Taboo is a term used by anthropologists to refer to a class of prohibitions, both formal and informal, stated and unstated, against incest, the practice of sexual relations between certain or close relatives, in human societies. There are various theories that seek to explain how and why an incest taboo originates. Some advocates maintain that some sort of incest taboo is universal, while others dispute its universality.
The anthropologist Claude Lévi-Strauss developed a general argument for the universality of the incest taboo in human societies. His argument begins with the claim that the incest taboo is in effect a prohibition against endogamy, and the effect is to encourage exogamy. Through exogamy, otherwise unrelated households or lineages will form relationships through marriage, thus strengthening social solidarity.
That is, Lévi-Strauss views marriage as an exchange of women between two social groups. This theory was debated intensely by anthropologists in the 1950s. It appealed to many because it used the study of incest taboos and marriage to answer more fundamental research interests of anthropologists at the time: how can an anthropologist map out the social relationships within a given community, and how do these relationships promote or endanger social solidarity? Although many anthropologists reject the universality of alliance theory most accept Lévi-Strauss' argument that the incest taboo is related to the preference for and advantages of exogamy.