Evolutionarily stable in-group favoritism and out-group spite in intergroup conflict

We study conflict between two groups of individuals. Using Schaffer's (1988) concept of evolutionary stability we provide an evolutionary underpinning for in-group altruism combined with spiteful behavior towards members of the rival out-group. We characterize the set of evolutionarily stable combinations of in-group favoritism and out-group spite and find that an increase in in-group altruism can be balanced by a decrease in spiteful behavior towards the out-group.

► We study evolutionary stability in the context of conflict between groups.
► A large set of combinations of in-group favoritism and out-group spite is evolutionarily stable.
► In-group altruism and spite towards the out-group are substitutes.
► Our framework has incomplete information and type unobservability.
► The results are neither based on the “transparent disposition approach” nor on kin-selection.