An avunculate marriage is a marriage with a parent's sibling or with one's sibling's child—i.e., between an uncle or aunt and their niece or nephew. Such a marriage may occur between biological (consanguine) relatives or between persons related by marriage (affinity). In some countries, avunculate marriages are prohibited by law, while in others marriages between such biological relatives are both legal and common, though now far less common.[citation needed]
If the partners in an avunculate marriage are biologically related, they normally have the same genetic relationship as half-siblings, or a grandparent and grandchild—that is they share approximately 25% of their genetic material. (They are therefore more closely related than partners in a marriage between first cousins, in which on average the members share 12.5% of inherited genetic material, but less than that of a marriage between, for instance, cousin-siblings, in which the partners share 37.5% of their inherited genetic material.)
Lucius Tarquinius Superbus and his brother Arruns Tarquinius respectively married sisters Tullia Major and Tullia Minor, who may have been their nieces. Superbus and Tullia Minor later disposed of their original spouses and married each other.
Prince William of Hesse-Philippsthal-Barchfeld and his half-niece Princess Juliane of Bentheim and Steinfurt (1873), and later his half-niece Princess Adelaide of Bentheim and Steinfurt (1879).
Avunculate marriage was a preferred type of union in some pre-modern societies. Marriages between such close relatives were frequent in Ancient Egypt among royalty.
Judaism
Judaism forbids marriage between an aunt and her nephew but allows marriage between an uncle and his niece.[19] The Talmud and Maimonides encourage marriages between uncles and nieces, though some Jewish religious communities, such as the Sadducees, believed that such unions were prohibited by the Torah.[20]
Christianity
Among medieval and especially early-modern Christians, a marriage between a woman and the sibling of a parent was not always interpreted as violating Leviticus 18; this was especially so among the royal houses of Europe, and in Catholic countries a papal dispensation could be obtained to allow such a marriage.
Marriage between an uncle and his niece is forbidden in Islam if they are blood relatives.[21]
Medieval European royals
Avunculate marriages were prominent in the House of Habsburg. For example, Charles II of Spain was the son of an uncle and niece, Philip IV and Mariana of Austria; in turn, both of Philip's parents (and therefore both of Mariana's maternal grandparents) were the children of uncle-niece marriages, one of which also produced Mariana's paternal grandfather. As a result, instead of Charles' parents, grandparents, great-grandparents, great-great-grandparents, great-great-great-grandparents, and great-great-great-great-grandparents adding up to 126 different individuals, they numbered only 50.
South India's Hindus
Avunculate marriage was common among South India's Hindus. Currently, it is mostly practiced in rural and small to medium cities. The most common form is where the elder daughter is married away to her youngest maternal uncle.[22] The wedding is usually called Maman Kalyanam (Thai Maman Kalyanam in Tamil Nadu). It was culturally preferred for at least one daughter to be married to an uncle. This is extensively featured as a plot device in many south Indian movies, such as Thaamirabharani (2007)[23] and Thai Maaman (1994).[24]
Genetics
In an uncle–niece or a double first cousin marriage, the couple is assumed to have inherited 1/4 of their genes from a common ancestor, whereas in first cousin unions the assumption is that the couple has inherited 1/8 of their genes from a common ancestor, and for a second cousin couple the comparable proportion is 1/32. This means that on average the progeny of an uncle–niece or a double first cousin marriage will be expected to have inherited identical gene copies at 1/8 of all their loci, defined as a coefficient of inbreeding F = 0.125. It follows that for first cousin progeny, F = 0.0625, that is, 1/16 loci predictably are homozygous, whereas for second cousins, F = 0.0156, that is, 1/64 of loci are homozygous.[25]
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%).[26] Malformations of major systems were significantly more frequent among the consanguineous couples, whereas malformations of the eyes, ears, and skin did not show any significant effect of consanguinity. 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. A significant decrease in the mean birth weight and head circumference of babies born to consanguineous parents was noted in both the poor and middle/upper socioeconomic class. The mean length was less in babies born to consanguineous parents belonging to the poor social class only.
^Pikkanen, Antti (24 July 2014). "Lapsena alttarille – Jenna Karjalainen meni naimisiin alaikäisenä". Nyt.fi. Helsingin Sanomat. Retrieved 26 July 2015. [Oikeusm]inisteriö käsittelee myös muita avioliittoon liittyviä poikkeuslupia. Lupaa voi anoa, jos esimerkiksi haluaa mennä naimisiin sisarensa lapsen kanssa. Mutta sellaisia hakemuksia tulee hyvin harvoin, 2000-luvulla pari kolme.
^Oliveira, Catarina. "Barão de Mauá". InfoEscola (in Portuguese). Retrieved 2023-08-27. In 1840, he left for England, where he came into contact with capitalist reality and the inventions of the Industrial Revolution. The following year, he returned and proposed to his niece. They married in 1841 and the union had 12 children, of which 10 survived.
