How our social structures shape our DNA — and vice versa

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The writer is a science commentator

Genetics does not get much of a look-in when it comes to the social sciences. That is a legacy from the dark days of eugenics, when researchers like Francis Galton thought that genius was hereditary and the future of humankind should lie exclusively in the hands — and wombs — of the elite.

But the omission, an international team of researchers suggests in a new analysis, glosses over a truth about the way societies are stratified today. Even though a person’s socio-economic status is broadly thought to reflect the influence of their environment, it cannot be neatly divorced from biology — and from genetics, in particular. Rather, they contend, genetics helps to shape an individual’s environment; and, in turn, the environment leaves its imprint on our genetic legacy by, for example, influencing health and who we choose to have children with.

That makes for a striking implication: that the stratified societies we create and perpetuate become crucibles for changing the genetic make-up of a population. Abdel Abdellaoui, the Amsterdam University geneticist who led the analysis, summed it up to me like this: “Societies should at least be aware that they are, intentionally or not, shaping genetic variation through social structures.” That poses a dilemma for policymakers: if our social environment is shot through with genetic influences, how should social inequality be addressed?

The title of the article, published in Nature Human Behaviour, spells it out: “Socio-economic status is a social construct with heritable components and genetic consequences.” It draws on a long human history of social stratification, going back 12,000 years to when a shift to agriculture allowed some to acquire more wealth and power than others, with those benefits tending to pass down the family line. Millennia later, in Confucian China and then Enlightenment Europe, merit-based social systems allowed individuals to socially advance more according to talent than parentage.

But large-scale studies point to valued traits, such as intelligence and education, having a heritable component — which means that genetics still plays a sorting role in social stratification. Genome-wide association studies (GWAS) look at thousands — and in some cases millions — of individual genomes to ferret out associations between genetic variants and particular traits, such as educational achievement or income.

Variations across hundreds, even thousands, of genes are combined into a “polygenic score” that captures the estimated heritability of a trait (defined as the proportion of the variation in a population that can be ascribed to inherited genetic factors). For example, a GWAS pooling 3mn genomes has found that polygenic scores, reflecting genetic factors, explain between 12 and 16 per cent of the variation in educational attainment between Europeans.

Our society then uses those traits — such as education and income — along with inherited privilege, to sort people into social strata with different social and environmental exposures, encompassing factors like housing quality, air pollution and dietary options.

Social stratification, and its genetic contribution, is also reflected in geography: in Britain, for instance, lower polygenic scores for educational attainment have been found to cluster in economically disadvantaged coal-mining towns; in Estonia, higher polygenic scores characterise the country’s two prospering university towns. The better-educated tend to live in “healthier” neighbourhoods; those left behind can be stranded in places that expose them to a greater risk of such conditions as obesity, diabetes and infectious diseases. This amounts to a “double advantage” for some — and a double disadvantage for others.

That divided state of affairs, the researchers theorise, can then be perpetuated through the generations thanks to “assortative” or non-random mating. That happens when we pick romantic partners who are socially, behaviourally and educationally like us. In this way, social standing can amplify social and genetic differences between those at the top of society and those at the bottom.

“Whether such feedback loops are a price societies pay for meritocratic progress, or something to counteract, is a question for broader debate,” Abdellaoui says, adding he does not advocate any genetic interventions given the history of eugenics, which included heinous practices such as forced sterilisation.

Rather, these complex findings challenge us to think hard about who succeeds and who gets left behind; what traits, skills and behaviours we value and reward; and how social structures of our own making have the power to shape our DNA.