Aphids are small, ordinary-looking insects whose sex lives could not be further from ordinary. Réaumur was one of the great authorities on insects, renowned for the breadth of his knowledge and the reliability of his observations. For several years he had been at work on what would become a six-volume Natural History of Insects. But in all his research, he noted, he had never seen aphids mate, and he had never even seen a male aphid. Yet aphids abounded. How could that be?
Bonnet set out to find the answer. His strategy could hardly have been simpler. On May 20, 1740, he took a single newborn aphid—female, of course—and put it on a branch cut from a bush. Then he put the branch inside a glass jar and sat down to watch. Alone in her glass prison, Bonnet’s aphid went on her buggie way. Bonnet kept watch “day by day and hour by hour,” he wrote, with a magnifying glass always at his eye. No one tampered with the jar. No hidden aphids sneaked their way out of the branch or crept under the glass. Still Bonnet watched.
On June 1, after eleven days in solitary confinement, the aphid gave birth. Bonnet kept watching. (He would stare through his microscope so intently, in such a variety of experiments, that by the age of twenty he had ruined his eyes. He never recovered his vision.) Over the next three weeks, more new aphids appeared. By June 24, the tally had reached ninety-five. There had been no males and no mating, but where there had originally been one lone aphid, now there were nearly one hundred.
In July 1740 Réaumur stood in front of the French Academy of Sciences and read aloud a letter from Bonnet describing his work. Bonnet’s reputation was made. The young naturalist, just turned twenty, had witnessed a virgin birth.
For scientists, this was shocking, especially since the hydra news and the aphid news arrived at nearly the same moment. The point was not that these tiny creatures were important in themselves; the point was that they had upended time-honored laws of nature. These were impossible creatures, and yet there they were, in countless ordinary ponds and bushes, carrying on in their paradoxical ways. (The modern-day counterpart would be something on the lines of the discovery of a butterfly that lived forever.) Everyone knew that God had decreed fixed and eternal rules that governed all life on earth. With Trembley’s indestructible creatures and Bonnet’s virgin births, God’s laws had been not dodged but shredded.
THE FIRST RESPONSE WAS TO TRY TO EXPLAIN AWAY THESE DISCOVERIES. Perhaps, once the initial shock had passed, they were not so strange, after all? Someone now recalled that decades before, back in 1696, Leeuwenhoek and another Dutch scientist named Steven Blanckaert had both written about aphids. Leeuwenhoek had described them carefully, although in an odd context that might have distracted his readers.
At the time, Leeuwenhoek had been preoccupied with the mystery of where spermatozoa, which he regarded as animals, came from. In the course of another project altogether—Leeuwenhoek was trying to sort out why the leaves on the cherry trees in his garden had curled up and died—he looked closely at aphids he had found on his trees and currant bushes. Here, where he had not even been looking for it, was the key to the spermatozoa riddle! Aphids began as lone, tiny dots and grew into swarms of full-fledged creatures, with no mating anywhere along the way. Perhaps spermatozoa did the same!
Spermatozoa, Leeuwenhoek proposed, arose out of some mysterious “essential stuff” in the testicles. Even to Leeuwenhoek, that seemed dismayingly vague. Still, this was a remarkable display of intellectual agility. To rescue his doctrine that, when it came to sex, only males counted, Leeuwenhoek had devised a theory in which males, and mating, played no role at all.
More study of his aphids revealed further surprises. Leeuwenhoek dissected an aphid and discovered within it a host of miniature, unborn aphids! He had expected to find eggs within the parent’s body, but to his astonishment he found instead “animals the shape of which resembled that of their Father or Mother as closely as two drops of water resemble each other.” Within a single parent, he found seventy offspring. And within those offspring, he detected even tinier micro-miniature aphids. This startling finding was absolutely correct; we now know that aphids do carry on exactly this way. Even Leeuwenhoek found it bizarre—“I was at my wits’ end to fathom this secret of generation,” he confessed—but it did seem to provide a fine example of preformation, so perhaps it made sense after all.*
IN THE 1740S, WITH THE SCIENTIFIC WORLD FLUMMOXED BY HYDRAS and aphids, the mysteries of regeneration and reproduction were up for grabs. Everyone wanted in on the game. From across Europe came an orgy of cracking and breaking and splitting seldom seen outside a Baltimore crab house. Bonnet guillotined snails and found that some kinds could grow entire new heads. He chopped up worms into dozens of pieces and found that, eventually, dozens of complete, intact worms wriggled away.
