That is what a new study written by James Cole of the University of Brighton in England says. Cole says compared to large animals, humans do not provide much food. His study was published in the journal Scientific Reports.
Cole studied nine places where fossils have been found and where researchers have found evidence of cannibalism. Such signs include cutting marks on the bones.
Scientists dated the sites to between 14,000 and more than 900,000 years ago. That is the so-called Paleolithic period, also known as the Stone Age.
Five of the sites had Neanderthal fossils, the remains of earlier human ancestors. Two sites had fossils of prehistoric members of our own species and the others had fossils from much earlier human ancestors.
Cole estimated how many calories each of the bodies at each site had. He used earlier studies that found eating an average-sized modern-day human could provide up to 144,000 calories. He then made his estimates, based on the ages of the bodies at the sites.
The researcher found that the hunters would not get as much energy from the humans as they would from one large animal -- like a mammoth, a woolly rhino or a bear. So, Cole asked, why would the early humans hunt and kill their own species?
"You're dealing with an animal that is as smart as you are, as resourceful as you are, and can fight back in the way you fight them," Cole noted.
He says our ancestors may have eaten members of their species who had died because they did not have to be hunted. But he says cannibalism probably took place for reasons other than the need for food. He said it could have happened after times of violence or to defend territory.
Tim White of the University of California, Berkeley and Paola Villa of the University of Colorado Museum in Boulder said they do not know any scientists who believe our ancestors hunted each other for food. In an email, Villa said the new study "does not change our general understanding of human cannibalism."
加州大学伯克利分校蒂姆·怀特（Tim White）和科罗拉多大学波尔得分校博物馆的波拉·维拉（Paola Villa）表示，他们不认识任何认为我们的祖先互相猎杀为食的科学家。维拉在一封邮件中表示，这项新研究“不会改变我们对人类同类相食的一般理解。”
But Palmira Saladie, of the Catalan Institute for Human Paleoecology and Social Evolution near Barcelona, Spain, said Cole's study "will undoubtedly be key in the interpretation of new sites and the reevaluation of old interpretations."
In an email, she wrote that, to understand why our ancestors sometimes ate each other, "we still have a long way to go."
I'm Dorothy Gundy.