Dysgenic trend in educational attainment in Iceland

This is a very important study which (if replicated in other countries, with more complex demography, less complete genealogy, but much larger sample sizes) bodes ill for the future. It should also prompt studies of the evolution of cognitive ability at longer time scales (beyond traditional genealogy). Much has been written about genetic differences between the human races, for example, with the "cold winters" theory proposed to explain them as a product of natural selection.

But, this assumes that these differences are long-standing and date to the time that modern humans left Africa for more northern (and colder) latitudes. There is good reason to doubt this explanation: ancient writers of the Mediterranean classical world predictably identified themselves as the optimum, but remarked on the spiritedness and dullness of northerners in contrast to the lack of spirit but intelligence of southerners, which seemingly contradicts present-day cognitive ability distributions. But, it may very well be that cognitive ability has changed dramatically over this time period; certainly the fact that one of its correlates (educational attainment) can change in a small isolated population (Icelanders) over a century does not add to one's confidence that this is a trait that has been stable for millennia (let alone since the time of harsh Ice Age winters). As more markers are discovered to predict cognitive ability in human populations and it becomes easier to study ancient ones, it might be possible to track this trait convincingly.

On the positive side, the pliability of the genetic influences on cognition undercuts arguments that possible differences in this trait among human races and ethnic groups are solidly entrenched and unalterable,. Rather they may be accidents of recent evolution which could, in principle, be reversed.


PNAS doi: 10.1073/pnas.1612113114

Selection against variants in the genome associated with educational attainment

Augustine Kong et al.

Epidemiological and genetic association studies show that genetics play an important role in the attainment of education. Here, we investigate the effect of this genetic component on the reproductive history of 109,120 Icelanders and the consequent impact on the gene pool over time. We show that an educational attainment polygenic score, POLYEDU, constructed from results of a recent study is associated with delayed reproduction (P less than 10−100) and fewer children overall. The effect is stronger for women and remains highly significant after adjusting for educational attainment. Based on 129,808 Icelanders born between 1910 and 1990, we find that the average POLYEDU has been declining at a rate of ∼0.010 standard units per decade, which is substantial on an evolutionary timescale. Most importantly, because POLYEDU only captures a fraction of the overall underlying genetic component the latter could be declining at a rate that is two to three times faster.

Link

Educational achievement predicted by DNA

Predicting 9% of educational achievement from DNA is quite good. The authors used genotype arrays, so there's obvious room for growth in rare variation that is not covered by such arrays.

I wonder when the public and policymakers will get wind of the fact that educational achievement is highly heritable and can even be somewhat predicted with existing DNA technology.

Genetic egalitarianism is an edifice on which too much has been invested and I doubt that it will go down without a fight. It's of course a great idea to optimize learning for the students you've got. But, at the end of the day there's only so much you can do to foster achievement in a trait that is mostly genetically determined.

Molecular Psychiatry advance online publication 19 July 2016; doi: 10.1038/mp.2016.107

Predicting educational achievement from DNA

S Selzam et al.

A genome-wide polygenic score (GPS), derived from a 2013 genome-wide association study (N=127,000), explained 2% of the variance in total years of education (EduYears). In a follow-up study (N=329,000), a new EduYears GPS explains up to 4%. Here, we tested the association between this latest EduYears GPS and educational achievement scores at ages 7, 12 and 16 in an independent sample of 5825 UK individuals. We found that EduYears GPS explained greater amounts of variance in educational achievement over time, up to 9% at age 16, accounting for 15% of the heritable variance. This is the strongest GPS prediction to date for quantitative behavioral traits. Individuals in the highest and lowest GPS septiles differed by a whole school grade at age 16. Furthermore, EduYears GPS was associated with general cognitive ability (~3.5%) and family socioeconomic status (~7%). There was no evidence of an interaction between EduYears GPS and family socioeconomic status on educational achievement or on general cognitive ability. These results are a harbinger of future widespread use of GPS to predict genetic risk and resilience in the social and behavioral sciences.

Link

Generalist Genes influence both reading and math ability

Nature Communications 5, Article number: 4204 doi:10.1038/ncomms5204

The correlation between reading and mathematics ability at age twelve has a substantial genetic component

Oliver S. P. Davis

Dissecting how genetic and environmental influences impact on learning is helpful for maximizing numeracy and literacy. Here we show, using twin and genome-wide analysis, that there is a substantial genetic component to children’s ability in reading and mathematics, and estimate that around one half of the observed correlation in these traits is due to shared genetic effects (so-called Generalist Genes). Thus, our results highlight the potential role of the learning environment in contributing to differences in a child’s cognitive abilities at age twelve.

Link

Inbreeding and cognitive ability

From the paper:

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.1, 2, 3 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 findings 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 lesser 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. 

