Sam Bowles: Santa Fe Institute

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 ones payoffs by comparison to what one would gain by eschewing these
behaviors. But parochial altruism could have evolved if parochialism promoted inter-group 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 is viable singly, but by promoting
group conflict, they could have evolved jointly.
http://www.bec.ucla.edu/Bowles.pdf