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The Long Arm of the Family

Nurture, not nature, explains why some societies have more social mobility than others

The question of how life-course outcomes depend on the institution of the family is central to sociology and social demography. Few outcomes are more important in life than one's educational attainment, and a large literature studies how it depends on the family of origin – so-called intergenerational mobility research. In this field there have always been two opposing views. One seeing intergenerational transmission as "mostly in the genes" and thereby difficult to influence by policy levers; another seeing outcomes as heavily dependent on social forces. While there is a great deal of research suggesting that both genes and environment matter for educational attainment, it has been unknown how the balance between the two depends on institutional context.

In a recent study in PNAS, Per Engzell and Felix Tropf tackle this question by combining two types of family studies in social stratification – intergenerational mobility and behavior genetics research. Behavior genetics uses the natural experiment of twins to estimate the relative importance of "nature" and "nurture" for population variance in an outcome. Monozygotic twins are created when one zygote splits into two embryos, and are genetically identical. Dizygotic or fraternal twins on the other hand share on average only half of their segregating genetic material. Assuming that both twin types share similar environments to the same extent, the more similarly identical twins end up doing compared to fraternal ones, the more we can say that genes matter. These studies are often 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 setting.

In their study, Engzell and Tropf ask: does the balance of "nature" and "nurture" depend on whether you grew up in a society with high or low social mobility? They compared data on educational attainment for men and women from 10 countries and several cohorts. It turns out that in places with low mobility – where children reach a similar educational level as their parents – the family environment does more explanatory work. Where institutions promote mobility on the other hand, social inheritance fades and leaves genetic influences. So, while genes and environment both influence education, variation in intergenerational mobility is linked to social inheritance, not genes. In other words, while genes may always have an influence, where there is less mobility this is because better-off parents can help their children by other means.

The finding that genetic influences become more important in more fluid societies with lower social barriers may seem counterintuitive. However, it is consistent with a view that has been common in the field of behavior genetics. Key to understanding this puzzle is that the difference is relative, not absolute: the reason that genetics explains a larger share of the variance in educational attainment is that the environmentally induced part is fading, not that genes become more important in an absolute sense. Social scientists often tend to shy away from the idea of genetic influences, thinking that it somehow implies a necessary stability in the current social order. In contrast, as this work shows, genetic influences are most strongly manifest when the social order is subject to change.

Engzell, Per, and Felix C. Tropf. 2019. "Heritability of education rises with intergenerational mobility." Proceedings of the National Academy of Sciences, 116 (51), 25386-25388.
Author(s) of the original publication: 
Per Engzell and Felix C. Tropf