more important for those in a relatively healthy environment. That is, the difference in heritability across the groups is due to differences in environmental variation rather than differences in the genetic effects. This can be seen in the components of the model where the genetic variance is virtually identical for the two groups (16.32 vs. 16.24), but there is more environmental variation among those with less than a college education than among college graduates (14.84 vs. 10.86). Comparable results are shown in the work of Johnson and colleagues (2011), who used a large study of twins from the Danish Twin Registry (~20,000 twin pairs) to calculate genetic and environmental contributions to BMI; increasing levels of education are associated with increasing heritability of BMI, but this is because there is less overall phenotypic variance among the most-educated. The genetic contribution to the overall variance remains virtually identical.
