Generation: The Seventeenth-Century Scientists Who Unraveled the Secrets of Sex, Life, and Growth

Generation: The Seventeenth-Century Scientists Who Unraveled the Secrets of Sex, Life, and Growth by Matthew Cobb, Bloomsbury Publishing; $24.95

Ovid and Virgil, two of ancient Rome s greatest poets, both gave the same cockamamy recipe for creating bees: Dig a very large hole; insert one dead bull; cover with earth, leaving nothing but the horns sticking out of the ground; wait several weeks; cut off the horns near the ground. Swarms of bees should now emerge from the holes in the buried carcass.

That intelligent men could agree on such preposterous stuff is mind-boggling. But as late as the 1600s, biological ignorance was so deep that most people accepted the idea that animals such as insects and worms were "generated" spontaneously from decaying matter. Everyone recognized that higher animals and humans did reproduce in kind, and that copulation surely had something to do with it. But there were profound misunderstandings. Medical scholars debated furiously whether babies came from a man's semen, from a woman's menstrual blood, or from some other emanation.

None of that confusion is surprising, given the sorry state of anatomy at the time. Leonardo da Vinci, in a strikingly explicit cross-sectional rendering of human lovemaking, drew a duct connecting the woman's nipples and her uterus, and another connecting the man's penis and his brain (the latter connection, some wag is sure to point out, still seems plausible). Nor, in retrospect, does it seem strange that physicians might have failed to recognize the role of the sperm and egg in the process. Both are far too small to be seen with the naked eye. Understanding reproduction, in short, demanded a closer look than anyone had yet thought to take.

According to Matthew Cobb, a lecturer in Life Sciences at the University of Manchester, England, physicians took that closer look during the latter half of the seventeenth century, with startling results. In the late 1660s an Italian physician and savant, Francesco Redi, published the results of a series of elegant experiments with rotting meat, which showed that baby insects actually hatched from eggs laid by other insects of the same species. It was a short jump from Redi's work to the conclusion that Ex ovo omnio: "Everything comes from an egg."

But were there human eggs? There were indeed, as three anatomists, the Dane Niels Stensen (Nicholas Steno) and two Dutchmen, Reinier de Graaf and Jan Swammerdam, discovered. Their collective skill in dissection and biological illustration enabled them to give the first reliable descriptions of the human reproductive system.

Cobb's scholarship is as meticulous as the work of his protagonists, and it crackles with lively anecdotes from their scientific reports. In December 1672, we learn, a shipment of representative specimens sent by Swammerdam arrived at the Royal Society in London, among them a preserved female uterus, a dissected penis, and a clitoris. All have since disappeared, though, according to Cobb, "the uterus may still be lurking somewhere in Bloomsbury." Equally memorable is the tale of Theodore Kerckring, who, to prove that the small, liquid-bearing structures in the ovaries of a woman's cadaver were indeed eggs, cooked and ate them. They hardened on heating, just like hen's eggs, but tasted "flat and unpleasant." Evidently, more work remained to be done.

The final chapters in Cobb's history belong to the early microscopists, notably the famous Dutchman Antoni van Leeuwenhoek. Looking through his lens, Leeuwenhoek was the first to report seeing hordes of "little animals" (sperm) in semen. By the eighteenth century, the idea that buried cattle gave birth to bees was beginning to sound as crazy as the notion that storks brought babies. Of course, the full story of reproduction, still emerging in this age of molecular genetics, in vitro fertilization, and cloning, is far stranger than anything our forebears could have imagined.

LAURENCE A. MARSCHALL, author of The Supernova Story, is W.K.T. Sahm Professor of Physics at Gettysburg College in Pennsylvania, and director of Project CLEA, which produces widely used simulation software for education in astronomy.

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