The Seeds of Life

by Edward Dolnick

  And the notion of an endless sequence of preformed miniatures veered near a crucial insight. Within every sperm and egg, we now know, is a double helix of DNA that serves as blueprint (actually, half the blueprint) for any child the parents conceive. In time that child may grow up and pass along her own DNA to a child, who may someday pass along her DNA, and so on. A long line of messages in cells is not the same as a sequence of dolls within dolls, though clearly there is some resemblance. The preformationists had thought too literally, but they had thought deeply.

  These near misses might make us think of the blind men and the elephant, but that is the wrong analogy. The blind men’s problem was that they had each grabbed a different part of the elephant and taken it for the whole beast. Here those who believed in preformation and those who favored epigenesis had hold of the same thing—the observation that living creatures somehow “know” how to grow—but both sides insisted that only their opinion was valid. Rather than an elephant, we might think of one of those drawings that show simultaneously a vase and faces in profile. “It’s a vase,” shouted the preformationists, and “No, it’s two faces,” their rivals shouted back.

  The shouting and skirmishing had gone on for almost a century, but a breakthrough was near at hand.

  NO ONE COULD HAVE FORESEEN THAT PROGRESS WOULD COME not from a new insight or a shocking discovery, but from the revival of an ancient and deeply mistaken belief. This irrepressible notion was dubbed “spontaneous generation”: the idea was that life could rise up, on its own, from a heap of rags or a lump of rotten meat. Deep inside a neglected bit of filth, flies or fleas or toads might stir themselves to creeping, hopping life.

  The idea had no merit. But it had appeared in so many guises through the millennia, after having been knocked down and left for dead time after time, that it seemed to be itself an example of how life could arise from nonlife. Now Buffon and Maupertuis had revived the old belief once again. This time, though, an array of great thinkers and experimenters felt moved to shoot down the spontaneous generation claims once and for all. And it was those efforts to prove where life did not come from that would, in the end, finally point the way to where it did come from.

  Foremost among these talented skeptics was an Italian priest and scientist with a reputation for designing original, but deeply odd, experiments. Now he would outdo himself.

  PART FOUR

  THE CLOCKWORK TOPPLES AND A NEW THEORY RISES

  It takes a thousand men to invent a telegraph, or a steam engine, or a phonograph, or a telephone or any other important thing—and the last man gets the credit and we forget the others.

  —MARK TWAIN

  NINETEEN

  FROGS IN SILK PANTS

  EVEN IN AN AGE OF ALL-AROUNDERS RATHER THAN SPECIALISTS, Lazzaro Spallanzani’s versatility set him apart. He was a mountain climber, a bold traveler who ranged as far afield as a sultan’s harem in Istanbul, a mathematician, a Greek scholar (his first publication was on The Iliad), and, most important, by one historian’s reckoning, “undoubtedly one of the greatest experimental biologists of all time.”

  It had seemed, early on, that his career would be more routine. In 1749 he had begun studying law at the University of Bologna, in line with his father’s wishes. Here he came under the sway of a remarkable woman who happened to be a cousin on his father’s side. Laura Bassi was a mathematician and a physicist, already famous as the first woman in Europe to hold a university professorship. Bassi recruited her young cousin to science (and convinced Spallanzani’s father to accept the decision).

  Once launched, Spallanzani never slowed down. He was a man of serial obsessions, and he poked his beaky nose and his dark eyes into everything. The living world beckoned him—How do bats navigate? How do deep-sea fish glow?—and so did the inanimate world—Why do thunderclouds form? What causes earthquakes? On the trail of a mystery, he made Inspector Javert seem like a slacker. Spallanzani once clambered up an erupting volcano, so close to the flowing lava that the fumes knocked him unconscious. (He wanted to know how fast lava travels.) Determined to learn how bats find their way, he methodically worked through each sense in turn, outfitting his poor captive bats with blinders, then with earmuffs, with nose plugs, and so on, to see if they could fly through a room bristling with obstacles.

