But that is to skip past an enormous riddle: Who’s following the recipe? It is no great feat to bake a tray of chocolate chip cookies. But imagine if chips and flour and butter had somehow discovered a way to make themselves into cookies. “Put simply,” writes the biologist Jamie Davies, “cardigans, symphonies, cars, and cathedrals do not build themselves.” But living creatures do.
It is even more surprising than that. Every home handyman knows that you turn the electricity off before you try installing a ceiling fan. When you finish, you start the power back up. But living organisms are always growing; they don’t have the option of shutting down temporarily. And where do the workers come from? It is not a matter of a lone cook in the kitchen. Think of a body’s intricate network of nerves and blood vessels. Who are the plumbers who connect mouth and gut? Who are the electricians who wire eyes and brain?
In the kind of building projects we’re familiar with, teams of workmen swarm over a house or an airplane while supervisors order them around. But inside the bodies of living animals, no workmen or bosses swoop in from somewhere else. Everything is managed by the body itself, using its own cells both as raw material and as craftsmen. So the cliché that compares difficult tasks to repairing an airplane in midair vastly understates the trick that nature has pulled off. To manage something comparable to what every dog or cat or baby does every day, an airplane would have to rebuild itself while flying, and it would have to grow the electricians and engineers who do the work.
All that is only part of the story. Scale makes the tricks that every cell in the body pulls off almost inconceivable. The cells that make up a living creature are invisible to the naked eye—in the human body there are trillions of cells, vastly more than there are stars in the Milky Way—and yet every one of those cells is a chemical factory jammed with pumps and motors and assembly lines, and far more complex than any actual factory.
On top of that, living creatures aren’t permanent structures like houses or factories, made of building blocks that rest in place. We are more akin to fountains, say, where the components change perpetually but the pattern endures. It is true that you can never step in the same river twice. But it is not just the river that is always changing.
In a living body, new cells constantly replace old ones. No matter your chronological age, you’re formed from parts that are at most a decade old. Scratch your forehead; ten years ago, neither that forehead nor that finger existed. When you meet a friend and say, “You haven’t changed a bit,” the chemist Addy Pross notes, your friend is in fact almost a completely different person from the one you last encountered.*
Amid such change, what is it that stays constant and makes you you? Can it really be that the six-year-old you who ran giggling through a garden sprinkler is the same person as the stiff and stodgy coot fumbling for his reading glasses? It seems both indisputable and unfathomable. In learned journals today, philosophers wrestle endlessly with such riddles. After a kidney transplant you would still be yourself. What about after a brain transplant? Would you be yourself, or would you be him wearing your body like a borrowed overcoat?
In the mid-1700s the details of such questions about personal identity had not yet emerged, but the makers of the modern age had glimpsed the complexity of the living world. Astonished and bewildered, they cast about for some model of how development could possibly take place.
They began with a giant step backward.
EIGHTEEN
A VASE IN SILHOUETTE
PERHAPS THE CLOCKWORK ANALOGY DID NOT APPLY TO LIVING creatures, the new generation of thinkers conceded, but that did not mean they had to give up on scientific explanations altogether. They began by wrapping themselves in the cloak of the revered Isaac Newton.
Pierre Louis Maupertuis, the French astronomer-turned-biologist who delighted in mocking the preformationists, was the first to make the new case. Newton and his successors, Maupertuis proclaimed in 1745, had shown how gravity explained the structure of the solar system. Now the time had come to “extend it further than the astronomers have done. Why if this force exists in Nature, should it not have a part in the formation of animal bodies?”
Maupertuis’s invocation of Newton and gravity was new. Oddly, he paired that new idea with an old one. Nearly a century before, scientists had rejected the theory that there were two semens, one male and one female. Maupertuis not only signed onto that long discredited view but promoted it enthusiastically. Male and female semen contain tiny particles that come from every part of each parent’s body, he explained. When a man and woman have sex, those “seminal particles” meet in the uterus, where gravity draws together particles from corresponding organs in the two parents, thus forming new organs that carry traits from both partners.
This was a bold—or far-fetched—suggestion, with several virtues. It explained why children could resemble either parent (or both), which preformation had conspicuously failed to do. Just as important, it moved away from the clockwork model but retained its most important element. Though cogs and gears were banished, Maupertuis’s picture still evoked the orderly, law-governed workings of the solar system, the grandest machine of them all.
As a bonus, Maupertuis managed to turn one of the oddest features of Newtonian science to his advantage. Newton’s picture of a perfectly regulated cosmos depended entirely on the all-embracing power of gravity, but Newton had never explained what gravity is. “Ye cause of gravity is what I do not pretend to know,” he acknowledged, and so he confined himself to describing the effects of that utterly mysterious force. Somehow it reached to the farthest corners of space, instantaneously, exerting its pull across billions of empty miles. From the most distant star to the nearest flower, every object in the universe felt gravity’s tug. Why shouldn’t gravity also draw the seminal particles together deep within a woman’s body?
