CAN GROUP-FUNCTIONAL BEHAVIORS EVOLVE BY CULTURAL-GROUP SELECTION - AN EMPIRICAL-TEST

Functionalists believe that social and cultural variation results from adaptation at the group level. Such explanations are controversial for two reasons: (1) Extensive analysis of mathematical models of group selection by evolutionary biologists suggests that group selection is unlikely to be important. (2) Group extinctions are too rare to generate sufficient evolutionary change. Boyd and Richerson have proposed a new model of group selection based on cultural variation that is theoretically more plausible than group selection on genetic variation. In this paper we present data on patterns of group extinction, group formation, and between-group variation in New Guinea which are consistent with the operation of this model. Observed rates of group extinction suggest that a minimum of 500 to 1,000 years would be required for the spread of a single group-beneficial trait under the influence of group selection. This result implies that group selection cannot explain cultural changes that take less than 500 to 1,000 years. It does not, however, preclude a role for group selection in explaining the evolution of human societies over the longer run.