Science 5 June 2009:
Vol. 324. no. 5932, pp. 1293 - 1298
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.
1 Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA.
2 University of Siena, Siena 53100, Italy. E-mail: samuel.bowles@gmail.com
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