In 1675, Leeuwenhoek discovered a universe of up-to-then-unknown creatures—bacteria and protozoa, mostly—in drops of stagnant water in a “water-butt” in his yard. He named them animalcules. It is difficult to properly appreciate the wonder and strangeness of this discovery. Think of scientists today discovering Martian life. Leeuwenhoek was appropriately awed. “For me this was among all the marvels that I discovered in nature the most marvelous of all, and I must say, that for my part, no more pleasant sight has met my eye than this of so many thousands of living creatures in one small drop of water.”
Leeuwenhoek bravely turned his instrument upon himself. “My teeth are not so cleaned …” he wrote, “but what there sticketh or groweth between some of my front ones and my grinders … a little white matter, which is as thick as if ’twere batter.” He mixed some of this batter with fresh rainwater and looked at a smear under the microscope. Did he find animalcules? You bet your water-butt he did. “All the people living in our United Netherlands,” he concluded, “are not as many as the living animals that I carry in my own mouth.” It is a testament to Leeuwenhoek’s love of biology that he could describe the bacteria in tooth scum as “very prettily a’moving.”
In a further exploration of oral fauna and the limits of spousal patience, Leeuwenhoek headed into the mouth of his wife, Cornelia, and their daughter Maria. “I examined … a little of the matter that I picked out with a needle from betwixt their teeth.” Next he recruited an old man who had “never washed his mouth in all his life” and noted that while his spittle held a normal number of these animalcules, the matter between his teeth held “an unbelievably great company of living animalcules.” Day by day, the foundations of modern oral hygiene took shape under Leeuwenhoek’s lens. He noted the relationship between a “stinking mouth” and “the animals living in the scum on the teeth.” In a three-hundred-years premature dig at Listerine, he observed that while wine-vinegar killed spittle animalcules on contact, it “didn’t penetrate through all the matter that is firmly lodged between the front teeth or the grinders and killed only those animalcules that were in the outermost parts of the white matter.”
While the fellows of the Royal Society were politely attentive to Leeuwenhoek’s oral safaris, they encouraged him to move on to the rest of man’s moistnesses. In particular, they wanted him to examine semen. Perhaps it would be possible at last to view the material of the human soul! Leeuwenhoek refused. “He questioned the propriety of writing about semen and intercourse,” wrote E. G. Ruestow in an article in the Journal of the History of Biology. Several years later, a medical student presented Leeuwenhoek with a vial of semen from a gonorrheaic man. (Hey, thanks!) The student said he’d found within it small animals with tails, which he assumed were related to the gonorrhea. Leeuwenhoek suspected otherwise, and set about examining his own semen. In a 1677 letter describing his findings, Leeuwenhoek was careful to point out that the material was a “residue after conjugal coitus,” and not the product of “sinfully defiling myself.”
In that letter Leeuwenhoek sets forth the first scientific description of sperm: animalcules so small that “a million of them would not equal in size a large grain of sand….” He describes the apparent difficulties of swimming in semen, noting that the animals had to “lash their tails eight or ten times before they could advance a hair’s-breadth.” He included eight drawings of “the little animals in the seed,” some with tails straight, looking like hat pins, others with winding sine-wave tails, clearly struggling against the custardy tide.
Then he commenced to tread the path that would lead to his biggest career blunder. He claimed to see a network of vessels within the sperm bodies, and imagined that it held the beginnings of all the organs that the human would one day possess. This line of thinking—called preformationism—would prove enormously popular and to this day provides publishers of embryology textbooks with irresistible images for their historical chapters: old woodcuts and engravings of sperm with microscopic humans inside, heads down and knees drawn up to their chests, like cramped, napping stowaways. One of these likely influenced Leeuwenhoek. He had received a letter from a French aristocrat named François de Plantade, which included two drawings of the miniature people inside sperm. In this case, they were depicted outside of their sperm hulls, standing with their hands crossed demurely over their little private parts. On their heads are what appear to be small hats or hooks, giving them the appearance of adorable human bracelet charms.
