History Main / RoyalInbreeding

** Politely referred to as [[FanNickname "eugenics"]] in the fandom, as some of the best character traits in the game are hereditary, and become more likely the more common they are in a newborn character's ancestry. The game's mechanics forbid marriage to a sibling, child or parent, but allow granparent-to-grandchild marriages, among other icky things. All of this is thrown off the window with Zoroastrians, for whom incestuous marriages are holy, and increase their popularity with vassals. To help keep Zoroastrian families from descending into deformed messes, the game lets their rulers keep three concubines for non-inbred -- but legitimate -- children, and also discreetly cheats by making negative "inbred" traits 75% less likely for Zoroastrian children.

* The House of Habsburg, which ruled most of Europe for several hundred years (with branches in Spain, France, England, the entire HolyRomanEmpire...), was notorious for this.

Oftentimes this is used to explain TheCaligula, RoyallyScrewedUp, and ItRunsInTheFamily.

->''The royal bloodline isn't what it used to be; too much inter-marrying, I suppose. I always say when you reduce a family tree to a family bush, you just can't hide as much beneath it!''
-->-'''Regent Virini''', ''Series/BabylonFive''.

* In LarryNiven's Svetz stories, the world is [[UnitedNationsIsASuperPower ruled by a hereditary Secretary-General]]; centuries of inbreeding have produced a feeble-minded and childish occupant of that office.

* Politely referred to as "eugenics" in the ''VideoGame/CrusaderKings 2'' fandom, as some of the best character traits in the game are hereditary, and become more likely the more common they are in a newborn character's ancestry. The game's mechanics forbid marriage to a sibling, child or parent, but allow granparent-to-grandchild marriages, among other icky things. All of this is thrown off the window with Zoroastrians, for whom incestuous marriages are holy, and increase their popularity with vassals. To help keep Zoroastrian families from descending into deformed messes, the game lets their rulers keep three concubines for non-inbred -- but legitimate -- children, and also discreetly cheats by making negative "inbred" traits 75% less likely for Zoroastrian children.

--> ''King: "But the earl is my uncle, that would make her my... half-sister?"''
--> ''Adviser: "It's the other one sir, she's your cousin."''

*** Queen Victoria was also a carrier for hemophilia, and the result was that most of the European royal families were hemophiliacs and carriers into the 20th century.
** When the post-Communist Russian government wanted to verify that the human remains found in Siberia were those of the late Tsar Nicholas, they needed a close relative to match the DNA. Prince Philip, Duke of Edinburgh was tactfully approached to give DNA samples. Which proved the Romanoff DNA beyond all possible doubt.
*** Nicholas II's son Alexei inherited the gene for hemophilia that Victoria carried because his mother was one of her grandchildren.

* In [[JidaiGeki ancient and feudal Japan]], it was common for noble and imperial families to arrange marriages between cousins and even aunts/uncles and nephews/nieces because ThePatriarch of these families tended to [[ReallyGetsAround have boatloads of children from many different women]], and this was a convenient way of tidying up familial loose ends and folding branches of the family back into the main House. In particular, it was rather common for the reigning emperor to be married to a close relative of his ruling shogun; since the latter tended to also form dynasties, this meant that the two family trees often intertwined.

* ''VideoGame/AssassinsCreedBrotherhood'': Implied BrotherSisterIncest between Cesare and Lucrezia Borgia. Not actual royalty, but given that their father is the Pope close enough.

* ''VideoGame/AssassinsCreedBrotherhood'': Implied BrotherSisterIncest between Cesare and Lucrezia Borgia.

** When the post-Communist Russian government wanted to verify that the human remains found in Siberia were those of the late Tsar Nicholas, they needed a close relative to match the DNA. Members of the British Royal Family were tactfully approached to give DNA samples. Which proved the Romanoff DNA beyond all possible doubt.
** Nicholas II's son Alexei inherited the gene for hemophilia that Victoria carried because his mother was one of her grandchildren.

