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{{Short description|Sexual activity between immediate family members or people considered too closely related to marry}}
{{About|the variable social, legal, religious, and cultural attitudes and sanctions concerning human sexual relations with close kin|a detailed description of its legal aspects worldwide|Legality of incest|the biological act of reproducing with close kin|Inbreeding|the descriptive term for blood-related kin|Consanguinity|other uses}}
{{Use dmy dates|date=May 2022}}
{{external links|date=March 2024}}
{{Family law|code}}

'''Incest''' ({{IPAc-en|ˈ|ɪ|n|s|ɛ|s|t|}} {{respell|IN|sest}}) is [[sexual intercourse|sex]] <!--NOTE: Using the term "sexual activity" is more accurate because the term "incest" does not only refer to sexual penetration, while the term "sexual intercourse" usually does imply sexual penetration.--> between [[kinship|close relatives]], for example a [[brother]] or [[sister]] or cousins.<ref>{{cite web|title=Incest|publisher=[[Oxford University Press]]|year=2013|access-date=27 August 2013|url=http://oxforddictionaries.com/us/definition/american_english/incest|archive-url=https://web.archive.org/web/20130626012345/http://oxforddictionaries.com/us/definition/american_english/incest|url-status=dead|archive-date=26 June 2013}}</ref><ref>{{cite web|title=Incest|publisher=[[Rape, Abuse & Incest National Network]] (RAINN)|year=2009|access-date=27 August 2013|url=http://www.rainn.org/get-information/types-of-sexual-assault/incest}}</ref> This typically includes sexual activity between people in [[consanguinity]] (blood relations), and sometimes those related by [[lineage (anthropology)|lineage]]. It is condemned and considered immoral in most societies, given that 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 [[taboo]]s, both in present and in past societies.<ref name="Bittles">{{Cite book |url=https://books.google.com/books?id=t6CsCXXE8skC&pg=PA178 |title=Consanguinity in Context |last=Bittles |first=Alan Holland |publisher=[[Cambridge University Press]] |year=2012 |isbn=978-0521781862 |pages=178–187 |access-date=27 August 2013}}</ref> Most modern societies have [[laws regarding incest]] or social restrictions on closely consanguineous marriages.<ref name="Bittles"/> In societies where it is illegal, consensual adult incest is seen by some as a [[victimless crime]].<ref name="spiegel">{{cite magazine |last=Hipp |first=Dietmar |url=http://www.spiegel.de/international/germany/0,1518,540831,00.html |title=German High Court Takes a Look at Incest |date=11 March 2008 |magazine=Der Spiegel |access-date=12 April 2008}}</ref><ref name= Wolf169>{{cite book |title=Inbreeding, Incest, and the Incest Taboo: The State of Knowledge at the Turn of the Century |first1=Arthur P. |last1=Wolf |first2=William H. |last2=Durham |author2-link=William H. Durham |year=2004 |publisher=Stanford University Press |page=169 |url=https://books.google.com/books?id=OW1nuQxcIQgC&pg=PA169 |isbn=978-0-8047-5141-4}}</ref> Some cultures extend the incest taboo to relatives with no consanguinity, such as [[Milk kinship|milk-siblings]], stepsiblings, and adoptive siblings, albeit sometimes with less intensity.<ref>Encyclopedia of Love in World Religions – Volume 1 – Page 321, Yudit Kornberg Greenberg – 2008</ref><ref>Language and Social Relations – Page 379, Asif Agha – 2007.</ref> 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.<ref>The Encyclopedia of Genetic Disorders and Birth Defects – Page 101, James Wynbrandt, Mark D. Ludman – 2009.</ref> Children of incestuous relationships have been regarded as [[Legitimacy (family law)|illegitimate]],{{Where|date=February 2024}} 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 [[inbreeding#Genetic disorders|genetic disorders]] suffered by the children of parents with a close [[Coefficient of relationship|genetic relationship]].<ref name=WolfDurham2005 /> 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.<ref name=WolfDurham2005>{{cite book |title=Inbreeding, Incest, and the Incest Taboo: The State of Knowledge at the Turn of the Century |first1=Arthur P. |last1=Wolf |first2=William H. |last2=Durham |year=2004 |publisher=Stanford University Press |page=3 |url=https://books.google.com/books?id=OW1nuQxcIQgC&pg=PA3 |isbn=978-0-8047-5141-4}}</ref><ref name=Afzal>{{cite journal |last1=Fareed |first1=M |last2=Afzal |first2=M |year=2014 |title=Estimating the inbreeding depression on cognitive behavior: A population based study of child cohort |journal=PLOS ONE |volume=9 |issue=10 |page=e109585 |doi=10.1371/journal.pone.0109585 |pmid=25313490 |pmc=4196914|bibcode=2014PLoSO...9j9585F |doi-access=free  |issn = 1932-6203}}</ref> 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.<ref name=WolfDurham2005 /><ref>{{cite journal | last1 = Schneider | first1 = D. M. | year = 1976 | title = The meaning of incest | journal = The Journal of the Polynesian Society | volume = 85 | issue = 2| pages = 149–169 }}</ref><ref>{{cite journal | last1 = White | first1 = L. A. | year = 1948 | title = The definition and prohibition of incest | journal = American Anthropologist | volume = 50 | issue = 3| pages = 416–435 | doi = 10.1525/aa.1948.50.3.02a00020 | pmid = 18874938 }}</ref><ref>{{cite journal | last1 = Schechner | first1 = R | year = 1971 | title = Incest and culture: A reflection on Claude Lévi-Strauss | journal = Psychoanalytic Review | volume = 58 | issue = 4| pages = 563–72 | pmid = 4948055 }}</ref>

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.<ref>[[Maurice Godelier]], Métamorphoses de la parenté, 2004</ref><ref>{{cite web |url=http://newleftreview.org/?view=2592 |title=New Left Review – Jack Goody: The Labyrinth of Kinship |access-date=24 July 2007}}</ref> 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.<ref>{{cite book |last= Lechte|first= John|date= 24 February 2003|title= Key Contemporary Concepts From Abjection to Zeno's Paradox|publisher= SAGE Publications|page= 82|isbn= 9780761965343}}</ref> However, sexual relations with a first-degree relative (meaning a parent, sibling, or child) are almost universally forbidden.<ref>''The Tapestry of Culture: An Introduction to Cultural Anthropology'', Ninth Ed., Abraham Rosman, Paula G. Rubel, Maxine Weisgrau, 2009, AltaMira Press, p. 101</ref>

==Terminology==
[[File:Table of Consanguinity showing degrees of relationship.svg|thumb|upright=1.35|The number next to each box indicates the degree of relationship relative to the given person.]]

The English word ''[[wikt:incest|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)<ref>[[OED]] [[Ancrene Riwle]] (c. 1225) has ''Incest‥is bituȝe sibbe fleschliche'', where either the generic or the narrow sense may be intended. See also [http://www.etymonline.com/index.php?search=incest&searchmode=none inetymonline.comest]</ref> and in the narrow modern sense. The derived adjective ''incestuous'' appears in the 16th century.<ref>''Oxford Concise Dictionary of Etymology'', T. F. Hoad (ed.) (1996), p. 232</ref> 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''<ref>{{cite book |last1=Wollert |first1=R |title=An analysis of the argument that clinicians under-predict sexual violence in civil commitment cases |date=2001 |pages=171–184 |url=http://www.richardwollert.com/BSLarticle.html |quote=His first criterion was that follow-up research on rapists and extrafamilial molesters should be studied while research on incesters and intrafamilial molesters should be screened out.}}</ref><ref>{{cite journal |last1=Crowley |first1=Sue |title=Exploring the multiplicity of childhood sexual abuse with a focus on polyincestuous contexts of abuse |journal=Journal of Child Sexual Abuse |date=2002 |volume=10 |issue=4 |publisher=[[Taylor & Francis]] |pages=91–110 |doi=10.1300/J070v10n04_07 |pmid=16221629 |s2cid=10707236 |quote=They also suggested that researchers have created "a false dichotomy" (p. 33) by studying extrafamilial child molesters (eg, those who abuse other families' children) as though they were distinct from intrafamilial child incesters (eg, those who molest children within their own family)}}</ref><ref>{{cite journal |last1=Caputi |first1=Jane |title=Unthinkable fathering: connecting incest and nuclearism |journal=[[Hypatia (journal)|Hypatia]] |volume=9 |issue=2 |date=2009 |publisher=[[Wiley Online Library]] |pages=102–122 |doi=10.1111/j.1527-2001.1994.tb00435.x |jstor=3810172|s2cid=145443764}}</ref> and ''incestual''<ref>{{cite book |last1=L Conyers |first1=James |title=Black Cultures and Race Relations |date=2002 |publisher=[[Rowman & Littlefield]] |isbn=9780830415748 |page=115 |url=https://books.google.com/books?id=l_dukyNja_YC&q=%22%22&pg=PA115}}</ref><ref>{{cite book |author=University of California |title=American Journal of Psychiatry |date=1945 |page=425 |edition=Volume 101 |quote=Psychoanalytic interpretations of some of the elements of incestuous reactions and a classification of incestuals are proposed.}}</ref> 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.<ref>{{cite book |last1=Charlesworth |first1=Deborah |title=Introduction to Plant Population Biology |date=2009 |publisher=[[John Wiley & Sons]] |page=80}}</ref>

==History==
===Antiquity===
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).<ref>{{cite book |last=Gulik |first=Robert Hans van |title=Sexual Life in Ancient China: a Preliminary Survey of Chinese Sex and Society from ca. 1500 B.C. till 1644 A.D. |publisher=Brill |location=Leiden |year=1974 |page=19 |url=https://books.google.com/books?id=u9MUAAAAIAAJ&pg=PA19 |isbn=978-90-04-03917-9}}</ref>

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.{{sfn|Brosius|2000}} According to [[Herodotus]], Shah [[Cambyses II]] supposedly married two of his sisters, [[Atossa]] and Roxane.{{sfn|Dandamayev|1990|pp=726–729}}{{sfn|Brosius|2000}} This would have been regarded as illegal. However, Herodotus also states that Cambyses married [[Otanes]]' daughter [[Phaedymia|Phaidyme]], whilst his contemporary [[Ctesias]] names Roxane as Cambyses' wife, but she is not referred to as his sister.{{sfn|Brosius|2000}} 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.{{sfn|Brosius|2000}}

Several of the Egyptian [[king]]s 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 [[papyrus|papyri]] and the Roman census declarations attest to many husbands and wives being brother and sister, of the same father and mother.<ref>{{cite book |last=Lewis |first=N. |title=Life in Egypt under Roman Rule |isbn=978-0-19-814848-7 |publisher=[[Oxford University Press|Clarendon Press]] |year=1983 |url-access=registration |url=https://archive.org/details/lifeinegyptunder0000lewi }}</ref><ref>{{cite book |last1=Frier |first1=Bruce W. |last2=Bagnall |first2=Roger S. |author2-link=Roger S. Bagnall |title=The Demography of Roman Egypt |publisher=[[Cambridge University Press]] |location=Cambridge, UK |year=1994 |isbn=978-0-521-46123-8}}</ref><ref>{{cite journal |last=Shaw |first=B. D. |title=Explaining Incest: Brother-Sister Marriage in Graeco-Roman Egypt |journal=Man |series=New Series |volume=27 |issue=2 |year=1992 |pages=267–299 |jstor=2804054 |doi=10.2307/2804054}}</ref><ref>{{cite journal |last=Hopkins |first=Keith |author-link=Keith Hopkins |year=1980 |title=Brother-Sister Marriage in Roman Egypt |url=http://humweb.ucsc.edu/jklynn/ancientwomen/HopkinsBrotherSisterMarriage.pdf |journal=Comparative Studies in Society and History |volume=22 |pages=303–354 |doi=10.1017/S0010417500009385 |issue=3 |s2cid=143698328 |access-date=21 July 2013 |archive-date=3 March 2016 |archive-url=https://web.archive.org/web/20160303180202/http://humweb.ucsc.edu/jklynn/ancientwomen/HopkinsBrotherSisterMarriage.pdf |url-status=dead }}</ref> However, it has also been argued that the available evidence does not support the view that such relations were common.<ref>Walter Scheidel. 2004. "Ancient Egyptian Sibling Marriage and the Westermarck Effect", in ''Inbreeding, Incest, and the Incest Taboo: the state of knowledge at the turn of the century'' Arthur Wolf and William Durham (eds) Stanford University Press. pp. 93–108</ref><ref>{{cite journal | last1 = Huebner | first1 = Sabine R | author-link = Sabine R. Huebner | year = 2007 | title = 'Brother-Sister' Marriage in Roman Egypt: a Curiosity of Humankind or a Widespread Family Strategy?. | journal = The Journal of Roman Studies | volume = 97 | pages = 21–49 | doi = 10.3815/000000007784016070 }}</ref><ref>Huebner, Sabine R. The family in Roman Egypt: a comparative approach to intergenerational solidarity and conflict. Cambridge University Press, 2013.</ref>

The most famous of these relationships were in the [[Ptolemaic dynasty|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 of Egypt|Cleopatra V]] and [[Ptolemy XII]], were also brother and sister. [[Arsinoe II]] and her younger brother [[Ptolemy II|Ptolemy II Philadelphus]] were the first in the family to participate in a full-sibling marriage, a departure from custom.<ref name="Familiarity Breeds: Incest and the">{{cite journal |last1=Ager |first1=Sheila L. |title=Familiarity Breeds: Incest and the Ptolemaic Dynasty |journal=The Journal of Hellenic Studies |date=2005 |volume=125 |pages=1–34 |doi=10.1017/S0075426900007084 |jstor=30033343 |pmid=19681234  |issn=0075-4269}}</ref> A union between full siblings was counternormative in Greek and Macedonian tradition, and prohibited by the laws of at least some cities.<ref name="Familiarity Breeds: Incest and the"/><ref name="The Routledge Companion to Women and Monarchy in the Ancient Mediterranean World">{{cite book |author=<!--Staff writer(s); no by-line.--> |title= The Routledge Companion to Women and Monarchy in the Ancient Mediterranean World|publisher= Taylor & Francis|date= 9 November 2020|isbn= 9780429783982}}</ref>

[[File:Tutankhamun and his wife B. C. 1330.jpg|thumb|Egyptian king [[Tutankhamun]] married his half-sister [[Ankhesenamun]].]]

