The setup: it's about a lost Mexican tribe, the Tarahumaras. The book: Born to Run by Christopher McDougall.
Distance running was revered because it was indispensable; it was the way we survived and thrived and spread across the planet. You ran to eat and to avoid being eaten; you ran to find a mate and to impress her, and with her you ran off to start a new life together. You had to love running, or you wouldn't live to love anything else. And like everything else we love--everything we sentimentally call our "passions" and "desires"--it's really an encoded ancestral necessity. We were born to run; we were born because we run. We're all Running People, and the Tarahumara have always known.