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Screenshot 2016-05-11 12.07.21

Screenshot 2016-05-11 12.20.14 No time to comment. Yes, the hits with SNPs are cool. But look at all the functional associations and analysis in this paper! Some serious biology in this. The figure from the paper to the left which shows how the genes associated with this SNP hits are expressed in different tissue/types and organs. These are the biggest effect SNPs for years of education in the genome, so it makes sense that they’d be way over-expressed in the brain. It is definitely more convincing to those who might be skeptical a priori than some statistically robust associations (well, it should be more convincing at least).

Genome-wide association study identifies 74 loci associated with educational attainment:

Educational attainment is strongly influenced by social and other environmental factors, but genetic factors are estimated to account for at least 20% of the variation across individuals1. Here we report the results of a genome-wide association study (GWAS) for educational attainment that extends our earlier discovery sample1, 2 of 101,069 individuals to 293,723 individuals, and a replication study in an independent sample of 111,349 individuals from the UK Biobank. We identify 74 genome-wide significant loci associated with the number of years of schooling completed. Single-nucleotide polymorphisms associated with educational attainment are disproportionately found in genomic regions regulating gene expression in the fetal brain. Candidate genes are preferentially expressed in neural tissue, especially during the prenatal period, and enriched for biological pathways involved in neural development. Our findings demonstrate that, even for a behavioural phenotype that is mostly environmentally determined, a well-powered GWAS identifies replicable associated genetic variants that suggest biologically relevant pathways. Because educational attainment is measured in large numbers of individuals, it will continue to be useful as a proxy phenotype in efforts to characterize the genetic influences of related phenotypes, including cognition and neuropsychiatric diseases.

• Category: Science • Tags: Genomics, IQ 
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Citation: Common genetic variants influence human subcortical brain structures, Nature (2015) doi:10.1038/nature14101

Citation: Common genetic variants influence human subcortical brain structures, Nature (2015) doi:10.1038/nature14101

Here’s what we know. Intelligence, as defined by a general factor which explains variation across a range of cognitive tasks, is substantially heritable, with a narrow sense heritability on the order of 0.25 to 0.75 depending on who you talk to and what context.* Intelligence itself exhibits correlations with other traits, from those of social importance, such as education, as well as biological parameters, such as brain size. Additionally, the effect size of genetic variants associated with general intelligence are likely to be very small. This means that you should be immediately skeptical of claims that a common variant segregating in the population explains a large proportion of the variation in intelligence within the population. The history of this area of research, which goes back to linkage studies, is one of non-reproducibility. Large effect quantitative trait loci should already have been picked up by linkage studies decades ago, so I am usually rather skeptical when this old wine is presented again in a genomic guise. In short, the genetic architecture of general intelligence is likely to resemble height, with many loci of small effect.**

This is what Rietveld et al. found last fall in Common genetic variants associated with cognitive performance identified using the proxy-phenotype method. The same sizes were on the order of 10,000 to 100,000 within this study. The top associations within this study explain less than 1% of the variation within the data. It seems likely that the largest effect alleles which influence intelligence variation are about an order of magnitude smaller in impact than those for height. A new paper in Nature, Common genetic variants influence human subcortical brain structures, looks at the morphology of the brain, synthesizing imaging, cognitive neuroscience, and genomics. Here’s the abstract:

…To investigate how common genetic variants affect the structure of these brain regions, here we conduct genome-wide association studies of the volumes of seven subcortical regions and the intracranial volume derived from magnetic resonance images of 30,717 individuals from 50 cohorts. We identify five novel genetic variants influencing the volumes of the putamen and caudate nucleus. We also find stronger evidence for three loci with previously established influences on hippocampal volume and intracranial volume. These variants show specific volumetric effects on brain structures rather than global effects across structures. The strongest effects were found for the putamen, where a novel intergenic locus with replicable influence on volume (rs945270; P = 1.08 × 10−33; 0.52% variance explained) showed evidence of altering the expression of the KTN1 gene in both brain and blood tissue. Variants influencing putamen volume clustered near developmental genes that regulate apoptosis, axon guidance and vesicle transport. Identification of these genetic variants provides insight into the causes of variability in human brain development, and may help to determine mechanisms of neuropsychiatric dysfunction.