Genetic variants were found to have a slight (though significant) reduction in minor allele frequency across the genome in individuals in the top quartile of general cognitive ability compared with those in the bottom quartile (means of 21823 and 21824), which in turn could lead to increased homozygosity by chance. This could indicate that these individuals descend from subtly different ancestral populations that experienced loss of variation. This difference in ancestry may be correlated with either genetic variants for improved cognitive ability, or with social or environmental backgrounds that lead to higher cognitive ability, though our analysis of FROH corrected for socio-economic status and population stratification. Another potential explanation is that the reduced minor allele frequency in the high cognitive ability is reflective of the less frequent allele being deleterious due to selection against it. As a result, these high-functioning individuals could benefit from having more major alleles at fixation and a reduced burden of rarer deleterious variants. 

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.

European Journal of Human Genetics , (17 July 2013) | doi:10.1038/ejhg.2013.155

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

Robert A Power et al.

The consequence of reduced cognitive ability from inbreeding has long been investigated, mainly restricted to cousin–cousin marriages. Molecular genetic techniques now allow us to test the relationship between increased ancestral inbreeding and cognitive ability in a population of traditionally unrelated individuals. In a representative UK sample of 2329 individuals, we used genome-wide SNP data to estimate the percentage of the genome covered by runs of homozygous SNPs (ROH). This was tested for association with general cognitive ability, as well as measures of verbal and non-verbal ability. Further, association was tested between these traits and specific ROH. Burden of ROH was not associated with cognitive ability after correction for multiple testing, although burden of ROH was nominally associated with increased non-verbal cognitive ability (P=0.03). Moreover, although no individual ROH was significantly associated with cognitive ability, there was a significant bias towards increased cognitive ability in carriers of ROH (P=0.002). A potential explanation for these results is increased positive assortative mating in spouses with higher cognitive ability, although we found no evidence in support of this hypothesis in a separate sample. Reduced minor allele frequency across the genome was associated with higher cognitive ability, which could contribute to an apparent increase in ROH. This may reflect minor alleles being more likely to be deleterious.

Link

From Skulls and Scans (Monge & Aguirre @ Penn)

An interesting talk on the uses and abuses of science.

 

I find this excerpt particularly offensive to my open science sensibilities (29:40 ff):

We were able to, after 10 years, actually get it published in PLoS Biology, took us 10 years, yeah, we were rejected every single place that we ever sent the manuscript. I find that interesting too, and we even had editors say to us that they didn't want to say anything against Stephen J Gould. Isn't that interesting?

Interesting indeed. As I wrote in my review of the Lewis et al. (2011) paper on the Gould vs. Morton affair:

It is remarkable that 30 years after the Mismeasurement of Man Gould's errors are uncovered. Why did it take so long? While one could understand why the (totally unfounded but -on the surface- plausible) idea of measurement bias could have gone unnoticed until someone actually re-measured the skulls, but the statistical error that Gould committed was there for anyone to see.

We now know why it took at least 10 out of these 30 years: stuck in journal limbo.

Shortage of female math geniuses not due to "stereotype threat"

Men are over-represented at the high end of math performance: there are more male math geniuses than female ones.

A theory that was proposed to explain that fact is that of stereotype threat. According to this theory, there is a stereotype in society that "women are bad in math"; women internalize this stereotype and lose confidence about their math abilities, and so they tend to perform sub-optimally in math tests, hence rendering the idea of "women are bad in math" a self-fulfilling prophecy.

This new study demonstrates that much of the literature that has accumulated around the idea of a "stereotype threat" can be relegated to the trash bin, and those who hope that fighting the stereotype will lead to more females joining the mathematical elite have their work cut out for them.

A video on the topic by the first author:






Review of General Psychology, Jan 16 , 2012, No Pagination Specified. doi: 10.1037/a0026617

Can stereotype threat explain the gender gap in mathematics performance and achievement?

Stoet, Gijsbert; Geary David C.

Men and women score similarly in most areas of mathematics, but a gap favoring men is consistently found at the high end of performance. One explanation for this gap, stereotype threat, was first proposed by Spencer, Steele, and Quinn (1999) and has received much attention. We discuss merits and shortcomings of this study and review replication attempts. Only 55% of the articles with experimental designs that could have replicated the original results did so. But half of these were confounded by statistical adjustment of preexisting mathematics exam scores. Of the unconfounded experiments, only 30% replicated the original. A meta-analysis of these effects confirmed that only the group of studies with adjusted mathematics scores displayed the stereotype threat effect. We conclude that although stereotype threat may affect some women, the existing state of knowledge does not support the current level of enthusiasm for this as a mechanism underlying the gender gap in mathematics. We argue there are many reasons to close this gap, and that too much weight on the stereotype explanation may hamper research and implementation of effective interventions.

