i've come to the thought that 250,000 years ago, there was one continent on this planet. all over that continent were the proto-humanoid lifeforms that would eventually evolve into humans. when the continents started drifting, there were some on all the pieces that drifted. since it was all still on earth the evolutionary process continued. some evolved on the chunks that would be the americas, some on the chunk that would be australia and some on the chunks that would be northern europe. those in the cold places kept their animal like natures longer because it was colder: thinner nostrils because cold air is thicker than warm, more hair because it was colder, and white skin because of all the hair blocking what sun there was so no need for the protection of malanin from the sun. also, since there wasn't as much of the natural environment around, they developed this attitude of "resource scarcity" and hoarding resources. today these folks still try to "de-nature" the areas that they have infested. they still believe in this "resource shortage" and having to fight for resources. they still believe that there isn't anything around but them, even though there are obviously people all over the place; they have consistently sought to shove those people right out of their homes and take what has been developed as their own.
no, in tens of thousands of years, there probably wouldn't have been the changes. but in hundreds of thousands of years?
as far as the American Indian; notice how much they resemble us? as well as the mexican/hispanic/latino? the native peoples of south america? also, notice the somewhat asian cast to the Eskimo? i do think that there was a migration across europe and into the americas. but i also think that there was someone already here when they arrived.
oh, and interestingly enough; in that quarter billion years of continental drift, Africa is the only continent on the planet that has not moved!! original peoples in their original place!! (i've also seen stuff that suggests that in another couple hundred thousand years, the continents will have drifted back together again. wonder what those folks will make of these "ancient civilisations" of ours?!)