Paul Thompson was involved in the research, so I am confident that it was be done thoroughly (and the author list is long enough that I hope they checked for obvious problems!). To correct for population stratification within this European sample they looked at the top for dimensions of variation, and used a regression model to capture other variables which might be confounded with the SNPs in question. The small proportion of variation explained actually increases my confidence, in that it seems to be in the same order of magnitude as the type of studies looking at endophenotypes.

Because of their sheer number I doubt that there’s a great short term likelihood of annotating all the genes responsible for variation in intelligence. Rather, I wonder if the ultimate goal is something similar to what occurred with statins. Find a small effect locus, and target a drug at that locus to help cure cognitive illnesses such as schizophrenia. It stands to reason that the same loci which impact general intelligence would also shape cognitive phenotypes which we term pathological.

* So if heritability in the narrow sense is 0.50 that means half the variation in intelligence in the population can be explained by variation of genes in the population. By way of comparison, height is 0.80 to 0.90 heritable in the narrow sense in the developed world. This does not mean that the correlation between parents and offspring is 0.80 or 0.90 for height. In fact the correlation is closer to 0.50 for height between parents and offspring and also between siblings.

** An alternative minority viewpoint is many rare alleles of somewhat larger effect.

• Category: Science • Tags: Genomics, GWAS, IQ 
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twohigIQkidsThe new paper in PNAS, Common genetic variants associated with cognitive performance identified using the proxy-phenotype method, has resulted in a fair amount of reaction. One of the major things that people grasp onto is that the effects of the variants in question are extremely smaller (here’s an FAQ for the current paper). Each variant is associated with a 0.3 increment or decrement in IQ, where the average IQ is 100 and the standard deviation is ~15 points. These results are not surprising, as the problems with earlier attempts to fix upon a genetic region which explains a great deal of variation in intelligence in the normal range have not been successful (i.e., they fail replication, so probably just a false positive). Taking these results at face value many have wondered what the big deal is, as the associations here have such a small impact.

First, a small effect does not preclude important practical consequences. The locus HMGCR has been implicated in variation in cholesterol levels at 0.1 standard deviation, but that is the locus that statins target. Does this mean that we can make a “genius pill” in the future? I’m moderately skeptical, and obviously there are major ethical issues with this. But, this sort of research shows that it may be possible, and in this big wide world of ours knowledge is hard to keep under control. As a normative matter I’m in the always better to know category for almost everything. So big surprise I have no issues with this line of research.

There is a second issue of more practical relevance, and that is that many people wish to reject a heritable component for intelligence. To be clear it is robust science that intelligence is 0.3 to 0.7 heritable. That means that 30 to 70 percent of the variation in intelligence in the population is due to variation in genes. Because the trait is highly polygenic, on the order of thousands of loci controlling variation in intelligence, it is difficult to pick any particular signal. But very few scientists are under the illusion that intelligence is not at least moderately heritable. A good analogy here is height, which is highly heritable, and controlled by many genes of small effect (the genetic architecture here is moderately more tractable from what I can tell). But for many people, especially in the public, they “need a gene.” It makes the abstract, ratio of additive genetic variance over total phenotypic variance, concrete.

But I find it more interesting that some are spinning this as a support for the low heritability of IQ, and the importance of environment. Personally I wish for my children that environment was less important, not more. The reason is simple: in a behaviour genetic sense we really don’t know what we’re talking about when we say “environment.” The Invisible Gorilla has a lot of illustrations on how tools and techniques which make us “smarter” really don’t work (or, their efficacy has not been scientifically validated). The same for infants and children. Obviously malnutrition and abuse are going to cause problems in relation to development, but the sort of “enriching” activities and practices de rigueur among upper middle class parents probably are irrelevant to the final outcome of the trait in question (this is clear when you look at the high level of variation cross-culturally, with some “best practices” being contradictory, but the results are the same nonetheless).