Link

Mastery through practice, but not for all

From the press release:

In one survey of chess players in Argentina, Campitelli and Gobet found that, indeed, practice is important. All of the players that became masters had practice at least 3,000 hours. "That was not surprising," he says. There is a theory in psychology that the more you practice, the better you'll do in areas like sports, music, and chess. "But the thing is, of the people that achieved the master level, there are people that achieved it in 3,000 hours. Other people did, like, 30,000 hours and achieved the same level. And there are even people that practiced more than 30,000 hours and didn't achieve this."

...

Campitelli and Gobet suggest that more intelligent children may be attracted to chess, and use their good reasoning skills to play well, but later they need to practice hard to learn all the strategies and plans that make a good chess player -- and intelligence isn't much help.

Intelligence is definitely necessary for achieving mastery in chess, but one of the most critical components of current practice is having a good memory. Without a substantial knowledge of opening and endgame theory, chess players of higher ability are at a disadvantage against less able but better prepared opponents. This knowledge can only be obtained by diligent study, but having the right hardware helps. But, even in the middle game one needs a good working memory, since one needs to basically do a tree traversal with a lot of redundancy whenever one analyzes variants.

Chess seems like the perfect game to use for analyzing learning and high-performance human brain functioning, as it is entirely rational, and there are literally millions of test subjects around the world.

Current Directions in Psychological Science October 2011 vol. 20 no. 5 280-285

Deliberate Practice Necessary But Not Sufficient

Guillermo Campitelli, Fernand Gobet

Deliberate practice (DP) occurs when an individual intentionally repeats an activity in order to improve performance. The claim of the DP framework is that such behavior is necessary to achieve high levels of expert performance. The proponents of the framework reject evidence that suggests that other variables are also necessary to achieve high levels of expert performance, or they claim that the relationship between those variables and expert performance is mediated by DP. Therefore, the DP framework also implies that DP is sufficient to achieve high levels of expert performance. We test these claims by reviewing studies on chess expertise. We found strong evidence that abundant DP is necessary (but not sufficient) and estimated that the minimum requirement to achieve master level is 3,000 hours of DP. We also review evidence showing that other factors play a role in chess skill: general cognitive abilities, sensitive period, handedness, and season of birth.

Link

Breaking down intelligence to environmental and genetic components

Razib has an interesting post in which he argues that as living conditions become good for most members of a society, the environmental component of intelligence should diminish, and the genetic one should increase.

The basic idea could be expressed as follows: give the exact same amount of water, sunlight, nutrients, etc. to two different trees, and the amount of fruit they will produce will depend entirely on their genes.

Likewise, make sure every kid has food, clean water, a home, medical care, schooling, etc. and then their differences in intelligence will depend entirely on their genes.

Hence:

A perfect meritocracy would replace cultural class with biological caste.

It's a seductive argument, that overlooks, I think, an important factor:

Different organisms have different optimal environments for their best performance.

Let's go back to the tree analogy. If you equalize their environments, then their output (fruit) will depend entirely on their genetic input (genes). But what environment should be chosen?

A desert plant is ruined by too much water, a jungle one by too little.

It is far from an obvious proposition that the "ideal environment" as currently envisioned by Western social policy makers is indeed the optimal one for all members of our species.

A Norwegian and a Nigerian will both suffer if they are exposed to the sun too much or too little, but their optimal "sun exposure" points are different; a Pygmy and an Eskimo will die of starvation with too little food and of a variety of ailments with too much, but their optimal "daily colorie intake" points are different. Even members of the same population differ in what is good for them.

In Aristotelian terminology, "mean is best", but "mean" is not the same for all, and what is an excess for one is a deficiency for another.

It could be argued that current affluent societies do not enforce particular environments, but give the freedom to their members to choose their own. In a truly affluent society where anyone has the means to adopt whatever lifestyle is best for them, it will be the case that variation in any particular trait (e.g., intelligence) will depend on one's genes: Norwegians, Nigerians, Pygmies, and Eskimos may choose what is good for them, they are not forced to live in a suboptimal environment

That, however, is a mixed blessing because a free society is also a very particular kind of society that is not necessarily best for all. It could very well be that some organisms reach their optimum performance under compulsion, and I see no reason to think that kids (or adults) become excellent by doing what they want and not by following the instructions of those who know better.

For example, kids learn to read and do multiplications by being forced to do a lot of tedious repetition. In a free society, an adult is largely free from compulsion, but that does not mean that he will choose to do what is best for himself.

In a free and affluent society everyone has the potential of having the best possible physique and the best possible cognitive ability that their genotype will allow: "money is no object." But, as we well know, few people use their freedom to achieve their full potential.

