Genetic Diversity in South America

["Peopling of the Americas" not "rock pile" related]

I tend to see these studies as somewhat naive but, for what it is worth: [Click here]

My problem is that in 200 years people could and would criss-cross the continent both east-west, north-south, etc. Add say 40 thousand years of mixing and where populations settled and live today is more a reflection of good vs bad environment than it is a reflection of which direction those populations came from originally. The argument about "founder affect" would seem to apply more to plants than people, since people are much more mobile than prehistorians give them credit for.