The fable of ''[[Oedipus]]'', with a theme of inadvertent incest between a mother and son, ends in disaster and shows ancient taboos against incest, since Oedipus blinds himself in disgust and shame after his incestuous actions. In the 'sequel' to ''Oedipus'', ''[[Antigone]]'', his four children are also punished for their parents' incestuousness. Incest appears in the commonly accepted version of the birth of [[Adonis]], when his mother, [[Myrrha]], has sex with her father, [[Cinyras]], during a festival, disguised as a [[prostitute]].

In [[ancient Greece]], [[Ancient Sparta|Spartan King]] [[Leonidas I]], hero of the legendary [[Battle of Thermopylae]], was married to his [[niece]] [[Gorgo, Queen of Sparta|Gorgo]], daughter of his half-brother [[Cleomenes I]]. Greek law allowed marriage between a brother and sister if they had different mothers: for example, some accounts say that [[Elpinice]] was for a time married to her half-brother [[Cimon]].<ref>{{cite encyclopedia |url=http://www.mlahanas.de/Greeks/Bios/Elpinice.html |title=Elpinice |last=Lahanas |first=Michael |year=2006 |encyclopedia=Hellenic World encyclopaedia |publisher=Hellenica |access-date=6 June 2009 |archive-url=https://web.archive.org/web/20090921025414/http://www.mlahanas.de/Greeks/Bios/Elpinice.html |archive-date=21 September 2009 }}</ref>

Incest is mentioned and condemned in [[Virgil]]'s ''[[Aeneid]]'' Book VI:<ref>[http://ancienthistory.about.com/library/bl/bl_text_vergil_aeneid_latin_6.htm Vergil Aeneid Book VI in Latin: The descent to the Underworld] {{Webarchive|url=https://web.archive.org/web/20110921102854/http://ancienthistory.about.com/library/bl/bl_text_vergil_aeneid_latin_6.htm |date=21 September 2011 }}. Ancienthistory.about.com (15 June 2010). Retrieved on 2011-10-01.</ref> ''hic thalamum invasit natae vetitosque hymenaeos''{{nbsp}}{{ndash}} "This one invaded a daughter's room and a forbidden sex act".

[[File:Yaxchilán lintel.jpg|thumb|Maya king [[Itzamnaaj B'alam II|Shield Jaguar II]] with his [[avunculate marriage|aunt-wife]], [[Lady Xoc]] AD 709]]

[[Roman law|Roman civil law]] prohibited marriages within four degrees of consanguinity<ref name="SRCL514">Patrick Colquhoun, ''A Summary of the Roman Civil Law, Illustrated by Commentaries on and Parallels from the Mosaic, Canon, Mohammedan, English, and Foreign Law'' (London: Wm. Benning & Co., 1849), p. 513-4</ref> but had no degrees of affinity with regard to marriage. Roman civil laws prohibited any marriage between parents and children, either in the ascending or descending line [[:wikt:ad infinitum|ad infinitum]].<ref name="SRCL514"/> Adoption was considered the same as affinity in that an adoptive father could not marry an [[:wikt:unemancipated|unemancipated]] daughter or granddaughter even if the adoption had been dissolved.<ref name="SRCL514"/> Incestuous unions were discouraged and considered ''[[nefas]]'' (against the laws of gods and man) in [[ancient Rome]]. In AD 295, incest was explicitly forbidden by an imperial edict, which divided the concept of ''incestus'' into two categories of unequal gravity: the ''incestus iuris gentium'', which was applied to both Romans and non-Romans in the Empire, and the ''incestus iuris civilis'', which concerned only Roman citizens. Therefore, for example, an Egyptian could marry an aunt, but a Roman could not. Despite the act of incest being unacceptable within the Roman Empire, Roman Emperor [[Caligula]] is rumored to have had sexual relationships with all three of his sisters ([[Julia Livilla]], [[Drusilla (sister of Caligula)|Drusilla]], and [[Agrippina the Younger]]).{{sfn|Potter|2007|p=62}} Emperor [[Claudius]], after executing his previous wife, married his brother's daughter, Agrippina the Younger, and changed the law to allow an otherwise illegal union.{{sfn|Potter|2007|p=66}} The law prohibiting marrying a sister's daughter remained.<ref>{{cite book |first=Judith Evans |last=Grubbs |title=Women and the Law in the Roman Empire: a Sourcebook on Marriage, Divorce and Widowhood |url=https://books.google.com/books?id=4X8HXDwMHawC&pg=PA137 |access-date=7 November 2011 |year=2002 |publisher=Psychology Press |isbn=978-0-415-15240-2 |pages=137–}}</ref> The taboo against incest in ancient Rome is demonstrated by the fact that politicians would use charges of incest (often false charges) as insults and means of political disenfranchisement.

In [[Norse mythology]], there are themes of brother{{ndash}}sister marriage, a prominent example being between [[Njörðr]] and his [[Sister-wife of Njörðr|unnamed sister]] (perhaps [[Nerthus]]), parents of [[Freyja]] and [[Freyr]]. [[Loki]] in turn also accuses Freyja and Freyr of having a sexual relationship.

===Biblical references===
{{Main|Incest in the Bible}}
The earliest Biblical reference to possible incest involves Cain. It was cited that he knew his wife and she conceived and bore Enoch.<ref name=":1">{{Cite book|title=Forensic and Medico-legal Aspects of Sexual Crimes and Unusual Sexual Practices|last=Aggrawal|first=Anil|publisher=CRC Press|year=2009|isbn=9781420043082|location=Boca Raton, FL|pages=320}}</ref> A literalist reading of this passage indicates that, during this period, there was no other woman except Eve, or there was an unnamed sister, in which case Cain had an incestuous relationship with his mother or his sister.<ref name=":1" /> According to the [[Book of Jubilees]], [[Cain]] married his sister [[Awan (religious figure)|Awan]].<ref>Cain and Abel in Text and Tradition: Jewish and Christian Interpretations of the First Sibling Rivalry, John Byron – 2011, page 27</ref><ref>The Empowerment of Women in the Book of Jubilees – Page 17, Betsy Halpern Amaru – 1999</ref> Later, in Genesis 20<ref>''Hebrew-English Bible,'' {{bibleverse||Genesis|20:12|HE}}</ref> of the [[Hebrew Bible]], the [[Patriarch]] [[Abraham]] married his half-sister [[Sarah]].{{sfn|Ska|2009|pp=26–31}} Other references include the passage in 2 Samuel 13 where [[Amnon]], King [[David]]'s son, rapes his half-sister [[Tamar (2 Samuel)|Tamar]].<ref>''Bible'', {{bibleverse|2|Samuel|13|NIV}}</ref> According to [[Michael D. Coogan]], it would have been perfectly all right for Amnon to have married her, the Bible being inconsistent about prohibiting incest.<ref>{{cite book|last=Coogan|first=Michael|title=God and Sex. What the Bible Really Says|url=https://archive.org/details/godsexwhatbi00coog|url-access=registration|quote=god and sex.|access-date=5 May 2011|edition=1st|year=2010|publisher=Twelve. Hachette Book Group|location=New York, Boston|isbn=978-0-446-54525-9|oclc=505927356|pages=[https://archive.org/details/godsexwhatbi00coog/page/112 112]–113}}</ref>

In Genesis 19:30{{ndash}}38, while living in an isolated area after the destruction of [[Sodom and Gomorrah]], [[Lot (biblical person)|Lot]]'s two daughters conspire to inebriate and rape their father due to the lack of available partners to continue his [[Lineage (anthropology)|line of descent]]. Because of intoxication, Lot "perceived not" when his firstborn, and the following night his younger, daughter lay with him.<ref>''Bible'', Genesis 19:32–35</ref>

Moses was also born of an incestuous marriage. Exodus 6<ref>''Hebrew-English Bible'', {{bibleverse||Exodus|6:20|HE}}</ref> details how his father, [[Amram]], was the nephew of his mother, [[Jochebed]].<ref name=":1" /> An account noted that the incestuous relations did not suffer the fate of childlessness, which was the punishment for such couples in Levitical law.<ref name=":2">{{Cite book|title=Sex, Marriage, and Family in John Calvin's Geneva: Courtship, Engagement, and Marriage|last1=John|first1=Witte Jr.|last2=Kingdon|first2=Robert|publisher=William B. Eerdmans Publishing Company|year=2005|isbn=9780802848031|location=Grand Rapids|pages=321}}</ref> It stated, however, that the incest exposed Moses "to the peril of wild beasts, of the weather, of the water, and more."<ref name=":2" />

===From the Middle Ages 
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 | caption1 = Table of prohibited marriages from ''The Trial of Bastardie'' by [[William Clerke (writer)|William Clerke]]. London, 1594
 | image2 = Rey_Carlos_II.jpg
 | caption2 = [[Charles II of Spain]] was born physically disabled, probably due to centuries of inbreeding in the [[House of Habsburg]], and suffered a particularly pronounced case of [[Habsburg jaw]] 
}}
Many European monarchs were related due to political marriages, such that many such marriages were between cousins of some degree, uncles and nieces, and so forth, and sometimes first cousins. This was especially true in the [[House of Habsburg|Habsburg]], [[House of Hohenzollern|Hohenzollern]], [[House of Savoy|Savoy]], and [[House of Bourbon|Bourbon]] royal houses. However, relations between siblings, which may have been tolerated in other cultures, were considered abhorrent. For example, the false accusation that [[Anne Boleyn]] and her brother, [[George Boleyn, 2nd Viscount Rochford|George Boleyn]], had committed incest was one of the reasons given for both being executed in May 1536. Historians agree that the false accusation against Anne Boleyn and George Boleyn was trumped up in order to ensure the king could go on to marry [[Jane Seymour]].<ref>[https://www.smithsonianmag.com/history/the-many-myths-of-lady-rochford-the-tudor-noblewoman-who-supposedly-betrayed-george-and-anne-boleyn-180980520/] Solly, Meilan. "The Myths of Lady Rochford, the Tudor Noblewoman Who Supposedly Betrayed George and Anne Boleyn". ''Smithsonian Magazine''. August 4, 2022.</ref> Sects deemed heretical, such as the [[Waldensians]], were accused of incest.<ref name="Gow Desjardins Pageau 2016 p. 64">{{cite book | last1=Gow | first1=A.C. | last2=Desjardins | first2=R.B. | last3=Pageau | first3=F.V. | title=The Arras Witch Treatises: Johannes Tinctor's Invectives contre la secte de vauderie and the Recollectio casus, status et condicionis Valdensium ydolatrarum by the Anonymous of Arras (1460) | publisher=Penn State University Press | series=Magic in History Sourcebooks | year=2016 | isbn=978-0-271-07750-5 | url=https://books.google.com/books?id=PW8RDAAAQBAJ&pg=PT64 | access-date=2023-04-01 | page=64}}</ref>

Incestuous marriages were also seen in the royal houses of ancient [[Japan]] and Korea,<ref>Smith, George Patrick (1998). [https://books.google.com/books?id=HLPDS2UXaqAC&pg=PA143 ''Family Values and the New Society: Dilemmas of the 21st Century'']. [[Greenwood Publishing Group]] via [[Google Books]]. p. 143.</ref> Inca [[Peru]], [[Ancient Hawaii]], and, at times, Central Africa, [[Mexico]], and [[Thailand]].<ref>"[https://web.archive.org/web/20100822132434/http://ngm.nationalgeographic.com/2010/09/tut-dna/dobbs-text/2 The Risks and Rewards of Royal Incest]". National Geographic Magazine.</ref> Like the kings of ancient Egypt, the [[Inca]] rulers married their sisters. [[Huayna Capac]], for instance, was the son of [[Topa Inca Yupanqui]] and the Inca's sister and wife.<ref>Sarmiento de Gamboa, Pedro. [https://books.google.com/books?id=T0q_A1BaSVsC&pg=PA151 ''The History of the Incas.''] Austin: University of Texas Press, 2007. p.171. {{ISBN|978-0-292-71485-4}}.</ref>

Half-sibling marriages were found in ancient Japan, such as the marriage of [[Emperor Bidatsu]] and his half-sister [[Empress Suiko]].<ref>Lloyd, Arthur (2004). [https://books.google.com/books?id=Pl_7PollB60C&pg=PA180 ''The Creed Of Half Japan: Historical Sketches Of Japanese Buddhism'']. [[Kessinger Publishing]] via [[Google Books]]. p. 180.</ref> Japanese [[Prince Kinashi no Karu]] had sexual relations with his full sister Princess Karu no Ōiratsume, although the action was regarded as foolish.<ref>[[Edwin Cranston|Cranston, Edwin A.]] (1998). [https://books.google.com/books?id=KqWjwalbmx4C&pg=PA805 ''A Waka Anthology: The Gem-Glistening Cup'']. [[Stanford University Press]] via [[Google Books]]. p. 805.</ref> In order to prevent the influence of the other families, Korean [[Goryeo]] dynasty monarch [[Gwangjong of Goryeo|Gwangjong]] married his half-sister Daemok in the 10th century.<ref>Shultz, Edward J. (2000). [https://books.google.com/books?id=fM9sEyxzVq8C&pg=PA169 ''Generals and Scholars: Military Rule in Medieval Korea'']. [[University of Hawaii Press]], p. 169.</ref> Marriage with a family member not related by blood was also regarded as contravening morality and was therefore incest. One example of this is the 14th century [[Chunghye of Goryeo]], who raped one of his deceased [[Princess Gyeonghwa|father's concubines]], who was thus regarded to be his mother.<ref>{{Cite book|author=Asogawa Shizuo 麻生川静男 |title=Hontōni hisan'na Chōsen-shi 'kōraishisetsuyō' o yomi kai |script-title=ja:本当に悲惨な朝鮮史 「高麗史節要」を読み解く |publisher=KADOKAWA |year=2017 |isbn=978-4-04-082109-2|pages=58–59|language=ja}}</ref>