In the judgment of posterity (though not of his own contemporaries), Maupertuis scored other coups, too. His gravitational theory explained why males and females of different species rarely breed (because the parents’ seminal particles are not enough alike) and why birth defects are not outlandish mistakes, like a foot growing where an ear belongs, but predictable errors, like six fingers rather than five (because gravity draws similar particles together). In some ways, Maupertuis even managed to anticipate Gregor Mendel’s account of genetics. Maupertuis suggested that particles can remain dormant for several generations, for instance, which would explain why a child of brown-haired parents might have flaming-red hair like her grandmother. And he suggested that particles might suddenly change, giving rise to new traits that later generations of scientists would dub “mutations.”
Claiming Newton’s support was good strategy, and Maupertuis quickly won allies. The most important was Georges-Louis Leclerc, later known as the Count de Buffon, a French scientist and a peacock in human form. (We briefly encountered Buffon once before, mocking the preformationists with a calculation that showed that Russian dolls would quickly shrink to microscopic size.) One of the most admired thinkers of the age, Buffon had nothing in common with the unworldly, socially inept caricatures who already featured in every popular account of science. “He loved money and became rich,” one biographer tells us. “He loved power, and he frequented those in power.… He loved women, and not just for their beautiful souls. His laboratory experiments were few and his assumptions often questionable. He let his imagination go well beyond the facts.” He was also, indisputably, both learned and brilliant.
Buffon began his career as a mathematician and a kind of European ambassador for Newtonian science. But he soared to fame on the strength of a monumental, thirty-six-volume work called Natural History that appeared over the course of his long life. These unlikely best sellers ranged over a multitude of subjects—mammals, birds, human beings, geology, anthropology—in lively and opinionated fashion. “Sloths are the lowest term of existence in the order of animals with flesh and blood,” Buffon noted. “One more defect would have made their existe
nce impossible.”
The public grabbed up Buffon’s books. He soared past Voltaire and Rousseau in renown, and his every pronouncement carried weight. (Thomas Jefferson grew so furious at Buffon’s claim that all forms of life in the New World were small and feeble that he instructed Lewis and Clark to keep their eyes out for mammoths and mastodons, which he believed still roamed the wild.) Buffon happily played the part of the great man: he favored silk waistcoats and lace cuffs and had his hair curled several times a day; he employed a renowned chef and presided at long dinners, where the sparkling conversation veered often to the scandalous; he spoke fondly and frequently of his many accomplishments. When he died, in 1788, fourteen liveried horses and a thirty-six-member choir led the funeral procession, and twenty thousand spectators along the parade route scrambled for a view.
So when this titan of science weighed in on sex and conception, everyone listened. Buffon began, like Maupertuis, by rejecting the notion that women have eggs. That long-held view, he declared magisterially, was “badly founded” and “explained nothing.” He noted, correctly, that no one had actually seen mammalian eggs but only the ruptured follicles that had presumably once contained the eggs. For de Graaf and his fellow anatomists, the presence of those burst follicles in the ovaries had testified unmistakably to the presence of eggs; this was hardly more of a leap than seeing cracked and empty eggshells on a kitchen counter and deducing that someone had made breakfast.
Buffon didn’t buy it. All that de Graaf had been entitled to conclude was that something had emerged from the follicles. De Graaf believed that mysterious something was an egg. Wrong, said Buffon. It was female semen.
This was considered racy, which only drew more notice. Buffon thrived on the controversy. His prose style was ornate, but he enjoyed hinting that his adversaries were scolds and prudes. (Buffon’s foes took his elegant prose as proof that his ideas were lightweight and unworthy. That he was French besides seemed to them further evidence of their charges.) Women could only produce the liqueur seminale that made conception possible, Buffon made a point of emphasizing, if they enjoyed themselves during sex.
In Buffon’s scenario, semen was “in both sexes, a sort of extract from all body parts.” When male and female extracts mixed, they produced “a sort of rough sketch of the animal, a small organized body in which only the essential parts are formed.” That was vague, and Buffon’s account of how it happened was vaguer still. Somehow gravity or some other force drew together bits that “need one another.”
This theory was closely related to the one that Maupertuis had proposed a few years earlier. Both men spoke of two semens; both talked of Isaac Newton and mysterious forces of attraction. But Maupertuis had presented his argument in an eccentric, quasi-erotic book called The Earthly Venus, which he published anonymously. (One modern historian describes it as a “serious physical argument” scattered within a “symphony of witty and learned smut.”) Buffon argued his case in an imposing volume that all Europe clamored to read. Maupertuis whispered, and Buffon roared.
The details in these new theories were not important. That was fortunate, since Buffon and Maupertuis had scarcely provided any details at all. What was important was that they had managed to jolt the sex and babies debate out of its old rut. Others before them had pointed out flaws in the preformationist theory—mules, monsters, family resemblances—but Buffon and Maupertuis had moved beyond criticizing. They had proposed an alternative, albeit a rudimentary one.
