The Seeds of Life

From Aristotle to da Vinci, from Sharks' Teeth to Frogs' Pants, the Long and Strange Quest to Discover Where Babies Come From


By Edward Dolnick

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Why cracking the code of human conception took centuries of wild theories, misogynist blunders, and ludicrous mistakes

Throughout most of human history, babies were surprises. People knew the basics: men and women had sex, and sometimes babies followed. But beyond that the origins of life were a colossal mystery. The Seeds of Life is the remarkable and rollicking story of how a series of blundering geniuses and brilliant amateurs struggled for two centuries to discover where, exactly, babies come from.

Taking a page from investigative thrillers, acclaimed science writer Edward Dolnick looks to these early scientists as if they were detectives hot on the trail of a bedeviling and urgent mystery. These strange searchers included an Italian surgeon using shark teeth to prove that female reproductive organs were not ‘failed’ male genitalia, and a Catholic priest who designed ingenious miniature pants to prove that frogs required semen to fertilize their eggs.

A witty and rousing history of science, The Seeds of Life presents our greatest scientists struggling-against their perceptions, their religious beliefs, and their deep-seated prejudices-to uncover how and where we come from.



1490—Leonardo da Vinci makes a cutaway drawing of a man and woman having sex.

1492—Columbus sets sail.

1543—Andreas Vesalius publishes one of the masterpieces in the history of anatomy.

1543—Copernicus says that the Earth goes around the sun, not vice versa.

1628—William Harvey shows that the heart is a pump.

1651—Harvey declares that "everything comes from the egg."

1669—Jan Swammerdam argues that God created all the generations of animals at the dawn of time, one inside the next like Russian dolls.

1672—Regnier de Graaf (almost) proves that female mammals have eggs.

1674—Antony van Leeuwenhoek sees countless "tiny animals," invisible to the naked eye, in a drop of pond water.

1677—Leeuwenhoek sees spermatozoa by the millions.

1694—Nicolaas Hartsoeker draws a miniature man inside a sperm cell.

1741—Abraham Trembley cuts a tiny organism called a hydra into pieces. Miraculously, each piece grows into a complete creature.

1745—French scientists propose a new theory of how living organisms develop: life is regulated not by clockwork but by a force akin to gravity.

1752—Ben Franklin flies a kite during a thunderstorm and proves that lightning is electrical.

1770s—Lazzaro Spallanzani puts male frogs in boxer shorts.

1776—American Revolution begins.

1791—Luigi Galvani zaps frog legs with electricity.

1818—Mary Shelley publishes Frankenstein.

1827—Karl von Baer becomes the first to see a mammal's egg.

1837—Queen Victoria takes the throne.

1830s–1860s—Cell theory emerges.

1861–1865—The American Civil War lasts four long years.

1875—Oscar Hertwig witnesses the union of sperm and egg.



"It is quite a three pipe problem, and I beg that you won't speak to me for fifty minutes."

—ARTHUR CONAN DOYLE, "The Red-Headed League"



BY THE LATE 1600S, THE ERA WHEN THE SCIENTIFIC WORLD began to take on its modern shape, explorers had circled the globe and mapped the heavens. They had calculated the weight of the Earth, traced the paths of comets that cut the sky only once in a lifetime, and divined the secret of the Milky Way. They had uncovered the mathematics at the heart of music and discovered the laws of perspective, so that an artist armed only with a paintbrush could pin reality to his canvas. But for thousands of years, long after Columbus and Magellan and Galileo, the deepest scientific riddle of all lay unsolved.

Where do babies come from? Such geniuses and creators of the modern era as Leonardo da Vinci and Isaac Newton did not know. They knew, that is, that men and women have sex and as a result, sometimes, babies, but they did not know how those babies are created. They did not know that women produce eggs, and when they finally discovered sperm cells, they did not know that those wriggly tadpoles had anything to do with babies and pregnancy. (The leading theory was that they were parasites, perhaps related to the newly discovered mini-creatures that swam in drops of pond water. This was Newton's view.)

Not until astonishingly recent times—in 1875, in a seaside laboratory in Naples, Italy—was the mystery of where babies come from finally solved.

