[prion]

A few years ago a tribe was discovered in the Amazon that was living a basically stone-age hunter/gatherer existence. They'd never had contact with the outside world until their discovery. And, they weren't the first tribe found in that region who'd never encountered more civilized races.

You have to be careful with this one, as the Tasadays (the prototypical tribe of this kind) were discovered to be a hoax. A better example, familiar to all of us, would be the American Indian. The vast majority of tribes remained hunter-gatherers right up until...well, as long as we let them.

You can't make the assumption that a life of cities and agriculture is happier than a nomadic life. If there's enough land to sustain you, why would you want to settle in one spot? And that's the rub. Agriculture developed first where there wasn't enough land to sustain a nomadic existence for the population.

Of course, when the Magic Book tells people that the giant grownup in the sky created the earth a few thousand years ago, you aren't going to get anywhere with argument.

[VadeRetro]

Agriculture developed first where there wasn't enough land to sustain a nomadic existence for the population.

Jared Diamond Guns, Germs, and Steel makes the point that the ancient Near East had a wonderful combination of factors, most of all a set of wild grasses which (although not nearly as productive as their modern descendant cultivars) had highly edible seeds.

There tends never to be "enough land" in a fertile valley in that it will either overpopulate or attract raiders by dint of its very fertility.