Why did our early ancestors eat one another? Some scientists say it may have been because they were hungry. But as Nicholas St. Fleur reports for The New York Times, a new study suggests that humans aren't particularly nutritious and speculates that ancient cannibals had other reasons for chowing down on their fellow bipeds.

James Cole, an archaeologist at the University of Brighton, is the sole author of the study, which was published recently in the journal Scientific Reports. Archaeological evidence shows that hominin species were eating each other as early as the Pleistocene era, prompting Cole to wonder whether humans constitute a nutritious snack. Armed with this rather macabre curiosity, he set out to calculate the number of calories contained within the human body.

He turned to studies from the 1940s and 50s, which analyzed the protein and fat content of four adult men, Alessandra Potenza explains in The Verge. Based on those analyses, Cole was able to calculate an average caloric value for various human body parts. The torso and head, for instance, contain 5,419 calories, according to Cole’s calculations. Meaty human thighs have 13,355 calories. The heart clocks in at around 651 calories, while the brain, spinal cord and nerve trunks collectively contain 2,706 calories.

All told, Cole concludes, the human body contains about 125,822 calories. That might seem like a lot, but it isn’t much in comparison to some of the other food sources consumed by our early ancestors. According to Cole’s calculations, a group of 25 modern humans could survive for about 60 days on the remains of a mammoth, which contains 3,600,000 calories. A human corpse, by contrast, would feed the same group for less than a day.

If nutrition alone cannot explain why humans resorted to eating each other, Cole suggests, it seems likely that cannibalistic episodes were driven by social and cultural motivations. “We know that modern humans have a range of complex motivations for cannibalism that extend from ritual, aggressive, and survival to dietary reasons,” he writes in the study. “Why then would a hominin species such as the Neanderthals, who seem to have had varying attitudes to the burial and treatment of their dead, not have an equally complex attitude towards cannibalism?”

This conclusion falls in line with an existing school of thought, which suggests, based on archaeological evidence, that cannibalistic episodes were motivated by social, cultural, and spiritual factors. At Gough’s Cave in England, for example, archaeologists found a large cache of human bones that showed evidence of defleshing and chewing, Becky Ferreira writes for Vice. The people who gnawed on those bones probably didn’t do so out of hunger; there were plenty of animal remains found within the cave, and some of the human bones appeared to have been marked with ritualistic etchings.

At the Gran Dolina cave in Spain, archaeologists found the butchered remains of 11 children and adolescents, who belonged to the species Homo antecessor. It is possible, writes Erika Engelhaupt for National Geographic, that the youths were “outsiders” and that the consumption of their remains served as a vicious warning to other groups.

But Cole’s caloric comparisons cannot discount the possibility that humans used one another to supplement their diets. Ancient humans were likely opportunistic feeders, as Cole acknowledges in his study. Perhaps they turned to cannibalism when someone passed away, as an easy way to fill their bellies. Perhaps they resorted to eating one another when other food sources were scarce.

“The issue is not one of nutrition as an alternative to large game,” Erik Trinkaus, an anthropologist at Washington University in St. Louis, told Engelhaupt. “It is an issue of survival when there are no other food sources, members of one's social group have died, and the surviving members consume the bodies of already-dead people.”

Ultimately, every cannibalistic episode happened under different circumstances, Cole writes in his study, and no one can say for sure why our ancestors opted for the occasional human smorgasbord. But Cole’s findings lend further credence to the notion that some ancient cannibals were acting out of choice, not desperation.