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The Recent African Origin model, also known as the (Recent) Out-Of-Africa model and the recent single-origin hypothesis, is a scientific hypothesis about the origin of humanity. It asserts that a common ancestor of all modern humans evolved in East Africa between 200,000 and 100,000 years ago. Around 60,000 years ago, a small sub-group left Africa to colonize the rest of the world, displacing other living species in the genus Homo, such as Homo neanderthalis, along the way. By about 15,000 years ago, all the continental land masses besides Antarctica were colonized by our species.
While the Recent African Origin model has become nearly universally adopted in the scientific mainstream today, this was not the case for many centuries. In fact, the Recent African Origin model was only formulated in the 1980s, based on studies of modern mitochondrial DNA (mDNA), and subsequently supported by work in physical anthropology. Prior to that, the dominant hypothesis was the multiregional hypothesis, which asserts that different races all independently developed from ancient species in the genus Homo. Multiregionalists often claim that Europeans descended from Neanderthals, for instance. Mitochondrial DNA studies have all but refuted these theories.
As previously stated, the original support for the Recent African origin model came from mitochondrial DNA testing of modern humans. Mitochondrial DNA is DNA contained within the mitochondria (power plants) of human cells, and is passed on from mother to children (matrilineally). Unlike most of the other DNA in the human body, this DNA stays essentially the same while passed from mother to child, though it does mutate over the years. Because the rearrangement of mDNA is much less extensive than that of the DNA in human chromosomes, it can be used to confirm membership of an individual in a given matrilineal lineage.
What mDNA tests have shown is that all human beings are relatively closely related for a species, and that everyone in the world can trace back their family tree to ancestors that lived in Africa less than about 60,000 years ago. The Recent African Origin model implies that humans originated fairly recently, and that most of the world was devoid of humans until fairly recently as well. Though there is a good degree of certainty on the timing of the dispersal of humans from Africa to Australia and Eurasia, there is a greater deal of uncertainty with regard to the spread of humans from Eurasia to the Americas. This event could have occurred as early as 30,000 years ago or as recently as 14,000 years ago.