War is not an inevitable feature of society, concluded two scientists who analyzed acts of aggression in 21 hunter-gatherer societies.

Among people who live today most like our ancestors did long ago, the duo reports in the journal Science, most acts of murder occur as a result of individual conflicts rather than as part of major battle-like events. That suggests that war is an artifice of society, not a feature of human nature.

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It’s a hopeful message, but one that has met with strong criticisms from a community of anthropologists that has long debated whether warfare has an extensive evolutionary history with roots embedded in the structure of our brains, or if war is a response to more recent developments in how societies are structured.

 “Our study questions the popular picture of ‘Man the Warrior,’ where groups of prehistoric humans are seen as participating in a constant struggle against each other, and where war is something that is almost in our genes,” said co-author Patrik Söderberg of Åbo Akademi University in Vasa, Finland.

“By showing that war is the exception rather than the norm in societies with a lifestyle resembling our ancestral past, the study supports a more optimistic view on the human potential for peace.”

Other experts disagree, pointing out the complexities of defining what “war” is and the ambiguity of interpreting what archaeological discoveries say about how ancient people died, among other problems.

“The evidence doesn’t really support the claim they’re making,” said Michael Wilson, an anthropologist at the University of Minnesota, Twin Cities. “It’s a hard question to study. If you look at the archaeological record, there’s evidence of violence going back pretty far. But if you find a spearhead or arrowhead in someone’s bones, which is common, is that war or an interpersonal dispute? You just don’t know.”

In an attempt to settle the debate about how built-in war really is, Söderberg and colleague Douglas Fry picked 21 groups of foragers that they felt best represented the way people lived before complex societies developed. In an attempt to be as authentic as possible, they excluded groups that rode horses, lived in large settlements, had access to stable sources of food like fisheries, or developed complex societies with social classes and hierarchies.

For each population included in the study, the researchers looked at high-quality ethnographies for examples of lethal aggression. They turned up nearly 150 cases of aggressive death.

Among the Tiwi people of Australia, the researchers found an unmatched 69 examples of lethal acts. Among the other 20 groups, there were an average of just 3.5 deadly events documented, ranging from zero to 15.