I watched History International last night. It had a three hour program on mankind in American. There is valid proof from bone found on the Islands just off CALIFORNIA of it being over 30,000 years old. And the many locations and digs now going on have produced tools and the waste from making them
for modern man in America from 15,000 to 12,000 years ago. It went back to studies of the evolution of man from the ape like creatures from Africa to Europe. But weather did have many effects on the early non modern mankind.
Then along comes modern mankind with the larger brain (which took about 80,000+ years to start using) and its development most likely by using language (another part of the theory) and the ability to think better to meet the requirements to survive the things nature placed in mankinds path.

But again all theories except the bones, tools and drawings which modern mankind left in the caves and on large stones in different places.