By David Brooks, The New Yorker 1/17/11 Harold and Erica got their first glimpse of each other in front of a Barnes & Noble. They smiled broadly as they approached, and a deep, primeval process kicked in. Harold liked what he saw, from the waist-to-hip ratio to the clear skin, all indicative of health...

Friends-they are generous and cooperative with each other in ways that appear to defy standard evolutionary expectations, frequently sacrificing for one another without concern for past behaviors or future consequences. In this fascinating multidisciplinary study, Daniel J. Hruschka synthesizes an array...