The secret of development, in their view, was not the unveiling of Russian dolls made at the dawn of time on God’s assembly line. Instead, living organisms not only grew but changed, by adding countless new structures that appeared from scratch. This was an old idea, as we have seen, with such formidable advocates as Aristotle and William Harvey. But in the past, developmental theories had been dismissed as unscientific and implausible—Do you mean to say that babies grow by magic? And is it your view that complicated structures like hands and eyes arise from nothing at all? Now, in the mid-1700s, Aristotle was out of fashion, and Harvey was long dead. Maupertuis was controversial but widely admired, and Buffon was the man of the hour.
With its allusions to mysterious particles tugged by gravity-like forces and somehow patted into shape, the new picture of development was more a suggestion than a proper theory. These were stumbling steps. But they were steps that headed off in a long-neglected direction (and in the direction that would prove, centuries later, to be the correct one). Buffon and Maupertuis had not solved the baby riddle, but they had revived an old idea and given it new respectability. Perhaps in time someone would build on their ideas and take them further.
INSTEAD, A LONG-SIMMERING BATTLE BROKE OUT INTO OPEN fighting. The differences between the scientists who espoused the Russian doll theory and those who favored the new, developmental model—between preformation and epigenesis, in the language the scientists used—seemed stark and momentous. The two sides flung angry charges back and forth.
Why did the preformationists insist that bodies do not change as they grow, except in size? That was plainly false, cried their rivals. The body can grow new bits, not just unroll preexisting ones, and they cited countless everyday examples. There was not even any need to venture into the charged territory of embryos and babies. Think of warts or tumors or moles, which appear out of nowhere. Think of how cuts heal, as new tissue mends tears in the flesh. Think of scars, which surely were not predestined.
The preformationists fought back with vigor and disdain. For years they had railed against the notion of a “vital force” that supposedly guided living creatures on their way. This talk of mysterious guiding forces was vague and empty; it conjured up images of a puppet master working invisible strings. All such theories, one preformationist charged, were “trash, regurgitations of occultism, irrationalism, and pseudo-science.”
And if the advocates of epigenesis maintained that somehow organisms grew without guidance, then how could they deny that their system relied on chance, that dangerous and damnable notion? If intricate new structures arose out of the blue, how did living creatures take on such perfect, complex form? Worse yet, the preformationists thundered, this dangerous doctrine threatened to push God out of the picture. “Beware,” one scientist warned, “that it is very dangerous to admit the formation of a finger by chance. If a finger can form itself, a hand will form itself, and an arm, and a man.”
Each charge drew a countercharge. The accusation that they believed in chance drew special fire from the epigenesis camp. False!, they shouted. Their opponents talked as if change and chance were the same thing. But everyone acknowledged that the body changes as if it were following a script. The merest glance tells us which act of the drama we are witnessing. What could be more predictable than the path from helpless baby to coltish teen to adult in full command of her powers?
Some changes are less welcome but roll out inexorably even so—backs stiffen, hair grays, skin wrinkles. These are not the nicks and dings of hard wear, akin to the scars that a kitchen table accumulates over the years, but built-in, universal features of life. None of this fit with the picture of life arising from miniature dolls.
FROM OUR POINT OF VIEW, DOWNSTREAM IN TIME, THE TWO SIDES appear closer than anyone could see at the time. Both had latched onto important truths. There is something preformed in an embryo, in the sense that development unfolds according to instructions that were written down at conception. And there is something more going on than unfolding, because completely new parts—not just miniatures grown big—do arise at specified junctures in the timetable.
Maddeningly, this was not a dispute that could be resolved by careful observation. No matter how meticulously you tracked new-laid chicken eggs, say, you could not be sure if heart or brain or beak had appeared one day where they had never been before, or if they had been present all along but in so tiny (or transparent or distorted) a form that they could not be recognized. Instead, each side told its own story over again and
crafted new insults for its rivals.
Between catcalls, both sides grudgingly shored up their own arguments. By the time they had finished adding caveats and concessions, they had gone a long way to bridging the gulf between them. The preformationists’ Russian dolls turned out to be unlike any dolls anyone had ever seen, so prone were they to changing shape and proportion. And the epigenics camp had backtracked and improvised, too. New structures did not truly materialize, they suggested, but grew out of buds or germs or precursors.
At the time, no one saw that the opposing factions had stumbled toward common ground. “What is the difference between saying that the whole organism preexists, but not in the form in which it will later appear,” asks one modern historian, in exasperation, “and saying that it exists only potentially, or that some precursors of its parts are present?”
Today’s textbooks tend to cast the tale as a battle between the far-seeing epigenesis side, who had the story nearly right, and their misguided rivals in the preformationist camp, who clung to a complicated and far-fetched doctrine. But though the preformationists lost out, their views were not as crazy as all that. We now know that on the day she is born—years before any thought of pregnancy will cross her mind—an infant girl carries within her body more than a lifetime’s quota of eggs, around one million altogether. (Men do not produce sperm until puberty.) That is a long way from saying that she carries an endless supply of miniature humans nested inside one another. But perhaps it is enough of a step in that direction to make us less inclined to deride our forebears for their foolishness.
The Seeds of Life Page 19