The Evolution of Social Interactions by Family Selection

Abstract

A population genetics model for the evolution of social behaviors by selection between families was presented. The effects of dominance and epistasis on the conditions for an increase in gene frequency and the rate of gene frequency change were described for diploid and haplo-diploid organisms. The conditions for the spread of genes determining social behaviors were identical to those of Hamilton''s kinship theory for diploid organisms. These conditions were independent of the degree of dominance (1- and 2-locus case) or epistasis (2-locus case) for the linear fitness model investigated. Haplo-diploidy alone conferred no advantage in terms of the evolution of social behaviors. Haplo-diploidy, when accompanied by female-biased sex ratios, favored the evolution of social behavior in 2 ways. It relaxed the cost-benefit restrictions which limit the evolution of social behaviors and increased the rate at which alleles for altruistic behavior spread through a population. The relative fitness of an individual is the result of a compromise between individual and family selection and inclusive fitness is not maximized in the evolution of altruistic behaviors.