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

“F_ROH 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 F_ROH and the three measures of cognitive ability (general, verbal, and non-verbal). F_ROH 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).

“Table 2 presents the results of the linear regression analyses. No significant regression was found between F_ROH 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).

“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 F_ROH 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 F_ROH 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.”
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so, although obviously Further Research is Required^TM, 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: 02/14/13

cousin marriage rates for german jews living in the prussian province of hohenzollern between ca. 1875-1920 (117 marriages):

– first cousin marriages = 16.2% ± 3.4%
– consanguineous marriage up to and including second cousins = 19.6% ± 3.7%

source [pdf]. original source: Reutlinger, W. 1922. Über die Häufigkeit der Verwandtenehen bei den Juden in Hohenzollern, und über Untersuchungen bei Deszendenten aus jüdischen Verwandtenehen. Arch. Rassenb. 14: 301-305.

a little more on these rates from In Search of Jewish Community: Jewish Identities in Germany and Austria 1918-1933 [pgs. 234 and 241]:

“On the other hand, there is considerable evidence to back up the impression that village Jews were marrying cousins and other close relatives in increasingly large numbers.[44] …

“[44] In Hohenzollern, there was an 11 percent rate of marriage to relatives (5 percent to first cousins) among Jewish couples who died before 1922; of those still alive in 1922, the rate had increased to 22 percent (16 percent to first cousins. These rates were several times as high as the rates for Christian marriages. See Wilhelm Reutlinger, ‘Uber die Haufligkeit der Verwandtenehen bei Juden in Hohenzollern und uber Untersuchungen bei Deszendenten aus judischen Verwandtenehene,’ Archiv fur Rassen- un Gesellschaftsbiologie 14 (1922): 301-303, quoted by Marion Kaplan The Making of the Jewish Middle Class: Women, Family, and Identity in Imperial Germany (New York, 1991), p. 273 note 206. See also Cahnman, ‘Village and Small-Town Jews,’ pp. 122-23, for an impressionistic discussion of the same phenomenon.”

so, the rates of consanguineous marriages increased for jews in hohenzollern over the period from 1875-1920. that pretty much mirrors the general trend of increasing cousin marriage rates right across europe at the time, only the actual rates for the hohenzollern jews were much higher than for most europeans — well, at least most germans.

this 11% consanguineous rate (5% to first cousins) for jewish couples who died before 1922 is a lot higher than the only other definite rate i have for european jews which is from alsace-lorraine in 1872-76 (so i’m thinking these might be kinda contemporaneous rates) — and that rate was 2.3% (consanguineous marriages).

see also: jewish mating patterns in nineteenth century russia.
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a bizarre story on a case of cousin marriage and inbreeding depression from china that … well, i’ll just let you read it for yourselves. from A Family That Climbed Out of Inbreeding Depression [pg. 1064]:

“In 2008, a family was fortuitously found in Northeast China. Before the 1948 Revolution, this family was wealthy and owned vast amount of land. After nationalization, the family was given a tiny house with a small plot of land. Subsequently, during the Cultural Revolution (1966-1976), all landowning families in the country were severely prosecuted and socially ostracized. The social stigma on the members of former land owning families was so persuasive that any form of association with them was deemed as dangerous. At that time, there were two children of marriageable age. As their parents were unable to find unrelated mates from the society, they arranged an intra-family marriage between available first cousins. The union produced five offspring: three mentally retarded girls, one deaf-mute girl, and one mentally retarded boy who did not survive (Figure 1). The consanguineous (first cousin) parents supported their four disabled daughters throughout their childhood. By the time these daughters were of marriageable age, the Cultural Revolution in China was over and the social stigma of land-owning families was lifted. Thus, the consanguineous parents were able to arrange marriages of their four unfit daughters with four biologically unrelated men. The deaf and mute girl was married to a deaf and mute man from the same village. The three mentally retarded daughters were married to healthy men, of low socioeconomic status, and they resided in their husbands’ homes in the same village. The most severely retarded daughter was married to a poor man who came to their family looking for food; he was offered this daughter and accommodation within the family household. After marriages of their daughters, the consanguineous parents continued to support all four families, and each of the four daughters produced one healthy child (maximally allowed number of children in China at the time). The most severely retarded daughter accidentally lost one child at birth. Today, the consanguineous couple has four grandchildren who are attending regular school and are expected to marry to biologically unrelated mates….”

