The latest focus of Quammen's careful attention is Charles Darwin, father of modern biology and source of an idea so radical its implications are still only imperfectly understood: evolution by natural selection. Rather than the extensively covered journey aboard the Beagle, Quammen's The Reluctant Mr. Darwin tracks the naturalist's life through the 20 years afterward -- 20 years when he kept his explosive idea under wraps, pondering when and how to release it to the world.