Asymmetric relations: Internal conflicts and the horror of incest

Incest can increase an individual's inclusive and individual fitness if the opportunity cost of incest is sufficiently small. As a corollary, genetic conflicts are possible between the two parties of an incestuous dyad if the y have different opportunity costs. The opportunity costs of casual sex usu ally are greater for females than for males. Therefore, females are predict ed to be more averse to incest than are males. Genetic conflicts also are p ossible between an individual's maternal and paternal genomes because of as ymmetries of relatedness. Large asymmetries of maternal and paternal relate dness are present between half-siblings, and in the relationship of offspri ng to parents. These asymmetries raise the possibility of strong internal c onflicts between an individual's maternal and paternal genomes over the cos ts and benefits of incest, Taboos and other social sanctions may serve to i ncrease male opportunity costs and thus serve as a disincentive to incest. (C) 1999 Elsevier Science Inc.