Though Leeuwenhoek himself never managed to find the preformed people inside sperm—despite having tried at one point to peel the “skin” off one—he came to believe they were in there. He believed that each sperm held a soul with the potential to become a human life, and that the woman’s role in reproduction was merely to receive and nourish the perfectly formed miniature human. (Leeuwenhoek wasn’t the first to espouse this line of thought. Hippocrates took the no doubt breakfast-inspired view that the egg was simply something for the developing human to eat. He further speculated that as soon as the egg was all eaten up, then the infant would hatch: birth as a sort of grocery-shopping trip.)
Leeuwenhoek was what became known as a spermist. The label suggests that there were ovists for the spermists to argue with over dinner, and indeed there were. I learned about the ovist-spermist debate in an amazing book called The Ovary of Eve, by Clara Pinto-Correia, who has the audacity to be both a literary success and a respected developmental biologist. I don’t know what Clara hatched from, but clearly better stuff than I.
The ovists pointed to the spherical shape of the ovum as befitting its lofty mission. The sphere is the shape of the planets and the stars: God’s perfect form. (Whereas sperm look like worms.) Leeuwenhoek took a different view. He didn’t think of ova as spheres; he thought of them as globules. “Do we not see that all excrements, discharged either by human beings or animals, consist of globules …?” he wrote. “And … we see that fat, pus, and certain parts of a horse’s urine also consist of globules.” This from the man who didn’t want to write about semen.
The ovum’s main shortcoming as the vessel of humanity was that it derived from the woman, who was in those days (more) universally considered a second-class organism. “If ovism was the true system of reproduction, God was sending a mixed message,” writes Pinto-Correia. “He had locked us inside perfection. And then he had locked perfection inside imperfection.”
The other argument for the primacy of sperm was that they moved. They appeared to possess some kind of animating spirit. On the other hand, if sperm was an animal, did that mean that it ate and defecated and copulated? Pinto-Correia’s book includes a detailed drawing by an overimaginative French embryologist purporting to show the wee digestive system of the human sperm. But if sperm hatched humans, who or what hatched sperm? Not surprisingly, there were competing theories as to sperm’s function. Some thought sperm had nothing to do with reproduction, and guessed them to be a symptom of testicle disease. Others thought the wrigglers’ job was to incite the male into having sex, presumably by causing some kind of physical itch or discomfort, though I like to envision a sort of Woody-Allen–style team effort involving tiny megaphones and shouts of encouragement.
The debate dragged on until Oskar Hertwig came along to set things straight. Following the discovery of conception, the question of the hour became: When does the soul enter this new being, this cellular amalgam of male and female? Conception—the mystical fusing of egg and sperm—was the logical choice, quickly supplanting Aristotle’s notion of the evolving soul.
Contemporary debate over the morality of abortion and stem cell research has sparked renewed interest in the timing of human ensoulment. The best book I found on the topic is a Cambridge University Press publication by Norman Ford, called When Did I Begin? Ford, a moral philosopher and a Salesian Catholic priest, makes the clean and quite elegant argument that personhood—to use the more secular term for ensoulment—cannot begin until after the point where identical twinning is no l
onger possible: about fourteen days after conception. Up until that point, it’s possible for the zygote to become two identical twins. If the soul had arrived at conception, what would happen then? Would it split into two, each twin making do with half a soul? No, Ford argues. Up until that point, the zygote—with its potential to become two distinct and separate human beings—cannot rationally be referred to as a person. “I contend that the cell cluster can best be understood as human biological material but not a unified living human organism,” he writes.
As for exactly what point after the fourteenth day personhood might begin, that is less clear. The fourteenth or fifteenth day heralds the arrival of the primitive streak, the early vestiges of the neurological system, and some argue for this point. But no one—at least on a scientific basis—knows for sure when the soul, the spirit, the self, is instilled, or installed, or whatever process it uses to get itself in there. Or what it consists of or where it’s located. Or even if it exists. Which brings us back to our basic quest.
Descartes became a familiar sight at the butcher shops in Amsterdam, where he would buy freshly slaughtered animals. When visitors asked to see his library, he would take them into a room where he kept carcasses in various stages of dissection. “These are my books,” he would say.
