We investigated the heritability of educational attainment and how it differed between birth cohorts and cultural–geographic regions. A classical twin design was applied to pooled data from 28 cohorts representing 16 countries and including 193,518 twins with information on educational attainment at 25 years of age or older. Genetic factors explained the major part of individual differences in educational attainment (heritability: a2 = 0.43; 0.41–0.44), but also environmental variation shared by co-twins was substantial (c2 = 0.31; 0.30–0.33). The proportions of educational variation explained by genetic and shared environmental factors did not differ between Europe, North America and Australia, and East Asia. When restricted to twins 30 years or older to confirm finalized education, the heritability was higher in the older cohorts born in 1900–1949 (a2 = 0.44; 0.41–0.46) than in the later cohorts born in 1950–1989 (a2 = 0.38; 0.36–0.40), with a corresponding lower influence of common environmental factors (c2 = 0.31; 0.29–0.33 and c2 = 0.34; 0.32–0.36, respectively). In conclusion, both genetic and environmental factors shared by co-twins have an important influence on individual differences in educational attainment. The effect of genetic factors on educational attainment has decreased from the cohorts born before to those born after the 1950s.
One of the stylized facts of behavior genetics that isn’t well known to the public is that “shared environment” doesn’t matter that much. By this, I mean shared home environment. This was the major thesis of Judith Rich Harris’ The Nurture Assumption. So what’s going on with this result? The shared environment does seem to matter for educational attainment!
First, I want to touch on how these sorts of results might be interpreted. On Twitter some have suggested that a low shared environment fraction is promoted by hereditarians to emphasize how we can’t change things in regards to the status quo. My first thought was fear that competitive investment in children does return positive yields, and how much more as a parent will I have to invest???
The point is that a particular empirical result has a lot of different conclusions for a lot of different people. It’s not as predictable as you might think.
But in regards to this result, I asked a friend who is a behavior geneticist, and his response calmed me. Basically educational attainment is an output that naturally has a lot of family inputs. Far more than raw IQ. For example, families may know how the college application process works, and how to write the essay, and which extracurriculars to do. Additionally, it’s pretty obvious difference families emphasize education differently, and this is going to matter for students on the margin. I know many people of the same rough intelligence, the ones who went to college had particular family expectations that differed from those who did not go to college.
If you care about social egalitarianism, I think one takeaway is to enforce mandatory standardized testing to identify students who might be promising, and subsidize university for them. Standardized tests are loaded toward the well-off, but far less than all other measures.