The incest taboo is one of the few truly universal human concepts. While the definition of "close kin" varies between cultures (some societies ban marriage between cousins, while others encourage it), the prohibition of direct-lineage relations (parent-child or sibling-sibling) is nearly constant.
Theories explaining the taboo generally fall into three categories: Incest Taboo 21 Lindsey Allen Fa
Proposed by Claude Lévi-Strauss, this suggests the taboo exists to force individuals to marry outside their group, creating social alliances and preventing isolation. The incest taboo is one of the few