Incest Taboo

An Incest taboo is any cultural rule or norm that prohibits practices of sexual relations between relatives. All human cultures have norms regarding who is considered suitable and unsuitable sexual or marriage partners, and usually certain close relatives are excluded as possible partners. Little agreement exists, however, among cultures about which types of blood relations are permissible partners and which are not. In many cultures, certain types of cousin relations are preferred as sexual and marital partners, whereas others are taboo. Sometimes relations between clan-members are excluded, even when no traceable genealogical relations exist, while members of other clans are permissible irrespective of the existence of blood ties. Many cultures allow sexual and marital relations between aunts/uncles and nephews/nieces. In some instances, brother-sister marriages have been practiced by the elites with some regularity. This poses the question of the origin of the incest taboo as a universal characteristic of culture, and the question has often been framed as a question of whether it is based in nature or nurture. Parent-child and sibling-sibling unions are almost universally forbidden.

One line of explanation sees the incest taboo as a cultural implementation of a biologically evolved preference for sexual partners with whom one is unlikely to share genes, since inbreeding may have detrimental outcomes. The most widely held hypothesis proposes that the so-called Westermarck effect discourages adults from engaging in sexual relations with individuals with whom they grew up. The existence of the Westermarck effect has achieved some empirical support.

Another school argues that the incest prohibition is a cultural construct which arises as a side effect of a general human preference for group exogamy, which arises because intermarriage between groups construct valuable alliances that improve the ability for both groups to thrive. According to this view the incest taboo is not necessarily a universal, but is likely to arise and become more strict under cultural circumstances that favour exogamy over endogamy, and likely to become more lax under circumstances that favor endogamy. This hypothesis has also achieved some empirical support.