Traditional psychology has primarily focused on the mechanism and development of human altruism. However, the functional significance and evolutionary origin of altruism are also important. The condition for altruism to evolve by natural selection is “positive assortment.” To guarantee positive assortment, variance within a group must be small, whereas variance between groups must be large, which results in “parochial altruism.” Some features of reasoning and memory in humans are believed to have been adapted to parochial altruism. However, humans sometimes show “generalized altruism” beyond each group they belong to. Clarifying the relationship between the function of the mind as a legacy of evolution and the structure of human social groups is important to understand altruism.
