It turns out human beings don't make for a terribly sustaining supper.

Research published Thursday in the journal Scientific Reports concludes our ancient ancestors who practised cannibalism probably weren't doing so for purely dietary reasons.

To study the topic, Dr. James Cole, a senior lecturer in archeology at the University of Brighton in England, developed a tool for evaluating the caloric value of a human compared to other fauna that lived at the time.

The conclusion? We don't really have that much meat on our bones.

To come up with a framework for just how much nutrition a human offers, Cole took published chemical analyses of male adults and calculated the caloric values of each body part based on four calories per gram of protein and nine calories per gram of fat. He determined that a 66 kg man is about 144,000 calories.

A mammoth, by contrast, offered 3.6 million calories.

Complicated motivations

Since it was probably so much bother to procure a fellow Neanderthal or other early hominin as a food source given the relatively low dietary value — "If you've got spears, they've probably got spears," said Cole — there were probably other reasons for eating their own.

"My thinking is that it might make more sense to go after one horse rather than six people to make up the same number of calories," Cole said in an interview with CBC News. "Obviously they weren't sitting there counting calories … but these ancient humans do have an idea about the amount of effort expended for reward in amount of food."

He said there's a complicated set of motivations for cannibalism — then and now — that includes medicinal purposes, warfare, territory defence and rituals.

Yes, the list also includes psychotic motivation of the kind that brings book and movie character Hannibal Lecter to mind, said Cole, but there are far less sinister examples in practice even today.

"There are tribes in the Amazon that still practise funerary cannibalism," he said, such as consuming a mouthful of a dead relative to carry their memory forward.

Our ancient human ancestors could be as complicated as modern human beings and the idea that they are brutal beasts, I think that's just not accurate. - James Cole, University of Brighton archeologist

Naturally, it's very difficult to assess why these populations that lived between 40,000 and a million years ago would have cannibalized each other, said Cole, but these findings suggest it was not as needs-based as some academics have assumed.

For Cole, exploring the topic is about more than just figuring out what our early ancestors had for dinner. "I'm really interested in finding ways or insights into how our hominin ancestors may have behaved and how they thought when they were alive.

"Our ancient human ancestors could be as complicated as modern human beings and the idea that they are brutal beasts, I think that's just not accurate."