That was the real secret of the Tarahumara: they'd never forgotten what it felt like to love running. They remembered that running was mankind's first fine art, our original act of inspired creation.

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 'Tarahumara' use their legs 'as designed.' By running at a young age with minimal footwear, they naturally develop the best biomechanical use of their legs. Cushioned shoes restrict foot movements and allow for over-striding. Short strides are natural.

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.

human urine is both nutrient-rich and an effective tooth whitener

In 'Tarahumara' land, there was no crime, war or theft. There was no corruption, obesity, drug addiction, greed, wife-beating, child abuse, heart disease, high blood pressure, or carbon emissions. They didn't get diabetes, or depressed, or even old: 50-year-olds outran teenagers.

Endurance, after all, is the only reason we even exist. We think of ourselves as nature's deadliest animals, but the truth is, a naked human is the biggest wimp in the wild. We have no fangs, no claws, no strength, and no speed.