In conclusion:

• Fix the genes (as in clones or identical twins) and all variation is due to the environment
• Fix the environment and all variation is due to genes
• The eugenicist's dream is to "improve the genes" -- but "better genes" for what environment?
• The social engineer's dream is to "improve the environment" -- but "better environment" for which genetic natures?

Collective intelligence in groups

The press release has more info. Not sure why the proportion of women resulted in higher "collective intelligence". The authors suggest that it is because of women's higher "social sensitivity". Personally, I think it may be because men (and women) tend to try to impress members of the opposite sex for obvious evolutionary reasons.

Science DOI: 10.1126/science.1193147

Evidence for a Collective Intelligence Factor in the Performance of Human Groups

Anita Williams Woolley et al.

Psychologists have repeatedly shown that a single statistical factor—often called "general intelligence"— emerges from the correlations among people's performance on a wide variety of cognitive tasks. But no one has systematically examined whether a similar kind of "collective intelligence" exists for groups of people. In two studies with 699 individuals, working in groups of two to five, we find converging evidence of a general collective intelligence factor that explains a group's performance on a wide variety of tasks. This "c factor" is not strongly correlated with the average or maximum individual intelligence of group members but is correlated with the average social sensitivity of group members, the equality in distribution of conversational turn-taking, and the proportion of females in the group.

Link

Breastfeeding and IQ (Steer et al. 2010)

The new article references an older article by Caspi et al, which studied the moderation of the association between breastfeeding and IQ by a genetic variant in FADS2:

Children's intellectual development is influenced by both genetic inheritance and environmental experiences. Breastfeeding is one of the earliest such postnatal experiences. Breastfed children attain higher IQ scores than children not fed breast milk, presumably because of the fatty acids uniquely available in breast milk. Here we show that the association between breastfeeding and IQ is moderated by a genetic variant in FADS2, a gene involved in the genetic control of fatty acid pathways. We confirmed this gene–environment interaction in two birth cohorts, and we ruled out alternative explanations of the finding involving gene–exposure correlation, intrauterine growth, social class, and maternal cognitive ability, as well as maternal genotype effects on breastfeeding and breast milk. The finding shows that environmental exposures can be used to uncover novel candidate genes in complex phenotypes. It also shows that genes may work via the environment to shape the IQ, helping to close the nature versus nurture debate.

The current study's sample:

In all, 5934 children of white European origin had genetic data with additional information on breastfeeding and IQ. Of these 83% were breastfed within the first month. These children had means (SDs) of 108 (16), 100 (17) and 105 (16) for verbal, performance and full-scale IQ respectively.

The breastfeeding association:

Breastfeeding showed a strong association with full-scale IQ with breastfed children scoring 8 points higher IQ on average in unadjusted analyses as has been previously reported [2], [3]. There were strong associations between breastfeeding and most confounders (see Table S2). The breastfeeding effect attenuated to a 3-point advantage after adjustment for these confounders (see Table 2).

The important caveat, referring to this earlier paper by Der et al. From the current paper:

A limitation of this study was the risk of bias due to the lack of controlling for other potentially important factors such as maternal IQ [34], maternal fish consumption during lactation and the ratio of omega-6 to omega-3 fatty acids. These data were not available within ALSPAC. However data on maternal educational qualifications were available. This measure is likely to be highly correlated with maternal IQ and more strongly related than other measures of education such as years of schooling. In addition, adjustment for educational qualifications did not change the conclusions despite being an important predictor of child IQ (p less than 0.001).

What Der et al. had proposed is that smart mothers breastfeed more, so the association between IQ and breastfeeding reflects the heredity of maternal IQ rather than benefits of the breastfeeding practice itself. The current study has used maternal educational qualifications as a proxy for IQ. This is unsatisfactory as education is not as tightly coupled with IQ as would be necessary to let us discount maternal IQ as a source of the breastfed children IQ's increase:

As I have noted in a previous post, extreme care is needed when using proxy variables. You can mentally analyze the IQ-educational attainment relationship into two parts:

1. Different educational levels (e.g., high school graduates vs. Master's holders) have different average IQ
2. Within educational levels (e.g., high school graduates) there is variation in IQ. Moreover, there is IQ overlap between educational levels

Using educational level as a proxy for IQ allows us to capture part of the maternal IQ variation. However, if maternal IQ and breastfeeding within an educational level are correlated, then the use of educational level as a proxy for IQ underestimates for the strength of the relationship.

The "meat" of the paper involves the effect of genotype on the IQ/breastfeeding association:

The fact that genotype in the two studied loci modifies the IQ/breastfeeding relationship is evident and needs no further comment.

The discussion of the paper goes into some detail on the technical reasons for the discrepancy between this study and Caspi et al.
PLoS ONE 5(7): e11570. doi:10.1371/journal.pone.0011570

FADS2 Polymorphisms Modify the Effect of Breastfeeding on Child IQ

Colin D. Steer et al.