The-Nurture-Assumption-Harris-Judith-Rich-9780684857077 The best way to think about it is that “environment” is just noise in your model. It is the genetic component you can control, or at least use to predict. Though heritability is a population wide statistic, it has some relevance for individuals. The mid-parent value of a trait for the parents can help you gauge your expectations for your offspring. When you standardize for sex the height of parents can tell you whether to expect tall or short offspring. This is not guaranteed, as there is a high standard deviation around the expected value, even for a highly heritable trait like height (the correlation between full-siblings for height is ~0.50). But, it does load the die. The correlation of IQ between full-siblings is also on the order of ~0.50. Remember here that environment, the noise parameter, changes your expected value. Since this isn’t heritable it drives the phenotype of the offspring back to the population mean. If IQ is less heritable, say 0.30, then if you and your spouse are deviated away from the mean, you can expect your children to regress back to the population mean, since they won’t inherit the magic mix of factors which resulted in high IQ. In contrast, if IQ is heritable on the order of 0.70, then you can update your expectations so that your children will be more likely to resemble you, assuming you are deviated from the norm.

Perhaps I’m a narcissist, but I want my children to be like me in cognitive profile. It makes it easier for me to understand where they are coming from. If I thought that I could as a parent control the environmental outcomes with a high degree of certainty I might be more sanguine about low heritability, but that’s not my hunch about this trait. Low heritability of intelligence to me connotes a flight back to mediocrity and a total lack of control. High heritability in contrast allows one to reclaim control, because you choose your spouse and you have a sense of their realized phenotype. Obviously this is conditional on where you stand on the distribution. So I emphasize the “I.” But many people at the higher end of the IQ distribution seem to want lower heritability, because they perceive that they can control outcomes through manipulation of environment. I’m not confident of this at all. Sometimes flighty academic abstractions can have real consequences in the choices we make in this world. This is one.

• Category: Science • Tags: IQ 
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Common genetic variants associated with cognitive performance identified using the proxy-phenotype method:

We identify several common genetic variants associated with cognitive performance using a two-stage approach: we conduct a genome-wide association study of educational attainment to generate a set of candidates, and then we estimate the association of these variants with cognitive performance. In older Americans, we find that these variants are jointly associated with cognitive health. Bioinformatics analyses implicate a set of genes that is associated with a particular neurotransmitter pathway involved in synaptic plasticity, the main cellular mechanism for learning and memory. In addition to the substantive contribution, this work also serves to show a proxy-phenotype approach to discovering common genetic variants that is likely to be useful for many phenotypes of interest to social scientists (such as personality traits).

Ewen Callaway has a write up in Nature. The issue here is that it’s been evident for the past 10 years or so intelligence variation is not due to alleles segregating at high frequencies with at least modest effects, so they’re hard to pick up in association studies (contrast with pigmentation, which is mostly controlled by a number of loci on the order of 10). Some, such as Kevin Mitchell, don’t think that common variants are the way to go, period. Common as in variants which are found across the population, even if their effect on the trait is very small. This group disagrees. One of the authors, Peter Visscher, has written up his own view of this line of research, Intelligence inheritance – three genes that add to your IQ score:

This study of normal variation in cognitive performance confirms that there is no gene with a large effect on this trait. There is no “gene for intelligence” – instead, cognitive performance is likely to be influenced by thousands of genes, each having a small effect.

While the individual effect of the genetic variants are extremely small, their identification may lead to knowledge of the biological pathways involved in cognitive performance and cognitive ageing. This insight may eventually lead us into a better understanding of the mechanism involves in memory loss and dementia.

Finally, because individual gene effects are small, an implication of the study is that even larger studies, for example on millions of people, will lead to the discovery of many more gene variants.

In sum, because intelligence is at least moderately heritable, but the causal variants are so diffuse and numerous, the best bet for having a smart child is picking a spouse with a deviated phenotype. Look for smart people to marry….

