Marriage

===The incest taboo, exogamy and endogamy===
{{Further|Prohibited degree of kinship|Cousin marriage|Affinity (Catholic canon law)|Avunculate marriage}}

Societies have often placed restrictions on marriage to relatives, though the degree of prohibited relationship varies widely. Marriages between parents and children, or between full siblings, with few exceptions,<ref>{{cite journal | last = Strong | first = Anise | title = Incest Laws and Absent Taboos in Roman Egypt | journal = Ancient History Bulletin | volume = 20 | year = 2006 | url = https://www.academia.edu/205164}}</ref><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 = 267–99 | 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 | journal = Comparative Studies in Society and History | volume = 22 | pages=303–54 | doi = 10.1017/S0010417500009385 | issue = 3| s2cid = 143698328 }}</ref><ref>{{cite web | last = remijsen | first = sofie | title = Incest or Adoption? Brother-Sister Marriage in Roman Egypt Revisited | url = https://lirias.kuleuven.be/bitstream/123456789/208733/2/Journal+of+Roman+Studies+2008+Remijsen.pdf}}</ref><ref>{{cite journal | last = Scheidel | first = W. | title = Brother-sister marriage in Roman Egypt | journal = Journal of Biosocial Science | year = 1997 | volume = 29 | issue = 3 | pages = 361–71 | doi = 10.1017/s0021932097003611 | pmid = 9881142 | s2cid = 23732024 | url = http://humweb.ucsc.edu/jklynn/AncientWomen/ScheidelBrotherSisterMarriages.pdf | access-date = 4 July 2013 | archive-date = 2 November 2013 | archive-url = https://web.archive.org/web/20131102012940/http://humweb.ucsc.edu/jklynn/AncientWomen/ScheidelBrotherSisterMarriages.pdf  }}</ref> have been considered [[incest]] and forbidden. However, [[cousin marriage|marriages between more distant relatives]] have been much more common, with one estimate being that 80% of all marriages in history have been between second cousins or closer.<ref>{{cite web|last=Conniff |first=Richard |url=http://discovermagazine.com/2003/aug/featkiss |title=Richard Conniff. "Go Ahead, Kiss Your Cousin." |publisher=Discovermagazine.com |date=1 August 2003 }}</ref> This proportion has fallen dramatically, but still, more than 10% of all marriages are believed to be between people who are second cousins or more closely related.<ref>{{cite news |first = Sarah |last = Kershaw |url = https://www.nytimes.com/2009/11/26/garden/26cousins.html?pagewanted=1&_r=1 |title = Shaking Off the Shame |date = 26 November 2009 | work=The New York Times}}</ref> In the United States, such marriages are now highly stigmatized, and laws ban most or all first-cousin marriage in 30 states. Specifics vary: in South Korea, historically it was illegal to marry someone with the same last name and same ancestral line.<ref>See [[Article 809 of the Korean Civil Code]] and {{Cite web|url=http://www.ccourt.go.kr/home/english/download/decision_10years.pdf |title=The first ten years of the Korean Constitutional Court |publisher=Constitutional Court of Korea |page=242 (p. 256 of the PDF)  |archive-url=https://web.archive.org/web/20120219184747/http://www.ccourt.go.kr/home/english/download/decision_10years.pdf |archive-date=19 February 2012 }}</ref>

An [[Avunculate marriage]] is a marriage that occurs between an uncle and his niece or between an aunt and her nephew. Such marriages are illegal in most countries due to incest restrictions. However, a small number of countries have legalized it, including Argentina, Australia, Austria, [[Malaysia]],<ref>[http://www.agc.gov.my/Akta/Vol.%204/Act%20164.pdf Law Reform (Marriage and Divorce) Act 1976] {{webarchive |url=https://web.archive.org/web/20120307174301/http://www.agc.gov.my/Akta/Vol.%204/Act%20164.pdf |date=7 March 2012 }} (for Hindus only)</ref> and [[Russia]].<ref>{{in lang|ru}} [[s:ru:Семейный кодекс РФ/Глава 3#Статья 14|The Family Code of the Russian Federation, Article 14 (in Russian)]]. Semkodeks.ru (13 May 2009). Retrieved on 5 September 2013.</ref>
[[File:Mahrams Chart.png|thumb|upright=1.35|Family chart showing relatives who, in Islamic Sharia law, would be considered ''mahrim'' (or ''maharem''): unmarriageable kin with whom [[sexual intercourse]] would be considered [[incest]]uous]]

In various societies, the choice of partner is often limited to suitable persons from specific social groups. In some societies the rule is that a partner is selected from an individual's own social group – [[endogamy]], this is often the case in class- and caste-based societies. But in other societies a partner must be chosen from a different group than one's own – [[exogamy]], this may be the case in societies practicing [[totem]]ic religion where society is divided into several exogamous totemic clans, such as most [[Aboriginal Australians|Aboriginal Australian]] societies. In other societies a person is expected to marry their [[Parallel and cross cousins|cross-cousin]], a woman must marry her father's sister's son and a man must marry his mother's brother's daughter – this is often the case if either a society has a rule of tracing kinship exclusively through patrilineal or matrilineal descent groups as among the [[Akan people]] of West Africa. Another kind of marriage selection is the [[levirate marriage]] in which widows are obligated to marry their husband's brother, mostly found in societies where kinship is based on endogamous clan groups.

Religion has commonly weighed in on the matter of which relatives, if any, are allowed to marry. Relations may be by [[consanguinity]] or [[Affinity (law)|affinity]], meaning by blood or by marriage. On the marriage of cousins, [[Catholicism|Catholic]] policy has evolved from initial acceptance, through a long period of general prohibition, to the contemporary requirement for a dispensation.<ref>
{{cite book |title=Forbidden Relatives: The American Myth of Cousin Marriage |chapter-url=https://archive.org/details/forbiddenrelativ00otte |chapter-url-access=registration |last=Ottenheimer |first=Martin |year=1996 |publisher=University of Illinois |chapter=Chapter 3}}</ref> [[Islam]] has always allowed it, while [[Hindu texts]] vary widely.<ref>{{cite web |url=https://archive.islamonline.net/?p=5223 |archive-url=https://web.archive.org/web/20070716082845/http://www.islamonline.net/servlet/Satellite?pagename=IslamOnline-English-Ask_Scholar%2FFatwaE%2FFatwaE&cid=1119503544772 |archive-date=16 July 2007 |title=Islamic View on Marrying Cousins |publisher=IslamonLine.net  |access-date=4 June 2017 }}</ref><ref name="indiasocialstructure">{{cite book |title=India: Social Structure |page = 55 |first=Mysore Narasimhachar |last=Srinivas |year=1980 |publisher=Hindustan Publishing Corporation |location=Delhi |isbn=978-1-4128-2619-8}}</ref>