In India, the largest proportion of women aged 13 to 49 who marry their close relatives are in [[Tamil Nadu]], then [[Andhra Pradesh]], [[Karnataka]], and [[Maharashtra]]. While it is rare for uncle{{ndash}}niece marriages, it is more common in [[Andhra Pradesh]] and [[Tamil Nadu]].<ref>{{cite book |last=Wal |first=Ruchi Mishra S. |title=Ency. Of Health Nutrition And Family Wel.(3 Vol) |url=https://books.google.com/books?id=89N78kYLFNQC |year=2000 |publisher=Sarup & Sons |isbn=978-81-7625-171-6 |page=[https://books.google.com/books?id=89N78kYLFNQC&pg=PA166 166]}}</ref><ref>{{cite book |author=United Nations Publications |url=https://books.google.com/books?id=zseZeGgQlDwC |title=Asia-Pacific Population Journal |publisher=United Nations Publications |year=2002 |isbn=978-92-1-120340-0 |page=[https://books.google.com/books?id=zseZeGgQlDwC&pg=PA23 23] }}{{dead link|date=May 2024}}</ref>

===Others===
In some Southeast Asian cultures, stories of incest being common among certain ethnicities are sometimes told as expressions of contempt for those ethnicities.<ref>{{cite book |last1=Edmunds |first1=Lowell |last2=Dundes |first2=Alan |title=Oedipus: A Folklore Casebook |date=1995 |publisher=Univ of Wisconsin Press |isbn=978-0-299-14853-9 |page=32 |url=https://books.google.com/books?id=m-3Hyd4ms_YC&q=Kalangs+incest&pg=PA32 |language=en}}</ref>

Marriages between younger brothers and their older sisters were common among the early [[Udege people]].<ref>{{cite book |last= Deusen|first= Kira|date= 2 February 2011|title= Flying Tiger: Women Shamans and Storytellers of the Amur|publisher= McGill Queen's Press|page= 25|isbn= 978-0773521551}}</ref>

==Prevalence and statistics==
Incest between an adult and a person under the [[age of consent]] is considered a form of [[child sexual abuse]]<ref>{{Cite book |title=Child Sexual Abuse: Intervention and Treatment Issues |first=Kathleen C. |last=Faller |publisher=DIANE Publishing |year=1993 |isbn=978-0-7881-1669-8 |page=64 |url=https://books.google.com/books?id=D-SEwHNu_NcC&pg=PA64}}</ref><ref>{{Cite book |title=Child Sexual Abuse: A Handbook for Health Care and Legal Professionals |first1=Diane H. |last1=Schetky |first2=Arthur H. |last2=Green |publisher=Psychology Press |year=1988 |isbn=978-0-87630-495-2 |page=128 |url=https://books.google.com/books?id=QYyzGgZbllYC&pg=PA128}}</ref> 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.<ref name= Courtois>{{cite book |title=Healing the Incest Wound: Adult Survivors in Therapy |last=Courtois |first=Christine A. |publisher=W. W. Norton & Company |page=208 |year=1988 |isbn=978-0-393-31356-7}}</ref> 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.<ref>{{cite book |last1=Nemeroff |first1=Charles B. |author-link=Charles Nemeroff |last2=Craighead |first2=W. Edward |title=The Corsini Encyclopedia of Psychology and Behavioral Science |publisher=Wiley |location=New York |year=2001 |isbn=978-0-471-24096-9}}</ref> Among women, research has yielded estimates as high as 20%.<ref name= Courtois/>

[[Father]]{{ndash}}[[daughter]] incest was for many years the most commonly reported and studied form of incest.<ref>''[[Aeneid]]'' by [[Virgil]], Book VI: "''hic thalamum invasit natae vetitosque hymenaeos;''" = "this [man being punished in [[Hades]]<nowiki>]</nowiki> invaded a daughter's private room and a forbidden marital relationship."</ref><ref name=Herman>{{cite book |last=Herman |first=Judith |author-link=Judith Lewis Herman |title=Father-Daughter Incest |publisher=Harvard University Press |year=1981 |location=Cambridge, Massachusetts |page=[https://archive.org/details/fatherdaughterin00herm_0/page/282 282] |isbn=978-0-674-29506-3 |url=https://archive.org/details/fatherdaughterin00herm_0/page/282 }}</ref>

[[Mother]]{{ndash}}[[son]] incest is rarely reported. According to Catanzarite (1980), between 1965 and 1980 only a handful such cases were documented. Catanzarite attributes this to selection bias and the lack of physical evidence in such cases.<ref>Catanzarite, Valerian A., and Sam Edward Combs. "Mother-son incest." JAMA 243.18 (1980): 1807-1808.</ref> According to Etherington (1997), one of the reasons of the under-reporting of such cases is that men often found difficulty in defining their mother's behavior as abuse.<ref>Etherington, Kim. Maternal sexual abuse of males. Child Abuse Review: Journal of the British Association for the Study and Prevention of Child Abuse and Neglect 6.2 (1997): 107-117.</ref> In a clinical study by Olson (1990), 30 men had been victims of incest; the mother was a perpetrator in 61.5 % of cases.<ref>Olson, P. E. (1990). The sexual abuse of boys: A study of the long-term psychological effects. In M. Hunter (Ed.), The sexually abused male: Vol. 1. Prevalence, impact, and treatment (pp. 137 - 152 ) . Lexington, MA: Lexington.</ref> In a clinical study by Kelly et al. (2002), among the 67 sexually abused men, in 17 cases the perpetrators were their mothers.<ref>Kelly, Robert J., et al. "Effects of mother-son incest and positive perceptions of sexual abuse experiences on the psychosocial adjustment of clinic-referred men." Child abuse & neglect 26.4 (2002): 425-441.</ref>

More recently, studies have suggested that [[sibling incest]], particularly older brothers having sexual relations with younger siblings, is the most common form of incest,<ref>{{cite journal |last1=Goldman |first1=R. |last2=Goldman |first2=J. |year=1988 |title=The prevalence and nature of child sexual abuse in Australia |journal=Australian Journal of Sex, Marriage and Family |volume=9 |issue=2 |pages=94–106|doi=10.1080/01591487.1988.11004405 }}</ref><ref>Wiehe, Vernon (1997). ''Sibling Abuse: Hidden Physical, Emotional, and Sexual Trauma''. Sage Publications, {{ISBN|0-7619-1009-3}}</ref><ref>Rayment-McHugh, Sue; Ian Nesbit (2003). "[https://web.archive.org/web/20070902110255/http://www.aic.gov.au/conferences/2003-abuse/nisbet.pdf Sibling Incest Offenders As A Subset of Adolescent Sex Offenders]." Paper presented at the Child Sexual Abuse: Justice Response or Alternative Resolution Conference convened by the Australian Institute of Criminology and held in Adelaide, 1–2 May 2003</ref><ref>{{cite journal |last1=Canavan |first1=M. C. |last2=Meyer |first2=W. J. |last3=Higgs |first3=D. C. |year=1992 |title=The female experience of sibling incest |doi=10.1111/j.1752-0606.1992.tb00924.x |journal=Journal of Marital and Family Therapy |volume=18 |issue=2 |pages=129–142 }}</ref><ref>{{cite journal |last1=Smith |first1=H. |last2=Israel |first2=E. |year=1987 |title=Sibling incest: A study of the dynamics of 25 cases |journal=Child Abuse and Neglect |volume=11 |pages=101–108 |doi=10.1016/0145-2134(87)90038-X |pmid=3828862 |issue=1}}</ref><ref>{{cite journal |last=Cole |first=E |year=1982 |title=Sibling incest: The myth of benign sibling incest |journal=Women & Therapy |volume=1 |issue=3 |pages=79–89 |doi=10.1300/J015V01N03_10}}</ref><ref>Cawson, P., Wattam, C., Brooker, S., & Kelly, G. (2000). [http://www.nspcc.org.uk/inform/research/findings/childmaltreatmentintheunitedkingdom_wda48252.html Child maltreatment in the United Kingdom: A study of the prevalence of child abuse and neglect] {{Webarchive|url=https://web.archive.org/web/20111103111326/http://www.nspcc.org.uk/Inform/research/findings/childmaltreatmentintheunitedkingdom_wda48252.html |date=3 November 2011 }}. London: National Society for the Prevention of Cruelty to Children. {{ISBN|1-84228-006-6}}</ref><ref>Sibling incest is roughly five times as common as other forms of incest according to Gebhard, P., Gagnon, J., Pomeroy, W., & Christenson, C. (1965). ''Sex Offenders: An Analysis of Types''. New York: Harper & Row.</ref><ref>{{cite book |title=Sexually Victimized Children |first=David |last=Finkelhor |author-link=David Finkelhor |publisher=Simon and Schuster |year=1981 |isbn=978-0-02-910400-2}}</ref> with some studies finding sibling incest occurring more frequently than other forms of incest.<ref>A large-scale study of (n = 3,000) by the UK's National Council for the Prevention of Cruelty to Children found that fathers committed about 1% of child sex abuse, while siblings committed 14%. See [http://news.bbc.co.uk/2/hi/health/1026797.stm BBC News Online: Health, Child Abuse Myths Shattered, November, 20, 2000]</ref> 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.<ref>O'Brien, M. J. (1991). "Taking sibling incest seriously." In M. Patton (ed.), ''Family Sexual Abuse: Frontline Research and Evaluation'', pp. 75–92. Newbury Park, CA: Sage Publications.</ref><ref>{{cite journal |last=Laviola |first=M. |year=1992 |title=Effects of older brother-younger sister incest: A study of the dynamics of 17 cases |journal=Child Abuse and Neglect |volume=16 |pages=409–421 |doi=10.1016/0145-2134(92)90050-2 |pmid=1617475 |issue=3}}</ref><ref>{{cite journal |last1=Cyr |first1=M.| last2=Wright |first2=J. |last3=McDuff |first3= P. |last4=Perron |first4=A. |year=2002 |title=Intrafamilial sexual abuse: Brother-sister incest does not differ from father-daughter and stepfather-stepdaughter incest |journal=Child Abuse and Neglect |volume=26 |pages=957–973 |doi=10.1016/S0145-2134(02)00365-4 |pmid=12433139 |issue=9}}</ref> South Africa,<ref>{{cite web | url=https://books.google.com/books?id=YBosAQAAMAAJ&q=%22highest+rate+of+incest%22 | title=Journal of Psychology in Africa (South of the Sahara, the Caribbean, and Afro-Latin America) | year=2003 }}</ref> Saudi Arabia, Sudan, Pakistan, and Nigeria are some of the countries with the most incest through consanguineous marriage.<ref>{{cite journal |last1=Bittles |first1=A. H. |last2=Black |first2=M. L. |title=Consanguinity, human evolution, and complex diseases |journal=Proceedings of the National Academy of Sciences |date=26 January 2010 |volume=107 |issue=suppl 1 |pages=1779–1786 |doi=10.1073/pnas.0906079106 |pmid=19805052 |pmc=2868287 |doi-access=free }}</ref>

==Types==

===Between adults and children===
{{Main|Child sexual abuse}}

Sex between an adult family member and a child is usually considered a form of child sexual abuse,<ref>{{Cite journal |last=Fridell |first=Lorie A. |title=Decision-making of the District Attorney: diverting or prosecuting intrafamilial child sexual abuse offenders |journal=[[Criminal Justice Policy Review]] |volume=4 |issue=3 |pages=249–267 |doi=10.1177/088740349000400304 |date=October 1990 |s2cid=145654768 }}</ref> also known as '''child incestuous abuse''',<ref>{{cite web |last=Trusiani|first=Jessica|title=Working with Survivors of Child Incestuous Abuse |website=Rutgers School of Social Work |url=http://socialwork.rutgers.edu/Libraries/VAWC/Trusiani_presentation.sflb.ashx|archive-url=https://web.archive.org/web/20141101063712/http://socialwork.rutgers.edu/Libraries/VAWC/Trusiani_presentation.sflb.ashx|archive-date=1 November 2014}}</ref> and for many years has been the most reported form of incest. Father–daughter and stepfather–stepdaughter sex are the most commonly reported forms of adult–child incest, with most of the remaining involving a mother or stepmother.<ref name=Turner>{{cite book |title=Encyclopedia of Relationships Across the Lifespan |last=Turner |first=Jeffrey S. |year=1996 |publisher=Greenwood Publishing Group |page=[https://archive.org/details/encyclopediaofre0000turn/page/92 92] |isbn=978-0-313-29576-8 |url=https://archive.org/details/encyclopediaofre0000turn/page/92 }}</ref> Many studies found that stepfathers tend to be far more likely than biological fathers to engage in this form of incest. One study of adult women in San Francisco estimated that 17% of women were abused by stepfathers and 2% were abused by biological fathers.<ref>{{cite book |last=Kinnear |first=Karen L. |title=Childhood Sexual Abuse: A Reference Handbook |page=8}}</ref> Father–son incest is reported less often, but it is not known how close the frequency is to heterosexual incest because it is probably more under-reported.<ref>{{Cite journal |doi=10.1007/BF00754448|title=Father-son incest: A review and analysis of reported incidents|journal=Clinical Social Work Journal|volume=16|issue=2|pages=165–179|year=1988|last1=Williams|first1=Mark|s2cid=144258944}}</ref><ref>{{Cite journal |doi=10.1176/ajp.135.7.835|pmid=665796|title=Father-son incest: Underreported psychiatric problem?|journal=American Journal of Psychiatry|volume=135|issue=7|pages=835–838|year=1978|hdl=1811/51174|last1=Dixon|first1=K. N.|last2=Arnold|first2=L. E.|last3=Calestro|first3=K.|citeseerx=10.1.1.1018.8536}}</ref><ref>{{cite book |title=Don't Tell: The Sexual Abuse of Boys |first=Michel |last=Dorais |translator=Isabel Denholm Meyer |year=2002 |page=24 |publisher=McGill-Queen's Press |isbn=978-0-7735-2261-9}}</ref><ref>{{cite book |title=Healing the Incest Wound: Adult Survivors in Therapy |first=Christine A. |last=Courtois |year=1988 |publisher=W. W. Norton & Company |isbn=978-0-393-31356-7}}</ref> The prevalence of incest between parents and their children is difficult to estimate due to secrecy and privacy.

