The effects of Twitter and Facebook and all those things on people's psychologies is a really interesting question to which nobody knows the answer.

Traditionally, psychology has been the study of two populations: university freshmen and white rats.

Empty heads, cognitive science has taught us, learn nothing. The powerful cultural and personal flexibility of our species is owed at least in part to our starting off so well-informed; we are good learners because we know what to pay attention to and what questions are the right ones to ask.

I think we're going to care more about Americans than Africans. I don't think that's ever going to go away, and I don't think it's ever going to go away that people care more about their families than strangers, and their communities over other communities. But I think it would transform the world in such a good way if we could just acknowledge, at least intellectually, that an African life and an American life are the same.

When people want to inspire you to turn against some group of people, they'll often use empathy. When Obama wanted to bomb Syria, he drew our attention to the victims of chemical warfare. And in both of the Iraq wars, politicians said, "Look at the horrific things that are happening." I'm not a pacifist. I think the suffering of innocent people can be a catalyst for moral action. But empathy puts too much weight on the scale in favor of war. Empathy can really lead to violence.

I think there's some evidence that when it comes to being a doctor or nurse, a police officer or therapist, that empathetic engagement leads to burn-out. Imagine if you're dealing with severely ill children, and you felt their pain all the time, and the pain of their parents - you wouldn't be able to do that job for very long. It would kill you.

The effects of Twitter and Facebook and all those things on people's psychologies is a really interesting question to which nobody knows the answer.