Starfish, crayfish, and salamanders joined the throngs of animals sacrificing their limbs to scalpel-wielding naturalists. Straightforward experiments gave way to clever but grim variations—What would happen if you amputated a lizard’s foot and it grew back, and then you amputated that new-grown foot? The answer, it turned out, was that the poor, tormented lizard once again grew a new foot.
For scientists in the 1700s, who took for granted that humans stood atop the peak of the pyramid of creation, these were bewildering observations. How could God have endowed crawling, scuttling creatures like worms and crabs with powers that human beings lacked? A human who lost his head was lost indeed; a beheaded snail shrugged his puny shoulders and carried on.
Nearly as puzzling, these stories of magical regenerative powers seemed to convey one message, while the aphid experiments conveyed a contrary one. On the one hand, the stories of regeneration undermined the theory of preformation. If any old piece of worm could give rise to a full worm, did that mean that worms in nested versions sat hidden everywhere inside a worm’s body? No one thought so. The lizard experiments posed a similar challenge. Did lizard feet come packed inside one another, at the ready for every devilish contingency, and with backups to the backups? Even the staunchest believers in preformation felt uneasy.
On the other hand, the discovery of aphids within aphids seemed to speak in favor of preformation. Still, a lone species of insect pest didn’t carry much clout. The skeptics outshouted the preformationists, confronting them with embarrassing challenges, mostly to do with heredity. Similar objections had been raised before, but the preformationists had managed to deflect them. Now the attackers moved in again. One eminent French scientist, Pierre Louis Moreau de Maupertuis, took the lead. Maupertuis had a taste for combat and a gift for posing vexing questions. Worse, he spoke from a position of authority.
Like many scientists in the 1700s, Maupertuis roamed from field to field. An astronomer and a physicist before he turned his attention to biology, Maupertuis had been a celebrity since the 1730s, when he had led a French expedition to the Arctic to sort out a controversy about the shape of the Earth. It turned out to be a squashed globe, pushed in a bit at the poles and bulging at the equator. This was what Maupertuis (and Isaac Newton) had predicted, and soon no literary evening or elegant dinner or royal ball was complete without Maupertuis.
Witty, vain, elegant, seductive in print and in person, Maupertuis spoke as if he had done the squashing himself. He courted controversy. “He who causes himself to be often spoken of is always discussed,” he advised a friend, “and that is everything.” Heeding his own advice, Maupertuis had shifted his focus from geography and geometry to sex and heredity.
In about 1750, he found a family in Germany in which, over the course of four generations, babies had been born with six fingers on each hand and six toes on each foot. For preformationists, that was an enormous riddle. When God created his Russian dolls at the beginning of time, why in the world would he have made some of them with extra fingers and toes? And yet Jacob Ruhe had been born with extra digits, and so had his mother, and her mother before her, as well as three of Jacob’s eight siblings. And when Jacob married (a woman with standard-issue hands), two of their six childr
en had extra digits.
Maupertuis tried to calculate the odds that a string of such unusual births could occur by chance. He surveyed the population as best he could and decided that, at most, one person in twenty thousand was six-fingered. A bit of multiplication led him to conclude that the odds were trillions to one against the possibility that all those Ruhes just happened to have six fingers. If that was coincidence, then “the best proven things in physics” were coincidence.
The story of the Ruhes cried out for some explanation involving traits passed from parent to child, Maupertuis insisted, but preformation ruled out such accounts. Odder still, the extra-finger trait seemed to follow the father’s line in some generations of the Ruhe family tree and the mother’s line in others. Neither ovism nor spermism permitted such things. Maupertuis gloated, and his preformationist rivals fumed.
