Illustration: Jim Cooke/Gizmodo

Humans have been eating other humans since the beginning of time, but the motivations behind this macabre practice are complex and often unclear. Some anthropologists say prehistoric cannibals were just trying to grab a nutritious snack, but new research shows that human flesh—as tasty as it is—doesn’t pack the same caloric punch as wild animals. In other words, cannibalism wasn’t worth the trouble given alternatives.

A new study published in Scientific Reports is the first to provide a caloric breakdown of the human body—from tip to toe and all the scrumptious parts in between—to assess the motivations of prehistoric cannibals. The sole author of the study, archaeologist James Cole from the University Brighton, used this data to compare the caloric value of humans to other animals around during this prehistoric time. In general, he found that the human body has the same nutritional value—in terms of fat and protein—of equally-sized creatures, but when compared to bigger prey, such as mammoths and woolly rhino, humans offered significantly fewer calories. The study suggests that any interpretation of cannibalism during the Paleolithic Era has to take other considerations into account, such as cultural, social, and religious practices.

“Cannibal feast on the Island of Tanna, New Hebrides,” by Charles E. Gordon Frazer (1863-1899). (Image: CC)

During the Paleolithic Era—a 2.6 million-year-long period that ended 10,000 years ago—some bands of ancient humans and hominins (that is, extinct human species and all our immediate ancestors?) engaged in cannibalistic practices, eating the flesh of their own. We know this from the clues they left behind—human remains exhibiting signs of defleshing, deliberate cut marks around the joints, human chewing, and the cracking of bones to get at the marrow.

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The reasons for cannibalism vary, ranging from religious rites and mortuary practices through to the intimidation of enemies and weeding out the sick and elderly. Some anthropologists, however, believe that cannibalism was done primarily for nutritional reasons (see examples here, here, and here). But there’s very little evidence to support this claim, and there hasn’t been a good way for scientists to quantify the nutritional benefits of cannibalism. Cole’s study is the first to correct this oversight.

“For the first time—as far as I am aware—someone has constructed a calorific template for the human body,” Cole told Gizmodo. “This was done in order to try and get a better understanding for the motivations behind episodes of Palaeolithic cannibalism.”

To create this grim and unconventional nutritional label, Cole took average weights and calorie values (from fat and protein) for each part of the body. This was done via a chemical composition analysis, and it was performed on four male individuals. The resulting data pertains to modern humans, who admittedly aren’t exactly like Paleolithic humans, or Neanderthals, whose large frame allowed for slightly more muscle mass than Homo sapiens. Still, it’s a safe bet these values are close—it’s not like ancient humans and hominins were ten times larger or smaller than we are today.

Mmmm, adipose tissue. (Credit: James Cole/Scientific Reports)

A quick scan of the chart shows that the total muscle mass of a 145 pound (66 kg) adult male consists of about 32,376 calories. That’s enough to sustain about two people for a week. Some of the more nutritious body parts include the liver (2,569 calories), thighs (13,354 calories), and the collective mass of adipose or fat tissue (a whopping 50,000 calories). Teeth are a light snack, at 36 calories per 1.44 ounces. Good to know in a pinch.

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Armed with this chart, Cole compared these calorific values to those of animal species whose remains were found at the sites of Paleolithic cannibals, including mammoths, wooly rhino, auroch, bison, boar, rabbits, and various species of deer. He found that humans produce nutritional values that are comparable to animals of similar size and weight—but the human body, not surprisingly, yields significantly fewer calories than the big animals. In the most extreme case, the muscle mass of a mammoth contains an estimated 3.6 million calories. A 6,600 pound (3,000 kg) mammoth could sustain 200 humans for a week from its muscle mass alone. Other big game include woolly rhino (1.2 million calories), bison (612,000 calories), and giant deer (163,680 calories).

Caloric content of animals that lived alongside ancient humans. (Credit: James Cole/Scientific Reports)

“From my study I have shown that humans and hominins are not particularly high in calorific content when compared to other fauna that are regularly exploited by our hominin ancestors such as a horse for example,” said Cole. “Therefore, I would question whether the motivation for the cannibalism act was due to nutritional needs or perhaps something more socially driven such as resource defense or something along the lines.”

An underlying assumption of the paper is that it made more sense from a caloric intake perspective for our ancestors to hunt or trap animals than feed off the human population, whether those humans were outsiders or from the same clan.

“I would argue that to hunt or capture a member of your own species—who is as intelligent as you, and as able to fight back as you—is probably harder than hunting another faunal species such as a horse,” explained Cole. “Both are obviously difficult and challenging acts, but I suspect hominins may have been more challenging. In addition, you only need to kill one horse to get the same or more calories than 4 to 6 individual hominins.”

That said, prehistoric humans likely resorted to cannibalism as a survivalist measure during times of drought or famine. Cole says we cannot rule this type of cannibalism out entirely. He also says we need to embrace the idea that other human species may have been as varied and as complex as our own species with regards to cannibalism. “Neanderthals, for example, were extremely complex behaviorally, they were a symbolic species with jewelry production, cultural diversity in terms of stone tool manufacture, and they had a complex attitude to the burial of their dead,” he said. “Why would they not have an equally complex attitude to the acts of cannibalism?”

Jerome Whitfield, a University College London biologist who wasn’t involved in the study, said Cole put together a solid paper, and agrees that ancient humans were unlikely to have been a primary food source for other ancient humans.

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“They would have been dangerous prey, but stragglers might have been killed as a warning to other groups to move away from another group’s resources,” Whitfield told Gizmodo. “[Cole] points out the low nutritional value of hominins in comparison to other species, which does suggest that most episodes of [cannibalism] must have been non-nutritional, and required a symbolic capacity.”

That said, Whitfield says it would have been worthwhile for Cole to look at the extensive literature on chimpanzee behavior in relation to mortuary rites and cannibalism to put these practices into an evolutionary perspective.

Danielle Kurin, a forensic anthropologist at UC Santa Barbara who likewise wasn’t involved in the study, says this paper serves as a reminder that the act of consuming human flesh has deep roots in human history.

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“Cole’s study demonstrates that this type of behavior is not the mere result of nutritive needs, but rather a process deeply imbued with symbolism and well-entrenched beliefs about how bodies—and body parts—should be understood and handled around the time of death,” Kurin told Gizmodo.

Cannibalism, says Kurin, was often an integral part of the bereavement process and an act of compassion. In other instances, it was a gesture directed towards social outcasts, or the final dramatic act of vanquishing an enemy. With just piles of gnawed bones to serve as anthropological evidence, we’ll likely never know the true motivations of Paleolithic humans. This is not to say that cannibals didn’t receive caloric benefits from the act—it probably just wasn’t the primary motivating factor.

“That our pre-human ancestors engaged in this sort of meaningful, ritualistic behavior suggests a need to reevaluate the uniqueness of Homo sapiens as a species, as well as the characteristics that define our very humanity,” said Kurin.

[Scientific Reports]