Here's an idea - the same emotion that drives altruistic people, drives psychopaths. It's not intuitive, but that's the finding of this week's guest, professor of psychology & neuroscience Abigail Marsh. She began her career studying child psychopathy - those kids who suddenly turn violent. She indicates how we process fear and empathize with other people's fear can be the key to understanding both altruism and psychopathy. We discuss her new book The Fear Factor: How One Emotion Connects Altruists, Psychopaths, and Everyone In-Between.