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 httpanimaldiversityummzumichedusiteaccountsinformationUrsusarctoshtml 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 werent for the barrier formed by sea water there wouldnt 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