Incest
Incest (/ˈɪnsɛst/ IN-sest) is human sexual activity between family members or close relatives.[1][2] This typically includes sexual activity between people in consanguinity (blood relations), and sometimes those related by lineage. It is forbidden and considered immoral in most societies, and can lead to an increased risk of genetic disorders in children in case of pregnancy.
This article is about the variable social, legal, religious, and cultural attitudes and sanctions concerning human sexual relations with close kin. For a detailed description of its legal aspects worldwide, see Legality of incest. For the biological act of reproducing with close kin, see Inbreeding. For the descriptive term for blood-related kin, see Consanguinity. For other uses, see Incest (disambiguation).
The incest taboo is one of the most widespread of all cultural taboos, both in present and in past societies.[3] Most modern societies have laws regarding incest or social restrictions on closely consanguineous marriages.[3] In societies where it is illegal, consensual adult incest is seen by some as a victimless crime.[4][5] Some cultures extend the incest taboo to relatives with no consanguinity, such as milk-siblings, stepsiblings, and adoptive siblings, albeit sometimes with less intensity.[6][7] 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.[8] Children of incestuous relationships have been regarded as illegitimate, 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.[9] 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.[9][10] 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.[9][11][12][13]
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.[14][15] 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.[16] However, sexual relations with a first-degree relative (meaning a parent, sibling, or child) are almost universally forbidden.[17]
History[edit]
Antiquity[edit]
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).[26]
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.[27] According to Herodotus, Shah Cambyses II supposedly married two of his sisters, Atossa and Roxane.[28][27] 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.[27] 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.[27]
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.[29][30][31][32] However, it has also been argued that the available evidence does not support the view that such relations were common.[33][34][35]
The most famous of these relationships were in the Ptolemaic royal family; Cleopatra VII was married to two of her younger brothers, Ptolemy XIII and Ptolemy XIV, whilst her mother and father, Cleopatra V and Ptolemy XII, were also brother and sister. Arsinoe II and her younger brother Ptolemy II Philadelphus were the first in the family to participate in a full-sibling marriage, a departure from custom.[36] A union between full siblings was counternormative in Greek and Macedonian tradition, and prohibited by the laws of at least some cities.[36][37]
Prevalence and statistics[edit]
Incest between an adult and a person under the age of consent is considered a form of child sexual abuse[67][68] that has been shown to be one of the most extreme forms of childhood abuse; it often results in serious and long-term psychological trauma, especially in the case of parental incest.[69] Its prevalence is difficult to generalize, but research has estimated 10–15% of the general population as having had at least one such sexual contact, with less than 2% involving intercourse or attempted intercourse.[70] Among women, research has yielded estimates as high as 20%.[69]
Father–daughter incest was for many years the most commonly reported and studied form of incest.[71][72] More recently, studies have suggested that sibling incest, particularly older brothers having sexual relations with younger siblings, is the most common form of incest,[73][74][75][76][77][78][79][80][81] with some studies finding sibling incest occurring more frequently than other forms of incest.[82] Some studies suggest that adolescent perpetrators of sibling abuse choose younger victims, abuse victims over a lengthier period, use violence more frequently and severely than adult perpetrators, and that sibling abuse has a higher rate of penetrative acts than father or stepfather incest, with father and older brother incest resulting in greater reported distress than stepfather incest.[83][84][85] South Africa,[86] Saudi Arabia, Sudan, Pakistan, and Nigeria are some of the countries with the most incest through consanguineous marriage.[87]
Offspring of biologically related parents are subject to the possible impact of inbreeding. Such offspring have a higher possibility of congenital birth defects (see Coefficient of relationship), because it increases the proportion of zygotes that are homozygous for deleterious recessive alleles that produce such disorders[148] (see Inbreeding depression). Because most such alleles are rare in populations, it is unlikely that two unrelated marriage partners will both be heterozygous carriers. However, because close relatives share a large fraction of their alleles, the probability that any such rare deleterious allele present in the common ancestor will be inherited from both related parents is increased dramatically with respect to non-inbred couples. Contrary to common belief, inbreeding does not in itself alter allele frequencies, but rather increases the relative proportion of homozygotes to heterozygotes. This has two contrary effects:[149]
The closer two persons are related, the higher the zygosity, and thus the more severe the biological costs of inbreeding. This fact likely explains why inbreeding between close relatives, such as siblings, is less common than inbreeding between cousins.[150]
There may also be other deleterious effects besides those caused by recessive diseases. Thus, similar immune systems may be more vulnerable to infectious diseases (see Major histocompatibility complex and sexual selection).[151]
A 1994 study found a mean excess mortality with inbreeding among first cousins of 4.4%.[152] A 2008 study also found decreased lifespan among offspring of first cousins, but no difference between lifespans after the second cousin level.[153] Children of parent–child or sibling–sibling unions are at increased risk compared to cousin–cousin unions. Studies suggest that 20–36% of these children will die or have major disability due to the inbreeding.[9] A study of 29 offspring resulting from brother–sister or father–daughter incest found that 20 had congenital abnormalities, including four directly attributable to autosomal recessive alleles.[154]