Mike, are you saying the various races, or colours, of humans have been on each separate continent since Gondwanaland broke up? We've been around for more than sixty five million years? Extremely unlikely.
Also don't forget that most deserts in the world have been much moister at times. As your original posting says, no problem for even H. erectus to move through the Gobi Desert at times. The article suggests that human movement has been going on much longer and at a greater level than we currently think.
There are many genetic markers of migrating populations besides the ones mentioned in your original posting. Regarding American Indians not being a hybrid population try this site:
Karafet et al (1999) Ancestral Asian Source(s) of New World Y-chromosome Founder Haplotypes. Am. J. Hum. Genet. 64: 817-831.
http://www.journals.uchicago.edu/AJHG/jo...6940161261Guest Y-chromosome from Central Asia, Mitochondrial DNA from further south: Mongolia, Tibet China and Korea.
Re horses and monkeys. It's my understanding that horses actually evolved in North America, moved out from about three million years ago and then were exterminated in North America by the ancestors of the American Indians. Monkeys seem to have become isolated in South America when that continent split from Africa near the end of the Cretaceous.
