What we are seeing evidence of and I have recently demonstrated this.
Is that the American Southeast is one of only a few places on Earth where a large human population can sustain themselves through just hunting and gathering. It appears that there have been "Era's" throughout time where the South was consistently warmer and wetter than it is today. During those time periods of warm/wet human populations got large, more food was available. At the end of the Ice Age, roughly 10-11k years before present the South had one of the largest populations of people in the America's.
It wasn't until the people of South and Central America began domesticating crops and started farming that their populations got larger than what was here. (Roughly 6-7000 yrs ago)
Beginning around 13-1100 years ago people in the South began maize horticulture and their population got significantly larger, rather quickly.
There is a lot more to it than that. You can learn more for cheap by joining the Alabama Archaeological Society.
http://www.alabamaarchaeology.org/ 
