Group selection models with population substructure based on social interaction networks

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AbstractMost models of evolution by group selection assume that groups have discrete boundaries with homogeneous levels of interaction within groups and no interaction between groups. While this assumption is analytically useful, it is not an accurate description of groups in nature. We use a generalization of D.S. Wilson's (Am. Nat. 111:157–185, 1977; The Natural Selection of Populations and Communities. Reading, Mass.: Benjamin/Cummings, 1980) concept of trait‐groups, in which groups are defined as sets of interacting individuals, to estimate the average degree of relatedness among groomers and groomees, referred to here as grooming‐groups. The average degree of relatedness is an important parameter in models of both kin and group selection.Data on grooming among 52 female rhesus macaques drawn from Group F on Cayo Santiago were used to represent the pattern and intensity of affiliative interactions. Degrees of relatedness among individuals and transferrin phenotypes were obtained from demographic and genetic records on the colony. The average degree of relatedness within grooming‐groups was estimated directly by calculating the average degree of relatedness among interactants (groomers and groomees), weighted by their frequency of interaction. Average degrees of relatedness among interactants were also estimated from the subjective frequency of the transferrin C allele.Our analysis indicates that the average degree of relatedness within grooming‐groups is 0.316 when estimated directly and 0.347 when estimated from the subjective frequency of the transferrin C allele. These values are much higher than are usually considered for group selection in primate societies and indicate the relative ease with which altruism may evolve given primate social structures.