Genes for class, education and IQ

Barely a week passes until another paper gets published in which researchers delve into genetic material and find associations with higher level human behaviours which have always been of great interest: the class or status a person achieves in society; the extent to which they have learned some of the collective wisdom of society; and their ability to solve problems on their own.

Frankly, I find these associations between DNA and human behaviours pretty surprising. It was not the way I was brought up. My early education, as far as I can recall it, hammered in the notion that most things in life depended on effort. Teachers argued that the diligent application of one’s self to set tasks would result in greater skills, and the building of character. From this perspective the real school motto was: Do your homework. The most savage judgment meted out by this Spartan system to miscreants was that they were: “steeped in self pity and lazy to the core”.  Your self was not considered a subject of interest, only your results.

My tertiary education took on a more sociological flavour. Of course some effort was required, the Professors argued, but if the class structures were not conducive, then all your efforts could come to naught. Class had a big effect on your life chances, and it was all very unfair. Hence the impact, as I have already described, of my being offered a university foundation year which itself had grown out of the Workers’ Educational Association, offering adult education to the British working class, based on interest and merit, not the capricious circumstances of class allocation. Finding many bright people in working class occupations who had not had the benefit of an education, many of these professors were tempted to argue that the only difference between social classes was due to the unmerited accumulation of wealth and social connections by exploitative practices. Given that assumption, then many things follow, among which is the assumption that it is always legitimate to “control” for social class as a handicapping variable, in the sense that there cannot really be any difference between classes other than the hand of fate. Therefore, poking about in the wriggly, squishy reproductive fluids would not be likely to have anything to say about the class structure of society.

E Krapohl and R Plomin (2015) Genetic link between family socioeconomic status and children’s educational achievement estimated from genome-wide SNPs.  Molecular Psychiatry (2015), 1–7

 http://www.nature.com/mp/journal/vaop/ncurrent/pdf/mp20152a.pdf

Krapohl and Plomin say in their abstract: One of the best predictors of children’s educational achievement is their family’s socioeconomic status (SES), but the degree to which this association is genetically mediated remains unclear. For 3000 UK-representative unrelated children we found that genome-wide single-nucleotide polymorphisms could explain a third of the variance of scores on an age-16 UK national examination of educational achievement and half of the correlation between their scores and family SES. Moreover, genome-wide polygenic scores based on a previously published genome-wide association meta-analysis of total number of years in education accounted for ~ 3.0% variance in educational achievement and ~ 2.5% in family SES. This study provides the first molecular evidence for substantial genetic influence on differences in children’s educational achievement and its association with family SES.

I do not know if you share my surprise that educational achievement and social class can now be linked to the molecular level. We live in interesting times. Moving onwards, there is a nexus between genes, class and attainments which it would be good to understand. Selection for intelligence makes sense to me, but selection for class takes a little more time to sink in.

Here we report the first investigation of genetic influence on the variance of children’s educational achievement using DNA alone. The same DNA-based methods can also be used to estimate genetic influence on the covariance between traits. This enabled us to investigate possible genetic mediation of the best predictor of children’s educational achievement, their family’s SES. This correlation is often interpreted causally as family SES causing differences in children’s educational achievement.20 However, it remains unclear whether and to what extent the association between family SES and children’s educational achievement is genetically mediated, because twin and family research is limited to studying phenotypes that can vary within a family. Key aspects of children’s environment such as poverty, parental education and neighbourhood cannot be investigated using the twin method because it is methodologically impossible to decompose variance in phenotypes shared within twin pairs.

The DNA-based technique, genome-wide complex trait analysis fits the effects of genome-wide single-nucleotide polymorphisms as random effects in a mixed linear model to estimate variance or covariance captured by all SNPs simultaneously. Contrary to traditional family-based methods that estimate the genetic contribution to phenotypic variation or co-variation by known kinship coefficients, GCTA relies on empirical genetic resemblance established from identity by state inferred from genome-wide SNP similarity of ‘unrelated’ individuals.

Our GCTA results show that SNPs that are associated with both family SES and GCSE scores account for about half of the phenotypic correlation between SES and GCSE. Mediation analysis suggests that about one-third of this genetic effect also extends to children’s intelligence, but two-thirds of the genetic association between family SES and GCSE scores is independent of intelligence. In GPS analysis, we show that SNPs associated with total years of education in adulthood discovered by an independent large GWA meta-analysis13 explain up to 3% of the variance in children’s educational achievement in our sample, and up to 2% of the variance after controlling for intelligence.

The GCTA heritability estimate of 31% for children’s performance on a UK national examination at the end of compulsory education corroborates the vast literature of traditional family based methods, mostly the twin method, showing that variation in children’s educational achievement is under substantial genetic influence,4,5,7–9,45,46 with heritability estimates converging at ~ 50%. This commonly observed discrepancy in phenotypic variance explained by pedigree-based methods (that is, twin and family) and population-based methods (that is, GCTA) occurs because GCTA only captures genetic variance contributed by additive effects of common SNPs that are in sufficient linkage disequilibrium with the causal DNA variants.

An interesting note of caution emerges about the power of intelligence:

we find that children’s intelligence accounts for about one-third of the GCTA association between family SES and children’s educational achievement. However, it is interesting that two-thirds of the GCTA association is not accounted for by children’s intelligence. This finding of intelligenceindependent shared genetic variance between family SES and children’s educational achievement suggests that differences in educational achievement at the end of compulsory education and the level of education and occupation attained in adulthood are not merely the manifestation of differences in intelligence. This is in line with twin research that suggests that the heritability of educational achievement reflects many genetically influenced traits such as personality and self-efficacy, not just intelligence.

 

In summary, different ways of looking at the genetic code are beginning to provide ways of generating small but interesting predictions about complex behaviour, which very probably will get stronger either as more methods of analysis are employed, or when someone comes up with a theory which simplifies the number of comparisons to be made. Will you, dear reader, come up with the next step?