Background
Breastfeeding is important for child cognitive development. A study by Caspi et al has suggested that rs174575 within the FADS2 gene moderates this effect so that children homozygous in the minor allele (GG genotype) have similar IQs irrespective of feeding method.

Methods and Principal Findings
In our study of 5934 children aged 8 years, no genetic main effect with IQ was found for rs174575. However, an interaction with this polymorphism was observed such that breastfed GG children performed better than their formula fed counterparts by an additional 5.8 points [1.4, 10.1] (interaction p = 0.0091). Interaction results were attenuated by about 10% after adjustment for 7 factors. This study also investigated rs1535, another FADS2 polymorphism in linkage disequilibrium with rs174575, together with performance and verbal IQ, finding similar results although effect sizes were generally reduced.

Conclusions and Significance
This study did not replicate the findings of Caspi et al. In contrast to their study, GG children exhibited the greatest difference between feeding methods such that breastfed children performed similarly irrespective of child genotype whereas formula fed GG children performed worse than other children on formula milk. Further studies are required to replicate these findings.

Link

Persistence of gender gap in top science and math performance

From the press release:

A study that examined 30 years of standardized test data from the very highest-scoring seventh graders has found that performance differences between boys and girls have narrowed considerably, but boys still outnumber girls by more than about 3-to-1 at extremely high levels of math ability and scientific reasoning.

At the same time, girls slightly outnumber boys at extremely high levels of verbal reasoning and writing ability.

Intelligence Volume 38, Issue 4, July-August 2010, Pages 412-423

Sex differences in the right tail of cognitive abilities: A 30 year examination

Jonathan Wai et al.

Abstract

One factor in the debate surrounding the underrepresentation of women in science technology, engineering and mathematics (STEM) involves male–female mathematical ability differences in the extreme right tail (top 1% in ability). The present study provides male–female ability ratios from over 1.6 million 7th grade students in the right tail (top 5% in ability) across 30 years (1981–2010) using multiple measures of math, verbal, and writing ability and science reasoning from the SAT and ACT. Male–female ratios in mathematical reasoning are substantially lower than 30 years ago, but have been stable over the last 20 years and still favor males. Over the last two decades males showed a stable or slightly increasing advantage in science reasoning. However, more females scored in the extreme right tail of verbal reasoning and writing ability tests. The potential role of sociocultural factors on changes in the male–female ability ratios is discussed and the introduction of science reasoning as a potential new factor in the debate is proposed. The implications of continued sex differences in math and science reasoning is discussed within the context of the many important interlocking factors surrounding the debate on the underrepresentation of women in STEM.

Link

Parasites and Intelligence (Eppig et al. 2010)

This is as good an explanation for global differences in IQ as I have ever seen. It proposes that IQ differences between human groups are created during ontogeny due to an energetic trade-off between brain development and immune response to infectious disease. In regions of the world with a high parasite burden, there is an elevated amount of energy used up to fight disease, at the expense of brain development.

Notice that this is not an explanation requiring genetic adaptation. Parasite burden inhibits cognitive function development. Indeed, if one were to make an adaptive argument (and I will not!), it would be in the direction of greater brain development genetic potential in parasite-heavy locales to counteract the effects of disease, i.e., the selection of individuals that may withstand the rigors of fighting off infectious disease without compromising cognitive function.

The authors write:

Multiple regression shows that, of infectious disease, temperature, evolutionary novelty and AVED, infectious disease is the best predictor of intelligence by a large margin.

...

If the general pathway we propose is correct, there are two plausible mechanisms by which a trade-off in allocation of energy to immune function versus brain development and maintenance may occur. First, parasitic infection may intermittently cause the redirection of energy away from brain development. In this case, during periods of infection, the brain receives fewer energetic resources, but this allocation to brain function will return to pre-infection levels during healthy periods. During periods of infection, whatever aspects of the brain that are growing and developing will suffer reduced phenotypic quality. Second, exposure to infectious agents may cause a developmental pathway that permanently invests more energy into immune function at the expense of brain growth. In this scenario, large amounts of energy would be allocated into immune function during periods of health, as opposed to only redirecting energy during periods of infection. This could operate through a variety of mechanisms. A plausible mechanism is that higher investment in immune system is triggered by individual exposure to infectious disease at some point during ontogeny. This may include triggering from exposure to maternal antibodies while in utero.

...

Our findings suggest that the heritable variation in intelligence may come from two sources: brain structure and immune system quality. Thus, two individuals may possess identical genes for brain structure, but have different IQ owing to differences in immune system quality reflecting their personal allocation of energy into brain development versus immunity.

...