  To see if snails could regrow their heads, he decapitated seven hundred of them. To see why stones skip across water, he flung thousands upon thousands and wrote a detailed mathematical analysis of how they bounce. To study digestion, he hid scraps of meat in linen bags, lowered them down the throats of turkeys and owls and frogs and newts and snakes and cats and dogs (and, with “some apprehension,” one human, Spallanzani himself), and then hauled them up again to have a look. To see if the body’s heat made food break down faster, he crammed bits of meat and crumbs of bread into glass tubes and kept the capsules tucked under his arms for two days. So formidable were his skills as an experimenter that Spallanzani’s peers dubbed him the “Magnifico.”

  His experiments with bats illustrate his persistence, his openness to even the unlikeliest possibilities, and his ingenuity. (They reveal, too, a casual willingness to inflict pain on animals that was a standard feature of his era.)* Spallanzani’s curiosity had been roused in the first place by watching a tame owl. The bird could find its way perfectly by the light of a single candle, but not in the dark. Bats could fly in the dead of night, though, and in the blackest caves. Could it be that bats had better night-vision than owls?

  Spallanzani caught three bats in a cave and brought them indoors, into a small room that he had made into a kind of obstacle course. Strings dangled from the ceiling, wide enough apart for a bat with outstretched wings to fly through. Strips of metal foil or tiny bells hung on each string and sounded if a bat brushed by. On a moonless night, Spallanzani, his brother Niccolo, and a cousin sat silently in the gloom. Twenty minutes of candlelight, then twenty minutes in the pitch-black, the cycle repeated over and over, the only sounds the occasional tinkling of a bell as a bat passed near a string and the beating of wings coming nearer, then receding, then returning.

  To test whether vision was crucial, Spallanzani blocked his bats’ eyes with small, opaque discs. Blind as bats, they nonetheless flew with their customary grace. Next, taste. He cut out their tongues. No problem (for Spallanzani, at any rate). Onto touch. Perhaps bats could feel tiny air currents bouncing against their bodies from obstacles as they flew by? Spallanzani painted his bats with shellac. Despite what he called a “light varnishing” (and then a second coat, and even a third), they flew perfectly. One unfortunate bat even navigated its way despite a messy coating of paste and flour. Now, smell. Spallanzani blocked the bats’ nostrils. Away they flew.

  Finally, sound. Spallanzani made tiny cones out of brass, shaped like cheerleaders’ megaphones, and wriggled them into the bats’ ears. Sporting their strange headgear, the bats flew along contentedly. (This first test was just a precaution. It might have been that the cones were so cumbersome that the bats couldn’t tolerate them.) Then came the key move: Spallanzani blocked the cones with tar, so that the bats couldn’t hear. This time the bats collided with one another, smacked into obstacles, and even crashed into the ground.

  These were astonishing experiments, and they won Spallanzani scorn as well as praise. “Since bats see with their ears,” another scientist mocked, “do they hear with their eyes?” Spallanzani had not sorted out the full story.* The great mystery he left unraveled was that bats could navigate by hearing even though they made no sound. What could they be listening to? Even so, Spallanzani had made giant headway on an ancient riddle. He had done it by devising experiments that few others would have thought of—bats in batter? bats wearing ear cones?—and by taking his findings seriously, no matter how unlikely they might be.

  Those were the very traits that would bring him nearer to the truth than anyone had come before, when he took on biology’s oldest, deepest riddle. It would be Lazzaro Spallanzani who took the
next giant step toward solving the mystery of fertilization. On history’s calendar, all this took place only yesterday. Spallanzani was a contemporary of George Washington and Thomas Jefferson. (In 1776, when Jefferson sat in Philadelphia writing the Declaration of Independence, Spallanzani was at work in Pavia, Italy, writing New Observations and Experiments Concerning the Spermatic Animalcules.)

  In the era of the founding fathers, no one in the world knew how fatherhood worked.

