The historical perspective on racial diversity begins with Homo sapiens when they emerged out of Africa, though there is some debate on this theory resulting from recent discoveries of extensive draught that would have prevented migration past the draught zone. The historical perspective holds that Homo sapiens from Africa spread over time to all the various regions where humanity now exists, in some cases using then existent land bridges for migration routes. The sequences of migrations were followed by species differentiation such as Darwin saw among finches in the Galapagos Islands.
DNA genome projects have now identified modifications to the historical theory as the DNA of Neanderthals and the newly discovered Denisovans are found in Europeans, Asians and inhabitants of New Guinea. Neanderthals DNA relates to Asians and to a lesser degree to Europeans while Denisovan DNA relates to New Guineans.