Scientifically, there is really only one race, the human race. The so called races are social constructs based on phenotype.
Mitochondrial DNA studies suggest that all humans, regardless of race or color, have a common ancestor, an African woman, who lived about 50,000 years ago. When the climate changed, bands of people migrated into the mideast, then from there some into Europe and some into Asia and eventually the Americas. Racial traits such as skin color, hair texture, etc, are thought to be the result of genetic drift and climate adaptations. We are mostly descended from the Cro-Magnon subspecies of hominids, although it is now becoming apparent that some people of European descent may have up to 5% Neanderthal genes. Bones recently found in a Croatian cave suggest hybridizing perhaps 25,000 years ago.
Some people say that the different varieties of humanity are the result of genetic experiments by extraterrestrials on various bands of humans at various times and places. Some of these experiments went awry, leading to various genetic defects that seem to concentrate in certain ethnic groups. I like this idea myself, although there is no scientific evidence to back it us. As a sci-fi fan, I feel it has far more appeal than other theories concerning the descendants of Seth, Cain, Ham, etc.