The ubiquitous Steven Pinker, a cognitive scientist at Harvard known for his bestselling books and occasional appearances on The Colbert Report, would like us to feel safe. Or at least safer than we tend to feel with all the headlines about terror, war, and crime. In his 2011 tome, The Better Angels of Our Nature: Why Violence Has Declined, Pinker showed that the rate at which we slaughter, rape, and torture each other has dropped dramatically over the centuries. Pinker says ancient tribal warfare was nine times as deadly as war and genocide in the 20th century. (Of course, this is partly a matter of proportions. The absolute numbers of dead have gone up dramatically because the population has gone up.) Now, with Rebecca Newberger Goldstein, a novelist and philosopher, Pinker is exploring the critical question of what’s inside us that has led so many societies to reject violence, impose rules of war, abolish slavery, criminalize torture, and end capital punishment. In a provocative lecture at the Santa Fe Institute this summer, Pinker and Goldstein asked if human savagery has declined because our hearts and consciences have evolved—or is it just a matter of reason winning the day? The answer: both.