inbreeding and cognitive ability among whites in the u.k.

via dienekes via jayman:

Genome-wide estimates of inbreeding in unrelated individuals and their association with cognitive ability

“INTRODUCTION

“Research on consanguineous marriages, and other forms of inbreeding, has long shown a reduction in cognitive abilities in the offspring of such unions. The presumed mechanism is that detrimental recessive mutations are more likely to be identical by descent in the offspring of such unions and so have a greater chance of being expressed. To date, research on the relationship between inbreeding and cognitive ability has largely been restricted to recent inbreeding events as determined by pedigree…. It has been suggested that intellectual disability is under negative selection, and that recent deleterious mutations have an important role in the underlying aetiology. The wealth of molecular genetic data currently available allows estimates of inbreeding on a genome-wide level and to examine the effects of long-term ancestral levels of inbreeding. Such an association with inbreeding, as measured by runs of homozygous polymorphisms (ROH), has previously been identified with several behavioural traits, such as schizophreniz, Parkinson’s disease and personality measures, as well as non-behavioural traits such as height.

“The relationship between inbreeding on a population level and cognitive ability is particularly interesting due to assortative mating, non-random mating, which is greater for cognitive ability than for other behavioural traits, as well as physical traits such as height and weight. Positive assortative mating has been reported for cognitive ability, particularly for verbal traits, with spousal correlations generally around 0.5. Assortative mating should lead to greater genetic similarity between mates at causal loci for cognitive ability and to a lesser extent across the genome, which in turn reduces heterozygosity at these local. In other words, in contrast to the genome-wide reduction of heterozygosity caused by inbreeding, the reduction of heterozygosity due to assortative mating for a trait is limited to loci associated with the trait…. Another difference between inbreeding and assortative mating is that the effects of inbreeding are expected to be negative, lowering cognitive ability, whereas the effects of assortative mating affect the high, as well as the low end of the ability distribution, thus increasing genetic bariance, that is, when high-ability parents mate assortatively, their children are more likely to be homozygous for variants for high ability, just as offspring of low-ability parents are more likely to be homozygous for variants for low ability….

“MATERIALS AND METHODS

“Participants

“The Twins Early Development Study (TEDS) recruited over 11 000 families of twins born within England and Wales between 1994 and 1996…. In this analysis, individuals were excluded if they reported severe current medical problems, as well as children who had suffered severe problems at birth or whose mothers had suffered severe problems during pregnancy. Twins whose zygosity was unknown or uncertain or whose first language was not English were also excluded. Finally, analysis was restricted to twins whose parents reported their ethnicity as ‘white’….

“Cognitive measures

“Verbal and non-verbal tests were administered using web-based testing. The verbal tests consisted the Similarities subtest and the Vocabulary subtests from the Wechsler Intelligence Scale for children (WISC-III-UK). The non-verbal tests were the Picture Completion subtest from the WISC-III-UK and Conceptual Grouping from the McCarthy Scales of Children’s Abilities. A general score was derived from the test battery as the standardized sum of the standardized subtest scores, which correlates 0.99 with a score derived as the first principle component of the test battery score.

“Runs of homozygosity

“FROH was defined as the percentage of an individual’s genome consisted of runs of homozygosity (ROH)…. [O]nly ROH with a minimum of 65 consecutive SNPs covering 2.3Mb were used when calculating the total proportion of the genome covered by ROH. In addition, the required minimum density in a ROH was set at 200kb per SNP, and the maximum gap between two consecutive homozygous SNPs was set at 500kb….

