Even Charles Darwin, that human decoder ring of bizarre behavior, found the idea of saving a stranger's life to be a total head-scratcher.

He was onto something. Something huge. It wasn't just how to run; it was how to live, the essence of who we are as a species and what we're meant to be.

But yeah, Ann [Trason] insisted, running was romantic; and no, of course her friends didn't get it because they'd never broken through. For them, running was a miserable two miles motivated solely by size 6 jeans: get on the scale, get depressed, get your headphones on, and get it over with. But you can't muscle through a five-hour run that way; you have to relax into it, like easing your body into a hot bath, until it no longer resists the shock and begins to enjoy it.

The words of the social critic Eric Hoffer were ringing true: "Every great cause begins as a movement, becomes a business, and turns into a racket."

Way before we were scratching pictures on caves or beating rhythms on hollow trees we were perfecting the art of combining our breath and mind and muscles into fluid self-propulsion over wild terrain.

Extreme heroism springs from something that no scientific theory can fully explain; it's an illogical impulse that flies in the face of biology, psychology, actuarial statistics, and basic common sense.

Know why people run marathons? …Because running is rooted in our collective imagination, and our imagination is rooted in running. Language, art, science; space shuttles, Starry Night, intravascular surgery; they all had their roots in our ability to run. Running was the superpower that made us human — which means its a superpower all humans posses.