  SPALLANZANI CAME TO THE STUDY OF SPERM AND EGGS BY WAY OF another of the age’s great preoccupations. This was the doctrine of spontaneous generation, which had been left for dead in the late 1600s but revived by Buffon and others in the mid-1700s. Perhaps that resurrection could have been foreseen, for a long, long roster of thinkers through the ages had argued vehemently that, in the right circumstances, living creatures might emerge from lifeless odds and ends. Deep into the 1600s, even the most eminent scientists took for granted that life—especially life in its nastiest forms—might climb out of nearly any dark corner. The most admired of all scientists, Isaac Newton, believed in spontaneous generation. So did the famously skeptical philosopher René Descartes. “So little is necessary to make an animal,” Descartes remarked, that it was no wonder that rodents, worms, and bugs arose spontaneously from dead flesh.

  The more lowly or despised the animal, the more likely that it popped into existence on its own. It was well known, for instance, that spiders emerged from rotting mushrooms. Both William Harvey and Robert Hooke reported, after careful investigation, that insects arose from dying plants. At a meeting of the Royal Society on June 24, 1663, Hooke was given the task of examining “viper-powder”—dried, ground-up snake—under a microscope to test eyewitness reports that “a box of viper-powder, which being opened and found extremely stinking, had [a myriad of] little moving creatures in it, like mites of cheese.”

  A year later, the Society still had not settled the question. Sir Robert Moray passed along an eyewitness account of “a pot with viper-powder in it, brought from Venice,” and kept tightly sealed. Six months later, it was “full of little live insects.” Another member of the Royal Society chimed in: “He had known a chemist who used to perfume his viper-powder with myrrh, to preserve it from breeding worms.”

  What scientists believed they had learned from the close observation of nature, ordinary people took for granted. No prudent person, warned a seventeenth-century English physician, should consume creatures that originated in “the excrements of the earth, the slime and scum of the water, the superfluity of the woods, and the putrefaction of the sea: to wit… frogs, snails, mushrooms, and oysters.” The English, who had long derided the French and Italians for their dining habits, now claimed that they had sound medical reasons for their disdain.

  Shakespeare reflected the same folk beliefs. Crocodiles creep forth from “Nilus’s slime,” he remarked in Antony and Cleopatra, and in Hamlet he commented matter-of-factly that “the sun breeds maggots in a dead dog.” This was little more than common sense. A vast gulf separated majestic creatures like lions and tigers and, of course, humans, from vermin and other lowly beasts. It would be no surprise if those debased forms of life originated in some way that matched their position in life’s cellar.

  Religion, it had long been assumed, taught the same moral. Noah did not bother to bring pairs of mice and flies and similar creatures aboard the ark, theologians had explained ever since Saint Augustine, because there was no need. Those ignoble animals would turn up on their own, spontaneously.

  Finally, in 1667, the debate had shifted. Francesco Redi, personal physician to the Medicis in Florence, had carried out a series of experiments on the origin of life that are still hailed today for their simple, clear design. Redi was a dazzler. He was elegantly slim (one admirer described him as “the picture of hunger”), effortlessly articulate, and a brilliant scientist as well as a witty and charming courtier. He wrote poetry (his ode to Tuscany’s wines is still read); he described his scientific ventures in chatty, engaging prose; he flattered with so light a touch that the praise seemed sincere rather than unctuous. Enthralled by Redi’s research and entranced by his manner, Archduke Ferdinand II indulged his scientific pet in all his far-ranging ventures.

  Redi had risen to fame by sorting out, in response to a request from the archduke, how venomous snakes do their damage. Snakes were a common hazard in Tuscany, but no one knew how they manufactured their venom or how it worked. Redi demonstrated that snakes killed their victims by injection. Venom did not work like poison; a person who swallowed venom would walk away unharmed. (Redi, who understood the Medici fondness for showmanship, enlisted the services of the royal snake catcher to show what he had learned. That intrepid fellow poured a spoonful of venom into a glass of wine and drank it, Redi noted, “as though it were some pearly julep.” Then he licked the spoon.)

  When Redi turned his attention to spontaneous generation, his findings were more important, but the show was not as engaging. Instead of an imperturbable snake catcher wrapped in writhing serpents, Redi’s props were festering hunks of meat. Redi set out boxes of meat scraps in the sun, some of the boxes covered with a gauze mesh and others identically prepared but open to the air. Within a few days, he found flies inside the open boxes and worms “creeping up, all soft and slimy,” but no maggots or flies in the covered boxes.

