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

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

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?

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

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

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.

Link

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.

Link

Literature review of Sub-Saharan African IQ

Intelligence doi:10.1016/j.intell.2009.05.002

A systematic literature review of the average IQ of sub-Saharan Africans

Jelte M. Wicherts et al.

Abstract

On the basis of several reviews of the literature, Lynn [Lynn, R., (2006). Race differences in intelligence: An evolutionary analysis. Augusta, GA: Washington Summit Publishers.] and Lynn and Vanhanen [Lynn, R., & Vanhanen, T., (2006). IQ and global inequality. Augusta, GA: Washington Summit Publishers.] concluded that the average IQ of the Black population of sub-Saharan Africa lies below 70. In this paper, the authors systematically review published empirical data on the performance of Africans on the following IQ tests: Draw-A-Man (DAM) test, Kaufman-Assessment Battery for Children (K-ABC), the Wechsler scales (WAIS & WISC), and several other IQ tests (but not the Raven's tests). Inclusion and exclusion criteria are explicitly discussed. Results show that average IQ of Africans on these tests is approximately 82 when compared to UK norms. We provide estimates of the average IQ per country and estimates on the basis of alternative inclusion criteria. Our estimate of average IQ converges with the finding that national IQs of sub-Saharan African countries as predicted from several international studies of student achievement are around 82. It is suggested that this estimate should be considered in light of the Flynn Effect. It is concluded that more psychometric studies are needed to address the issue of measurement bias of western IQ tests for Africans.

Link

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.

Link

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.

Link

Eminence, IQ, physical and mental health

The negative relationship between physical health and IQ is the most noteworthy finding, as it goes against the observation of IQ being associated with good health. To explain this, the authors propose either that "the course that leads from initial talent to extraordinary achievement may require pathways of intellectual and social development that diverge radically from normal personal growth," or "Excessive selection can truncate the variable variances so that correlations are reduced to zero. [...] As an example, among students accepted to graduate school in psychology, the undergraduate grade point average can be negatively correlated with scores received on the Graduate Record Examination (Dawes, 1975)."

From the paper:

Relative to the average, IQ was higher among the philosophers and imaginative writers, but lower among the commanders, composers, and artists.

...

commanders, enjoyed a level of early physical health substantially above the average. [...] Second, one domain stands out as being the lowest in mental
health: the imaginative writers.

Psychological Science doi:10.1111/j.1467-9280.2009.02313.x

Eminence, IQ, Physical and Mental Health, and Achievement Domain: Cox's 282 Geniuses Revisited

Dean Keith Simonton and Anna V. Song

Abstract

Catharine Cox published two studies of highly eminent creators and leaders, the first in 1926 as the second volume of Terman's landmark Genetic Studies of Genius and the second in 1936 as a coauthored article. The former publication concentrated on the relation between IQ and achieved eminence, and the latter focused on early physical and mental health. Taking advantage of unpublished data from the second study, we examined, for the first time, the relationships among achieved eminence, IQ, early physical and mental health, and achievement domain. The correlation and regression analyses showed, for these 282 individuals, that eminence is a positive function of IQ and that IQ is a positive function of mental health and a negative function of physical health, implying an indirect effect of physical and mental health on eminence. Furthermore, levels of early physical and mental health vary across 10 specific domains of achievement.

Link

According to Flynn, nutrition not behind "Flynn effect"

See a recent paper by Lynn where the importance of nutrition for the Flynn effect (secular increase in IQ) was argued. Another paper on Denmark (and another) which also sees a recent decline in IQ scores, a reversal of the Flynn effect.

From this paper's conclusions:

The totality of the evidence supports a summary conclusion. Enhanced
nutrition has made us taller people and poor nutrition has made us more obese. But
our diet today probably does not make us very different people from our grandparents as far as cognitive competence is concerned. Our brains have altered since 1900, and they are better brains for solving the problems of our time. But they have altered rather like a muscle, that is, they have altered because we use them differently than our parents and grandparents did. The causes of this are many and the effects of nutrition, at least since privation has been banished, are too weak to stand out from the crowd.