“RESULTS

“Table 1 includes descriptive statistics for FROH and the three measures of cognitive ability (general, verbal, and non-verbal). FROH is slightly positively skewed, as it represents the total percentage of the genome that includes runs of homozygosity (ROH). The average percentage of genome covered by ROH was 0.7% (95% CI 0.65-0.72%). Verbal and non-verbal abilities correlate 0.49; because general cognitive ability is the sum of the standardized verbal and non-verbal subtests, they correlate much more highly with general ability (0.87 and 0.86, respectively).

inbreeding and iq - table 01

“Table 2 presents the results of the linear regression analyses. No significant regression was found between FROH and the cognitive measures after correction for multiple testing, although the association with non-verbal cognitive ability was nominally significant (P=0.03). Although this association was not statistically significant, it is noteworthy that every regression in Table 2 is *positive*, indicating that increased homozygosity tends to be associated with *higher* cognitive scores across different measures of cognitive ability (general, verbal and non-verbal).

inbreeding and iq - table 02

“Our analysis identified 87 loci where ROH overlapped in 10 or more individuals. For these overlapping regions we tested for association with each of the cognitive measures and again showed no significant associations after correction for multiple testing (P-values of less than 5.7 x 10-4). A sign test of the direction of effect across all ROH showed a disproportionately large number of *positive* associations, indicating that ROH are associated with higher cognitive ability (P=0.002). The sign test was non-significant for verbal ability but highly significant for non-verbal ability (P<10-6). The sign test for non-verbal ability alone remained significant after correcting for an individual’s genome-wide FROH score (P<10-6).

“As explained earlier, positive assortative mating can also lead to genome-wide homozygosity for trait-specific loci, and, unlike inbreeding, assortative mating can affect the high as well as the low end of the ability distribution. One possible explanation for the trend suggesting a positive correlation between homozygosity and cognitive scores in our data is that positive assortative mating on intelligence might be greater for high cognitive ability individuals….

“DISCUSSION

“Our results show that within a representative UK population sample there was a weak nominally significant association between burden of autosomal runs of homozygosity and higher non-verbal cognitive ability. This nominal association with *increased* cognitive ability is counterintuitive when compared with the results from more extreme inbreeding based on pedigree information. A potential explanation for this direction of effect is that individuals with higher cognitive ability might show greater positive assortative mating, which would lead to increased homozygosity at loci for higher cognitive ability in their offspring. However, in a separate sample we showed that greater positive assortative mating was not associated with higher cognitive ability. While these findings seem to provide clear evidence against this hypothesis, it is possible that the genome-wide genetic finding reflect historical mating habits that no longer exist today. It should also be noted that there was a reduction in the standard deviations for spousal correlations in the increased cognitive ability groups by an average of 6% compared with the decreased cognitive ability group (see Table 3), which could reflect less genetic variability in the high ability couples or a ceiling effect on the cognitive tests. This lesser phenotypic variability at the high ability end would have a small effect in reducing the spouse correlations and potentially confound our analysis….

“Overall, these results highlight the importance of understanding mating habits, such as inbreeding and assortative mating, when investigating the genetic architecture of complex traits such as cognitive ability. The results certainly suggest that there is no large effect of FROH on reduced cognitive ability, the expected direction of effect. The nominally significant associations found in this study may even suggest that in the case of non-verbal cognitive ability, beneficial associations with homozygosity at specific loci might outweigh the negative effects of genome-wide inbreeding and that the relationship between inbreeding and cognitive ability may be more complicated than previously thought.
_____

so, although obviously Further Research is RequiredTM, these researchers have concluded that both the absence of reduced cognitive ability and the slight increase in cognitive ability which they found in individuals who had runs of homozygosity (roh) in their genomes (evidence of matings between genetically similar individuals) were probably NOT due to assortative mating (i.e. smart people mating with smart people).

furthermore, they suggest that the inbreeding-causes-reduced-cognitive-ability meme is incorrect — or at least that the situation is more complicated than the idea that it’s the accumulation of recent deleterious mutations which haven’t been selected away that is the (whole) problem. in fact, a little inbreeding seems to have a positive effect on some cognitive abilities!

i’ve suggested a couple of times one way in which inbreeding might result in a low average iq in a population, and that is if the inbreeding leads to clannish, altruistic behaviors between extended family members which then result in the deleterious mutations NOT being weeded out.

one real world example i’ve offered is how life works in egyptian villages and how the more successful and affluent (and, presumably, more intelligent) members of a clan are obliged to help out their less successful and poorer (and, presumably, less intelligent) clan members. so, apart from mentally retarded individuals not reproducing, where is the negative selection for deleterious mutations here? there is none. or it’s a lot weaker than in more individualistic societies (like gregory clarks’ medieval england) where it’s more every man for himself — in clannish societies, deleterious mutations might be able to hang around for a long time, riding on the coattails of those with fewer deleterious mutations.