could the cultural revolution have encouraged cousin marriages during the time period in china? at least in some sectors? weird.
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weregilds. did you know that weregild payments were made directly from one clan/kindred member to his corresponding clan/kindred member in the other clan/kindred (whichever was the aggrieved clan)? i didn’t.

i always imagined that all the weregild payments were sorta pooled together and passed from one clan to the other, but no … the father in one clan paid directly the father in the other clan, the father’s brother in one clan paid directly the father’s brother in the other clan, and so on and so forth. at least that’s how it was done in iceland … at least according to phillpotts [pg. 13]:

“Each class pays to the corresponding class of the opposite side, thus the father, son and brother of the slayer pay to the corresponding kinsmen of the slain. It is to be observed that the slayer pays nothing, the assumption being that he was exiled and his goods forfeited.”

huh.
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i mentioned over here that edmund i (922–946) seems to have been one of the first anglo-saxon/english kings to have really tried to put an end to the traditional blood feuds in england (which were tied to the weregild payments — see above — if the weregild wasn’t paid when someone was slain, the aggrieved clan/kindred had the right to exact revenge on the slayer’s clan/kindred). re. one of his law codes (from phillpotts – pgs. 218-19):

“Eadmund’s secular laws mark a notable advance in one respect: private warfare between families, as a result of a slaying, is to be stamped out, and the slayer alone is to bear the feud, if feud there is to be.

“II. 1. ‘If henceforth anyone kills any man, let him himself bear the feud, unless with the help of friends he pays full wergild within 12 months, whatever the birth (of the slain man,’ i.e. however high the wergild be).

“It must be remembered that a slayer is not involved in a feud unless he cannot or will not pay wergild; and if he can pay wergild there is no feud. So here we must assume that the slayer has not been able to produce the sum out of his own pocket, and that his kinsmen have been unable or unwilling to help him. That even this secondary liability of the kinsmen is purely voluntary is seen from the next clause:

“1. ‘If the *mægð* [kindred/extended family] forsakes him, and will not pay for him, then I will, that all the *mægð* be without feud, save the actual delinquent, if they give him thereafter neither food nor protection.

“2. ‘If however thereafter any one of his kinsmen shelter him, then let him be liable to the king for all that he possesses, and bear the feud with the *mægð* (of the slain), for they (the kinsmen) had before forsaken the slayer.

“3. ‘If however one of the other *mægð* takes vengeance on any other man than the actual delinquent, let him be outlaw to the king and to all his (the king’s) friends, and lose all that he possesses.'”

so edmund is the earliest example i know of in england of the state trying to position itself in between all of the homicidal lunatics in order to put an end to the violence. he (or the crown, i suppose) would pay the weregild if a clan/kindred wouldn’t in order to stop a blood feud from erupting.

edmund didn’t live very long though — he died (heh) in a fight when he was just 26 — so i don’t know how well-enforced his edict ever was.

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italy – reversal of fortune?

who knows?

but italy could be another place to look for a possible rapid inbreeding drop-off/rapid iq increase connection (see yesterday’s post) just ’cause the consang data are available. and they did, indeed, have a pretty rapid decrease in cousin marriage rates — at least in northern italy — not so much in the south. (i can’t think of any other examples where consang data are readily available — i mean without delving into church records or something like that.)

no idea if there are any early iq data available for italy, though. i won’t be looking for them (iq questions? – meh) — just wanted to let anyone who might be interested know that the numbers for the drop in inbreeding do exist for italy. (^_^)

look for the consang data here: Consanguinity, Inbreeding and Genetic Drift in Italy (tables also available here).

i put together a table of the first and last lustra in cavalli-sforza’s data set for a previous post, but there are data for each lustrum in between, too. you can get an idea of the scale of the drop-off (in the regions where there was a drop-off) from my nifty table:

previously: japan – reversal of fortune?

