Targaryen genetic load

By Razib Khan | March 27, 2012 11:57 am

I have to point you to this post on royal inbreeding in A Song of Ice and Fire. They reference my post on the Habsburgs. Well done! In any case, one possibility is that the Targaryen lineage may have purged their genetic load through inbreeding. The basic logic is that all the recessive traits are going to be “exposed” every generation, resulting in a far stronger selection coefficient against those alleles than would be the case in a outbreed population (where most deleterious variants with recessive expression are masked by being present heterozygote genotypes).

CATEGORIZED UNDER: Genetics
  • Elfino

    You forget that Targaryen have blood of the dragon. Such extrange genetic contribution may have turned them invulnerable to inbreeding in ways we can’t imagine.

    Of course, I don’t want to think how such extrange contribution was made by the ancerstors of Daenerys Targaryen…

  • http://racefortheironthrone.wordpress.com StevenAttewell

    Your post on the Hapsburgs was very helpful. While it’s been a while since I’ve done genetics – as a historian – I’m quite astonished at how the Targaryens survived, given their penchant for extremely direct incest. Brother-to-sister, uncle-to-nieces, and cousins-to-cousins pretty much throughout (although they did occasionally bring in the occasional Arryn, Martell, Hightower, etc.) must really increase the odds of genetic disorders.

    As for the “blood of the dragon” protecting – I doubt it. We know that there was a recurring “madness” in the family (although nature vs. nurture is hard to figure out in this family), and Maelys the Monstrous was pretty deformed, which suggests there’s some problems in the family tree.

  • Elfino

    StevenAttewell… Daenerys (SPOILER: END OF 1st BOOK)… walks into fire without problem.

    You know, in fantasy stories, whenever you find something extrange and there is not explanation… A magician did it.

    In Science Fiction is… Casimir effect in combination with dark matter cinetics.

  • http://racefortheironthrone.wordpress.com StevenAttewell

    Elfino – yes, but GRRM has explained that that was a specific situation tied to her use of blood magic to wake her dragon eggs. Keep in mind that Rhaenrya Targaryen was burned to death by her brother’s dragon, Aerion Targaryen died drinking wildfire, and the Tragedy at Summerhall claimed the lives of Aegon V and Prince Duncan Targaryen.

    To the extent that the Targaryens have magic in their blood, it deals with some ability to control dragons, and a recessive tendency to clairvoyancy. They are not fireproof. And they do get mutants.

  • Jessica C

    I’ve only watched the TV series, but my impression is that the Targaryens probably wouldn’t mind practicing infanticide, and if they were willing to kill up through toddler age, they’d probably do pretty well at removing a lot of the homozygotes with obvious defects. It also helps that unlike in the Hapsburg situation, there’s only one Iron Throne so they really just need two healthy Targaryens per generation (and sans birth control, 10 or more offspring wouldn’t be unreasonable!) Plus don’t forget the “coefficient” of dragon blood — who knows what effect that has on their genetics!

    Anyway, moderate levels of consanguinity aren’t as deleterious as we (Western Euro/American types) have been brought up to think. (a few papers have shown that a bit of inbreeding is actually better for you, at least as measured by some quantitative traits including certain measures of fertility)

    And, since I have the very citation handy in my current manuscript: ;)

    Kimura, M., Maruyama, T., and Crow, J. (1963). The mutation load in small populations. Genetics 48, 1303–1312.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    NERDZ!!!!!!!!!!!!

  • http://racefortheironthrone.wordpress.com StevenAttewell

    I agree, Jessica. I’d only add that they weren’t practicing moderate levels of consanginuity – we’re talking brother-sister marriage as a regular practice. That’s pretty extreme.

  • Konkvistador

    I read “dragon blood” as basically just being a few genes acquired through mutation or magic that change them in a way dragons can detect (perhaps smell?) making them more friendly or obedient towards anyone carrying them, not something silly like direct dragon ancestors.

    Also didn’t some ancient Egyptian royal families have incest rates comparable to this? I recall brother sister marriage was practised for example.

  • Elfino

    Another theory. In the novels infidelity is common in kings. Perhaps is common in queens, too. So every one hundred years there is an illegitimate king, with his fresh genetic contribution.

  • Konkvistador

    @Elfino: Historical reality shows that infidelity in kings is a common vice, infidelity among queens is high treason however.

  • Eurologist

    NERDZ!!!!!!!!!!!!

    I get the eerie feeling Razib is maniacally laughing in the background, updating his 1950′s blinking computer database that adds points to “smart” contributors yet wields the power of subtraction onto others.

    Having said that, we don’t pay for HBO, but my wife bought season 1 on DVD so we could watch some bouncing breasts together, and the stellar performance of Peter Dinklage.

  • Bobby LaVesh

    As #9, Elfino suggests, I wonder how much “not-really-inbreeding” happenened in inbred royal families such as the Egyptians, Hapsburgs, etc.

    The egypitans think wedding to brother to sister would keep blood lines pure- but any infidelity on the part of the woman would break that- and given human’s natural defence against in-breeding (chemical pheremonal cues to breed with one with different immunity) the temptation to stray MUST have been stronger the inbred couples.

    Game of thrones is fiction [gasp!!!!!] but the same could possibly be true of the Targaryen in that book. Also, I agree with #10- I take “dragon blood” figuratively, perhaps meaning a genetic predisposition to being able to tame dragons rather than any actual dragon ancestors.

    As for “blood magic” being the reason Daenerys being able to resist fire (read it above- now I can’t find it again) – that isn’t true. If I recall from the first book (read it so many years ago) there were events prior to her hatching the dragon eggs where she was not burnt when she should have been.

