The Seeds of Life

by Edward Dolnick

  With the animalcules now in a starring role, Leeuwenhoek banished the other player in the drama altogether. Despite what Harvey and de Graaf had insisted, the egg had no role in conception. In Leeuwenhoek’s account, the male delivered the animalcules to the female, where they burrowed into the uterus, which nourished them.

  Leeuwenhoek’s picture drew heavily on the old analogy between a man’s semen and a tree’s seeds. Animalcules grew into animals, he explained, just as apple seeds grew into apple trees. The analogy was based on a deep misunderstanding. The seed of a plant is an embryo, a product of sexual fertilization, rather than just a male sex cell. But scientists did not start to sort out the riddles of plant sex until around 1700. (Everyone knew that plants grow from seeds, but nobody understood where those seeds came from.) Leeuwenhoek had scurried by other trouble spots, too. He simply declared that the animalcule gave rise to the embryo, for instance, without explaining how in the world that could happen. Nor did he explain why a man produced millions upon millions of sperm cells, if a single one would have sufficed.

  Instead, he devoted his energy to shooting down his rivals. They claimed that the egg made its way from the ovaries to the womb. Leeuwenhoek demanded to know how that happened. Were we to believe that somehow an “egg was sucked from the egg-nest” by the floppy Fallopian tubes, like a sailor snatched from the deck of Odysseus’s ship by some long-tentacled sea monster?

  More ludicrous still, de Graaf’s supposed eggs were large (as we have seen, de Graaf had confused egg follicles with the much smaller eggs within them), while the tubes they purportedly passed through were small. How did that work? And if eggs played such a key role in conception, why was it that Leeuwenhoek saw no sign of them when he examined female dogs with his microscope? After all, he had discovered sperm cells, which were far tinier. In December 1684 and again in January, Leeuwenhoek examined the Fallopian tubes of dogs who had mated moments before. He saw nothing noteworthy except a few “globules” that were certainly not eggs. “Had there been one particle in them no bigger in size than the hundredth of a grain of sand, I doubt not but I should have found it.”

  Why he did not is a genuine mystery. Leeuwenhoek’s honesty is beyond question. By fluke or bad fortune, the eggs he might have seen somehow escaped him. Perhaps he had inadvertently dislodged them in the course of his probing.

  Never a man for diplomatic phrase making, Leeuwenhoek denounced the egg theory as “addle-pated,” “fantastic,” and “entirely erroneous.” He had looked in “so-called ovaries” and he could report that the “so-called eggs” they supposedly contained did not exist. So Leeuwenhoek proclaimed, and so he would argue for the rest of his long life.

  Better still, he told the Royal Society in 1685, he might have seen something that cracked the conception mystery wide open. “I have sometimes imagined, as I examined the animalcules in the male seed of an animal, that I might be able to say, there lies the head, and there, again, lie the shoulders, and there the hips.” Straining to make out tiny details at the limits of human perception, Leeuwenhoek was sincere but mistaken.

  He immediately added that he was far from sure that he had truly seen this marvelous sight. “Not having been able to judge of this with the slightest degree of certainty, I shall not, therefore, affirm this as definite, but rather hope that we may, at some time, have the good fortune to come across an animal whose male seeds will be so large that we can recognize in it the figure of the creature from which it has come.”

  He continued searching. Fifteen years later, on Christmas day in 1700, he wrote to the Royal Society about the animalcules he had seen in a ram’s semen. “The parts lying in such an animalcule do not resemble a lamb, he conceded, “yet the parts lying therein may in a short time assume the shape of a lamb when they have received nourishment in the womb.”

  Leeuwenhoek pressed on, certain that the future animal had somehow to be concealed inside the sperm cell. It was a question of logic. How could a tree sprout branches if the branches were not somehow in the seed already? Something could not materialize from nothing.

  He vowed to look harder.

  PART THREE

  RUSSIAN DOLLS

  ”Very dangerous things, theories.”