** Her current Majesty and her husband are 2nd cousins.

* In [[JidaiGeki ancient and feudal Japan]], it was common for noble and imperial families to arrange marriages between cousins because ThePatriarch of these families tended to [[ReallyGetsAround have boatloads of children from many different women]], and this was a convenient way of tidying up familial loose ends and folding branches of the family back into the main House. In particular, it was rather common for the reigning emperor to be married to a close relative of his ruling shogun; since the latter tended to also form dynasties, this meant that the two family trees often intertwined.

* In ''Literature/ASongOfIceAndFire'' the Targaryen dynasty wed brother to sister for centuries, often blamed in universe for their tendency to produce [[TheCaligula mad kings]]. Later Cersei and Jaime Lannister are twins who secretly have an affair and three kids, which ends up starting a five-way civil war, though their parents were first cousins and no one thought that unusual.

* The ''Literature/CiaphasCain'' series partially blames the overall incompetence of much of the Imperial aristocracy (including the majority of planetary governors we meet) on an excess of inbreeding.

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* In the second trilogy of ''Literature/KushielsLegacy'' Imriel de la Courcel falls in love with and ''eventually'' marries Princess Sidonie de la Courcel. Imriel is the son of Sidonie's uncle, making them first cousins once removed.

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* In traditional Arab society, it is customary for cousins to marry.

* In [[JidaiGeki ancient and feudal Japan]], it was common for noble and imperial families to arrange marriages between cousins because ThePatriarch of these families tended to [[ReallyGetsAround have boatloads of children from many different women]], and this was a convenient way of tidying up familial loose ends and folding branches of the family back into the main House. In particular, it was rather common for the reigning emperor to be married to a close relative of his ruling shogun; since the latter tended to also form dynasties, this meant that the two family trees often intertwined.

* In [[JidaiGeki ancient and feudal Japan]], it was common for noble and imperial families to arrange marriages between cousins because ThePatriarch of these families tended to [[ReallyGetsAround have boatloads of children from many different women]], and this was a convenient way of tidying up familial loose ends and folding branches of the family back into the main House.

* This trope drives the main plot and two subplots in Gilbert and Sullivan's ''Theater/HMSPinafore.'' Sir Joseph Porter, the First Lord of the Admiralty, boards the Pinafore to court Josephine, daughter of the ship's captain. However, seaport floozy Buttercup declares that, in her youth, she breastfed both Captain Corcoran and seaman Rackstraw, and inadvertently [[SwitchedAtBirth mixed up the two infants]]. Sir Joseph then declares that he cannot marry Josephine, as she is the daughter of a mere seaman, her charm and grace notwithstanding. This allows now-Captain Rackstraw to propose to Josephine, and demoted-to-seaman Corcoran to pursue Buttercup. Sir Joseph resigns himself to courting his cousin Hebe.

* In just the third episode of ''Series/TheTudors'' Henry VII arranged a marriage between his daughter Mary and her mother's nephew the Holy Roman Emperor Charles II, though the engagement was called off later. Note that Charles and his aunt were Hapsburgs (see Real Life).

* ''Literature/HarryPotter'': The wizarding world doesn't have royalty, but it does have pureblood lines. As such, many of them use intermarrying to keep the bloodline pure, and disowning anyone who marries "mudbloods". Dumbledore mentions this was the case with the Gaunt family, the last descendants of Salazar Slytherin, who had inherited their family's violent temper due to inbreeding.

* ''Literature/HarryPotter'': The wizarding world doesn't have royalty, but it does have pureblood lines. As such, many of them use intermarrying to keep the bloodline pure, and disowning anyone who marries "mudbloods". Dumbledore mentions this was the case with the Gaunt family, the last descendants of Salazar Slytherin, who had inherited their family's violent temper due to interbreeding.

* After all sorts of trouble was had in the Centuari court on ''Series/BabylonFive'', one of the ministers blames it on too much inbreeding.

* In ''Literature/ASongOfIceAndFire'' the Targaryan dynasty wed brother to sister for centuries, often blamed in universe for their tendency to produce [[TheCaligula mad kings]]. Later Cersei and Jaime Lannister are twins who secretly have an affair and three kids, which ends up starting a five-way civil war, though their parents were first cousins and no one thought that unusual.