A quantitative genetic model of altruistic selection

Summary

A quantitative genetic model for evolution by altruistic selection based on family selection models used in agricultural genetics is presented. A quantitative genetic version of Hamilton's rule is derived which indicates that evolution will proceed in an altruistic direction whenever the ratic of between-to within-family (or group) heritability exceeds the absolute value of the within-to between-family selection differential ratio. This ratio of heritabilities is equal to a ratio which includes only the phenotypic and genetic intraclass correlation coefficients, thus no heritabilities actually need to be estimated in determining the possibility of altruistic evolution. The phenotypic intraclass correlation can be estimated with standard analysis of variance methods. The genetic intraclass correlation may be estimated by the average within-group coefficient of relationship using genealogical data, by Wright's F-statistics using allele frequency data, or by a theoretical model based on a knowledge of interaction and mating patterns. Selection differentials may be measured by the regression of relative fitness, or one of its major components, on the phenotype of interest. Selection can be considered altruistic only if within-and between-family selection differentials have opposite signs. Consideration of empirical data on genetic and phenotypic intraclass correlations indicates that evolution may proceed in an altruistic direction even if the within-family selection differential exceeds the one between families, especially in situations in which pertinent environmental factors are randomly distributed among families.