Twins Say It’s Both, And Nurture Enters Early

As expected, genes played a big role in influencing general cognitive ability, with genetic influences measured by age 7 accounting for about half of the variation in scores at age 30.

But environment also had a significant and lasting impact.

One of the most exciting findings was that 10% of the variability in adult cognitive ability was explained by environmental influences before year one or two.

The older the children got, the more influence genes had and the less environment had.

This suggests that even the pre-preschool environment matters.