Levels of selection, altruism, and primate behavior

Altruistic behaviors seem anomalous from a traditional view of Darwinian na tural selection, and evolutionary explanations for them have generated much discussion. The debate caters around four major explanations: classic indi vidual-level selection, reciprocity and game theory kin selection, and trai t-group selection. The historical context and defining criteria of each mod el must be reviewed before its validity can be assessed. Of these proposed mechanisms, group selection historically has been the most controversial. A lthough the extent to which empirical data support group selection hypothes es is uncertain there is evidence for group-level selection among avirulent virus strains and foraging ant queens. Researchers studying mammalian beha vior, particularly primatologists, have largely dismissed models of group-l evel selection. Most discussion of altruism among primates has focused on d ifferences in fitness among individuals within a single group, but students of altruistic behaviors exhibited by primates also need to investigate int ergroup variation with respect to these behaviors. Various altruistic behav iors are likely to have evolved through different forms of selection, and e ach example of apparent altruism therefore needs to be evaluated separately .