Intergroup violence in the Pan-Homo last common ancestor was limited by low male relatedness

The origins of human intergroup conflict are poorly understood despite the volume of attention the topic has received. Recent research suggests that, among mammals, violence is especially commonplace in primates, particularly social and territorial species. Here we use Bayesian phylogenetic methods to reconstruct the evolution of lethal violence across the ape lineage to understand better the roots of human lethal violence. Of the five key traits underpinning lethal violence, our reconstructions suggest that male coalitions, male dominance over females, and male-biased territorial defence were all present in the Pan-Homo last common ancestor. However, there was no support for the presence of exclusively hostile interactions with other groups or male natal residence, contrasting with extant chimpanzees. Our results suggest humans evolved from an ancestor whose lethally violent tendencies may have been tempered, compared with extant chimpanzees, by low male relatedness and coalitions between unrelated females.