Four of the world's most renowned thinkers take on one of the biggest debates of the modern era. "It's just a brute fact that we don't throw virgins into volcanoes any more. We don't execute people for shoplifting a cabbage. And we used to." (Steven Pinker). "The idea that because things have gotten better in the past they will continue to do so in the future is a fallacy I would have thought confined to the lower reaches of Wall Street." (Malcolm Gladwell).