Not until 1875 did a German scientist finally put the sperm and the egg together conceptually.

Egg, Meet Sperm: The Stubborn Secrets of Sex

The 17th century ushered in an astonishing age of scientific discovery, from Galileo’s positioning of the sun in the heavens to Newton’s Laws of Motion to Francis Bacon’s empiricism. Armed with new swagger and understanding, the scientific rationalists of the day figured the pivot from astronomy and physics to biology would be a piece of cake. The workings of the universe had been proved to adhere to laws and formulas. All would be properly unveiled in due time.

BOOK REVIEW — “The Seeds of Life: From Aristotle to da Vinci, From Sharks’ Teeth to Frog Pants, the Long and Strange Quest to Discover Where Babies Come From,” by Edward Dolnick (Basic Books, 320 pages).

How mistaken they were.

As Edward Dolnick writes in his amusing and informative “The Seeds of Life,” “The bold men of science raced off to take on the mystery of life and promptly face-planted.” In fact, they were fairly undone, partly by their own pigheaded biases and partly by the truly mystifying matters of genes and heredity, for which they were woefully ill prepared.

It was not until 1875 that a German scientist finally put the sperm and the egg together conceptually. The journey to that insight was sometimes comical, sometimes misguided, and usually revealing of cultural mores, gender politics, and societal blind spots. Consider, for example, the common scientific belief that a woman’s contribution to baby-making must surely be minimal.

Four centuries before Christ, Aeschylus wrote: “The woman you call the mother of the child/ Is not the parent, just a nurse to the seed. …The man is the source of life — the one who mounts.” To which the women of the day must surely have rolled their eyes. Alas, they were not the ones doing the science, or perhaps it wouldn’t have taken 22 centuries to settle the question.

The general idea was that the womb provided merely a soft field in which the male seed was sowed. This marked just the beginning of a long line of convenient theoretical blunders that served to bolster men’s self-regard. Witness Linnaeus’s condemnation of wet-nursing as a violation of the laws of nature (he disapproved of biological mothers leaving the house), Freud’s penis envy, and, more recently, the Oxford zoologist Desmond Morris’s theories about breasts evolving as a sexual signal intended for potential mates. Especially when it comes to sexuality, such prejudices have kept our heads in the sand far longer than they should have.

Then in 1672, a Dutch physician named Regnier de Graaf found ovaries full of eggs in a number of mammals, and although he couldn’t find any eggs in humans, he was convinced they must be there somewhere. It would take 150 years and a microscope before anyone would confirm the notion.

What the male seed looked like, exactly, no one knew, other than that it had something to do with male emissions. Conventional wisdom during the age of da Vinci held that the penis grew inflated with air (and eating “windy” food like beans would help the process). If the egg was hard to see, sperm was even harder. Sperm cells are the smallest cells in the body, and it wasn’t until Antony van Leeuwenhoek sprang up from his marital bed to spread his semen on a microscope in 1677 that anyone saw them. Unfortunately, Leeuwenhook fatally misjudged what he was seeing, at least at first, believing the sperm to be “so great a number of living animalcules.” In other words: parasites mucking up the otherwise magical seminal fluid. It was a mistake that had legs, as it were. Well until the 1800s, the parasite or “worm” theory held strong.

Dolnick, a former science writer for The Boston Globe, takes great delight in these fumbles, combining slapstick with clever metaphors and merciless physical descriptions. The 17th-century anatomist William Harvey is “impatient, dyspeptic.” Dolnick imagines Pleistocene couples “discovering” sex and congratulating themselves “as if they had managed the prehistoric equivalent of putting together a table from IKEA instructions.” He unfolds with particular glee an experiment that was both absurd and brilliant. In the 1770s, an Italian biologist named Lazzaro Spallanzani meticulously sewed and fitted male frogs with tight knickers through which semen could not pass. He observed that the dudes in the underwear were unable to fertilize eggs. If this seems glaringly obvious, it was actually the first definitive proof that fertilization requires both egg and seminal fluid, and not some mysterious male aura, contagion, or whisper of the divine.

It would still take another 100 years before biologists achieved full consummation, with the knowledge that sperm were not in fact parasites but crucial vehicles carrying instructions for a developing embryo. I’ll save that story for the reader.

Even fans of science history may be surprised by the level of attention and even obsession that the giant figures of the day devoted to attempting to understand reproduction. Dolnick reminds us that this history is not only fascinating but a cautionary tale of the hubris and bias that still infuse good intentions. An eager sperm does not always meet its mark.

Florence Williams is the author of “The Nature Fix: Why Nature Makes Us Happier, Healthier, and More Creative” (W.W. Norton, 2017) and “Breasts: A Natural and Unnatural History.”