• Category: Science • Tags: IQ 
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From what people tell me IQ is a social construct which is totally controlled by environmental variables, and so is not of much interest. But curiously the other day when I looked at the hits on this website over the past 3+ years a huge number of highly accessed posts had to do with intelligence and IQ. In any case, seeing as how many readers of this weblog are having, or going to have, children at a relatively advanced age (in an evolutionary sense) I thought this post would be a good public service announcement. Below is a figure from a preprint posted on arXiv, The effect of paternal age on offspring intelligence and personality when controlling for paternal trait level (via Haldane’s Sieve):

I’m assuming that there’s initially an upward slope because more intelligent men tend to reproduce later (you can confirm this by looking at AGEKDBRN and WORDSUM variables in the GSS). Once you control for education and IQ the effect disappears. But there isn’t a downward slope, which you might predict if the hypothesis of increased mutational load was valid. IQ is a high polygenic trait with variation controlled likely by thousands of genes, but one would presume that large effect de novo variants could change that architecture.

As always, more data is welcome.

(Republished from Discover/GNXP by permission of author or representative)
• Category: Science • Tags: Behavior Genetics, IQ, Psychology 
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Prompted by a comment below I was curious as to the correlation between intelligence and income. To indicate intelligence I used the GSS’s WORDSUM variable, which has a ~0.70 correlation with IQ. For income, I used REALINC, which is indexed to 1986 values (so it is inflation adjusted) and aggregates the household income. Finally, I limited my sample to non-Hispanic whites over the age of 30 (for what it’s worth, this choice also limited the data set to respondents from the year 2000 and later).

The results don’t get at the commenter’s assertions, because 10 out of 10 on WORDSUM does not imply that you’re that smart really. But the trendline is suggestive. Note that aggregated 0-4 because the sample size at the lower values is small indeed.

(Republished from Discover/GNXP by permission of author or representative)
• Category: Science • Tags: Data, Data Analysis, GSS, IQ 
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A few people have forwarded me this paper, Identification of common variants associated with human hippocampal and intracranial volumes:

…Whereas many brain imaging phenotypes are highly heritable…identifying and replicating genetic influences has been difficult, as small effects and the high costs of magnetic resonance imaging (MRI) have led to underpowered studies. Here we report genome-wide association meta-analyses and replication for mean bilateral hippocampal, total brain and intracranial volumes from a large multinational consortium. The intergenic variant rs7294919 was associated with hippocampal volume (12q24.22; N = 21,151; P = 6.70 × 10−16) and the expression levels of the positional candidate gene TESC in brain tissue. Additionally, rs10784502, located within HMGA2, was associated with intracranial volume (12q14.3; N = 15,782; P = 1.12 × 10−12). We also identified a suggestive association with total brain volume at rs10494373 within DDR2 (1q23.3; N = 6,500; P = 5.81 × 10−7).

Look at the sample sizes. Beware of behavior genomics with small sample sizes. Paul Thompson, one of the many authors of this paper, is giving media interviews. To me that’s a good sign, as he’s a very smart guy. He has some confidence in this study. Here’s the section which is resulting in the forwards:

… In addition, the C allele of rs10784502 is associated, on average, with 9,006.7 mm3 larger intracranial volume, or 0.58% of intracranial volume per risk allele and is weakly associated with increased general intelligence by approximately 1.29 IQ points per allele.

I’m a homozygote for the T allele for what it’s worth. But that’s not surprising. Look at the population distribution of the C allele from the HapMap:

I think CD-CV is played out when it comes to IQ or height. Note that the gene in which this SNP is located, HMGA2, is also implicated in height variation. In fact, aside from pathological mutations, this locus may have the largest effect height and IQ polymorphisms in replicable studies (genetic and genomic, linkage and GWAS, IQ studies have a history of not being replicated, probably because of low power).

Update: See Luke Justins’ comment. My post above was rooted in a mild misipression due to read-post-and-dash. My bad. So we’ll see if the ‘endophenotype’ pans out.

(Republished from Discover/GNXP by permission of author or representative)
• Category: Science • Tags: Genetics, Genomics, Human Genetics, Human Genomics, IQ 
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Several readers have pointed me to this amusing story, Court OKs Barring High IQs for Cops:

A man whose bid to become a police officer was rejected after he scored too high on an intelligence test has lost an appeal in his federal lawsuit against the city.

“This kind of puts an official face on discrimination in America against people of a certain class,” Jordan said today from his Waterford home. “I maintain you have no more control over your basic intelligence than your eye color or your gender or anything else.”

