There are lots of reasons why cannibalism isn’t a good idea.
For one, most cultures would consider it unethical, even if there was no actual killing involved. For another, it can make you pretty sick. The Fore tribe of Papua New Guinea practiced cannibalism as part of a preservation ritual for their dead—and were stricken with a deadly disease called kuru that is spread through the consumption of human brains and organ meat.
But even if you were trapped on a desert island with your worst enemy, and starving, you’d probably be better off eating any of the other animals in the vicinity if you wanted to stay alive—it turns out human meat isn’t all that nutritionally valuable.
Humans have engaged in cannibalism throughout history, says James Cole, an archeologist at the University of Brighton in England, for ritual and medicinal purposes, and as the result of psychosis and warfare, among others, Even before our ancestors evolved to be Homo sapiens, they were eating each other. Archeologists have found evidence of cannibalism in the skeletons of early hominins found all over Europe.
Hominins are a group that includes modern humans, extinct human species (like the Neanderthals), and the immediate ancestors to humans. In studying hominin species that preceded Neanderthals and Homo erectus, archeologists have found bones that had burn marks similar to those found on animal remains—marks scientists believed to have been made by cooking the animals (and humans) over a fire.
The hominin remains also had human teeth marks, missing cranial bases on otherwise whole skeletons (suggesting the skulls had been taken apart to get to the brain), and something called “peeling,” when fresh bones are broken and dismantled, often to get to the yummy marrow. Archeologists have also found hominin bones thrown away with animal bones, as if they were all part of the same meal. In all but one of these cases, cannibalism was attributed to a nutritional need or to stave off starvation (the last case was warfare cannibalism).
Considering that humans have had all sorts of reasons for eating each other, it seemed odd to Cole that these other early hominins only had one. He wanted to see if it actually made sense for our ancestors to eat members of their own species based on nutritional value, compared to all the other animals they could have been eating. So, he took all the data he could find about the fat and protein content of various human organs, and calculated an approximate caloric value of a typical person in a paper published April 6.
For his approximation, he used studies from the 1940s and 50s that were done on autopsies of men. (In this case, I’m okay with a male bias in health research). Cole collected the average weight and muscle mass of these men, and the known distributions of protein and fat in organs known to be routinely eat. (He assumed the pancreas, spleen, intestines, and teeth were not routinely eaten, for example, based on other studies (paywall) of cannibalism.) Basic nutrition says that every gram of fat has nine calories, and every gram of protein has four; scale up and, voila: an adult man is roughly 126,000 calories.
Cole also analyzed the human skeletal muscle—the most similar to animal muscle composition—to estimate the calories in animals that hominins are thought to have dined on, like the woolly mammoth and Megaloceros (the giant deer), both now extinct. Pound for pound, hominin and animal muscle weren’t too different in terms of calorie count. But, of course, each one of those megafauna carried much more meat. Taking into account the relative effort of hunting an intelligent hominin and a big but dumb animal, you’d be better off eating almost anything other than another hominin:
“Even if you ate six individual [hominin]s, you’d still not have as many calories as if you ate one horse,” says Cole. His conclusion: at least some of the time, hominins were eating their peers for other reasons, like fulfilling rituals or putting a (grim) end to conflicts.
To be sure, Cole’s estimates of how many calories are in each animal aren’t perfect. He’s working off size estimates for some extinct species, like the mammoth. And hominins probably didn’t eat every last piece of their hominin meals. When asked if the calorie count for the hominin skeleton was referring to bone marrow, Cole said he wasn’t sure how much of the bone was being eaten. “It’s just not possible with the data I had available to tease them out,” he says. Also, some of the cannibalized skeletal remains include women and children, whose specific fat and protein distributions would undoubtedly be different.
“Data for females and subadults are not available within the published literature, and the collection of primary data of this nature was outside the ethical (and legal) scope of this study,” Cole writes. Indeed.
Of course there’s really no reason we need exact caloric estimates of our fellow humans or even for extinct animals. The point of the study, Cole says, was to show that our ancestors were more socially complex than we usually give them credit for. They had jewelry. They probably kissed. It’s not a stretch to say that they had more complicated social dynamics and rituals than had been considered before, too—like ritual cannibalism. “This work suggests, but doesn’t prove, we need to be more inclusive and see these other species more like us,” he says.
Update 4/20: This article has been updated to clarify that Cole was calculating the total calories in each animal, and not the caloric density of each animal. It also reflects that hunting large animals would yield a larger caloric return relative to effort than hunting humans.