Group selection is a theory to explain why living things engage in behaviors that contribute to the survival and reproduction of others, often at the expense of their own survival and reproduction. Such behaviors are classified as examples of altruism (see Altruism ). Group selection proposes that altruism evolved (developed gradually over time) because both groups and individuals are subject to natural selection. Natural selection is the evolutionary process by which living things better suited to their environment tend to leave more descendants (see Natural selection ). Natural selection is typically described in terms of the reproductive success of individuals, rather than that of groups. According to group selection, traits such as altruism can evolve whenever selection among groups is stronger than selection within groups.
Within a group, natural selection often appears to favor selfishness over altruism. For example, a selfish individual may be saved from starvation by hoarding food. An individual that shares food, on the other hand, may starve. Thus, selfish individuals may be more successful than altruistic individuals within a group. However, a group of altruistic individuals can help one another in ways that increase the group’s overall reproductive success. As a result, altruistic groups can outcompete selfish groups, leading to the spread of altruistic traits.
As selection among groups becomes sufficiently strong, the individuals in a group can develop extremes of altruism and interdependence. Some scientists think such a group may evolve into a higher-level individual. For example, some scientists have argued that colonies of social insects, such as ants and honey bees, should be considered higher-level individuals called superorganisms. The development of higher-level individuals may explain certain major transitions in evolution. For example, selection among groups of single-celled organisms may explain the rise of multicellular life.
Group selection was first proposed by the British naturalist Charles Darwin. The theory was widely accepted by scientists until the mid-1900’s. At that time, most biologists rejected it in favor of explanations of altruism based on individual self-interest. One such explanation, called kin selection, holds that altruism serves to improve the reproductive success of close relatives (see Kin selection ). Many scientists now regard kin selection as a form of group selection. Group selection has gradually regained acceptance, though the subject remains controversial.