    By the way- I’m not a prude, and I know GRRM was involved with the HBO version- but I was kinda disappointed with it. They were too obsessed with showing flesh- and less concerned with telling the story. For those who have only seen the TV show- the books are a million times better… yes, I know that is said about most things (exception Forrest Gump) but in the case of Game Of Thrones it is more true than ever.

  • Naughtius Maximus

    I’m on my second reading of the books and have a question; was the tv series commissioned on the back of a resurgence of interest in the books and if so what caused the resurgence (as A Game of Thrones is quite old)?
    Also what historical groups do people think inspired the various groups in the books?
    I would have associated the Dothraki with the Mongols but author in the link above tends to see them based on the Huns.
    Also I think the Kingdom in the North seems to be based on Scotland, and I think there are similaritys between the Tutha de Danann of Irish mythology and the Children of the Forest SPOILERS
    with them being driven under gorund after the arrival of another group.

  • Bobby LaVesh

    Incidentally, regarding incest, infidelity, and inbreeding:

    I recall one of the kingdoms visited in Gary Jenning’s fictional account of Marco Polo that the heir to the throne was descended traditionally from the King’s sister when available not from the King. (at least I think it was in that book- historical fiction is my favourite fiction genre so I read a lot of them).

    This is because the King’s wife could be untrue- but if the child descended from the King’s sister- would carry his blood anyway.

    Jenning’s book was definately fiction- not historical- but Jenning’s does base a lot of events in his stories on real events. Whether such a system existed anywhere I don’t know. Makes sense from a 21st century perspective- don’t know if it would have anywhere in the 13thC.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    I would have associated the Dothraki with the Mongols but author in the link above tends to see them based on the Huns.

    i asked GRRM this in a chat in march of 1999 on this specific question. they’re composites of central eurasians. or at least that is what he told me. unlike kate elliott in her crown of stars series the historical analogs aren’t supposed to be obvious, easy, or even there.

    re: incest. ancient egyptian royalty alternated between inbreeding and outbreeding. also, not just brother sister, was also aunt-nephew. had to do with a old matrilineal aspect of egyptian society.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    #11, u are actually not far off the mark in terms of my methodology of commenter filtering/sorting.

  • Sniffnoy

    @Naughtimus Maximus: I think it’s safe to say that it’s the TV show that caused the resurgence of interest in the books. Recall that the HBO first bought the rights to make the show back in 2007.

    As another example of mixing historical influences, consider what went into Dorne…

  • http://dispatchesfromturtleisland.blogspot.com ohwilleke

    The Egyptians are pretty much the only historically attested culture with brother sister marriage, although brother-sister households that were not sexual were apparently pretty common in hunter-gatherer societies.

    As we get DNA evidence from mummies, it seems that there were high degrees of fidelity and that this did produce inbreeding fitness impairments.

    The idea of purging a genetic load through inbreeding is an interesting one, and one way to think about the Hapburgs is that they were done in not simply by inbreeding, but by inbreeding from a recently established and cosmopolitian set of aristocrats who had not had sufficient time in previous generations to dump their mutation loads. Their dynasty was the first truly transcontinental empire in centuries.

    A natural test population for the hypothesis would be Middle Eastern Arab populations, which have been inbred for a much longer time period. If they have a relatively light load of recessive genes, the theoretical prediction of load dumping would be supported. But, it doesn’t take a lot of influx of outsiders with new recessive genes at each generation to screw up load dumping and depress fitness with inbreeding.

    It is also worth considering that if you have large numbers of children per family, high infant and youth mortality, and highly concentrated power and wealth in a society, the fitness costs of inbreeding could be tolerable, especially if the current regime can appoint successors from anyone in a large pool of descendants and cadet lines.

    Elevating the odds of a damaging recessive gene combination from say, 0.4% to even 40%, can be tolerable as long as you have lots of kids, lots of kids aren’t going to survive to reach adulthood in any case, and you can decide after you’ve seen the results which one will be the heir to the kindgdom. The goal is to get at least a couple of kids who has as many of the desirable traits of his or her parents as possible, and if the price of that is many kids who have huge problems, so what. The kingdom still prospers.

    On the other hand, if the success of the kingdom depends upon having as many competent descendants as possible to make family control competent at the most finely grained possible level, inbreeding fitness depression is a real problem.

  • http://blogs.discovermagazine.com/gnxp Razib Khan

    The Egyptians are pretty much the only historically attested culture with brother sister marriage,

    hawaii too

  • http://dispatchesfromturtleisland.blogspot.com ohwilleke

    Interesting. Hawaii was at the end of the Austronesian chain of expansion, which happened sequentially over many hops from Taiwan to Hawaii, so my intuition would be that Hawaiians overall must have been pretty inbred (in the manner that your Hapsburgs post illustrates, with multiple lines of descent from the same ancestor to the same currently living person).

    I wonder if the fitness disadvantage of brother-sister marriage is reduced when you are only modestly more closely related to a sibling than to, for example, a second cousin.

  • Spike Gomes

    20:
    It was only the royal class that did that as a regular practice. And there was quite a bit of “fooling around” among the chiefs that probably alleviated the incest effect somewhat. Hawaiian culture even after the introduction of Christianity had a difficult time with the whole monogamy thing.

    The practice originated out of the beliefs in the concentration of mana and the development of a caste system of sorts. That said, often the system would reset itself. Kamehameha I was the offspring of a lesser wife of a lower chiefly caste.

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Gene Expression

This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

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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