Contributor(s): Professor Steven Pinker | One of the world's best-known psychologists argues that violence within and between societies - both murder and warfare - has declined from prehistory to today. He discusses the influence of organised government and the extraordinary power of progressive ideas - and offers insights into what this trend tells us about ourselves. Steven Pinker is the Johnstone Family Professor in the Department of Psychology at Harvard University and is the author of six books, including The Language Instinct, How the Mind Works, The Blank Slate and The Stuff of Thought. This event marks his new book The Better Angels of our Nature: The Decline of Violence in World History and Its Causes.