Humans inherited a propensity for violence from our primate ancestors, a new study says, making it easy to think, “Ah, see—we really are just animals.” But that doesn’t give animals enough credit.

The first humans were about as violent as could be expected based on their family tree, researchers report September 28 in the journal Nature. The scientists pored through examples of lethal violence—not animals killing other species, such as predators and prey, but killings within a species, whether by cannibalism, infanticide, or aggression.

They looked for evidence of this ghastly activity among four million recorded deaths in more than a thousand different mammals, from shrews to primates. On top of that, they compiled a history of human slayings.

One pattern stood