Our findings are consistent with a number of other findings in the literature. In particular, the Flynn effect (Flynn 1987) demands that any hypothesis regarding the worldwide variation and distribution of intelligence must be able to account for some factor that allows for large IQ gains over time spans seemingly too short to be attributed to evolution by natural selection. The parasite-stress hypothesis allows for such a factor in the form of reduced parasitic infection. As societies become modernized, decreased parasite stress may occur through multiple pathways. As national wealth increases, medicine, vaccinations and potable water can be purchased by both the government and by individuals. Moreover, there is cross-national evidence that, as democratization increases, there are corresponding increases in public health legislation and infrastructure. Democratization also increases levels of education, better allowing individuals to seek out and understand information that reduces parasitic infection (Thornhill et al. 2009). This source of endogeneity is not a flaw, but a prediction of our hypothesis.

Related:

• Pathogens and Collectivism
• Religious Diversity and pathogens

Proceedings of the Royal Society B doi:10.1098/rspb.2010.0973

Parasite prevalence and the worldwide distribution of cognitive ability

Christopher Eppig et al.

Abstract

In this study, we hypothesize that the worldwide distribution of cognitive ability is determined in part by variation in the intensity of infectious diseases. From an energetics standpoint, a developing human will have difficulty building a brain and fighting off infectious diseases at the same time, as both are very metabolically costly tasks. Using three measures of average national intelligence quotient (IQ), we found that the zero-order correlation between average IQ and parasite stress ranges from r = −0.76 to r = −0.82 (p less than 0.0001). These correlations are robust worldwide, as well as within five of six world regions. Infectious disease remains the most powerful predictor of average national IQ when temperature, distance from Africa, gross domestic product per capita and several measures of education are controlled for. These findings suggest that the Flynn effect may be caused in part by the decrease in the intensity of infectious diseases as nations develop.

Link

Listening to Mozart does not make you smart

It's a shame that it took us 17 years to put the "Mozart makes you smart" meme to rest. I wonder how much money in research grants was wasted over the years (40 studies!) on the question. So, a big thanks to Pietschnig, Voracek, and Formann for debunking the Mozart-effect theory. I predict that the theory will -unfortunately- survive in popular culture, for a long time to come; but if it leads to people learning to enjoy good music, it might be worth it.



Intelligence doi:10.1016/j.intell.2010.03.001

Mozart effect–Shmozart effect: A meta-analysis

Jakob Pietschnig et al.

The transient enhancement of performance on spatial tasks in standardized tests after exposure to the first movement “allegro con spirito” of the Mozart sonata for two pianos in D major (KV 448) is referred to as the Mozart effect since its first observation by Rauscher, Shaw, and Ky (1993). These findings turned out to be amazingly hard to replicate, thus leading to an abundance of conflicting results. Sixteen years after initial publication we conduct the so far largest, most comprehensive, and up-to-date meta-analysis (nearly 40 studies, over 3000 subjects), including a diversity of unpublished research papers to finally clarify the scientific record about whether or not a specific Mozart effect exists. We could show that the overall estimated effect is small in size (d = 0.37, 95% CI [0.23, 0.52]) for samples exposed to the Mozart sonata KV 448 and samples that had been exposed to a non-musical stimulus or no stimulus at all preceding spatial task performance. Additionally, calculation of effect sizes for samples exposed to any other musical stimulus and samples exposed to a non-musical stimulus or no stimulus at all yielded effects similar in strength (d = 0.38, 95% CI [0.13, 0.63]), whereas there was a negligible effect between the two music conditions (d = 0.15, 95% CI [0.02, 0.28]). Furthermore, formal tests yielded evidence for confounding publication bias, requiring downward correction of effects. The central finding of the present paper however, is certainly the noticeably higher overall effect in studies performed by Rauscher and colleagues than in studies performed by other researchers, indicating systematically moderating effects of lab affiliation. On the whole, there is little evidence left for a specific, performance-enhancing Mozart effect.

Link

Genome-wide associate studies and cognitive performance

This ties in with what I've written before, namely, that complex phenotypes don't have a set of population-common genetic causes, but are caused by different combinations of "commodity" alleles.

Just as you can drink water from a cup, or a glass, or a bucket, or a spoon, or your hands, i.e., you can achieve the same functional effect by very different means, so you can achieve the same phenotypic effect (e.g., intelligence) by very different genetic means.

Using a different analogy, the effect of a "cross" can be achieved both like this:


**0**
**0**
00000
**0**
**0**


and like this:


00*00
00*00
*****
00*00
00*00


You wouldn't have a clue that these ASCII characters both create a "cross" if you limited yourself to testing whether a bit of information was "0" or "*". It is in their arrangement that the pattern emerges.

