In my Response to the target article, “Natural Language and Natural Selection,” co-authored by Steven Pinker and Paul Bloom (BBS 13(4):769), the journal printed the following sentence, “Rather, different mutations are stored independently in different lineages, and recombination brings them together to form vast numbers of new combinations, in people, in their descendents,” in error. The sentence should have read: “Rather, different mutations are stored independently in different lineages, and recombination brings them together to form vast numbers of new combinations, in parallel, in their descendents.”

Evolutionary theory predicts that humans should avoid incest because of the negative effects incest has on individual reproduction: production of defective offspring. Selection for the avoidance of close-kin mating has apparently resulted in a psychological mechanism that promotes voluntary incest avoidance. Most human societies are thought to have rules regulating incest. If incest is avoided, why are social rules constructed to regulate it? This target article suggests that incest rules do not exist primarily to regulate close-kin mating but to regulate inbreeding between more distant kin (especially cousin categories) and sexual relations between affinal relatives (often nonkin). Three evolutionary hypotheses about cousin marriage and affinal kin mating follow from this suggestion: (1) Rules regulating mating between affinal kin are means of paternity protection. Cousin marriage (inbreeding) is regulated because, if it occurs, it can concentrate wealth and power within families to the detriment of (2) the powerful positions of rulers in stratified societies and (3) the relatively equal social statuses of most men in egalitarian societies. Tests using the comparative method on a worldwide sample of 129 societies supported the three hypotheses. Two alternative anthropological hypotheses (derived from Freudian theory and alliance theory) failed to be supported.