. One of the ships that sent Huxley mud was a sounding vessel called

HMS Cyclops. In June 1857 it left Valentia, Ireland, for Newfoundland, passing along the way over a vast rise of seafloor called Telegraph Plateau. The captain, Joseph Dayman, expected it to be ribs of granite. Instead, his

crew hauled up a “kind of soft, mealy substance, which, for want of a better

name, I have called ooze.”

When the ooze arrived in London, Huxley discovered that it contained

odd microscopic buttons. Each button was made of concentric layers that

surrounded a central hole. Huxley wasn’t sure if they had broken off of

animals that lived in the ooze or had fallen from higher in the ocean to their

resting place on Telegraph Plateau. Still, they warranted a name, so Huxley

dubbed them coccoliths. He filed a short report with the navy and put the

ooze on a shelf, where it sat for ten years. It would prove a busy decade for

Huxley as he helped usher in a new theory of life. —

On Huxley’s return home from the Rattlesnake expedition in 1850, one of the most important new friends he made was Charles Darwin. Darwin,

forty-one at the time, was known mostly for his own voyage around the

world aboard HMS Beagle. As far as anyone knew, he had busied himself

ever since with barnacles. Darwin and Huxley came from different

universes within England: while Huxley had grown up poor, Darwin came

from a wealthy family and had never worked for a living. But they

immediately recognized that they both shared an obsession with life in all

its baffling diversity and were desperate to find a principle to make sense of

it all. In 1856, Darwin invited Huxley to his country house for a weekend visit. There he let Huxley in on a great secret: like his grandfather Erasmus,

Charles Darwin had become convinced that life evolved. But Charles had

not produced a poem about the idea. Instead, he had developed a detailed

theory, which he explained to Huxley. Natural selection turned old species

into new ones, into new forms of life. Every species, Darwin argued, was

merely a branch on the tree of life. Before that moment Huxley had been skeptical about evolution, but now

he began to warm to it, recognizing that Darwin had succeeded where

others had failed. While Darwin holed up on his country estate, Huxley

championed his theory on the lecture circuit and in magazines. He called on

his fellow biologists to carry Darwin’s project further, to join all the

branches of the tree of life together. As they came to better understand the

evolutionary tree, they would be able to make their way down to the base—

to the stage of history when life first arose. “If the hypothesis of evolution is true, living matter must have arisen from not-living matter,” Huxley

declared. The best place to search for evidence of that transition, Huxley decided,

was the ooze. Huxley’s suspicions had a long pedigree. Their origins reached back

over a century, to Abraham Trembley’s work with polyps. Trembley had

discovered a jellylike substance in the animals that seemed endowed with

vital force. Albrecht von Haller recognized this substance in the animals he

dissected and speculated that it was responsible for irritability. The vitalists who followed Trembley and Haller went even further. They claimed that the

goo was the stuff of life, found in every species. A German biologist named Lorenz Oken even gave this gelatinous mass

a name: Urschleim, or primal slime. Oken envisioned the primal slime as a vast, continuous substance that formed spontaneously on the early earth. It

then broke up into microscopic blobs of living matter, which then evolved

into complex life as we know it. Yet even today, Oken argued, the primal

slime continued to go through cycles of creation and destruction inside all

living things. Oken championed Urschleim in wildly Romantic speculations that had

no basis in experimental evidence. Nevertheless, even more sober-minded

biologists gradually came to agree that life was built from a universal goo. In the 1830s a French zoologist named Félix Dujardin found a “living jelly”

inside single-celled microbes. More evidence came from microscopic studies on the tissues of plants and animals, which revealed that they were

masses of cells. When nineteenth-century biologists looked inside cells,

they always found the same living jelly. “The cell was redefined around a

frothing lump of mucus,” writes the historian Daniel Liu. This mucus moved and quivered. It pushed cells from within. “I dare not

venture to express the slightest suspicion of the cause of this motion,’’ the

German biologist Hugo von Mohl declared in 1846.

Within a few years

scientists agreed to call this mysterious frothing mucus “protoplasm.” And

soon a suspicion emerged that protoplasm didn’t just have a vital power of

motion; it might also carry out the chemistry that produced organic

molecules. It might organize the interiors of cells. It might pull apart one

cell to make two and drive the development of cells into complex embryos. It seemed like there was nothing protoplasm couldn’t do. Huxley, while not a cell biologist or chemist himself, kept close watch

on the growing evidence for protoplasm as the basis of life. If evolution was

like a river flowing through time, he recognized, protoplasm was its water. It was protoplasm that was passed down from one generation to the next,

and somehow generating evolution’s new forms. “If all living beings have

been evolved from pre-existing forms of life,” Huxley wrote, “it is enough

that a single particle of living protoplasm should once have appeared on the

globe.”

In the early 1860s researchers in Canada discovered what looked like

fossil protoplasm. From some of the oldest rocks known to scientists at the

time, they found fossils of a speck-sized, shell-covered creature. The

biologist William Carpenter, who examined the organism carefully under a

microscope, described it as “a little particle of apparently homogeneous

jelly.”

Carpenter called the new species Eozoön, or dawn animal. When

Darwin read about it, he updated his 1866 edition of The Origin of Species

to include the discovery as further evidence for evolution. “After reading

Dr. Carpenter’s description of this remarkable fossil, it is impossible to feel any doubt regarding its organic nature,” he declared. Geologists found more Eozoön, uncovering vast sheets of fossils in

Canada and beyond. Judging from the different layers where they found the

fossils, Eozoön seemed to have endured for vast stretches of time. In fact, Carpenter declared at a geology meeting in London that he “should not be

astonished even if such a structure as Eozoon were found in deep-sea dredgings of the present day.”

In 1868, shortly after Carpenter published his study of Eozoön, Huxley did something odd: after a decade, he took the ooze from the Cyclops off its shelf to give it a fresh look. No one knows exactly why he decided to break

the ten-year spell. Maybe he thought Eozoön was still alive on the bottom of the ocean. Maybe he thought the ooze contained the primal slime

predicted by Oken. Maybe he was just excited to try out the powerful new

microscopes he had just acquired. Whatever the reason, Huxley looked at his ooze, and the ooze now gave

Huxley a start. He saw something in it that had not been visible before:

“lumps of a transparent, gelatinous substance.” The substance formed a

blobby network across Huxley’s field of view, scattered with the tiny

coccolith buttons as well as strange “granule-heaps,” as he called them. If Huxley looked long enough, the lumps moved. He concluded that this

gelatinous substance was protoplasm. He must be looking at “simple,

animated beings.” If the ooze collected by the Cyclops was typical of the Atlantic, then the whole ocean might be covered by what he called a “deep-sea ‘Urschleim.’”

Huxley concluded that in this slime he had discovered a species in its

own right, unlike any form of life previously found, which he named

Bathybius haeckelii. Bathybius meant deep life, and haeckelii honored the German biologist Ernst Haeckel, the leading proponent that all life evolved

from a simple, protoplasm-filled ancestor. “I hope that you will not be

ashamed of your godchild,” Huxley told Haeckel. Huxley unveiled Bathybius in August 1868 at a scientific meeting. A

reporter there marveled at the idea of a “living paste on the floor of the

Atlantic.” Huxley presented Bathybius as evidence of a sweeping theory

about life—about its very nature and its entire history. In the months that

followed, he roamed Britain giving a series of lectures on the physical basis

of life. From one city to the next, he made a profound impression in the

crowded halls and churches where he spoke. “The audience seemed almost

to cease to breathe, so perfect was the stillness,” a journalist reported from

his talk in Edinburgh. “What hidden bond can connect the flower which a girl wears in her hair

and the blood which courses through her youthful veins?” Huxley asked his

listeners. The answer was protoplasm. “It may be truly said that the acts of all living things are fundamentally one,” Huxley said. Protoplasm was simply an arrangement of organic molecules whose

functions no one yet understood, Huxley declared, but which ordinary

physics would suffice someday to explain. There was no need to imagine a

mysterious vitality in living things. That made as much sense as saying

water had “aquosity.”

Ministers might tell their congregation that everything comes from dust

and to dust returns. But protoplasm revealed a different cycle, one in which

life turns to life. “I might sup upon lobster, and the matter of life of the

crustacean would undergo the same wonderful metamorphosis into

humanity,” Huxley said. “And were I to return to my own place by sea, and

undergo shipwreck, the crustacea might, and probably would, return the

compliment, and demonstrate our common nature by turning my

protoplasm into living lobster.”

The delicate balance of scandal and science Huxley delivered proved a

smash. Three months after his lecture in Edinburgh, the text was published

in Fortnightly Review as an essay called “On the Physical Basis of Life.”

Now protoplasm became famous far beyond Scotland. The issue of

Fortnightly Review went into seven editions to meet the demand, and

newspapers abroad reprinted great swaths of it. As Huxley scurried from lecture to lecture around England, a scientist

named Charles Wyville Thomson was sailing a small steamship called the

HMS Lightning north of Scotland. By the 1860s, scientists like Thomson

wanted to study the ocean for the ocean’s sake. He wondered just how

much life existed in the deep ocean: Was it an underwater desert or a

jungle?

The Admiralty provided him with the Lightning, a small converted gunboat, for a trial run. Thomson and his crew scooped up bits of the

seafloor, and sometimes they brought up an oddly sticky hunk of mud. Mindful of the newly discovered Bathybius, they looked at the mud under a microscope and saw movement. It had a strange egg-white appearance, like

protoplasm. “This mud was actually alive,” Thomson declared. After the six-week voyage of the Lightning, Thomson delivered the mud

to Huxley, who pronounced it a second sample of Bathybius. Still more

Bathybius came to light in the South Atlantic and the Pacific. In August 1872 American explorers searching for the North Pole found what looked

like an even more primitive version of Bathybius in the Arctic Ocean, which they dubbed Protobathybius. With his primitive creatures turning up all over the world, Huxley now

saw Bathybius as a kind of global carpet. “It probably forms one continuous scum of living matter girding the whole surface of the earth,” he said. Some scientists rejected all this evidence and denied that Bathybius

existed. A biologist named Lionel Smith Beale called it “fanciful and

improbable.” But Beale did not attack Huxley out of some disinterested

skepticism. He was a vitalist, and he saw Bathybius as a threat to the

fundamental divide between life and everything else. “Life is a power,

force, or property of a special and peculiar kind, temporarily influencing

matter and its ordinary forces, but entirely different from, and in no way

correlated with, any of these,” Beale wrote. For the most part, though, scientists saw the discoveries of Bathybius

around the world as proof that it was real. In 1876 a zoology textbook put

Bathybius and its shredded tapestry of protoplasm on its first page. In Germany, Haeckel was as delighted by Huxley’s discovery as the critics

were appalled. Urschleim, he said, “has become a complete reality through Huxley’s discovery of Bathybius.” Haeckel shared Huxley’s new vision of the planet, declaring that “huge masses of naked, living protoplasm cover

the greater ocean depths.”

Haeckel wondered where those huge masses came from. “Is protoplasm

perhaps originating continually through spontaneous generation?” he asked. “Here we stand before a series of dark questions, the answers to which can

only be hoped for from subsequent researches.”

Charles Wyville Thomson used his success aboard the Lightning to win

support for a survey of the deep sea across the entire globe. When the

Challenger expedition came together, Thomson was appointed its scientific director. The ship had a captain, but it was Thomson who was really in

charge. He oversaw a staggering amount of research into biology, geology,

and meteorology. The Challenger crew collected birds of paradise and

seaweed and human remains. They prepared reports on the plants of

Bermuda, on the chemical composition of the oceans, on barnacles. Ultimately their data would fill fifty volumes. Thomson would be long dead

by the time the last volume came out. But amidst all their shipboard work, the crew of the Challenger always

made time to search for Bathybius. They had every reason to expect to find

it in abundance, and they were eager to study the fresh samples in their shipboard laboratory, rather than just store them away for the long voyage

home. It took a few weeks for the crew to get adept at scooping up deep mud

on their way across the Atlantic. John Murray, Thomson’s second-in-

command, began carefully skimming off water from the mud’s surface,

where he believed fresh Bathybius would most likely be found. He put the samples under the ship’s powerful microscopes and searched them for

hours, looking for the blobby networks of protoplasm that so many others

had found. He found nothing. As each sample came up, Murray and his colleagues would store some

of the mud in jars with alcohol so that Huxley and other scientists back

home might someday study it and perhaps have better luck. One day

Murray glanced at the jars and observed that a translucent layer had formed

on top of some of their mud. He took the jars down and inspected the layer. It had the consistency of jelly. The ship’s chemist, a wealthy young Scotsman named John Buchanan,

was intrigued by Murray’s discovery. Perhaps what previous scientists had

taken for Bathybius was not some form of life in the sea floor ooze, but a jelly-like byproduct of chemical reactions that took place in the jars. To test these possibilities, he let a sample of deep-sea water evaporate. “If the jellylike organism which had been seen by some eminent naturalists in

specimens of ocean-bottom and called Bathybius really formed, as was

believed, an all-pervading organic covering of the sea-bottom, it could

hardly fail to show itself when the bottom-water was evaporated to dryness

and the residue heated,” he later wrote. But it did fail. Once the water evaporated, Buchanan could find no

organic remains. He turned to the jelly that Murray had spotted in the jars. His

experiments revealed that they contained no organic matter either. Buchanan found instead calcium and sulphate—gypsum, in other words. As

the Challenger sailed from Hong Kong to Yokohama, Buchanan ran more

experiments and realized what had happened. Putting the deep-sea mud in

alcohol had driven the calcium and sulphate to form a jellylike mass. With a few shipboard experiments, Buchanan and Murray had wiped the

planet clean of its most primordial, fundamental form of life. They wrote up

their obituary for Bathybius in cold, clinical prose. “In placing it amongst living things,” Buchanan concluded, “the describers have committed an

error.”

You might expect that Thomson responded by quelling his team’s

blasphemy. After all, seven years earlier, on the other side of the world,

Thomson himself had dredged up Bathybius. He had written glowingly

about the species in a best-selling book about the sea before setting sail on

the Challenger. But Thomson held on to his convictions lightly. Buchanan and Murray convinced him their science was good, and so, on June 9, 1875,

Thomson composed a letter to Huxley to relay the bad news. “You should be told exactly how it stands,” he told Huxley. “None of us

have ever been able to see a trace of Bathybius, although it has been looked for throughout with the most utmost care.” Murray and the other members

of the team, Thomson wrote, “deny that such a thing exists.”

When Huxley received the letter, he did not hide the disastrous message. Instead, he passed it on to the journal Nature for publication, with a note of his own at the end: “I am mainly responsible for the mistake, if it be one.”

By the time the Challenger returned to England on May 24, 1876,

Bathybius was pretty much dead. Among its few remaining defenders was

Haeckel, who was dismayed to see Huxley give up the fight for his

namesake. “The more the real parent of Bathybius shows himself inclined to give up his child as hopeless, the more I feel bound, as its godfather, to

look after its rights,” he once said. But Haeckel had nothing to offer against

the Challenger’s evidence. Bathybius soon disappeared from textbooks, dismissed as a spectacular mistake. Its fossil forerunner, Eozoön, soon followed the same path to obscurity—a deceptive crystallization, it turned

out, rather than the mark of ancient primitive life. In fact, it was Huxley’s enemies who did the most to keep the memory

of Bathybius alive. In 1887 the Duke of Argyll, the leading opponent of Darwinism in the nineteenth century, revived the embarrassment to question

Huxley’s entire view of life. The duke called the affair “a case in which a

ridiculous error and a ridiculous credulity were the direct result of

theoretical preconceptions. Bathybius was accepted because it was in

harmony with Darwin’s speculations.”

Huxley, who had a low opinion of the Duke of Argyll for not doing any

science of his own, freely granted that he had made an error. But, he added,

“the only people, scientific or other, who never make mistakes are those who do nothing.”

Still, the duke did have a point, as the historian Philip Rehbock later

observed. “Bathybius was a highly functional concept,” Rehbock wrote, “an explanatory device which made sense in the context of mid-nineteenth-century biological and geological thinking.”

In the borderland between the living and the nonliving, conceptual

mirages have a way of taking shape and gaining fame. Yet, despite his

planet-wide error, Huxley’s reputation remained intact. When he died in

1895, the Proceedings of the Royal Society of London sang his praises in an obituary that ran twenty pages. “Whatever bit of life he touched in his

search, protozoan, polyp, mollusc, crustacean, fish, reptile, beast, and man

—and there were few living things he did not touch—he shed light on it,

and left his mark,” the journal declared. In all those pages, they couldn’t

find room to mention Bathybius. A generation later, John Butler Burke would suffer a harsher fate when

his radiobes proved false. Although Huxley had been fooled by a mirage, he

was still right about life’s big picture. Evolution is real, and protoplasm

does indeed unite all of life. But it does so with a bond far more intricate

than Huxley could have imagined. A PLAY OF WATER

Bathybius was dead, but protoplasm lived on. As the nineteenth

century drew to a close, its inner workings slowly began to emerge. Some of the first clues came not from the seafloor but from beer. Throughout history, making beer had been a kind of alchemy. People

began brewing at least 13,000 years ago, when glaciers covered New York

and woolly mammoths trundled across Siberia. The first brewers, who lived

somewhere in the Near East, collected wheat and barley plants and boiled

them into a concentration of sugar known as a wort. They then waited for

the wort to ferment into a bubbling brew that could get them drunk. What

happened during fermentation was anyone’s guess. In the nineteenth century, chemists offered one answer and

microbiologists offered another. The chemists, working in the tradition of

Friedrich Wöhler, thought of fermentation in terms of molecules becoming

new compounds. To them, it seemed that plant sugar underwent chemical

reactions that produced alcohol and other molecules, along with bubbles of

carbon dioxide gas. The microbiologists meanwhile looked at fermentation as an act of life. The dregs in the wort—long known as yeast—turned out to be composed of

living single-celled organisms. Fermentation could not take place without

them. For thousands of years, brewers had unknowingly inoculated their

beer by leaving their wort open to the air. Drifting yeast spores naturally

settled on it and took over the fermentation from there. Life was essential to

the process. A sterilized wort could never become beer. By the end of the

nineteenth century, microbiologists had turned brewing into a kind of

industrial biology. Brewers could pick out which species of yeast they

wanted to use, ensuring that their beer would wind up with a predictable

flavor. Every pint of beer raised in every pub seemed proof of life’s vital

force. When sugar came into contact with living matter, it turned to alcohol in a reaction that could otherwise never take place. The chemists were not impressed. The notion that tiny cells of yeast

guzzled wheat and magically pissed out alcohol seemed like absurd

vitalism. A young German chemist named Eduard Buchner won a Nobel Prize by

trying to broker a truce between the two sides of the great beer debate. By

the late 1800s, scientists knew that living things made a special class of

proteins called enzymes that were remarkably good at breaking down

certain other molecules. Some researchers proposed that yeast contained an

enzyme that could cut apart sugar. Yes, yeast were essential to fermentation,

but, no, they contained no vital forces. In the 1890s Buchner set out to find these imaginary enzymes. He mixed

yeast powder with a fine grit and then ground it in a mortar into a dark,

damp dough. The membranes of the yeast cells tore open, dumping out their

protoplasm. Buchner spread this new concoction on a flat surface and crushed it

under a hydraulic press. Out came a pleasant-smelling yeast juice. To kill

any cells that managed to slip into the juice, Buchner added arsenic and

other poisons. The juice was now completely robbed of life. And yet, when Buchner added sugar to this lifeless juice, it gave off a

fizz of carbon dioxide bubbles and turned to alcohol. Fermentation did not

depend on living cells, Buchner’s experiment showed. It didn’t even need

bits of living protoplasm. An ordinary enzyme must be responsible. At first the idea seemed outrageous to biologists and brewers alike. They could not conceive of protoplasm as a jumble of specialized

molecules, each carrying out its assigned reaction. One expert on

fermentation predicted that Buchner’s claim “will enjoy none too long a

life.”

But soon other scientists succeeded in repeating Buchner’s experiment,

and they pushed the work even further, isolating Buchner’s enzyme and

giving it the name zymase. The French microbiologist Émile Duclaux

declared that Buchner was “opening up a new world.” It was a world of

biochemistry, in which living things were filled with a zoo of active

proteins. When Buchner went to Stockholm in 1907 to accept his Nobel Prize, he

tried to play the part of peacemaker. Mechanists and vitalists didn’t have to

fight over fermentation. The vitalists had been right that yeast is essential to fermentation. Enzymes couldn’t exist without this living thing to create

them. But yeast did not use mysterious vital forces to ferment beer. They

made zymases: ordinary molecules that followed the ordinary laws of

chemistry. Removed from a cell, an enzyme was lifeless—but it could still

carry out the same chemical reactions. “The differences between the vitalistic view and the enzyme theory have

been reconciled,” he announced. “Nobody is ultimately the loser.”

If Buchner imagined he could broker a truce in a war that had lasted by

then for over two centuries, he must have been deeply disappointed. The

arguments over the nature of life only grew louder in the years after he

picked up his prize. The biochemical vision of life—like the mechanical

ones that came before—left many scientists dissatisfied. It was all well and

good to find one enzyme that broke down sugar and another that broke

down starch. But no one could piece together a few such reactions into the

grand transformations essential to life—the way plants turned sunlight into

roots and flowers, for example, or how a single cell became a human being. As microscopes grew even more powerful, biologists were discovering that

protoplasm was actually as busy as a city, crammed with compartments,

filaments, and granules. No one could tell yet what went on in those secret

chambers or how many were even real. Some appeared one day under the

microscope and then vanished the next. “Which of them are alive?

Which of them, if any, constitute the physical

basis of life?” asked the American cell biologist Edmund Wilson in 1923.

“These are embarrassing questions.”

Some scientists argued that these questions would remain embarrassing

forever. The simple chemistry carried out by enzymes could not guide an

egg into an embryo. Trembley’s polyps needed more than molecules to

rebuild their bisected bodies. But the scientists who rejected a purely

mechanistic view of life weren’t arguing for a mystical vital force, either. What made life special was that it existed on more than one level. Lower levels spontaneously gave rise to higher ones. One enzyme might

only be able to do one thing—fuse two molecules together, for example—

but bring together billions of enzymes, carrying out billions of different

tasks, and you suddenly had a cell. Step up to the next level, and a group of

cells became a body. Bodies combined into populations, populations into

ecosystems. Once you hopped to a new level, you had to stay there to make sense of it. Try to understand a cell by breaking it back down to enzymes, and you

kill it. The cells inside the bodies of snowshoe hares cannot explain the

booms and busts their populations go through across Canada every few

years. The answer lies in the bloody dance of hares and lynx. The public at large followed these debates closely. The emerging

science of biochemistry seemed poised to give humanity a Frankensteinian

power over life. But in the process, it seemed as if would reduce life—

especially human life—to depressingly small bits. Memories, emotions—

our very selves—seemed to dwindle down to blind jostling of proteins. People wanted more from their lives, more from life itself, and vitalism

seemed to offer what they craved: a vital force that lay beyond the

biochemist’s reach. At the dawn of the twentieth century, the vital force grew into something

like a religious phenomenon: the human spirit to some, the spark of the

divine to others. The French philosopher Henri Bergson gained a huge

following with his claims that all of life shared a vital impulse, or élan vital. “Life is, more than anything else, a tendency to act on inert matter,” he

wrote in his 1911 book, Creative Evolution. Murky and meandering, it

nevertheless became a best seller. When Bergson traveled to New York to

deliver a series of lectures, he reportedly created the city’s first traffic jam. A thousand people showed up just to gawk at him as he sipped tea with the

wives of Columbia University professors. Bergson and the other neo-vitalists did not impress the biochemists. In a

1925 essay, the British scientist Joseph Needham declared that they “have

won no confidence at all among the research workers in biochemistry and

physiology.” Talking of vital forces was nothing but a celebration of

ignorance. In the nineteenth century, many physicists sought to explain how

light traveled through space by claiming it was filled with a substance

called ether. It was weightless, transparent, frictionless, and undetectable—

and yet was supposed to suffuse the universe. As soon as modern physics

emerged, it proved to be a fiction. In the early 1900s, biochemists like

Needham felt confident that vital forces also disappear, remembered as

life’s ether. Needham accepted that all of life could not be explained merely in terms

of atoms. It had many levels, each of which deserved attention. But that was

no reason to abandon a mechanistic foundation. Even if a single enzyme

could not explain an eagle, it was certainly a good place to start. In the 1920s, biochemists were discovering how enzymes worked together in

teams. One enzyme might cut part of a molecule off and then hand over the

molecule to another enzyme to change it in another way. Gradually these

chains of enzymes grew into great interlocking loops of metabolism. And,

meanwhile, what were the vitalists discovering?