Economics & Human Biology doi:http://dx.doi.org/10.1016/j.ehb.2009.01.009

Requiem for nutrition as the cause of IQ gains Raven's gains in Britain 1938 to 2008

James R. Flynn

Abstract

The hypothesis that enhanced nutrition is mainly responsible for massive IQ gains over time borrows plausibility from the height gains of the 20th century However, evidence shows that the two trends are largely independent. A detailed analysis of IQ trends on the Raven's Progressive Matrices tests in Britain dramatizes the poverty of the nutrition hypothesis. A multiple factor hypothesis that operates on three levels is offered as an alternative instrument of causal explanation.

The Raven's data show that over the 65 years from circa 1942 to the present, taking ages 5 to 15 together, British school children have gained 14 IQ points for a rate of 0.216 points per year. However, since 1979, gains have declined with age and between the ages of 12 to 13 and 14 to 15, small gains turn into small losses. This is confirmed by Piagetian data and poses the possibility that the cognitive demands of teenage subculture have been stagnant over perhaps the last 30 years.

Link

IQ and death from unintentional injury

Am J Epidemiol. 2009 Jan 15. [Epub ahead of print]

IQ in Early Adulthood, Socioeconomic Position, and Unintentional Injury Mortality by Middle Age: A Cohort Study of More Than 1 Million Swedish Men.

Batty GD, Gale CR, Tynelius P, Deary IJ, Rasmussen F.

The authors evaluated the little-examined association between intelligence (IQ) and injury mortality and, for the first known time, explored the extent to which IQ might explain established socioeconomic inequalities in injury mortality. A nationwide cohort of 1,116,442 Swedish men who underwent IQ testing at about 18 years of age was followed for mortality experience for an average of 22.6 years. In age-adjusted analyses in which IQ scores were classified into 4 groups, relative to the highest scoring category, the hazard ratio in the lowest was elevated for all injury types: poisonings (hazard ratio (HR) = 5.82, 95% confidence interval (CI): 4.25, 7.97), fire (HR = 4.39, 95% CI: 2.51, 7.77), falls (HR = 3.17, 95% CI: 2.19, 4.59), drowning (HR = 3.16, 95% CI: 1.85, 5.39), and road injury (HR = 2.17, 95% CI: 1.91, 2.47). Dose-response effects across the full IQ range were evident (P-trend < 0.001). Control for potential covariates, including socioeconomic position, had little impact on these gradients. When socioeconomic disadvantage-indexed by parental and subject's own occupational social class-was the exposure of interest, IQ explained a sizable portion (19%-86%) of the relation with injury mortality. These findings suggest that IQ may have an important role both in the etiology of injuries and in explaining socioeconomic inequalities in injury mortality.

Link

IQ and survival in war (Scottish soldiers of WWII)

Intelligence should be positively correlated with survival in war; on the other hand, intelligence may be correlated with the amount of risk shouldered, as more intelligent men may be preferred to carry out complex high-risk mission. So, it's not clear whether smarter-than-average or not tend to survive wars.

This study shows that among Scottish Army participants of WWII, survivors were less intelligent than non-survivors, but also that non-participants in the Army were more intelligent than participants. Of course, this latter finding may be due to non-Army men being e.g. in the Navy, for which no data exist.

Certainly this data shows some relationship between IQ and military participation/survival, although the effect does not seem to be very pronounced.

The WWII experience was probably one of near-universal participation by the combat-age male population of the countries involved, and it would be interesting to see comparable data from volunteer Armies, such as the current US Army, where IQ data probably exist.


Intelligence doi:10.1016/j.intell.2008.11.003

Childhood IQ and in-service mortality in Scottish Army personnel during World War II

Janie Corley et al.