Jordan, a 49-year-old college graduate, took the exam in 1996 and scored 33 points, the equivalent of an IQ of 125. But New London police interviewed only candidates who scored 20 to 27, on the theory that those who scored too high could get bored with police work and leave soon after undergoing costly training.

The average score nationally for police officers is 21 to 22, the equivalent of an IQ of 104, or just a little above average.

But the U.S. District Court found that New London had “shown a rational basis for the policy.” In a ruling dated Aug. 23, the 2nd Circuit agreed. The court said the policy might be unwise but was a rational way to reduce job turnover.

First, is the theory empirically justified? If so, I can see where civil authorities are coming from. That being said, it’s obvious that there are some areas where “rational discrimination” is socially acceptable, and others where it is not. The same arguments used to be applied to women, in terms of the actuarial probabilities that they would get pregnant and so have to leave the workforce. And disparate impact always looms large in the utilization of these sorts of tests.

Second, can’t you just fake a lower score on an intelligence test? Do police departments hire statisticians to smoke out evidence of conscious selection of incorrect scores? I doubt it. Jordan may be smart, but perhaps he lacks common sense if the upper bound for IQ was well known.

My initial thought was that an IQ of 104 seemed too low for a median police officer, but poking around it does seem plausible as a descriptive statistic. Honestly I don’t have much acquaintance with the police, so I’ll trust the scholars no this. That being said, is it in our social interest for police officers to be so average? I don’t know. Though is it in the social interest that someone with an IQ as high as Robert Jordan’s ends up a prison guard?

(Republished from Discover/GNXP by permission of author or representative)
• Category: Science • Tags: IQ, Psychology 
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Every time I use the WORDSUM variable from the GSS people will complain that a score on a 10-question vocabulary test is not a good measure of intelligence. The reality is that “good” is too imprecise a term. The correlation between adult IQ and WORDSUM = 0.71. The source for this number is a 1980 paper, The Enduring Effects of Education on Verbal Skills. I’ve reproduced the relevant table…

Estimated Correlations for Variables in a Model of Enduring Effects of Education for White, Native-Born People 25 to 72 Years Old in the Contemporary [1970s] United States
  Child IQ Age Sex Father’s Educ Father’s SEI Educ Adult IQ WORDSUM
Child IQ - 0 0 0.31 0.30 0.51 0.80 -
Age - - 0.026 -0.304 -0.130 -0.304 -0.42 -0.005
Sex - - - -0.054 0.058 0.050 0 -0.121
Father’s Educ - - - - 0.488 0.469 0.30 0.302
Father’s SEI - - - - - 0.347 0.31 0.285
Educ - - - - - - 0.66 0.511
Adult IQ - - - - - - - 0.71
WORDSUM - - - - - -   -

Obviously since the WORDSUM test was not given to those under 18 you can’t calculate the correlation between childhood IQ and WORDSUM score. Additionally, I suspect since 1980 there’s been a bit more cognitive stratification by education. I notice in the GSS sample that there are many older people, especially women, who have high WORDSUM scores but no college education. In the younger age cohorts this pattern is not as evident because if you are intelligent the probability is much higher that you’ll obtain a university education.

A correlation of 0.71 is not mind-blowing, there’s a significant difference between IQ and WORDSUM as they relate to each other linearly. But I think it’s good enough to get a sense that WORDSUM is a serviceable substitute for a more rigorous measure of g in lieu of any alternatives, and not so clumsy a proxy so as to be useless. Though that call is up to you, and readers are free to disagree with the methodology of the model used to obtain this correlation. Additionally, I would point out that WORDSUM is a subset of the vocabulary subsection of the Wechsler Adult Intelligence Scale. WORDSUM is in effect a slice of an IQ test.

I am bookmarking this post so that in the future I can simply place a link in the comment threads in response to objections to WORDSUM.

Note: Thanks to Bryan Caplan for pointing me to this paper.

Citation: Lee M. Wolfle, Sociology of Education, Vol. 53, No. 2 (Apr., 1980), pp. 104-114

(Republished from Discover/GNXP by permission of author or representative)
• Category: Science • Tags: Blog, Data, Data Analysis, GSS, IQ, WORDSUM 
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Steve Hsu has been interesting of late (interesting like Steve, not Malcolm). So, IQ, compression and simple models and If you’re so smart, why aren’t you rich?. For a theoretical physicist I find Steve to be eminently clear in his exposition of abstract topics (perhaps he has practice from having to talk to experimental physicists?).