Over and over again they

did nothing but point to the open questions scientists had yet to answer. To

Needham they were no better than nineteenth-century theologians, denying

evolution by pointing to gaps in the fossil record. “In the laboratory,” Needham sighed, “it simply will not do.”

—

Needham’s words proved prophetic. As the twentieth century rolled on,

vitalism yielded more of its ground to chemistry and physics. Even

irritability, that fundamental force that seemed unique to life, yielded to the research of an extraordinary Hungarian physiologist named Albert Szent-Györgyi. Before he was done, he could conjure irritability on demand. “My inner story is exceedingly simple, if not indeed dull,” Szent-

Györgyi said late in life. His existence was devoted to science, full stop. As

for his external life, Szent-Györgyi acknowledged that it had been “rather

bumpy.” That’s putting it mildly. Some of those bumps would have gotten

most people killed. Szent-Györgyi was a medical student when World War I broke out. He

joined the Hungarian army and served for three years, until he could see

that the war was lost and fighting any longer was a senseless sacrifice. “The

best service I could do for my country was to stay alive,” Szent-Györgyi

wrote. “So, one day, when in the field, I took my gun and shot myself

through the bone of my arm.”

His self-inflicted wound allowed Szent-Györgyi to return to Hungary

just in time for a Communist uprising. His family lost virtually all their

possessions, and he fled the country with his wife and child. In Prague and

then Berlin, they verged at times on starvation. Szent-Györgyi managed to

continue his medical studies, but in time he came to realize that he didn’t

actually want to cure people. “I wanted to understand life,” Szent-Györgyi

said. To do so, he joined the efforts to dissect protoplasm. He studied how

enzymes cooperated inside our cells in the transformation of food to fuel,

eventually earning a PhD at the University of Cambridge. The reactions Szent-Györgyi uncovered would turn out to be key steps in the loops of

metabolism that keep us alive. In enzymes Szent-Györgyi saw a unity in

life. “There is no basic difference between man and the grass he mows,” he

said. He proved it with a discovery that earned him the Nobel Prize, a

discovery that started with his puzzling over potatoes and lemons. When

potatoes are cut, they turn brown, but lemons do not. Szent-Györgyi

reasoned that oxygen reacted with a compound in the potatoes, but the

lemons contained a second compound that slowed those reactions down. He searched for that second compound for years, eventually finding it in

the cells of many plants as well as some animals. When Szent-Györgyi was

ready to publish a paper on the molecule in 1928, there was still much about

it he didn’t understand. If you had asked him about it, he would have

shrugged and said, “God knows.” In fact, he asked his editors at the

Biochemical Journal if he could name the molecule “Godnose,” just to

make his ignorance clear. They forced him to call it hexuronic acid. It later came to be known as vitamin C. Scientists determined that it’s

essential for repairing cellular damage, building proteins, and many other

functions. While lemons and some other plants have genes for making

vitamin C, we humans have to get our supply in our food. Szent-Györgyi’s

discovery made it possible to synthesize the molecule from scratch, but he

refused to put a patent on it, believing vitamin C belonged to all humanity. It didn’t make him rich, but he did get a summons from Stockholm. At age forty-four, with a Nobel Prize, Szent-Györgyi finally considered

himself ready for serious science. “I felt I had now enough experience for

attacking some more complex biological process, which could lead me

closer to the understanding of life,” he said. He chose to study muscle. “Its

function is motion,” Szent-Györgyi said, “which has always been looked

upon by man as the criterion of life.”

At the University of Szeged in Hungary, where Szent-Györgyi was

appointed a professor, he put together a team of young scientists to take on

the mystery that had vexed Albrecht von Haller two centuries earlier: how

muscles moved. He knew that if you soaked muscles in a solution of salt,

their cells released a viscous ooze. In the ooze were filament-shaped

proteins called myosin that many scientists suspected generated the force

that made muscles contract. Another molecule that caught Szent-Györgyi’s fancy was ATP. It had been discovered in 1929, but no one knew yet what it was for. Some

researchers suspected that muscles used ATP as fuel, capturing the energy

released when its bond was broken. In 1939, Szent-Györgyi learned that

Russian biologists had discovered myosin could grab ATP molecules and

split them. Szent-Györgyi decided to look more closely at that reaction. As he began this new line of research in the late 1930s, Szent-Györgyi

became cut off from the world. Hungary had formed a loose alliance with

Nazi Germany against Russia in the hopes of getting back some of the land

they lost in the Treaty of Versailles. Britain then declared war on Hungary,

and the country became isolated behind the Axis lines. Over the course of

his career, Szent-Györgyi had built up an international network of

collaborators. Now he and his colleagues at Szeged had to work alone. Soon his lonely team of scientists saw something extraordinary. They

isolated threads of myosin and dropped them into boiled muscle juice. In a

matter of seconds, the long, translucent threads scrunched into dark stubs. Szent-Györgyi and his colleagues were seeing muscles contract on a

molecular scale. To understand how this motion occurred, the researchers stripped the

boiled muscle juice to its bare essentials. They prepared a solution

containing just ATP, along with some potassium and magnesium to keep the

cells working properly. Those three ingredients were enough. When the

scientists dropped myosin threads into this mixture, the proteins contracted. They had re-created one of life’s most basic functions in a test tube. One member of Szent-Györgyi’s team, Bruno Straub, called it “the most

beautiful experiment I ever witnessed.” Another, Wilfried Mommaerts, said

it was “possibly the greatest biological observation.” Part of what made it

so great, Mommaerts felt, was its simplicity—“the hallmark of true genius.”

This work of genius was all the more remarkable because Szent-

Györgyi was splitting his time between science and spy craft. He had been

appalled by Hitler’s rise and helped Jewish scientists escape from Germany. At Szeged he stood down mobs of fascist students hunting for Jews at the

university. When Szent-Györgyi received his Nobel Prize winnings, he

invested them only in stocks that wouldn’t benefit from the war economy. (He lost it all.) And once the war broke out, Szent-Györgyi quietly joined a

resistance group. In 1943 he boarded a train for Istanbul on a secret mission. For his cover, he delivered a scientific lecture at a Turkish university. But he then

met secretly with British intelligence agents, letting them know that

Hungary might consider switching sides and joining the Allies. Returning to Hungary, Szent-Györgyi believed his mission was a

success. He was wrong. Nazi spies learned of his betrayal, and Hitler

screamed for his extradition to Germany. The Hungarian government tried

to placate Hitler by putting Szent-Györgyi under house arrest. He managed

to slip away and remained in hiding for months, staying one step ahead of

the Gestapo as they massacred fellow members of the resistance. All the

while Szent-Györgyi’s team at the university continued running their

experiments on muscles and writing up their results. From time to time

Szent-Györgyi would unexpectedly turn up at the lab in Szeged to check on

their progress and then vanish again. Staying alive was less important to Szent-Györgyi than letting the world

know about his experiments. If the Gestapo put a bullet in his head, the

world might never know what he and his colleagues had done. Szent-

Györgyi arranged for a few hundred copies of their papers to be printed up,

but he struggled to get them to friends outside of Hungary. Eventually

Szent-Györgyi found a place where he thought he could hide safely: the

Swedish legation in Budapest. But his cover was blown when a Swedish

scientist sent a wire to the legation letting Szent-Györgyi know he had

gotten the manuscript about his work on muscles. The Gestapo prepared to storm the legation, eager to catch the spy who

had eluded them now for months. When the legation learned of their

impending attack, the Swedish ambassador drove off in a limousine with

Szent-Györgyi hidden in the trunk. The war came at last to Hungary. Nazi and Soviet forces began fighting

for Budapest, destroying it in the process. Szent-Györgyi hid in bombed-out

buildings in the no-man’s-land between the two armies until the Soviet

foreign minister dispatched a squadron to find him. They whisked him and

his family to a Soviet military base south of Budapest where they lived for

three months, until the war was over and they could return home. Szent-Györgyi returned to the ruins of Budapest a national hero. And

the scientific world—which had feared he was dead—marveled at the 116-

page report published in the journal Acta Physiologica in which he and his colleagues explained their solution to one of life’s mysteries. Szent-Györgyi thought at first that the Soviet Union would help Hungary become a thriving postwar democracy. He set to work rebuilding

his homeland’s scientific establishment, and gossip spread that he might

soon be elected president. It didn’t take long for Szent-Györgyi to recognize

that Hungary had traded an old oppressor for a new one. The Soviets began

torturing dissidents, then killing them. Szent-Györgyi reached out to

contacts in the United States, hoping to land a job as a professor at an

American university. But the American government saw his friendly

dealings with his Soviet overlords as a sign he might be a spy rather than a

Nobel-winning refugee. As part of his campaign for entry, Szent-Györgyi traveled to Boston to

give a series of lectures at MIT. There he told his American audience the

story of his wartime work on muscles. He spoke of filaments and myosin,

of ATP and ions. And once he made his way through his findings, Szent-

Györgyi stopped to reflect on what he had learned. “I have come to my journey’s end and now you probably expect me to

finish my lecture in a dramatic way by telling you what life is,” he said. Biochemists had been doing this for decades now. In 1911, the Czech

scientist Friedrich Czapek crafted a succinct definition: “On the whole what

we call life is nothing else but a complex of innumerable chemical reactions

in the living substance which we call protoplasm.”

Over the course of his own career, Szent-Györgyi came up with

definitions of his own, if only to mock the idea that a simple definition

would ever be possible. “Life,” he liked to say, “is just the play of water.”

Plants and bacteria split water through photosynthesis to build

carbohydrates. And in the respiration of cells—either in the plants or in

animals like us that eat the plants—the liberation of the energy in those

carbohydrates requires putting the water molecules back together again. “What we call ‘life’ is a certain quality, the sum of certain reactions of

systems of matter, as the smile is the quality or reaction of the lips,” Szent-

Györgyi once said. When he stopped to reflect more deeply on what he and his fellow

biochemists were learning about life, Szent-Györgyi found it hard to offer a

meaningful definition. If the definition of life involved something that

sustained itself through chemical reactions, then a candle flame might be

alive. What about a star, or a civilization?

All living things, Szent-Györgyi explained to his audience at MIT, shared some hallmarks. But thinking too categorically about those

hallmarks was a one-way ticket to absurdity. “One rabbit could never

reproduce itself,” Szent-Györgyi observed. “And if life is characterized by

self-reproduction, one rabbit could not be called alive at all.”

We can find different features of life at different scales, Szent-Györgyi

said, but only depending on the features of life we cherish most. “The noun

‘life’ has no sense,” Szent-Györgyi declared, “there being no such thing.”

Soon after his visit to MIT, Szent-Györgyi won permission to move to

the United States. But his attempts to land a professorship failed, and he

wound up on Cape Cod in Massachusetts with a tenuous connection to the

Marine Biological Laboratory. Still, he made the most of life in his new

homeland. Each summer he hosted scientists at his rambling seaside house

in the village of Woods Hole. He grew famous for his parties, for his

nighttime expeditions to fish for striped bass, for leading armadas of

backstrokers around a nearby peninsula, for dressing up for parties as

Father Time or Uncle Sam or Saint George, armed with an aluminum foil

sword and shield. Szent-Györgyi also kept doing research in Woods Hole, supporting his

efforts by creating an institute funded by patrons. There he opened a new

line of research to find the fundamental difference between living and

nonliving matter. Living things were endowed with a special sort of chemistry, which

Szent-Györgyi called “subtle reactivity and flexibility.” He believed life

gained this power from the electrons that shuttle from atom to atom within

proteins. Molecules like vitamin C, he believed, could move electrons from

oxygen to other molecules without causing damage inside a cell. “It is

involved in bringing matter to life,” Szent-Györgyi declared. His intuition pointed him in the right direction. To stay alive, cells must

manage their electric charge and prevent charged compounds from pinging

around their interiors, destroying DNA and proteins. But Szent-Györgyi,

with no training in quantum physics, had at last gotten in over his head. Ever the showman, he confidently promised that he would learn how matter

is brought to life—and thereby find a cure for cancer. Not long before Szent-Györgyi died in 1986, he made an extravagant

request to the National Institutes of Health for millions of dollars. John

Edsall, a Harvard biologist and a longtime admirer of Szent-Györgyi,

reviewed his application and visited his lab to take stock of his work. Finding little in Woods Hole to inspire confidence, Edsall turned him down. “I felt, with pain, that he had lost the special touch and instinct that had

guided him aright in his brilliant pursuit of significant problems in the

past,” Edsall said. Nothing could take away Szent-Györgyi’s Nobel Prize or

his wartime discoveries about muscles. But his colleagues were sad to see

the mystery of life finally have its vengeance on him. What made it all the

sadder was that Szent-Györgyi could see what was happening as well, as

documented in an essay he wrote in 1972:

“I moved from anatomy to the study of tissues, then to electron

microscopy and chemistry, and finally to quantum mechanics. This

downward journey through the scale of dimensions has its irony, for in my

search for the secret of life, I ended up with atoms and electrons, which

have no life at all. Somewhere along the line, life has run through my

fingers.”

SCRIPTS

In the 1920s the world was still coming to terms with the weirdness of

quantum physics. People could be forgiven for thinking that physicists

had lost their minds. Up until then they had presided over a stately,

predictable cosmos that followed Newton’s clocklike laws, and now they

were announcing that the foundations of that cosmos defied common sense. Light was both a particle and a wave. An electron could be here and there at

once. Energy was a series of quantum jumps. But when Max Delbrück discovered this new world as a physics student

in Germany, he immediately felt at home. He impressed his teachers with

his ability to uncover new implications of the theory of quantum physics

and use them to explain properties of real atoms. Delbrück might have gone

on to a successful career doing just that if he hadn’t traveled to Denmark in

1931.

He went there to study under the Nobel Prize–winning physicist Niels

Bohr, only to discover that Bohr didn’t consider quantum physics the

strangest thing in the world. Life was stranger. Niels Bohr argued that physicists would never be able to see all physical

reality at once. If they wanted to study light, for example, they could study

it as a particle or as a wave but not both at the same time. Bohr believed life had a two-sided nature as well. A physicist could make sense of the gases

and liquids in a body, but physics could not explain how a body could keep

its gases and liquids stable in order to survive. “He talked about that a lot,” Delbrück later recalled of Bohr. “You could

look at a living organism either as a living organism or as a jumble of

molecules.”

Bohr helped Delbrück to see life as a frontier where a physicist might be

able to discover something radically new. “If one looks at even the simplest

kind of cell, one knows it consists of the usual elements of organic

chemistry and otherwise obeys the laws of physics,” Delbrück said. “One can analyze any number of compounds in it but one will never get a living

bacterium out of it, unless one introduces totally new and complementary

points of view.”

Life maintains an extraordinary kind of order, even though the universe

seems purpose-built to tear order apart. It’s not surprising to see a wineglass fall to the ground and shatter into a hundred shards. It is surprising to see a hundred shards assemble into a wineglass. Heat a pot of water, squirt an

assortment of food dyes into it, and you don’t expect to see them organize

into a beautiful rainbow. You see the color of mud. Life defies this

directive. Eggs hatch into swans, and seeds sprout into zinnias. Even a

single cell can maintain an astonishing molecular order. “The meanest living cell becomes a magic puzzle box,” Delbrück later

explained, “full of elaborate and changing molecules, and far outstrips all

chemical laboratories of man in the skill of organic synthesis performed

with ease, expedition, and good judgment of balance.”

After he finished studying with Bohr in Denmark, Delbrück returned to

Germany, where he worked in the Berlin laboratory of the physicist Lise

Meitner. By day he worked on questions such as how to steer the path of

gamma rays. At night he tried to learn biology pretty much from scratch. Delbrück felt as if he were the only person on Earth who had taken up

Bohr’s mission. “I mean the physicists didn’t know enough biology, and didn’t care

about it on the whole,” Delbrück said, “and the biologists, for them

anything like quantum mechanics was utterly beyond their ken.”

Eventually Delbrück found a few other people wandering these

borderlands: “a group of, as it were, exiled, internal exiled, theoretical

physicists,” he called them. Delbrück had admired the way Bohr built a

little society of physicists in Copenhagen to explore quantum physics

together, and so he followed suit in Berlin. He invited his new friends to

gather for meetings at his mother’s house. The agenda of the gatherings was

“to jointly consider some of the riddles of life.”

Whenever Buchner ground yeast, out came zymase. But when

biochemists pulled apart the cells of other species, they found other

enzymes instead. How did zymase wind up in yeast cells and not in our

own?

And why was it that when one yeast cell divided in two, the new cells

still maintained their own supply of zymase?

When Delbrück turned to

biology in 1932, biologists had only hazy guesses. They suspected that hereditary factors—what they called genes—were part of the answer. But

they couldn’t say what genes were. It was possible, in fact, that a gene was nothing but an abstraction. Heredity’s patterns might emerge from a combination of certain subtle

features inside cells. But as scientists looked more closely at cells, they

came to suspect that genes had something to do with mysterious, thread-

shaped objects known as chromosomes. They could see the twenty-three

pairs of chromosomes in each of our cells. They could watch them double

into two sets when the cell divided. They could observe sex cells end up

with just one copy of each chromosome, to be joined to the other copy at

fertilization. But no one knew what controlled these movements, or how

inherited chromosomes might influence our traits. Trying to describe this dance in 1923, the biologist Edmund Wilson

confessed that it was so intricate that he found it hard to accept as real. “We find ourselves fairly gasping for breath,” Wilson admitted. “Such results are

indeed staggering—to a certain type of mind even harder to assimilate than

those which physicists are now asking us to accept concerning the structure

of atoms.”

Some of the most important clues about chromosomes and heredity

came from a room full of flies at Columbia University. There a biologist

named Thomas Hunt Morgan led a team of scientists who examined the

chromosomes of fruit flies under microscopes. Chromosomes have bands

along their length, like cellular snakes. By tracing the molecules from one

generation to the next, they could track pairs of chromosomes as they traded

sections with each other. Morgan’s team proved that inheriting a short piece of a chromosome

could determine a trait in a fly. It could set the color of a fly’s eye to red or white. It could make a fly withstand the cold or freeze to death. These

drastic results made Morgan suspect that genes lurked in these

chromosomal segments. He couldn’t say much more. For one thing, chromosomes were a

hideous biochemical mess, a mash-up of proteins and a particularly strange

substance known as nucleic acid. But one of Morgan’s students, Hermann

Muller, gained a crucial clue about genes by blasting flies with X-rays. Every now and then he produced a mutation in a fly—a fly whose ancestors

all had red eyes suddenly developed brown ones, for example. If Muller

then bred a mutant fly, it could pass down the new trait. In other words, he had changed a gene. Muller suspected that mutations happened on a regular basis. Nature

didn’t need an X-ray machine to change genes. High temperatures or certain

kinds of chemicals might randomly alter a gene every now and then. And

from such blind changes, all of life’s variations arose. In 1926, Muller

declared that the gene was “the basis of life.”

In 1932, Muller came to Berlin to work with geneticists there, trying out

different kinds of radiation on flies to see what sort of mutations they might

create. Delbrück was awestruck when he met Muller and decided he would

bring his knowledge of quantum physics to bear on the phenomenon. After

Muller left Berlin for a job in the Soviet Union, Delbrück began

collaborating with the geneticists, carrying out what he called his “black

market research.”

Delbrück recognized that genes, whatever their exact nature, were

deeply paradoxical. They were stable enough to be passed down for

thousands of generations, only to abruptly mutate and then become stable

once more. Delbrück saw a solution to the paradox in physics. If an atom absorbs a photon of light, one of its electrons may jump to a

higher energy level, where it will remain. X-rays might have the same effect

on a gene. The fact that X-rays, with their exquisitely narrow beams, could

cause a mutation also meant that genes must be exquisitely small. “These are primarily speculations,” Delbrück and his colleagues warned

in a 1935 paper, “which rest on still shaky ground.”

If they were worried that their paper would trigger a wave of

misconceptions, they would have been relieved. It appeared in a journal that

Delbrück later said nobody read. Their ideas, he said, “got a funeral first

class.”

Soon after the publication of his gene paper, Delbrück escaped Nazi

Germany. He left behind not just his country but his science. Giving up

physics to become a full-blown biologist, Delbrück made his way to the

laboratory of Thomas Hunt Morgan, who was now working at Caltech. But

once he got there, Delbrück felt that he had made a terrible mistake. Morgan “didn’t know what to do with this theoretical physicist,” Delbrück

later recalled. And when he tried to run experiments on Morgan’s flies, he

found the work tedious and the results inscrutable. In a stroke of good fortune, Delbrück ran into a biochemist named Emory Ellis one day. He was intrigued to discover that Ellis studied phages

instead of animals. The experiments Ellis ran were simple yet powerful. He

added bacteria-killing viruses to petri dishes, where he could see ghostly

holes form where the phages killed millions of their hosts. He needed only

transfer a bit of the agar from a hole into an uninfected dish to unleash a

new outbreak. The phages appeared to have genes of their own, but they

reproduced simply by making copies of themselves. There were no messy

blendings of chromosomes to struggle through. Delbrück fondly called viruses the “atoms in biology.” He began

running experiments of his own, which soon blossomed into work that

would later earn him the Nobel Prize. Viruses mutated like flies, it turned

out. Some mutations took away their power to infect a strain of bacteria;

others let them attack a new one. By counting the ghostly holes in his petri

dishes, Delbrück could make precise measurements of how often mutations

arose. He was happy in his new incarnation, even if few people at the time

recognized the new kind of science he was building. In 1945, a few years into his new career, a friend handed Delbrück a

slender new book that was all the rage. The title was What Is Life?

, and it left Delbrück gobsmacked. The author was Erwin Schrödinger, a physicist

whom Delbrück knew back in his old quantum physics days in Germany. And to answer the question that formed the book’s title, Schrödinger had

resurrected the paper of Delbrück’s that had gotten a funeral first class. —

Erwin Schrödinger was born in Vienna in 1887 and went on to become a

physics professor in Zurich, where he developed an equation that would

bear his name. The Schrödinger equation predicts how a system—be it a

photon or an atom or a group of molecules—changes through time and

space in a wavelike fashion. But Schrödinger’s name also became affixed to

the most famous thought experiment involving a cat. Schrödinger recognized the profound weirdness that his work and that

of other quantum physicists implied. He offered a way to picture that

weirdness: Think of a cat in a box. The box is rigged up with a device that

can flood it with poison and kill the cat. Now imagine that the device can

activate in response to a radioactive atom spontaneously decaying. According to the leading interpretations of quantum physics in the 1930s, the atom could exist in a decayed state and an undecayed one at the

same time. Only an observation would force its wavelike nature to collapse

into one state or the other. If quantum physics was correct, Schrödinger

argued, the cat had to be at once dead and alive. Only when an observer

looked in the box did the cat receive just one fate. To Schrödinger, life and death were more than just fodder for thought

experiments. His father, a botanist, had introduced him as a boy to the

complexities of plants. As a university student, he devoured biology books. Later, when Muller created mutations with X-rays, Schrödinger became

intrigued by the nature of genes. He developed a layman’s curiosity about

“the fundamental difference between living and dead matter,” as he once

put it. When a friend passed Delbrück’s 1935 paper about genes to

Schrödinger, it became the nucleus around which his own thoughts grew. At

the time, Delbrück and Schrödinger were professional colleagues who

traveled in Europe’s rarefied circles of quantum physicists. But Schrödinger

never once spoke or wrote to Delbrück about the inspiration he provided. Like Delbrück, Schrödinger sought refuge from the Nazis. Instead of

California, he ended up in Ireland, where the government built him a

research center to run. One of the requirements of the job was a series of

public lectures at Trinity College. Schrödinger decided not to talk about his

equations, since he would not be speaking to an audience of quantum

physicists. Instead, he would deliver a course of lectures on his private

thoughts about the nature of life. A vast crowd descended on the lecture hall in February 1943.