  —DOROTHY SAYERS, The Unpleasantness at the Bellona Club

  TWELVE

  DOLLS WITHIN DOLLS

  THE STAGE SEEMED SET FOR A GIANT ADVANCE. THE ANATOMISTS, with de Graaf in the lead, had made their breakthrough—women had eggs; that was their role in conception. The microscopists, following Leeuwenhoek, had their own triumph to celebrate—the “tiny animals” that swam in semen, and not the semen itself, were crucial. Thrilled at the discovery of those animalcules, Leeuwenhoek’s camp scarcely had time for anyone’s talk of eggs.

  The next task, one might have guessed, would be for the two sides to make a truce and come to some agreement on just what roles egg and sperm played. It didn’t work out that way. Instead, scientists split into two warring camps, ovists and spermists, each dedicated to the proposition that their side was truly vital, while the other was necessary, perhaps, but distinctly secondary.

  Worse still, the two sides did manage to come together on one key issue, but that one instance of agreement led not to progress but to a crucial wrong turn. That mistake was an astounding theory called preexistence, which would entrap scientists for generations.

  The problem began with the battles between ovists and spermists. We have seen already how Leeuwenhoek sneered at his “addle-pated” rivals for their devotion to the egg. Ovists lobbed back insults of their own. Such name-calling was far more than the customary squabbling of competitors scrambling for recognition. The two sides had made the crucial mistake of thinking that they could get along without one another.

  Ovists insisted that the embryo lay concealed within a woman’s egg. It had been there all along, before any man had ever come into the picture. To hear the ovists tell it, semen was simply the key that set a living clockwork in motion. Spermists maintained just as fervently that the embryo lay concealed within the sperm. It had always been there, waiting. When a couple have sex, the man’s sperm carries the embryo to his partner, where it grows. Either there is no egg at all (this was Leeuwenhoek’s view), or egg and womb are merely food and incubator for the new arrival.

  The striking feature, to modern eyes, is that neither side granted the other any role in forming the embryo in the first place. Instead, they proposed a remarkable alternative: parents do not form their children. On the contrary, those children were preformed before their parents ever laid eyes on one another. On this point, and only on this point, both sides agreed. It was God who had done the preforming, and according to the most popular version of this theory, he had done so at the dawn of time.

  This was a misguided, not to say bizarre, theory. But it is crucial to note that this was mainstream science, not a fringe doctrine, and Europe’s most eminent thinkers all signed onto it. The preexistence theory, as it was called, would reign for more than a hundred years, from late in the 1600s to the very end of the 1700s. In hindsight, a hundred-year reign of error is a colossal blunder, but in all those years most scientists had no inkling that they had veered off course.

  At the time, the new theory seemed all but irresistible. Scientists embraced it so ardently partly because they had come to scorn a belief that had satisfied all their predecessors since the Greeks. From Aristotle to Harvey, scientists had taken for granted that some intangible force directed the embryo’s development; this vital spirit, though nearly impossible to describe, guided living plants and animals in a myriad of ways. This life force directed plants to send out shoots and roots, broken bones to mend, and wounds to heal. Above all, this animating spirit directed embryos to take on their destined shape.

  In the new, mechanically minded age, that notion had come to seem alarmingly vague, perhaps even empty. To say that the embryo somehow “knows” how to grow from a featureless blob into a full-fledged organism with wings and a bea
k or with fingers and toes was to invoke magical or occult forces. That was less an explanation than a shout of “Abracadabra!”

  Who would cling to such an outmoded creed when they could opt for a scientific, hard-headed alternative?

  THE PATH TO THE NEW THEORY WAS A CURIOUS ONE. IT RELIED partly on experiment and observation, as you might guess, but far more heavily on faith. That faith took various forms: faith in the power of reason, faith in the orderliness of nature, and, above all, faith in God. Armed with unshakable religious faith, physicists in the Age of Science had explained the workings of the heavens. Armed with unshakable religious faith, biologists in the Age of Science raced into a swamp where they wandered, lost and frustrated, for a century.

