ALTRUISM AMONG NON-RELATIVES - ALTERNATIVES TO THE PRISONERS-DILEMMA

Trivers' model of reciprocal altruism, and its descendants based on the Prisoner's Dilemma model, have dominated thinking about cooperation and altruism between non relatives. However, there are three alternative models of altruism directed to non-relatives, These models, which are not based on the Prisoner's Dilemma, may explain a variety of phenomena, from allogrooming among impala to helping by non-relatives in cooperatively breeding birds and mammals.