Avunculate marriage

Avunculate marriage refers to a marriage between an uncle and a niece or between an aunt and a nephew (third degree relations). In some societies avunculate marriage is prohibited as a form of incest, while in others it is legal, even common.

The partners of an avunculate marriage have the same genetic relationship as half-siblings or a grandparent and grandchild, sharing on average 25% of their genetic material. This is more than that of a first cousin relationship, in which on average the members would share 12.5% of their genetic material, but less than that of full siblings.

Avunculate marriages were once frequent among the royal houses of Europe, as Leviticus 18 was not interpreted to explicitly forbid the marriage of a man with the daughter of his sibling; in Catholic countries a papal dispensation could be and often was obtained to allow such a marriage.

Avunculate marriage is currently illegal in most Anglophone nations, but is allowed in Argentina, Australia, Austria, Brazil, France, Malaysia, and Russia. Avunculate marriage is the preferred type of union among the Awá-Guajá people of eastern Amazonia. It is also a fairly common practice in the southern Indian states of Andhra Pradesh, Tamil Nadu, and Karnataka.

List of avunculate marriages

 * Leonidas, King of Sparta and his half-niece, Gorgo
 * Roman Emperor Claudius and his fourth wife and niece, Agrippina the Younger
 * Vietnamese Prince Tran Hung Dao and his consort and paternal aunt, Princess Thien Thanh
 * Joanna of Naples and her nephew, King Ferdinand II of Naples (1496)
 * Philip II of Spain and his niece, Anna of Austria (fourth wife) (1570)
 * Ferdinand II, Archduke of Austria, and his niece, Anne Juliana Gonzaga (1582)
 * Chiefess Kapohauola and her nephew, Chief Kakae
 * Philip IV of Spain and his niece, Mariana of Austria (second wife) (1646)
 * Voltaire (François-Marie Arouet), lived in concubinage with his niece, Marie Louise Mignot Denis.
 * Prince Augustus Ferdinand of Prussia and his niece Margravine Elisabeth Louise of Brandenburg-Schwedt (1755)
 * Pedro III of Portugal and his niece Maria I of Portugal (1760)
 * Infanta Benedita and her nephew, José, Prince of Brazil (1777)
 * King Kamehameha the Great of Hawaii and his niece, Queen Keōpūolani (c.1796)
 * Sir John Acton, 6th Baronet, Prime Minister of Naples and his niece Marianna Acton (1799)
 * Francis IV, Duke of Modena, and his niece, Maria Beatrice of Savoy (titular queen of England and Scotland according to the Jacobite succession) (1812)
 * Infante Carlos, Count of Molina, and his niece, Infanta Maria Francisca of Portugal (1816), and later his niece, Maria Teresa of Portugal (1838)
 * Kamehameha II and his half-niece Kalani Pauahi
 * Ferdinand VII of Spain and his niece Maria Isabel of Portugal (1816), and later his niece Maria Christina of the Two Sicilies (1829)
 * Infante Francisco de Paula of Spain and his niece Princess Luisa Carlotta of Naples and Sicily (1819)
 * James Mayer de Rothschild, founder of the French branch of the Rothschild banking family, and his niece Betty Salomon von Rothschild (c.1825).
 * Richard von Metternich (son of the famous Austrian Chancellor) and his niece, Pauline von Metternich (1856).
 * Amadeo I of Spain and his niece, Maria Letizia Bonaparte (second wife) (1888)
 * Porfirio Díaz, president of Mexico (1876–80, 1884–1911), and his niece Delfina Ortega Diaz
 * Henryk Sienkiewicz, Polish novelist, and his niece, Maria Babska. (1904)
 * Klara Hitler, daughter of Johann Pölzl and Johanna Hiedler and Adolf Hitler's mother. Either her grandfather Johann Nepomuk Hiedler or his brother was likely her husband Alois Hitler's biological father. Moreover, Johann was her future husband's step-uncle. Even after they were married, Klara still called her husband "uncle".