The Couple Behind "Cosmos" Explores the Unlikely Evolution of Life on Earth

Daniel Lieberman is a professor in the department of human evolutionary biology at Harvard. He says that the notion of "getting exercise" — movement just for movement's sake — is a relatively new phenomenon in human history. His new book is Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding.

Thor Hanson's new book looks at the evolutionary significance of feathers in birds. Hanson tells Fresh Air that he's amazed by birds' magnitude of feathers, how feathers grow and how they're the "most efficient insulation known."

Have you ever wondered about the personal life of the man who developed the theory of evolution? On today's Fresh Air, the conservationist Randal Keynes — Charles Darwin's great-great grandson — talks about the man behind the science: his relationship with his wife, Emma, and how they handled the death of their daughter. In 2002, Keynes wrote a book on the subject called Annie's Box, which shares personal letters and diaries documenting how Darwin cared for his daughter in the last months of her life. The book is the basis for the new film Creation.