Until then everything to do with conception and development was wrapped in darkness. For centuries, scientists struggled to find out if the woman merely provides a fertile field for the man's seed, or if she produces some kind of seed of her own. They did not know how twins come to be. (Too much semen? Two bouts of sex in quick succession? Sex with two different men?) They did not know if conception is more likely on the night of a full moon or a new moon or if timing makes any difference at all. They did not know, though they assumed, that a baby has only one father, as it has only one mother. They did not know why babies resemble their parents, and sometimes one parent more than the other.

Where do we come from? How does life begin? These were the most urgent of all scientific questions. The world is festooned with mystery and miracle. But not everyone has wondered why the stars shine or why the Earth spins. Every person who has ever lived has asked where babies come from. For millennia, the deepest of thinkers (and every ordinary person) had pondered this cosmic riddle.

No one had a clue.

PART OF THE REASON FOR THE PERPLEXITY WAS STRAIGHTFORWARD. We tend to forget how astonishing the story of life truly is. We've heard the explanation so often that we take it to be common sense. Every fourth grader knows where babies come from. Both parents contribute equally, we learn early on, the mother providing an egg and the father sperm. Each month one of a woman's ovaries releases an egg, which travels through a Fallopian tube toward her uterus. If a couple has sex at the right time, some of the millions of sperm cells in a man's semen make their way from her vagina and cervix toward that egg. One of those sperm cells may fuse with the egg. In time that newly merged cell divides into two joined cells, and then into four and eight and so on. After nine months, a new human being bursts, howling, into the world.

The truth is so far-fetched that it is a wonder that anyone believes it.

In textbook accounts of science, far-seeing researchers systematically gather facts and pile them in sturdy and imposing towers. The story of sex and babies was nothing like that steady advance toward a goal. The scientists who finally solved the case ventured off course for decades at a time. They raced at top speed down long, dark alleys chasing suspects who turned out to have airtight alibis. They concocted elaborate scenarios that collapsed in fantasy. They wandered in a daze, stymied by observations they could not fit into any pattern. They found some clues by deep and careful investigation and others by tripping over them as they raced in the wrong direction in the dark.

Progress came in fits and lurches, but that is the way with all true mysteries. Only in old-school television does insight arrive on cue, just in time for the closing credits. The problem was not that the scientists were incompetent—they were human and fallible, but many were dazzlingly intelligent, and nearly all were diligent—but that the truth was so well concealed.

To crack the case, scientists would need new tools, notably the microscope, and new ideas, notably the insight that the body is made of cells, trillions upon trillions of them, which all arise from a single progenitor. More than tools and ideas, they would need whole new ways of thinking. Suppose, for a moment, that some early savant had somehow leapt to the true conclusion that a living organism begins as a single cell. What then? Immediately scientists would have found their path blocked by a Sphinx posing a bewildering follow-up riddle—how does that single tiny cell "know" how to transform itself into a gurgling, six-pound baby?

Tackling that question would have required these early scientists to understand that a living organism could assemble itself! Through most of the history of the world, this was unthinkable, as outlandish as the idea that a cathedral could build itself. Today it is a concept hammered into every student who takes high school biology.

The path to that insight was tangled and difficult. It required, among other things, drawing analogies from machines like player pianos and, later, computers, that carried out complicated actions by following instructions written in code. In the twentieth century, such mechanical devices would lead to the discovery that life itself followed instructions written in a genetic code. But in the 1600s and 1700s no such machines existed; no one could look at the ghostly motions of a player piano's keys, governed by a musical roll, and shout, "Eureka!"

Instead, scientists looked around them in every direction for clues to the riddles of conception and development. How could it possibly work? Baffled but determined, they ventured down the most unlikely paths. They studied insects with obsessive care, for example, in the hope that those startling transformations—a wriggling caterpillar inside its cocoon emerges as a butterfly with gossamer wings!—would throw light on the changes in infants and babies. They studied fish and frogs and dogs and deer to see what they shared in the way of anatomy and mating behavior. They tackled the narrowest of questions—How do snails, which have both male and female genitals, sort out who will do what to whom?—and the grandest of themes—Do living organisms possess a "vital force" that sparks them to life?

Often a quest that started in one direction ended far afield, in a landing spot no one had anticipated. The search for the vital force, for instance, led to strange and dangerous experiments with electricity and lightning, and even an encounter with Dr. Frankenstein and his monster.