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japan – reversal of fortune?

a couple of months ago, greg cochran wrote about how a population (any given population) might raise its average iq quickly — like over two or three generations. one possible method, he suggested, was to quit inbreeding. here’s what he said:

“I’ve been thinking, off and on, about sudden changes in the cognitive abilities of populations: groups low suddenly scoring much higher or lower on a time scale too short to be explained by selection: say, three generations or less…. I can think of two perfectly feasible strategies that *would* cause significant one-generation increases in intelligence, in certain populations. Iodine supplementation, in places where it’s short, has a big payoff…. The other practical, low-tech strategy would be stopping cousin marriage. The next generation would be in much better shape, since the children of first cousins take a substantial IQ hit – maybe six points or so.“

i think i may have stumbled across an example of a population rapidly dropping cousin marriage and, also very rapidly, gaining iq points.

japan.

yesterday, i was working on a completely different post about japan and cousin marriage, when i rediscovered this [pg. 30] (click on chart for LARGER version):

that’s the decline in the average national consanguinity rates in japan from 1947 to the early-1980s. but the consang rates were even higher in the 1910s-1920s at 22.4% [pg. 29] (and who knows how high the rates might’ve been even further back?), so the chart above should look something more like this (pardon my crayola — and note that i just eyeballed it — click on chart for LARGER version):

when i rediscovered this yesterday, i remembered what greg had written, and got to wondering if there were any historic data for japanese iqs and if there’d been any changes in those iqs over time. so i googled (as one does) … and found this:

The Rise of National Intelligence: Evidence from Britain, Japan and the U.S.A. [pdf] – lynn and hampson.

from that article [pgs. 27-31]:

“It has been possible to find five studies providing evidence on the secular trend of intelligence in Japan for the post World War II period….

“(1) Ushijima’s study (1961)….

“Here the Ushijima intelligence test was administered to 1365 children in 1953 and to a comparable sample of 1370 children in 1960 with the objective of determining any change in the mean over this relatively short period. The children were aged 9-15 years.

“(i) All age groups show a rise in scores for all abilities. The overall mean increase was 0.66 standard deviations, the equivalent of 9.9 IQ points, and representing an IQ gain of 14.1 IQ points per decade. This is of course a very considerable increase and much greater than anything found in either Britain or the U.S.A.

“(ii) The IQ increases are in general greater among the younger age groups than among the older….”

see my crayola chart above. kids who were fifteen in 1953 would’ve been born way back in 1938 when the consang rates were above 15% — maybe 17 or 18% (remember, i just eyeballed it, so this is a complete guess really) — while kids who were nine in 1953 would’ve been born in 1944 when consang rates were hovering right around 15%, in other words lower. same for the later cohort from 1960: fifteen year olds would’ve been born in 1945, nine years old in 1951. the younger the kids in the cohorts, the less chances their parents were related.

more from the article…

“(2) Kaneko’s study (1970)….

“Kaneko’s invetigation of a possible rise in the scores on this test was carried out in 1963….

“Hence the mean IQ in these schools has risen 10.38 IQ points over the 9-yr period … represents an IQ gain of 11.4 IQ points per decade. This figure is evidently broadly similar to the rise of 14.1 IQ points per decade for 1953-1960 found by Ushijima and confirms a very considerable rate of IQ gain in Japan in these early post World War II years.

“(3) Sano’s study (1974)….

