Where Do Babies Come From? And Why Did It Take Scientists So Long to Find Out?

    By Abraham Verghese | 23 June 2017
    The New York Times

    Leonardo da Vinci’s sketch ”Study of the foetus in the womb,” ca. 1510. (Credit Image from “The Seeds of Life”)

    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
    Edward Dolnick
    Illustrated. 309 pp. Basic Books. $28.

    Where do babies come from? The answer to that question is now common knowledge, yet in “The Seeds of Life,” the veteran science writer Edward Dolnick tells us that for centuries it proved elusive, even to the greatest minds. Profound discoveries were being made in medicine, mathematics, astronomy and other fields, but it would take until 1875 for us to fully comprehend the process of human gestation.

    When men and women have sex, children can result. That link was understood for a long time (although well into the modern era there were holdouts, such as the inhabitants of the Trobriand Islands, now part of Papua, New Guinea). Yet the precise means by which sex led to a baby remained hidden. For early investigators, the biggest obstacle was their inability to look inside a living body. Studying the dead might have provided some answers, but that wasn’t easy. Church and state considered it a sin or a crime. “You might be stopped by your disgust,” Leonardo da Vinci wrote, “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.” Arguably the first great anatomist, Leonardo was allowed the chance to dissect hospital patients and recently deceased criminals, but as interested as he was in the uterus, leaving behind wonderful drawings of the womb with a fetus within, he couldn’t say how the fetus had got there. Later researchers were similarly thwarted. The supply of corpses was simply too limited, even after the dangerous practice of grave robbing emerged to meet such demands.

    The male sexual organs were easily studied. Although semen was an obvious byproduct of sex, its function was unclear. “The standard notion among scientists (virtually all of them male, in these early days),” Dolnick writes, “was that semen was a magical, almost divine concoction. Precisely what form that magic took was in dispute: Did semen exert its influence without physical contact, as sunlight nurtured plants, or did it serve as the key ingredient in a divinely ordained recipe, as a kind of baby batter?

    Female anatomy was largely hidden and therefore poorly understood. Even more perplexing was the matter of heredity. “If babies somehow combined features of their two parents, as experience seemed to demonstrate, how was it that newborns were either boys or girls rather than a combination of the two? And if the two parents each contributed to forming their baby, why weren’t babies born as monsters with two heads and four arms and four legs?”

    A major impediment was what Dolnick calls “the vexed matter of eggs.” After all, many creation myths have the first humans emerging from an egg. “In the 17th century,” Dolnick explains, “scientists found still another reason to look with special favor on eggs and ovals of all sorts. God the mathematician, they declared, had favored the circle above all other shapes, because it was geometrically perfect.”

    In the mid-1600s, a Dutchman, Regnier de Graaf, came close to sorting it all out. As he studied the female reproductive organs of many species, he found that they all “have ovaries full of eggs” and that the eggs of mammals “are fertilized and reach the uterus in the same way as in birds.” He made particularly careful observations of the reproductive organs of rabbits. “His tools,” Dolnick reminds us, “were little more than sharp eyes and the ability to count. Instead of dissecting his rabbits only a few hours or even a few days after they had mated, he waited several days. Now he found ruptured follicles in the ovary and tiny embryos in the uterus.” De Graaf’s advance was conceptual, clarifying the distinction between the new living organism and the female’s contribution to it: “De Graaf cleared things up and convinced the world to shift focus. In his picture, the egg emerged from the female’s ovary and combined somehow with semen from the male to form a new organism.” This was a daring proposition, since de Graaf had never seen the egg itself — the tools were simply not there. He’d noted the follicles on the ovary, then seen them ruptured, by which time an embryo or fetus (the fertilized egg) could be found in the uterus.

    Leeuwenhoek’s microscope was the necessary next step. A skilled lens maker, he found himself witnessing a tiny world teeming with life. One night, after making love with his wife, he examined his own sperm under his microscope and described the tiny creatures he saw, “furnished with a thin tail, about five or six times as long as the body,” that moved like “a snake or an eel swimming in water.”

    This observation triggered a great debate, pitting “spermists” against “ovists.” De Graaf had seen the eggs. Others saw the motile creatures in the semen and believed them to be the source of the future baby. At the heart of the spermists’ case was the claim by a mathematician named Nicolaas Hartsoeker that each sperm “actually encloses and hides an even smaller being under a tender and delicate skin.” As part of his argument, he presented a drawing that, as Dolnick puts it, “generations of histories and textbooks have made notorious ever since, of a bigheaded person curled up inside a sperm cell, hands clutching knees as if he has just been told to brace for a crash.”

    A consequence of this notion was an obsession with not spilling sperm. “Decade after decade,” Dolnick writes, “medical writers barraged the reading public with horror stories.” “Every seminal emission out of nature’s road — I must speak plainly, gentlemen! — every act of self-pollution is … an earthquake,” a London authority declared, “a blast, a deadly paralytic stroke.” Even as noted a figure as Rousseau warned against “the most deadly habit to which a young man can be subject.” Dolnick adds more names to the roster: “Kant proclaimed masturbation more sinful than suicide. By far the most important and influential of these naysaying authorities was Samuel Tissot, one of Europe’s most acclaimed physicians. In 1762 he produced a tome called ‘A Treatise on the Diseases Produced by Onanism.’”

    The perils of onanism aside, it would seem an easy matter for the two sides to come to an understanding of the importance of both egg and sperm. Yet that’s not what happened. “Instead,” Dolnick tells us, “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.”

    This debate dragged on and on. It was not till a spring day in 1875 that the answer came. A German scientist named Oscar Hertwig put a sea urchin egg under his microscope. The distinctively transparent nature of the egg lent itself to this kind of voyeurism, as did the fact that fertilization in sea urchins takes place outside the body, as it does in frogs. Dolnick sets the scene: “Hertwig poked a drop of sea urchin semen near the egg. A tiny sperm cell pushed against the egg’s outer surface. Moments later the nucleus of the sperm cell came into view, inside the egg, like a message thrust inside a bottle. … Suddenly the two nuclei were in contact, and then — before Hertwig’s eyes — the two nuclei fused into one. No one in history had ever seen the process of fertilization play out. Until Hertwig. The emergence of a single nucleus where there had been two, he wrote, in perhaps the only lapse into poetry in his long career, ‘arises to completion like a sun within the egg.’”

    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. In his acknowledgments, he cites the anthropologist Max Gluckman’s remark that “the fool of this generation can go beyond the point reached by the genius of the last generation.” Scientific questions almost as fundamental as the genesis of the embryo remain to be answered — the black box of the brain is far from unlocked. Future historians will wonder what took us so long to find the answers.

    Abraham Verghese is the Linda R. Meier and Joan F. Lane provostial professor and vice chair in the department of medicine at Stanford University, and the author, most recently, of a novel, “Cutting for Stone”.

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