For example, Tutankhamun married his half-sister Ankhesenamun, and was himself the child of an incestuous union between Akhenaten and an unidentified sister-wife. Several of the Egyptian Kings married their siblings and had several children with them to continue the royal bloodline. In ancient China, first cousins with the same surnames (i.e., those born to the father's brothers) were not permitted to marry, while those with different surnames could marry (i.e., maternal cousins and paternal cousins born to the father's sisters).
Table of prohibited marriages from The Trial of Bastardie by William Clerke. However, sexual relations with a first-degree relative (meaning a parent, sibling or child) are almost universally forbidden. For example, in Ancient Egypt, as in Samoa, marriage between a brother and an older sister was allowed, while marriage between a brother and a younger sister was declared as unethical. Some societies have different views about what constitutes illegal or immoral incest.
In some societies, such as those of Ancient Egypt, brother–sister, father–daughter, mother–son, cousin–cousin, aunt–nephew, uncle–niece, and other combinations of relations within a royal family, were married as a means of perpetuating the royal lineage. However, cultural anthropologists have noted that inbreeding avoidance cannot form the sole basis for the incest taboo because the boundaries of the incest prohibition vary widely between cultures, and not necessarily in ways that maximize the avoidance of inbreeding. Such children are at greater risk for congenital disorders, death, and developmental and physical disability, and that risk is proportional to their parents' coefficient of relationship-a measure of how closely the parents are related genetically. In most cases, the parents did not have the option to marry to remove that status, as incestuous marriages were, and are, normally also prohibited.Ī common justification for prohibiting incest is avoiding inbreeding: a collection of genetic disorders suffered by the children of parents with a close genetic relationship.
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.