Hawkish but helpful: When cultural group selection favors within-group aggression

The origin of cooperation is a central problem in evolutionary biology and social science. Cultural group selection and parochial altruism are popular but controversial evolutionary explanations for large-scale cooperation. Proponents of the cultural group selection hypothesis argue that the human tendency to conform--a consequence of our reliance on social learning--maintained sufficient between-group variation to allow group selection (which favors altruism) to overpower individual selection (which favors selfishness), whereupon large-scale altruism could emerge. Proponents of the parochial altruism hypothesis argue that altruism could emerge in tandem with hostility toward other groups if