The above passage, from science writer Carl Zimmer’s Soul Made Flesh,* describes one of philosopher René Descartes’s lesser-known projects: to figure out the workings of the human machine. One of the specific things Descartes was doing with his carcasses was looking for the soul. He assumed it resided somewhere in the brain, and so his most well-thumbed “books” took the form of cow heads. One paragraph up, Zimmer writes that Descartes spent much of that period of his life in self-imposed exile, “craving solitude.” The carcasses surely helped.
Descartes is one of the few early philosopher/scientists to have physically searched for the soul, actually opened up bodies and looked for it. He eventually nominated the pea-sized pineal gland. To those who know the gland’s actual function (it regulates melatonin production), it may seem an unlikely choice. Descartes was swayed by the gland’s position at the center of the head, and by dint of its being one of the few brain structures that don’t exist in pairs. He didn’t think the ugly little gland was the soul per se; more that it was a sort of hub, a meeting point for sensory information and the flowing streams of spiritus (akin to Aristotle’s pneuma) that carried out the self ’s higher functions.
Descartes dreamed up an elaborate model of the nervous system with strings and valves and tiny bellows. He described spiritus flowing through the nerves—which he envisioned as tubular—and into the muscles, causing them to contract by inflating parts of them. In a paper called “On the ‘Seat of the Soul’: Cerebral Localization Theories in Mediaeval Times and Later,” neurologist O. J. Grüsser writes that Descartes’s model for this system was the organ, then in its heyday as a popular musical instrument. Fifteen centuries earlier, Grüsser adds, the Greek physician Galen based his system of spiritus flow on the mechanics of Roman bathhouse heating systems. Meanwhile, the philosopher Albertus Magnus found inspiration in the equipment used to distill brandy. And so it went, on into the twentieth century, when tape recorders and computers took hold as the working models of consciousness.
A couple years back, I corresponded with a computer professional named Betty Pincus, who has been in the industry some forty years. “It always interested me the way some of my colleagues would use the technical vocabulary to describe how their minds worked,” she wrote. “In the sixties, they talked about ‘running out of tape’ or ‘her accumulator overflowed.’ As the technology changed, it became ‘running out of disk space’ or ‘multitasking.’ I’ve often wondered whether the inventors of these machines created them in their own image of how their minds worked or if they related the machine to the mind after the machines were created.”
I managed to find only two other references to scientists rummaging around in corpses looking for souls. One comes from the Midrash, a collection of ancient rabbinical commentaries on the Torah. The Midrash makes reference to a single indestructible bone, called the luz. The luz is shaped like a chickpea (or an almond, depending on which rabbi you listen to) and located at the top of the spine (or the bottom, depending on which rabbi you listen to). From this bone, the Midrash states, a person is reconcocted after death. It’s the soul bone.
The Midrash includes a description from the Torah of an experiment to prove the unique indestructibility of the luz. The project was carried out by Rabbi Joshua ben Hananiah upon being confronted by the Roman emperor Hadrian. “Prove it to me,” Hadrian is quoted as saying. So the rabbi did. “He had one brought….” (Like he just turned to some underling: Smetak! Fetch me a luz!) “He put it in fire, but it was not burnt, he put it in a mill but it was not ground. He placed it on an anvil and struck it with a hammer; the anvil split and the hammer was broken but all this had no effect on the luz.”
Needless to say, there was much chatter about the luz over the centuries, and when the science of anatomy began to gain momentum in the Middle Ages, its practitioners sought to find it. They nominated, among other bones, the coccyx, the sacrum, the twelfth dorsal vertebra, the wormian bones of the skull, and the tiny sesamoid bones of the big toe. Of course, these bones are all easily destroyed, and the anatomists eventually decided it was a matter best left to the philosophers. The famed Renaissance anatomist Vesalius, having spent an afternoon mucking around with a set of sesamoid bones, more or less laid the matter to rest: “We should attach no importance whatever,” he wrote in De humani corporis fabrica, “to the miraculous and occult powers ascribed to the internal ossicle of the right great toe.”
