The 'Out of Africa' theory is that all humans now living are descended from ancestors who came out of Africa 60,000 years ago and spread out throughout the world. Therefore the argument goes there is no such thing as race because we are all descended from the same ancestors.
The only trouble is that some of the evidence doesn't tally up with the 'Out of Africa' theory and the alternative Multi-regional Theory looks to be a viable alternative explanation. The Multi-regional Theory is that modern humans evolved from and interbred with more ancient humans from successive waves of 'Out of Africa' that happened many times over a long period of time, and that they subsequently evolved to become modern humans in the different regions of the globe.
For instance the archaeology of Australia is intriguing and there is evidence that suggests that Homo Erectus may have made it all the way into Australia as shown by the Kow Swamp skeletons. And that these more ancient humans co-existed in Australia with a more gracile and modern looking type of human called Mungo Man.
http://www.convictcreations.com/aborigines/prehistory.htm