In a 1999 news story, the [[BBC]] reported: "Close-knit family life in India masks an alarming amount of sexual abuse of children and teenage girls by family members, a new report suggests. Delhi organisation [[RAHI Foundation|RAHI]] said 76% of respondents to its survey had been abused when they were children{{nbsp}}{{ndash}} 40% of those by a family member."<ref>{{Cite news |url=http://news.bbc.co.uk/2/hi/south_asia/259959.stm |title=India's hidden incest |date=22 January 1999 |work=BBC News}}</ref>

According to the National Center for Victims of Crime a large proportion of [[rape]] committed in the United States is perpetrated by a family member:
{{blockquote|1=Research indicates that 46% of children who are raped are victims of family members (Langan and Harlow, 1994). The majority of American rape victims (61%) are raped before the age of 18; furthermore, 29% of all rapes occurred when the victim was less than 11 years old. 11% of rape victims are raped by their fathers or stepfathers, and another 16% are raped by other relatives.<ref>{{cite web|url=http://www.ncvc.org/ncvc/main.aspx?dbName=DocumentViewer&DocumentID=32360|title=Incest|work=National Center for Victims of Crime and Crime Victims Research and Treatment Center|year=1992|publisher=National Center for Victims of Crime|access-date=27 March 2008|archive-date=10 August 2020|archive-url=https://web.archive.org/web/20200810214920/http://www.ncvc.org/ncvc/main.aspx?dbName=DocumentViewer&DocumentID=32360|url-status=dead}}</ref>}}

A study of victims of father–daughter incest in the 1970s showed that there were "common features" within families before the occurrence of incest: estrangement between the mother and the daughter, extreme paternal dominance, and reassignment of some of the mother's traditional major family responsibility to the daughter. Eldest and only daughters were more likely to be the victims of incest. It was also stated that the incest experience was psychologically harmful to the woman in later life, frequently leading to low self-esteem, very unhealthy sexual activity, contempt for other women, and other emotional problems.<ref>{{Cite journal | doi=10.2307/3961672| jstor=3961672|title = Emotional Inheritance: A Dubious Legacy|journal = Science News| volume=111| issue=21| pages=326|year = 1977}}</ref>

Adults who as children were incestuously victimized by adults often suffer from low [[self-esteem]], difficulties in interpersonal relationships, and [[sexual dysfunction]], and are at an extremely high risk of many mental disorders, including [[Clinical depression|depression]], [[anxiety disorder]]s, [[Phobia|phobic avoidance reactions]], [[somatoform disorder]], [[substance abuse]], [[borderline personality disorder]], and [[complex post-traumatic stress disorder]].<ref name= Courtois/><ref>{{cite book |last2=Barrett |first2=Mary Jo |title=Systemic Treatment of Incest: A Therapeutic Handbook |last1=Trepper |first1=Terry S. |publisher=Psychology Press |year=1989 |isbn=978-0-87630-560-7}}</ref><ref>{{cite book |title=Incest-Related Syndromes of Adult Psychopathology |first=Richard P. |last=Kluft |year=1990 |publisher=American Psychiatric Pub, Inc. |pages=83, 89 |isbn=978-0-88048-160-1}}</ref>

The [[Goler clan]] in [[Nova Scotia]] is a specific instance in which child sexual abuse in the form of forced adult{{ndash}}child and sibling{{ndash}}sibling incest took place over at least three generations.<ref name="cruise">{{Cite book |title=On South Mountain: The Dark Secrets of the Goler Clan |last1=Cruise |first1=David |last2=Griffiths |first2=Alison |publisher=Penguin Books |year=1998 |isbn=978-0-670-87388-3}}</ref> A number of Goler children were victims of sexual abuse at the hands of fathers, mothers, uncles, aunts, sisters, brothers, cousins, and each other. During interrogation by police, several of the adults openly admitted to engaging in many forms of sexual activity, up to and including full intercourse, multiple times with the children. Sixteen adults (both men and women) were charged with hundreds of allegations of incest and sexual abuse of children as young as five.<ref name="cruise" /> In July 2012, twelve children were removed from the [[Colt clan incest case|'Colt' family]] (a pseudonym) in [[New South Wales]], Australia, after the discovery of four generations of incest.<ref name=ccnsw>{{cite web|url=http://www.caselaw.nsw.gov.au/action/PJUDG?jgmtid=167373 |title=DFaCS (NSW) and the Colt Children [2013] NSWChC 5 |publisher=Children's Court, New South Wales |date=13 September 2013 |archive-url=https://web.archive.org/web/20131217044158/http://www.caselaw.nsw.gov.au/action/PJUDG?jgmtid=167373 |archive-date=17 December 2013 }}</ref><ref name=nca131210>{{cite news |url=http://www.news.com.au/lifestyle/real-life/the-case-of-incest-and-depravity-which-came-to-rest-in-the-hills-of-a-quiet-country-town/story-fnixwvgh-1226780575248 |title=The case of incest and depravity which came to rest in the hills of a quiet country town |first=Candace |last=Sutton |work=[[News Corp Australia]] |date=10 December 2013 |access-date=14 December 2013 |archive-date=8 November 2016 |archive-url=https://web.archive.org/web/20161108041054/http://www.news.com.au/lifestyle/real-life/the-case-of-incest-and-depravity-which-came-to-rest-in-the-hills-of-a-quiet-country-town/story-fnixwvgh-1226780575248 }}</ref> Child protection workers and psychologists said interviews with the children indicated "a virtual sexual free-for-all".<ref name=nca131212>{{cite news |url=http://www.news.com.au/national/nsw-act/the-family-tree-of-the-depraved-family-who-live-in-the-hills-of-a-quiet-country-town/story-fnii5s3x-1226781805877 |title=The family tree of the depraved family who live in the hills of a quiet country town |first=Candace |last=Sutton |work=[[News Corp Australia]] |date=12 December 2013 |access-date=14 December 2013 |archive-date=25 September 2016 |archive-url=https://web.archive.org/web/20160925061616/http://www.news.com.au/national/nsw-act/the-family-tree-of-the-depraved-family-who-live-in-the-hills-of-a-quiet-country-town/story-fnii5s3x-1226781805877 }}</ref>

In Japan, there is a popular misconception that mother–son incestuous contact is common, due to the manner in which it is depicted in the press and popular media. According to Hideo Tokuoka, "when Americans think of incest, they think of fathers and daughters; in Japan one thinks of mothers and sons" due to the extensive media coverage of mother–son incest there.<ref>{{cite journal|last1=Tokuoka |first1=Hideo |last2=Cohen |first2=Albert K.|title=Japanese Society and Delinquency|journal=International Journal of Comparative and Applied Criminal Justice|year=1987|volume=11|issue=1–2|pages=13–22|doi=10.1080/01924036.1987.9688852}}</ref> Some Western researchers assumed that mother–son incest is common in Japan, but research into victimization statistics from police and health-care systems discredits this; it shows that the vast majority of sexual abuse in Japan, including incest, is perpetrated by men against young girls.<ref>{{cite journal |last=Gough |first=David |title=Child Abuse in Japan |journal=[[Child and Adolescent Mental Health]] |date=February 1996 |volume=1 |issue=1 |pages=12–18 |doi=10.1111/j.1475-3588.1996.tb00003.x }}</ref>

While incest between adults and children generally involves the adult as the perpetrator of abuse, there are rare instances of sons sexually assaulting their mothers. These sons are typically mid-adolescent to young adult, and, unlike parent-initiated incest, the incidents involve some kind of physical force. Although the mothers may be accused of being seductive with their sons and inviting the sexual contact, this is contrary to evidence.<ref name="Courtois 2">{{cite book |last=Courtois |first=Christine  |title=Healing the Incest Wound: Adult Survivors in Therapy |year=2010 |publisher=W. W. Norton & Company |isbn=978-0-39370-547-8 |pages=71–72 }}</ref><ref name="Ward">{{cite book |last=Ward |first=Elizabeth  |title=Father-Daughter Rape |year=1985 |publisher=W. W. Norton & Company |isbn=978-0-39462-032-9 }}</ref> Such accusations can parallel other forms of rape, where, due to [[victim blaming]], a woman is accused of being at fault for the rape. In some cases, mother–son incest is best classified as [[acquaintance rape]] of the mother by the adolescent son.<ref name="Courtois 2"/><ref name="Ward"/>

===Between children===
Childhood [[Sibling incest|sibling–sibling incest]] is considered to be widespread but rarely reported.<ref name=Turner /> Sibling–sibling incest becomes [[child-on-child sexual abuse]] when it occurs without consent, without equality, or as a result of [[coercion]]. In this form, it is believed to be the most common form of intrafamilial abuse.<ref>{{cite book |last=Kalogerakis |first=Michael G. |author2=American Psychiatric Association. Workgroup on Psychiatric Practice in the Juvenile Court |title=Handbook of psychiatric practice in the juvenile court: the Workgroup on Psychiatric Practice in the Juvenile Court of the American Psychiatric Association |year=1992 |publisher=American Psychiatric Pub |isbn=978-0-89042-233-5 |page=106 |url=https://books.google.com/books?id=nsUloUgZwRoC&pg=PA106 }}</ref> The most commonly reported form of abusive sibling incest is abuse of a younger sibling by an older sibling.<ref name=Turner /> A 2006 study showed a large portion of adults who experienced sibling incest abuse have "distorted" or "disturbed" beliefs (such as that the act was "normal") both about their own experience and the subject of sexual abuse in general.<ref name="Carlson">{{cite journal |last1=Carlson |first1=Bonnie E. |year=2006 |pmid=17200052 |title=Sibling Incest: Reports from Forty-One Survivors |journal=Journal of Child Sexual Abuse |volume=15 |issue=4 |pages=19–34 |doi=10.1300/J070v15n04_02 |last2=MacIol |first2=K |last3=Schneider |first3=J|s2cid=20799279 }}</ref>

[[Sibling abuse#Sexual abuse|Sibling abusive incest]] is most prevalent in families where one or both parents are often absent or emotionally unavailable, with the abusive siblings using incest as a way to assert their power over a weaker sibling.<ref name=leder>{{cite news|last=Leder |first=Jane Mersky |title=Adult Sibling Rivalry: Sibling rivalry often lingers through adulthood |url=https://www.psychologytoday.com/us/articles/199301/adult-sibling-rivalry |work=Psychology Today |volume=January/February 93 |publisher=Sussex Publishers }}</ref> Absence of the father in particular has been found to be a significant element of most cases of sexual abuse of female children by a brother.<ref name=rudd>{{cite journal |last1=Rudd |first1=Jane M. |last2=Herzberger |first2=Sharon D. |title=Brother-sister incest—father-daughter incest: a comparison of characteristics and consequences |journal=Child Abuse & Neglect |volume=23 |issue=9 |date=September 1999 |pages=915–928 |doi=10.1016/S0145-2134(99)00058-7 |pmid=10505905}}</ref> The damaging effects on both childhood development and adult symptoms resulting from brother–sister sexual abuse are similar to the effects of father–daughter, including substance abuse, depression, suicidality, and eating disorders.<ref name=rudd /><ref name=cyr>{{cite journal |last1=Cyr |first1=Mireille |last2=Wrighta |first2=S John |last3=McDuffa |first3=Pierre |last4=Perron |first4=Alain |title=Intrafamilial sexual abuse: brother–sister incest does not differ from father–daughter and stepfather–stepdaughter incest |journal=Child Abuse & Neglect |volume=26 |issue=9 |date=September 2002 |pages=957–973 |doi=10.1016/S0145-2134(02)00365-4 |pmid=12433139}}</ref>

===Between adults===
Proponents of incest between consenting adults draw clear boundaries between the behavior of consenting adults on one hand and rape, child molestation, and abusive incest on the other.<ref name="guardian2002">{{cite news |last=Hari |first=Johann |date=9 January 2002 |title=Forbidden love |url=https://www.theguardian.com/Archive/Article/0,4273,4331603,00.html |access-date=11 April 2008 |newspaper=[[The Guardian]] |issn=0261-3077}}</ref> However, even consensual relationships such as these are still legally classified as incest<ref>{{cite book |author=Roffee |first=James |title=Rape Justice: Beyond the Criminal Law |year=2015 |isbn=9781137476159 |pages=72–91 |chapter=When Yes Actually Means Yes |doi=10.1057/9781137476159.0009}}</ref> and criminalized in many jurisdictions (although there are [[Legality of incest|certain exceptions]]). James Roffee, a senior lecturer in criminology at [[Monash University]] and former worker on legal responses to familial sexual activity in England and Wales, and Scotland<ref>{{cite web|url=http://monash.edu/research/explore/en/persons/james-roffee(896c15d7-6f28-4bf0-8a0f-b7d6ff1553e0).html|title=Dr James Roffee|publisher=Monash university|access-date=22 May 2017|archive-url=https://web.archive.org/web/20170204003059/http://monash.edu/research/explore/en/persons/james-roffee%28896c15d7-6f28-4bf0-8a0f-b7d6ff1553e0%29.html|archive-date=4 February 2017}}</ref> discussed how the [[European Convention on Human Rights]] deems all familial sexual acts to be criminal, even if all parties give their full consent and are knowledgeable to all possible consequences.<ref>{{cite journal|doi=10.1093/hrlr/ngu023|title=No Consensus on Incest? Criminalisation and Compatibility with the European Convention on Human Rights|journal=Human Rights Law Review|volume=14|issue=3|pages=541–572|year=2014|last1=Roffee|first1=J. A.}}</ref> He also argues that the use of particular language tools in the legislation manipulates the reader to deem all familial sexual activities as immoral and criminal, even if all parties are consenting adults.<ref>{{cite journal |author=Roffee |first=J.A. |year=2014 |title=Synthetic Necessary Truth Behind New Labour's Criminalisation of Incest |journal=Social & Legal Studies |volume=23 |pages=113–130 |doi=10.1177/0964663913502068 |s2cid=145292798}}</ref>
====Aunts, uncles, moms, dads, nieces or nephews====
{{see also|Avunculate marriage}}
In the [[Netherlands]], marrying one's nephew or niece is legal, but only with the explicit permission of the Dutch government, due to the possible risk of [[genetic defects]] among the offspring. Nephew-niece marriages predominantly occur among foreign immigrants. In November 2008, the Scientific Institute of the Christian Democratic Party (CDA) announced that it wanted a ban on marriages to nephews and nieces.<ref>{{cite web|url=http://gatesofvienna.blogspot.com/2008/11/gates-of-vienna-news-feed-11262008.html|title=Gates of Vienna News Feed 11/26/2008|first=Baron|last=Bodissey|date=26 November 2008}}</ref> Consensual sex between individuals aged 18 and older is always lawful in the Netherlands and Belgium, even among closely related family members. Sexual acts between an adult family member and a minor are illegal, though they are classified not as incest but as abuse of the authority such an adult has over a minor, comparable to that of a teacher, coach, or priest.<ref>{{cite web|url=http://www.elfri.be/incest-strafbaar |title=is incest strafbaar ? &#124; Goede raad is goud waard – Advocatenkantoor Elfri De Neve |publisher=Elfri.be |date=15 July 2009 |access-date=30 July 2013|language=nl}}</ref> In [[Florida]], consensual adult sexual intercourse with someone known to be one's aunt, uncle, niece, or nephew constitutes a felony of the third degree.<ref>Criminal Law – Page 200, John M. Scheb – 2008</ref> Other states also commonly prohibit marriages between such kin.<ref>Family Law in the USA – Page 207, Lynn Dennis Wardle, Laurence C. Nolan – 2011</ref> The legality of sex with a half-aunt or half-uncle varies state by state.<ref>The Encyclopedia of Genetic Disorders and Birth Defects – Page 101, James Wynbrandt, Mark D. Ludman – 2010</ref> In the United Kingdom, incest includes only sexual intercourse with a parent, grandparent, child, or sibling,<ref>{{cite web|title=Incest by a man.|url=http://www.legislation.gov.uk/ukpga/Eliz2/4-5/69/part/I/crossheading/incest|work=Sexual Offences Act 1956|publisher=National Archives UK|access-date=28 March 2014}}</ref> but the more recently introduced offense of "sex with an adult relative" extends as far as half-siblings, uncles, aunts, nephews, and nieces.<ref name=ref1>{{cite web|title=Sexual Offences Act 2003|url=http://www.legislation.gov.uk/ukpga/2003/42/section/64|work=legislation.gov.uk|publisher=The National Archives of United Kingdom|access-date=28 March 2014}}</ref> However, the term 'incest' remains widely used in popular culture to describe any form of sexual activity with a relative. In Canada, marriage between uncles and nieces and between aunts and nephews is illegal.

