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 radiumlaced 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.