Contemporary rabbinical discussion of the luz is harder to come by. On the website Ask the Rabbi, a mohel from Paris posted an e-mail seeking information about the luz. The rabbi’s reply confirmed the bone’s alleged indestructibility and added that it has been described as “having within it many intertwined spider-like blood vessels.” He referred the mohel to a Dr. Eli Temstet of Paris for more information. I e-mailed the mohel to see what he’d found out. “Dr. Eli Temstet of Paris has gone to a better world,” came the reply. “Now, he sure knows where and what exactly is the luz.” I sent an e-mail to Ask the Rabbi. Was there a paper on the spider-like blood vessels of the luz? The rabbi did not Answer the Writer. I consulted a book on Talmudic medicine, but no mention was made of the spidery veins of the soul bone.*
The very first person to poke around for a soul in a human cadaver was the third-century B.C. physician Herophilus, of Alexandria. Herophilus is thought to be the first person in history to have dissected human cadavers for the purpose of scientific enlightenment. As such, he bagged a lot of anatomical discoveries. One of these was the four chambers, or ventricles, of the brain. He believed that the soul was headquartered in the fourth one. Why was Herophilus looking around for a soul inside a dead man, especially given that Egyptians believed in an afterworld† for souls to retire to? I can’t tell you for sure, but I can tell you that Herophilus was rumored to have dissected live humans as well. Two colleagues accused him of vivisecting hundreds of criminals. Perhaps his soul-related aspirations explain his poor table manners.
If your goal was to pinpoint the soul, it obviously made more sense to experiment on the living than on the dead. The simplest plan of action would be to systematically scramble, excise, or otherwise disable the likely structures and watch to see if the lights went out. And this, more or less, is what got done. Like Descartes, most scientists had zeroed in on the brain. (From early on, observations of personality changes caused by head injuries suggested a link between brain and self.) Galen was one of the earliest of the neuro-vivisectors; he experimented with cutting (and getting on) the nerves of his neighbors’ pigs. Based on this work, he decided that the soul was situated in the substance of the brain and not, as Herophilus had maintained, in the ventricles.
Leonardo da Vinci further narrowed it down. In 1996
, McGill University professor of neurosurgery Rolando Del Maestro curated an exhibition called “Leonardo da Vinci: The Search for the Soul.” In the materials for the exhibit, Del Maestro describes a 1487 manuscript in which Leonardo made notes about a passage he had read in a book about the Carthaginian War. The passage describes the quickest way to kill an injured elephant: by pounding a stake between the animal’s ears at the top of the spinal column. Intrigued, Leonardo took to pithing frogs in a similar manner. “The frog instantly dies when its spinal medulla is perforated,” Del Maestro quotes Leonardo as having written. “And previously it lived without head, without heart or any interior organs, or intestines or skin. Here, therefore, it appears, lies the foundation of movement and life.” (I think that what he meant is that the skinned, gutted, headless, heartless frogs lived for a little while.)
Only one soul-seeking man of science carried out this sort of cavalier slice-and-see experimentation on a living human being. As the king’s surgeon and the founder of France’s Royal Academy of Surgery, Gigot de La Peyronie could pretty well do what he felt like. In 1741, he published a paper entitled “Observations by Which One Tries to Discover the Part of the Brain Where the Soul Exercises Its Functions.” The subject was a sixteen-year-old boy whose skull had been cracked by a rock. After three days of worsening symptoms, the youth fell unconscious. La Peyronie “opened up his head” and found a suppurating abscess deep down inside the brain, at the corpus callosum. He drained the wound, taking care to measure the runoff, which amounted to “about the volume of a hen’s egg.” As soon as the pus* that had weighed upon the corpus callosum was drained, he wrote, the coma lifted. La Peyronie noted that when the cavity had refilled with ooze, the youth fell unconscious again. He reemptied it, and again the boy awoke. The corpus callosum, he reasoned, must be the seat of the soul. Just to be sure, La Peyronie decided to undertake a little experiment. He filled a syringe with saline and injected it directly into the newly drained wound. As predicted, the boy lost consciousness. And was brought back to his senses when La Peyronie pumped the water back out.