The

organizers had to turn thousands away. When Schrödinger rose to speak, he

warned the packed hall that he spoke not as an expert but as “a naive

physicist.” And he had a naive question to ask—the same one that Georg

Stahl had asked nearly 250 years earlier: What is life?

Much of the biology that Schrödinger described to his Dublin audience

was not new. And much of what was new in his lectures would eventually

prove to be wrong. And yet he managed to frame much of modern science’s

approach to what it means to be alive. His ideas guided a generation of

scientists who put biology on a molecular footing. And, just as importantly,

he made clear to physicists just how badly their theories failed when they

crossed into life’s territory. Eighty years later, they’re still struggling to

meet his challenge. “What an organism feeds upon is negative entropy,” Schrödinger declared. Entropy is essentially a measurement of disorder. The jostling of

atoms and molecules naturally increases entropy over time. For life to

maintain its order, it needs to draw in energy in a way that counteracts the

rise of entropy. And it extends its order into the future by passing on its

genes to its descendants. To explain heredity, Schrödinger relied on Delbrück’s work a decade

earlier on chromosomes. Schrödinger envisioned them as stable crystals

that contained genes, and that could be replicated from one generation to

the next. Schrödinger had only the vaguest idea how this arrangement would

work. The crystals would have to be what he called “aperiodic.” Ordinary

crystals repeat themselves in periodic patterns: ice is a latticework of water

molecules, table salt a series of cages made of sodium and chloride. No

matter where you move around inside these crystals, the pattern is identical. But chromosomes, Schrödinger speculated, have arrangements of atoms

with variations that do not merely repeat—like a string of letters chosen

from an alphabet. Those variations could serve as a “code-script,” as

Schrödinger called it, that could produce an entire organism. “The difference in structure,” Schrödinger speculated, “is of the same

kind as that between an ordinary wallpaper in which the same pattern is

repeated again and again in regular periodicity and a masterpiece of

embroidery, say a Raphael tapestry, which shows no dull repetition, but an

elaborate, coherent, meaningful design traced by the great master.”

—

Despite his musings on entropy and code-scripts, Schrödinger’s lectures

proved immensely popular—so popular, in fact, that he had to deliver them

in full a second time. As reports of his sensational ideas spread, a publisher

invited him to write them up as a short book. What Is Life?

became a hit the following year. The book didn’t just fascinate the public; it also steered the

course of science. Within nine years of its publication, two readers of What Is Life?

would discover that Schrödinger’s aperiodic crystal was not just an idea but a real molecule: the DNA nestled in each of our cells. One of those readers was an English physicist named Francis Crick. Born in 1916 to middle-class parents in suburban England, Crick lost his

faith by his early teens, turning instead to science to understand the world. The mysteries that science had yet to explain, he later wrote, “serve as easy refuge for religious superstition.” Crick chose to study physics at University

College London but did not impress his teachers. In graduate school he was

assigned the task of measuring the viscosity of water, which he called “the

dullest problem imaginable.”

Crick spent World War II working at Britain’s Admiralty Research

Laboratory, designing underwater mines to sink Nazi ships. When peace

came, Crick didn’t want to go back to the viscosity of water, nor did he

want to build more war machines. He craved something profound. One day

he happened to read about the recent discovery of antibiotics, and the idea

that these molecules could save people’s lives left him electrified. When

Crick told his friends about them, he was struck by the enthusiasm in his

voice. He wondered if, at age thirty, he could make a radical shift to become

a biologist. It was around that time that he read What Is Life?

Schrödinger gave

Crick an infusion of confidence that the shift to biology might not be so

radical after all. Life was just a part of the world that physics had yet to

explain very well. Crick decided he wouldn’t limit his focus to a single

antibiotic or some other organic molecule. He was attracted instead to what

he called “the borderline between the living and the nonliving.”

Crick’s hostility to religious superstition helped push him in that

direction, too. His boyish contempt for the church expanded in adulthood. He despised intellectuals who claimed that life would always defy a

reduction to simple mechanisms. To Crick, they were just leftover vitalists. Even after World War II, the French philosopher Henri Bergson remained

trendy, while the theologian and paleontologist Pierre Teilhard de Chardin

rose to fame for claiming that molecules were infused with purpose, giving

rise first to life and ultimately to consciousness. In England, the writer C. S. Lewis cast scorn on modern science’s bleak vision of the world, hoping it

would be replaced by an investigation of nature that did not destroy life’s

glories. “When it explained it would not explain away,” Lewis said in 1943.

“When it spoke of the parts it would remember the whole.”

For Crick, the only way to understand the whole was to start with the

parts. He landed a spot at the Cavendish Laboratory, the same institution

where John Butler Burke had been fooled by radiobes some four decades

earlier. In the early 1900s, Burke’s obsession with life made him stand out

as an oddity at the Cavendish. All of his colleagues were content to study

electrons, radioactivity, and other lifeless things. By the 1940s, however, the Cavendish physicists were using their expertise to make sense of biological

molecules. To figure out the structure of life’s compounds, they coaxed the

molecules to assemble into crystals. The scientists then blasted them with

X-rays, which glanced off the crystals and crashed into photographic plates. The ghostly spots and curves that formed in the photographs hinted at the

repeating structure of the crystals. The Cavendish researchers could then

use mathematical equations to work their way back from the marks in the

photographs to the shapes of the molecules. They started simply, with

vitamins and other small molecules, and moved on to the daunting

challenge of proteins, which were huge snarls of amino acid chains. Working out the structures of proteins would help scientists understand

how they behaved and what jobs they served. Biochemists were already

somewhat familiar with enzymes, which were proteins that sped up

chemical reactions. Other proteins seemed to serve as signals, and others

locked together like bricks for the body’s edifice. In the 1940s many

biochemists suspected that genes were made of proteins nestled in the

chromosomes. After Crick arrived, he quickly impressed the scientists at the Cavendish

with his preternatural ability to picture the twists and folds of proteins in his mind and see what their X-ray portrait would look like. But not long after

he started on this work, Crick became distracted. A series of experiments in

the late 1940s and early 1950s showed that proteins were not, after all, the

carriers of hereditary information. DNA, a nucleic acid also found in the

tangle of chromosomes, proved essential. At the time no one knew much about DNA’s structure. Crick mused

about what sort of shapes DNA would need to act as Schrödinger’s

aperiodic crystal. His bosses at the Cavendish discouraged him from his

daydreaming, but in 1951 he met a young American visiting Cambridge

who also loved What Is Life?

James Watson was happy to talk about DNA

with Crick for hours on end. Their conversations could only take them so far, though. If DNA was

the code-script of life, they wanted to know how it stored genes. Crick and

Watson knew that a team of scientists in London was trying to create the

first good pictures of DNA crystals. Led by Rosalind Franklin, they worked

carefully and methodically to prepare the molecules, bombed them with X-rays from different angles, and inspected the images the beams produced. Franklin had no tolerance for Crick and Watson’s impatience, once even

ejecting Watson from her lab so she could get back to her work. When they

tried building a model based on some preliminary images, she traveled to

Cambridge and explained to them that it was all wrong. Later, unbeknownst

to her, Crick and Watson got to see some of her unpublished work. Those

clues were finally enough for them to come up with a new structure that

they believed could fit what scientists knew about DNA’s chemistry and

even explain how DNA could serve as the stuff of genes. Compared to proteins, with their maddening switchback curves and

intertwining clumps, DNA was graceful in its simplicity. Crick and Watson

recognized that DNA was a pair of twisting backbones with rung-like

connections linking them together. Each rung was composed of a pair of

compounds, called bases. At each rung in a piece of DNA, a base can take

one of four forms. Each gene, stretching for thousands of base pairs, is a

unique sequence of these bases. “Now we believe that the D. N.A. is a code,” Crick wrote his twelve-

year-old son Michael in 1953.

“That is, the order of the bases (the letters)

makes one gene different from another gene (just as one page of print is

different from another).”

Crick and Watson’s model also showed how living things could

maintain the order of their genes. A cell could make a copy of its DNA by

pulling its two backbones apart, each with a set of bases still dangling from

it. Each kind of base can only bond with one other kind of base, making it

easy for two accurate copies to take shape. On the day that Crick and Watson realized they had worked out the

structure of DNA, they marched to a nearby pub to celebrate their

breakthrough. Crick shouted that they had “found the secret of life.” It was

a cry of victory in his war against the vitalists. Along with Franklin and

their other colleagues, they wrote up their results, and the batch of papers

appeared in Nature on April 25, 1953, laying out the double-helix model and the evidence for it. When the New York Times interviewed Crick, he

said that, for now, the idea “simply smells right.”

In August Crick sent reprints to Schrödinger in Dublin, with a short

note: “You will see that it looks as though your term ‘aperiodic crystal’ is

going to be a very apt one.”

—

DNA did not immediately become the icon of life that it is today. When

Crick and Watson shared the Nobel Prize in 1962, it gained some fame. (Franklin could not be considered for the award because she died of cancer

in 1958.) But the molecule only penetrated pop culture when Watson

published a best-selling account of the discovery in 1968, The Double

Helix. In its pages he reprinted a photograph taken of himself and Crick shortly after their paper came out in Nature. The two scientists posed in their Cavendish lab next to a man-sized

model of the double helix they had built from rods and plates and screws. Watson looked on as Crick pointed to a twist in the backbones with a slide

rule. That photograph came to represent the turning point in our modern

conception of life. One historian ranked it as one of the most important

photographs of twentieth-century science, along with Einstein’s portrait and

the image of a mushroom cloud. But icons inevitably distort history. Rosalind Franklin is missing from

the photograph, for one thing. And the picture also does a disservice to

Crick’s memory. It traps him in the frame with the double helix, as if that

were his sole accomplishment. But Crick went on to do work that proved to

be just as profound: he joined forces with an international network of

scientists to figure out the rules by which cells translate the information in

genes into the structure of proteins. They named the rules the genetic code. No one photographed Crick pointing a slide rule at the code. Yet its

discovery was arguably just as important as that of the double helix. Genes and proteins, Crick recognized, are spelled out in different

alphabets. DNA is made out of four different bases. Proteins, on the other

hand, are assembled from about twenty different amino acids. Once our

cells make an RNA copy of a gene, they feed it into a protein-making

factory called a ribosome. Crick and his colleagues figured out that the

ribosome reads three bases in a row in order to determine which amino acid

to add to a protein. If a mutation changes one of those bases, it may result in cells building a protein with a different amino acid in that position. For Crick, the genetic code didn’t just smell right; it represented the

triumph of his scientific approach to life. “It is, in a sense, the key to

molecular biology,” he declared. “It will be difficult, after this, for doubters

not to accept the fundamental assumptions of molecular biology which we have been trying to prove for so many years.”

But Crick could not stay gracious in victory. Much to his dismay, the

discovery of the genetic code failed to make the vitalists see the error of

their ways. All around him, Crick saw vitalists on the rise. One day a

Cambridge clergyman informed him that DNA might be evidence for

extrasensory perception. Crick read with horror of a Princeton physicist

named Walter Elsasser, famous for working out how Earth generates a

magnetic field, who decided to try his hand at biology. In 1958, Elsasser

claimed to discover “biotonic phenomena” that “cannot be explained in

terms of mechanistic functioning.” Another scientist wrote to the journal

Nature to claim that what distinguished the living from the nonliving was a

“biological urge” that could never be explained with atoms and molecules. Crick got so exasperated that he began giving lectures around

Cambridge warning of the threat vitalism posed to civilization. Soon

afterward the University of Washington asked him to give a series of

lectures in Seattle about the impact of science and philosophy on “man’s

perception of a rational universe.” Crick used the opportunity to deliver a

high-profile attack on his enemies. He entitled his talks, “Is Vitalism

Dead?”

In Seattle, Crick regaled his audience with the dizzying advances he had

been a part of: making sense of heredity, the genetic code, the workings of

cells. In spite of all that evidence, he ruefully observed, vitalism still

lingered. Crick blamed its endurance on our weakness for superstitions. The

only solution Crick could think of was to take over the schools. To

counteract the illusions fostered by the arts, all students should be required

to take a heavy load of science classes. The old literary culture was “clearly

dying,” Crick declared, and would be replaced by a new culture based on

“science in general, and natural selection in particular.”

Crick closed his Seattle lectures with a harsh warning. “And so to those

of you who may be vitalists I would make this prophecy: what everyone

believed yesterday, and you believe today, only cranks will believe

tomorrow.”

As adept as Crick might be as a scientist, he turned out to be a clumsy

polemicist. When his lectures were published in 1966 as the book Of

Molecules and Men, one reviewer called it “a frightening mixture of naïveté and bigotry.”

It was so bad that many of his toughest critics were his fellow scientists. Vitalism had spiraled into scientific oblivion by the 1930s. The

embryologist Conrad Waddington wondered if Crick was just “flogging a

dead horse.” Sir John Eccles, a leading neuroscientist, praised the parts of

his lectures where Crick described the new science of molecular biology. But he dismissed Crick’s science-centered vision of society as a “dogmatic

religious assertion.” Eccles also took Crick to task for crudely dismissing

anything that lay beyond atoms and molecules as vitalism. “In biology,” Eccles argued, “there are new emergent properties not

predictable from chemistry, just as chemistry is not predictable from

physics.”

Crick would never vanquish his vitalists. Part of his problem was that he

used the term as a broad-brush insult against anyone who didn’t see things

his way: a motley crew of novelists, fans of extrasensory perception, and

even some full-time scientists. But another part of the problem lay in his

own work on DNA and the genetic code. As profoundly important as it was,

it still left many big questions unanswered about what set the living apart

from the nonliving. In 2000, four years before Crick’s death, a trio of

leading biologists published a review they called “Molecular Vitalism.”

They argued that a simple, machine-based view of life with DNA serving as

instructions was not powerful enough to explain some of the most important

features of the living world: how cells remain stable in a world of flux, for

example, or how embryos reliably develop into complex anatomies. Looking over the gene-centered state of biology at the turn of the

millennium, they doubted that it would “convince a nineteenth century

vitalist that the nature of life was now understood.”

As Crick got older, he indulged in reflections on life that a young

scientist would rarely dare. He mused about aliens. Perhaps they were like

us. Perhaps they even seeded Earth with life in the first place. Or perhaps

aliens were chemically different from life as we know it. Perhaps they lived

on a gas planet, or inside a sun. No matter how strange alien life might turn

out to be, though, Crick suspected that it would probably turn out to be a lot

like life on Earth. There existed something Crick called “the general nature

of life.”

Crick sketched out that general nature in 1981.

“The system must be

able to replicate directly both its own instructions and indirectly any

machinery needed to execute them,” he wrote in his book Life Itself. “The

replication of the genetic material must be fairly exact, but mutations—

mistakes which can be faithfully copied—must occur at a rather low rate. A

gene and its ‘product’ must be kept relatively close together. The system

will be an open one and must have a supply of raw material, and, in some

way or another, a supply of free energy.”

Only fifty years had passed since Max Delbrück had contemplated the

riddles of life in his furtive Berlin get-togethers. Now his intellectual

grandchildren thought about life largely in terms of genes—the ability that

genes had to encode the molecules necessary to copy themselves and the

power they had to drive evolution. Crick’s work had a profound impact on

how other scientists defined life. In 1992, for example, his influence could

be felt at a meeting that NASA organized to come up with ideas for how to

study the possibility of life on other worlds. One of the scientists at the meeting, Gerald Joyce, later described the

meeting to me. “We’re talking about the search for life and the origin of

life,” he recalled, “and someone said, ‘Do you think we should actually

define what it is we’re talking about?’”

The scientists started throwing out ideas, shooting some down and

merging others together. The conversation started at the official meeting

and lasted through dinner. Like Crick, the NASA group saw metabolism as

essential—but mostly because it provided the material and energy to make

new copies of genes. Life couldn’t copy those genes perfectly, however. Only if it made mistakes could evolution emerge and allow life to adapt and

take on new forms, which could then be passed down through the

generations. “History starts to be written in molecules,” Joyce told me later. “That’s why biology is different than chemistry.”

By the end of dinner the scientists had distilled their ideas down to

eleven words:

“Life is a self-sustained chemical system capable of undergoing

Darwinian evolution.”

Crisp and concise, short enough to memorize, their wording took hold. People started referring to it simply as “the NASA definition of life,” as if

the space agency had given it an official stamp of approval. At scientific

conferences, speakers flashed those eleven words in their slide decks. They

made their way into textbooks. Reading the definition, students could be

forgiven for assuming that the whole matter was settled. Far from it. Like its predecessors, the NASA definition of life did not come with a list of the things that qualified as life and the ones that didn’t. And when scientists turned to the real things with which we share the

world, they couldn’t agree on what belonged. PART FOUR

RETURN TO THE BORDERLAND

HALF LIFE

“Mr. Burke is not prepared to affirm with positiveness that these

organisms are quite alive. They may be half alive.”

In the spring of 2020, coyotes strolled down the daytime streets of San

Francisco. Pods of pink dolphins cavorted in the waters around Hong

Kong. A herd of mountain goats took over a town in Wales, and jackals

wandered a city park in Tel Aviv. In Venice, cormorants plunged into the

suddenly clear canals to chase after fish, while Canada geese escorted their

goslings down the middle of Las Vegas Boulevard, passing shuttered-up

shops selling Montblanc pens and Fendi handbags. A strange expansion of life was taking place, thanks to the retreat of our

species. Billions of people went into lockdown for months, a movement that

scientists dubbed the anthropause. For the lucky ones, the greatest challenge

of this retreat was boredom. For the unlucky, unemployment, hunger, and

other disasters awaited. For the most unlucky of all, there was sickness. Their bodies flared with fever and shook with raw coughs. Some of the sick

shivered at night so violently they chipped their teeth. Four out of five

sickened people rode out the disease at home. One out of five ended up in

the hospital. The lungs of some became wastelands of pus and

inflammation. Hundreds of thousands died. In New York City, backhoes

dug trenches on Hart Island to bury the overflow of coffins. The new pneumonia first came to light in late 2019 in the Chinese city

of Wuhan. Within a few weeks Chinese researchers had isolated the

microscopic thread that tied all the cases together: a virus, which virologists named SARS-CoV-2.

They analyzed its genes and reconstructed parts of its

history recorded in mutations. SARS-CoV-2 arose from bats, as have a number of other dangerous viruses in recent decades. And like those

viruses, SARS-CoV-2 evolved adaptations that let it thrive inside humans

instead. A cough or even a song could loft a spray of virus-laden droplets into

the air, ready to be inhaled by someone riding the same bus, sharing the

same breakfast table, praying in the same church. Once inside a new nose,

the virus could infect a new host. The virus was studded with proteins that

could latch onto a protein on the surface of certain cells in the airway. Its

membrane fused with the cells, and it dumped its genes inside. They were

spelled out according to the same genetic code our cells use to build

proteins. As a result, the cells translated the virus’s genes into proteins as

they would their own. Now the cells filled themselves with viral proteins

that shut down their ordinary work and forced them to make new viruses. They made new copies of the virus’s genes, which were then cradled inside

new protein-studded membranes. The new viruses gathered into bubbles

that migrated to the border of the infected cells and spilled open, delivering

millions of new viruses into the airway. In most people the immune system got wind of the invasion while the

viruses were still establishing themselves in their noses. They mounted a

defense, learning how to deliver a precise attack with antibodies that could

stop the viruses from infecting new cells. But the viruses had their own

cunning evasions encoded in their genes. They could silence the alarm

systems inside the cells they invaded. In some people, they proliferated

beyond control, working their way down into the lungs. The immune

system lost its surgical precision, resorting to brute-force attacks, spewing

toxic compounds in all directions. The virus’s victims slowly drowned in an

ocean of their own making. If SARS-CoV-2 always laid its victims so low, it might have been easier

to battle. When people became ill, they could be put into quarantined

hospital rooms. But SARS-CoV-2 lurked quietly in its hosts for days before

creating its first symptoms. People went about their lives unaware of the

multiplying viruses inside them or the clouds of infection they exhaled. They lingered over lunch at restaurants, they worked at call centers, they

leaned on the railings of cruise ships plowing the Pacific. After infecting

people around them, some of the virus’s hosts finally developed symptoms. Others never did. The unwittingly infected exported Covid-19 out of Wuhan. Some

traveled across China to celebrate the Lunar New Year with their families. Planes delivered infected passengers to Europe, and from there to other

continents. The virus mutated as it multiplied, and new lineages emerged,

marked by different gene signatures. Scientists reconstructed their journeys

from their mutations as they moved between countries and among cities. Some nations managed the pandemic well, while others—due to the limits

of poverty or the arrogance of wealth—suffered its full ravages. It is hard to think of something that has laid such a heavy blow on

humanity in so little time. It is hard to think of something that has done a

better job at reproducing, using our species to make quadrillions of copies

of itself in a matter of months. And yet, for all that, there are many scientists who would say that

SARS-CoV-2 is not alive. It does not deserve entry into the exclusive club

called Life. For thousands of years, people knew of viruses only through the death

and destruction they caused. Doctors gave their diseases names, like

smallpox, rabies, and influenza. When Antonie van Leeuwenhoek peered at

drops of water with his microscope in the 1600s, he discovered bacteria and

other minuscule wonders, but he could not see the even tinier viruses. Two

centuries later, when scientists finally discovered viruses, they did so

without actually seeing them. In the late 1800s a handful of scientists in Europe studied a disease of

tobacco plants called tobacco mosaic disease. It stunted the plants and

covered their leaves with spots. Mashing up a sick leaf in water, the

scientists injected the fluid into healthy plants and watched them get sick,

too. But when they searched for the pathogen in the fluid, they couldn’t find

bacteria or fungi. It had to be something fundamentally different. A Dutch scientist named Martinus Beijerinck poured mashed-up leaves

from a sick tobacco plant through a porcelain filter. The pores were too

small for any bacteria to sneak through. He was left with a clear liquid. But

that was enough, when injected into a new plant, to pass on the disease. Beijerinck concluded that some invisible agent multiplied in tobacco plants. In 1898 he dubbed it a virus, using an ancient word for toxin. Virologists went on to find the viruses that caused rabies, influenza,

polio, and many other dread diseases. Some viruses infected certain species

of animals, while others infected only plants. Biologists discovered phages,

the viruses that only infect bacteria. And it was a phage that became the first virus ever seen by humans. In the 1930s engineers built electron microscopes powerful enough to

bring the viral world into focus. The device revealed phages sitting atop a

bacterial host. They looked like crystals set on leglike wires. Other viruses

turned out to resemble serpents; others, soccer balls. SARS-CoV-2 belongs

to the coronaviruses, named for the halo of proteins that adorn their surface. They reminded virologists of a solar eclipse, when the sun’s corona of

streaming gas becomes visible. Biochemists broke down viruses into their molecular ingredients. They

started with Beijerinck’s tobacco mosaic virus, finding that it contained

proteins built from the same set of amino acids as our own. But among

those proteins biochemists could not find any of the enzymes that our own

cells use for metabolism. Viruses do not eat or grow. Old viruses do not

beget new ones, at least not directly. A virus is just a reorganized package

of its host’s own atoms. For biologists searching for a definition of life, viruses became a

headache. They couldn’t dismiss viruses altogether, because they clearly

had some of life’s hallmarks. And yet they lacked others. It would have

been convenient if viruses had turned out to be mirages like Bathybius or radiobes. But the more that scientists studied viruses, the more real they

proved to be—and the more perplexing their nature. “When one is asked whether a filter-passing virus is living or dead,” the

British virologist Norman Pirie wrote in 1937, “the only sensible answer is:

‘I don’t know; we know a number of things it will do and a number of

things it won’t and if some commission will define the word “living” I will

try to see how the virus fits into the definition.’”

Pirie and his fellow virologists went on to discover crucial features of

viruses. Inside their protein shells and oily membranes, they contain

bundles of genes, along with some proteins to hold them together. But they

contain none of their own ATP to fuel reactions. On the outside, viruses

have a furry coat of sugar-frosted proteins. The proteins typically fit

precisely onto proteins on the surface of cells. This latching is the first step of a virus infection, and it has to be a precise fit, like a key in a lock. That’s one reason why viruses are so selective about the species they infect and

why they can invade some types of cells but not others. Once a virus enters a cell, its shell or membrane breaks apart and it delivers its payload of genes. If the copying of genes is the crux of life, then viruses should certainly qualify as living. Some viruses have genes encoded

in DNA, using the same four-letter alphabet that spells out our own

heredity. An infected cell will read that viral DNA and make RNA

molecules, which it can then turn into proteins for the virus. But Pirie and other virologists discovered that many viruses have

streamlined this transformation. In the 1930s, Pirie found hints that the

genes of tobacco mosaic viruses were made not of DNA but of RNA. Later

research revealed that many other viruses use RNA for their genes,

including SARS-CoV-2.

