The unselfish, altruistic behavior of insect societies can be explained by way of unusually close genetic relatedness, while the cooperative behavior of chimpanzee and other distantly related mammalian social groups results from their daily, social \"fit-for-tat\" trading of favors. These sociobioiogical explanations, however, are inadequate to explain altruistic behavior among human groups with members numbering in the thousands or millions, groups consisting for the most part of genetically unrelated individuals with little or no daily social contact. Religion, cultural evolutionary theory suggests, may be the glue that binds them together