====Between adult siblings====
{{main|Sibling incest}}

One of the most public cases of adult sibling incest in the 2000s is the case of [[Cases of Stübing v. Germany|Patrick Stübing and Susan Karolewski]], a brother{{ndash}}sister couple from Germany. Because of violent behavior on the part of his father, Patrick was taken in at the age of 3 by foster parents, who adopted him later. At the age of 23 he learned about his biological parents, contacted his mother, and met her and his then 16-year-old sister Susan for the first time. The now-adult Patrick moved in with his birth family shortly thereafter. After their mother died suddenly six months later, the siblings became intimately close, and had their first child together in 2001. By 2004, they had had four children together: Eric, Sarah, Nancy, and Sofia. The public nature of their relationship, and the repeated [[prosecution]]s and jail time they have served as a result, have caused some in Germany to question whether incest between consenting adults should be punished at all. An article about them in ''[[Der Spiegel]]'' states that the couple are happy together. According to court records, the first three children have mental and physical disabilities, and have been placed in foster care.<ref name="spiegel" /> In April 2012, at the [[European Court of Human Rights]], Patrick Stübing lost his case that the conviction violated his right to a private and family life.<ref>{{cite web|url=http://www.cnn.com/2012/04/13/world/europe/germany-incest-court/index.html?hpt=hp_bn2|title=German incest couple lose European court case |website=[[CNN]]|date=13 April 2012}}</ref><ref name="ECtHR judgment">[http://cmiskp.echr.coe.int/tkp197/view.asp?action=html&documentId=905957&portal=hbkm&table=F69A27FD8FB86142BF01C1166DEA398649 Judgment] on the ''Stübing vs. Germany'' case. [[European Court of Human Rights]].</ref> On 24 September 2014, the [[German Ethics Council]] recommended that the government abolish laws criminalizing incest between siblings, arguing that such bans impinge upon citizens.<ref>{{cite web|url=http://www.thedailybeast.com/cheats/2014/09/24/german-ethics-council-incest-is-a-right.html |title=German Ethics Council: Incest Is a Right |website=The Daily Beast |date=24 September 2014 |access-date=5 October 2014}}</ref><ref>{{cite news|url=https://www.telegraph.co.uk/news/worldnews/europe/germany/11119062/Incest-a-fundamental-right-German-committee-says.html |archive-url=https://ghostarchive.org/archive/20220111/https://www.telegraph.co.uk/news/worldnews/europe/germany/11119062/Incest-a-fundamental-right-German-committee-says.html |archive-date=11 January 2022 |url-access=subscription |url-status=live |title=Incest a 'fundamental right', German committee says |newspaper=The Telegraph |date=24 September 2014 |access-date=5 October 2014}}{{cbignore}}</ref>

Some societies differentiate between full-sibling and half-sibling relations.<ref>Roger S. Bagnall, Bruce W. Frier, ''The Demography of Roman Egypt'', 2006, p.128</ref><ref>[[Roy Porter]], [[Mikuláš Teich]], ''Sexual Knowledge, Sexual Science: The History of Attitudes to Sexuality'', 1994, p.239</ref>

====Cousin relationships====
{{See also|Cousin marriage|List of coupled cousins}}
[[File:Incest_World_Wide_Chart_(Borysk5_orig_amended_by_Tyir86_with_title,_legend,_bkrd_color).png|thumb|Legal status of incest, globally]]

Marriages and sexual relationships between first cousins are stigmatized as incest in some cultures, but tolerated in much of the world. Currently, 24 [[US states]] prohibit marriages between first cousins, and another seven permit them only under special circumstances.<ref>Joanna Grossman, [http://writ.news.findlaw.com/grossman/20020408.html Should the law be kinder to kissin' cousins?]</ref>
The United Kingdom permits both marriage and sexual relations between first cousins.<ref name=Ref1>{{cite web |last=Boseley |first=Sarah |title=Marriage between first cousins doubles risk of birth defects, say researchers |url=https://www.theguardian.com/science/2013/jul/04/marriage-first-cousins-birth-defects |work=[[The Guardian]] |access-date=28 March 2014 |date=4 July 2013}}</ref>

In some non-Western societies, marriages between close biological relatives account for 20{{ndash}}60% of all marriages.<ref>{{cite web|url=https://www.larasig.com/node/2020|title=Consanguinity Fact Sheet – Debunking Common Myths|access-date=23 December 2017|archive-url=https://web.archive.org/web/20171223160732/https://www.larasig.com/node/2020|archive-date=23 December 2017}}</ref><ref>{{cite book|url=https://books.google.com/books?id=t2XgDgAAQBAJ&q=20+to+60+%25+of+all+marriages+between+close+biological+relatives&pg=PT282|title=Family Law: Theoretical, Comparative, and Social Science Perspectives|first=James|last=Dwyer|date=9 December 2014|publisher=Wolters Kluwer Law & Business|via=Google Books|isbn=9781454831556}}</ref><ref>"In some parts of the world 20–60% of all marriages are between close biological relatives (Bittles, 1998)"
 [https://www.researchgate.net/profile/Alan_Bittles/publication/226985985_Genetic_Counseling_and_Screening_of_Consanguineous_Couples_and_Their_Offspring_Recommendations_of_the_National_Society_of_Genetic_Counselors/links/0c960528ac23292963000000.pdf Genetic Counseling and Screening of Consanguineous Couples and Their Offspring: Recommendations of the National Society of Genetic Counselors]</ref>

First- and second-cousin marriages are rare in Western Europe, North America, and Oceania, accounting for less than 1% of marriages, but reach 9% in South America, East Asia, and South Europe, and about 50% in regions of the Middle East, North Africa, and South Asia.<ref>{{cite journal |doi=10.1016/j.paed.2008.02.008 |title=Consanguinity and child health |url=http://www.channel4.com/microsites/D/Dispatches/when_cousins_marry/cousins_10.pdf |year=2008 |last1=Saggar |first1=A |last2=Bittles |first2=A |journal=Paediatrics and Child Health |volume=18 |issue=5 |pages=244–249}}</ref> Communities such as the Dhond and the [[Bhittani]] of Pakistan clearly prefer marriages between cousins due to the belief they ensure purity of the descent line, provide intimate knowledge of the spouses, and ensure that [[Property|patrimony]] will not pass into the hands of "outsiders".<ref>{{Cite book |title=Encyclopedia of Women & Islamic Cultures: Family, Body, Sexuality and Health |first1=Suad |last1=Joseph |author-link=Suad Joseph |first2=Afsaneh |last2=Najmabadi |author2-link=Afsaneh Najmabadi |publisher=Brill |year=2003 |isbn=978-90-04-12819-4 |page=261 |url=https://books.google.com/books?id=bzXzWgVajnQC}}</ref> [[Parallel and cross cousins|Cross-cousin]] marriages are preferred among the [[Yanomami]] of Brazilian Amazonia, among many other tribal societies identified by anthropologists.

[[File:Cousin_marriage_map1.svg|thumb|right|Cousin marriage laws in the United States, by state]]

There are some cultures in Asia which stigmatize cousin marriage, in some instances even marriages between second cousins or more remotely related people. This is notably true in the culture of [[Korea]]. In South Korea, before 1997, two people with the same last name and clan were prohibited from marrying. In light of this law being held unconstitutional, South Korea now only prohibits up to third cousins (see [[Article 809 of the Korean Civil Code]]). [[Hmong people|Hmong]] culture prohibits the marriage of anyone with the same last name{{nbsp}}{{ndash}} to do so would result in being shunned by the entire community, and they are usually stripped of their last name.<ref>{{Cite book|url=https://books.google.com/books?id=kgaGCwAAQBAJ&q=Hmong+culture+prohibits+the+marriage+of+anyone+with+the+same+last+name&pg=PA192|title=Hmong Refugees in the New World: Culture, Community and Opportunity|last=Vang|first=Christopher Thao|date=16 May 2016|publisher=McFarland|isbn=9781476622620}}</ref>

In a review of 48 studies of children parented by cousins, the rate of birth defects was twice that of non-related couples: 4% for cousin couples as opposed to 2% for the general population.<ref>{{cite news |last=Towie |first=Narelle |url=http://www.perthnow.com.au/kissing-cousins-ok/story-fna7dq6e-1111116504749 |title=Most babies born to first-cousins are healthy |newspaper=Perth Now |date=31 May 2008 |access-date=5 January 2012 |archive-url=https://web.archive.org/web/20120202060753/http://www.perthnow.com.au/kissing-cousins-ok/story-fna7dq6e-1111116504749 |archive-date=2 February 2012 }}</ref>

====Defined through marriage====
Some cultures include relatives by marriage in incest prohibitions; these relationships are called [[Affinity (law)|affinity]] rather than [[consanguinity]]. For example, the question of the legality and morality of a widower who wished to marry his [[Deceased Wife's Sister's Marriage Act 1907|deceased wife's sister]] was the subject of long and fierce debate in the [[United Kingdom]] in the 19th century, involving, among others, [[Matthew Boulton]]<ref>{{cite book |last=Pollak |first=Ellen |title=Incest and the English Novel, 1684–1814 |publisher=Johns Hopkins University Press |location=Baltimore MD |year=2003 |page=38 |isbn=978-0-8018-7204-4}}</ref><ref>{{cite book |last=Tann |first=Jennifer |title=Oxford Dictionary of National Biography |publisher=Oxford University Press |location=Oxford, England |date=May 2007 |chapter=Boulton, Matthew (1728–1809)|title-link=Oxford Dictionary of National Biography }}</ref> and [[Charles La Trobe]]. The marriages were entered into in Scotland and Switzerland respectively, where they were legal. In medieval Europe, [[Lateran IV]] ruled that standing as a [[godparent]] to a child also created a bond of affinity; which precluded legal marriage.<ref name="b310">{{cite book | last1=Ferraro | first1=J.M. | last2=Pedersen | first2=F. | title=A Cultural History of Marriage in the Medieval Age | publisher=Bloomsbury Publishing | series=The Cultural Histories Series | year=2021 | isbn=978-1-350-17971-4 | url=https://books.google.com/books?id=bqVQEAAAQBAJ&pg=PA133 | access-date=2024-08-23 | page=133}}</ref> But in other societies, a deceased spouse's sibling was considered the ideal person to marry. The Hebrew Bible forbids a man from marrying his brother's widow with the exception that, if his brother dies childless, the man is required to marry his brother's widow so as to "raise up seed to him".<ref>''Hebrew-English Bible'' {{bibleverse||Deuteronomy|25:5–6|HE}}</ref> Some societies have long practiced [[sororal polygyny]], a form of [[polygamy]] in which a man marries multiple wives who are sisters to each other (though not closely related to him).

In Islamic law, marriage among close blood relations like parents, stepparents, parents in-law, siblings, stepsiblings, the children of siblings, aunts, and uncles is forbidden, while first or second cousins may marry. Marrying the widow of a brother or the sister of a deceased or divorced wife is also allowed.

