Children of incestuous relationships have been regarded as illegitimate, and are still so regarded in some societies today. Third-degree relatives (such as half-aunt, half-nephew, first cousin) on average have 12.5% common genetic heritage, and sexual relations between them are viewed differently in various cultures, from being discouraged to being socially acceptable. Some cultures extend the incest taboo to relatives with no consanguinity such as milk-siblings, step-siblings, and adoptive siblings, albeit sometimes with less intensity. In societies where it is illegal, consensual adult incest is seen by some as a victimless crime. Most modern societies have laws regarding incest or social restrictions on closely consanguineous marriages. The incest taboo is one of the most widespread of all cultural taboos, both in present and in past societies. This typically includes sexual activity between people in consanguinity (blood relations), and sometimes those related by affinity ( marriage or stepfamily), adoption, or lineage. Incest ( / ˈ ɪ n s ɛ s t/ IN-sest) is human sexual activity between family members or close relatives.
