Violence and brutality are grim realities of life. So why are some people violent, and others aren’t? Are some of us born that way, or can anyone be pushed into committing acts of cruelty? What would it take for an ordinary person to become violent? In this hour, TED speakers explore the sinister side of human nature, and whether we’re all capable of violence. Psychologist Philip Zimbardo tells the story of his notorious Stanford Prison experiment and how easy it is for people to turn violent. Neuroscientist Jim Fallon uncovers the wiring of a psychopathic killer. Writer Leslie Morgan Steiner tells the harrowing story of her abusive relationship, and shares why victims of domestic violence often don’t leave. Psychology professor Steven Pinker charts the whole of human history, and says we are living in the most peaceful time in our existence.