Abstract

The Scottish Mental Survey of 1932 (SMS1932) provides a record of intelligence test scores for almost a complete year-of-birth group of children born in 1921. By linking UK Army personnel records, the Scottish National War Memorial data, and the SMS1932 dataset it was possible to examine the effect of childhood intelligence scores on wartime military service mortality in males. There were 491 matches between World War II (WWII) Scottish Army fatalities and the SMS1932 database; 470 (96%) had an age 11 mental ability score recorded. The mean (S.D.) age 11 IQ score of those who died on active service in WWII was 100.78 (15.56), compared with 97.42 (14.87) for male Army survivors (p less than 0.0001; Cohen's d = 0.22). Men who took part in the SMS1932 and who were not found in the Army database had a higher mean score (100.45, S.D. =14.97) than those men who had been in the Army, regardless of whether they died or survived (mean IQ = 97.66, S.D. = 14.94; p less than 0.0001; Cohen's d = 0.19). Male soldiers with a higher childhood IQ had a slightly increased risk of dying during active service in WWII. Men who did not join the Army had a higher IQ than men who did. Further research in this area should consider naval and air force personnel records in order to examine more fully the complex relationship between IQ and survival expectancy during active service in WWII.

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Inbreeding depression and IQ

Intelligence doi:10.1016/j.intell.2008.10.007

Inbreeding depression and IQ in a study of 72 countries

Michael A. Woodley

Abstract

In this ecological study, a robust negative correlation of r = − .62 (P less than .01) is reported between national IQs and consanguinity as measured by the log10 transformed percentage of consanguineous marriages for 72 countries. This correlation is reduced in magnitude, when IQ is controlled for GDP per capita (r = − .41, P less than .01); education index (r = − .40, P less than .01); and democracy index (r = − .42, P less than .01). Multiple regression analysis revealed that in the absence of the democracy index; percentage consanguineous marriages, education index and GDP per capita all exhibited stable final standardized β coefficients, however consanguinity had the least impact (β = 0, P greater than .05) whereas GDP per capita had the highest (β = .35, P greater than .01). This result is interpreted in light of cultural feedback theory, whereby it is suggested that consanguinity could subtly influence IQ at larger scales as a result of small IQ handicaps bought about through inbreeding being amplified into much larger differences through their effect on factors that maximize IQ such as access to education and adequate nutrition. Finally, consideration is given to future potential research directions.

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Brain volume and IQ in children

Intelligence doi:10.1016/j.intell.2008.10.005

A genetic analysis of brain volumes and IQ in children

Marieke van Leeuwen et al.

Abstract

In a population-based sample of 112 nine-year old twin pairs, we investigated the association among total brain volume, gray matter and white matter volume, intelligence as assessed by the Raven IQ test, verbal comprehension, perceptual organization and perceptual speed as assessed by the Wechsler Intelligence Scale for Children-III. Phenotypic correlations between the brain volumes and intelligence traits ranged between .20 and .33. Processing speed and brain volume did not correlate. The relation between brain volume and intelligence was entirely explained by a common set of genes influencing both sets of phenotypes.

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ADRB2 allele associated with intelligence

The results of this study are entirely in synch with my recent thoughts on genes and intelligence. In this case, the same gene was found to have opposite effects on intelligence, indicating that it acts differently (positively) in the cohort of young related people and (negatively) in the cohort of older unrelated Scottish people. 

Behav Genet. 2008 Oct 15. [Epub ahead of print]

A Functional Polymorphism under Positive Evolutionary Selection in ADRB2 is Associated with Human Intelligence with Opposite Effects in the Young and the Elderly.

Bochdanovits Z, Gosso FM, van den Berg L, Rizzu P, Polderman TJ, Pardo LM, Houlihan LM, Luciano M, Starr JM, Harris SE, Deary IJ, de Geus EJ, Boomsma DI, Heutink P, Posthuma D.