So it is with many complex human phenotypes. As humans, we are machines with billions of independent variables (alleles) which can produce the same (or similar) outcomes in a manifold number of ways.

European Journal of Human Genetics doi: 10.1038/ejhg.2010.2

Common genetic variation and performance on standardized cognitive tests

Elizabeth T Cirulli et al.

Abstract

One surprising feature of the recently completed waves of genome-wide association studies is the limited impact of common genetic variation in individually detectable polymorphisms on many human traits. This has been particularly pronounced for studies on psychiatric conditions, which have failed to produce clear, replicable associations for common variants. One popular explanation for these negative findings is that many of these traits may be genetically heterogeneous, leading to the idea that relevant endophenotypes may be more genetically tractable. Aspects of cognition may be the most important endophenotypes for psychiatric conditions such as schizophrenia, leading many researchers to pursue large-scale studies on the genetic contributors of cognitive performance in the normal population as a surrogate for aspects of liability to disease. Here, we perform a genome-wide association study with two tests of executive function, Digit Symbol and Stroop Color-Word, in 1086 healthy volunteers and with an expanded cognitive battery in 514 of these volunteers. We show that, consistent with published studies of the psychiatric conditions themselves, no single common variant has a large effect (explaining >4–8% of the population variation) on the performance of healthy individuals on standardized cognitive tests. Given that these are important endophenotypes, our work is consistent with the idea that identifying rare genetic causes of psychiatric conditions may be more important for future research than identifying genetically homogenous endophenotypes.

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Genetic Covariation Between Brain Volumes and IQ, Reading Performance, and Processing Speed (Betjemann et al. 2010)

Related:

• Big-brained people are smarter
• Expanding Heads and Shrinking Faces
• Neuroanatomical correlates of intelligence
• Intelligence predicted by brain structure and function
• Brain volume and IQ in children

Behav Genet. 2010 Jan 14. [Epub ahead of print]

Genetic Covariation Between Brain Volumes and IQ, Reading Performance, and Processing Speed.

Betjemann RS, Johnson EP, Barnard H, Boada R, Filley CM, Filipek PA, Willcutt EG, Defries JC, Pennington BF.

Although there has been much interest in the relation between brain size and cognition, few studies have investigated this relation within a genetic framework and fewer still in non-adult samples. We analyzed the genetic and environmental covariance between structural MRI data from four brain regions (total brain volume, neocortex, white matter, and prefrontal cortex), and four cognitive measures (verbal IQ (VIQ), performance IQ (PIQ), reading ability, and processing speed), in a sample of 41 MZ twin pairs and 30 same-sex DZ twin pairs (mean age at cognitive test = 11.4 years; mean age at scan = 15.4 years). Multivariate Cholesky decompositions were performed with each brain volume measure entered first, followed by the four cognitive measures. Consistent with previous research, each brain and cognitive measure was found to be significantly heritable. The novel finding was the significant genetic but not environmental covariance between brain volumes and cognitive measures. Specifically, PIQ shared significant common genetic variance with all four measures of brain volume (r (g) = .58-.82). In contrast, VIQ shared significant genetic influence with neocortex volume only (r (g) = .58). Processing speed was significant with total brain volume (r (g) = .79), neocortex (r (g) = .64), and white matter (r (g) = .89), but not prefrontal cortex. The only brain measure to share genetic influence with reading was total brain volume (r (g) = .32), which also shared genetic influences with processing speed.

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Height-IQ-Gender interplay

Am J Psychol. 2009 Winter;122(4):527-36.

The role of height in the sex difference in intelligence.

Kanazawa S, Reyniers DJ.

Recent studies conclude that men on average have higher intelligence than women by 3-5 IQ points. However, the ultimate evolutionary question of why men should have evolved to have higher intelligence than women remains. We suggest that men may have slightly higher intelligence than women through 4 mechanisms: (1) assortative mating of intelligent men and beautiful women, (2) assortative mating of tall men and beautiful women, (3) an extrinsic correlation between height and intelligence produced by Mechanisms 1 and 2, and (4) a higher-than-expected offspring sex ratio (more sons) among tall (and hence intelligent) parents. Consistent with our suggestion, we show that men may have higher IQs than women because they are taller, and once we control for height women have slightly higher IQs than men.The correlation between height and IQ and the female advantage in intelligence persist even after we control for health as a measure of genetic quality, as well as physical attractiveness, age, race, education, and earnings. Height is also strongly associated with intelligence within each sex.

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Hijab wearing and perception of intelligence/attractiveness

Body Image. 2009 Oct 6. [Epub ahead of print]

The influence of the hijab (Islamic head-cover) on perceptions of women's attractiveness and intelligence.

Mahmud Y, Swami V.

