Incest

Incest (/ˈɪnsɛst/ IN-sest) is sex between close relatives, for example a brother, sister, or parent. This typically includes any kind of sexual activity between people in consanguinity (blood relations), and sometimes those related by lineage. It is condemned and considered immoral in many societies. It can lead to an increased risk of genetic disorders in children in case of pregnancy from incestuous sex.

The incest taboo is one of the most widespread of all cultural taboos, both in present and in past societies. Most modern societies have laws regarding incest or social restrictions on closely consanguineous marriages. In societies where it is illegal, consensual adult incest is seen by some as a victimless crime. Some cultures extend the incest taboo to relatives with no consanguinity, such as milk-siblings, stepsiblings, and adoptive siblings, albeit sometimes with less intensity. 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. Children of incestuous relationships have been regarded as illegitimate,^[where?] and are still so regarded in some societies today. 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.

A common justification for prohibiting incest is avoiding inbreeding, a collection of genetic disorders suffered by the children of parents with a close genetic relationship. Such children are at greater risk of congenital disorders, developmental and physical disability, and death; that risk is proportional to their parents' coefficient of relationship, a measure of how closely the parents are related genetically. 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.

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, or echoing the practices in their creation myths, and were considered normal. Some societies have different views about what constitutes illegal or immoral incest. For example, in Samoa, a man was permitted to marry his older sister, but not his younger sister. However, sexual relations with a first-degree relative (meaning a parent, sibling, or child) were almost universally forbidden in connection with multiple cases of disorders and organ failures.

The English word incest is derived from the Latin incestus, which has a general meaning of "impure, unchaste". It was introduced into Middle English, both in the generic Latin sense (preserved throughout the Middle English period) and in the narrow modern sense. The derived adjective incestuous appears in the 16th century. Before the Latin term came in, incest was known in Old English as sib-leger (from sibb 'kinship' + leger 'to lie') or mǣġhǣmed (from mǣġ 'kin, parent' + hǣmed 'sexual intercourse') but in time, both words fell out of use. Terms like incester and incestual have been used to describe those interested or involved in sexual relations with relatives among humans, while inbreeder has been used in relation to similar behavior among non-human organisms.

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).

In Achaemenid Persia, marriages between family members, such as half-siblings, nieces and cousins took place but were not seen as incestuous. However, Greek sources state that brother-sister and father-daughter marriages allegedly took place inside the royal family, yet it remains problematic to determine the reliability of these accounts. According to Herodotus, Shah Cambyses II supposedly married two of his sisters, Atossa and Roxane. This would have been regarded as illegal. However, Herodotus also states that Cambyses married Otanes' daughter Phaidyme, whilst his contemporary Ctesias names Roxane as Cambyses' wife, but she is not referred to as his sister. The accusations against Cambyses of committing incest are mentioned as part of his "blasphemous actions", which were designed to illustrate his "madness and vanity". These reports all derive from the same Egyptian source that was antagonistic towards Cambyses, and some of these allegations of "crimes", such as the killing of the Apis bull, have been confirmed as false, which means that the report of Cambyses' supposed incestuous acts is questionable.

Several of the Egyptian kings married their sisters and had several children with them to continue the royal bloodline. 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 scholars, such as Frier et al., state that sibling marriages were widespread among all classes in Egypt during the Graeco-Roman period. Numerous papyri and the Roman census declarations attest to many husbands and wives being brother and sister, of the same father and mother. However, it has also been argued that the available evidence does not support the view that such relations were common.