In 1977, I read Arthur Jensen about how the weakness of environment within groups suggested the same weakness between groups. This meant, in his mind, that no environmental explanation of the IQ gap between black and white was possible. It raised problems, in my mind, about whether we could ignore the role of environment between generations.

In 1987, I showed that there had been massive IQ gains (later called the “Flynn Effect”). Jensen (1998) responded that most of these gains were not true intelligence (or g) gains. In 2000, Dickens and Flynn showed that environment could be powerful between groups despite its weakness within groups. By 2007, I could show that even though IQ gains were not g gains, this did not undermine their significance and actually raised questions about the significance of g. Today, I can offer a range of insights: how to measure the factors that enhance IQ over time; how parents try to be fair to their children; how age affects cognitive competence; what signs environment gives of its ever-present causal potency; how the genetic determination (that twin studies imply) leaves room for human autonomy.