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• Category: Science • Tags: IQ 
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A genome-wide study of common SNPs and CNVs in cognitive performance in the CANTAB:

Psychiatric disorders such as schizophrenia are commonly accompanied by cognitive impairments that are treatment resistant and crucial to functional outcome. There has been great interest in studying cognitive measures as endophenotypes for psychiatric disorders, with the hope that their genetic basis will be clearer. To investigate this, we performed a genome-wide association study involving 11 cognitive phenotypes from the Cambridge Neuropsychological Test Automated Battery. We showed these measures to be heritable by comparing the correlation in 100 monozygotic and 100 dizygotic twin pairs. The full battery was tested in 750 subjects, and for spatial and verbal recognition memory, we investigated a further 500 individuals to search for smaller genetic effects. We were unable to find any genome-wide significant associations with either SNPs or common copy number variants. Nor could we formally replicate any polymorphism that has been previously associated with cognition, although we found a weak signal of lower than expected P-values for variants in a set of 10 candidate genes. We additionally investigated SNPs in genomic loci that have been shown to harbor rare variants that associate with neuropsychiatric disorders, to see if they showed any suggestion of association when considered as a separate set. Only NRXN1 showed evidence of significant association with cognition. These results suggest that common genetic variation does not strongly influence cognition in healthy subjects and that cognitive measures do not represent a more tractable genetic trait than clinical endpoints such as schizophrenia. We discuss a possible role for rare variation in cognitive genomics.

David Goldstein is one of the authors. I wonder if this influenced his views on the evolution of intelligence.

(Republished from by permission of author or representative)
• Category: Science • Tags: IQ, Population Genetics 
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A reader points out that David Shenk is blogging genetics & IQ over at The Atlantic. If you have some free time to kill in comment sections, you might be interested. To get a flavor, a post titled The Truth About IQ has a footnote to Stephen Jay Gould’s Mismeasure of Man.

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• Category: Science • Tags: IQ 
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IQ Explains Some Of The Difference In Heart Disease Between People Of High And Low Socio-economic Status:

Authors of the study published in the European Heart Journal on 15 July…analysed data from a group of 4,289 former soldiers in the USA. They found that IQ explained more than 20% of the difference in mortality between people from socio-economically disadvantaged backgrounds compared to those from more advantaged backgrounds. Importantly, this was in addition to the classical, known risk factors for heart disease, such as smoking and obesity.

“The difference between the second and third analyses showed that IQ alone explained a further 23% of the differences in mortality between the higher and lower ends of the socio-economic spectrum, in addition to the other, known risk factors,” said Dr Batty. “IQ wasn’t a magic bullet in this study, but this psychological variable had additional explanatory power on top of the classic variables such as smoking, high blood pressure, high blood glucose and obesity. It has partially explained the differences in death from heart disease and all causes.”

…there could be three possible explanations for Dr Batty’s findings: “(i) intelligence might lead to greater knowledge about how to pursue healthy behaviours; (ii) intelligence may “cause” socioeconomic position, i.e. more intelligence leads to more education, income, occupational prestige . . .; and (iii) intelligence may be a marker for something else, and it is that something else, early life exposures, for example, that leads to mortality.”….

When correlations between socioeconomic status and health outcomes emerge, generally there is an assumption that the differences are due to disparate access to health care, or, more vaguely to the mysterious effect of low social status on someone’s health. Matt Ridley actually posited the second explanation in Genome. As noted above intelligence does not explain everything, but its role is unfortunately not considered all too often. If, for example, intelligence has some correlation with time preference, and time preference modulates one’s risk calculus, the causal chain which might result in disparate health outcomes is obvious. In The Myth of the Rational Voter Bryan Caplan has a reasonable number of references to the literature which show that the more intelligent may not be particularly rational in any absolute sense, but they are far more rational than the conventionally dull in a relative sense.