In hindsight, that zigzag progress seems inevitable, for two seemingly different questions were deeply entangled. The question, Where do babies come from? proved impossible to separate from What is life? Thus, straightforward inquiries about sperm and eggs and anatomy opened up into profound riddles about the nature of living organisms. Scientists who merely wanted to know about the body's nooks and crannies found themselves wondering what the world was made of. How could it be that the same, ordinary stuff that forms lumps of mud and murky puddles, when rearranged in the right way, can burst into crying, crawling life?

This was, moreover, an era when science and religion wrapped around one another, so that every statement about life implied a judgment about God the Creator. With one peek through a microscope, a scientific observation could provoke a religious battle.

The search for the solution to the sex and conception mystery would consume careers and span centuries. My focus is on the heart of the tale, from about 1650 to nearly 1900. During that time, scientists in half a dozen countries—in Holland, France, England, Germany, Italy, even the newborn United States—would pass the torch, or burn their hands and drop it. It is surprising, in hindsight, that it did not take them longer.

THEY SET OUT, NOT WITH HESITANCY OR TREPIDATION, BUT WITH eagerness and swagger, for their peers had just won a colossal victory. In a torrent of discoveries all through the 1600s, physicists and astronomers had demonstrated that the universe was a clockwork, the stars and planets its cogs and wheels. Spirits and demons had been banished. Nature obeyed laws and equations, not caprice. Comets were not heavenly messengers. God was a mathematician.

The seventeenth century was a tumultuous age, bubbling over with intellectual ambition. The roll call of genius went on and on. Shakespeare, Galileo, Rembrandt, Descartes, Newton were not busts on a library shelf but flesh-and-blood titans who wielded almost unfathomable powers. The secrets of the human heart and the natural world seemed destined to give way before them.

The scientists in that starry roster shared not merely an ambition but a way of thought. From Galileo and Newton on, they believed with an unshakable faith that their mission was to study God's creation and proclaim the glory of his craftsmanship. This they had begun to do, and when they rattled off the list of their triumphs they were making a twofold claim. First, they had done great things. They had unraveled the rainbow and harnessed the tides. Second, and just as important, they had cracked a cosmic code. They had found out how to think of the world: it was an encrypted message written by God.

The world was not just beautiful, like a painting that moved onlookers to delight; it was a beautifully constructed riddle that contained secrets within secrets. Humankind's highest task, these early scientists fervently believed, was to solve that riddle, the better to honor the Creator. (And why had God made matters so difficult? If he wanted trembling homage, why not arrange the stars to spell out BEHOLD in letters of fire? For the devout scientists of the 1600s, the answer was plain. God had given humankind its defining gift, a far-ranging intellect, and he meant for us to use it.)

The book of nature was written in the language of mathematics, Newton and his contemporaries insisted, and only the mathematically literate could read it. This was an austere view. Romantic poets would later howl that the scientists' "cold philosophy” had drained the world of its sap and energy, as if a lush Gauguin landscape had been set aside in favor of a diagram in a geometry textbook.* But despite their somber mathematical talk, the scientists of the seventeenth century tackled the world with gusto and high hopes.

They talked of God the mathematician, but they seemed to picture him in less imposing terms. Francis Bacon, one of the pioneers of the Scientific Revolution, took this to an extreme. His God seemed less the Almighty on a celestial throne than an indulgent parent who had devised an Easter egg hunt for a pack of toddlers. God "took delight to hide his works," wrote Bacon, "to the end to have them found out."

Bolstered by their successes in understanding the physical world, scientists made bold plans to continue their advance, this time moving to living creatures. If the proud heart could be understood as a pump, the rest of the body seemed sure to follow. Muscles and bones and arteries would play the roles of levers, pulleys, and pipes; food would serve for fuel; filters and springs, plumbs and bellows, would all have their natural counterparts.

In time, the body would yield its secrets like a watch opened up on a craftsman's bench. Humans and animals would show themselves as more wondrous versions of the ingenious mechanical figures that adorned the clock towers of Europe's cathedrals and emerged, on the hour, to march a few proud steps and raise trumpets to their metal lips.

