In high school, I wondered whether the Jamaican Americans who made our track team so successful might carry some special speed gene from their tiny island. In college, I ran against Kenyans, and wondered whether endurance genes might have traveled with them from East Africa. At the same time, I began to notice that a training group on my team could consist of five men who run next to one another, stride for stride, day after day, and nonetheless turn out five entirely different runners. How could this be?
