Prohibited degree of kinship

In law, a prohibited degree of kinship refers to a degree of consanguinity (blood relatedness), or sometimes affinity (relation by marriage or sexual relationship) between persons that makes sex or marriage between them illegal.

An incest taboo between parent and child or two full-blooded siblings is a cultural universal. Taboos against sexual relations between individuals of other close degrees of relationship vary. The probable biological basis for the generality of the marital incest taboo is that matings between close relatives lead to progeny that tend to experience inbreeding depression, due largely to the increased expression of recessive deleterious mutations.^[1]