When RNA viruses invade a cell, their genes get

translated straight to proteins. It is an exquisitely efficient way for viruses to make us sick for their own benefit. And yet only viruses have discovered

this particular kind of biochemistry. Whether viruses use DNA or RNA to encode their genes, they can get

by with astonishingly few. We carry 20,000 protein-coding genes. SARS-

CoV-2 was able to hurl the global economy into an abyss with only twenty-

nine. Each time SARS-CoV-2 invades a cell in someone’s airway, the

millions of new viruses that come out bear those twenty-nine genes, usually

in identical form. But some bear mistakes. Viruses mutate like more familiar forms of life. In fact, they mutate at a

far higher rate than humans, plants, or even bacteria. Our cells contain a

molecular staff of proofreaders checking new sequences of DNA for errors

and sending most mistakes back for fixing. Most viruses can’t check for

errors. SARS-CoV-2 and other coronaviruses are peculiar because they

carry a gene for a primitive proofreading protein. Even though they don’t

mutate as fast as most other viruses, they still build up mutations thousands

of times faster than we do. Sometimes those new mutations give a virus a competitive edge over

other viruses. They may speed up the time it takes to replicate. They may

enable a mutant virus to become invisible on the immune system’s radar. These viruses will be favored by natural selection. The modern study of viruses has revealed, in other words, that viruses

share yet another hallmark of life: evolution. They can evolve resistance to

antiviral drugs. They can evolve to adapt to a new host species. Evolution

figured prominently in the NASA definition of life, and yet Gerald Joyce,

one of its architects, didn’t think the evolution of viruses was enough to

make up for the fact that they are not a self-sustained chemical system. Viruses get their sustenance inside the chemical system of a cell, and only

inside a cell can they evolve. “According to the working definition, a virus doesn’t make the cut,”

Joyce decreed in an interview with Astrobiology Magazine. Viruses have had their defenders, though. Starting in 2011, the French

scientist Patrick Forterre made a series of arguments in favor of viruses as

being alive. At least, they’re alive some of the time, he said. To Forterre, the cell is the fundamental feature of life. And when a virus invades it, the cell

effectively becomes an extension of the virus’s genes. Forterre likes to call

it a virocell. “Whereas the dream of a normal cell is to produce two cells,

the dream of a virocell is to produce a hundred or more new virocells,” he

wrote in 2016.

Forterre did not win over many of his fellow virologists. Purificación

López-García and David Moreira called his argument “alien to logic.”

Others dismissed the virocell as mere poetic license. Viruses can no more

live than they can dream. And when the International Committee on

Taxonomy of Viruses established a modern system of classification, they

flatly declared that “viruses are not living organisms.”

“They lead only a kind of borrowed life,” one committee member

explained. It’s strange that people can push viruses out of the house of life and

leave them hanging around the doorstep. It’s awfully crowded out there. There are more viruses in a liter of seawater than there are human beings on

the entire planet. The same is true for a spoonful of dirt. If we could count

up all the viruses on Earth, they would outnumber every form of cell-based

life combined, perhaps by a factor of ten. The diversity of viruses is also colossal. Some virologists have

estimated that there may be trillions of species of viruses on the planet. When virologists find new viruses, they’re often from a major lineage no

one knew about before. Ornithologists get justifiably excited when they

discover a new species of bird. Imagine what it would be like to discover

birds for the first time. That’s what it’s like to be a virologist. Can we exile all this biological diversity from life?

To exile viruses also

means we have to discount how intimately woven they are into life’s

ecological web. They rival predators in their slaughter, whether they are

killing off a coral reef or wiping out Pseudomonas in a lung. Viruses also

have peaceful relationships with many of their hosts. Our healthy bodies are home to trillions of viruses collectively known as a virome. Most of them

infect the trillions of bacteria, fungi, and other single-celled members of our microbiome. Some studies suggest that the human virome keeps our

microbiome in balance, contributing to our own well-being. The earth has a virome of its own, one that acts as a geochemical force. Each time you blink an eye, 10 billion trillion phages in the ocean infect

marine bacteria. Many of them kill their microbial hosts, dumping about

three gigatons of organic carbon into the water every year, stimulating the

growth of new life. Some phages are more merciful: they slip inside their

hosts and let them go on with their lives for a while. Some even bring genes

with them that help their hosts thrive. There are phages that float from host

to host in the ocean with genes for photosynthesis. The microbes they infect

do better at harnessing sunlight. The oxygen we breathe is brought to us in

part by these viruses. These phages came by their light-harvesting genes by theft. When their

ancestors infected other photosynthetic microbes, they accidentally folded

their host’s genes into their own as they replicated. But viruses can also

donate new genes to the genomes of their hosts. Bacteria can gain resistance

to antibiotics through a viral infection, for example. Our own genome

contains tens of thousands of viral fragments, adding up to 8 percent of our

DNA. Some of those fragments have evolved into genes and switches for

turning genes on and off. If viruses are lifeless, then lifelessness is stitched into our being. Viruses are not the only things that straddle life’s edge. Think of the red

blood cells that course through your veins. You’d be dead without them,

starved of the oxygen they ferry from the lungs throughout the body. Red

blood cells (also known as erythrocytes) have membranes, just as bacteria

and slime molds do. Inside, they are full of sophisticated enzymes and other

proteins. Red blood cells even get old and die. “The life span of

erythrocytes amounts to some 100–120 days,” a team of scientists reported

in a 2008 review. If something has a life span, surely it has a life. And yet, by many definitions, red blood cells aren’t alive, either. Unlike

other cells in our bodies, they have a peculiar path of development. They

arise from precursor cells in our bone marrow and then get released into the

bloodstream. They take with them the hemoglobin and other proteins they

will need to carry oxygen. But they don’t take any DNA. As a result, a

mature red blood cell lacks the genetic cookbook to make its own proteins and divide into new cells. Red blood cells are different from other cells in another important

respect: they cannot make their own fuel, because they lack the factories for

making it. Other cells contain dozens of free-floating bags of enzymes

called mitochondria. And it turns out that mitochondria, too, are a form of

half life. Each mitochondrion carries thirty-seven of its own genes, along

with ribosomes it uses to make proteins from them. And from time to time a

mitochondrion will multiply the way bacteria do, pinching itself off down

the middle and becoming two new mitochondria, each with its own circle of

DNA. The solution to the puzzle of mitochondria lies deep in our history. Two

billion years ago the ancestors of our mitochondria were free-living

bacteria. They were engulfed by a larger cell, and the two species formed a

partnership. In exchange for ATP the mitochondria got shelter. No longer

required to survive on their own, mitochondria lost most of their genes—

but not all of them. And they have not lost the ability to divide as their

bacterial ancestors did. Run down a typical list of requirements for life, and mitochondria have

most of them—more than red blood cells, in fact. Yet they cannot exist

outside their host cells. They cannot find their own food. They cannot build

their genes or proteins on their own. They were certainly once living things,

but now it’s hard to say what they’ve become. Calling them dead certainly

doesn’t seem right, since our own lives depend on them. Still, mitochondria and red blood cells are so small that perhaps we can

ignore them. Out of sight, out of mind. But some of life’s paradoxes are not

invisible to the naked eye. In 1948, Albert Szent-Györgyi slyly observed

that if life were characterized by self-reproduction, then a single rabbit was

not alive. After all, a single rabbit cannot make more rabbits. Many

scientists have ignored Szent-Györgyi’s warning, judging from the fact that

they’ve made self-reproduction a requirement for life. We can be charitable

and assume the people who made these definitions think Szent-Györgyi was

merely playing word games. It doesn’t matter if one rabbit can’t reproduce

because it belongs to a species that can. But nature, it turns out, causes more trouble than even Szent-Györgyi

could. In the 1920s a husband-and-wife team of naturalists named Carl and Laura Hubbs traveled around Mexico and Texas catching fish. They got to

know the animals in intimate detail, down to their stripes, spots, and rays. This loving, encyclopedic attention revealed to them that many species of

freshwater fish evolved through interbreeding. Two species interbred, and

their hybrid offspring could now only mate among themselves. But one of

these hybrid species, a relative of guppies called Poecilia formosa, proved remarkably different from the others. “Not a single male has been found, among about two thousand

specimens examined from Tamaulipas and Texas,” the Hubbses reported. They nicknamed the fish Amazon mollies—not for the river but for the

female warriors of ancient tales. Amazon mollies evolved about 280,000 years ago from the

interbreeding of two species of fish: the Atlantic molly and the sailfin

molly. Once the new species evolved, it never left its parents. Today

Amazon mollies are always found alongside either Atlantic mollies or

sailfin mollies. It is as if the survival of the species depended on their

company. To make sense of these patterns, the Hubbses brought all three species

back to their laboratory at the University of Michigan. They dropped the

fish into tanks and let nature take its course. The female Amazon mollies

mated with both Atlantic and sailfin males. They laid eggs, out of which

Amazon mollies always hatched. And, true to their name, all those Amazon

offspring were daughters. “Although the broods have been large and many,” the Hubbses

observed, “not a single male has appeared among them.”

In the mid-1700s, Abraham Trembley observed that female aphids could

reproduce without males, producing a line of daughters and granddaughters. In later generations others found more invertebrates that could perform this

kind of virgin birth, known as parthenogenesis. Their eggs spontaneously

developed into embryos without any need for a male’s sperm. And when the

Hubbses investigated Amazon mollies some two centuries later, they

discovered that vertebrates can be parthenogenetic, too. Unlike aphids, however, Amazon mollies need to mate with males. As

later experiments revealed, the sperm from males reach an Amazon molly’s

eggs and fuse with them, injecting their genes. But the paternal and

maternal genes don’t organize themselves into a new genome. Instead,

enzymes in the eggs shred the would-be father’s DNA. All that an Amazon molly needs from a male is a trigger that starts her eggs turning into

embryos. And that’s why the Amazon mollies make trouble for those who would

draw sharp lines around life. One Amazon molly cannot reproduce. But two

Amazon mollies cannot, either. In fact, the entire species of Amazon

mollies is unable to create offspring on its own. The fish are sexual

parasites, depending on other species for their reproduction. If life must be

defined as a species that can self-reproduce, then these outwardly ordinary

fish straddle its edge. Of course, Amazon mollies are not entirely separated from more

ordinary forms of life. They descend, after all, from mollies that display all

the familiar hallmarks of life. The same is true for the other straddlers, the

other half lives we can find around us today. Mitochondria descended from

run-of-the-mill ocean bacteria that just so happened to get guzzled by our

single-celled ancestors, entering 2 billion years of a twilight existence. Even viruses can often be traced back to rogue bits of parasitic DNA that started

out in ordinary organisms. But if we push back further, perhaps 4 billion years, all of life gives way

to half life, and then to no life at all. DATA NEEDED FOR A

BLUEPRINT

David Deamer looked out across the crater and felt as if he were

standing on an infant Earth. It had taken him days to get here, first

flying from California to Alaska, and then over the Bering Sea to

Russia’s eastern fringe. In the city of Petropavlovsk-Kamchatsky, Deamer

boarded an old army troop carrier with a team of American and Russian

scientists, and they drove for five hours to the mouth of a canyon. The crew

hiked into the canyon on a muddy trail that eventually ascended the slope of

Mount Mutnovsky, a lively volcano. The year was 2004.

Mutnovsky had

last erupted in 2000.

At sixty-five, Deamer was Lincoln tall and Eisenhower bald. He

clambered around looming boulders, past ash and frozen lava flows. The

horizon crested with the peaks of neighboring volcanoes. After climbing

2,000 feet, Deamer and his fellow scientists reached the rim of Mutnovsky’s

crater. Nothing grew there on the expanse of black and gray rock. Steam

roared out of the ground. Deamer put on a gas mask and descended into the

maw. For the next few days the team of scientists surveyed the crater of the

volcano and then its flanks. They collected samples of water and mud. And

then Deamer began an experiment. His lab bench was a field of boiling hot springs with the rotten-egg stink

of hydrogen sulfide. For his test tube Deamer picked out a puddle the size

of a modest pothole. The water, as acidic as vinegar, was loaded with

whitish clay. At the center of the puddle, a column of boiling bubbles

pushed through the slurry. On his climb up the volcano, Deamer had brought a powder of life he

had concocted in California. Its ingredients included the four nucleotides of

RNA, as well as four amino acids, the building blocks of protein: alanine, aspartic acid, glycine, and valine. Deamer had finished the powder off with

myristic acid, a component of coconut oil. Deamer dipped a beaker into the scalding water and scooped up a liter. He sprinkled in his powder, and the water turned milky. Once it was well

mixed, he leaned carefully over the puddle and poured out the solution. He was doing something akin to what John Butler Burke had done a

century before. To understand the nature of life, he was carrying out an

experiment, putting lifeless chemicals into a container where they might

take on some of the properties of living things. While Burke was a physicist

with little understanding of the molecular basis of life, Deamer had four

decades of modern biochemistry under his belt. But even with all that

expertise, Deamer couldn’t predict what would happen next on the volcano. As soon as he emptied the beaker into the pond, a white froth appeared

on its steaming surface. Nature had surprised him once more. Deamer

bottled some of the froth and scraped some clay to take home, in the hopes

of getting a little closer to understanding how life began 4 billion years ago

—perhaps at a place like Mount Mutnovsky. —

“It is mere rubbish thinking, at present, of origin of life; one might as well

think of origin of matter,” Charles Darwin wrote to his friend Joseph

Hooker in 1863.

Charles was far more conservative than his grandfather Erasmus. He

refused to speculate in public about how life might have arisen from lifeless

matter. Writing On the Origin of Species, he alluded to the question only once. “Probably all the organic beings which have ever lived on this earth

have descended from some one primordial form, into which life was first

breathed,” Darwin wrote. Darwin would come to regret using that last word. “Breathed” was

redolent of biblical creation. The only thing Darwin meant to convey was

that living things must have arisen at some point in the distant past. How it

happened, he couldn’t say. In another letter to Hooker, Darwin mused about how a “warm little

pond” might serve as a flask for chemical reactions that produced simple

organisms. He never shared that notion in public, let alone developed it into

a full-fledged theory. But to his friends he confided how thrilled he’d be by

the discovery that life arose from chemicals, “for it would be a discovery of transcendent importance.” He would be just as thrilled if someone

disproved it. “But I shall not live to see all this,” he predicted. Darwin’s reticence disappointed his disciples. Their hero had developed

a theory that made it possible to tackle one of the greatest questions in

science, only to stop in his tracks. “The chief defect of the Darwinian

theory,” Ernst Haeckel complained, “is that it throws no light on the origin

of the primitive organism—probably a simple cell—from which all the

others have descended. When Darwin assumes a special creative act for this

first species, he is not consistent, and, I think, not quite sincere.”

Haeckel and other followers of Darwin did not hesitate to take the leap. They marshaled evidence for how life may have begun. They wrote books,

gave sensational lectures, and battled religious opponents who declared

God alone could bring life into existence. But as they walked along life’s

edge, they found the path dangerously slippery. Huxley thought he had

discovered the planet-spanning Bathybius, only to discover bad chemistry had led him astray. John Butler Burke may have been one of the first

scientists to try to rerun the origin of life in a test tube. But within a few

months of becoming a worldwide celebrity, he sank from view. In hindsight it seems foolish to have even tried to trace the origin of life

in an era when scientists knew so little about life itself. Huxley could talk

about protoplasm, but only in terms that made it sound like a near-mystical

jelly. When it came to heredity, no one in the nineteenth century—not even

Darwin—could make sense of it. Huxley had been dead for five years when

the very word genetics was coined in 1900.

In the first few decades of the twentieth century, biologists finally laid spontaneous generation to rest. They began deciphering a few enzymes and tracking a few genes through

generations of fruit flies. In the Soviet Union, a biochemist named Alexander Oparin became

convinced that these advances had finally made it possible to start thinking

sensibly about the origin of life. At last science had safely put vitalism

behind. “The numerous attempts to discover some specific ‘vital energies’

resident only in organisms invariably ended in total failure,” he concluded. To Oparin, it was hard to distinguish living things from the rest of the

universe. Our bodies were made up of carbon, oxygen, and other elements

that could be found in ocean waves, stratospheric clouds, and grains of

sand. Our bodies used enzymes to make new molecules, but some of the same chemical reactions could take place outside a living thing. Living

things could grow in complex patterns, but crystals could, too. The

flowerlike crystals of ice that formed on windows in winter were evidence

enough. “In their delicacy, complexity, beauty and variety these ‘ice flowers’

may even look like tropical vegetation while all the time being nothing at

all but water, the simplest compound we know,” Oparin said. The reason

that ice flowers were not in fact alive was that they lacked some of the other

features required for life. “Life is not characterized by any special

properties,” Oparin concluded, “but by a definite, specific combination of

these properties.”

Looking at life this way made understanding its origins less daunting. The question of how life began was not all that different from how Earth

began. By the 1920s astronomers already recognized that the solar system

had started out as a disk of dust. Gravity caused the grains to draw together,

to clump and crash until they formed planets. When Earth formed, it was a

ball of molten rock. Over millions of years it cooled to form a hard crust. The atmosphere rained down an ocean. Oparin saw all of these

transformations as a grand chemical experiment producing all sorts of new

compounds that could then react with each other to create still more

compounds, which gradually joined together all the properties required for

life. Oparin laid out some of his ideas in a small book in 1924.

He wrote it in

Russian, and only a few of his fellow Soviet scientists read it. But that

disappointing reception did not cause Oparin to abandon his train of

thought. Instead he ran experiments and read widely. He wove together new

ideas from microbiology to chemistry, geology, and astronomy, seeing

connections between the fields that narrow experts might have missed. In

1936, Oparin turned those new insights into a much longer book, The

Origin of Life, which was translated into English, reaching a far bigger audience. He opened his readers’ minds to a crucial realization: the planet

on which life began was profoundly different from the planet on which we

live today. We breathe in air that is 21 percent oxygen. The oxygen molecules in

the atmosphere steadily vanish because they react easily with other

compounds. The planet’s oxygen supply is replenished by plants, algae, and

photosynthetic bacteria. Before life began, the atmosphere would have been almost oxygen-free. Oparin recognized that chemical reactions on such a

world would operate in a profoundly different way than they do today. And

he argued that some of these reactions produced the first building blocks of

life. Oparin speculated that steam from volcanoes could react with minerals

to produce hydrocarbons. Those hydrocarbons could, in turn, go through

other reactions to produce more complex compounds. The compounds

started to clump together and began to grab molecules from their

surroundings. They built more clumps like themselves and gradually turned

into cell-based life as we know it. No time machine could carry Oparin back to the young Earth to see if

his own scenario was correct. Scientists would have to carry out

experiments and gather clues from Earth and other planets to test their

hypotheses and develop better ones. “The road ahead of us is hard and long,” Oparin warned, “but without

doubt it leads to the ultimate knowledge of the nature of life.”

Oparin was not the only scientist musing about the young Earth in the

1920s. J. B. S. Haldane published an essay of his own on the origin of life

in 1929.

Although they were unaware of each other, Haldane’s and Oparin’s

thoughts ran along parallel tracks, back to the time when living things first

emerged. “We may, I think, legitimately speculate on the origin of life on

this planet,” Haldane wrote. Like Oparin, Haldane recognized that the differences between Earth

now and at its birth would be crucial to those speculations. He mused about

ultraviolet light acting on water, carbon dioxide, and ammonia, producing

sugars and amino acids that would accumulate in the ocean until it gained

the consistency of what he called “hot dilute soup.”

For all the similarities in their thinking, Oparin and Haldane emphasized

different aspects of life. Oparin saw it fundamentally as a chemical

problem. Look in the index of The Origin of Life and you will find plenty of entries about metabolism, such as hydrolysis and oxidation. But there’s no gene, no heredity. Haldane was first and foremost a geneticist, and for him the great

question about the origin of life was how it started to copy its genetic

information. He held that genes emerged early in the origin of life. Our

genes may be swaddled today in deep layers of proteins and membranes

within our cells. But the first genes must have been naked molecules building copies of themselves out of Haldane’s hot dilute soup. A generation after Haldane and Oparin first put forward their ideas, a

graduate student at the University of Chicago heard about them for the first

time. Sitting in a departmental seminar, Stanley Miller was intrigued but

also puzzled: Why had no one successfully tested these ideas yet?

