By guest blogger Stuart Ritchie
For decades, we’ve known from twin studies that psychological traits like intelligence and personality are influenced by genes. That’s why identical twins (who share all their genes) are not just more physically similar to each other than non-identical twins (who share half their genes), but also more similar in terms of their psychological traits. But what twin studies can’t tell us is which particular genes are involved. Frustratingly, this has always left an ‘in’ for the incorrigible critics of twin studies: they’ve been able to say “you’re telling me these traits are genetic, but you can’t tell me any of the specific genes!” But not any more.
With a new method, “polygenic scoring”, behaviour geneticists can now look to see whether people have specific genetic variants or not, and based on this, make some impressively accurate predictions about how they will behave in the future. Particularly in the case of two new studies, this development also means researchers are getting themselves into a whole new set of controversies.
The method is relatively simple. Imagine you’d found in a study that smarter people are much more likely to have one particular version of a gene than people who are less intelligent. You could then, in an entirely new sample, see if people with this “intelligence gene” were doing any better than those without it. The polygenic scoring method is just this, writ large – instead of looking at whether people have one specific genetic variant that’s linked to a particular psychological measure, geneticists look across hundreds of thousands of points on the genome, totting up who has more of the genetic variants that make them susceptible to the trait in question.
Two new papers have applied this technique in the context of educational success – in this case, they built their polygenic scores on the basis of previous gene-hunting studies that had identified the specific gene variants found more often in people who stay in school for longer.
In the first paper in Psychological Science, with the not-at-all-provocative title “The Genetics of Success”, Daniel Belsky and colleagues aimed the education polygenic score at a whole host of life outcomes in the thousand-strong Dunedin Study, a cohort of New Zealanders who have been followed from birth up to age 38. The results are comprehensive, and pretty stunning.
The children with more education-linked genes (that is, higher polygenic scores) learned to read faster. They did better on intelligence tests. They were more likely to go to university, and less likely to have financial problems. They were more likely to leave New Zealand to find job opportunities abroad, and more likely to choose a partner of higher social status. The idea is that the education-linked genes make people smarter, harder-working, and more socially successful—traits that help you lead a more “successful” life. Importantly, all this was predictable from a score that, in theory, could have been calculated on (or even before) the day the participants were born.
All of the above predictions were pretty weak though, in the sense that the polygenic score generally only explained one or two percent of the variance in each of the above traits and outcomes. This is where the second paper published in Molecular Psychiatry comes in. Using an even newer polygenic education estimate from a more recent gene-finding study (published in Nature this year), Saskia Selzam and colleagues found that their polygenic score explained a remarkable 9.1 per cent of the variance in age-16 GCSE results in a sample of 4,300 British teenagers. Because of this impressive effect size, Selzam and colleagues said their study “…represents a turning point in the social and behavioural sciences”. This is a little over the top: I see it more as an incremental (yet vital) step in a long march of studies that are changing the way we think about education.
The polygenic scores are already pretty good predictors: in Selzam’s study, they have just about half of the predictive value of asking about the parent’s socio-economic status, or testing the child’s IQ at age 7 (and the scores are based on DNA variants that are unchanged since birth and can be measured with a simple saliva or blood test). As we discover more about the genetics of education, the predictions will become more and more powerful. Then what? Do these studies usher in a new era of genetic testing to select children for different types of education? Not quite.
First, these results ‘explain variance’ at the group level, and we can’t easily translate this to individual prediction – yet. To do that, we’d need a representative reference panel with which to compare individuals, like the standardization samples used in IQ research. It’s only a matter of time before this becomes a reality for many traits. Second, as the authors of these new polygenic studies note, these results don’t necessarily have clear policy implications: some might argue that we should use the scores to predict who will do best in school and select them into higher-quality education; others may argue we should use the scores to identify those who are likely to struggle. Some will suggest both, some neither.
These varying interpretations – and the quickly advancing science – are why it’s crucial to begin a proper, fact-based debate about the potential uses of these genetic predictors. Is it acceptable to predict people’s educational attainment from a genetic score in practical settings, or should these methods only be used in research? Is it just like giving children an aptitude test, like the 11+, early in life, and if so do the same caveats apply? What if the long-term consequences of this genetic research involve screening and selecting embryos for higher polygenic education scores, as has previously been suggested? The only way to answer these thorny ethical questions is to understand the details and limitations of the genetic research: ignorance and denial are no longer an option.
Post written by Stuart J. Ritchie for the BPS Research Digest. Stuart is a Research Fellow in the Centre for Cognitive Ageing and Cognitive Epidemiology at the University of Edinburgh. His new book, Intelligence: All That Matters, is available now. Follow him on Twitter: @StuartJRitchie