Still not satisfied, Maupertuis and other skeptics mounted yet another attack on the preformationists. This time they focused on what the eighteenth century insisted on calling “monsters.” How did the preformationists explain birth defects? Could God really have stocked his Russian dolls with twisted, malformed infants, a nightmare nursery of blind and hunchbacked babies? One indignant ally of Maupertuis fumed at the idea that God had designed “monstrous eggs” at the Creation.
The preformationists fell back under these assaults, but they were hardly routed. The argument about “monsters,” for instance, was easy enough to counter. Did Maupertuis presume to instruct God on how to manage creation? God’s ways were not for men and women to judge. Everyone had always known that fate was cruel and the world a vale of suffering. What was new there? And surely God did not avert his eyes from pain. Hell, after all, was a place universally believed in, and countless souls endured endless torment there.
But the intellectual tide had turned. Arguments that had once been cited as strengthening the case for preformation were now invoked against it. The most important was the infinite sequence of dolls within dolls that lay within the egg or sperm. Originally, that infinite chain had testified to God’s infinite power. Now the same observation was cited as highlighting preformation’s absurdity. The Count de Buffon, one of the great mathematicians of the 1700s, took the trouble to calculate just how tiny those Russian dolls were. By his reckoning, they grew tiny impossibly fast. Even if you started with a Russian doll as big as the entire universe, within a mere six generations—by the sixth doll inside a doll—you would need a microscope to find the smallest doll. And six generations was hardly any time at all; hundreds of generations had passed since Adam and Eve.
THE ASSAULT ON PREFORMATION WAS A TEAM EFFORT, WITH Trembley (and his hydra) recruiting Bonnet (with his worms and snails), who enlisted Maupertuis (with his six-fingered families), who tapped Buffon (with his calculations about infinitesimally small Russian dolls). Preformationists reeled under those attacks. But even though they had no good answers to most of these challenges, believers in preformation had come closer to the truth than they knew. They had sensed correctly that much of a person’s destiny—whether she will have curly hair or dark eyes or straight teeth—is imprinted on her from her earliest days.
Their problem was that they could not imagine how that information could be conveyed. How could they, without any useful analogies to draw on? Harvey had his pump, Newton had his clockwork, but biologists in the 1600s and 1700s had no technology they could look at to spur their imagination. What they lacked was any example of a machine that could follow instructions written in code.
Scientists by this time knew how to make all sorts of sophisticated mechanical devices. Clocks and watches could be started up and set running, almost as if they were alive, and engineers had outfitted palaces and country estates with arrays of fountains that spurted water high into the air in carefully choreographed sequences. But those machines always did precisely the same thing, over and over again (that was, after all, the point of a time-keeping machine).
In the winter of 1738, all Paris had lined up to see a mechanical marvel that represented the height of the inventor’s art. This was a metal duck, complete with copper feathers, that could stretch its neck toward a visitor, take a kernel of corn from his hand, swallow it, and—here was the great, spectator-pleasing touch—“discharge it, digested, by the usual Passage.” Two other automatons, one a drummer whose mechanical hands tapped out a rhythm with his drumsticks and the other a flutist who tweeted away, competed for notice.
All three figures enthralled the crowds. (The flutist contained an “infinity of wires and steel chains…,” one admirer wrote, “[which] form the movements of the fingers in the same way as in living man, by the dilation and contraction of the muscles.”) But the defecating duck was the star of the show, even though his inventor admitted that matters were not quite what they appeared. The duck did not really digest his food and excrete it, Jacques de Vaucanson admitted, but simply ground it up and left it sitting at the base of its mouth tube; at each meal, the duck’s tail-end had to be loaded separately with soon-to-be-excreted pellets.