==Inbreeding==
{{Main|Inbreeding}}
Offspring of biologically related parents are subject to the possible impact of inbreeding. Such offspring have a higher possibility of [[Congenital disorder|congenital birth defects]] (see [[Coefficient of relationship]]), because it increases the proportion of zygotes that are [[homozygous]] for deleterious [[recessive allele]]s that produce such disorders<ref>{{cite journal |last=Livingstone |first=F. B. |year=1969 |title=Genetics, Ecology, and the Origins of Incest and Exogamy |journal=Current Anthropology |volume=10 |pages=45–62 |doi=10.1086/201009|s2cid=84009643 }}</ref> (see [[Inbreeding depression]]). Because most such [[allele]]s are rare in populations, it is unlikely that two unrelated marriage partners will both be heterozygous carriers. However, because close relatives [[Coefficient of relationship|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:<ref>{{cite book |last=Thornhill |first=Nancy Wilmsen |title=The Natural History of Inbreeding and Outbreeding: Theoretical and Empirical Perspectives |publisher=[[University of Chicago Press]] |location=Chicago |year=1993 |isbn=978-0-226-79854-7 |url=https://books.google.com/books?id=ZFXYeHxwD10C}}</ref>
* In the short term, because incestuous reproduction increases [[zygosity]], deleterious recessive alleles will express themselves more frequently, leading to increases in [[Miscarriage|spontaneous abortions]] of zygotes, perinatal deaths, and postnatal offspring with birth defects.
* In the long run, however, because of this increased exposure of deleterious recessive alleles to [[natural selection]], their frequency decreases more rapidly in inbred population, leading to a "healthier" population (with fewer deleterious recessive alleles).
The closer the relationship between two persons, the higher the zygosity, and thus the more severe the biological costs of inbreeding. This fact probably explains why inbreeding between close relatives, such as siblings, is less common than inbreeding between cousins.<ref>{{cite journal |last1=Antfolk |first1=Jan |last2=Lieberman |first2=Debra |last3=Santtila |first3=Pekka |title=Fitness Costs Predict Inbreeding Aversion Irrespective of Self-Involvement: Support for Hypotheses Derived from Evolutionary Theory |journal=PLOS ONE |volume=7 |issue=11 |doi=10.1371/journal.pone.0050613 |pages=e50613 |pmid=23209792 |pmc=3509093|year=2012 |bibcode=2012PLoSO...750613A |doi-access=free }}</ref>

There may also be other deleterious effects besides those caused by recessive diseases. Thus, similar [[immune system]]s may be more vulnerable to infectious diseases (see [[Major histocompatibility complex and sexual selection]]).<ref name=moral>{{Cite journal |last1=Lieberman |first1=D. |last2=Tooby |first2=J. |last3=Cosmides |first3=L. |doi=10.1098/rspb.2002.2290 |title=Does morality have a biological basis? An empirical test of the factors governing moral sentiments relating to incest |journal=Proceedings of the Royal Society B: Biological Sciences |volume=270 |issue=1517 |pages=819–826 |year=2003 |pmid= 12737660|pmc=1691313}}</ref>

A 1994 study found a mean excess mortality with inbreeding among first cousins of 4.4%.<ref>{{cite web |last=Bittles |first=A.H. |title=A Background Summary of Consaguineous marriage |url=http://www.consang.net/images/d/dd/01AHBWeb3.pdf |publisher=consang.net |year=2001 |access-date=19 January 2010 |archive-date=27 September 2018 |archive-url=https://web.archive.org/web/20180927023329/http://www.consang.net/images/d/dd/01AHBWeb3.pdf }}, citing {{Cite journal |last1=Bittles |first1=A. H. |last2=Neel |first2=J.V. |year=1994 |title=The costs of human inbreeding and their implications for variation at the DNA level |journal=Nature Genetics |issue=2 |pages=117–121 |pmid=7842008 |volume=8 |doi=10.1038/ng1094-117|s2cid=36077657 }}</ref> A 2008 study also found decreased lifespan among offspring of first cousins, but no difference between lifespans after the second cousin level.<ref>{{Cite journal |last1=Helgason |first1=Agnar |last2=Pálsson |first2=Snæbjörn |last3=Guðbjartsson |first3=Daníel F. |last4=Kristjánsson |first4=þórður |last5=Stefánsson |first5=Kári |date=2008-02-08 |title=An Association Between the Kinship and Fertility of Human Couples |url=https://www.science.org/doi/10.1126/science.1150232 |journal=Science |language=en |volume=319 |issue=5864 |pages=813–816 |doi=10.1126/science.1150232 |pmid=18258915 |bibcode=2008Sci...319..813H |s2cid=17831162 |issn=0036-8075}}</ref> A 1990 study conducted in South India found that the incidence of malformations was slightly higher in uncle-niece progeny (9.34%) compared to the first cousin progeny (6.18%).<ref>{{Cite journal |last1=Kulkarni |first1=M L |last2=Kurian |first2=M |date=June 1990 |title=Consanguinity and its effect on fetal growth and development: a south Indian study. |journal=Journal of Medical Genetics |volume=27 |issue=6 |pages=348–352 |doi=10.1136/jmg.27.6.348 |issn=0022-2593 |pmc=1017129 |pmid=2359095}}</ref> Stillbirth rates were significantly higher among consanguineous couples irrespective of the mother's socioeconomic status, and were higher in uncle-niece mating's compared to first cousin and beyond first cousin unions in both the poor and middle/upper class. Children of parent{{ndash}}child or sibling{{ndash}}sibling unions are at increased risk compared to cousin{{ndash}}cousin unions. Studies suggest that 20–36% of these children will die or have major disability due to the inbreeding.<ref name="WolfDurham2005" /> A study of 29 offspring resulting from brother{{ndash}}sister or father{{ndash}}daughter incest found that 20 had congenital abnormalities, including four directly attributable to autosomal recessive alleles.<ref name="Baird">{{cite journal |doi=10.1016/S0022-3476(82)80347-8 |last1=Baird |first1=P. A. |last2=McGillivray |first2=B. |year=1982 |title=Children of incest |journal=The Journal of Pediatrics |volume=101 |issue=5 |pages=854–7 |pmid=7131177}}</ref>  

==Laws==
{{Main|Legality of incest}}

Laws regarding sexual activity between close relatives vary considerably between jurisdictions, and depend on the type of sexual activity and the nature of the family relationship of the parties involved, as well as the age and sex of the parties. Prohibition of incest laws may extend to restrictions on marriage rights, which also vary between jurisdictions. Most jurisdictions prohibit parent{{ndash}}child and sibling marriages, while others also prohibit first-cousin and uncle{{ndash}}niece and aunt{{ndash}}nephew marriages. In most places, incest is illegal, regardless of the ages of the two partners. In other countries, incestuous relationships between consenting adults (with the age varying by location) are permitted, including in the [[Netherlands]], [[France]], [[Slovenia]], and [[Spain]]. [[Sweden]] is the only country that allows marriage between half-siblings, and they must seek government counseling before marriage.<ref>[http://news.bbc.co.uk/1/hi/6424337.stm Incest: an age-old taboo]. BBC. 12 March 2007. retrieved 22 January 2011</ref>

While the legality of consensual incest varies by country, sexual assault committed against a relative is seen as a very serious crime. In some legal systems, the fact of a perpetrator being a close relative to the victim constitutes an [[aggravating circumstance]] in the case of sexual crimes such as [[rape]] and [[child sexual abuse|sexual conduct with a minor]]{{nbsp}}– this is the case in [[Romania]].<ref>See Articles 218–221 of the [[Penal Code of Romania#The Penal Code of 2014|Romanian Penal Code]] [http://www.avocatura.com/ll491-noul-cod-penal.html] {{Webarchive|url=https://web.archive.org/web/20150517054948/http://www.avocatura.com/ll491-noul-cod-penal.html|date=17 May 2015}}</ref>

==Religious and philosophical views <span class="anchor" id="Religious views"></span>==

===Jewish===
{{main|Jewish views on incest}}
According to the [[Torah]], per Leviticus 18,<ref>''Hebrew-English Bible'', {{bibleverse||Leviticus|18|HE}}</ref> "the children of Israel"{{nbsp}}{{ndash}} Israelite men and women alike{{nbsp}}{{ndash}} are forbidden from sexual relations between people who are "near of kin" (verse 6), who are defined as:
* Children and their mothers (verse 7);
* Siblings and half-siblings (verses 9 and 11). Relationships between these are particularly singled out for a curse in [http://www.mechon-mamre.org/e/et/et0527.htm Deuteronomy 27], and they are of the only two kinds of incestuous relationships that are among the particularly singled-out relationships{{nbsp}}{{ndash}} with the other particularly singled-out relationships being ones of non-incestuous family betrayal (cf. verse 20) and bestiality (cf. verse 21);
* Grandparents and grandchildren (verse 10);
* Aunts and nephews, uncles and nieces, etc. (verses 12–14).<ref>Also see the [[Central Conference of American Rabbis]]' [https://ccarnet.org/responsa/142-marriage-mothers-sister-or-half-sister-aunt-or/ Responsum 142].</ref> Relationships between these are the second kind of relationships that are particularly singled out for a curse in [http://www.mechon-mamre.org/e/et/et0527.htm Deuteronomy 27], and the explicit examples of children-in-law and mothers-in-law (verse 23) serve to remind the Israelites that the parents-in-law are also (or at least should also be) the children-in-law's aunts and uncles:<ref>{{Cite web|url=https://www.mechon-mamre.org/e/et/et0436.htm|title=Numbers 36 / Hebrew Bible in English / Mechon-Mamre|website=www.mechon-mamre.org|access-date=14 August 2021|archive-date=25 September 2021|archive-url=https://web.archive.org/web/20210925053705/https://www.mechon-mamre.org/e/et/et0436.htm|url-status=dead}}</ref>

<blockquote>And Moses commanded the children of Israel according to the word of the LORD, saying: 'The tribe of the sons of Joseph speaketh right. This is the thing which the LORD hath commanded concerning the daughters of [[Zelophehad]], saying: Let them be married to whom they think best; only into the family of the tribe of their father shall they be married. So shall no inheritance of the children of Israel remove from tribe to tribe; for the children of Israel shall cleave every one to the inheritance of the tribe of his fathers. And every daughter, that possesseth an inheritance in any tribe of the children of Israel, shall be wife unto one of the family of the tribe of her father, that the children of Israel may possess every man the inheritance of his fathers. So shall no inheritance remove from one tribe to another tribe; for the tribes of the children of Israel shall cleave each one to its own inheritance.' Even as the LORD commanded Moses, so did the daughters of Zelophehad. For Mahlah, Tirzah, and Hoglah, and Milcah, and Noah, the daughters of Zelophehad, were married unto their father's brothers' sons.<ref>''Hebrew-English Bible'' {{bibleverse||Leviticus|18:12–14|HE}}</ref></blockquote>

Incestuous relationships, along with the other forbidden relationships that are mentioned in Leviticus 18, are considered so severe among [[Chillul Hashem|''chillulim HaShem'']], acts which bring shame to the name of God, as to be punishable by death as specified in [http://www.mechon-mamre.org/e/et/et0320.htm Leviticus 20].

In the 4th century BC, the [[Soferim]] (''scribes'') declared that there were relationships within which marriage constituted incest, in addition to those mentioned by the Torah. These additional relationships were termed ''seconds'' (Hebrew: ''sheniyyot'') and included the wives of a man's grandfather and grandson.<ref name="TosYeb23">Yebamot ([[Tosefta]]) 2:3</ref> The classical rabbis prohibited marriage between a man and any of these ''seconds'' of his, on the basis that doing so would act as a ''safeguard'' against infringing the biblical incest rules,<ref name="Yeb21a">Yebamot 21a</ref> although there was inconclusive debate about exactly what the limits should be for the definition of ''seconds''.<ref name="JewEncInce">{{Jewish Encyclopedia|article=incest|url=http://www.jewishencyclopedia.com/view.jsp?artid=126&letter=I}}</ref>

Marriages that are forbidden in the Torah (with the exception of uncle{{ndash}}niece marriages) were regarded by the rabbis of the Middle Ages as invalid{{nbsp}}– as if they had never occurred;<ref name="EbenezerSA">''[[Shulchan Aruch|Shulchan 'Aruk]]'', ''Eben ha-'Ezer'', 16, 1</ref> any children born to such a couple were regarded as [[mamzer|bastards under Jewish law]],<ref name="EbenezerSA" /> and the relatives of the spouse were not regarded as forbidden relations for further marriage.<ref>Yebamot 94b</ref> On the other hand, relationships that were prohibited due to qualifying as ''seconds'' and so forth were regarded as wicked but still valid;<ref name="EbenezerSA" /> while such a couple may have been pressured to divorce, any children of the union were still seen as legitimate.<ref name="EbenezerSA" />

===Christian===

{{See also|Incest in the Bible}}

The New Testament condemns relations between a man "and his father's wife" (1 Corinthians 5:1{{ndash}}5). It is inevitable for Bible literalists to accept that the first children of Adam and Eve would have been in incestuous relations as we regard it today. However, according to the Bible, God's law forbidding incest had not at that time been given to men and was delivered to Moses after Adam and Eve were created. Protestant Christians who adopt the Old Testament as part of their rule of faith and practice distinguish between the ceremonial law and the moral law given to Moses, with the demands of the ceremonial law being fulfilled by Christ's atoning death. Protestants view Leviticus 18:6{{ndash}}20 as part of the moral law and still applicable,  thus condemning sexual/marriage relations between a man and his mother, sister, stepsister, or stepmother (if a man has more than one wife, it is forbidden for a son to have relations with or marry any of his father's wives), aunt, granddaughter, or his brother's wife. Leviticus 18 goes on to condemn relations between a man and the daughter of a woman he is having relations with and the sister of a woman he has had sexual relations with while the first sister is still alive.

The [[Book of Common Prayer]] of the [[Anglican Communion]] allows marriages up to and including first cousins.<ref>{{cite book|url=http://prayerbook.ca/resources/bcponline/|year=1962|place=Canada|title=Book of Common Prayer|chapter=A Table of Kindred and Affinity|chapter-url=http://prayerbook.ca/resources/bcponline/kindred-and-affinity/|access-date=26 December 2014|archive-date=29 November 2014|archive-url=https://web.archive.org/web/20141129094409/http://prayerbook.ca/resources/bcponline/}}</ref>

The [[Catholic Church]] regards incest as a sin against the [[Marriage in the Catholic Church|Sacrament of Matrimony]].<ref>{{Cite web|url=https://www.vatican.va/archive/ccc_css/archive/catechism/p3s2c2a6.htm|title=Catechism of the Catholic Church 2388}}</ref> For the Catholic Church, at the heart of the immorality of incest is the corruption and disordering of proper family relations. These disordered relationships take on a particularly grave and immoral character when it becomes [[child sexual abuse]].

As the ''[[Catechism of the Catholic Church]]'' says: <blockquote>'''2388''' ''Incest'' designates intimate relations between relatives or in-laws within a degree that prohibits marriage between them. St. Paul stigmatizes this especially grave offense: 'It is actually reported that there is immorality among you...for a man is living with his father's wife...In the name of the Lord Jesus...you are to deliver this man to Satan for the destruction of the flesh....' Incest corrupts family relationships and marks a regression toward animality.

