inbreeding and iq

i’ve mentioned the following idea in a couple of comments here and there recently, but i thought i may as well make it a full blog post…

in a previous post i linked to a study by an iranian (iirc) researcher, m. sadaat, who found a negative correlation between a nation’s inbreeding coefficient and iq — in other words, the more inbreeding in a population, the lower the iq.

inbreeding depression would seem like the likely explanation (edit: or maybe low iq people just inbreed more), and maybe it is; but i’ve been wondering if what might happen at least maybe in some cases is that, since regularly inbreeding populations become clannish or tribal, perhaps low iq individuals (and their genes/alleles) are not weeded out of the population because they benefit from being members of a clan/tribe which takes care of them even to the degree that they are able to successfully reproduce. in other words, maybe inbreeding can lead to a dysgenic situation — the opposite of, for instance, gregory clark’s eugenic medieval/early modern england in which only the cleverest and hard-working survived.

here’s an example of how a clannish or tribal society might be especially beneficial to low iq individuals — from Development and Social Change in Rural Egypt (1986), pgs. 150-51:

“The importance that poor peasants attach to the brokerage services by a single wealthy patron can be seen in the continuing importance of the extended family unit in rural Egypt. In the village of El-Diblah [pseudonymous village representative of upper egypt], as well as other Egyptian communities, politics and much of life itself are organized on the basis of large, extended families numbering 500 members or more. These extended families are broad patrilineal structures, which may or may not be able to trace themselves back to a single historical founder. While these extended families do not represent monolithic social structures, most fellahin are animated by a real feeling of belonging to a particular extended family unit. When they need a loan or help with outside government officials, poor peasants will often turn to the leader or a prominent person within their extended family. In the village of El-Diblah three of the four leading extended families are headed by rich peasants. In the eyes of most fellahin, this is exactly as it should be. In the countryside wealth acquired by virtually any means provides a good indication of an individual’s ability to deal with (or against) the ouside world.

“‘Zaghlul,’ for example, is the rich peasant head of one of the leading extended families in El-Diblah. A short, wiry 55-year-old fellah, whose dress and mannerisms are almost indistinguishable from those of other peasants in the village, Zaghlul now owns about 25 feddans of land. Much of this land is planted in sugar cane, a crop that he uses to supply his own cane press that produces black molasses for local sale. As the owner of 25 feddans of land, and the proprietor of one of the few ‘manufacturing’ enterprises in the village, Zaghlul is able to dispense a wide number of agricultural and non-agricultrual work opportunities to favored members of his extended family. Many of the poorer members of his extended family live in a mud-brick settlement surrounding Zaghlul’s modern two-story, red-brick house. In the evenings a steady stream of these poor people come to Zaghlul’s house, seeking brokerage and intercessionary services (for example, help in securing agricultural inputs and medical services from the government)….

so the smarter individuals in egyptian clans give jobs to and generally help out the not-so-smart members of their clans. not so good maybe.

this scenario doesn’t seem to apply to the chinese or european jews who have high average iqs despite lots of long-term inbreeding — at least the chinese have inbred a lot for a loooong time anyway. not so sure about the jews.

maybe what’s required to get to my proposed dysgenic situation is a true tribal society in which it’s tribe vs. tribe 100% of the time — and maybe you can only get to a true tribal society via father’s brother’s daughter marriage which only the arabs/north africans/south asians practice. dunno.

otoh, maybe the average iqs of chinese people and ashkenazi jews would’ve been even higher if they hadn’t have bred so closely. hmmmm.

maybe somebody’s already discussed this possible scenario elsewhere, but i haven’t come across it before. -?-

previously: inbreeding and nat’l iq and family type in egypt

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14 Comments

  1. @HBD_Chick

    RE: “…..doesn’t seem to apply to the chinese or european jews who have high average iqs despite lots of long-term inbreeding….”

    Two intersecting axis, not one:
    x) Inbreeding->Outbreeding.
    y) deaths, survivability, or suppression of lower caste birth rates.

    In both the chinese and ashkenazi examples there was a great deal of selection going on. China from disease, hunger and death, Jews from selective breeding and abandoning of lower end mates.

