`  ::I thought of an example. The Alaska brown bear and the Grizzly bear are the same species, Ursus arctos, but they differ in size and color in different places. Ursus arctos exist in N. America and in Eurasia. So they are a pretty good ``model`` for human diversity. Then there is the Kodiak Brown Bear, which has been isolated on the Kodiak Islands and is the largest of all the Ursus arctos. It is considered a subspecies.  See: http://animaldiversity.ummz.umich.edu/site/accounts/information/Ursus_arctos.html So biologists would call the Kodiak bears a separate ``race`` or subspecies, but the way we are using ``race`` here, the Alaska Brown Bear and the Grizzly Bear are different races. The differences among the varieties of Ursus arctos seem to be color and size. If it weren't for the barrier formed by sea water, there wouldn't be a Kodiak bear because they would have been able to mate with Brown bears in surrounding territories. Just to round out the picture, the black bears are a different species from the brown bears.  So we are all like brown bears and maybe the Neanderthals are like black bears.`