A big part of the story of our species, and of how variation is apportioned within it, involves how our ancestors spread over the globe. After all, if we had simply stayed in our place of origin in Africa and not ventured out, there would be no question that we are a single entity. That is because if our species had been restricted to a single location (as many others are), two things would have ensured that differentiation into separate entities would not have occurred.