Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?

Modern behavior, including the development of advanced tools, musical instruments, and art, seems to have arisen in humans in stages. The earliest hints are seen in Africa about 70 to 90,000 years ago, but later in Europe about 45,000 years ago. An ongoing discussion centers on the origins and significance of human prosociality. During early human development, could the benefits of altruistic behavior have outweighed its costs (see the Perspective by Mace)? Bowles (p. 1293) constructed a model of conflict between groups of humans and extracted estimates of the critical parameters from archaeological and ethnographic data sets. Provocatively, it appears that warfare might have enhanced the emergence and persistence of altruistic behavior. Powell et al. (p. 1298) present a population model that shows that the development of modern behaviors may rely on the attainment of critical population densities and migratory patterns required for stable cultural transmission. The model is consistent with genetic inferences of population dynamics in Africa and Europe and suggests that these cultural changes may not solely reflect increased cognitive evolution.

Since Darwin, intergroup hostilities have figured prominently in explanations of the evolution of human social behavior. Yet whether ancestral humans were largely “peaceful” or “warlike” remains controversial. I ask a more precise question: If more cooperative groups were more likely to prevail in conflicts with other groups, was the level of intergroup violence sufficient to influence the evolution of human social behavior? Using a model of the evolutionary impact of between-group competition and a new data set that combines archaeological evidence on causes of death during the Late Pleistocene and early Holocene with ethnographic and historical reports on hunter-gatherer populations, I find that the estimated level of mortality in intergroup conflicts would have had substantial effects, allowing the proliferation of group-beneficial behaviors that were quite costly to the individual altruist.