This may be a book about running by feel, but I will be the first person to tell you that you will run better if you run by feel against others or against time than you will if you run by feel alone. It is easy to see why this is the case. The capabilities and limitations of every species are always linked to survival. Humans exhibit a tendency to fatigue more quickly during running (or any other form of exercise) when there is no particular urgency to the running task. How does this tendency help us survive? That’s obvious: It helps us survive by limiting unnecessary exposure to the health risks of extreme fatigue. On the flip side, it is easy to see how our capacity to run harder when there is an urgent need to run harder also helps us survive. Before there were footraces of any kind, there were humans hunting prey by running and humans fleeing predators by running. In the good old days we ran frequently to satisfy urgent needs, and it was a blessing that we could run faster and longer when chasing an antelope or being chased by a lion. Human-versus-human competitive running undoubtedly began as a form of serious play, where men established an order of rank with respect to this critical survival skill. While there is nothing so great at stake in training and racing in the twenty-first century, our genes don’t really know that. Through evolution, our species developed an instinctual tendency to run harder when chasing or fleeing something outside ourselves, a tendency that remains with us, because while our environment has changed significantly since the birth of humankind, our DNA has changed little. So today we can, if we choose, manipulate this instinct to make a game of running faster by consciously trying to run faster against the clock.