The persistence of altruism and spite remains an enduring problem of social evolution. It is well known that selection for these actions depends on the structure of the population—that is, on actors' genetic relationships to recipients and to the ‘neighbourhood’ impacted by their actions. Less appreciated, however, is that population structure can cause genetic asymmetries between partners whereby the relatedness (defined relative to the neighbourhood) of an individual i to a partner j will differ from the relatedness of j to i. Here, the authors introduce a widespread mechanism of kin recognition to a model of dispersal in subdivided populations. In so doing, they uncover three remarkable consequences of asymmetrical relatedness. First, altruism directed at phenotypically similar partners evolves more easily among migrant than native actors. Second, spite directed at dissimilar partners evolves more easily among native than migrant actors. Third, unlike migrants, natives can evolve to pay costs that far outstrip those they spitefully impose on others. They find that the frequency of natives relative to migrants amplifies the asymmetries between them. Taken together, results reveal differentiated patterns of ‘phenocentrism’ that readily arise from asymmetries of relatedness.
Within a group, those individuals who appear very different from most will evolve to be altruistic towards similar partners, and will be only spiteful to those who do not appear similar to them.
Within a group, those Individuals who appear very similar to the rest will evolve to be only slightly altruistic towards similar partners. However, they will be spiteful, even to extreme lengths, to the individuals who are dissimilar.
Those who appear similar to each other can evolve to pay costs that are greater than the costs they spitefully impose on others.
Results reveal differentiated patterns of ‘phenocentrism’ as a result of asymmetrical relatedness.