The inner workings of life, the deepest mysteries of how animals move and breathe and reproduce, would be unveiled. God, who had placed the stars in the sky and carved towering mountains, had surely lavished even greater care on the details of a bird's wing and a whale's fin and, especially, on the human beings he had fashioned in his own image.

Scientists pictured the living world as a straightforward target. The inanimate world, with its hurtling planets and remote, untouchable stars, seemed more forbidding, and, indeed, Newton and his peers had needed to invent a mathematical language to describe it. Even today, we think of physics, with its black holes and hidden dimensions and parallel universes, as the realm of the incomprehensible. Biology, in contrast, deals with everyday, literally down-to-earth objects like dogs and plants and snails. Scientists had conquered physics even so. Biology would fall, too. They would make quick work of it.

They didn't. The bold men of science raced off to take on the mystery of life and promptly face-planted. Life was messy, it turned out almost at once, fragile and unpredictable and maddeningly coy about its secrets. A cannonball in flight plainly has no desire to go this way rather than that. Why shouldn't a few simple laws suffice to describe its motion? But consider the gulf between a chunk of metal and a sunflower craning toward the light, or a dog tugging on its leash, or a human being. On the one side, mere matter. On the other, breathing, pulsing life. How could the same sort of laws account for both?

Planets were easy; plants were hard. And sex and reproduction proved hardest of all. For nearly three hundred years, from about 1600 until nearly 1900, the question of where babies came from defeated one thinker after another. The vanquished lay in heaps, like soldiers on a battlefield. Late in the 1700s one scientist took the trouble to compile a list of failed theories. Scanning the centuries, he tallied "262 groundless hypotheses." ("And nothing is more certain," one eminent biologist remarked at once, "than that his own system is the 263rd.")



WE KNOW HOW THE SEX-AND-BABIES STORY TURNED OUT. THAT can make us smug—how foolish of our forebears to have lived so long ago—but it shouldn't. To understand the plight of our predecessors, think of modern-day scientists as they wrestle with their own grand mysteries. The hardest problem in science today—so difficult that scientists refer to it simply as "the Hard Problem," as if there were no other—is to explain perhaps the simplest fact in the world. Why is it that it feels like something to be us? Why is it that a robot, even one that can find its way around the room and beep and blink and play chess, is simply a lifeless collection of parts, whereas we humans swim in a sea of smells and sights and memories? What, in short, is consciousness?

If every object in the world is just a collection of atoms lumped together, how is it that some lumps just sit there but the three-pound lump that is our brain conjures up a world? How can mere stuff do that? In the words of the poet and essayist Diane Ackerman, "How do you begin with hydrogen and end up with prom dresses, jealousy, chamber music?"

Today the deepest thinkers in the world can only stammer in response. One day, the answer may be so obvious that nobody will understand how there could ever have been any confusion. In the future, nine-year-olds may read books called Where Ideas Come From.

In centuries past, the riddle of life seemed every bit as intractable as the riddle of consciousness does today. We understand perfectly well that brain gives rise to mind; the problem is that we cannot sort out just what that means. The scientists who made the modern world understood that certain bits of matter were alive and others weren't; the problem was that they couldn't sort out how that could be.

We cannot grasp how the brain, a lump of meat locked inside a dark, bone-framed cave, can create a light-soaked world. They could not grasp how a few inert odds and ends could take the shape of a leaping tiger with daggers for teeth. To try to make headway by focusing on what seemed a narrower question, Where do babies come from?, turned out in fact to make matters even harder. Tackling the riddle of life was challenge enough; explaining new life was harder still. Within a woman's womb a microscopic bit of tissue grows into a baby. But how did it get there? It couldn't appear out of nothing. Where did it come from in the first place, and then how did it grow?

MOST CONFUSING OF ALL, TO THE MALE SCIENTISTS CONTEMPLATING these riddles, was sorting out the woman's role in this story. Plainly she carried the baby and delivered it, but what did she contribute to the making of it? The male produced semen. What did the woman do? In the twentieth century Freud would famously ask, "What does woman want?" In the seventeenth century the question was, "What are women for?"

The simplest answer, a favorite of male thinkers since ancient times, was that woman was the field where a man planted his seed. That view was always presented as if it were the merest common sense. Aeschylus had spelled it out four centuries before Christ.

The woman you call the mother of the child

Is not the parent, just a nurse to the seed,

the new-sown seed that grow and swells inside her.

