We've created an unnatural form of running. It's not just the shoes, but we run on artificial surfaces - straight ahead, hard and steady - instead of speeding up and slowing down, reacting to the terrain with changes of pace and rhythm.

We're constantly told that running will ruin our knees and outrage our hearts, but for nearly all of human existence, it was associated with freedom, vitality, and eternal youth.

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.

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.

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.

We run when we're scared, we run when we're ecstatic, we run away from our problems and run around for a good time.