Editing Inbreeding (section)

===Royalty and nobility===
{{Main|Royal intermarriage}}
{{see also|List of coupled cousins}}
[[File:Carlos II de España, por Juan Carreño de Miranda (Museo del Prado).jpg|thumb|[[Charles II of Spain]], a member of the famously inbred [[House of Habsburg|Habsburgs]] with an [[Habsburg jaw|extremely pronounced lower jaw]]]]
Inter-nobility [[marriage]] was used as a method of forming [[political alliance]]s among elites. These ties were often sealed only upon the birth of progeny within the [[arranged marriage]]. Thus marriage was seen as a union of lines of nobility and not as a contract between individuals.

[[Royal intermarriage]] was often practiced among European royal families, usually for interests of state. Over time, due to the relatively limited number of potential consorts, the [[gene pool]] of many ruling families grew progressively smaller, until all European royalty was related. This also resulted in many being descended from a certain person through many lines of descent, such as the numerous European royalty and nobility descended from the British [[Victoria of the United Kingdom|Queen Victoria]] or [[King Christian IX of Denmark]].<ref name="beechegotha1">{{cite book | title=The Gotha: Still a Continental Royal Family, Vol. 1 | publisher=Kensington House Books | last = Beeche | first = Arturo | year=2009 | location=Richmond, US | pages=1–13 | isbn=978-0-9771961-7-3}}</ref> The House of [[Habsburg]] was known for its intermarriages;  the [[Prognathism|Habsburg lip]] often cited as an ill-effect.  The closely related houses of Habsburg, [[House of Bourbon|Bourbon]], [[House of Braganza|Braganza]] and [[House of Wittelsbach|Wittelsbach]] also frequently engaged in first-cousin unions as well as the occasional [[Cousin#Additional terms|double-cousin]] and uncle–niece marriages.

In [[ancient Egypt]], royal women were believed to carry the bloodlines and so it was advantageous for a [[pharaoh]] to marry his sister or half-sister;<ref>{{cite web | title = Women in Ancient Egypt, Women and Law | last = Seawright | first = Caroline | work = thekeep.org | url = http://www.thekeep.org/~kunoichi/kunoichi/themestream/women_egypt.html | access-date = 2010-12-29 | archive-date = 2010-12-27 | archive-url = https://web.archive.org/web/20101227173747/http://www.thekeep.org/~kunoichi/kunoichi/themestream/women_egypt.html | url-status = dead }}</ref> in such cases a special combination between [[endogamy]] and [[polygamy]] is found. Normally, the old ruler's eldest son and daughter (who could be either siblings or half-siblings) became the new rulers. All rulers of the [[Ptolemaic dynasty]] uninterruptedly from [[Ptolemy IV]] ([[Ptolemy II]] married his sister but had no issue) were married to their brothers and sisters, so as to keep the Ptolemaic blood "pure" and to strengthen the line of succession. King [[Tutankhamun]]'s mother is reported to have been the half-sister to his father,<ref>[https://web.archive.org/web/20100218120151/http://news.nationalgeographic.com/news/2010/02/100216-king-tut-malaria-bones-inbred-tutankhamun/ King Tut Mysteries Solved: Was Disabled, Malarial, and Inbred]</ref> [[Cleopatra VII]] (also called Cleopatra VI) and [[Ptolemy XIII]], who married and became co-rulers of [[ancient Egypt]] following their father's death, are the most widely known example.<ref>{{cite web|title= The House of Ptolomey | vauthors = Bevan ER | work =  uchicago.edu | url = https://penelope.uchicago.edu/Thayer/E/Gazetteer/Places/Africa/Egypt/_Texts/BEVHOP/13*.html}}</ref>