David Epstein was always interested in science. And when he began running on the Evanston Township High School track team, he started asking himself all kinds of questions. Like, how could a group of guys, the same age, the same general size, with exact same training routines end up with completely different times for their races? The answers to those questions and more came from scientists on the frontier of genetics, and Epstein dissects it all in his book The Sports Gene: Inside the Science of Extraordinary Athletic Performance. He details what he found in his research. Photo: Flickr/fdecomite