(note: comments do not require an email. i’m my own grandpa! [no, I’M not! it’s just the song.])

20 Comments

  1. Dear HBD Chick, I thought this post was going to address the English upper and educated classes and their long history of inbreeding which your excellent and fascinating but ideologically driven writings have consistently ignored. The obvious place for you to start would be with Charles Darwin and his wife, also his first cousin. If you could apply your insights to the Darwin and Galton clans, and then extend the inquiry more broadly among the English ruling classes, you will be hard put, I imagine, to reconcile the results with your wishfully thought notion of the English as being notably outbred. Well, the middle and lower classes are/were … But that fact doesn’t work too well with your notions either.

    Videlicet

    Reply

  2. @videlicet – “you will be hard put, I imagine, to reconcile the results with your wishfully thought notion of the English as being notably outbred.”

    i’ve already addressed this, thankuverymuch. the cousin marriage rates for the upper crusties in darwin’s time were miniscule: 4.5% for the peerage. that’s nothing — NOTHING — compared to the 50%+ we see in saudi arabia or pakistan today (and they’ve probably had rather high rates for the last two millennia at least given the fact that their cultures encourage cousin marriage).

    in case you’re confused, the point is not that the english (and other nw europeans) are completely, entirely, 100% outbred. the point is that they are more — MUCH more — outbred than just about anybody else (except maybe for the semai).

    Reply

  3. @t.greer – “I have a big post look at the lineage evidence for this point (and a few others problems with the theory), but I don’t think it will be ready for at least a month…”

    ah! cool! i look forward to it. (^_^) (keep me posted!)

    @t.greer – “…(goin’ on a trip).”

    happy trails! (^_^)

    Reply

  4. Another point (that you may have addressed earlier) is that this is a White sample. If there is an individual variation in the effects of inbreeding you might find that an individualistic culture would weed out the inbred – or to be more precise – weed out those on which it has a detrimental effect. But in places where it was very common it may be that the whole society changed into the clannish type and most inbred would survive. As a consequence, the effect of inbreeding would then vary between cultures.

    Reply

  5. @hbd chick: “A sign test of the direction of effect across all ROH showed a disproportionately large number of *positive* associations, indicating that ROH are associated with higher cognitive ability (P=0.002). The sign test was non-significant for verbal ability but highly significant for non-verbal ability (P<10-6). " Hmm. So inbreeding is bad and too much outbreeding might be bad. Maybe. It's kind of a comfort. If we gotta go there maybe it won't cost ALL our brains. Of course as you point out there are different interpretations.
    By the way, feel free to ignore everything I've ever said. In the past few weeks some evidence has come my way that may knock everything into a cocked hat. It is by no means contradictory, but it means all the bets are back on the table. I'll let you know if I ever make any sense of it.

    Reply

  6. Was any attempt made to account for small amounts of jewish ancestry? Apparently, on 23andme all people with any jewish ancestry show up as cousins. Even if the amount of jewish ancestry is small (and thus not responsible for the above average IQ) it would still correlate with IQ because of assortive mating.

    Reply

  7. hbchick, I don’t know if dumber clan members have really ever gotten much of a great deal under collectivist systems.

    It seems more likely (being cynical) that their resources and labor would get eaten up by smart clan members than vice versa, because what’s collectivism all about if it isn’t about making the dumber members of the group run at a line of guns for the good of the people?

    Not to mention there’s probably a lot of competition, just within the clan itself.

    I mean, these are largely competitive, agonistic pastoralists and horticulturalists were talking about here, not exactly socially egalitarian bushmen (or other hunter gatherers) or any kind of janteloven people.

