The cultural contagion of conflict

This article proposes that psychological research published in APA journals focuses too narrowly on Americans, who comprise less than 5% of the world's population. The result is an understanding of psychology that is incomplete and does not adequately represent humanity. First, an analysis of articles published in six premier APA journals is presented, showing that the contributors, samples, and editorial leadership of the journals are predominantly American. Then, a demographic profile of the human population is presented to show that the majority of the world's population lives in conditions vastly different from the conditions of Americans, underlining doubts of how well American psychological research can be said to represent humanity. The reasons for the narrowness of American psychological research are examined, with a focus on a philosophy of science that emphasizes fundamental processes and ignores or strips away cultural context. Finally, several suggestions for broadening the scope of American psychology are offered.

Altruism-benefiting fellow group members at a cost to oneself-and parochialism-hostility toward individuals not of one's own ethnic, racial, or other group-are common human behaviors. The intersection of the two-which we term "parochial altruism"-is puzzling from an evolutionary perspective because altruistic or parochial behavior reduces one's payoffs by comparison to what one would gain by eschewing these behaviors. But parochial altruism could have evolved if parochialism promoted intergroup hostilities and the combination of altruism and parochialism contributed to success in these conflicts. Our game-theoretic analysis and agent-based simulations show that under conditions likely to have been experienced by late Pleistocene and early Holocene humans, neither parochialism nor altruism would have been viable singly, but by promoting group conflict, they could have evolved jointly.