(Republished from by permission of author or representative)
• Category: Science • Tags: Human Biodiversity, IQ 
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As many have noted, The New Republic is now publishing perceptions that Sonia Sotomayor is not that intelligent. Granted, even if affirmative action played a role in her acceptance to Princeton and Yale law school, the fact that she graduated and passed the bar suggests a minimum threshold of ability. But that’s not good enough, it seems that many liberals would like someone who can go toe-to-toe with the conservatives on the court intellectually, and she doesn’t pass the grade on that elevated level. When the stakes are high, and a Supreme Court position is arguably one of the most powerful positions within the American government, the perceived marginal returns on more g become stark for those who would pooh-pooh it in other contexts.

Addendum: As noted in the comments, yes, it doesn’t take a genius to know how political confederates want you to rule. I happen to think that most moral & political reasoning is really moral & political rationalization. So the key is simply to find people who can argue in a crisp manner in favor of positions they already hold a priori. More generally I accept there is some systematic tendencies in terms of what the smart, as opposed to the dumb, believe, regardless of their ideology. See The Myth of the Rational Voter for examples. But let’s not confuse the signal for the noise.

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• Category: Science • Tags: IQ, Politics 
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Steve points me to a profile of Greg & Henry, with a focus on Jewish genetics & smarts.

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• Category: Science • Tags: IQ, Jews 
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Several people have emailed me (and emails and forward are appreciated by the way) about two articles in The New York Times about IQ. IQ Harmed by Epilepsy Drug in Utero, which Steve’s already commented on. And the most emailed article currently, Nicholas Kristof’s How to Raise Our IQ. Some of you who have been reading this blog since the beginning might have noticed that I long ago stopped talking much about psychometrics. Why? I’d rather not waste my time trying to convince smart people that they are actually smarter than stupid people. If I had a penny every time someone with an elite college education in the hard sciences explained that “they don’t believe in IQ”…. Of course, on the other hand these aren’t the huge majority of people. Many who were nerds or of high intelligence know that there’s a qualitative difference between themselves and the herd, in particular those from families with several siblings where psychometric variance is rather obvious. How much more “shared” can environment exactly get?

But in any case, many of the intelligent refuse to assent to the position that intelligence actually exists, and that it can be measured. A few conversations aren’t going change opinions here, as the opinions aren’t based on empirical data. Rather, it’s a theory to which one is socialized (and which socialization can reverse, but this requires a great deal of time investment which isn’t going to happen with most people). My own experience with the crowd that runs with Robin Hanson and Eliezer Yudkowsky is that 1) they tend toward the retarded end of social intelligence 2) are invariably accepting of, or open to, the reality of g. In other words, my assumption is that most people who “don’t believe in intelligence,” don’t for reasons of socialization, because they know the rewards built into the incentive structure of human groups for conformity. Of course, there is “believe,” and then there is believe. The same people who don’t believe in intelligence are proud of their GRE scores, convinced that Republicans and religious people have lower IQs, and outraged when the mentally deficient, as measured on IQ tests, are executed. This probably reflects some mental modularity. People might say they don’t believe in IQ, but the decisions they make are to some extent informed by the assumption that intelligence exists, and individuals vary. This shouldn’t be a surprise, our executive functions have only a loose control over the different subfunctions which define our cognition. Ironically it might reflect the limits of the conscious rationalin enforcing its well on subconsciously operating modules. The long arm of intelligence reaches only so far into the crevasses of one’s mind.

So the best way to increase the intelligence of your offspring? Fuse your gametes with someone intelligent! You don’t even have to believe in intelligence to do this, as many who do just this don’t. The main issue isn’t that people won’t be a position to fuse their gametes with individuals in the same range as themselves in terms of intelligence. Rather, it’s that they won’t let the fusion come to fruition!

(Republished from by permission of author or representative)
• Category: Science • Tags: IQ, Psychometrics 
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Follow up to the post below, Jake Young at Pure Pedantry has a thorough review.