Miller

wasn’t interested in doing the experiments himself; he considered

experiments in general to be a messy waste of time. He preferred lofty

theoretical science instead, and was planning to spend his time in graduate

school pondering how stars made new elements. Those plans fell through when his advisor left Chicago for a job in

California. Desperate for a research project, Miller thought back to the

origin of life. The more Miller thought about it, the less crazy an

experiment to test Oparin’s ideas seemed. He was not going to make

radiobes, let alone full-blown life. He would merely test the proposition that

the chemistry of the early Earth gave rise to organic molecules. The seminar where Miller had learned about Oparin had been presented

by a Nobel Prize–winning chemist named Harold Urey. Miller tracked Urey

down in his office and proposed his plan. Urey replied that it was a bad idea

for a graduate student, since it was likely to end in failure. He tried pushing Miller to other projects that were less ambitious but more reliable, like

cataloging the chemicals in meteorites. But Miller wouldn’t budge, and

Urey eventually relented. He allowed Miller a year to tinker with the

experiment in his lab. If Miller didn’t make any progress after a year, he’d

have to move on. For the experiment, Miller and Urey set out to mimic the early Earth on

a countertop. “We then designed a glass apparatus that contained a model

ocean, an atmosphere, and a condenser to produce the rain,” Miller later

recalled. Into this flask Miller added gases believed to be common on the early

Earth: water vapor, methane, ammonia, and hydrogen. The energy for

chemical reactions on the early Earth might have come from lightning,

Miller speculated, so he inserted electrodes into the apparatus to deliver

sparks. After a few initial trials and adjustments, Miller powered up the

apparatus and let it run overnight. The next day the solution had turned to a reddish muck. When Miller

emptied the flask, he found that the muck now contained amino acids—the

building blocks of proteins—along with a host of other carbon-bearing molecules. Miller published his results in May 1953, at the tender age of twenty-

three. “The reaction to the paper startled me,” he later recalled. Like John Butler Burke before him, Miller was beset by a swarm of reporters. The

news of his experiment was so sensational that Gallup conducted a poll to

find out how many people thought it was possible to create life in a test

tube. Only 9 percent said yes. With that one experiment Miller created a new field of science that came

to be known as prebiotic chemistry. Scientists created more amino acids and

even some of the bases that today are parts of DNA and RNA. Haldane,

who had helped seed the field with ideas as a young man, now looked on

from old age at the new discoveries. He also found inspiration in the work

of molecular biologists like Francis Crick, who were working out how life

could store information in genes and then extract it. Even in the 1960s, Haldane had fresh ideas to sow. Life, he came to

believe, was the “indefinite replication of patterns of large molecules.” The

first patterns must have been much simpler than the ones that surround us

today. The fact that some viruses used single-stranded RNA instead of

double-stranded DNA got Haldane thinking that perhaps RNA evolved

first. In 1963, Haldane traveled to Florida to talk about his ideas at a

conference attended by Oparin and other leading researchers on the origin

of life. Haldane entitled his talk “Data Needed for a Blueprint of the First

Organism.” He envisioned a long-vanished form of life, a Bathybius for the modern era. It was a free-living microbe that stored its genes in RNA, not

DNA. It could use its RNA genes as a guide to build proteins, which could

then make new copies of its own genes. Just how few genes such an RNA-

based life-form needed, Haldane couldn’t say. “The initial organism may

have consisted of one so-called ‘gene’ of RNA,” he speculated. The idea was potent—so potent, in fact, that it independently occurred

to Crick and other scientists as well. But Crick, Haldane, and every other

scientist who promoted RNA-based life could speak of it only in the haziest

of terms. On the modern Earth, the only RNA-based life-forms are viruses,

which need a host to reproduce them. On the early Earth, RNA-based life

would have had to fend for itself. —

David Deamer’s journey to a Russian volcano began in 1975, over

cucumber sandwiches on the side of an English road. He was having lunch

with a British biophysicist named Alec Bangham, and the topic of

conversation was membranes. Life depends on genes for heredity and on proteins for its metabolism,

but it also needs membranes to survive. They are the boundaries that keep

life’s chemistry bottled up and busy. Life, as far as we know, cannot exist as

a boundless cloud of chemicals. But it wasn’t until the 1950s that scientists

like Bangham began pulling apart membranes and figuring out for the first

time what they’re made of. One of the most common kinds of molecules in membranes is chains of

carbon atoms called lipids. Some types of lipids are short and some are

long; some have decorations of elements such as oxygen that alter their

chemistry. But lipids all share a remarkable power of self-organization. One

end of the lipid chain repels water molecules. The other attracts them. If

loose lipids float in water, they spontaneously assemble into a two-layer

film. The water-repelling ends tuck inside, while the water-loving ends face

out. In the early 1960s, Bangham shook these films and found that they fell

apart and then re-formed in three-dimensional shapes. At first they formed

snakelike tubes. Then they pinched off into hollow spheres. These oily

shells came to be known as liposomes. Deamer, eight years younger than Bangham, had studied lipids in

graduate school at Ohio State University, extracting them from egg yolks,

spinach leaves, and rat livers. He traveled to California to become a

postdoctoral researcher at Berkeley, where he learned how to freeze

membranes and then crack them open to examine their inner structures. Deamer continued this line of work when he got a job at the University of

California, Davis. At age thirty-six he arranged to spend a year working

with Bangham in England. The two scientists carried out a series of important new studies on lipids. They invented a syringe that could produce an abundance of liposomes of

uniform size. Advances like these would turn liposomes into a medical tool. Drugmakers would later insert their compounds in liposomes to deliver

them inside cells. When Covid-19 struck, vaccine makers slipped viral

genes into liposomes, which could sneak them into our cells. One day in 1975, Bangham and Deamer took a drive to London. When they stopped by the side of the road for lunch, Deamer mentioned hearing

that Bangham had ideas about how life began. He was curious to hear what

they were. Bangham replied that life began with liposomes. —

For Haldane and his intellectual descendants, genes above all other things

make life special. For Oparin’s followers, the great question about the

origin of life is how metabolism arose. But life could not have arisen

without boundaries as well, and Bangham’s work with lipids gave him an

idea for how the first primitive cells had formed. If lipids existed on the

early Earth, they would have spontaneously turned into liposomes—ready-

made containers for life’s molecules. It would take far more time for the

planet to produce primitive forms of DNA, RNA, and proteins. The one

great shortcoming of Bangham’s idea was that no one could say if lipids

were indeed present before life began. And even if they were, no one knew

if those primordial lipids had the right form to become hollow shells that

could shelter life. After Bangham and Deamer chatted about these profound matters, they

finished their sandwiches and drove on to London. “I thought, ‘I’m going to go back to Davis to find which lipids can do

this,’” Deamer later told me. One of Deamer’s graduate students, Will Hargreaves, volunteered to test

out an assortment of lipids. He worked his way down from long lipids to

short ones. Most lipids in living cells are twelve to eighteen carbon atoms

long, but Hargreaves found that lipids with just ten carbons apiece could

still make stable liposomes. When Hargreaves finished his degree in 1980, Deamer was left

wondering whether indeed the early Earth could have supplied these short

lipids. Soon afterward he met a NASA scientist named Sherwood Chang

who gave him a chance to find out. Chang was in possession of an

extraordinary marble-sized rock, and he was willing to give Deamer a piece

of it. The rock had once been part of an asteroid that formed at the birth of the

solar system 4.57 billion years ago. Another asteroid crashed into it,

ejecting a meteor that then wandered the solar system until 1969, when it

arrived in our cosmic neighborhood. Earth’s gravitational field greedily drew the meteor in, and one morning the residents of an Australian town

called Murchison looked up to see fireballs trailing smoke across the sky,

followed by a clap of thunder. When people fanned out across the

surrounding outback, they found hundreds of black stones. NASA researchers got hold of some of these stones and discovered they

were actually loosely joined mineral grains. Placed in water, they simply

fell apart. Even more remarkable was what was inside the grains: amino

acids, along with a host of other organic compounds. Life did not have to

depend only on the chemistry taking place on our own planet for its

ingredients, the Murchison meteorite showed. Many of its building blocks

formed in space and then fell to Earth. Chang gave Deamer a tiny sample of the Murchison meteorite. Back at

Davis he treated it with chloroform and other chemicals to extract any lipids

it might contain. He put the chloroform liquid on a slide to let it evaporate. It gave off a musty smell that gave him hope he had found something. Once the chloroform had vanished, Deamer moistened the slide and

peered through his microscope. He saw movement, organization. The water

penetrated the dried extract, which swelled and grew into spheres. He had

made liposomes. Deamer got out his camera and furiously photographed

them. It was a moment worth memorializing, one over 4.5 billion years in

the making. The experiment suggested that lipids raining down from space might

have spontaneously formed stable liposomes. But on their own the

liposomes would be nothing but hollow shells. Deamer and his students

began playing with mixtures of liposomes and organic molecules to see if

they could fill the shells with the precursors of life. If they dried liposomes and DNA and then returned them to water, the liposomes re-formed with

DNA inside them. These experiments led Deamer to imagine a protocell with an enzyme

inside that could build RNA molecules. But in order to build RNA, it would

need a supply of bases. If bases were also produced on the early Earth, it

might be able to pull them in. But this solution led to a problem of its own. Our cells pull compounds in from their surroundings through special

channels encoded by our genes. Early protocells must have had a far

simpler way to pull in their bases. Perhaps a molecule drifting past a

protocell could get stuck on its membrane. Then it might slowly get drawn inside. Deamer and his colleagues decided to build a model of a primordial

membrane to see how it might work. They made sheets of lipids, into which

they lodged proteins. They then added compounds to see if the proteins

could shepherd them from one side of the sheets to the other. In 1989, Deamer took a break from this work for a vacation in Oregon. On a long drive along the McKenzie River, he kept thinking about

protocells and how they might pull in molecules. His mind wandered until

he was daydreaming about streams of bases flowing into protocells through

primordial channels. He would need a way to pull them through—perhaps

an electric field. He pictured the base slowly wiggling through the channel,

blocking the smaller charged atoms behind it like a slow-moving truck with

a line of cars piling up behind it. It occurred to Deamer that this traffic jam would slow the current through the channel momentarily. He wondered

what would happen if he and his students measured the channel’s current as

the base went through. “Maybe we’d see a little blip,” he later recalled. What if, instead of a single base, Deamer tried snaking a piece of DNA

through?

Instead of a blip, would he see a series of blips?

Each of the four

bases in DNA has a different size and shape. Maybe the blips would look

different. Maybe he could spell out the sequence in a piece of DNA by

pulling it through a channel. Suddenly, in the middle of the Cascade Mountains, Deamer realized that

thinking about the origin of life had led him to something he never

anticipated. He was thinking of a way to read DNA. In 1989 the idea of quickly reading a piece of DNA was close to magic. The standard methods at the time were so slow that scientists could read

only a few hundred bases each day. At that pace they’d need upwards of

100,000 years to sequence a single human genome. Some scientists were

dreaming of ways to speed up the process, and now Deamer had become

one of the dreamers. He imagined DNA shooting through a channel, singing

out its sequence in an aria of electricity. —

When Deamer finished his Oregon drive in 1989, he took out a red pen and

drew his vision in a notebook. He sketched DNA slipping through a

channel. He drew an imaginary graph showing the blips of voltage he imagined each base would create. “The channel must be of the dimensions

of DNA in cross-section,” Deamer wrote. Deamer enlisted other scientists to help him make the idea real. For

starters, they would have to find a channel of the right size and shape to

create a DNA traffic jam. In 1993, Deamer learned about one that might do

the trick, a channel made by bacteria called hemolysin. He traveled to the

laboratory of a hemolysin expert named John Kasianowicz at the National

Institute of Standards and Technology in Maryland, bringing with him

strands of RNA to thread through a molecular needle. Together, Deamer and Kasianowicz created a lipid membrane stretched

across a circular opening. In the middle of the membrane, they inserted a

single hemolysin channel. When they switched on an electric field, they

could drag RNA into the hole. And they could see a series of blips. The

number of blips matched the number of bases on the strands. That success was enough to publish a paper in 1996.

But it was still a

long way from a DNA reader. They had yet to figure out how to tell all four

bases apart. It was as if Deamer and Kasianowicz were looking at blacked-

out sentences in a redacted government document. They could count the

number of letters in the sentences but had no idea of the words the letters

spelled out. One of Deamer’s former students, Mark Akeson, came back to

California to take over the project. His goal was to pull the mask away from

the letters. Akeson and his colleagues tuned their electronics to detect even

subtler changes in the current while making them less sensitive to

distracting noise. They took advantage of the fact that two of DNA’s four

bases, adenine and guanine, are much bigger than cytosine and thymine. Akeson and his colleagues proved that the big bases led to big drops in the

current, and the small bases led to small ones. Deamer could not yet hear the language of genes clearly. But now, at

least, he could tell its vowels from its consonants. —

I first met David Deamer in 1995.

I traveled to Santa Cruz, where he had

moved after marrying Ólöf Einarsdóttir, a professor at the University of

California campus at the north end of the city. Deamer had traded Davis’s landscapes of flat farmland for the brooding beauty of the coast, a place where elephant seals lounged on the beaches,

watched over by pines and redwoods on the hillsides. On my first night in

Santa Cruz, I wandered downtown. The Loma Prieta earthquake of 1989

had left its mark six years earlier. I passed silent abandoned buildings,

following the stark gashes in the dark, deserted streets. In the morning I

found my way to Deamer’s lab. “Do you want to smell outer space?” Deamer asked. He offered me a

sample of Murchison lipids to sniff. It reminded me of an attic. “Do you

want to hear insulin?” he asked. A few years before, Deamer converted the

sequence of genes into musical notation: adenine became A, guanine

became G, cytosine became C, and thymine—without a T in the scale—

became E. He began to hum a gene to me, which sounded vaguely like a

song. Deamer was fifty-six at the time. A decade had passed since he made

liposomes from a meteorite, and in the intervening years he had developed

an elaborate scenario for the origin of life, drawing on both his own work

and that of other scientists. The idea that life started out based on RNA,

originally conceived by Haldane and others in the 1960s, had gained a lot of

favor over the years. RNA had proven to be exquisitely versatile—perhaps

versatile enough to sustain life on the early Earth. At the University of

Colorado, for example, a biochemist named Thomas Cech discovered a

remarkable RNA molecule in a freshwater protozoan called Tetrahymena. This molecular strand could spontaneously bend around and cut out a piece

of itself, like a self-acting enzyme. Soon researchers were finding other

RNA molecules that can behave like enzymes—what came to be known as

ribozymes. Ribozymes revealed that RNA can do two things at once: they can store

genetic information like DNA, and they can also carry out enzymatic

reactions like proteins. In 1986 a Harvard biochemist named Walter Gilbert

used their discovery to update the hypotheses of Haldane and others about

the origin of life. He called his theory “the RNA World.”

Gilbert proposed that life initially used RNA alone, long before DNA

and proteins even existed. An RNA-based form of life might carry a set of

RNA molecules, each adapted for certain jobs. Some might carry genetic

information, while others might grab compounds to build new RNA

molecules. RNA-based life could evolve because it would make mistakes as it made new copies of its genes. Eventually, Gilbert proposed, RNA-based life evolved proteins and

DNA. RNA molecules might have gained the ability to link amino acids

together to make very short proteins. These new molecules may have been

able to help the cells survive, and as the proteins got longer, they may have

outperformed the RNA molecules. RNA genes may have evolved into the

double-stranded form of DNA, which proved a more stable way to encode

genes. Gilbert followed in Haldane’s gene-centered tradition. He focused

entirely on the evolution of RNA molecules without giving any attention to

how they would be housed in cells. Using his liposomes, Deamer pursued

that unaddressed question. He hypothesized that primitive cells might have formed from the lipids

delivered by meteorites. Some of these meteorites might have landed on the

newly forming volcanoes that rose above the ocean. The lipids were washed

into ponds and hot springs—along with an assortment of other potential

building blocks for proteins and RNA. Periodically the water would

evaporate, leaving a kind of primordial bathtub ring behind, which was later

submerged once more in rain or floods. Working with Ajoy Chakrabarti, a postdoctoral researcher in his lab,

Deamer re-created this ancient chemistry for me. He opened a jar of egg

yolk lipids and added some to the water in a test tube. The tube turned

cloudy as it filled with microscopic bubbles. Deamer then turned to a second test tube, adding dried white threads of

DNA from salmon sperm as if he were a chef sprinkling saffron into a dish. (Salmon sperm DNA is cheap and easy to order from a biological supply

company; it stood in well enough for RNA.) The DNA threads turned

gooey. Deamer spiked the solution with a fluorescent stain. He then

combined the lipids and the DNA on some slides. “Why don’t we get the hot plate going?” he said to Chakrabarti. Chakrabarti switched it on and put the slides on its surface. “That’s our tide pool,” Deamer said. In a primordial pool, lipids might have formed into liposomes drifting

around in the water. But as the sun beat down, the water would disappear

and the liposomes would get crowded together. When they touched, they

fused. As more water evaporated, they turned from bubbles to sheets, sandwiching other molecules between their layers. The same thing was happening on the slide. After a few minutes Deamer

removed it from the hot plate. The DNA and lipids had dried to a thin film. Now Deamer refilled his miniature tide pool by adding back a few drops of

water. He put the moistened slide under a fluorescent microscope, and

Chakrabarti turned out the lights. Through the eyepiece I saw lipids squirting out from the dried film into

the surrounding water. At first they writhed like snakes, and gradually they

swelled into bubbles. Some of the bubbles were dim, but others glowed

with the intense fluorescent green dye, letting me know that they had

swallowed up DNA. This exercise was a far cry from a proof of how life began. Deamer just

wanted to show one step in the scenario he and like-minded researchers

favored. At the time, they were under heavy fire from RNA-World skeptics. No one could yet say how RNA molecules could come together from

simple building blocks to begin with. As for where life might have begun, a

number of scientists were looking away from the volcanic ponds that

Deamer favored. They looked instead to the bottom of the ocean. In the 1970s oceanographers investigated mid-ocean ridges, the seams

between continental plates that run from pole to pole, where magma rises

up from deep within the earth and adds new margins to the seafloor. The

researchers were surprised to discover huge black chimneys sitting on the

ridges, spewing dark smoke. It turned out the chimneys were deep-sea

versions of hot springs. Ocean water was making its way down through the

fissures in the ridges, where it heated up and reacted with the surrounding

minerals. When it rose back to the seafloor, it brought a heavy load of

subterranean compounds. Hitting the cold sea-water, the minerals in the

fluid suddenly underwent chemical reactions and formed hollow piles of

rock on the seabed. On closer inspection, scientists discovered that these vents harbored life

—ecosystems unlike any others on Earth. Microbes harvested energy from

the chemicals spewed from the vents. They became food for larger

organisms. Blind shrimp crawled the flanks of chimneys. Tube worms grew

like bamboo forests. More than 4 billion years ago, when the earth cooled

from a molten ball and developed a crust, the early ocean would have

contained many such vents. The heat and exotic chemistry present in them might have fueled the rise of genes, metabolism, and cells. Deamer was not having it. The prebiotic manna from heaven—organic

compounds falling from space—would get diluted in the ocean’s great

expanse before it could reach vents on the seafloor. Liposomes that formed

in the ocean would get torn apart by its salty chemistry. Still, Deamer had a lot of work before him. If life started in surface

pools, it would need some way to get an energy supply. Today, algae and

bacteria in ponds can harness sunlight, but they use a complex network of

proteins to do the job. A protocell could not have relied on such a

sophisticated natural solar panel. But Deamer wondered if simple solar

panels might already be floating around them. The Murchison meteorite

contained molecules called polycyclic aromatic hydrocarbons, or PAHs for

short. When light shines on a PAH, it can give off an electron. Perhaps, Deamer speculated, PAHs from meteorites could insert

themselves in liposomes. When sunlight hit them, the PAHs would release

electrons that they could use. They could generate the power protocells

needed to carry out their chemistry. Nobody could say whether this scenario would work or not, because

nobody had ever tried mixing PAHs with liposomes before. So Deamer and

his students tried. “We’d like to make them capture energy in a useful form,” Deamer told

me. “Nobody’s particularly impressed yet.”

—

Four years later, in 1999, Deamer met a Russian volcanologist named

Vladimir Kompanichenko at a conference on the origin of life. When

Kompanichenko learned of Deamer’s obsession with primordial pools, he

invited him to come to Kamchatka. It would be the closest thing to time

travel Deamer would ever experience. The peninsula of Kamchatka was

packed with active volcanoes, and the conditions were so harsh that little

could survive there. If he made the trip, Deamer would be able to study

crater lakes, hot springs, ponds, and all manner of other bodies of water. Rather than imagine the chemistry of the early Earth, he could look at it up

close. Deamer took Kompanichenko up on the offer. He organized a team of

scientists to travel to Kamchatka in 2001.

They rode a military helicopter

from volcano to volcano, as brown bears scurried away on the tundra below. One volcano lake was turquoise blue, while another was topped with

petroleum—not from an oil spill but from the swift breakdown of plant

matter that blew into the water. Ordinarily it takes hundreds of millions of

years for plant matter to turn to petroleum. In this strange place it took only centuries. On the flanks of the volcanoes Deamer scooped water from steam-

blasting fumaroles and inspected hot springs bordered by bathtub-like rings

—exactly the wetting and drying cycles he hoped to find in nature. The

ponds contained different combinations of minerals, reached different

temperatures, and varied in many other ways. There was so much for

Deamer to take in that he knew he would have to return. And it was on his

second trip, in 2004, that he brought his powder of life. For thirty years Deamer had been studying the origin of life in the

tradition of Stanley Miller, working in the confines of a laboratory. He

carried out experiments in glass tubes with pure ingredients and precisely

controlled temperatures. Those controls allowed him to know whether his

results were significant or not. But they also left him wondering if the

processes he studied in his lab would work in the rough-and-tumble world

where life has to survive. And as soon as he poured his powder into the Mutnovsky puddle and the

froth appeared, Deamer knew something strange had happened. The froth

was made up of lipids that had organized into membranes. But he had to get

back to Santa Cruz to figure out exactly what he had witnessed. He and his

colleagues discovered that many of the compounds in his powder had

gotten stuck to the clay particles in the water. But the lipids had captured

others. The lipids did not immediately turn into bubbles as they might in

Deamer’s laboratory. Iron and aluminum in the water had reacted with the

lipids and turned them to floating curds. Deamer did not make life from scratch on Mount Mutnovsky, but the

experience had a profound influence on his thinking. The ponds and hot

springs on the volcano all had high temperatures and low pHs, but they

were also different in many ways. Some ponds were laced with clay or

aluminum that might block the development of life, while others might be

more favorable. Deamer began surveying the diversity of hydrothermal

springs in other parts of the world. Sometimes he visited himself, and

sometimes he arranged for colleagues and students to do the fieldwork. They went to Yellowstone, Hawaii, and Iceland. On a trip to New Zealand, his colleague Bruce Damer brought an aluminum block loaded with test

tubes. Each test tube had a dried film of RNA and other chemicals. Damer

pushed the block into the mud and filled it periodically with water from the

spring. They succeeded in producing liposomes containing small molecules

of RNA. These trips were expensive, demanding, and relatively brief. To

continue the research back at home in Santa Cruz, Deamer built an artificial

volcanic pond. “I’m mimicking what I saw on Mount Mutnovsky,” he told

me. Deamer constructed a clear plastic box the size of a suitcase. He sealed

it so that he could flood its interior with carbon dioxide, giving it an

atmosphere more like the one that existed on Earth 4 billion years ago. Inside the box, Deamer installed a metal disk with holes around the edge

into which he could slot two dozen tubes. Each tube could mimic a pond in

Kamchatka, with hot acidic water laced with various chemicals like the

ones he sampled on Mount Mutnovksy. He created his own cycle of drying

and wetting. The disk slowly rotated, so that each tube passed under a tube

blasting carbon dioxide for half an hour twice a day, evaporating its water

and leaving behind bathtub rings of chemicals. As the disk rotated more, the

dried tube moved underneath another tube that delivered a splash of water. Deamer and his colleagues filled the tubes with lipids and bases, the

building blocks of RNA and DNA. After the tubes went through hours of

wetting and drying, they found liposomes with bases trapped inside them. And in a small fraction of these shells they found something even more

remarkable: the bases had joined together. Some of the new molecules were

up to a hundred nucleotides long. “We’ve made an RNA-like molecule,”

Deamer said. In our own cells, bases form bonds only with the help of highly evolved

enzymes. Deamer and his colleagues had sidestepped this requirement by

using the peculiar chemistry of a primordial pond. When the liposomes

dried, they fused and flattened into sheets. These thin layers became liquid

crystals where the bases no longer bounced around in endless agitation. Instead, they fell into an orderly arrangement, in which they were more

likely to bond together. When water returned to the tubes, the layers swelled

and budded off as bubbles, taking the RNA-like molecules away with them. With each round of wetting and drying, the molecules got longer. In Walter Gilbert’s RNA World, the first living things needed a ribozyme to build RNA molecules. Now Deamer’s experiments suggested

something even more radical: no ribozyme was required because lipids

could do the work of building RNA on their own. Before there was an RNA

World, his work suggested, there might have been a Lipid World. —

I visited David Deamer for a second time in the fall of 2019.

Twenty-six

years had passed since my first trip to Santa Cruz. I had become a gray-

haired father, while Deamer had just celebrated his eightieth birthday. I had

flown to San Francisco for work, and Deamer insisted on picking me up at

my hotel and chauffeuring me down to Santa Cruz for an afternoon. He was

in good health, I could see; he credited it to biochemistry. Experiments he

had carried out in the 1970s had convinced him of the benefits of

antioxidants, and so he started taking supplements. “And here I am, still

going strong,” he said. Still, Deamer asked me to stay quiet so he could concentrate on getting

us safely out of the city and onto the freeway. Once we reached the pine

groves and the coastal cliffs, he relaxed. He began humming a song of

DNA. I asked Deamer what, after all this time, he thought life was. He still

didn’t have a good answer, he admitted. “We will know when the molecular

systems we’ve assembled happen to have certain properties of life,” he

replied. Deamer then rattled off some of those properties. Was he defining

life, I asked, or just characterizing life as we know it?

Did life have to be based on chain-shaped molecules like DNA and proteins?

“I’m stuck in my little box,” Deamer admitted. “I can’t imagine

anything other than a nucleic acid and proteins that can do what they do. You ask me how I think about all this. I like to do experiments. I like to

watch things happen. I just think, ‘What’s the next simple thing I can do?’”

When we got to Santa Cruz, I could see that the damage from the

earthquake had healed over since my last visit. But other fissures had

opened up since then, ones that would be harder to fix. Wealthy tech

workers priced out of Silicon Valley had streamed over the mountains,

offering a million dollars for a petite bungalow. Near the town bus station I

watched a woman slowly wander barefoot, mimicking a cigarette to

passersby as a silent request. Deamer did not take me to the redwood grove where his university laboratory had once been. Instead, we headed to a warehouse-like building

at the edge of town near the railroad tracks. The year before, he had

launched a company in an incubator called Startup Sandbox. It housed start-

ups developing bone grafts, cancer tests, and smart gardens. Deamer was

three times older than most of the people there. We settled into his second-floor office. It had the hollow feel of a place

barely moved into. A framed photograph of a shooting star hung on a wall. A science fiction novel by Stanislaw Lem sat alone on a shelf. From under a

table Deamer pulled out his artificial pond to show me how it worked. “There’s not much to it,” he said, “but it’s the only one in the world.”

I, in turn, had something to show Deamer. I pulled up a picture on my

phone that a biologist I knew had recently sent me. It showed a metal block

the size of an eight-hole harmonica. Next to it was an opened box, labeled

MinION. “My new toy arrived,” my friend texted. “$1000 sequencer. Less than

your iPhone!

