How much of greatness is nature vs. nurture? Sports Illustrated writer David Epstein challenges Malcolm Gladwell’s “10,000 hours” rule in a new book about the science of training, The Sports Gene. A lot depends on individual biology, and there are cultural factors, too:

“Usain Bolt is a great example. He was 6’4” when he was 15 years old and blazing fast. He wanted to play soccer or cricket. What are the chances anyone lets him run track in the U.S.? To me, it’s zero. There’s no way he’s not playing basketball or football. Nowhere but Trinidad, the Bahamas, Barbados, and Jamaica would a guy that’s 6’4”, with blinding speed, be allowed to run track instead of something else. People have asked me, ‘Should we do genetic screening for the best athletes or at least some sort of measurements?’ Yes, measuring kids and trying to fit them into the right sport for their body type absolutely works. That’s why you saw Australia and Great Britain up their medal haul with their talent search programs when they had their Olympics. However, when there’s a sport that’s most popular in an area, you don’t have to do that because you already have the natural sifting program. You don’t have to go hunt for the best football players in America because they’re already going to go play football and then we select them.”