Comparative genomics offers a novel approach to unravel the genetic basis of complex traits. We performed a two stage analysis where genes ascertained for enhanced protein evolution in primates are subsequently searched for the presence of non-synonymous coding SNPs in the current human population at amino acid sites that differ between humans and chimpanzee. Positively selected genes among primates are generally presumed to determine phenotypic differences between humans and chimpanzee, such as the enhanced cognitive ability of our species. Amino acid substitutions segregating in humans at positively selected amino acid sites are expected to affect phenotypic differences among humans. Therefore we conducted an association study in two family based cohorts and one population based cohort between cognitive ability and the most likely candidate gene among the five that harbored more than one such polymorphism. The derived, human-specific allele of the beta-2 adrenergic receptor Arg16Gly polymorphism was found to be the increaser allele for performance IQ in the young, family based cohort but the decreaser allele for two different measures of cognition in the large Scottish cohort of unrelated individuals. The polymorphism is known to affect signaling activity and modulation of beta-2 adrenergic signaling has been shown to adjust memory consolidation, a trait related to cognition. The opposite effect of the polymorphism on cognition in the two age classes observed in the different cohorts resembles the effect of ADRB2 on hypertension, which also has been reported to be age dependent. This result illustrates the relevance of comparative genomics to detect genes that are involved in human behavior.

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Carl Zimmer article on Intelligence (and some thoughts on nature/nurture and IQ)

Carl Zimmer blogs about his Scientific American article on Intelligence. From the article:

It was with great delight that Plomin got his hands on microarrays that could detect 500,000 genetic markers--hundreds of times more than he had previously used. He and his colleagues got cheek swabs from 7,000 children, isolated their DNA, and ran it through the microarrays. And once more the results were disappointing.

“I’m not willing to say that we have found genes for intelligence,” Plomin declares, “because there have been so many false positives. They’re such small effects that you’re going to have to replicate them in many studies to feel very confident about them.”

I had blogged about this study when it came out. I repeat my comments from 2006 which are still valid today:

It appears that the hunt for genes affecting intelligence is not going well. I can't say that I'm surprised, because I have always maintained that intelligence is an emergent property of a set of co-operating genes during development in a particular environment and I don't anticipate that the geno-centric approach will take us closer to understanding it.

Intelligence, and -I believe- other complex traits are like complex dishes with many ingredients. The ingredients themselves (e.g., salt, lettuce, or chicken) are themselves unremarkable, but it is the way that they are put together and turned on and off by internal and external stimuli (the pot, the temperature, time, etc.) that makes a good dish.

I have expressed the same view in the recent entry on genome-wide association studies:

This Lego-block paradigm is based on the notion that most of our alleles are commodity "building blocks"; if they are brought together harmoneously, they produce positive results. The occasional allele may have a large effect, and some alleles fit better together than others. Yet, most of the success or failure of a construction depends on how the components fit together, and not what they are.

From the Carl Zimmer article:

Researchers have made images of their developing brains once a year, and Shaw has focused much of his attention on what the pictures reveal about the growth of the cortex, the outer rind of the brain where the most sophisticated information processing takes place.

...

In all children the cortex gets thicker as new neurons grow and produce new branches. Then the cortex thins out as branches are pruned. But in some parts of the cortex, Shaw found, development took a different course in children with different levels of intelligence. “The superclever kids started off very thin,” Shaw says. “They got really relatively thicker, but in adolescence they got thinner again very quickly.”

I had blogged about this study in 2006; check out that blog entry to see the thickness curves of cortex in development.

At the dawn of the genetics era, physical anthropologists' ideas that intelligence was correlated with the brain's observable properties were often ridiculed. And, yet neuronatomical correlates are pretty much the only game in town when it comes to giving a prediction (admittedly a very coarse one) of a person's IQ

That doesn't mean that genes don't play a role in intelligence; they do, and it's a sizeable one. But that role is hidden in a gene-gene and gene-environment interaction web of thousands of factors, where the individual components aren't really important, but the way they are put together are.

