As a senior writer for Sports Illustrated, Dave Epstein helped break the story that Alex Rodriguez tested positive for steroids in 2003. He's written for the Swimsuit Edition--which he describes as the cushiest assignment ever--and he covered the 2008 Beijing Olympics. Like anyone who has spent a lot of time in and around sports, one question has always nagged at him: how much of a difference do genetics make in athletic performance. Wading into issues like race and gender, Epstein's book lays out the scientific realities of what we today know about the role of genetics in top-level athletic performance. In today's episode, Dave tells us about hyper-muscular babies, the African tribe that dominates distance running and what trait is over represented among top female athletes and fashion models.

The Sports Gene: Inside the Science of Extraordinary Athletic Performance is available in all good bookstores. Be sure to Rate and Comment on iTunes.