    Now would competing within what are effectively micro societies and populations blunt the effect of selection? As an analogy, imagine no breeding barriers between euro nations. Would the actual selective force on IQ be stronger (in whatever direction it is moving in)?

    Selection would certainly be slower, because what would definitely happen in a landscape with many inbred groups (as opposed to the outbred situation) is that mutations would spread less strongly, but that is less mutational potential to respond to selective pressure which seems different from less selective pressure.

    Also because of this there would be more parallel, possibly redundant, solutions to the same problems, because a mutation that works for one inbred population wouldn’t spread as easily to another. Possibly (or not) this might lead to hybrid vigor if these populations crossed up, and these parallel solutions came together, but that wouldn’t exactly be reversing “inbreeding depression” as such, even if it looked a bit similar.

    Reply

  8. I’m not sure testing for the effect of inbreeding in one of the most outbred populations in the world makes a lot of sense except as a control.

    However if they take this study, repeat it with Pakistanis in the UK and then compare the two then we might have something interesting.

    Reply

  9. @grey – “I’m not sure testing for the effect of inbreeding in one of the most outbred populations in the world makes a lot of sense except as a control.”

    heh! i know. but they haven’t (nobody has!) thought of that. (~_^)

    @grey – “However if they take this study, repeat it with Pakistanis in the UK and then compare the two then we might have something interesting.”

    yes. i wish somebody would! there really isn’t any good inbreeding and iq studies out there, believe it or not. there are just a couple here and there, and a few more that are mostly about particularly inbred individual families and their freakishly low iqs. surprisingly, afaict, inbreeding and iq hasn’t been that well researched! (inbreeding/outbreeding really is off most westerners radar.)

    Reply

  10. @lolkatzen – “Why were twins chosen?”

    i think in this particular case, the fact that the subjects were twins didn’t matter. they just used the data from the teds because they are there (i.e. the genetic data are there, and then they could simply test the subjects’ iqs).

    Reply

  11. @matt – “I don’t know if dumber clan members have really ever gotten much of a great deal under collectivist systems. It seems more likely (being cynical) that their resources and labor would get eaten up by smart clan members than vice versa….”

    could be, could be. and, yet, there is the example above i gave of the egyptian case — and the other examples i’ve given elsewhere. the headman of the clan (headman in the sense that he’s economically the most well off) has to set aside a couple of hours EVERY evening to receive his less well off clansmen and their petitions for assistance (help them to get jobs, help them negotiate some problem with gov’t authorities, whatever). it’s expected. and the people think this is a fine arrangement — that one of their relatives should be much better off than the rest of them, because then he’ll be in a position to help them, of course.

    what somebody needs to do, of course, is to sit down and figure out if the fitness of these lower clansmen is in actuality high or not. higher than, say, lower class westerners (in the past — not in modern welfare states). maybe one of these days. (~_^)

    @matt – “Selection would certainly be slower, because what would definitely happen in a landscape with many inbred groups (as opposed to the outbred situation) is that mutations would spread less strongly, but that is less mutational potential to respond to selective pressure….”

    that’s an interesting idea! thanks!

    @matt – “Also because of this there would be more parallel, possibly redundant, solutions to the same problems….”

    yes. i’ve been wondering this about the arab populations and all of their really local, familial genetic conditions, a lot of which have to do with the adrenal system (adrenaline? agression? maybe? maybe not — may simply hydration). there appears to be a lot of unique mutations located within family/clan/tribal lines — redundant solutions to the same problems maybe.

    Reply

  12. @t – “Was any attempt made to account for small amounts of jewish ancestry?”

    no, not as far as i saw. they just looked at “whites” — as self-identified.

    Reply

  13. @linton – “By the way, feel free to ignore everything I’ve ever said. In the past few weeks some evidence has come my way that may knock everything into a cocked hat. It is by no means contradictory, but it means all the bets are back on the table. I’ll let you know if I ever make any sense of it.”

    ah ha! i love it when someone/something pulls the rug out from under you (me — anybody!)! (^_^) keep us posted!

