QUOTE : BORN TO RUN In his book Racing the Antelope: What Animals Can Teach Us about Running and Life, biologist Bernd Heinrich describes the human species as an endurance predator. The genes that govern our bodies today evolved hundreds of thousands of years ago, when we were in constant motion, either foraging for food or chasing antelope for hours and days across the plains. Heinrich describes how, even though antelope are among the fastest mammals, our ancestors were able to hunt them down by driving them to exhaustion—keeping on their tails until they had no energy left to escape. Antelope are sprinters, but their metabolism doesn’t allow them to go and go and go. Ours does. And we have a fairly balanced distribution of fast-twitch and slow-twitch muscle fibers, so even after ranging miles over the landscape we retain the metabolic capacity to sprint in short bursts to make the kill.