Research Findings

What studying twins tells us about inequality of educational opportunity

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March 26, 2020

Why do the children of highly educated parents so often turn out highly educated themselves? Is this inheritance largely a social affair, that the welfare state can compensate for by levelling the playing field? Or is educational attainment “mostly in the genes” and thereby beyond the influence of policy levers?

Historically, sociologists have tended to favor social explanations. At the same time we have often shied away from competing perspectives (with important exceptions). Recently, that has begun to change. Understanding the links between genetics and the social environment in generating social inequalities is increasingly a concern for social scientists.

In a recent study in PNAS, we draw on data on nearly 50,000 twins across 10 countries to show how the balance between genetic and social influences on education depends on the policy context. The countries we study are all high-income economies but range from the mobility-promoting Scandinavian welfare states to the more unequal systems found in the US or southern Europe.

In unequal countries where schooling is strongly transmitted from parent to child, the family environment turns out to be a more important channel. Conversely, in egalitarian systems where the influence of family background is less pronounced, genetic factors gain in explanatory power.

This result tells us that sociological and genetically informed perspectives are not as irreconcilable as they first might seem. But how can we know this is the case?

For as long as it has existed, sociology has grappled with the question of intergenerational status inheritance. Thanks to a long line of research we know that social mobility tends to be higher in countries with liberal social policies and more equal access to high-quality education and healthcare. Most sociologists would therefore tell you that social mechanisms are important. At the same time, our work has always been vulnerable to the objection that by failing to account for genetic inheritance, we are poorly equipped to say what is “nature” and “nurture”.

We decided to tackle this objection by comparing intergenerational mobility estimates with the large body of evidence generated by twin research.

Twin research contrasts correlations in a trait for fraternal and genetically identical twin pairs. Given certain assumptions, twice the difference between the two correlations is an estimate of the population variance accounted for by genetic differences, so-called heritability. By subtracting this figure from the total correlation in outcomes between identical twins, an estimate of the influence of shared family environment is obtained.

Such studies have been used to argue that “nurture” – social influences of the family of origin – is overrated. But relatively little attention has been paid to how this might differ by institutional context.

We wanted to know whether the balance of “nature” and “nurture” depends on whether you grew up in a society with high or low social mobility. We leverage variation across the 10 countries we study, but also across genders and birth cohorts.

The striking result is that the balance between social and environmental factors depends on the amount of intergenerational mobility in a society. Only in societies where each child is given a fair chance at success – that is, where parents’ education matters less for their children’s attainment – is the genetic pathway relatively more important. In places and times where advantage is more persistent from parent to child, factors that siblings share over and above their genes turn out to matter more.

This implies that while genes and environment both influence education, variation in intergenerational mobility is linked to social inheritance, not genes. Where there is less mobility, this is because better-off parents can help their children by other means.

What conclusions can we draw about inequality of opportunity from this work? All in all, social policies aiming to reduce socially based inequalities appear to be successful. They reduce the social transmission of education, equalizing opportunities at birth. But thereby they also unintentionally heighten the importance of genetics.

Crucially, however, this difference is relative, not absolute: the reason that genetics explains a larger share of educational attainment in egalitarian contexts is that the environmentally induced part is fading, not that genes become more important in an absolute sense.

What remains to be learned? The twin method is now rapidly being outdated by new data and methods – genome-wide association studies, polygenic scores, and so on – that allow genetic information to be incorporated in standard social science analyses. This allows us to address a whole new set of questions about which genes actually influence education, whether different traits are influenced by the same or different genes, and how this all depends on social context. It is therefore an exciting time to be a social scientist.

Genetically informed research designs come with several assumptions and limitations, and many sociologists will be tempted to dismiss them as antithetical to our discipline. Others argue that if interpreted with caution, such methods can speak to sociological concerns. Our results side with this view: by using a design explicitly taking account of genes, we were able to show just how much the environment matters.

As we continue to discover how the influence of genetics is shaped by and dependent on social context, the engagement of social scientists in this work will remain crucial.

Read more

Per Engzell and Felix Tropf. “Heritability of education rises with intergenerational mobility” in Proceedings of the National Academy of Sciences 2019.

Image: jeonsangoviaPixabay (Pixabay License)

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