Current genetic research has demonstrated that human populations native to the African continent are the most genetically diverse. Human genetic diversity decreases in native populations with migratory distance from Africa, and this is thought to be the result of bottlenecks during human migration. Humans have lived in Africa for the longest period of time, but only a part of Africa's population migrated out of the continent into Eurasia, bringing with them just a portion of the original African genetic variety. Non-African populations, however, acquired new genetic inputs from local admixture with archaic populations, and thus have much greater variation from Neanderthals and Denisovans than is found in Africa. African populations also harbour the highest number of private genetic variants, or those not found in other places of the world. While many of the common variants found in populations outside of Africa are also found on the African continent, there are still large numbers which are private to these regions, especially Oceania and the Americas. Furthermore, recent studies have found that populations in sub-Saharan Africa, and particularly West Africa, have ancestral genetic variation which predates modern humans and has been lost in most non-African populations. This ancestry is thought to originate from admixture with an unknown archaic hominin that diverged before the split of Neanderthals and modern humans.