    Reply

  14. what somebody needs to do, of course, is to sit down and figure out if the fitness of these lower clansmen is in actuality high or not. higher than, say, lower class westerners (in the past — not in modern welfare states). maybe one of these days. (~_^)

    Yep. Seems tricky but there might be some data out there to begin make estimates with.
    And whether all the balance of exchanges between upper clansmen and lower ultimately worked out in either’s favor or affected fitness, is still the question which would remain.

    I’m just cynical that Godfather style arrangements don’t work out being in the Godfather’s interest (and reproductive interest at that).

    Another angle might also be that the higher class clansman might also have more similar genetics to the low class clansmen (if they’re more inbred), with more of their IQ advantage due variation due to environment / random, so it would be less dysgenic / anti-eugenic for him to improve their fitness anyway (because what makes him smarter is less likely to be his genetics).

    that’s an interesting idea! thanks!

    its another “West Hunter” idea, in the context of India, so I can’t take any credit here. its interesting how the effects of assortative mating and population structure in creating new niches for selection balance against their effects in slowing flow of useful mutations.

    Reply

  15. @matt – “Another angle might also be that the higher class clansman might also have more similar genetics to the low class clansmen (if they’re more inbred), with more of their IQ advantage due variation due to environment / random, so it would be less dysgenic / anti-eugenic for him to improve their fitness anyway (because what makes him smarter is less likely to be his genetics).”

    yes, good point.

    there’s nothing to say either, i suppose, that “genes for altruism” (or “genes for (my) familial altrusim”) would necessarily work with other sorts of genes. i mean, they could — fitness-wise — be in competition with other sorts of genes, couldn’t they?

    high-iq genes might make individuals really fit in one way, but “genes for altruism” could pull in a different fitness direction, couldn’t they? intergenomic conflict sorta stuff i’m think of here.

    (sorry — can’t expand on that thought right now. pressed for time!)

    Reply

  16. Dr. Nicolai Sennels is a Danish psychologist who has done extensive research into a little-known problem in the Muslim world: the disastrous results of Muslim inbreeding brought about by the marriage of first-cousins.

    There is no doubt that the wide spread tradition of first cousin marriages among Muslims has harmed the gene pool among Muslims.

    Because Muslims’ religious beliefs prohibit marrying non-Muslims and thus prevents them from adding fresh genetic material to their population, the genetic damage done to their gene pool since their prophet allowed first cousin marriages 1,400 years ago are most likely massive. (This has produced) overwhelming direct and indirect human and societal consequences.

    Reply

    1. @Simon Allach

      That’s certainly the nigh universal party line right now. I know of only 5 papers (including one by me) that go toe to toe challenging that (obviously politically advantageous) line at present. Of course I consider my own paper God’s Truth or whatever; call it Darwin’s Truth if you prefer, or the Extra-Galactic Blessing, maybe if you prefer that, only it;s not; it’s an inescapable necessity resulting from inheritable variation, selection and Mendel’s laws. No magic needed. (I used to say it was also due to sexual reproduction, but the 17th chapter of Handbook on Evolution and Society, a mainstream textbook, points it out in bacteria; they have been found showing a preference for relatives. Each of the other three papers is a block buster, published in a top journal and overwhelming even alone.

      So watch this space. We may be living, intellectually, on a different planet by the end of the year. If not, just forget I said anything. Knowing more would only make you unhappy with nothing to be done about it.

      Reply

  17. @ HBD chick. Thanks for digging up the article. You are incredibly in your energy and your search strategy. I should never have found this one. Maybe I should have mentioned it in my note to Simon Allach, but it’s not quite powerful enough to be a game changer standing alone. I suspect gifted people have, or recognize, a wider social horizon, and thus are more outbred than average. And indeed maybe altruism and intelligence are related in a complex way. Hang in there. While I remain a tad skeptical of your general conclusions (despite the massive evidence you have accumulated — I recently repeated a study that easily surpassed the p less than 5 standard deviations test that the Higgs bozon discovery boasted only to see it go splat on repetition) I like your work. I think it’s very important and I do think that one day soon it will command the consensus, if other approaches support it.

    Reply

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