  Religion guided physicists to discovery after discovery because it seemed that God truly is a mathematician. No one has ever explained why, but for proof you had only to look up. Take Halley’s comet, for instance. For countless millennia, on a once-every-seventy-five-years timetable, it had traced an enormous ellipse across the heavens. Throughout nearly all that expanse of time, no human being had ever imagined such a thing as an ellipse. Finally, in 1705, Edmond Halley proved that the comet now named after him had been tracing perfect ovals all through the numberless generations when human beings still cowered in caves and struggled to count on their fingers.

  It’s easy to imagine a universe where things happen any which way. The sun and stars would flicker and blink randomly, and comets and planets would travel not in smooth, perfect curves but in a drunkard’s zigzagging lurches. But that is not our world. Falling rocks obey mathematical law. So do crumpled pieces of paper tossed toward a wastebasket. Rainbows form precise arcs. The ripples that spread across a pond when a duck lands on the water move outward in perfect circles, at rates governed by specific laws, and the sounds of the duck’s quacking obey yet another set of concise mathematical laws.

  The physicist Eugene Wigner, a Nobel laureate, wrote what is still the best attempt to explain why the universe follows such neat rules. But even this landmark essay, from 1960, amounts to an eloquent confession of ignorance. Wigner acknowledged his mystification in his title, “The Unreasonable Effectiveness of Mathematics in the Physical Sciences.” He concluded on a humble note. “The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve.” All physicists share Wigner’s feeling of baffled gratitude.

  But for the biologists of the late 1600s and 1700s, religion led not to enlightenment but to muddle. For these early scientists, the great, unfathomable mystery was explaining how anything as complicated as a living creature could ever have been formed. They could imagine only two possibilities.

  Think of any bit of matter whatsoever, from a boulder to a leopard. Either it had been built according to a plan, or it had arisen by chance. In the case of a living organism, there was no room for doubt. The closer one looked at a living creature, with its countless parts, each exquisite in itself and all of them working together in perfect harmony, the more the designer’s hand proclaimed itself. And that infinitely skilled and infinitely patient designer, every scientist recognized, could be none other than the Creator himself.

  Not even Isaac Newton, perhaps the most brilliant scientist who ever lived, could imagine that there could be design without a designer. So mad a notion practically rebutted itself. Suppose for a minute, for the sake of argument, that the universe was composed entirely of tiny billiard balls and that those balls collided according to strict mechanical laws. It was not just ludicrous but blasphemous to think that those careening atoms might spontaneously form a table or a house, let alone a mouse or a mastodon. How could chaos give rise to order?

  If the atheists were right, the world would be awash in monsters, misshapen beasts with legs sprouting from their backs or blinking, useless eyes. “Were men and beast made by fortuitous jumblings of atoms,” Newton scoffed, “there would be many parts useless in them––here a lump of flesh, there a member too much.”

  Later thinkers took up the argument. The more details they filled in, the more iron-clad it seemed. Suppose you happened to stub your toe on a stone, wrote the clergyman and naturalist William Paley. You might say, “What of it? Perhaps it had been lying in the grass forever.” But suppose you stubbed your toe on a watch. Notice how the wheels and gears mesh perfectly. Observe how they would not work at all if any of them was even the tiniest bit bigger or smaller. Look at the steel springs and the glass face, each material perfectly suited to its purpose. In such an event, Paley demanded, who could fail to see that the watch had been designed? And who would deny that a living creature was vastly more complex than the most sophisticated watch?

  Nearly two centuries would pass before a shy, sickly, mathematically illiterate Englishman named Charles Darwin explained where Newton and Paley had gone wrong. In the meantime, Leeuwenhoek and all his contemporaries took for granted that God had designed every feature of heaven and earth, down to the last detail. This was intelligent design with a vengeance.