The man is the source of life—the one who mounts.

She, like a stranger for a stranger, keeps

the shoot alive unless god hurts the roots.

In England twenty centuries later, many still clung to the same view. The king's royal physician put it briskly, in a book on anatomy published in 1618: "The woman hath a womb ordained by nature as a field or seed-plot to receive and cherish the seed." But confront those learned authorities with everyday observations, and their certainty vanished. If the mother is merely a field where the infant grows, why do children so often look like their mother? That hit close to home. Maybe women did shape their babies in some way? On the one hand, that seemed unlikely, given women's second-class status. On the other, it seemed indisputable, for how else to explain family resemblances. What was going on?

FROM A DISTANCE, SEX LOOKS SIMPLE ENOUGH, A BIT OF HUFFING and puffing and some rudimentary choreography. But the key scenes in the drama—conception and then development over the course of nine months—take place deep inside the body, hidden from view. Nature, lamented William Harvey, concealed these biological secrets "in obscurity and deep night."

And even if you could see, you could not expect much from a search where you were not certain what you were looking for. No one knew, for instance, if women had eggs. Scientists split into feuding camps—one insisted that women, like birds, produced eggs; their rivals shouted that women, like men, produced a sort of semen.

Opinions abounded, but facts were rare and elusive. Egg and sperm, we now know, were not merely hidden but tiny. The human egg, though it is the largest cell in the body, is only the size of the period at the end of this sentence. Sperm cells are the smallest in the body, far too little to see with the naked eye. (An egg outweighs the sperm cell that fertilizes it by a million to one, the difference between a Thanksgiving turkey and a housefly.) The mystery of human development was never going to be as simple to investigate as the path of a falling rock.

Merely sorting out the basic facts of human anatomy was hard, grim work. To peer inside the living body was next to impossible.* Dead bodies were the only alternative but a poor fallback when your goal was understanding life. Dissections were carried out in the cold (to keep the corpse from decomposing) while the anatomist poked his knife into dark, wet crevices. Fascination and horror twined around one another. "You might be stopped by your disgust,” Leonardo da Vinci wrote, no matter how strong your curiosity, "and if that did not hinder you, then perhaps by the fear of spending the night hours in the company of those dead bodies, quartered and flayed and terrifying to behold."

High as the practical hurdles were, others stood higher still. All questions that had to do with birth and babies were charged and not simply because they had to do with that most fraught of all subjects, sex. In a God-drenched age like the 1600s, a venture into science was a dive into religion. Those were roiling waters. Everyone believed that God had fashioned the world and all its inhabitants, as the Bible detailed. God alone had the power to create life. How could one speak of the exalted work of creation and, in the same breath, of ordinary men and women clutching one another and gasping in the dark?

The whole scientific enterprise, with its talk of humans as sophisticated machines, was dangerous in two different ways at once. First, it threatened to push God to one side. That was blasphemy, and no more hideous charge could have been imagined. Second, and almost as bad, the scientific way of thinking seemed to drain purpose and meaning from the world. An assemblage of lifeless parts was not responsible for its actions. If humans were machines, a husband might strangle his wife and bear no more blame than a runaway carriage that plowed into a crowd.

In a different age, those contrasting approaches to the world would have pitted scientists against religious believers. That conflict would have been clear-cut. But in this case the scientists and the believers were the same people. The battle lines ran not between opposing factions but through the minds of individual men. Brilliant, ambitious, confused, conflicted, these reluctant revolutionaries sought desperately to find a way to fit their new discoveries with their old beliefs.

When it came to sex, they found themselves more confused than ever. They could not imagine, first of all, why God had devised so bizarre a system for preserving the human species. What could be less dignified? "Who would have solicited and embraced such a filthy thing as sexual intercourse?" demanded France's royal physician, in 1600. "With what countenance would man, that divine animal full of reason and wisdom, have handled the obscene parts of women, befouled with such great quantities of muck and accordingly relegated to the lowest part of the body, the body's bilge as it were?"

And, the learned physician went on, women didn't fare so well out of this sex business, either. "What woman would have rushed into a man's embrace unless her genital parts had been endowed with an itch for pleasure past belief? The nine months of gestation are laborious; the delivery of the fetus is beset with dreadfully excruciating pains and often fatal; the rearing of the delivered fetus is full of anxiety."*

In the end, though, it was God who had ordained this odd system, just as he had created the sky and the seas. No doubt he had his reasons.

