Genetic prediction of educational attainment: the important role of parental behaviour

Scientists are building powerful predictors of our educational attainment based on genetic information. These ‘polygenic scores’ measure the genetic load that individuals carry for a specific trait. Considered individually, genetic variants have tiny effects, but when these are added up into a polygenic score, they explain a considerable proportion of the variability that is seen in educational outcomes across a population (up to 16% in school achievement (1)).

This ability to explain variation means that polygenic scores are described as game changers, rivalling other standard predictors of how well we do on our educational journeys such as family socioeconomic status (2). Although polygenic scores for educational attainment are not able to predict how far one particular person goes in education, they are valuable tools for population-level research, for example on the mechanisms and consequences of social change (3) and social mobility (4).

However, we need to know where the predictive value of polygenic scores for educational attainment stems from, and it’s not only genes…

 

Our new study published in the journal Psychological Science provides evidence that a considerable fraction of the predictive value of polygenic scores for education actually comes from the influence of the home environment provided by genetic relatives.

To study the complex entwining of the influences of genes and the home environment on education, we drew upon the classic ‘natural experiment’ for disentangling nature and nurture – adoption. Figure 1 below depicts how comparing adopted and non-adopted individuals allows us to extricate genetic influences from environmental effects (5).

In genetically related families (left part of Figure 1), children’s polygenic scores for education are associated with their own educational attainment, but are also correlated with their parents’ genetic variation. This parental genetic variation influences child education indirectly, via parental behaviours that shape the home environment, such as reading books together.

Without adjusting for these indirect effects of parental genetics on child education, estimates of effects of children’s polygenic scores may be inflated, since they reflect effects of the child’s genes and environmentally mediated effects of the parent’s genes.

In contrast, when children are adopted (right; Figure 1), the link between their polygenic scores for education and the family environment is broken, because adoptees are not genetically related to the parents. Therefore, their polygenic score can only be connected to their educational outcome ‘directly’ without any indirect influences of their parents’ genes acting through the environment.

Figure 1: comparing the polygenic score prediction of educational attainment in non-adopted and adopted individuals.

Within an unusually large and relatively unexplored sample of ~6000 adoptees from the UK Biobank (6), we observed that polygenic scores explained 3.7% of the variation in educational attainment. This reflects the direct effect of individuals’ own genetic material on their educational attainment. Strikingly, education polygenic scores explained double this amount (7.4%) in a large sample of participants who were not adopted and reared with their biological parents. This suggests that half of the prediction of education polygenic scores, in samples of non-adopted individuals, stems from effects of parental genes that are linked to education and act via the environment. The results are consistent with results from several recent studies using different family-based polygenic score study designs (7–9).

Importantly, the environment is still important for the direct genetic effect among adoptees. Especially for complex human behaviours like educational outcomes, individuals’ genes link to their educational attainment via intermediate pathways that are likely to be both social and indirect. For example, children’s genetic variation influences them to seek and evoke chances to learn new things from the people around them. So the term ‘direct’ just means that the polygenic score association stems from children’s own genomes rather than their parents’. Another reason that polygenic scores are socially contingent is that they are specific to the study population. Someone with a high polygenic score for spending time in education in the United Kingdom might have a completely different polygenic score if it were calculated in the context of a different socio-cultural and educational system.

Clearly, we need to consider for the social contingency of polygenic scores for educational attainment. But this study also shows that it is essential to account for the role of genetics in studies of parental influences on education. ‘Environmental’ measures like parents’ education cannot be assumed to have environmental effects on children. Parental education is partly influenced by parents’ genes, and may predict child education because these genes were transmitted to children. Polygenic scores provide useful control variables to allow social science researchers to rule out genetic confounding of environmental effects.

In short, genes and home environments work together to shape educational attainment, with genetic influences on how parents create educationally supportive environments for their children playing an important role. We found that associations between polygenic scores and educational attainment partly reflect these effects of environments created by genetically related parents. This evidence goes against genetically or environmentally deterministic explanations of why people achieve a certain level of education, and adds to the pressure to interpret findings based on polygenic scores for complex socially contingent traits with caution (10).

References

  1. Allegrini AG, Selzam S, Rimfeld K, von Stumm S, Pingault JB, Plomin R. Genomic prediction of cognitive traits in childhood and adolescence. Mol Psychiatry. 2019 Apr 11;24(6):819–27.
  2. Plomin R, von Stumm S. The new genetics of intelligence. Nat Rev Genet. 2018 Jan 8;19(3):148–59.
  3. Rimfeld K, Krapohl E, Trzaskowski M, Coleman JRI, Selzam S, Dale PS, et al. Genetic influence on social outcomes during and after the Soviet era in Estonia. Nat Hum Behav. 2018 Apr 9;2(4):269–75.
  4. Ayorech Z, Krapohl E, Plomin R, von Stumm S. Genetic influence on intergenerational educational attainment. Psychol Sci. 2017 Sep;28(9):1302–10.
  5. Rutter M. Genes and Behavior: Nature-Nurture Interplay Explained. Wiley; 2006.
  6. Allen NE, Sudlow C, Peakman T, Collins R, UK Biobank. UK biobank data: come and get it. Sci Transl Med. 2014 Feb 19;6(224):224ed4.
  7. Kong A, Thorleifsson G, Frigge ML, Vilhjalmsson BJ, Young AI, Thorgeirsson TE, et al. The nature of nurture: Effects of parental genotypes. Science (80- ). 2018 Jan 26;359(6374):424–8.
  8. Bates TC, Maher BS, Medland SE, McAloney K, Wright MJ, Hansell NK, et al. The Nature of Nurture: Using a Virtual-Parent Design to Test Parenting Effects on Children’s Educational Attainment in Genotyped Families. Twin Res Hum Genet. 2018 Mar 13;21(2):73–83.
  9. Selzam S, Ritchie SJ, Pingault J-B, Reynolds CA, O’Reilly PF, Plomin R. Comparing Within- and Between-Family Polygenic Score Prediction. Am J Hum Genet. 2019 Aug 1;105(2):351–63.
  10. Response to Charles Murray on Polygenic Scores – Michelle Meyer – Medium [Internet]. [cited 2020 Apr 9]. Available from: https://medium.com/@michellenmeyer/response-to-charles-murray-on-polygenic-scores-e768cf145cc
Rosa Gillespie Cheesman

Author Rosa Gillespie Cheesman

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