'''2389''' Connected to incest is any sexual abuse perpetrated by adults on children or adolescents entrusted to their care. The offense is compounded by the scandalous harm done to the physical and moral integrity of the young, who will remain scarred by it all their lives; and the violation of responsibility for their upbringing.<ref>{{Cite web|url=https://www.vatican.va/archive/ccc_css/archive/catechism/p3s2c2a6.htm|title=Catechism of the Catholic Church 2388–2389}}</ref></blockquote>

===Islamic===

{{main|Mahram}}
The [[Quran]] gives specific rules regarding incest, which prohibit a man from marrying or having sexual relationships with:

* his father's wife<ref>{{qref|4|22|c=y}}</ref> (his mother,<ref name="qref 4:23">{{qref|4|23|c=y}}</ref> or stepmother,<ref name="qref 4:23" /> his mother-in-law, a woman from whom he has nursed, even the children of this woman);<ref name="qref 4:23" />
* either parent's sister (aunt);<ref name="qref 4:23" />
* his sister, his half-sister, a woman who has nursed from the same woman as him, and his sister-in-law (wife's sister) while still married. Half relations are as sacred as full relations;<ref name="qref 4:23" />
* his niece (child of sibling);<ref name="qref 4:23" />
* his daughter, his stepdaughter (if the marriage to her mother was [[consummation|consummated]]), his daughter-in-law.<ref name="qref 4:23" />

Cousin marriage finds support in Islamic scriptures and is [[Cousin marriage in the Middle East|widespread in the Middle East]].<ref>{{cite book |last1=Inhorn |first1=Marcia C. |first2=Wendy |last2=Chavkin |first3=José-Alberto |last3=Navarro |date=2014 |title=Globalized Fatherhood |location=New York City |publisher=Berghahn Books |page=245 |isbn=9781782384380 }}</ref>

Although Islam allows cousin marriage, there are [[hadith]]s attributed to Muhammad calling for distance from the marriage of relatives. However, Muslim scholars generally consider these hadiths unreliable.<ref>{{cite web|author1=Shaykh Faraz A. Khan|title=Did the Prophet (Peace Be Upon Him) Discourage Marrying Cousins? – SeekersHub Answers|url=http://seekershub.org/ans-blog/2011/10/07/did-the-prophet-peace-be-upon-him-discourage-marrying-cousins/|website=SeekersHub Answers|access-date=12 August 2017|date=7 October 2011|archive-date=2 May 2019|archive-url=https://web.archive.org/web/20190502215209/http://seekershub.org/ans-blog/2011/10/07/did-the-prophet-peace-be-upon-him-discourage-marrying-cousins/|url-status=dead}}</ref><ref>{{cite web|author1=Saleem Ahmed, Ph.D|title=Cousin Marriage Among Muslims|url=http://muslimcouncilofamerica.org/cousin-marriage-among-muslims/|website=Muslim Council of America Foundation|access-date=12 August 2017|archive-date=12 August 2017|archive-url=https://web.archive.org/web/20170812173119/http://muslimcouncilofamerica.org/cousin-marriage-among-muslims/|url-status=dead}}</ref>

===Zoroastrian===
{{Main|Xwedodah}}
In [[Ancient Persia]], incest between cousins is a blessed virtue, although, in some sources, incest is believed to be related to that of parent{{ndash}}child or brother{{ndash}}sister.<ref name=":0">{{Cite book|url=https://books.google.com/books?id=0qcdrMTprSMC|archive-url=https://web.archive.org/web/20200803085652/https://books.google.com/books?id=0qcdrMTprSMC|url-status=dead|archive-date=3 August 2020|title=Sex and Punishment: Four Thousand Years of Judging Desire|last=Berkowitz|first=Eric|date=2012|publisher=Counterpoint Press|isbn=9781582437965|pages=21–22}}</ref> Under [[Zoroastrianism]], royalty, clergy, and commoners practiced incest, though the extent in the lattermost class was unknown.<ref name="Skjaervo 2013">{{Cite web|url=http://www.iranicaonline.org/articles/marriage-next-of-kin|title=Marriage II. Next-Of -Kin Marriage In Zoroastrianism|last=Skjaervo|first=Prods Oktor|author-link=Prods Oktor Skjaervo|website=www.iranicaonline.org|publisher=[[Encyclopaedia Iranica]], online edition|date=2013|access-date=20 August 2018}}</ref><ref name=":0" /> This tradition was called [[Xwedodah]]<ref>{{Cite journal|last=Bigwood|first=Joan M.|date=December 2009|title='Incestuous' Marriage in Achaemenid Iran: Myths and Realities|journal=Klio|volume=91|issue=2|pages=311–341|doi=10.1524/klio.2009.0015|s2cid=191672920|issn=0075-6334}}</ref><ref>{{Cite journal|last=Scheidel|first=Walter|date=1 September 1996|title=Brother-sister and parent-child marriage outside royal families in ancient egypt and iran: A challenge to the sociobiological view of incest avoidance?|url=https://www.researchgate.net/publication/223430185|journal=Ethology and Sociobiology|volume=17|issue=5|pages=319–340|doi=10.1016/S0162-3095(96)00074-X}}</ref><ref>{{Cite journal|last=García|first=María Olalla|date=2001|title="Xwedodah": el matrimonio consanguíneo en la Persia Sásanida. Una comparación entre fuentes pahlavíes y greco-latinas|url=https://publicaciones.unirioja.es/ojs/index.php/iberia/article/view/267|journal=Iberia. Revista de la Antigüedad|language=es|volume=4|pages=181–197|issn=1699-6909}}</ref> ({{Langx|ae|Xᵛaētuuadaθa }}).<ref name="Skjaervo 2013"/><ref>{{Cite book|url=https://books.google.com/books?id=cNUEnHU0BPoC&q=xwedodah&pg=PA430|title=Traditions of the Magi: Zoroastrianism in Greek and Latin Literature|last=Jong|first=Albert De|date=1997|publisher=BRILL|isbn=978-9004108448|pages=430–433}}</ref> The tradition was considered so sacred that the bodily fluids produced by an incestuous couple were thought to have curative powers.<ref name=":0" /> For instance, the [[Vendidad]] advised corpse-bearers to purify themselves with a mixture of the urine of a married incestuous couple.<ref name=":0" /> [[Friedrich Nietzsche]], in his book ''[[The Birth of Tragedy]]'', cited that among Zoroastrians, a wise priest is born only by Xvaetvadatha.<ref>''The Birth of Tragedy'', Friedrich Nietzsche. Anaconda Verlag – 2012.</ref>

To what extent Xvaetvadatha was practiced in [[Sasanian]] Iran and before{{nbsp}}{{ndash}} especially outside the royal and noble families ("dynastic incest") and, perhaps, the clergy{{nbsp}}{{ndash}} and whether practices ascribed to them can be assumed to be characteristic of the general population is not clear. There is a lack of genealogies and census material on the frequency of Xvaetvadatha.<ref>Michael Mitterauer, "The Customs of the Magians: The Problem of Incest in Historical Societies," in Roy Porter and Mikuláš Teich, eds., Sexual Knowledge, Sexual Science: The History of Attitudes to Sexuality, Cambridge, UK, and New York, 1994, pp. 231–50.</ref><ref name="Fischer 2007">Fischer, Michael MJ. "Ptolemaic Jouissance and the Anthropology of Kinship: A Commentary on Ager" The Power of Excess: Royal Incest and the Ptolemaic Dynasty"." Anthropologica 49, no. 2 (2007): 295–299.</ref> Evidence from [[Dura-Europos]], however, combined with that of the Jewish and Christian sources citing actual cases under the Sasanians, strengthens the evidence of the Zoroastrian texts. In the post-Sasanian Zoroastrian literature, Xvaetvadatha is said to refer to marriages between cousins instead, which have always been relatively common.<ref>*Jakob Eduard Polak, Persien, das Land und seine Bewohner: ethnographische Schilderungen, 2 vols in one, Leipzig, 1865; tr. Kaykāvus Jahāndāri as Safar-nāma-ye Polāk: Iran wa Irāniān, Tehran, 1982.
*James Darmesteter, Ormazd et Ahriman, leurs origines et leur histoire, Bibliothèque de l'Ecole des hautes études ... Sciences philologiques et historiques 29, Paris, 1877.
*{{cite journal | last1 = Givens | first1 = Benjamin P. | last2 = Hirschman | first2 = Charles | s2cid = 143341230 | year = 1994 | title = Modernization and Consanguineous Marriage in Iran | journal = Journal of Marriage and the Family | volume = 56 | issue = 4| pages = 820–34 | doi = 10.2307/353595 | jstor = 353595 }}
*[[Clarisse Herrenschmidt]], "Le xwêtôdas ou mariage «incestueux» en Iran ancien," in Pierre Bonte, ed., Epouser au plus proche, inceste, prohibitions et stratégies matrimoniales autour de la Méditerranée, Paris, 1994, pp. 113–25.
*Alan H. Bittles et al., "Human Inbreading: A Familiar Story Full of Surprises," in Helen Macbeth and Prakash Shetty, eds., Health and Ethnicity, Society for the Study of Human Biology Series 41, London, 2001, pp. 68–78.</ref> It has been observed that such incestuous acts received a great deal of glorification as a religious practice and, in addition to being condemned by foreigners (though the reliability of these accusations is questionable since accusations of incest were a common way of denigrating other groups),<ref>Porter, Roy, and Mikulas Teich, eds. Sexual Knowledge, Sexual Science. CUP Archive, 1994, p.237</ref> were considered a great challenge by their own proponents, with accounts suggesting that four copulations was deemed a rare achievement worthy of eternal salvation. It has been suggested that because taking up incestuous relations was a great personal challenge, seemingly repugnant even to Zoroastrians of the time, it served as an [[honest signal]] of commitment and devotion to religious ideals.<ref>Scheidel, Walter. "Evolutionary psychology and the historian." The American Historical Review 119, no. 5 (2014): 1563–1575.</ref><ref name="Fischer 2007"/>

===Hindu===
[[Rigveda]] regards incest to be "evil".<ref>{{cite book |last=O'Flaherty |first=Wendy Doniger |title=The Origins of Evil in Hindu Mythology |page=7 |publisher=University of California Press}}</ref> [[Hinduism]] speaks of incest in abhorrent terms. Hindus believe there are both [[karmic]] and practical bad effects of incest and thus practice strict rules of both [[endogamy]] and [[exogamy]] in relation to the family tree (''[[gotra]]'') or bloodline (''[[Pravaras|Pravara]]''). Marriage within the ''gotra'' (''swagotra'' marriage) is banned under the rule of exogamy in the traditional matrimonial system.<ref>"There can be no matrimony between the sects of Gehlawat and Kadiyan as they have a 'brotherhood' akin to consanguinity."[http://www.indianexpress.com/news/haryana-panchayat-takes-on-govt-over-samegotra-marriage/491548/ "Haryana panchayat takes on govt over same-gotra marriage"]. ''Indian Express''. 20 July 2009</ref> People within the ''gotra'' are regarded as kin, and marrying such a person would be thought of as incest. Marriage with paternal cousins (a form of [[Parallel and cross cousins|parallel-cousin]] relationship) is strictly prohibited. Traditional Hindu laws of marriage suggest that, between a man and a woman who are about to marry, there should be no common ancestor (gotra) between the groom and the bride for up to 6 generations on the father's side of the groom and bride and up to 4 generations on the mothers' side of the groom and bride. Some orthodox Hindus might extend this limit to up to 8 generations on the father's side and six generations on the mother's side (for both the bride and groom).

Although marriages between persons having the same ''gotra'' are generally frowned upon,<ref>''The Illustrated Encyclopedia of Hinduism: N-Z'', James G. Lochtefeld, Rosen Publishing Group, 2002; p. 526.</ref> how this is defined may vary regionally. Depending on the culture and [[Indian caste system|caste]] of the population in the region, marriage may be restricted up to seven generations of ''gotra'' of father, mother, and grandmother. Marriage is banned within the same local community in a few rural areas.<ref>"In India these rules are reproduced in the form of that one must not marry within the Gotra, but not without the caste" [http://www.sanathanadharma.com/samskaras/marriage/mar3.htm#Limitations "Limitations of Marriage"] {{webarchive|url=https://web.archive.org/web/20101103062452/http://www.sanathanadharma.com/samskaras/marriage/mar3.htm |date=3 November 2010 }}. sanathanadharma.com</ref>

===Stoicism===
The founder of [[Stoicism]], [[Zeno of Citium]], stated that incest was permissible in ''[[Republic (Zeno)|Republic]]'', as did the later prominent Stoic philosopher [[Chrysippus]]. However, Zeno only advocates for incest under unique circumstances, such as procreating with one's ailing mother to beget "glorious" children, thus comforting her. Otherwise, incest is condemned as being contrary to Nature. Zeno further condemns incest from a moral and psychological perspective, considering it to be a sign of [[Plato]]'s tyrannical soul, defined as a soul that is governed by illimitable desire. He uses [[Oedipus]] as a tragic example.<ref>{{cite journal |last1=Hook |first1=Brian S. |title=Oedipus and Thyestes among the Philosophers: Incest and Cannibalism in Plato, Diogenes, and Zeno |journal=Classical Philology |date=January 2005 |volume=100 |issue=1 |pages=17–40 |doi=10.1086/431428 |s2cid=161961479 }}</ref> Nonetheless, later Stoic disciples by the 1st century BC downplayed the pro-incest advocacy, accusing Zeno of being "young and thoughtless" when he wrote ''Republic''.<ref>A view attributed to some contemporary Stoics by [[Philodemus]], ''On the Stoics'', c. 2. col 9. ed. Dorandi.</ref>

==Animals==
{{see also|Animal sexual behavior#Inbreeding avoidance}}
[[File:Fruit flies mating.jpg|thumb|[[Drosophila melanogaster|Common fruit fly]] females prefer to mate with their own brothers over unrelated males.<ref name="fruit-flies">{{cite journal |last1=Loyau |first1=Adeline |last2=Cornuau |first2=Jérémie H. |last3=Clobert |first3=Jean |last4=Danchin |first4=Étienne |date=10 December 2012 |title=Incestuous Sisters: Mate Preference for Brothers over Unrelated Males in Drosophila melanogaster |journal=PLOS ONE |volume=7 |issue=12 |pages=e51293 |bibcode=2012PLoSO...751293L |doi=10.1371/journal.pone.0051293 |pmc=3519633 |pmid=23251487 |doi-access=free}}</ref>]]

Inbreeding avoidance is rare in non-human animals.<ref>{{Cite journal |last1=de Boer |first1=Raïssa A. |last2=Vega-Trejo |first2=Regina |last3=Kotrschal |first3=Alexander |last4=Fitzpatrick |first4=John L. |date=July 2021 |title=Meta-analytic evidence that animals rarely avoid inbreeding |url=https://www.nature.com/articles/s41559-021-01453-9 |journal=Nature Ecology & Evolution |language=en |volume=5 |issue=7 |pages=949–964 |doi=10.1038/s41559-021-01453-9 |pmid=33941905 |bibcode=2021NatEE...5..949D |s2cid=233718913 |issn=2397-334X}}</ref> [[North Carolina State University]] found that [[bed bug]]s, in contrast to most other insects, tolerate incest and are able to genetically withstand the effects of inbreeding quite well.<ref>{{cite web |url=http://www.laboratoryequipment.com/news/2011/12/insect-incest-produces-healthy-offspring |title=Insect Incest Produces Healthy Offspring |date=8 December 2011 |access-date=14 February 2017 |archive-date=16 May 2017 |archive-url=https://web.archive.org/web/20170516080757/http://www.laboratoryequipment.com/news/2011/12/insect-incest-produces-healthy-offspring |url-status=dead }}</ref>

Many species of [[mammal]]s, including humanity's closest [[primate]] relatives, tend to avoid mating with close relatives, especially if there are alternative partners available.<ref>{{cite book |title=Inbreeding, Incest, and the Incest Taboo: The State of Knowledge at the Turn of the Century |first=Arthur P. |last=Wolf |author2=William H. Durham |year=2004 |publisher=Stanford University Press |page=169 |url=https://books.google.com/books?id=OW1nuQxcIQgC&pg=PA6 |isbn=978-0-8047-5141-4}}</ref> However, some chimpanzees have been recorded attempting to mate with their mothers.<ref>[http://www.livescience.com/2226-incest-taboo-nature.html Incest not so taboo in nature] Livescience, retrieved 29 January 2012</ref> Male rats have been recorded engaging in mating with their sisters, but they tend to prefer non-related females over their sisters.<ref>[https://books.google.com/books?id=bsCiWUiPY5UC&pg=PA293 Sexual Behaviour In Animals] A. Sarkar; retrieved 29 January 2012</ref>

[[Livestock]] breeders often practice controlled breeding to eliminate undesirable characteristics within a population, which is also coupled with the [[culling]] of what is considered unfit offspring, especially when trying to establish a new and desirable trait in the stock.