Vaucanson’s mechanical duck made a fitting emblem for the state of biology in this era. On the one hand, its wing-waving, tail-flapping, bill-dipping performance looked uncannily ducklike. An ingenious designer, it was now plain, could build a machine that would charm the grouchiest spectator. On the other hand, all that ingenuity only highlighted the gulf between the most sophisticated cogs-and-gears machine and the most ordinary living duck. Vaucanson’s duck was a marvel, but it had nothing to do with life. A leap in the air was a feat, but it was not progress toward a voyage to the moon.
So, for eighteenth-century scientists trying to understand how a baby comes to resemble its parents, the problem was not that they lacked mechanical know-how. Nor was the problem a failure to grasp the importance of codes. The idea that a string of mysterious symbols could carry a message was an old one. The message might be Attack at dawn!, but everyday examples abounded, too. The earliest musical notation dates from the Middle Ages, for example, and notes drawn on a staff are a kind of code telling a musician what to sing. Written language, for that matter, conveys meaning through a sequence of cryptic lines and curves drawn on a page. Learning to read is code breaking.
The problem for scientists grappling with the riddles of heredity was that they could not come up with an analogy that might have spurred their imagination: they had never seen a machine that could follow instructions and proceed down one path rather than another. If they had seen such a fantastic machine, perhaps they would have wondered if a human being, too, could grow and develop by employing the same strategy.
Programmable machines would come along in the next century, in the early 1800s. The player piano was one. It could plink out any tune at all, from a lullaby to a Bach minuet, depending on the roll that an operator gave it. And automated looms, controlled by punchcards that specified various designs, would weave carpets in an endless variety.
Those new machines would arrive a century before the first modern computers, but player pianos and similar inventions might conceivably have appeared even earlier than they did. In many elegant homes in the 1700s, visitors looked on as their proud hosts displayed an amusing contraption called a music box. Only a narrow gap separated that music-producing machine from a player piano, but nobody made the jump. (A music box typically played only a single tune, which depended on the arrangement of pins on its revolving wheel, but there was nothing to rule out a system of easy-to-install, interchangeable pinwheels.)
And it was as early as 1679 that Gottfried Leibniz, one of the most far-seeing geniuses the world has ever known, imagined the computer, or something close to it. But at that point even electricity was still completely mysterious—Leibniz’s computer was a sort of colossal pinball machine, with marbles rolling down ramps—and he never built one. No one, in fact, built an instruction-following machine in the 1700s.
Had anyone done so, the scientists trying to make sense of heredity might have had an easier time. How does a
baby “know” to grow straight, black hair? The preformationists had sensed, correctly, that in some sense the black hair was foreordained. If computers had been an everyday fact of life, someone almost surely would have said, Hidden somewhere inside that tiny lump of tissue is a program specifying black hair. Instead, they saw no alternative to the theory that the black hair itself had existed all along, in miniature form.
It is hard not to feel sorry for our baffled scientist-detectives. Unable to imagine a technology that would not appear for decades to come, they found themselves in the predicament of a time-traveling Sherlock Holmes trying to solve a twenty-first-century murder. “Now, Watson, let us examine the facts. We know that a man walking to his place of work in a great city carried on a conversation with another man in that city, without raising his voice, at a distance of some ten miles. The testimony on this point is incontrovertible. And, yet, it is impossible.”
This kind of forgivable blind spot features often in the sex-and-babies story. Often in science, the problem is the other way around: rather than flail about because they cannot imagine a model that accounts for the facts, scientists take the reigning technology of their day and apply it willy-nilly. In ancient Greece, the heart was a furnace. By the 1600s, it had become a pump. At the end of the nineteenth century, the brain (or the mind) was a steam engine in which the pressure of repressed memories and dark desires could lead to catastrophic explosion. In the early twentieth century, the brain was a telephone switchboard staffed by teams of operators manipulating a cat’s cradle of cords and plugs. A few decades later, the brain was a clicking, whirring computer.
The cliché is right in insisting that to the person whose only tool is a hammer, the world looks like a nail. But it is also true that to a person without a metaphor, the world looks like a blur.
The Seeds of Life Page 17
