[DannyTN]

"You do realize, of course, that there are people living in South America who never discovered agriculture until contacted by explorers?"

You have a reference? That's pretty hard to believe given the ancient empires of South America. It is easier to believe that a jungle people might choose not to use much agriculture, simply because the Jungle provides sufficiently. But to not even be aware of it, I think is suspect.

[Junior]

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.

Hell, in Africa, we have the bushmen of the Kalahari who still lead a stone-age hunter/gatherer existence despite having frequent contact with their more civilized neighbors. IIRC, there are still tribes of pygmies in the central parts of Africa that haven't made the leap from the stone age yet either.