Reconstructions of a Neanderthal man, left, and woman at the Neanderthal museum in Mettmann, Germany. (AP Photo/Martin Meissner)

Scientists know that our ancient human cousins ate one another, at least on occasion. At a handful of European sites scattered across some 250,000 years, researchers have dug up hominin bones that bear telltale markings: blade scratches, teeth marks, burns.

What they can't be sure of is why. Modern humans have long practiced cannibalism for a variety of ritual reasons — to frighten enemies, cure illness, honor the dead — but anthropologists have no evidence that Neanderthals or other hominin species had a cultural motivation for consuming their kin. So, for the most part, researchers assumed ancient cannibalism was “nutritional,” or purely for the purpose of survival.

Which got University of Brighton archaeologist James Cole wondering: If hominins ate each other for nutrition, then how nutritious were they?

For a paper published Thursday in the journal Scientific Reports, Cole calculated the number of calories that could be gotten from one adult human male. Compared to other creatures our ancient cousins ate — mammoths, steppe bison, deer — it turned out that hominins were a pretty low-calorie snack. A 150-pound person provides about 32,376 calories, enough for a troop of 25 adult Neanderthals for about a third of a day. A mammoth, on the other hand, could feed the group for a month.

“Doing research into the subject, I found that no one had ever defined a calorie value for the human body, and if they did, they were kind of throwaway numbers with no indication of how they arrived there,” Cole said.

Cole's calculations, on the other hand, are unnervingly specific. His paper contains a chart listing the estimated weight and calorie value for every component of the human body. Head and torso: 5,418.67 calories. Upper arms: 7,4571.16 calories. Thighs: 13,354.88 calories. Skin: 10,278 calories. Teeth: 36 calories.

“When you stack up muscle values in terms of weigh, we actually fall right where we should — right between saiga and roe deer, which are animals roughly about our same size,” Cole said, impressively matter-of-fact for someone essentially writing an FDA nutritional facts label for members of his own species.

Neanderthals and other ancient hominin species, he noted, were far bulkier than modern humans, with big muscles and sturdy builds. They might have been a bit more filling than a Homo sapiens meal, but not by much.

“It's interesting because if you’re labeling these acts as nutritional cannibalism … and you compare how nutritional we are compared to game, we actually aren’t a very good return,” Cole said.

Of course, the Neanderthals weren't calorie counters. But they would have been able to tell that a person didn't provide as much sustenance as a boar or a horse. And unlike a boar or a horse, a hominin would be exactly as cunning and skillful as the person who'd like to eat him — meaning he's much more difficult to kill.

To Cole, this suggests that ancient hominins could have had ritual motivations for consuming members of their own species, just as modern humans did. This shouldn't be surprising he said — Neanderthals are already known to have made art, worn jewelry, and developed sophisticated communication.

“Clearly these are complex and diverse human species and their attitude to cannibalism I would suggest is going to be as complex and diverse as our own,” he said.

Paola Villa, a Neanderthal expert and researcher at the University of Colorado at Boulder, said that Cole's calculations offer some interesting information, but should not change our understanding of ancient hominin cannibalism. A person may not have offered the same caloric return as a deer, she said, but hominins weren't hunting each other the way they hunted deer anyway.

“There never was a suggestion that humans were hunted as food animals,” she wrote in an email. “Eaten as food, yes, but the cause has always been described as either aggressive cannibalism (well-documented in mammals including primates) or starvation or as a ceremonial mortuary practice.”

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