Theories of social selection in human populations.

Using Huntington disease, mental retardation, and schizophrenia, it has been shown that two individuals with identical genotypes or phenotypes have different fitnesses because of affected nuclear family members. Such fitness interaction seems to occur because of cultural and social reactions due to the presence of affected individuals, and the interaction has been termed "social selection." Without assuming any specific genetic control for the social behavior, we can study the effect of social behavior on the incidence of a genetic disease.