Spook: Science Tackles the Afterlife Read online

  Of late, I find myself wondering about the mechanics of it, the unfathomable blending of metaphysics and embryology. How would the suddenly homeless soul get itself situated someplace new? How does spirit, for want of a more precise word, infuse itself into a clump of cells quietly multiplying on a uterus wall? How do you get in there?

  Scientists and philosophers of bygone years had a name for the impossible moment. They called it ensoulment, and they debated it for centuries. If the National Science Foundation had existed in the 1600s, there would have been an entire lavishly funded Institute of Ensoulment, devoted to studying the mysteries of human generation, the how and when of life’s initial spark. Most of the research covered in this book focuses on things that happen to a person as, and after, his body reaches the finish line, but it makes sense to spend a little time at the other end of the footrace, too.

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  The Little Man Inside the Sperm, or Possibly the Big Toe

  Hunting the soul with microscopes and scalpels

  THERE’S A VERY good chance that you underestimate the historic import of the sea urchin.* In 1875, a German biologist named Oskar Hertwig watched a sea urchin sperm nose its way into a sea urchin egg and fuse with it to form a single nucleus, right there under his microscope. It took civilized man six thousand years to figure out how life begins, and the honors go to humble Oskar and his amorous echinoderms.

  Scientists had long suspected that human generation had something to do with eggs—most everyone who owned a chicken suspected this—and they knew it had to do with intercourse and semen, but beyond that they were unclear on the specifics. This was largely because they couldn’t see the specifics. The sea urchin’s eggs offered two advantages: (a) they’re see-through, and (b) they’re fertilized outside of the female’s body, in the ocean or, in occasional cases, under some German dude’s microscope.

  This means that for six thousand years, there was lots and lots of entertaining speculation about the creation of new human beings. Some of the earliest and most thorough speculating was done by Aristotle. The learned Greek—who, I was interested to read, went through life with a lisp—decided that the man’s semen supplied the soul of the new individual. The spirit, in those days, was envisioned as a kind of vapor or breath, which was understandable given breathing’s obvious connection to being alive. Hence Aristotle’s name for the spirit: pneuma, which is Greek for “wind.” He believed it was this pneuma, carried in the semen, that orchestrated the creation of a budding human being. Upon arrival inside the uterus, the pneuma would set to work, building new life out of the materials it had on hand: menstrual blood, to be unpleasantly specific. Aristotle described the process as a sort of coagulation, using the apt if inelegant analogy of a cheese-maker’s rennet solidifying milk. It took seven days for the new entity to “set,” at which time the pneuma would infuse it with the first of three eventual souls. This vegetative soul, as it was called, was a sort of starter soul, a learner’s permit for human existence. You were a thing that eats and grows: more than a potato but less than a human.

  On the fortieth day, Aristotle theorized, the proto-human morphed into what he called the sensitive soul. By “sensitive,” he meant “relating to the senses,” for forty days is about when the embryo’s sense organs begin to appear. After some further, unspecified amount of time had passed, the pneuma would allow the newly minted sensitive soul to upgrade to a rational soul. Here was the black belt of humanness, the sort of spirit that rises above animal lusts and girly emotions and pays no heed to people who make fun of the way it says semen.

  And that’s pretty much what people believed for the two thousand years after Aristotle put the word out. The man who elevated the ovum to a leadership role in the proceedings was seventeenth-century English physician William Harvey. Harvey is best known for figuring out that blood circulates in a closed system of arteries and veins, a feat he managed by dissecting cadavers, including that of his sister. For his pioneering work in reproduction, you will be relieved to learn that Harvey left the womenfolk alone. Here he turned to a herd of deer that wandered, ever more warily, the grounds of his employer, King Charles I. As a student of Aristotle’s teachings, Harvey expected to find the requisite coagulated blob when he dissected the deer’s uteruses. He was astonished to instead find the beginnings of tiny deer: embryos and fetuses encased in sacs, which he mistakenly identified as eggs. The egg, Harvey felt, contained the makings of “all that is alive.” Semen was relegated to the role of a “contagion,” prompting human generation much as a virus does a cold.

  And how would the life force, the soul, get into the egg? Here science abandoned Harvey, and he fell back on religion: “It is given…by the heavens or the sun or the Almighty Creator.”

  Like most biologists of his day, Harvey was limited by his equipment. He couldn’t see what was going on at the cellular level. He couldn’t see sperm. He had a magnifying glass, but what he needed was a microscope. And so it is not surprising that the next milestone fell to Antoni van Leeuwenhoek: the man who loved microscopes. Leeuwenhoek did not invent the microscope, nor was he a scientist by training. The Dutchman worked as an accountant for a haberdasher and, later, as Chamberlain of the Council-Chamber of the Worshipful Sheriffs of Delft, which is a ten-gallon way of saying that he tidied the chamber. The post left him plenty of time for hobbies, of which he had just one: grinding lenses and building microscopes. The microscopes Leeuwenhoek built were superior to those of the main maker of the day, and soon they were in demand by members of the Royal Society of London for the Improving of Natural Knowledge, more or less the National Science Foundation of its day. Over time, the Royal Society began publishing Leeuwenhoek’s letters about his findings as well, and he was on his way to a historical, if unpaid, career as the founding father of microbiology.

  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 Societ
y 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 longer 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 stru
ctures 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.”