[etangent]

> A complex society or a natural disaster (a la dinosaurs) wiping out megafauna sounds much more plausible than the equivalent of the primitive societies we see today.

The problem with your argument is best illustrated with that famous picture of airplane with bullet holes; the only primitive societies you see today are those that are more or less sustainable; any unsustainable primitive society would have gone into a conflict with a major industrial power and ended up being wiped out. That of course does not prove that unsustainable primitive societies never existed; in fact I would say they were the norm as humans were expanding (when the frontier is constantly expanding, there is no need to sustain anything!).