==See also==
{{Portal|Human sexuality}}
* [[Accidental incest]]
* [[Adelphogamy]]
* [[Avunculate marriage]]
* [[Genetic distance]]
* [[Genetic diversity]]
* [[Genetic sexual attraction]]
* [[Incest between twins]]
* [[Incest taboo]]
* [[Incest in The Bible]]
* [[Incest in folklore and mythology]]
* [[Incest in literature]]
* [[Incest in media]]
* [[List of coupled siblings]]
* [[Prohibited degree of kinship]]
* [[Proximity of blood]]
* {{section link|Sibling relationship#Sibling marriage and incest}}
* [[Watta satta]]
* [[Westermarck effect]] which prevents most incest

==References==
;Citations
{{Reflist}}

;Bibliography
{{Refbegin}}
* {{cite encyclopedia | article = Women i. In Pre-Islamic Persia | last = Brosius | first = Maria | url = http://www.iranicaonline.org/articles/women-i | encyclopedia = Encyclopaedia Iranica, Vol | location = London et al. | year = 2000 | title = <!-- nope --> | access-date = 2019-09-21 | archive-url = https://web.archive.org/web/20200313213156/http://www.iranicaonline.org/articles/women-i | archive-date = 2020-03-13 | url-status = dead }}
* {{cite encyclopedia | title = Cambyses II | last = Dandamayev | first = Muhammad A. | url = http://www.iranicaonline.org/articles/cambyses-opers | encyclopedia  = Encyclopaedia Iranica, Vol. IV, Fasc. 7 | pages = 726–729 | year = 1990 }}
* Bixler, Ray H. (1982) "Comment on the Incidence and Purpose of Royal Sibling Incest," ''American Ethnologist'', ''9''(3), August, pp.&nbsp;580–582. {{JSTOR|680655}}
* Leavitt, G. C. (1990) "Sociobiological explanations of incest avoidance: A critical claim of evidential claims", ''American Anthropologist'', 92: 971–993. {{JSTOR|644006}}
* {{cite book |last=Potter |first=David Morris |title=Emperors of Rome |publisher=Quercus |location=Englewood Cliffs, N.J |year=2007 |isbn=978-1-84724-166-5}}
* Sacco, Lynn (2009). ''Unspeakable: Father–Daughter Incest in American History''. Johns Hopkins University Press. 351 {{ISBN|978-0-8018-9300-1}}
* Indrajit Bandyopadhyay (29 October 2008). "A Study In Folk "Mahabharata": How Balarama Became Abhimanyu's Father-in-law". ''Epic India: A New Arts & Culture Magazine''
* Đõ, Quý Toàn; Iyer, Sriya; Joshi, Shareen (2006). The Economics of Consanguineous Marriages. World Bank, Development Research Group, Poverty Team.
* {{cite book |last1=Ska |first1=Jean Louis |title=The Exegesis of the Pentateuch: Exegetical Studies and Basic Questions |year=2009 |publisher=Mohr Siebeck |url= https://books.google.com/books?id=7g4yqsv0S0cC&pg=PA260 |isbn=978-3-16-149905-0 |pages=30–31, 260 }} [https://books.google.com/books?id=7g4yqsv0S0cC&q=%22Abraham+cycle%22+Isaac+inheritance&pg=PA30 link pp. 30–31]
* {{cite book|last=Ska |first=Jean Louis |title=Introduction to Reading the Pentateuch |year=2006 |publisher=Eisenbrauns |isbn=978-1-57506-122-1 |url= https://books.google.com/books?id=7cdy67ZvzdkC }}
{{Refend}}

==External links==
{{Commons category}}
{{Wikiquote}}
* {{cite EB1911|wstitle=Incest |volume=14 |short=x}}
* [http://www.clinicalsocialwork.com/incest.html "Incest / Sexual Abuse of Children" by Patricia D. McClendon, MSSW]

{{Incest}}
{{Sex}}
{{Human sexuality}}
{{Sexual ethics}}
{{Authority control}}

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[[Category:Sex crimes]]

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Template:Category handler (view source) (protected)
Template:Cbignore (view source) (template editor protected)
Template:CiteQuran Ayah (view source) (semi-protected)
Template:Cite EB1911 (view source) (template editor protected)
Template:Cite Jewish Encyclopedia (view source) (extended confirmed protected)
Template:Cite book (view source) (protected)
Template:Cite encyclopedia (view source) (protected)
Template:Cite journal (view source) (protected)
Template:Cite magazine (view source) (protected)
Template:Cite news (view source) (protected)
Template:Cite web (view source) (protected)
Template:Cite wikisource/make link (view source) (template editor protected)
Template:Commons category (view source) (template editor protected)
Template:DMCA (view source) (template editor protected)
Template:Dated maintenance category (view source) (template editor protected)
Template:Dated maintenance category (articles) (view source) (template editor protected)
Template:Dead link (view source) (template editor protected)
Template:Delink (view source) (protected)
Template:En dash (view source) (template editor protected)
Template:External links (view source) (template editor protected)
Template:FULLROOTPAGENAME (view source) (template editor protected)
Template:Family law (edit)
Template:Fix (view source) (protected)
Template:Fix/category (view source) (protected)
Template:Hlist/styles.css (view source) (protected)
Template:Human sexuality (edit)
Template:IPAc-en (view source) (template editor protected)
Template:ISBN (view source) (template editor protected)
Template:Icon (view source) (template editor protected)
Template:If then show (view source) (template editor protected)
Template:Incest (edit)
Template:JSTOR (view source) (template editor protected)
Template:Jewish Encyclopedia (view source) (extended confirmed protected)
Template:Langx (view source) (template editor protected)
Template:Law sidebar style (view source) (semi-protected)
Template:Longitem (view source) (template editor protected)
Template:Main (view source) (template editor protected)
Template:Main other (view source) (protected)
Template:Multiple image (view source) (template editor protected)
Template:Multiple image/styles.css (view source) (template editor protected)
Template:Navbox (view source) (template editor protected)
Template:Nbsp (view source) (protected)
Template:Ndash (view source) (template editor protected)
Template:Ns has subpages (view source) (protected)
Template:Pagetype (view source) (protected)
Template:Plainlist/styles.css (view source) (protected)
Template:Portal (view source) (protected)
Template:Portal-inline (view source) (template editor protected)
Template:Px2 (view source) (template editor protected)
Template:Qref (view source) (semi-protected)
Template:Refbegin (view source) (template editor protected)
Template:Refbegin/styles.css (view source) (template editor protected)
Template:Refend (view source) (template editor protected)
Template:Reflist (view source) (protected)
Template:Reflist/styles.css (view source) (protected)
Template:Respell (view source) (template editor protected)
Template:SDcat (view source) (protected)
Template:Section link (view source) (template editor protected)
Template:See also (view source) (template editor protected)
Template:Sex (view source) (semi-protected)
Template:Sexual ethics (edit)
Template:Sfn (view source) (template editor protected)
Template:Short description (view source) (protected)
Template:Short description/lowercasecheck (view source) (protected)
Template:Side box (view source) (template editor protected)
Template:Sidebar with collapsible lists (view source) (template editor protected)
Template:Sister project (view source) (template editor protected)
Template:Sister project/styles.css (view source) (template editor protected)
Template:Spaces (view source) (protected)
Template:Tooltip (view source) (template editor protected)
Template:Tooltip/styles.css (view source) (template editor protected)
Template:Two pixel space (view source) (template editor protected)
Template:Use dmy dates (view source) (template editor protected)
Template:Webarchive (view source) (template editor protected)
Template:Where (view source) (template editor protected)
Template:Wikiquote (view source) (template editor protected)
Template:Yesno (view source) (protected)
Template:Yesno-no (view source) (template editor protected)
Template:Yesno-yes (view source) (template editor protected)
Template:Zero width joiner (view source) (extended confirmed protected)
Module:About (view source) (template editor protected)
Module:Arguments (view source) (protected)
Module:Authority control (view source) (template editor protected)
Module:Authority control/auxiliary (view source) (template editor protected)
Module:Authority control/config (view source) (template editor protected)
Module:Bibleverse (view source) (template editor protected)
Module:Catalog lookup link (view source) (template editor protected)
Module:Category handler (view source) (protected)
Module:Category handler/blacklist (view source) (protected)
Module:Category handler/config (view source) (protected)
Module:Category handler/data (view source) (protected)
Module:Category handler/shared (view source) (protected)
Module:Check for unknown parameters (view source) (protected)
Module:Check isxn (view source) (template editor protected)
Module:Citation/CS1 (view source) (protected)
Module:Citation/CS1/COinS (view source) (protected)
Module:Citation/CS1/Configuration (view source) (protected)
Module:Citation/CS1/Date validation (view source) (protected)
Module:Citation/CS1/Identifiers (view source) (protected)
Module:Citation/CS1/Utilities (view source) (protected)
Module:Citation/CS1/Whitelist (view source) (protected)
Module:Citation/CS1/styles.css (view source) (protected)
Module:Delink (view source) (protected)
Module:Disambiguation/templates (view source) (protected)
Module:EditAtWikidata (view source) (protected)
Module:Exponential search (view source) (template editor protected)
Module:Footnotes (view source) (template editor protected)
Module:Footnotes/anchor id list (view source) (template editor protected)
Module:Footnotes/anchor id list/data (view source) (template editor protected)
Module:Footnotes/whitelist (view source) (template editor protected)
Module:Format link (view source) (template editor protected)
Module:Hatnote (view source) (template editor protected)
Module:Hatnote/styles.css (view source) (template editor protected)
Module:Hatnote list (view source) (template editor protected)
Module:IPAc-en (view source) (template editor protected)
Module:IPAc-en/data (view source) (template editor protected)
Module:IPAc-en/phonemes (view source) (template editor protected)
Module:IPAc-en/pronunciation (view source) (template editor protected)
Module:Icon (view source) (template editor protected)
Module:Icon/data (view source) (template editor protected)
Module:Labelled list hatnote (view source) (template editor protected)
Module:Lang (view source) (template editor protected)
Module:Lang/ISO 639 synonyms (view source) (template editor protected)
Module:Lang/configuration (view source) (template editor protected)
Module:Lang/data (view source) (template editor protected)
Module:Lang/data/iana languages (view source) (template editor protected)
Module:Lang/data/iana regions (view source) (template editor protected)
Module:Lang/data/iana scripts (view source) (template editor protected)
Module:Lang/data/iana suppressed scripts (view source) (template editor protected)
Module:Lang/data/iana variants (view source) (template editor protected)
Module:Lang/langx (view source) (template editor protected)
Module:Message box (view source) (protected)
Module:Message box/ambox.css (view source) (protected)
Module:Message box/configuration (view source) (protected)
Module:Multiple image (view source) (template editor protected)
Module:Namespace detect/config (view source) (protected)
Module:Namespace detect/data (view source) (protected)
Module:Navbar (view source) (protected)
Module:Navbar/configuration (view source) (protected)
Module:Navbar/styles.css (view source) (protected)
Module:Navbox (view source) (template editor protected)
Module:Navbox/configuration (view source) (template editor protected)
Module:Navbox/styles.css (view source) (template editor protected)
Module:Ns has subpages (view source) (protected)
Module:Pagetype (view source) (protected)
Module:Pagetype/config (view source) (protected)
Module:Pagetype/disambiguation (view source) (protected)
Module:Pagetype/rfd (view source) (protected)
Module:Pagetype/setindex (view source) (protected)
Module:Pagetype/softredirect (view source) (protected)
Module:Portal (view source) (protected)
Module:Portal-inline (view source) (template editor protected)
Module:Portal/images/h (view source) (template editor protected)
Module:Portal/styles.css (view source) (protected)
Module:Respell (view source) (template editor protected)
Module:SDcat (view source) (protected)
Module:Section link (view source) (template editor protected)
Module:Side box (view source) (template editor protected)
Module:Side box/styles.css (view source) (template editor protected)
Module:Sidebar (view source) (template editor protected)
Module:Sidebar/configuration (view source) (template editor protected)
Module:Sidebar/styles.css (view source) (template editor protected)
Module:String (view source) (protected)
Module:TableTools (view source) (protected)
Module:Template wrapper (view source) (template editor protected)
Module:Unicode data (view source) (template editor protected)
Module:Unicode data/scripts (view source) (template editor protected)
Module:Unsubst (view source) (protected)
Module:Webarchive (view source) (template editor protected)
Module:Webarchive/data (view source) (template editor protected)
Module:WikidataIB (view source) (template editor protected)
Module:WikidataIB/nolinks (view source) (template editor protected)
Module:WikidataIB/titleformats (view source) (template editor protected)
Module:Wikitext Parsing (view source) (protected)
Module:Yesno (view source) (protected)

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