Trends in inequality of opportunity: changes in heritability of education over time in The Netherlands

Inequality of opportunity and its trend over time is one of the most prominent policy concerns in Western countries. In social sciences, intergenerational transmission of education is often used as an indicator of inequality of opportunity. However, this neglects the role of genes. Twin studies parse out the effects of genes, the shared environment and the non-shared environment. This study uses population-wide data on twins and siblings from integral registers of Statistics Netherlands to assess trends in genetic influence (‘heritability’) and the influence of the shared environment on educational attainment in birth cohorts 1964–1997, including trends in gene × SES interactions. We adapt the classical twin design to estimate heritability in the absence of zygosity information. We found no evidence that inequality increased. In contrast, heritability of educational attainment increased and the shared environmental influence decreased between 1964 and 1970 and again between 1992 and 1997. Furthermore, the 1964–1979 cohort group but not the 1980–1997 cohort group showed a gene × SES interaction: heritability was lower in the lowest SES group than in the highest SES group.