Outbreeding won't save the British royal family

By Razib Khan | April 26, 2011 1:47 am

Image credit: Wikimedia

A few years ago I blogged a paper on how inbred the last Spanish Habsburgs had become, leading to all sorts of ill effects. Take a look at Charles II of Spain! He was as inbred as the product of a sibling mating. An extreme case of pedigree collapse in humans if there was one. This came to mind when an amusing feature in The Philadelphia Inquirer popped into my RSS feed, In royal/commoner marriage, a happy mix of genetic diversity. The writer gets a good number of choice quotes from one of the coauthors of the Habsburg paper, who observes that Prince Charles is moderately inbred, but his pairing with the very distantly related Diana (who came from the nobility as well) basically meant that his sons were outbred. Nevertheless, there is the suggestion that extra genetic diversity can’t hurt. I don’t think this is really a major positive worth mentioning. First, there is the possibility of outbreeding depression. Honestly I doubt this will be an issue.  But secondly, I think more relevant is that gains to outbreeding hit massive diminishing marginal returns rather quickly. For example, here’s the coefficient of relationship between pairs of relatives:

0.5 = Full siblings, parent-child
0.25 = Half siblings, Uncle/aunt-niece/nephew
0.125 = First cousins
0.03125 = Second cousins
0.0078125 = Third cousins

As you can see the genetic relevance of relatedness really drops off rapidly in a conventionally outbred population. There isn’t much gain I’d say to Prince William marrying a female who has a greater genetic distance from him. Though the marriage of a common Englishwoman, Kate Middleton, into the British royal family moves it further on from its relatively recent dominant German character.


Comments (20)

  1. Jumblepudding

    Are the royals really in any genetic danger right now? (aside from the pronounced ears?)

  2. elle

    Kate Middleton was found to be distantly relates to Big Willie anywho

  3. #2, did you just leave an obscene comment?

  4. Naughtius Maximus

    Charles must be delighted about his only son getting married!

  5. Ben

    Could you please explain this a little more for the slow folk in your audience? Basically, everything between the words “coefficient” and “conventionally” didn’t make sense to me.

  6. ben , basically once your are no longer inbred, it makes little sense to say you are getting less inbred in a practical sense. by analogy. assume that you score a 50 out of 100 on a test. you take 1 pill to make you smarter, and you score 95 out of 100. if someone tells you taking 2 pills will make you even smarter, you’ll be able to go no higher than 5 units to 100. there’s only so high you can score. william & harry are pretty outbred now. since william is not closely related to kate, there kids aren’t going to be that much more outbred.

  7. Ian

    Between his mother and his great-grandmother (the Queen Mother) William is probably the least German heir to the throne since Stuart times.

    @ #1, the ears explained (also some important information about the origins of the Royal family), courtesy “Goodness Gracious Me”: http://www.youtube.com/watch?v=JXAu6QSMyj0

  8. Ben

    Thanks for the response. That helps!

  9. David

    Thanks for providing the links to those articles, and your own paper on the Habsburg’s of Spain. Very interesting, even for a layman.
    After spending several years researching genealogies, I think a lot of people, (especially some who don’t consider themselves as…. “common”) would be a little surprised to learn that some of their own ancestors going back to as little as 100 to 150 years ago married a cousin or two.

  10. Courtney

    When I was studying genetics, the textbook had several pedigrees of various well-known families and their various genetic disorders. According to one of those pedigrees, the entire royal family either has or carries hemophilia. I would not say that this necessarily puts them in genetic danger, since the condition is not exactly a death sentence, but it is a good reason to add some genetic diversity.

  11. Jean

    @ Courtney – If you revisit those charts, you will see that Queen Victoria was the carrier who brought haemophilia into the British and other royal families. Since the gene fault responsible is on the X chromosome, she was unaffected herself (having another X which was free of the mutation), but her son Leopold suffered from the disease, and two of her daughters were carriers. http://en.wikipedia.org/wiki/Haemophilia_in_European_royalty

    Since her eldest son Edward did not suffer from the disease, it is clear that he did not inherit the mutation. Males not having another X, if they have the mutation, they manifest the illness. The current British royal family is descended from Edward. So they neither have nor carry the mutation.

