But a recent study found that men in small-scale societies, such as the Amazon’s Yanomamö people, tend to partner with other men from nearby villages to whom they bear little or no relation. The research suggests warriors from these groups would rather fight alongside neighbouring strangers or in-laws than blood relatives.
“We think that what is going on with humans is that we make this unique group structure that’s different from all other organisms,” said University of Utah anthropologist Shane Macfarlan, who co-authored the study.
The Yanomamö are an indigenous group of about 35,000 people in the Amazon rainforest who live in about 250 villages near the border between Venezuela and Brazil.
Macfarlan used data gathered during the 1960s and 1970s by controversial American anthropologist Napoleon Chagnon, who spent decades in the Amazon amassing information about the group.
The benefits of fighting alongside distant cousins, said Macfarlan, come from the alliances themselves rather than from victories.
The study, published Monday in Proceedings of the National Academy of Sciences, looked at the lives of 118 Yanomamö warriors or “unokais.” Macfarlan determined that these men enjoyed higher social status and more wives than those who had not killed. The villages involved in the alliance often combined to make a stronger, more prosperous one.
“The benefits that are obtained via warfare are different from how most people conceive of it,” he said. “Most people conceive of warfare as ‘to the victor go the spoils,’ but, with humans, it looks like what you’re getting is a good alliance partner with someone outside of your group.”
Macfarlan said he expected to find that the Yanomamö took a “band of brothers” approach to war, fighting alongside male kin like fathers, sons, and brothers much the way the chimpanzees engage in war.
“When chimpanzees enact warfare, they actually benefit productively from it. They get more land and more resources in their territory,” he said. “We assumed that it was going be a chimpanzee-like structure because there’s a large body of literature in anthropology that suggested that these groups are going to be composed of these really tight-knit communities with men from the same patriline.”
But the human ability to form strategic alliances could help us understand human warfare more broadly.
“It might shape discussions of how we think about warfare,” said Macfarlan, “what happens to men and women psychologically when they enact war and how this bonds people together in a very meaningful way that can feel kind of like a bond of brotherhood.
“It seems that our co-operative tendencies and our lethal tendencies go hand in hand.”