In our own species, those bloodthirsty Aztecs and their prehistoric descendants were notorious for their sacrifice and cannibalism rituals. These were largely symbolic religious events, but some scholars have suggested that the greasy surfeit of Aztec sacrifice victims may have also been a high-energy nutritional supplement for the wealthy elite, who had first dibs on this "man corn." Noncannibalistic people may be the weird ones, cross-culturally speaking. Researchers have documented evidence of ritual anthropophagy throughout non-state societies in Africa (Zandelande, Sierra Leone, the Belgian Congo), South America (Eastern Brazil, Ecuador, Western Columbia, Paraguay), the New Hebrides (Fiji, Papau, New Guinea, Vanuatu, East New Guinea Highlands), and Native America. It's appeared in modern "civilized" societies, too, including famine-stricken China and Soviet-era Russia.
The bottom line, says Petrinovich, is that when you're hungry enough, ravenous really, and when all other food sources—including "inedible" things you'd rather not stomach such as shoes, shoelaces, pets, steering wheels, rawhide saddlebags, or frozen donkey brains—have been exhausted and expectations are sufficiently low, even the most recalcitrant moralist among us would shrug off the cannibalism taboo and savor the sweet meat of man … or woman, boy or girl, for that matter. It's either that or die, and among the two choices, only one is biologically adaptive.
A behavior can be adaptive without being an inherited biological adaptation, of course. But because starvation occurred with such regularity in our ancestral past, and because the starving mind predictably relaxes its cannibalistic proscriptions, and because eating other people restores energy and sustains lives, and because the behavior is universal and proceeds algorithmically (we eat dead strangers first, then dead relatives, then live slaves, then foreigners, and so on down the ladder to kith and kin), there is reason to believe—for Petrinovich, at least—that anthropophagy is an evolved behavior. The taboo against cannibalism is useful in times of health and prosperity; groups wouldn't survive very long if members were eating one another up. Yet starvation has a way of releasing the cannibal within.
In fact, starvation cannibalism may have been so prevalent in the ancestral past that it literally changed our DNA. Modern human populations appear to contain specific genetic adaptations designed to combat cannibalistic viruses. Typically, when a predator species consumes a prey species, there are substantive differences in immune systems between the two, with different varieties of pathogens. But the more similar are the eater and the eaten, the more vulnerable is the former to debilitating food-borne disease. This is what likely happened with the New Guinea Fore people in the case of kuru, a neurodegenerative disease that devastated that population in the early half of the last century. Epidemiologists traced the disease to mortuary cannibalism; women and children were eating the brains of the recently deceased as part of a funerary ritual. (Pork had fallen into short supply, so human brains infused a healthy dose of protein.) The interesting thing is that kuru is a variant of Creutzfeldt-Jakob Disease and probably resulted, originally, from a single case of cannibalism among the Fore of a CJD-ridden brain, with kuru then evolving on its own course. In a 2003 issue of Current Biology, University of Nottingham geneticist John Brookfield speculated that over the past 500,000 years, human beings developed increasing variation in the gene for the human prion protein. Those who are heterozygous for this gene, points out Brookfield, were protected against CJD through cannibalism. "This sustained heterozygote advantage [was possibly] created by a lifestyle of habitual cannibalism," suggests Brookfield, "implying a new vision of the lifestyles of our ancestors."
As we've seen, not all cases of cannibalism are due to nutritional needs. Sociopathic individuals such as Jeffrey Dahmer, Armin Meiwes and Issei Sagawa lived in urban environments peppered with fast-food restaurants and overflowing grocery stores, yet still they dined on people. In his book SuperSense, University of Bristol psychologist Bruce Hood argues that such cases reflect essentialism beliefs, the idea that the victims' hidden "essences" or personality attributes are acquired by physical ingestion. It's also interesting that many such cases have a sexual component. As the author of To Serve Man: A Cookbook for People wrote teasingly: "There is no form of carnal knowledge so complete as that of knowing how somebody tastes." I suspect there's some truth to that uncomfortable joke. Essentialism beliefs may account for our species' peculiar—and surprisingly recent—history of medical cannibalism as well. The conquistadors and their New World heirs were known to have used human fat from agile natives to grease their arthritic joints. Long before Armin Meiwes was even a twinkling in his mother's eye, pregnant Ache women of Paraguay were nibbling on boiled penises in the hopes it would bring them sons.
So with all of these scenes swimming in my head, and pragmatist that I am, I'm left wondering why, exactly, it is that the consumption of already dead human bodies is such a taboo, especially for societies in which the soul is commonly seen as flitting off at death like an invisible helium balloon. If you subscribe to such dualistic notions, after all, the body is only some empty shell that the now-liberated spirit no longer needs. All those poor starving children of the world, surrounded by—as some epicures swear—the most succulent meat on the planet. Even resurrectionists should gleefully feed the impoverished with their own flesh, lest they, God forbid, allow such a bounty of edible meat to go to rot. All those wasted commercial goods, burned down to sticky dust in crematories, squirreled away behind ornate vaults, fed extravagantly to bloated subterranean organisms! If you'd rather not eat meat from aged or possibly diseased dead people, and if you're worried about the dignity of the individual, it would be easy enough to breed and then factory-farm brain-dead or free-ranging anencephalic human beings *, treating them humanely, of course, but enforcing food safety standards to control for outbreaks.
A parting tip for the entrepreneur: Rumor has it there's already some prime breeding stock—unfortunately a bit marbled with adipose tissue but with all the lucidity of dairy cows—readily available as founder lines in select communities. Want to buy in? E-mail me for details.
Watch: Robert Wright of BloggingHeads.tv and psychologist Paul Bloom of Yale on what motivates cannibals.
Correction, Dec. 20, 2010: The original incorrectly referred to "hydrocephalic" human beings, who would have a less severe condition characterized by an excess of cerebrospinal fluid. (Return to the corrected sentence.)