But what really brought me back to him was that I started thinking about writing a book about kids — what we think of sometimes as a perfect child . How do we parent, what are the mechanics of giving your children what they need, so that they turn out whole and happy and strong, which is what every parent wants? And when I started looking at the research on parenting, I started seeing Harry in there. It was as if his shadows were in all this modern research. One day, I said to myself, you know, Harry Harlow's all over this, and no one knows it. He's disappeared. And wouldn't it be interesting to combine the two — to take the story of someone I thought was a genuinely fascinating person with something that I thought was genuinely fascinating science?

It changed after I started writing, because what I hadn't appreciated — and what I loved as I got into it — was how much of a revolutionary he was. So the story became the story of this very idiosyncratic psychologist and the way he pushed a revolution in psychology. At the same time, the revolutionary push was about love and relationships, so it was also the story of the way we redefined love in his lifetime. Sometimes those stories intersect, and sometimes they don't. But it's about both.