I can’t decide whether to be excited or horrified.”

I scrolled down to the next message, which my friend sent me a few

weeks later. He wanted to find out what sort of microbes grow on paintings,

so he pried a speck of paint from an old artwork, extracted genetic material

from it, and then placed a DNA-loaded drop into his MinION sequencer. He

sent me a video of the MinION hooked up to his laptop, which was busy

reading the DNA sequences. In five hours, the MinION had read 42 million

base pairs. “Ta da!” my friend texted. “Hard to believe this will feel old-fashioned

in my lifetime.”

“Oh, look at that!” Deamer said in soft delight. I wasn’t surprised that

the video would make him happy. The machine my friend was using had its

origins in Deamer’s dream three decades earlier. In 2007 a company called Oxford Nanopore Technologies licensed the

patent Deamer and his colleagues had filed for their concept of a DNA

sequencer. In the years that followed, Deamer and other scientists found

ways to improve the design. Better channels came to light in other bacteria. Oxford Nanopore figured out how to fit many channels on a single

membrane so that they could sequence many copies of DNA at once. They

also started spending time in court. As the technology grew more

promising, other DNA-sequencing companies started challenging the patents. “We’re continually being sued,” Deamer told me. Oxford Nanopore began selling their first DNA reader in 2015.

Compared to other technologies, it was tiny, easy, and cheap. Scientists

began using it to read DNA that would have otherwise gone unread. During

the 2015 West Africa Ebola outbreak, it took only a day for scientists to

read the genes of viruses after they were extracted from patients. In the

forests of Uganda, wildlife biologists rapidly identified new insect species. In 2016, NASA sent the MinION to the International Space Station, where

the astronaut Kathleen Rubins carried out the first DNA sequencing in

space. Someday, Deamer hoped, a nanopore sequencer might discover

genes on another planet. —

Deamer’s ideas were becoming real in another way: younger scientists were

building more elaborate protocells to explore the RNA World. A biologist

named Kate Adamala came up with her own recipe for lipid bubbles, into

which she slipped RNA molecules. She created protocells that grew and

split in two. She created protocells that gave off a flash of light when they

detected a certain chemical. She made protocells that could talk to each

other. None of Adamala’s protocells could do all of these things at once,

though. She dealt each protocell a different hand of RNA. But collectively

Adamala’s creations offered glimpses at what life might have been like

before life as we know it—if we are willing to accept something without

DNA as alive. In his own lab Deamer worked with his students to uncover more of the

steps by which loose lipids and nucleic acids might have assembled into

those first protocells. In 2008 they discovered that liposomes that went

through cycles of wetting and drying could produce RNA molecules up to

one hundred bases long. But skeptics observed that these molecules were

much shorter than any RNA virus’s genome. It was hard to see how such

brief genetic instructions could launch life on its journey. So Deamer and

his team tried to make bigger ones. Not long before my visit, they began using a new tool to look at what

they created. The device, called an atomic force microscope, taps a

minuscule metal finger over molecules, mapping each of their atoms. Deamer showed me one of the maps. It was a biochemical Jackson Pollock: a field of strings, tangles, loops. “If we’re right, those are the longest strands ever made in the history of

this research,” Deamer said. “If you’re going to make a ribozyme, it’s got to

be long enough to fold. We have ribozymes to spare here in terms of

length.”

The tangles gave Deamer more evidence for his vision of life’s

beginnings. After the earth formed, volcanoes rose above the ocean, and

rain fell along their flanks. Ponds filled, and heated groundwater rose up

through geysers and bubbling hot springs. Asteroids, meteorites, and dust

fell from the sky, delivering trillions of tons of organic compounds. The

volcanoes acted as chemical reactors, too, supplying their own compounds. When lipids reached bodies of water, they sometimes formed into bubbles,

enveloping compounds and then delivering them to drying bathtub rings. RNA molecules grew in their liquid crystals, and when water returned, the

dried layers became trillions of liposomes carrying new molecules. Many of those bubbles ripped apart, but some remained stable. The

RNA they carried inside acted as a brace, holding them together from

within. These stabilized bubbles were more likely to survive long enough to

get into the next bathtub rings, and their RNA was more likely to get into

the next generation of bubbles. Deamer and his colleagues have found that a

single strand of DNA can act as a template for a corresponding strand in

these liquid crystals. On the early Earth, RNA molecules might have started

getting copied in the bathtub rings, long before enzymes took over the job. Over time, these networks of RNA added new molecules, and the

molecules got longer. They took on new roles inside the liposomes. Some

poked through the membranes to serve as primitive channels. Some

snagged bases, speeding up the growth of new RNA molecules. The

liposomes liberated themselves from their liquid crystal nursery and began

to divide on their own. They may have powered their growth by trapping

sunlight in pigments from meteorites. In Deamer’s telling, these protocells were the first truly living things. They were fragile organisms, to be sure. But without any competition, they

could thrive. They evolved the ability to bring together amino acids,

forming short chains and then longer ones that folded into true proteins. These proteins were stronger and more chemically versatile. Single-

stranded RNA also evolved into double-stranded DNA, which proved to be

a more stable way to store genetic information. In time, the new DNA-based organisms drove RNA-based life extinct. In recent years paleontologists have been pushing back the fossil record

of life on Earth, and some of the oldest evidence they’ve found comes from

rocks in Australia dating back 3.5 billion years. They contain thick layers

that may have been formed by microbial mats growing in volcanic ponds—

precisely the places Deamer predicted that early life would thrive. If you went back in time to the dawn of life, you might have observed

puffy cushions of microbes lining bubbling springs on the flanks of

volcanic islands. The islands were otherwise bare black rock sprinkled

across a green ocean under an orange sky. Clouds sometimes rolled

overhead, and rain washed down the islands. The streams moved microbes

from pond to pond. In the ponds where microbes already resided, the

newcomers mixed their genes with the old. The rain clouds traveled out to

sea, leaving the islands to bake. The ponds dried out and winds picked up

their dust, carrying microbial spores for miles. As they flew and swam

downhill, the microbes reached salty estuaries. As they adapted to these

new environments, they became ready to spread into the ocean. Once they

reached the sea, the whole planet became alive. “I’d give myself a hundred million years for something to happen,”

Deamer said. I thought back to Darwin doubting he would live to see the origin of life

settled. Here I was, nearly 150 years later, listening to a scientist talk about his life’s work, dedicated to that mystery. I wondered what Deamer would

live to see in the years he had left. Would the story he told grow stronger?

Or would he be remembered as the John Butler Burke of his time?

He still had many opponents. One of the fiercest was a scientist named

Michael Russell, who was also eighty years old. Russell’s path to the origin

of life was lined not with lipids but with minerals. He traveled to Pacific

islands and Irish mines searching for seams of silver and fool’s gold. In his

journeys he recognized that some of those minerals had originally been

produced around hydrothermal vents. These were not the superheated black

smokers on the mid-ocean ridges, however. In other parts of the ocean, a

different kind of chemistry took place. In these places the seafloor is lined with olivine, a rock rich in

magnesium and iron. Water flowing into the cracks reacts with the olivine,

releasing hydrogen and heat. The rocks absorb the warmth and in turn boil

the water, which shoots back up to the seafloor, bringing with it minerals, methane, and a host of other compounds. Many of the positively charged

hydrogen atoms get combined into these compounds, which changes the

fluid’s pH. It goes from acidic to alkaline. When this hot fluid comes out of

the seafloor and hits the cold, acidic bottom water, it dumps minerals that

pile up into giant hollow chambers topped by towers that can reach two

hundred feet high. To Russell, these chambers seemed like the perfect place where life

could arise. They became extraordinary chemical reactors, thanks to the

difference between the water within and outside the chamber walls. The

high pH of the alkaline water inside the chamber attracted the hydrogen

atoms from the acidic seawater outside. The hydrogen atoms would have to

make their way through microscopic channels in the walls. To Russell, their

flow was a striking parallel to the way hydrogen atoms flow through

channels in cell membranes—a flow our cells exploit to capture energy. In

fact, Russell didn’t think this was a coincidence. Our metabolism was built

on the chemistry of the chambers. The hydrogen atoms streaming into the walls of the alkaline vents could

have powered chemical reactions, creating new compounds that could go

through reactions of their own. Over time, the chambers created many of

the ingredients necessary for life. Russell speculated that pockets in the

minerals might serve as cells before cells existed. In these rock-lined

chambers, a primitive metabolism could grow. Eventually that metabolism

became able to support full-blown life. By the early 2000s alkaline vents and volcanic ponds were the two

leading scenarios for how life began. Both could not be right. In a 2017

cover story for Scientific American, Deamer and his coauthors made their case for life forming on the planet’s surface, complete with elaborate

diagrams of life starting high on volcanoes and flowing downhill to the sea. Their scenario, they argued, found much more support from experiments

than Russell’s alkaline vent theory. Russell struck back with barbs. In the work of scientists like Deamer, he

saw that vitalism was alive and well. Experiments that generated lifelike

molecules in mimic ponds were “utterly irrelevant and misleading.” The

idea that cells could have started out as liposomes bobbing in water was,

Russell declared, “fundamentally flawed.”

Only alkaline vents, Russell argued, offered the right flow of energy for producing the specific reactions that living things use today. Heating up a

volcanic pond and bathing it in sunlight would do nothing but create a lot of

competing reactions that would not add up to any complexity. The idea was

as ridiculous as Dr. Frankenstein using jolts of electricity to bring dead

body parts back to life. “The Frankenstein idea is just false, whether it be cast in chemistry or in

corpses,” Russell declared. When I brought up Russell’s alkaline vent theory, Deamer cataloged the

many problems he saw in it. One major flaw was that the walls of vents

were too thick to generate the kind of energy Russell needed. Think about

trying to generate electricity with a water wheel, Deamer said. If you put

the water wheel directly under a waterfall, you can capture the energy of

water falling a great vertical distance while flowing only a short distance

downstream. “But if you take the waterfall over a kilometer, you cannot run

a generator, because you just don’t have that energy,” Deamer said. On the day of my visit, Deamer was running a new experiment. The

reason he had brought me to Startup Sandbox was because he had recently

launched a company called UpRNA. A Santa Cruz graduate student named

Gabe Mednick had signed on as his sole employee. His microscopic

company had one mission: to create another biotechnology based on the

peculiar chemistry at the origin of life. In August 2018, for the first time in its history, the U. S. Food and Drug

Administration approved a drug made of RNA. A company called Alnylam

Pharmaceuticals created it as a way to treat a disease called transthyretin

amyloidosis. The disease is brought about by a mutant gene that creates a

defective protein. Over the years, the damage from these faulty proteins

causes people to waste away, to struggle to walk, to suffer seizures, and to

die of heart attacks. To create their drug, Alnylam created liposomes, using the techniques

Deamer had helped pioneer forty years before. Into these oily bubbles they

placed custom-made RNA molecules. The liposomes slipped inside cells,

where they released the artificial RNA. These molecules then grabbed onto

the messenger RNA for the faulty gene, preventing the cell from using it to

make the faulty proteins. Alnylam’s success raised the prospect of using RNA to fight high

cholesterol, cancer, and other disorders. But there was a catch: it costs a lot

of money to make an RNA-based drug. Alnylam mimicked nature, using enzymes to read an artificial gene and then building the RNA molecule one

base at a time. When Alnylam got approval for their drug, they put the price

for a year’s supply at $450,000.

Deamer suspected he could make custom RNA molecules for a lot less

money. Instead of mimicking life as we know it today, he would mimic life

in the RNA World. Deamer and Mednick were putting genes of DNA into

his artificial pond and then trying to build matching RNA molecules by

drying and wetting the tubes. For their first try, they were going to make an

RNA molecule that would switch off a gene for a glowing protein. If he

added the RNA to a dish of luminous cells, it would grab the messenger

RNA for the protein and the cells would go dark. And if they could reach

that milestone, they would start work on RNA molecules that could block

disease-causing proteins. Deamer had no idea if it would succeed. But all the lessons he had

learned about life as it first existed gave him confidence that it might. “Everything I do,” he said, “is based on knowing that life began.”

NO OBVIOUS BUSHES

The February sunshine was almost too much to bear. I emerged out of

a Lyft in front of the badging office at the NASA Jet Propulsion

Laboratory in Pasadena, California, having just spent several months

in chilly New England under a sky that had been mostly cloudy, dark, or

both. A JPL scientist named Laurie Barge came into the office to meet me

and led me inside the facility. Along the way, she slipped on a pair of

Michael Kors sunglasses, which hid her eyes behind obsidian walls. As we

walked across a palm-lined courtyard, I squinted like a miner just rescued

from a cave-in. I had come to JPL to talk to Barge about her work on astrobiology. “It’s,

essentially, how does life start and how do we find it?” she said as we

settled down in the shade with coffee. It was the right kind of science for

someone like Barge, who was full of big questions as a teenager. “I wanted

to know why we’re here,” she said. “I wanted to know: Where did the sun

come from?

Why is there a universe?

Why is there Earth?

Why is Earth the

way it is?

Is life specific to Earth?”

It was hard to imagine someone like Barge anywhere else but JPL. It

was one of the most important places on Earth for investigating the

possibility that we are not alone. My visit with Barge was my first chance to

see JPL for myself, and I will admit feeling like a pilgrim finally paying a

visit to a sacred site. I belonged to the generation born in the 1960s, when life on Earth

suddenly extended its tendrils past the bacteria-laden stratosphere and into

space. We sat cross-legged on carpets in front of bulging glass television

screens, watching fuzzy images of two-legged mammals, encased in little

chambers of Earth’s atmosphere, walk on the moon. In the movies and TV

shows we watched, humans traveled across the galaxy and met an endless

procession of other life-forms that had an odd resemblance to the two-legged mammals who go to Hollywood casting calls. It seemed like the

interplanetary age had begun. Astronauts only got as far as the moon, though, and they never stayed

long before coming home. By the 1970s their ambitions had contracted

down to low Earth orbit. Their cramped space stations flew overhead, close

enough to leave a glint on the night sky. Instead of humans, it was machines

that explored the other planets. And many of those machines came from

JPL. It was at JPL that engineers built the first spacecraft to visit another

planet— Mariner 2, which flew past Venus in 1962, and Mariner 4, which paid humanity’s first visit to Mars three years later. It looked down at the

red planet and snapped pictures, and when the pixels arrived at JPL,

scientists saw a cratered desert. The scientists at JPL included geologists who investigated how the

planets had formed from clouds of pebbles. There were atmospheric

scientists pondering swirls of carbon dioxide and sulfur dioxide. And JPL

had biologists on staff, too. They did not study life as we know it, so much

as contemplate life as it might be. In 1960 the microbiologist Joshua

Lederberg had given this new field a new name: exobiology. One scientist

scoffed that exobiologists were actually ex-biologists. The JPL

exobiologists brushed away the mockery and worked on ways to detect

extraterrestrial life. The exobiologists at JPL could be roughly split into two camps. Some

of them thought the best way to search for life was to search for it up close. They wanted to send probes to other planets, where they could run

experiments. In one project, a group of exobiologists built a growth

chamber into which they could scoop dirt on another planet and watch

organisms metabolize carbon dioxide or some other gas. Other exobiologists at JPL thought they’d have more luck by looking for

life from a distance. The most prominent voice for a distant search was

James Lovelock, a British-trained scientist who worked at JPL in the 1960s. To Lovelock, the idea of putting a growth chamber on Mars was absurdly

provincial. We ought not limit our search for life to life that played by

exactly the same rules as, say, bacteria that live in the ground on Earth. To

Lovelock, the crucial fact of life was that it had the power to push chemistry

away from equilibrium—not just within its own cells but across our entire

planet. It flooded oxygen into the atmosphere. It eroded rocks, sending minerals into the ocean. At JPL, Lovelock tinkered with devices that might

be able to see the signature of life in atmospheres on distant planets. At first Venus and Mars seemed like the best places to start looking. They were practically neighbors, for one thing, and they both had a solid

crust—as opposed to the gas giants farther out in the solar system. When

Mariner 2 visited Venus, however, it proved to have an atmosphere that

trapped enough heat from the sun to melt lead. Exobiologists struck it off

their very short list. As for Mars, the pictures that Mariner 4 sent back weren’t quite so bleak. The Martian deserts were cold and cratered. But

even on Earth, life wasn’t limited to lush rain forests. Mars might overlap

with the harshest habitats on our own planet. “The fact is that nothing we have learned about Mars—in contrast to

Venus—excludes it as a possible abode of life,” Norman Horowitz, the head

of JPL’s bioscience division, said in 1966.

“We can say although the

situation is not brimming with hope, neither is it hopeless.”

Two years later NASA moved forward with the Viking mission: a

project to put a pair of spacecraft in orbit around Mars. Each would drop a

probe to the planet’s surface for a closer look. The Viking rockets finally

left Earth in the summer of 1975.

At the time, I was nine. It took the spacecraft almost a year to reach

Mars, which is practically a geological epoch for a fourth grader. I waited

and waited, hoping that the probes would discover Martians. They didn’t

have to be Hollywood extras. I’d have been fine with Martian snakes or

skunks. Even a shrub or some bacteria would do, at least for the time being. While the Viking probes flew through space, my family moved from a

suburban house to a little farm in the country. Life now seemed to

constantly demand my attention. Snapping turtles lurked in ponds;

swallows darted in and out of the barn all day; cicadas whirred in the trees. I think now that this experience fooled me into thinking that life is hard to

miss. I came to believe the history of space exploration would be written in

short, quick headlines. MAN WALKS ON THE MOON. LIFE ON MARS. In July 1976, Viking 1 landed and sent its first pictures up to the orbiter, which relayed them in turn millions of miles to Earth, where JPL engineers

deciphered them. We saw the first pictures on the evening news: gray rocks

on a gray background. It was exhilarating and underwhelming at once. If I

lay down on my driveway and looked out at the bits of gravel, I could have seen the same thing. JPL held a live press conference where members of the Viking 1 team

watched the first images arrive. The astronomer Carl Sagan stared at a

nearby monitor, trying to make sense of them. In the months before the

launch of Viking 1, he had mused that Mars might be home to multicellular organisms that would be easy to photograph. Now he strained to see

anything at all. “There certainly are no features, to the best of my knowledge, in these

pictures which have to be due to life,” he said, his eyes still locked on the

monitor. “No obvious bushes, trees, or anybody else.”

The following day, Viking 1’s first color pictures arrived. They painted the land red and the sky pink. Looking out for miles across the landscape,

we saw no bushes, no trees, nobody else. Later Viking 1 put a shovel in the ground. It began analyzing the Martian dirt for signs of life. At the time, I was too young to understand what

exactly they were doing to it; as far as I could tell, it seemed like they

would cook it. Life being life, I assumed the tests would provide a clear yes

or no. The first tests were promising, but Horowitz warned the New York Times

not to read too much into them. “We have not discovered life on Mars—

not,” he said. And when Viking 1 looked in two samples of soil for carbon compounds produced by life, it came up empty. “Organically speaking, both

samples were very clean material,” said Klaus Biemann. Joshua Lederberg, the original exobiologist, was cosmically crestfallen. “We can no longer be confident that no matter where you look you will find

life,” he said. I believed with the faith of a child that more visits to Mars would soon

clear up the mystery. After all, Sagan and other scientists said Viking 1

should be the first step in a sustained search for life. But its disappointing

results drained the fuel out of exobiology’s rocket engines. NASA engineers

built more probes to land on Mars, but they were mostly designed to work

out the planet’s geology and atmosphere, not to search for hints of life. In the years after Viking 1, the closest thing to a search for life was an eavesdropping project. The Search for Extraterrestrial Intelligence, or SETI

for short, was a NASA program that would scan the sky for radio

communications from alien civilizations. JPL offered up its network of

radio telescopes as our interstellar ears. Despite hostility from Congress, NASA managed to scrape together enough funds to keep developing plans

for SETI through the 1980s. They even switched on their scan for a year

before Congress shut down the operation. “We shouldn’t be spending precious dollars to look for little green men

with misshapen heads,” said Silvio Conte, a Massachusetts congressman

who helped kill the project. Just as NASA was winding down SETI, one of their scientists made a

discovery in Houston that revived the world’s curiosity about little green

men, or at least little green microbes. The Johnson Space Center possessed

a collection of meteorites, and one day in 1993 a scientist named David

Mittlefehldt noticed something odd about one of them, a four-pound rock

called Allan Hills 84001.

It had been discovered back in 1984 by a team of

geologists snowmobiling across the Allan Hills range in Antarctica. The

meteorite was sitting in the middle of an ice field. It could not have eroded

from the underlying ground. There were no nearby mountains from which it

could have tumbled. It could only have come from the sky. After it was

transported to the Johnson Space Center, scientists there identified it as a

fragment of an asteroid. It sat in a nitrogen-filled cabinet for years, until

Mittlefehldt got suspicious. He ran tests on the rock that revealed it didn’t

have the chemical signature of an asteroid. Instead, it had come from Mars. Four billion years ago, the rock had formed on the red planet, where it

had remained until an asteroid crashed into Mars, catapulting debris into

space. The rock drifted for millions of years until Earth drew it into its

gravity well. Thirteen thousand years ago it fell to Antarctica. It rested in

the Allan Hills as the Ice Age glaciers retreated, farmers discovered

agriculture, cities rose, and rockets shot into space. When geologists finally discovered it, only eleven other Martian

meteorites had ever been found. Short of sending a geologist to Mars, Allan

Hills 84001 was one of the few opportunities for NASA to understand the

makeup of the planet. A postdoctoral researcher named Christopher

Romanek carefully inspected the rock and found blotches that suggested

water had once flowed into cracks. If Mars was as warm and wet as Earth

early in its history, perhaps life existed there, and perhaps life left behind

microbial fossils. Romanek joined a team of colleagues led by David McKay, and together

the scientists looked for signs of life in the rock. When they bombarded bits

of it with lasers, they liberated rings of carbon atoms that can form from decaying organic matter. A powerful scanning electron microscope revealed

wormlike shapes that looked like cells. When McKay asked his thirteen-

year-old daughter what a photograph of the worms looked like, she replied,

“Bacteria.” Kathie Thomas-Keprta then found crystals of magnetic minerals

in the rock. On Earth, those minerals are made by bacteria, which use them

as miniature compasses to help them navigate. Had the scientists found once-living bacteria that swam in Martian

oceans that dried up billions of years ago?

Did Allan Hills 84001 hold proof

of life?

Or had they been fooled by Eozoön on Mars?

