The question is not whether nurture has a role to play, because nobody of any sense has ever gone on record as denying that it does, but whether nature has a role to play at all. When my one-year-old daughter discovered a plastic baby in a toy pram one day while I was writing this chapter, she let out the kinds of delighted squeals that her brother had reserved at the same age for passing tractors. Like many parents, I found it hard to believe that this was purely because of some unconscious social conditioning that we had imposed. Boys and girls have systematically different interests from the very beginning of autonomous behaviour.