In chapter two of Racing the Antilope: What Animals Can Teach us About Running & Life by Bernd Heinrich, he says:
"With the help of our infinite imagination and the technologies it has produced, we now travel faster, more economically, and well beyond the range of our muscle power. But for millions of years, our ultimate form of locomotion was running. We are, deep down, still runners, whether or not we declare it by our actions. And our minds, as much as our lungs and muscles, are a vital force that empowers our running."
"I've run at varying distances and intensities almost all of my life, probably because the primal unadorned simplicity of running appeals to me. Various games incorporate running, but only running itself touches the pure and basic essence of the tension between speed and endurance, stripped bare of our everyday world of technology, beliefs and hype."