Sex Differences in Intergroup Competition, Aggression, and Warfare

The social science literature abounds with examples of human tribalism, the tendency to categorize individuals on the basis of their group membership and treat in-group members benevolently and out-group members malevolently. I argue that this tribal inclination is an evolved response to the threat of intergroup violence and warfare that was endemic in ancestral human environments (and is still common today). Here I hypothesize that intergroup conflict has profoundly affected the social psychology of human males in particular--the male warrior hypothesis--and present evidence consistent with this claim. I also discuss implications of this hypothesis for managing intergroup relations in our society.