“It will be seen that in all samples there were considerable increases in mean IQ from 1954 to 1972. The increases appear to be a little greater among the city children than among those from the prefrecture. When the results for 10- and 11-yr olds are combined, city children gained 18.04 IQ points and prefrecture children 15.07 IQ points….”

that the city children had greater gains than the rural kids is not surprising if inbreeding is the factor making the difference here. even up to the 1980s, consanguinity rates have been quite a bit lower in urban areas in japan as compared to rural areas (see table in this post for example). (more on this soon in that upcoming post on japan.)

“The average of the two gains is 16.56 IQ points, representing a gain of approx. 9.15 IQ points per decade for the entire sample.

“Sano also considered the question of whether the IQ gains in Japan have been increasing at a constant rate. For this he used Kaneko’s 1964 data which were available for two of the schools. He calculated that the increase in mean IQ was 10.47 points for 1954-1963 and 3.42 for 1963-1972…. ([I]t will also be noted that the gain of 10.47 IQ points for 1954-1963 is closely similar to Kaneko’s figure of 10.38 for the same period.)

“It is apparent therefore that there was a considerable deceleration in the rate of increase in intelligence over the period 1954-1972….”

again, see my crayola chart. the decline in cousin marriage rates is much sharper in the decades preceding 1954 than during those preceding 1963. in other words, there was a deceleration in the reduction of cousin marriages over time, so perhaps we shouldn’t be surprised at a deceleration in the increases in iq over time.

“(4) Wechsler studies….

“Thus after making these adjustments we have Japanese mean IQs of 101.9 for 1951 and 107.4 for 1975. Hence over this 24-yr period (1951-1975) the Japanese mean IQ increased by 5.5 IQ points relative to the American IQ…. This represents a Japanese IQ gain of 5.75 IQ points per decade. This rate of increase for the period of 1951-1975 is somewhat less than Sano’s result of a 9.15 IQ point per decade increase over approximately the same period (1954-1972)….

“A second Japanese study using the WISC and WISC-R is also available (Anon, 1981)…. This gives a rise of 20.03 IQ points over the 24-yr period, making 8.34 IQ points per decade….”

lynn and hampson conclude:

“The conclusion of the Japanese studies is as follows. Two studies of the early post World War II period show substantial IQ gains of 9.9 and 11.4 IQ points per decade. Three studies of a longer period from approx. 1950-1975 show lower IQ gains of 9.1, 8.3 and 5.7 IQ points per decade, giving an average gain of 7.7 IQ points per decade. Since the early part of this period was characterized by a greater rate of gain, it appears that since around 1960 the IQ gains in Japan have decelerated to approx. 5 IQ points per decade….

“It is not particularly surprising that the Japanese gains should have been the greatest of the three countries. Japan was a relatively underdeveloped country in the 1930s with a per capita income about one eighth of that of the U.S.A.”

but the country was probably relatively underdeveloped because the japanese had a lower average iq at the time, and it’s since increased phenomenally … due to the sharp and rapid decline in inbreeding in japan? and so has their economic success obviously.
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i’d be curious to know two things:

– why did the japanese quit marrying their cousins? was there some official policy out there discouraging it — as part of their general modernization, “be more like the westerners” move? did the people just naturally adopt it as part of that westernization package? was it connected to christianity in japan? (japanese catholics historically had lower first cousin marriage rates than other religious groups — i’ll get to this in my upcoming post on japanese cousin marriage — the one that i was working on yesterday!). was it related to industrialization and urbanization? all of the above? none of the above?

– has something similar happened in china and/or korea (or elsewhere for that matter — i mean in modern times)? the cousin marriage rates for china are reportedly very low — today — but i’m pretty sure they were much higher in the past — even the recent past (see mating patterns in asia series below ↓ in the left-hand column), but i don’t have as good data for china as what i’ve presented here for japan. but inquiring minds want to know!

see also: Reversal of Fortune

previously: historic mating patterns in japan

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