NASA’s new definition of life didn’t provide much help. McKay’s team

couldn’t tell if the magnetic worms were self-sustained chemical systems. If

they ever had been alive, they would have stopped sustaining themselves

billions of years ago. As for evolution, that’s something that a

microbiologist can observe with a simple experiment moving slimy beads

from tube to tube. But the NASA scientists had no way of tracking

evolutionary change in their enigmatic structures. The researchers chose instead to consider the ways in which both

geology and biology can bring together atoms—either into lifeless minerals

or into living cells. Each feature of the stony worms, taken on its own,

could have formed without the presence of life. But, taken altogether, the

NASA scientists decided, the evidence swung in favor of primitive cells. When Daniel Goldin, the administrator of NASA, got wind of the study,

he worried that news of it would be a disaster. Congress was fresh off of

killing SETI, and a major vote on the future of NASA’s funding was

coming up. He called in the leaders of the project and interrogated them for

hours. In the end he decided their work was sound and let it go forward. The journal Science accepted their paper, but it leaked before publication. As giddy speculations spread like the flu, NASA rushed to put together a

press conference. Twenty years after Viking 1 failed to find life, even the hint of life 4

billion years ago on Mars was enough to earn some time on television news

and space on front pages. President Bill Clinton even saw fit to draw

attention to the discovery by issuing a statement at the White House. “If this

discovery is confirmed, it will surely be one of the most stunning insights

into our universe that science has ever uncovered,” he said. That prediction did not pan out. In the years after the paper was published, scientists found more evidence that lifeless chemistry could have

produced the lifelike shapes. Shock waves could create magnetic minerals

that looked a lot like the ones in Allan Hills 84001, for example. Twenty

years after the publication of the NASA paper, the journalist Charles Choi

asked a group of experts what they thought about the meteorite. Not one of

them was confident that the rock contained signs of life. Yet Allan Hills 84001 still mattered to the history of science. By making

an argument that it contained fossils of once-living things, the NASA

scientists focused attention on the question of life elsewhere in the universe. If Allan Hills 84001 was too ambiguous to prove life once existed on Mars,

perhaps what was needed was a return mission to the planet to better

understand its geology. Some researchers even pondered how they could

deliver more rock back from Mars. Instead of waiting for an asteroid to

blast it our way, a space probe could carefully deliver it home in pristine

shape. The debate over Allan Hills 84001 also had the good fortune of erupting

just as NASA was in the midst of turning its old exobiology program into

something far more ambitious. They called the new discipline astrobiology,

which they defined as “the study of the living universe.” To advance

astrobiology, NASA supported scientists like David Deamer as they studied

how life on Earth began. But they also supported research on the broad

sweep of the evolution that followed, as life flooded the planet with oxygen

and then produced animals, plants, and other multicellular creatures. Other

astrobiologists charted the extreme forms that life takes on Earth, which

might serve as analogs for alien life that could endure in extreme

environments. As for life on other planets, astrobiologists could now consider not just

worlds within our own solar system but planets beyond. In 1995, Swiss

researchers discovered that a sunlike star called 51 Pegasi had a tiny

wobble, the gravitational tug of an orbiting planet. Since then, astronomers

have discovered thousands of exoplanets of all sorts and sizes. Astrobiologists began to consider which of these exoplanets might be

habitable. All life as we know it needs liquid water to survive. If a planet

were too close to a hot sun, the water would boil off. Too far away, and it

would freeze solid. The more astrobiologists thought about habitability, the trickier the concept became. For one thing, a planet’s habitability could change over

time. In 2004, scientists at the NASA Jet Propulsion Laboratory landed a

pair of rovers on Mars. As they rambled around, they came across rocks that looked as if they had formed at the bottoms of lakes and rivers long

ago. If Mars wasn’t habitable today, it might have been in the past. By then the children who had watched Viking 1’s adventures were all

grown up, paying off mortgages, and raising children of our own. We had

other distractions from the heavens. Some of NASA’s satellites looked

down at our own planet and charted the jagged rise of its global average

temperature. Viking 1’s children could start to see the changes for ourselves: the skating ponds that stopped freezing in winter, the king tides rolling

through the Florida streets, the designer masks on sale for wildfire season. SETI managed to emerge, phoenixlike, from congressional flames,

funded by a new generation of technology tycoons. But year after year

passed without any signal rising above the interstellar noise of pulsars,

black holes, and leftover ripples of the Big Bang. Some researchers argued

that if life is abundant on exoplanets, then SETI should have been

unnecessary. Surely some intelligent aliens would have gotten in touch with

us by now, either to greet or to conquer. Instead, we were surrounded by

what’s come to be known as the Great Silence. —

By the time Laurie Barge got to the University of Southern California in

2004 to work on her PhD, she had narrowed down the scope of her curiosity

to planets. “In grad school, I was obsessed with Mars,” she told me. At the time, the rovers Spirit and Opportunity were ambling around the

planet. One of their stranger discoveries was blueberries—mysterious

miniature blue spheres embedded in the rocky surface of Mars. Some

geologists suggested the Martian blueberries had formed long ago when

liquid water flowed over carbonate rocks. Barge learned how to run

experiments with water and minerals to see what Martian chemistry might

be capable of. After earning her PhD, Barge got hired at JPL as a postdoctoral

researcher. She worked her way up to become a co-leader of the Origins

and Habitability Lab. Along the way she turned her attention and her skills

with chemistry beyond Mars, to consider the possibility of life on more distant worlds: the icy moons of Saturn and Jupiter. Galileo first spotted some of the moons of these giant planets, but it

wasn’t until the late 1970s that a series of JPL probes flew by them and sent

back intimate portraits. Some were cratered balls of rock. Others were

covered in ice. Those frozen worlds were so different from other members

of the solar system that some researchers began wondering if they had

conditions suitable for life. Barge and a number of other scientists have grown especially curious

about an Arizona-sized moon of Saturn called Enceladus. In 2005 the

Cassini probe flew past the south pole of the moon and spotted a vast plume of vapor rising from giant fractures in the ice. That surprise led the engineers at JPL to steer a new course for Cassini. The probe made its way back to Enceladus for a closer flyby, then back

again, returning twenty-three times in total. On each visit it gulped clouds

of vapor and analyzed their contents. The plume, the scientists discovered,

contains a mix of water, carbon dioxide, carbon monoxide, salt, benzene,

and an assortment of other organic compounds. That deep-space mist offered a vision of what lay below the ice. Scientists eventually concluded that its frozen shell extends down about

fifteen miles, serving as a roof for a salty ocean twenty miles thick. Even

though Enceladus is only 314 miles across, its ocean is much deeper than

ours. The deepest point in Earth’s oceans, a place called Challenger Deep, is

less than seven miles. Enceladus is 148,000 miles away from Saturn, but it takes the moon

only thirty-three hours to complete an orbit around the planet. The

gravitational force exerted by Saturn regularly stretches the core of

Enceladus, a waterlogged ball of sand and gravel. The cycle of flexing

creates enough friction to heat the core’s water to a boil. It rises up to the

ocean, reacting along the way with minerals and becoming a chemical-rich

soup. The chill of space keeps the skin of Enceladus’s ocean frozen. But

Saturn’s tides have broken the surface with crevices, out of which blast

plumes of vapor from the warm ocean below. Liquid water, heat, organic compounds—Enceladus has a lot of the

ingredients that seem to be essential for life. In the years since Cassini’s visit, astrobiologists like Barge have been contemplating what organisms

might lurk under the ice and how to find out if they’re there. One idea is to

go back to the south pole. If there are living things in the ocean of Enceladus, some of them might get shot into space in the plume. Some

researchers have tinkered with nanopore sequencers to see if they could

detect signs of life in the icy mist. The devices are small enough to fit

aboard a space probe, and the tests astronauts have run on them aboard the

International Space Station show that they can work in low gravity. On a

visit to Enceladus, a probe might concentrate DNA out of the plume and

run it through a nanopore sequencer in order to read its sequence. Life on another world might be based on DNA, or it could conceivably

use another genetic molecule. If life started on Earth based on RNA, there

would be no reason to rule out RNA-based life elsewhere in the universe. It

was also possible that alien life used an entirely different alphabet to spell

out its genetic information. Schrödinger’s aperiodic crystal may take many

forms that we can only barely imagine at this point. Yet, even in our

ignorance, we might be able to use a nanopore sequencer to detect this alien

version of life on a flight over Enceladus. If its genetic molecules are long

chains encoding instructions, the sequencer may be able to slurp them

through its pores and get a rough idea of their extraterrestrial scripts. If Barge had her way, though, NASA would not give up on Enceladus

after collecting some secondhand vapor. It would drop a submarine through

an ice canyon into the ocean and dive to the gravelly seafloor. Barge

wouldn’t simply want to search for life there; she would want to explore the

physical world that might have given rise to it—or might yet do so. Such a mission may never happen. It may only get the green light after

Barge has retired. Or she may get to play the part of Carl Sagan, looking in

perplexity at the pictures and data that a submarine sends back from

Enceladus. In the meantime Barge is content to try creating Enceladus in

miniature. She builds mimics of the moon in JPL’s Science Division

Building. On my visit, Barge gave me a beginner’s lesson in moon building. We

put on purple gloves, and then Barge handed me a vial of lime-colored

crystals made of iron chloride. At her direction I poured the crystals into a

clear tube of water laced with sodium silicate. “Put a lid on it and see what happens,” she said. I held the tube up at eye

level. Most of the crystals fell into a heap at the bottom. After a few

seconds I noticed one of them grow, stretching up like a bubble. “Oh, you’re getting a bulb—excellent!” Barge said. “That’s what I wanted you to see. That’s a good bulb—you got lucky.”

The bubble stopped growing when it got to the size of a pea. Now its top

began to bulge again, and a new bubble took shape. When that one stopped,

another grew atop it. The heap of crystals was turning into a crooked

column reaching up toward the top of the tube. I would have felt proud of my good bulb if I knew how I had managed

to make it. Instead, I asked Barge what I was seeing. “If you could zoom in, you would see the iron crystals are dissolving,”

Barge said. As the iron rose from the crystals, it immediately encountered

the silicate. The two substances combined and formed a porous membrane. The water trapped inside this bubble had a high pH, which caused the

surrounding water to rush in through the pores. The force of the flood

cracked the top of the bubble, setting the iron free to rise up farther, where it could extend the wall farther. I was reenacting an old experiment. Alchemists who mixed together

chemicals in this way described their creations as philosophical trees. It

turned out that many crystals could assemble into hollow towers in water,

and geochemists eventually discovered that Earth makes its own

philosophical trees. Where mineral-laced water rises from the seafloor or a

lake bed, it can build giant versions of the tower I had created in Barge’s

lab. Barge suspected that Enceladus grew its own philosophical trees in its

sunless ocean. “Basically, Enceladus at the seafloor has conditions that you could find

in Earth’s oceans,” said Barge, “which means that the stuff you see in our

oceans is possible. But in order to actually see a chimney, you’d have to go

under the ice. So that’s a problem.”

To get a sense of what might grow on Enceladus, Barge was building

her own chimneys, trying out different combinations of minerals and

conditions known to produce ones on Earth. Her efforts were far more

sophisticated than the little ferrous chloride bulb I made under her tutelage. In one corner of Barge’s lab, she was mimicking a 150-foot-tall tower

off the coast of Iceland, known as the Strytan Hydrothermal Field. She had

filled a fat syringe full of hot fluid laced with magnesium chloride that she

was steadily injecting into a sealed glass bottle full of imitation seawater. A white tuft the size and shape of a baby rabbit’s tail was growing inside. Barge was planning on growing it again without oxygen, to mimic the early Earth. She had no idea what it would look like then. When she used

other ingredients, she got black chimneys and others streaked in green and

orange stripes. Some formed hairy plumes, and others rose like little

mountains. Some turned out so strong that they stood on their own after she

drained the bottles. Others fell apart like sandcastles. “Every chimney has its own ways,” Barge said. Once Barge built her chimneys, she could run intimate experiments. She

could fit them with electrodes to trace the flow of current they generate—

enough in some cases to power a small LED light. In another experiment

Barge and her colleagues found that amino acids, the building blocks of

proteins, can form in the mineral-rich sediments that build up around

chimneys as they grow. If life exists on Enceladus, it needs a source of energy to survive. Almost a billion miles from the sun, trapped under a frozen ceiling, it

cannot count on light. But Barge’s research hints that it might not need it. The tidal forces acting on Enceladus ultimately produced stores of energy

that life could harvest in its oceans, from hydrogen atoms cast off in

chemical reactions to the electric currents generated in chimneys. “Life can live without the sun,” Barge said, “which is a big deal,

because then you can have life in an ice-covered ocean.”

I was struck by how Barge used the word life casually, without

explaining what she meant by it. “Is there a definition of life that is guiding your work?” I asked. “Not really, and I actually try not to have one,” Barge said. “I’ve been

really surprised and impressed with what organic chemistry can do when

you remove life from the system. And I don’t know how far it can go,

honestly.”

Barge’s reply reminded me of the words of Stéphane Leduc, a scientist

who produced dazzling philosophical trees in the early 1900s. They took on

the appearance of shells, mushrooms, and flowers. Leduc believed the way

his creations grew and organized themselves was not just an analogy to life. They captured some of the spirit of life. “Since we cannot distinguish the

line between life and the rest of nature’s phenomena, we should conclude

that this line does not exist,” Leduc wrote in 1910.

It’s conceivable that something we’d easily recognize as life exists on

Enceladus. In 2018, researchers at the University of Vienna found that a

microbe that lives in the deep ocean on Earth had a metabolism that might let it survive on Saturn’s moon. They re-created the ocean of Enceladus in

their lab and found that the microbe could grow. But it’s also conceivable

that something exists on Enceladus that has no counterpart on Earth today. Perhaps there are no microbes there. Perhaps its philosophical trees are

building up a rich bounty of chemicals that gets more complex each year. They might include lipids that form oily sheets and bubbles, chains of

amino acids, RNA-like threads. Enceladus might be an icy version of

Darwin’s warm little pond, lacking full-blown life that would otherwise

feast on these chemicals. It would be wrong to call the moon’s ocean a

prebiotic soup, because no one can look into the future and declare that in a

thousand years full-blown life will arise on Enceladus. For now, and

perhaps into the future, it may hover in the borderland, where words fail. “If we found, let’s say, cells that act like cells that we observe on Earth,

I’d say, ‘Yeah, that’s life,’” Barge told me. “If you found a lot of complex

organics that look kind of biological but you don’t really know how they

got there, I would say, ‘Maybe, but let’s wait and see.’ If you found

physical membranes full of organics, I would be very interested to know

more about them. There’s a lot of stuff in between. Understanding life in the

universe is about more than just finding life.”

FOUR BLUE DROPLETS

Three hundred and fifty miles to the north of John Butler Burke’s

beaker of radiobes, and over a century forward in time, runs a

strangely similar experiment. It unfolds near the river Clyde, in the

Joseph Black Building at the University of Glasgow. No scientist stands

over the lab bench boiling broth or purifying radium. The experiment runs

itself. It was set in motion by Lee Cronin, a chemist at the university. He and

his students built a robot that could mix chemicals on its own. The robot

does not walk around its lab, though. Its skeleton is a black frame anchored

atop a table. Bolted to one of the frame’s crosspieces is a syringe full of oil. It glides along the crosspiece until it hovers over a petri dish, into which it squirts four blue droplets. As the syringe slides away, the droplets start to

move. They glide away from each other, rushing to the sides of the dish. Slowing down, they bank away and reverse course. They head back toward

their fellow droplets, but they do not collide and merge. Instead, the

droplets veer away at the last minute and head off in different directions. Sometimes they twirl around each other like dancing partners and

sometimes they fall into formation, traveling in circles like a school of fish

in a tank. In 1944, two psychologists named Fritz Heider and Marianne Simmel

created a cartoon with triangles and rectangles they cut from a piece of

cardboard. The animation began with a large triangle trapped inside a four-

sided box. Heider and Simmel nudged the shapes frame by frame so that the

triangle moved around inside the box until one side swung open. It then left

the box and encountered a smaller triangle along with a circle. Heider and Simmel, who both taught at Smith College, asked thirty-four of their students to watch the short movie and then write down what

happened. Only one described the movie as a group of shapes moving

around a frame. The rest wrote things like this:

A man has planned to meet a girl and the girl comes along with another

man. The first man tells the second to go; the second tells the first, and he shakes his head. Then the two men have a fight, and the girl starts to go

into the room to get out of the way and hesitates and finally goes in. When Heider and Simmel asked another group of students to describe

the personalities of the shapes, most of them picked out the same words. The big triangle was a bully, the little circle was scared, the little triangle was defiant. And when the psychologists ran the movie backwards, their

students talked of different stories and different personalities. Heider and Simmel’s movie helped establish that our brains are keenly

tuned to signs of life. When we see things move in complex ways, we

recognize them as living things. We then quickly read their movements to

figure out what their intentions are. It is so automatic that we think we are

just seeing what’s plainly obvious. But because it’s automatic, we can’t help

but invest circles and triangles with life, too, even when two psychologists

are nudging them around a piece of glass to create an amateur movie. The darting droplets in Cronin’s lab have the same effect on the brain. They seem at turns giddy, hesitant, gregarious, solitary. The experience

would be strange enough if Cronin were secretly steering the droplets by

turning the knob on a magnetic field. But he has no control over them. His

robot prepared the droplets by mixing together four simple molecules. They

include octanoic acid, an ingredient in plastic. Another molecule, 1-

pentanol, is made in pineapples. When the robot mixes these four chemicals

together and squirts them into water, they seem to come to life, to become

what John Butler Burke imagined he saw when he dropped radium into a

tube of beef broth. These blue droplets are some of the strangest residents of life’s edge. Viruses may embroil scientists in debates about whether they are alive or

not, but at least viruses are made of genes and proteins. Even a liposome

with a few bits of RNA inside has some link to our own biology. Cronin’s

droplets are just crowded blobs of ordinary molecules. It’s hard to find

words for what the robot has created in its Glasgow lab. When I talked with Cronin about his droplets, the word I settled on was lifelike. And Cronin took that as a compliment. “I would say that lifelike came before life,” he said. —

Biology entered the twenty-first century triumphant. While scientists had

not yet found life beyond Earth, they had gotten to understand our own

planet’s inhabitants in luxurious detail. They knew that genes are encoded

in DNA, which they could now read quickly and cheaply. They could

reconstruct the genomes of Neanderthals who died 100,000 years ago. They

could pick out a single cell from a drop of blood and draw up a list of every

gene that was active inside it. They turned brains transparent and traced the

spidery connections joining thousands of neurons in a three-dimensional

network. They could find life deep underground, feeding on radioactivity. And yet all those new points of data, all those astonishing finds, did not

cohere into a clear definition of life that everyone could agree on. Living paradoxes such as viruses, mitochondria, and Amazon mollies

kept getting in the way. NASA’s definition of life, while memorable, didn’t

help NASA’s own scientists as they struggled to figure out if Allan Hills

84001 contained relics of life or not. Some critics found NASA’s definition

not just impractical but misleading. It narrowed the possibilities that life

might take. Consider its requirement that life be capable of Darwinian evolution, for

example. That’s a very particular kind of change over time. It occurs when

genes get precisely—but not perfectly—copied from generation to

generation. Individuals with certain combinations of genes fare better at

reproducing than others, and natural selection spreads those fitter versions. Over time, natural selection turns many mutations to produce new

adaptations. But can we be so sure that evolution isn’t unfolding somewhere else in

some other manner?

Is there no chance, for example, that a different kind of

biology might allow for the inheritance of acquired traits—often called

Lamarckian evolution?

What if heredity could flow not just between the

generations but between individuals in the same generation?

This kind of dissatisfaction led to an explosion of hundreds of new

definitions. Life is an expected, collectively self-organized property of catalytic polymers. Life is a metabolic network within a boundary. Life is a new quality brought upon an organic chemical

system by a dialectic change resulting from an increase in the

quantity of complexity of the system. This new quality is

characterized by the ability of temporal self-maintenance and

self-preservation. Life is the process of existence of open non-equilibrium

complete systems that are composed of carbon-based polymers

and are able to self-reproduce and evolve on the basis of template

synthesis of their polymer components. Life is a far from equilibrium self-maintaining chemical

system capable of processing, transforming and accumulating

information acquired from the environment. The existence of the dynamically ordered region of water

realizing a boson condensation of evanescent photons inside and

outside the cell can be regarded as the definition of life. Life is a monophyletic clade that originated with a last

universal common ancestor, and includes all its descendants. And a frank one:

Life is what the scientific establishment (probably after some

healthy disagreement) will accept as life. “It is commonly said,” the scientists Frances Westall and André Brack

wrote in 2018, “that there are as many definitions of life as there are people

trying to define it.”

As an observer of science and of scientists, I find this behavior strange. It is as if astronomers kept coming up with new ways to define stars. I once

asked Radu Popa, a microbiologist who started collecting definitions of life

in the early 2000s, what he thought of this state of affairs. “This is intolerable for any science,” he replied. “You can take a science

in which there are two or three definitions for one thing. But a science in

which the most important object has no definition?

That’s absolutely

unacceptable. How are we going to discuss it if you believe that the definition of life has something to do with DNA, and I think it has

something to do with dynamic systems?

We cannot make artificial life

because we cannot agree on what life is. We cannot find life on Mars

because we cannot agree what life represents.”

—

With scientists adrift in an ocean of definitions, philosophers rowed out to

offer lifelines. Some tried to soothe the debate, assuring the scientists they could learn

to live with the abundance. We have no need to zero in on the One True

Definition of Life, they argued, because working definitions are good

enough. NASA can come up with whatever definition helps them build the

best machine for searching for life on other planets and moons. Physicians

can use a different one to map the blurry boundary that sets life apart from

death. “Their value does not depend on consensus, but rather on their

impact on research,” the philosophers Leonardo Bich and Sara Green

argued. Other philosophers found this way of thinking—known as

operationalism—an intellectual cop-out. Defining life was hard, yes, but

that was no excuse not to try. “Operationalism may sometimes be

unavoidable in practice,” the philosopher Kelly Smith countered, “but it

simply cannot substitute for a proper definition of life.”

Smith and other foes of operationalism complain that such definitions

rely on what a group of people generally agree on. But the most important

research on life is at its frontier, where it will be hardest to come to an easy agreement. “Any experiment conducted without a clear idea of what it is

looking for ultimately settles nothing,” Smith declared. Smith argued that the best thing to do is to keep searching for a

definition of life that everyone can get behind, one that succeeds where

others have failed. But Edward Trifonov, a Russian-born geneticist,

wondered if a successful definition already exists but is lying hidden amidst

all the past attempts. In 2011, Trifonov reviewed 123 definitions of life. Each was different,

but the same words showed up again and again in many of them. Trifonov

analyzed the linguistic structure of the definitions and sorted them into

categories. Beneath their variations, Trifonov found an underlying core. He

concluded that all the definitions agreed on one thing: life is self-reproduction with variations. What NASA’s scientists had done in eleven words, Trifonov now did with three. His efforts did not settle matters. All of us—scientists included—keep a

personal list of things that we consider to be alive and not alive. If someone

puts forward a definition, we check our list to see where it draws that line. A number of scientists looked at Trifonov’s distilled definition and did not

like the line’s location. “A computer virus performs self-reproduction with

variations. It is not alive,” declared the biochemist Uwe Meierhenrich. Some philosophers have suggested that we need to think more carefully

about how we give a word like life its meaning. Instead of building

definitions first, we should start by thinking about the things we’re trying to define. We can let them speak for themselves. These philosophers are following in the tradition of Ludwig

Wittgenstein. In the 1940s, Wittgenstein argued that everyday conversations

are rife with concepts that are very hard to define. How, for example, would

you answer the question, “What are games?”

If you tried to answer with a list of necessary and sufficient

requirements for a game, you’d fail. Some games have winners and losers,

but others are open-ended. Some games use tokens, others cards, others

bowling balls. In some games, players get paid to play. In other games, they

pay to play, even going into debt in some cases. For all this confusion, however, we never get tripped up talking about

games. Toy stores are full of games for sale, and yet you never see children

staring at them in bafflement. Games are not a mystery, Wittgenstein

argued, because they share a kind of family resemblance. “If you look at

them you will not see something that is common to all,” he said, “but

similarities, relationships, and a whole series of them at that.”

A group of philosophers and scientists at Lund University in Sweden

wondered if the question “What is life?” might better be answered the way

Wittgenstein answered the question “What are games?” Rather than come

up with a rigid list of required traits, they might be able to find family

resemblances that could naturally join things together in a category we

could call Life. In 2019 they set out to find it by carrying out a survey of scientists and

other scholars. They put together a list of things including people, chickens,

Amazon mollies, bacteria, viruses, snowflakes, and the like. Next to each

entry the Lund team provided a set of terms commonly used to talk about living things, such as order, DNA, and metabolism. The participants in the study checked off all the terms that they believed

to apply to each thing. Snowflakes have order, for example, but they don’t

have a metabolism. A human red blood cell has a metabolism but it

contains no DNA. The Lund researchers used a statistical technique called cluster analysis

to look at the results and group the things together based on family

resemblances. We humans fell into a group with chickens, mice, and frogs

—in other words, animals with brains. Amazon mollies have brains, too,

but the cluster analysis put them in a separate group close to our own. Because they don’t reproduce by themselves, they’re set a little apart from

us. Further away, the scientists found a cluster made up of brainless things,

such as plants and free-living bacteria. In a third group was a cluster of red

blood cells and other cell-like things that can’t live on their own. Furthest away from us were things that are commonly not considered

alive. One cluster included viruses and prions, which are deformed proteins

that can force other proteins to take their shape. Another included

snowflakes, clay crystals, and other things that don’t replicate in a lifelike

way. The Lund researchers found that they could sort things pretty well into

the living and the nonliving without getting tied up in an argument over the

perfect definition of life. They propose that we can call something alive if it has a number of properties that are associated with being alive. It doesn’t

have to have all those properties, nor does it even need exactly the same set

found in any other living thing. Family resemblances are enough. —

One philosopher has taken a far more radical stand. Carol Cleland argues

that there’s no point in searching for a definition of life or even just a

convenient stand-in for one. It’s actually bad for science, she maintains,

because it keeps us from reaching a deeper understanding about what it

means to be alive. Cleland’s contempt for definitions is so profound that

some of her fellow philosophers have taken issue with her. Kelly Smith has

called Cleland’s ideas “dangerous.”