This study examined the effects of wearing the hijab, or Islamic headwear, on men's perceptions of women's attractiveness and intelligence. A total of 57 non-Muslim men and 41 Muslim men rated a series of images of women, half of whom were unveiled and half of whom wore the hijab. For attractiveness and intelligence ratings, a mixed analysis of variance showed a significant effect of hijab status, with women wearing the hijab being rated more negatively than unveiled women. For attractiveness ratings, there was no significant effect of participant religion, although non-Muslim men rated unveiled women significantly higher than veiled women. For intelligence ratings, non-Muslim men provided significantly higher ratings than Muslim men for both conditions. In addition, Muslim men's ratings of the attractiveness and intelligence of women wearing the hijab was positively correlated with self-reported religiosity. These results are discussed in relation to religious stereotyping within increasingly multi-cultural societies.

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Birth size and IQ in Asian children

2.19 IQ points for an extra kg of birth weight seems quite meager.

Pediatrics. 2009 Jun;123(6):e1011-e1016.

The Influence of Birth Size on Intelligence in Healthy Children.

Broekman BF, Chan YH, Chong YS, Quek SC, Fung D, Low YL, Ooi YP, Gluckman PD, Meaney MJ, Wong TY, Saw SM.

OBJECTIVE. Birth parameters have been hypothesized to have an influence on IQ. However, studies within the range of normal birth size have been sparse. With this study we examined the associations between birth length, birth weight, head circumference, and gestational age within the normal birth size range in relation to childhood IQ in Asian children. METHODS. A cohort of 1979 of 2913 Asian children aged 7 to 9 years, recruited from 3 schools in Singapore, were followed yearly from 1999 onward. Birth parameters were recorded by health personnel. Childhood IQ was measured with the Raven's Standard Progressive Matrices at ages 8 to 12. RESULTS. The mean IQ score across the sample (n = 1645) was 114.2. After controlling for multiple confounders for every 1-cm increment in birth length, 1 kg in birth weight, or 1 cm in head circumference, there was a corresponding increase in IQ of 0.49 points (P for trend less than .001), 2.19 points (P for trend = .007) and .62 points (P for trend = .003), respectively. These associations persisted even after exclusion of premature children and children with extreme weights and head circumferences. CONCLUSIONS. Longer birth length, higher birth weight, or larger head circumferences within the normal birth size range are associated with higher IQ scores in Asian children. Our results suggest that antenatal factors reflected in altered rates of growth but within the normative range of pregnancy experiences play a role in generating cognitive potential. This has implications for targeting early intervention and preventative programs.

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Brain structure and IQ

PLoS Comput Biol doi:10.1371/journal.pcbi.1000395

Brain Anatomical Network and Intelligence

Yonghui Li et al.

Abstract

Intuitively, higher intelligence might be assumed to correspond to more efficient information transfer in the brain, but no direct evidence has been reported from the perspective of brain networks. In this study, we performed extensive analyses to test the hypothesis that individual differences in intelligence are associated with brain structural organization, and in particular that higher scores on intelligence tests are related to greater global efficiency of the brain anatomical network. We constructed binary and weighted brain anatomical networks in each of 79 healthy young adults utilizing diffusion tensor tractography and calculated topological properties of the networks using a graph theoretical method. Based on their IQ test scores, all subjects were divided into general and high intelligence groups and significantly higher global efficiencies were found in the networks of the latter group. Moreover, we showed significant correlations between IQ scores and network properties across all subjects while controlling for age and gender. Specifically, higher intelligence scores corresponded to a shorter characteristic path length and a higher global efficiency of the networks, indicating a more efficient parallel information transfer in the brain. The results were consistently observed not only in the binary but also in the weighted networks, which together provide convergent evidence for our hypothesis. Our findings suggest that the efficiency of brain structural organization may be an important biological basis for intelligence.

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Reading, Intelligence and Memory in Children

Behav Genet. 2009 Apr 4.

Genetic Covariance Structure of Reading, Intelligence and Memory in Children

van Leeuwen M, van den Berg SM, Peper JS, Hulshoff Pol HE, Boomsma DI.

This study investigates the genetic relationship among reading performance, IQ, verbal and visuospatial working memory (WM) and short-term memory (STM) in a sample of 112, 9-year-old twin pairs and their older siblings. The relationship between reading performance and the other traits was explained by a common genetic factor for reading performance, IQ, WM and STM and a genetic factor that only influenced reading performance and verbal memory. Genetic variation explained 83% of the variation in reading performance; most of this genetic variance was explained by variation in IQ and memory performance. We hypothesize, based on these results, that children with reading problems possibly can be divided into three groups: (1) children low in IQ and with reading problems; (2) children with average IQ but a STM deficit and with reading problems; (3) children with low IQ and STM deficits; this group may experience more reading problems than the other two.

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