The evolutionary significance of incest rules

Abstract

Evolutionary theory predicts that humans should avoid incest because the behavior depresses individual fitness through production of defective offspring. Selection for avoidance of close-kin mating has resulted in a developmental mechanism that promotes voluntary incest avoidance. If avoided, why are social rules constructed in most cultures to regulate incest? The suggestion in this article is that incest do not regulate close-kin mating, but instead regulate inbreeding between more distant kin and sexual relations between nonkin. Inbreeding (e.g., cousin marriage) is hypothesized to be regulated because if it occurs, it can concentrate wealth and power within families threatening the powerful positions of rulers in the society. The hypothesis was supported using a worldwide sample of 129 societies, whereas two other alternative hypotheses (one dealing with coadapted genomes, and the other with sexual reproduction and host/ parasite coevolution), were not.