[RightWhale]

We might also assume some societal organization. The explorers would report back with fantastic tales of great spots they had found and individual clans would indeed pick up and migrate. To end up with 50 million in the Amazon basin just 1000 to 500 years ago would indicate a fairly large movement of population. I would imagine that once they reached America, they would explore the whole place immediately. Should we accept that the few archaeological sites we know would give a true picture of the nature of the populating of America?

[HamiltonJay]

New evidence can always change what we know, however we do know this, tribes tend to grow to about 30 members, when they get above this size, new tribes branch off and form, and move away to set up new encampments not very far from the original territory in agregarian societies.

Nomads follow food, not exploration, moving with the animals they hunt migrating over distances through the seasons.

At this point there is no evidence that humans conquered the americas in weeks or decads. Could it have happened that way? Sure, but right now there isn't.

I think you may have misread something, the land bridge was believe crossed during last ice age about 10-15k years ago, if I am not mistaken, and once in the americas took about another 1000 years to spread throughout the land, that would mean that people were in the amazon 9000-14000 years ago... which is more than enough time to have millions of inhabitants in a tropical rain forest basin where food is plentiful and temperature is moderate.