This realization also leads one to question genetic fetishists' conclusions about environmental influences on IQ.

It is true that scientists have looked at a lot of possible environmental influences on IQ and have come up short on significant environmental factors that can boost a person's IQ. There is simply very limited evidence that any particular environment can achieve this --sort of really bad influences such as malnutrition or some infectious diseases in childhood. And, yet we know that part of the variation of IQ is due to environmental influences. What gives?

What scientists have looked at are recognizable, "obvious", environmental influences (parenting style, schooling, etc.), which are analogous to the "common variants" in genetics.

Just as a microarray-based genome-wide association study has no clue about the rare family-level gene complexes and disease factors, so studies of environmental influences have no clue about the rare family/school/peer group micro-environments affecting a person's development.

Thus, the failure to find strong environmental influences on IQ doesn't strengthen the nature side of the nature-nurture divide, just as the failure to find strong genetic influences on IQ doesn't strengthen the nurture side.

The truth is, that Intelligence is an emergent property of a complex web of genetic and non-genetic interactions.

A human being is like a black box with zillions of inputs, some of them genetic, others environmental. We know that the box's output, e.g. its IQ score on a test is related to its inputs; but the relationship isn't linear and tidy: you can try different inputs from here to eternity, but you won't be able to figure out what the output is.

As I wrote in my post on height and body mass index, real progress will come about only when we finally look into the box:

Real progress will only come about with more developmental and functional studies, i.e. studies that actually look at what genes do in the body.

Figuring out how humans "work" is easier said than done. But, I believe, there is no shortcut.

Political orientation and IQ

There are tons of debates whether left- or right-wing people are more intelligent. This paper shows that context matters, and political orientation can be predictive of intelligence.

From the paper:

Second, there was also much evidence to support Hypothesis 3, the notion of a curvilinear relationship with political extremists commanding greater cognitive resources than those in the political center 

Not too surprising for anyone who pays attention to political campaigns. Also:

First, there was substantial support for Hypothesis 1 concerning a negative, linear relationship between conservatism and cognitive ability: conservative gender role attitudes and self-descriptions predicted SAT-V and ACT.

and:

Although conducted at a different level of analysis than Study 1, Study 2 yielded some support for Hypothesis 1: In states with high political involvement, there was a linear and positive relationship between state-IQ and the proportion of Democrats in the state legislature. This finding represents a conceptual replication of important aspects of Study 1. At the same time, Study 2 also replicated an unanticipated finding in Study 1, namely, that some conservative leanings were related to higher cognitive ability. In Study 2, this finding was quite robust, but was confined to states with comparatively low political involvement. Unfortunately, Study 2 did not allow the examination of different kinds of conservative leanings, but relied on the proportion of Democratic lawmakers in a state’s legislatures. Similarly, Study 2 did not permit the examination of different aspects of cognitive ability; thus, it remains open whether observed effects were largely driven by verbal ability, as suggested by Study 1.

Personality and Individual Differences doi: doi:10.1016/j.paid.2008.08.003

Is there a relationship between political orientation and cognitive ability? A test of three hypotheses in two studies

Markus Kemmelmeier

Abstract

Two studies tested one linear and two curvilinear hypotheses concerning the relationship between political conservatism-liberalism and cognitive ability. Study 1, focusing on students at a selective US university (n = 7279), found support for the idea that some dimensions of conservatism are linked to lower verbal ability, whereas other dimensions are linked to higher verbal ability. There was also strong support for political extremists both on the left and right being higher in verbal ability than centrists. Study 2 employed aggregate data pertaining to the 50 US states and demonstrated that conservatism was linked to lower cognitive ability in states with high political involvement, but found conservatism to be correlated with higher average ability in states with low political involvement. The discussion addresses potential implications and criticisms of this research.

Link