@feld dog and horse breeds =/= human races. all dog breeds are descended from the same common ancestor, wolves, and all horses descend from the horses first domesticated in the Eurasian steppes. And so consequently genetic health increases when you mix dog or horse breeds, many of which have been seriously inbred into poor health outcomes. For humans, genetic studies have disproved the out of Africa hypothesis for humans, we seem to have evolved convergently from a number of distinct but different early hominid ancestor species (10% of the genome of sub Saharan Africans is from an unknown ancestor different from any other race) that have different degrees of compatibility. Rather than comparing us to dog breeds a better comparison is donkeys and horses or lions and tigers. They can breed because they have enough common ancestry but their offspring are not as genetically healthy as offspring of lions and other lions, etc.