In this the second part of his investigation of the rise, fall and rise of the genetics of intelligence, Adam Rutherford explores an era post World War Two when behavioural genetics fell far from grace. The social not biological sciences reigned supreme in the the study of intelligence and differences between children were attributed to nurture not nature.

Adoption studies were conducted to demonstrate the power of different home or school environments to transform lives.

More recent studies, however, reveal that nurture is not what most of us imagine. Parenting accounts for just a small part of the variation between children's academic performances. The environment in the womb is as important, if not more so, than conditions at home or in the classroom. Not to mention the role of chance.