Towards the elucidation of evolution of out-group aggression.

We focus on the implications of De Dreu and Gross's findings for the evolutionary perspective on out-group aggression and in-group cooperation. Although their experimental protocols are potentially useful in determining the origins of out-group aggression in humans, they so far provide inconclusive evidence only. We suggest ways of furthering our understanding of the connection between parochial cooperation and intergroup conflict.