In accounts of men in battle, there is an incredible adrenaline rush from group-versus-group conflict. The fervor and passion of partisans is clearly rewarding; and if it's rewarding, it involves dopamine; and if it involves dopamine, then it is potentially addictive.

People are wrong when they say that everything should be more diverse, even, say, rock bands. It's an error, an overgeneralization.

The final moment of success is often no more thrilling than taking off a heavy backpack at the end of a long hike. If you went on the hike only to feel that pleasure, you are a fool. Yet people sometimes do just this. They work hard at a task and expect some special euphoria at the end. But when they achieve success and find only moderate and short-lived pleasure, they ask is that all there is? They devalue their accomplishments as a striving after wind. We can call this the progress principle: Pleasure comes more from making progress toward goals than from achieving them.

Reciprocity is a deep instinct; it is the basic currency of social life.

Diversity is not a virtue. Diversity is a good only to the extent that it advances other virtues, justice or inclusiveness of others who have previously been excluded.

I think the greatest work in social psychology from the 1950s and '60s is enormously important. I wish every high school kid could take a course in social psychology. I think we're making enormous strides in understanding the brain. These aren't yet giving us great insights, but I feel like we're on the verge of it. In five or ten years this basically searching the brain is really going to change things.

What set us apart from most or all of the other hominid species was our ultrasociality, our ability to be highly cooperative, even with strangers, people who are not at all related to us.