An evolutionary analysis of rules regulating human inbreeding and marriage

Abstract

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.

Avoidance of close consanguineous inbreeding in captive groups of rhesus macaques

“…Dispersal of one or the other sex, usually males, from their natal group before, or soon after, reaching the age of sexual maturity [e.g., Packer, 1979;Pusey and Packer, 1987;Pusey, 1990; for another interpretation of the function of male dispersal in group-living primates, see Moore and Ali, 19841, preference for unfamiliar mates [Harcourt, 1978;Pusey, 19901, kin recognition [Wu et al, 1980;Walters, 19871, or a psychological aversion to mating with close childhood associates [Thornhill, 1991 1 are examples of strategies that could minimize inbreeding. Avoidance of sexual activity between matrilineal kin that are sexually mature has been reported for chimpanzees [Pusey, 19801, Japanese macaques [Tokuda, 1961-62;Chapais & Mignault, 19911, Barbary macaques [Paul & Kuester, 19851, stump-tail macaques [Murray & Smith, 19831, and rhesus macaques [Sade, 1968;Manson & Perry, 19931.…”

Evitação e proibição do incesto: fatores psicobiológicos e culturais

“…Except for the cases of incest due to sexual abuse (for the abusive nature of the relationship and of the involuntary and not consensual character regarding the victim), the answers are not clear. As previously explained, the sexual intercourse between parents and children are the genuine incest typification (Thornhill, 1991). As more distant kinship degrees are included, the incest concept tends to dilute.…”

“…Thornhill (1991) formulates that behaviors referred to as incestuous in social sciences literature can be divided into three categories: incestuous endogamy, which is concerned to sexual intercourse between individuals with family relationship, that is, whose kinship is by direct descent (for instance, between parents and children or between siblings); the non-incestuous endogamy, which encompasses the sexual intercourse between individuals with more distant kinship (between cousins, for instance); and the sexual activity coming from the adultery between persons without genetic kinship in the familiar context (stepson and stepmother, for instance).…”

“…What Thornhill (1991) classifies as incestuous endogamy seems to more robustly delimit the incest conceptual core as the sexual intercourse between close relatives (between parents and children, between siblings), since that type of sexual intercourse leads to greater probability of defective offspring due to the greater chances of receiving a harmful recessive allele inherited from a common ancestral. It is worth mentioning that endogamy and incest are terms that have been more commonly used in biological and social sciences, respectively, many times imprecisely (Moore, 1992).…”

“…From the differentiation aforementioned of Thornhill (1991), the term incest will be treated here as reference to the incestuous endogamy classification. The prohibition of sexual intercourse between siblings or parents and children carries the smallest occurrence of this modality of kinship relationship, being understood that those are the genuine type of incest, in which social prohibitions act more strongly when compared with the relationships between relatives of second or third degrees (Saggar & Bittles, 2008).…”