  Life came from life! Flies did not arise from dead flesh but from eggs laid by other flies. Redi’s experiments rank as landmarks in the history of science. Still, his findings did not mark the end of the controversy over spontaneous generation, because its proponents could always come up with new candidate creatures. Okay, not flies, but what about…?

  The trend through the years was that the proposed organisms grew steadily smaller and less imposing. In the mid-1600s, well-regarded scientists had published recipes for producing mice. (The key ingredients were a sweat-soaked shirt and a few grains of wheat. Presumably it was the wheat that confused matters, by luring mice that had been created in the usual fashion.) Later in the century, the focus shifted to insects and flies. Later still, when the microscope came along, the discovery of countless new forms of life revived the old debate.

  IN THE MID-1700S, SPONTANEOUS GENERATION ROSE TO PROMINENCE yet again. Two men in particular, our old friend the Count de Buffon and an English priest-turned-scientist named John Turberville Needham, fueled the rise. The two scientists collaborated, Buffon sticking mostly to writing and Needham to the microscope, both of them convinced that nature possessed a “vegetative force” that could bring matter to life. In a series of famous experiments in 1748, Needham boiled mutton broth and then poured the steaming liquid into glass flasks and sealed them. If any microorganisms appeared, Needham announced, that would prove that life could arise spontaneously. Days later, he found the broth teeming with microorganisms. Life had appeared, out of nowhere, in a sterile soup!

  Spallanzani took up that challenge. In a series of experiments akin to Redi’s, Spallanzani boiled broth and poured some into flasks that sat open to the air; he poured identical batches of broth into identical flasks, and sealed the second set of flasks. Then he sat back to watch for signs of life.

  The key was how Spallanzani’s approach differed from Needham’s. Instead of boiling his samples for ten minutes, he boiled them for an hour. Instead of sealing his flasks with corks, he melted the necks over a flame, which made them airtight.* In every case, broth exposed to the air (or in flasks sealed only with a cork) quickly swam with microorganisms. Broth in sealed flasks remained lifeless.

  Spallanzani, an even-tempered man who permitted himself an occasional sharp-edged remark, proclaimed victory. The newfangled “vegetative force” was nothing but the old, foolish doctrine of spontaneous generation in disguise. This was old wine, gone bad, in a new bottle. Satisfied that he had dealt a death blow to spontaneous generation, Spallanzani now turned to a closely related but even more ambitious question. If life arises only from life, exactly how does tha
t work? In particular, Spallanzani wanted to know, what does semen have to do with fertilization?

  THIS WAS STILL A QUESTION MIRED IN DARKNESS. THE LEADING view, that semen worked its influence by “aura” or “emanation,” dated back more than a century to William Harvey (and, in a different form, all the way back to Aristotle). The rival view focused on the “animalcules” Leeuwenhoek had found swimming by the millions in semen, some eighty years before. Those tiny swimmers were the secret to life. Somehow they contained a miniature of the not-yet-developed organism. Ejaculated by the male, they swam into the female, where one of the millions of racers burrowed into the uterus and started to grow. That was Leeuwenhoek’s view (he made no allowance for the egg, as we have seen). But, put off by the incredible number of sperm cells and their wormy appearance, nearly everyone else disagreed.

  Spallanzani’s first inspiration was to use frogs as his experimental subjects, because they shed their eggs outside the body, which brought the fertilization process out into the open, where it was easy to see. This was not as straightforward as it sounds. The great Swedish naturalist Carl Linnaeus had proclaimed, with characteristic certainty, that “in Nature, in no case, in any living body, does fecundation or impregnation of the egg take place outside the body of the mother.”

  To contradict so eminent a figure took daring. Linnaeus was consumed with two subjects above all. The first was finding order within the endless variety of the natural world. The second was his own magnificence. “God creates, Linnaeus arranges,” he boasted. He once commissioned an engraving of Apollo for a botanical work and instructed the artist to depict the Greek god with Linnaeus’s face. But Spallanzani, an odd mix of swashbuckling adventurer and detail-driven perfectionist, was temperamentally not much inclined to defer to even the most august authority.