Cleland had a slow evolution into a firebrand. When she enrolled in the

University of California, Santa Barbara, she started off studying physics. “I

was a klutz in the lab, and my experiments never turned out right,” she later told an interviewer. From physics she turned to geology, and while she liked

the wild places that the research took her to, she didn’t like feeling isolated as a woman in the male-dominated field. She discovered philosophy in her

junior year and was soon grappling with deep questions about logic. After

graduating college and spending a year working as a software engineer, she

went to Brown University to earn a PhD in philosophy. In graduate school Cleland mulled space and time, cause and effect. Here’s a taste of her thinking from that period:

A dyadic relation R is supervenient upon a determinable non-

relational attribute P if and only if

1.

□ (∀ x,y) ~◇[R( x,y) and there are no determinate attributes

Pi and Pj of determinable kind P such that Pi( x) and Pj( y)]; 2.

□ (∀ x,y){ R( x,y) ⊃ there are determinate attributes Pi and Pj of determinable kind P such that Pi( x) and Pj( y) and □ (∀ x,y)

[( Pi( x) and Pj( y)) ⊃ R( x,y)]}.

When Cleland finished grad school, she moved on to subjects that were

easier to talk about at dinner parties. She worked at Stanford University for

a time, contemplating the logic of computer programs. She then became an

assistant professor at the University of Colorado, where she remained for

the rest of her career. In Boulder, Cleland turned her attention to the nature of science itself. She examined how some scientists, like physicists, could run experiments

over and over again, while others, like geologists, couldn’t replay millions

of years of history. It was while she was reflecting about these differences

that she learned about a Martian rock in Antarctica that was posing a

philosophical conundrum of its own. A lot of the arguments over Allan Hills 84001 had less to do with the

rock itself than with the right way to do science. Some researchers thought

the NASA team had done an admirable job of studying it, but others

thought it was ridiculous to conclude from their findings that the meteorite

might contain fossils. The planetary scientist Bruce Jakosky, one of

Cleland’s colleagues at the University of Colorado, decided to organize a

public discussion where the two sides could air their views. But he realized that judging Allan Hills 84001 required more than running some

experiments to measure magnetic minerals. It demanded thinking through

how we make scientific judgments. He asked Cleland to join the event, to

talk about Allan Hills 84001 as a philosopher. What started as a quick prep for a talk turned into a dive into the

philosophy of extraterrestrial life. Cleland concluded that the fight over

Allan Hills 84001 sprang from the divide between experimental and

historical sciences. The critics made the mistake of treating the meteorite

study as experimental science. It was absurd to expect McKay’s team to

replay history. They couldn’t fossilize microbes on Mars for 4 billion years

and see if they matched Allan Hills 84001.

They couldn’t hurl a thousand

asteroids at a thousand copies of Mars and see what came our way. Cleland concluded that the NASA team had carried out good historical

science, comparing explanations for the ones that explained their evidence

best. “The martian-life hypothesis is a very good candidate for being the

best explanation of the structural and chemical features of the martian

meteorite,” she wrote in 1997 in the Planetary Report. Cleland’s work on the meteorite impressed Jakosky so much that he

invited her in 1998 to join one of the teams at NASA’s newly created

Astrobiology Institute. In the years that followed, Cleland developed a

philosophical argument for what the science of astrobiology should look

like. She informed her ideas by spending time with scientists doing different

kinds of research that fit under the umbrella of astrobiology. She traveled

around the Australian outback with a paleontologist searching for clues to

how giant mammals went extinct 40,000 years ago. She went to Spain to

learn how geneticists sequence DNA. And she spent a lot of time at

scientific meetings, roaming from talk to talk. “I felt like a kid in a candy

store,” she once told me. But sometimes the scientists Cleland spent time with set off her

philosophical alarms. “Everybody was working with a definition of life,”

she recalled. NASA’s definition, only a few years old at that point, was

especially popular. As a philosopher, Cleland recognized that the scientists were making a

mistake. Their error didn’t have to do with determinate attributes or some

other fine philosophical point understood only by a few logicians. It was a

fundamental blunder that got in the way of the science itself. Cleland laid

out the nature of this mistake in a paper, and in 2001 she traveled to Washington, D. C., to deliver it at a meeting of the American Association for

the Advancement of Science. She stood up before an audience made up

mostly of scientists, and told them it was pointless to try to find a definition of life. “There was an explosion,” Cleland recalled. “Everyone was yelling at

me. It was really amazing. Everyone had their pet definitions and wanted to

air them. And here I told them the whole definition project was worthless.”

Fortunately, some people who heard Cleland talk thought she was onto

something. She began collaborating with astrobiologists to explore the

implications of her ideas. Over the course of two decades she published a

series of papers, culminating in a book, The Quest for a Universal Theory of Life. The trouble that scientists had with defining life had nothing to do with

the particulars of life’s hallmarks such as homeostasis or evolution. It had to do with the nature of definitions themselves—something that scientists

rarely stopped to consider. “Definitions,” Cleland wrote, “are not the proper

tools for answering the scientific question ‘what is life?’”

Definitions serve to organize our concepts. The definition of, say, a

bachelor is straightforward: an unmarried man. If you’re a man and you’re

unmarried, you are—by definition—a bachelor. Being a man is not enough

to make you a bachelor, nor is being unmarried. As for what it means to be

a man, well, that can get complicated. And marriage has its own

complexity. But we can define “bachelor” without getting bogged down in

those messy matters. The word simply links these concepts in a precise

way. And because definitions have such a narrow job to do, we can’t revise

them through scientific investigation. There is simply no way that we could

ever discover that we were wrong about the definition of a bachelor as

being an unmarried man. Life is different. It is not the sort of thing that can be defined simply by

linking together concepts. As a result, it’s futile to search for a laundry list of features that will turn out to be the real definition of life. “We don’t want to know what the word life means to us,” Cleland said. “We want to know what life is.” And if we want to satisfy our desire, Cleland argues, we need to give up our search for a definition. Before the modern age of chemistry, alchemists tried to define water in

the same way many biologists define life: by putting together a list of its

qualities. Water is a liquid, it’s clear, it’s a solvent that breaks up other substances, and so on. Far from clearing up the mystery of water, however,

this definition only got the alchemists into more trouble when they

discovered that not all water is alike. Some kinds of water dissolved

different substances and not others. So the alchemists gave different names

to those waters. But then they got into even more trouble with their

definitions when they watched water freeze or boil. Ice and vapor do not

share the properties of liquid water. The alchemists were forced to declare

that they were entirely different substances. The quandary was so deep that it left even Leonardo da Vinci confused:

And so [water] is sometimes sharp and sometimes strong,

sometimes acid and sometimes bitter, sometimes sweet and

sometimes thick or thin, sometimes it is seen bringing hurt or

pestilence, sometimes health-giving, sometimes poisonous. So

one would say that it suffers change into as many natures as are

the different places through which it passes. And as the mirror

changes with the colour of its object so it changes with the nature

of the place through which it passes: health-giving, noisome,

laxative, astringent, sulphurous, salt, incarnadined, mournful,

raging, angry, red, yellow, green, black, blue, greasy, fat, thin. Crafting a new definition of water wouldn’t have freed Leonardo from

his ignorance. The difficulty lay elsewhere: in just how little he and

everyone else in the Renaissance knew about chemistry. It took three centuries for a mature theory of chemistry to emerge, one

that explained that the universe is made up of atoms belonging to many

elements, which can bond together to form different molecules. Water, once

thought to be an element, turned out to be made of molecules that were a

combination of two elements: a pair of hydrogen atoms and an oxygen

atom. These molecules made up the liquid water in a lake as well as the

water in a block of ice or in a cloud of vapor. Chemists also determined that

strong water and noble water were not water at all, since they were made up

of different molecules. But even H2O is not the definition of water. A single molecule cannot

do the things that water does. When water freezes, for example, it expands

as many molecules of H2O spontaneously lock into a crystal lattice. “Talking about water being H2O tells you nothing about that,” said Cleland. Instead, knowing about H2O opens the way to learning more about the

nature of water. When it comes to life, Cleland argues, we are still alchemists. We use

our intuitions to decide which things are alive or not and make arbitrary

lists of the features they share. We paper over our ignorance with

definitions that never manage to capture the thing we’re trying to

understand. The best thing that scientists can do right now, Cleland argues,

is work toward a theory that explains life. I’ve met many scientists who agree with Cleland on this point. They do

not have a theory of life yet. They’re confident that someday a theory will

emerge, but for now they can only guess what it will be. It’s as if they’re

reading the shadows that the theory is casting back to us from the future. I

once asked a biophysicist to describe what the theory would sound like. “This is what life has to be,” he replied. —

Theories don’t pop into existence. They only emerge after scientists have

carried out lots of tedious measurements of the world. The architects of

modern chemistry ran countless experiments to determine the ratios that

made up compounds such as water. They discovered that the ratios were

simple, made up of integers. Water was made up of two parts hydrogen to

one part oxygen. Methane was four parts hydrogen to one part carbon. Out

of this painstaking accounting emerged the profound realization that these

compounds were molecules made out of atoms. Some scientists today believe that a theory of life can emerge only from

exacting measurements of living things. They are inventing tools to

precisely measure the timing by which genes turn on and off, the rate at

which cells grow, the interconnected links by which living things sense the

world and make decisions about what to do next. It may take decades

before these precise measurements reveal patterns that let scientists

recognize a full-blown theory. Other scientists are not so patient. They’ve created theories that explain

life based on what scientists have already discovered. Even a simple

precursor of a full-blown theory may be useful, they argue, if only to give scientists an idea of what they need to measure to build a better theory. The first theories of life took shape once molecular biologists worked

out some of the basic rules of DNA and protein in the mid-1900s. Only a

few scientists dared to build theories at first, and they worked mostly in

obscurity. It was an obscurity partly of their own making. They invented

personal languages to think through their ideas, which they didn’t put much

effort into helping other people understand. The story goes that two of these

theorists, Robert Rosen and Francisco Varela, met each other once at a

scientific meeting. They couldn’t think of a single thing to say to each other. For all their mutual incomprehension, life’s theorists worked in much

the same way. They developed compressed descriptions of life that could

account for the patterns seen in living things. To do so required looking

beyond the marvels and puzzles of pythons and slime molds, to see the

essential conditions for something to stay alive. It was as if they were

physicists encountering airplanes for the first time. If they wanted to figure

out how planes fly, it would have been a waste of time to study a modern

airliner. They’d get lost in video screens, call buttons, and snack carts. To

discover the things that matter to flight itself, they’d be better off going to Kitty Hawk and studying the Wright Flyer, with its simple wings of spruce and ash. In the 1960s a medical student named Stuart Kauffman joined this tiny

society. At the time, biologists were discovering some of the deep

connections between genes and proteins that make life possible. They were

finding that certain genes become active only if a certain protein lands on

the DNA nearby. They found some of the links in the long chains of

reactions that make metabolism possible. Kauffman wondered if some basic

principles lurk under the dizzying details of particular proteins in particular species. Kauffman developed a kind of algebra for the cell, which he used to

create hypothetical genes and proteins on a computer. In one experiment he

tried to build a simple metabolism. For food he created two molecules: Call

them A and B. An A and a B had a certain probability of joining together to

make a bigger molecule, AB. And AB in turn had a certain probability of

combining to make even bigger molecules. Add an extra B to make ABB;

combine two ABs to make ABAB. While Kauffman’s metabolism could

build up bigger molecules, he also programmed it so that it could break some of the bigger ones back down into fragments. Using different rules for building and breaking molecules, Kauffman

tested out a number of networks. Most of them failed to do much of

anything. They only managed to use the As and Bs he fed them to make

small molecules but never any big ones. But every now and then he found a

network that seemed to come to life. In these networks Kauffman

discovered that a few of the possible molecules became abundant. Once

those few molecules grew common, they stayed common as long as

Kauffman kept feeding the network. Kauffman discovered that the successful molecules had joined together

into loops of chemical reactions. One molecule would spur the growth of a

second, which spurred the growth of a third, and so on until the last

molecule in the loops, which helped the first. As each molecule became

more abundant, it could help build its partners in a self-sustaining cycle. Kauffman named these networks autocatalytic sets. The name refers to

catalysts, which are any sort of substance that speeds up a chemical reaction

between two other substances. Enzymes are just one kind of catalyst, as are

certain kinds of metals. In cars, for example, platinum acts as a catalyst to

break down exhaust in catalytic converters. Oil is the product of catalysts

deep under the ocean floor. Autocatalytic sets were different from ordinary

catalysts, Kauffman argued, because they catalyze each other. Even though he discovered them on a computer, Kauffman became

convinced that autocatalytic sets captured something essential about life. Living things sustain themselves with networks of real molecules, he

suggested. A theory of life based on autocatalytic sets would have no need

for a mystical vital force giving life to lifeless matter. When Kauffman built

random networks, the autocatalytic sets spontaneously took shape within

them. By the 1980s a number of other scientists picked up Kauffman’s ideas

about autocatalytic sets. His theory proved a useful guide to thinking about

life. But the only place where scientists could watch autocatalytic sets in

action was on a computer, where networks could feed on digital grub. Eventually, though, chemists succeeded in crafting autocatalytic sets out of

actual molecules rather than ones and zeros. One of the most complex

autocatalytic sets was built by Reza Ghadiri, a chemist at Scripps Research

Institute. He and his colleagues used small chains of amino acids called

peptides. They designed a set of peptides that could line up peptide fragments and bond them together. After mixing together dozens of

different kinds of peptides and fragments, the scientists stepped back and let

them mingle. An autocatalytic set spontaneously emerged, made of nine

peptides that could build each other out of the fragments, multiplying into

millions of new copies. Autocatalytic sets are not just mathematical dreams, it turns out. But that

doesn’t mean they’re common in nature. A mixture of chemicals is far more

likely to just reach an equilibrium and do nothing more. Why autocatalytic

sets only arise rarely remains an open question. They may require a supply

of molecules that are in just the right proportion. Otherwise they can’t build

up enough new molecules to sustain the right reactions. It’s also possible

that autocatalytic sets are rare because they are prone to collapsing. Only if

they have a resilient structure—perhaps loops within its loops—can they

withstand hard times when their ingredients run low. Scientists will have to settle questions such as these before autocatalytic

sets can become part of a mature theory of life. Such a theory might explain

how life sustains itself and perhaps even how it emerged in the first place. In 2019, Stuart Kauffman and two colleagues considered David Deamer’s

scenario in which life started as RNA-based protocells in drying ponds. They made some rough estimates of the variety of RNA molecules that

could have formed in such a pond. Kauffman and his colleagues concluded

that a single pool could very well have produced an autocatalytic set of

RNA molecules. Once this kind of self-sustaining chemistry got started, it

could then evolve into living things. Before there was life, in other words,

there may have been autocatalytic sets. —

Living things are special, but they’re not the only special things in the

universe. In 1911 the Dutch physicist Heike Kamerlingh Onnes discovered

that a mercury wire chilled down to close to absolute zero becomes very

special indeed. At ordinary temperatures a current loses some energy as it

travels down a metal wire—a property called resistance. When Onnes

cooled his mercury wire in a bath of liquid helium, the resistance gradually

dropped until it reached –452°F. Then, suddenly, its resistance fell to zero. If he fashioned a loop of metal, a current could travel around it indefinitely

without any loss at all. “Mercury has passed into a new state,” Onnes declared, “which on account of its extraordinary electrical properties may be called the

superconductive state.”

Onnes later found that other metals, like tin and lead, could also enter

this new state when they got close to absolute zero. Certain mixtures of

metals could become superconductive at warmer temperatures. Physicists

searched for superconductivity in all its forms, eager to find materials to

build fundamentally new kinds of technology. But their research remained

little more than a game of trial and error for decades. Ordinary physics

seemed unable to explain it, and there was no rhyme or reason to why some

substances were superconductive and not others. Albert Einstein tried to explain superconductivity with an elegant

theory, which turned out to be wrong. So did Niels Bohr, Richard Feynman,

and other leading figures in twentieth-century physics. Finally, in the 1950s,

John Bardeen, Leon N. Cooper, and Robert Schrieffer came up with a

theory that made sense of the senseless. Resistance is the result of electrons

hopping around in a disorderly way, sending off the energy of a current in

all directions. Bardeen, Cooper, and Schrieffer argued that some of the

electrons in superconducting material form pairs that travel along the same

path. Their order counteracts the chaos in a conducting metal, wiping away

all resistance to a current. The new theory of superconductivity explained

why some metals entered the strange state and not others, and it helped

bring this special state of matter closer to our ordinary lives—in magnets

that support high-speed trains and in microprocessors that may become the

brains of a new generation of computers. A theory of life may end up looking a lot like the theory of

superconductivity. It may explain life as a particular configuration of matter

that gets a special quality from the physics of the universe. Lee Cronin has

been working with Kate Adamala and Sara Walker, a physicist at Arizona

State University, on an explanation of life as a special way of putting things

together. They call it assembly theory. You can think of the history of the universe as 13.7 billion years of

things being put together. After the Big Bang, subatomic particles formed

hydrogen atoms; helium atoms came about as hydrogen atoms joined

together. Stars were assembled from hydrogen and helium, and in their

stellar forges, new elements formed. Atoms assembled into molecules;

molecules became grains. Planets and moons were built from them. On Earth snowflakes formed in the sky. Underground, minerals took shape. Once life emerged, it made things of its own. Organisms began making

sugars, proteins, and cells. They grew tusks and flowers. Animals

constructed beehives, beaver lodges, double-hulled canoes, and space

probes. Cronin, Adamala, and Walker worked with colleagues on an

objective way to compare how things get assembled, whether life is

involved or not. The assembly of things happens in steps. A simple molecule may need

just a single step to form from atoms. But it takes more steps to add extra

atoms or to join two molecules together. Cronin and his colleagues figured

out a way to estimate the number of steps it takes to make a molecule: by

smashing it. Think of molecules as Lego constructions that you take apart at

random. If someone gives you a hundred constructions that are made of just

two Lego blocks snapped together, you will be able to break them only into

the same two blocks over and over again. But now imagine someone gives

you a Lego Hogwarts Castle, complete with turrets, buttresses, and

archways. It can be split into many different fragments. Cronin and his

colleagues found that the number of fragments a molecule can be broken

down to is a good guide to the number of steps it takes to build it in the first place. Cronin and his colleagues carried out a survey by smashing, breaking

apart over a hundred different materials. They smashed quartz and

limestone. They broke apart Taxol, a molecule made by yew trees that turns

out to be a powerful drug for cancer. They followed Stanley Miller’s recipe

and made a prebiotic soup and then broke its molecules back down. They

broke down beer and granite. All the materials that were not made by living things needed under

fifteen steps to assemble, the researchers determined. Even when they

experimented with a tiny sample of the Murchison meteorite—packed with

lipids, amino acids, and other building blocks of life—they never found a

molecule that needed fifteen steps. “Although there’s a billion molecules in

it, it’s all boring,” Cronin told me. Living things, by contrast, were not boring. Although they assembled

some simple molecules, they also made exquisitely complex ones, some of

which needed far more than fifteen steps. It’s possible assembly theory has revealed a line cutting through life’s borderland. Ordinary chemistry may not be able to assemble a material that

needs fifteen steps or more. Any one reaction may take place, given enough

time. But the odds may be vanishingly small that a series of certain

reactions happens in the right order—and happens in that order again and

again. Life, on the other hand, is a state of matter that can spontaneously

make things with a lot of assembly steps. Adamala, Cronin, and Walker have proposed that what allows life to do

this is the special way in which information flows through it. In life,

information is able to control matter. Genes and other molecular structures

can store information, copy it into their offspring, and then channel that

information through networks of proteins in order to do precise tasks—such

as making things in many steps of assembly. Assembly theory might offer a way to look for life on other planets. It

might be possible to detect life on planets orbiting other stars without even

visiting them. Astronomers could use telescopes to scan the atmospheres of

exoplanets for molecules. If they detect a molecule with a high assembly

number in abundance, they can be confident that it didn’t come into being

through random chemistry. Only information could guide its production. But Cronin doesn’t have to wait for a billion-dollar probe to get to the

other side of the solar system or for a new space telescope to go up into

geosynchronous orbit. “I can now go look for life-forms in my lab,” he said. “Forget whether life is like a flame, forget whether it has a metabolism. Does the object have enough features to say that it can’t have formed

randomly?

And do you find it in abundance?

If yes, then it’s alive. If no,

you can’t tell whether it was alive or not.”

Cronin chose droplets as his raw material for making life. Compared to

David Deamer’s liposomes, they’re even simpler—just blobs of oil. They

crowd together thanks to the difficulty they have bonding with water

molecules. Mixing other chemicals into the oil can make droplets do

intriguing things. Alcohol, for example, is attracted to both oil molecules

and water molecules. When Cronin mixes it into a droplet, it will leak out

slowly. As each alcohol molecule leaves, it gives the droplet a little push,

moving it in the opposite direction. If enough alcohol flows out, the droplet

will look as if it’s swimming. Different mixtures of chemicals will make

droplets behave differently. Even a slight twist to a recipe can lead to

unexpected behaviors. To explore the universe of possibilities, Cronin realized that he and his team couldn’t just carry out experiments by hand. They had to build a robot

to run them. Cronin christened it the DropFactory. The DropFactory began

running thousands of experiments in a row. To make droplets that could

race, it started by mixing four oils together and pouring droplets into petri

dishes. It then moved the dishes under a video camera to film them, washed

out the dishes, and then mixed the oils into a new combination. Some

recipes made droplets that didn’t budge, and others made them move faster. The DropFactory used these results to make a model of the chemistry in the

droplets, which it updated with each new experiment. At the end of this

robotic evolution, the droplets were racing like puppies set loose in a dog

run. The DropFactory can learn to make droplets that do other things. It has

come up with a recipe that made the droplets wobble as if Glasgow were

the epicenter of an earthquake. In another trial, the droplets gained the

ability to split in two, producing a nest of little offspring. Cronin’s team

programmed the robot with curiosity, so that it would notice odd new

behaviors on its own and make them stronger. The robot discovered a recipe

for droplets that dawdled at room temperature and then took off in a sprint

when the air got only a few degrees warmer. These lifelike droplets, these skittering blobs of active matter, are not

life. But they could be a dry run for making it. Into these droplets Cronin

plans to introduce more chemicals—sugars, pyrite, silicates—that another

robot in his lab is busy creating through its own rounds of chemical

reactions. Cronin hopes that his robots will ultimately create droplets that are

capable of behaving in complex ways and can also carry out complex

chemistry to make new compounds. It’s possible that this prebiotic

evolution will favor chemicals that can store information and pass it along

when a single droplet splits in two. Cronin hopes the droplets will mimic

Kauffman’s autocatalytic sets, cooperating to carry out complex chemistry

that would be too much for one droplet to handle on its own. Assembly theory could potentially let Cronin and his colleagues make

sense of these changes in the droplets. If they start assembling chemicals

that couldn’t be produced without the information-guided processes, then

the scientists can declare the droplets alive. Cronin wouldn’t be surprised if

the chemistry that brings them to life has nothing to do with life as we know

it, based on DNA or even RNA. “It’s like saying gravity only works on this kind of rock,” he said. Cronin knows that a lot of scientists are skeptical that a robot can make

life from simple chemicals. Surely, it must have taken a long time for an

entire planet to get the job done. But Cronin thinks that has to be wrong. Primordial molecules were too fragile to sit around for very long. If life

formed, it had to form fast. “Just the back-of-an-envelope calculation tells me ten thousand hours,”

Cronin said. “I’m pretty sure we will crack the origin-of-life problem in the

next few years. But then everyone will go, ‘Oh, that was easy.’”

Cronin’s confidence was at once so sincere and so strange that I began

planning a trip to Glasgow in a decade to visit his lab—either to admire his

flock of living droplets, or to observe what happens when radiobes get the

better of a scientist once more. “I’m either mad,” Cronin declared, “or completely right.”