  For physicists, the notion of a designer at the controls posed no problem. They had only one creation to explain, and they had the story on the best possible authority. God had created the sun and the starry heavens once and for all. Then he’d set the clockwork running. But for biologists, the problem was enormous. Since every living creature had been designed by an all-knowing, all-powerful Creator, every feature of that design had to be impeccable. That was trouble. How to account, for instance, for babies born blind or missing an arm or for twins joined at the head?

  For Darwin, such tragedies had a straightforward explanation: in the tricky business of development, a lot can go wrong. Suppose, though, you took as an unchallengeable premise that God’s design was perfect in every feature. Then what?

  And not only was the living world marred by mishap and tragedy. Even when things ticked along according to plan, life on earth was not only disorderly—in utter contrast with the harmony that marked the cosmos—but teeming with ugly and badly behaved creatures. Why had the Creator fashioned tapeworms and rats and fleas? What of the poor lamb, torn open by wolves?* The best of all possible designers, though indisputably a master of technique, had a hard-to-deny quirky streak. Couldn’t the camel have been a touch handsomer? What good were houseflies? Was there really an urgent need for hundreds of thousands of species of beetle?†

  Before Darwin, these were baffling questions. Afterward, in the dog-eat-dog world that evolution would one day describe, it was no surprise that some dogs thrived and many faltered (and that cats had to watch out). But none of that made sense in the 1600s and 1700s, when the natural world was supposedly not a scrum but a waltz.

  Far more important and more perplexing, though, was this riddle: What was God’s role, today, in the creation of life? The Bible spelled out the details of the original creation—God had created plants and trees on the third day, birds and fish on the fifth, and humans and land animals on the sixth—but new life popped into existence every minute of every day, right now. Did God watch over the first appearance of every new plant, animal, and human being?

  Think just of human babies. It hardly fit with the seventeenth century’s notion of divine dignity to picture God, like a voyeur, looking in on every conception in the world.

  But what was the alternative?

  THE ALTERNATIVE WAS ASTONISHING. IT WAS, HOWEVER, A MATTER of inexorable logic. God, a designer whose way of working was necessarily perfect, did not act in one way here and in a different way there, or in one way today and in a different way yesterday. His divine guidelines spanned the universe. He had created the inanimate world in one go. That was certain. It followed, inevitably, that he had created the living world in one go.

  It didn’t look that way, but that was because people had not looked hard enough. Science taught a different lesson: Every person who would ever live, down to the end of time, had been created at the same time. (And no
t just every person, though human beings are our focus here, but every living plant and animal of whatever sort.) God had created them all in the beginning, and since that first flurry of activity, there had never again been any new creation of life.

  That was the only possibility that was in keeping with God’s nature. But where had the countless creatures who were created so long ago kept themselves all this while? In particular, what had God done, in the world’s first week, with all the humans destined to be born in the 1200s or 1500s or in some century yet to come? He had stashed them away. They waited, like a series of ever-smaller Russian dolls one inside the other, in Adam’s testicles or in Eve’s ovaries. When the time came, each one would have its turn on stage.*

  The picture of worlds within worlds, forever, sounds like a druggy hallucination. But scientists in the seventeenth century managed, more or less, to accept the big picture. They concentrated their energy, instead, on fighting over whether it was Adam or Eve who carried that infinite doll collection.

  Scientists spoke casually of “encasement” and “preformation” and “preexistence.” Today, in much the same way, we attach names like “Big Bang” or “black hole” to impossibly arcane notions, as if the act of labeling provides insight. A French scientist, writing in 1700, tried to color in some details. “In one single spermatic worm, there is an infinity of organized bodies capable of producing fetuses and children, for infinite centuries, always smaller and smaller in relation to one another.” Perhaps sensing his reader’s perplexity, he added a censorious remark. This picture would “only appear bizarre to those who measure the wonders of the infinite powers of God according to the idea of their senses and of their imagination.”