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• Category: Science • Tags: IQ, Neuroscience 
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Positive association between cognitive ability and cortical thickness in a representative US sample of healthy 6 to 18 year-olds:

Neuroimaging studies, using various modalities, have evidenced a link between the general intelligence factor (g) and regional brain function and structure in several multimodal association areas. While in the last few years, developments in computational neuroanatomy have made possible the in vivo quantification of cortical thickness, the relationship between cortical thickness and psychometric intelligence has been little studied. Recently, cortical thickness estimations have been improved by the use of an iterative hemisphere-specific template registration algorithm which provides a better between-subject alignment of brain surfaces. Using this improvement, we aimed to further characterize brain regions where cortical thickness was associated with cognitive ability differences and to test the hypothesis that these regions are mostly located in multimodal association areas. We report associations between a general cognitive ability factor (as an estimate of g) derived from the four subtests of the Wechsler Abbreviated Scale of Intelligence and cortical thickness adjusted for age, gender, and scanner in a large sample of healthy children and adolescents (ages 6–18, n = 216) representative of the US population. Significant positive associations were evidenced between the cognitive ability factor and cortical thickness in most multimodal association areas. Results are consistent with a distributed model of intelligence.

See ScienceDaily.

(Republished from by permission of author or representative)
• Category: Science • Tags: IQ 
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Readers of this weblog from back in 2002 know that we used to point to Paul Thompson’s research. So see this, Genetics of Brain Fiber Architecture and Intellectual Performance:

The study is the first to analyze genetic and environmental factors that affect brain fiber architecture and its genetic linkage with cognitive function. We assessed white matter integrity voxelwise using diffusion tensor imaging at high magnetic field (4 Tesla), in 92 identical and fraternal twins. White matter integrity, quantified using fractional anisotropy (FA), was used to fit structural equation models (SEM) at each point in the brain, generating three-dimensional maps of heritability. We visualized the anatomical profile of correlations between white matter integrity and full-scale, verbal, and performance intelligence quotients (FIQ, VIQ, and PIQ). White matter integrity (FA) was under strong genetic control and was highly heritable in bilateral frontal….bilateral parietal…and left occipital…lobes, and was correlated with FIQ and PIQ in the cingulum, optic radiations, superior fronto-occipital fasciculus, internal capsule, callosal isthmus, and the corona radiata…for PIQ, corrected for multiple comparisons). In a cross-trait mapping approach, common genetic factors mediated the correlation between IQ and white matter integrity, suggesting a common physiological mechanism for both, and common genetic determination. These genetic brain maps reveal heritable aspects of white matter integrity and should expedite the discovery of single-nucleotide polymorphisms affecting fiber connectivity and cognition.

Here’s the summary at ScienceDaily.

(Republished from by permission of author or representative)
• Category: Science • Tags: IQ, Neuroscience 
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Low-carbohydrate weight-loss diets. Effects on cognition and mood:

To examine how a low-carbohydrate diet affects cognitive performance, women participated in one of two weight-loss diet regimens. Participants self-selected a low-carbohydrate (n = 9) or a reduced-calorie balanced diet similar to that recommended by the American Dietetic Association (ADA diet) (n = 10). Seventy-two hours before beginning their diets and then 48 h, 1, 2, and 3 weeks after starting, participants completed a battery of cognitive tasks assessing visuospatial memory, vigilance attention, memory span, a food-related paired-associates a food Stroop, and the Profile of Moods Scale (POMS) to assess subjective mood. Results showed that during complete withdrawal of dietary carbohydrate, low-carbohydrate dieters performed worse on memory-based tasks than ADA dieters. These impairments were ameliorated after reintroduction of carbohydrates. Low-carbohydrate dieters reported less confusion (POMS) and responded faster during an attention vigilance task (CPT) than ADA dieters. Hunger ratings did not differ between the two diet conditions. The present data show memory impairments during low-carbohydrate diets at a point when available glycogen stores would be at their lowest. A commonly held explanation based on preoccupation with food would not account for these findings. The results also suggest better vigilance attention and reduced self-reported confusion while on the low-carbohydrate diet, although not tied to a specific time point during the diet. Taken together the results suggest that weight-loss diet regimens differentially impact cognitive behavior.

Also at ScienceDaily. Small N’s. What were the N’s on the Creatine studies???

(Republished from by permission of author or representative)
• Category: Science • Tags: IQ 
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Razib Khan
About Razib Khan

"I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. If you want to know more, see the links at"