THE GREAT INVESTIGATION STARTED WITH A FEW FACTS THAT EVERYONE could agree on, but these were isolated landmarks in a vast and empty landscape. Nearly every culture had figured out early on that it takes two to tango. Of the two partners, males presented fewer mysteries than females because they kept their working parts on the outside, on conspicuous display, in the mode of the Pompidou Center.


  • Finalist for the 2017 Kirkus Prize for Nonfiction
  • "An engaging and exuberant tour through centuries of thought about reproduction."
    Wall Street Journal
  • "Dolnick weaves a suspenseful tale of discovery, failure and often just plain weirdness while never losing sight of the mystery at hand."
    Scientific America
  • "As a record of a long biological quest, The Seeds of Life is full of detours, but that structure mimics the nature of scientific progress, illustrating how science is promoted or held back by colorful characters, by state and church intrusion or assistance, never lacking for rivalries and power struggles. Fascinating reading, Dolnick's book should evoke in us a sense of humility rather than amusement at the ignorance of the scientists of old."
    New York Times Book Review
  • "Full of intriguing anecdotes and colorful historical figures."
    Science Magazine
  • "Edward Dolnick's absorbing detective story spans outlandish ancient theories on baby-making and the nineteenth-century dawn of embryology, led by pioneers such as Oscar Hertwig."
  • "The Seeds of Life is science-history writing at its very best. It tells a great story that reads like a mystery novel. But Dolnick also uses the story to demonstrate how science advances: through curiosity, brilliant insight, analogy, logic, experimentation, and hard work. Equally, he shows how it can be retarded by unexamined assumptions, ad hominem arguments, misplaced ego, and stubborn adherence to outworn theories."
    Commentary Magazine
  • "Combining first-class research and a truly delightful writing style, Dolnick shares his fascination with the
    history of science and our perception of reproduction in this enlightening and enjoyable read."
  • "A story with many wrong turns and near misses, skillfully tantalizing modern readers with hints of a great truth obscured by lack of information. [Dolnick] does an excellent job of explaining the critical role that religion played for early modern biologists."
    Library Journal
  • "A delightful history...[The Seeds of Life is] the best sort of science history, explaining not only how great men made great discoveries, but why equally great men, trapped by prejudices and what seemed to be plain common sense, missed what was in front of their noses."
    Kirkus, starred review
  • "Edward Dolnick delightfully unravels the strange, unreal, and often laugh-inducing tales born from man's long quest to find out 'where babies come from.' Well-researched and engagingly written, The Seeds of Life is a charmer of history: quotable, fast-paced, and a reminder that science's messy, fumbling, and flat-out faulty progress is often much stranger than fiction!"
    Cristin O'Keefe Aptowicz, author of Dr. Mutter's Marvels: A True Tale of Intrigue and Innovation at the Dawn of Modern Medicine
  • "Like all good history, The Seeds of Life reminds us of so much we take for granted. Any high school student who pays attention in biology class knows some secrets about sex that eluded generations of brilliant investigators. In clear and engaging prose, Edward Dolnick traces the fascinating breakthroughs, and even more interesting blind alleys, explored by these pioneers of procreation. It's a history lesson and a biology lesson, enriched by vivid portraits of the often eccentric but always remarkable men who wielded scalpels and microscopes, trying to explain where babies come from."
    Ernest Freeberg, author of The Age of Edison: Electric Light and the Invention of Modern America
  • "A wonderful, astonishing story, beautifully told. Edward Dolnick has surpassed himself (and everyone else)!"
    David Wootton, author of The Invention of Science: A New History of the Scientific Revolution

On Sale
Jun 6, 2017
Page Count
320 pages
Basic Books

Edward Dolnick

About the Author

Edward Dolnick is the author of The Forger’s Spell, Down the Great Unknown and the Edgar Award-winning The Rescue Artist. A former chief science writer at the Boston Globe, he has written for the Atlantic Monthly, the New York Times Magazine, and many other publications. There are over 130,000 copies of his books in print. He lives with his wife near Washington, D.C.

Learn more about this author