    Reply

  2. On chinese evolutionary pressures, see Plagues and Peoples by McNeill. Then follow references to and from. He also compares the yellow river disease gradients with those in Africa.

    Reply

  3. @curt – “In both the chinese and ashkenazi examples there was a great deal of selection going on. China from disease, hunger and death, Jews from selective breeding and abandoning of lower end mates.”

    sure. but then, perhaps (perhaps), the chinese clans and/or the ashkenazi extended families didn’t look after their dumbest members the way the arab/egyptian tribes seem to. i’m not 100% certain about this … it’s just a thought. (^_^)

    @curt – “On chinese evolutionary pressures, see Plagues and Peoples by McNeill.”

    thnx! i’ll check it out.

    Reply

  4. the chinese clans and/or the ashkenazi extended families didn’t look after their dumbest members the way the arab/egyptian tribes seem to

    Or maybe they looked after the smarter ones more.

    Reply

  5. Chinese do charity. There’s no tradition of helping out, and a lot of pressing people to perform.
    Jews also had an outlet for non-performers: let them convert to christianity. In a sense, altruism towards the family only makes sense in a lawless situation, when you might need them for violence clashes with other clans. Jews and chinese didn’t have that problem most of the time.

    Reply

  6. @ihtg – “Or maybe they looked after the smarter ones more.”

    maybe. but how would that work?

    i mean, i wonder what the iq threshold would be to be smart enough to figure out that looking after even smarter individuals in your family would be the best strategy. not 90. not even 100, i think. i even doubt 110 or 115 would be clever enough. Maybe people at 120+ might be able to work that out, but there’s not that many of those people around.

    Reply

  7. @spandrell – “In a sense, altruism towards the family only makes sense in a lawless situation, when you might need them for violence clashes with other clans.”

    the ironic thing, though, is that you seem to get violent clashes with other clans from too much inbreeding. and then maybe you’re also more altruistic towards the family in that case, too. sounds like a bizarre sort-of altruism-genes arms race.

    Reply

  8. “In a sense, altruism towards the family only makes sense in a lawless situation”

    I’d agree it makes more sense the more lawless the situation but barn-building, lambing, long-distance droving – lots of manual tasks are easier with multiple pairs of hands. The question then becomes what is the optimal number of pairs of hands needed in a particular environment?

    Reply

  9. “I’ve done a follow-up on this. See here”

    Good stuff. I wonder if one of the competitive catalysts for IQ is the specializion that comes with urbanization as that creates competition for the better life that goes with having a skilled trade.

    Say for the sake of illustration
    – the “preparing for winter” IQ bonus (latitude) moving from subtropical to mid-latitude is 5 pts
    – the same bonus but for moving from mid-latitudes to northern is also 5 pts
    – the specialization IQ bonus is 5 pts
    and say at the start the subtropical IQ averaged 85.

    Then the sequence over time might be
    1) People from from the sub-tropics move to mid-latitudes +5pts
    2) The people in the mid-latitudes develop farming, urbanization, specialization etc +5pts
    3) People from the mid-latitudes move to northern latitudes and gain another +5pts
    4) Farming, urbanization, specialization etc reaches northern latitudes +5pts

    so
    sub-tropics 85
    – mid-latitudes 90 (latitude)
    — mid-latitudes 95 (specialization)
    — northern latitudes 95 (latitude)
    —-northern latitudes 100 (specialization)

    with the northeast asian versus northwest euro difference being that the environment (rice?) allowed high density farming, urbanization and specialization to spread to the northern latitudes earlier.

    Reply

  10. So if inbred populations are dumber, does that mean many of the alleles for higher IQ are homozygous-recessive? That would explain a lot.

    Reply

  11. @bleach – “So if inbred populations are dumber, does that mean many of the alleles for higher IQ are homozygous-recessive?”

    yeah, could be! and like you say — would explain a lot.

    wait … aren’t some/all of the ashkenazi smart genes homozygous recessive? i mean the ones that cochran/hardy/harpending looked at?

    Reply

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