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


“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….



“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….


“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….


“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.

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random notes: 11/09/12

about the semai, i forgot to mention that, apart from conflict, they also don’t like competition in activities like sports — from wikipedia (see also Cooperation and competition in peaceful societies):

“The games Semai children play are non-competitive…. A game of badminton for example uses no partition nets and keeps no score. The shuttlecock is deliberately hit so that it could be easily intercepted by the other player and passed back, and so forth.”

more on the clannish albanians:

“An Insider’s View of EU Efforts in Kosovo”
“‘We Have Achieved Almost Nothing’

“Since 2008, the EU has had thousands of soldiers, judges and prosecutors in Kosovo to help it become a Western-style constitutional democracy. But a German police officer with years of experience there says it is still dominated by corruption, clan loyalties and drugs — with officials just waiting for the high-minded reformers to leave….

“[A] recent report by the European Court of Auditors finds that there have been hardly any successes. It concludes that levels of organized crime and corruption remain high, while the judiciary is inefficient and suffers from too much political influence. A German police officer familiar with conditions in Kosovo for many years confirms the report’s findings based on his own experiences in the country….

“It’s my impression that corruption is quite high among Kosovar police officers. I was told that, if you’re caught with a stolen car, all you have to do is pay the officer a bribe to take care of the problem.

The major criminals are already out of reach, protected by traditional clan structures and the old-boys’ networks within the former Kosovo Liberation Army (KLA), from which many police officers were recruited….

Kosovo is a country in which centuries-old traditions live on, and blood feuds are part of the culture. We Central Europeans have not been able to convince the Kosovars of the benefits of adopting a new legal and value system like the one we have in the West. That’s because they see that the old structures remain powerful while government institutions are weak. I fear that the Kosovars will ride us out, just as the Taliban are waiting for Western troops to withdraw from Afghanistan….”

the danes consider decriminalizing incest. danish geneticist points out that inbreeding can be a good or a bad thing:

“Aarhus siblings’ love child sets off incest debate”

“The recent case of a brother and sister in the city of Aarhus who said that they are in love and have a five-month-old child together has raised a national debate about sibling sex. The couple, who share the same father but have different mothers, face jail time for violating Denmark’s current statute prohibiting incest and inbreeding….

“The possibility of passing on genetic defects and damaging the social order have been the main reasons cited for making it illegal for siblings to have sex and produce offspring. But Niels Tommerup, a professor of genetics at the University of Copenhagen, said that mutations resulting from inbreeding can be both positive and negative.

“‘Our focus is always on the negative consequences like diseases and malformations,’ he told Information newspaper. ‘But positive mutations help develop the species.’

Tommerup said that mutations like those that occur due to inbreeding can be ‘biologically positive’.

“‘It is hard to imagine that there would be the formation of new species without some form of inbreeding,’ he said.

“Tommerup would not go as far as changing the law prohibiting sex between brother and sister, however. He recommended that family sex get no closer than cousins.

“He said that the famous Danish blue eyes are a mutation that could only have occurred via inbreeding sometime in history.

‘If inbreeding is banned, the possibility of promoting new, positive variants could be lost,’ he said.

“Vagn Greve, a law professor at Copenhagen Business School, would like to see even more taboos removed. Greve said there is ‘no logical reason’ that sex between parents and their children should be against the law.

“‘In my view, we should decriminalise sex between father and daughter as long as they are both adult and the relationship is voluntary,’ Greve told metroXpress newspaper. ‘There is no reason to treat the biological family different from the social family, but the age limit should be 18 or 20-years-old.’

Greve said that sex among immediate family members has been legal in countries like Spain, Italy, the Netherlands and France for 200 years, and that there is no evidence that it has damaged either families or society….


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