  12. pconroy


    And Victoria inherited the disease from her biological father Sir John Conroy, who looked a little like Prince Charles, with his long narrow nose and large ears…

  13. Walter Sobchak

    From http://en.wikipedia.org/wiki/Prince_Philip,_Duke_of_Edinburgh:

    “Elizabeth and Margaret, who were Philip’s third cousins through Queen Victoria, and second cousins once removed through King Christian IX of Denmark.”

    Upon Accession, William would be the first King of England to have an English mother since Elizabeth I (as did her brother and predecessor Edward VI). The genetic diversity clearly helped William, as his father clearly has a very limited IQ.

    William’s brother Harry raises an interesting question. Harry is rumored to have been the biological son of Diana’s lover (legally he is Charles’ son). And as noted above Victoria is rumored to have been the child of a similar misalliance.

    Official records are of course heavily censored, but we can wonder how often were such things allowed or condoned for the purpose of promoting the health of the breed.

    Asian royalty has less frequently faced the problem of inbreeding. Polygamy, harems, and the lack of primogeniture have meant that kings have been the children of harem girls who may have been the the daughters of barbarian chieftains, or even slaves, but, who, at any rate, did not share much genetically with their consorts.

    Despite these features, dynasties in Asia, like those in Europe, have seldom lasted more than 3 or 4 centuries. The above mentioned Spanish Hapsburgs ran just under 200 years, which is more typical of successful dynasties.

  14. Jean


    And Victoria inherited the disease from her biological father Sir John Conroy

    Not possible. As I said, a male carrying the mutation will have the disease. The idea that she was Conroy’s child is wishful thinking. Her eyes and face shape are so like those of Prince Edward, Duke of Kent that you scarcely need DNA. 🙂

  15. pconroy


    But AFAIK, none of the Royals before Victoria showed any signs of the disease, so where did it come from.

    Also bear in mind that Sir John Conroy was Irish, and many, many Irish – including my father (who may be related) and sister – carry the SNP for Haemochromatosis aka Iron Overload disease. Could it be that Sir John Conroy also carried this, and this allowed him to also be a Carrier of Haemophilia, without too much ill effect?! Remember that one of the treatments for Haemochromatosis was to regularly bleed the sufferer… something that Haemophiliacs do naturally…

    What say you???

  16. Huxley

    Regarding the origin of hemophilia in the family, I’ve read that spontaneous mutation is responsible 30% of the time, and Victoria’s father was in his 50s when she was conceived. I think it is not really realistic that Conroy had hemophilia and made it to 67 as a soldier. Also, Victoria clearly looked like the rest of the Hanovers.

  17. Pohranicni Straze

    Re: Asian royalty, one notable exception would be the Thai monarchy, which prior to the current king was highly inbred. I would love to see an inbreeding coefficient calculated for Mahidol Adulyadej. He only had three grandparents, as his father (Rama V) and mother were children of Rama IV by different wives. Rama V’s father, Rama IV, was the great-uncle of Rama V’s mother (the two being, respectively, a son and a great-granddaughter of Rama II). Rama IV’s parents were 1st cousins (his paternal grandfather being Rama I and his maternal grandmother being Rama I’s sister). I would bet that Prince Mahidol’s inbreeding coefficient would rival that of the later Spanish Hapsburgs, which could partially explain why he died so young. Mahidol married a commoner, so the current king Rama IX is not too inbred. However, his wife is a 1st cousin once removed through Rama V (actually closer genetically, as she is a double descendant of Rama IV), so the future King Rama X will have a pretty large inbreeding coefficient himself.


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About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at http://www.razib.com


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