Out of Africa
The Out of Africa theory is the dominant model of the geographic origin and early migration of anatomically modern humans (Homo sapiens)(a) . It arose from discoveries in East Africa less than a century ago. Previously, a more popular idea prevailed which claimed that modern humans arose from different populations of earlier hominids in various regions of the world. This regional development still has some advocates(c).
While details of the OoA theory are continually being modified in the light of new discoveries, genetic studies have only strengthened support for the theory. The most recent genetic studies suggest that “a vast inland oasis in present-day northern Botswana was once home to the founder population of all modern humans.” (b)
*New studies suggest that the early development of homo sapiens may have been more complex than previously thought(e). Chris Stringer, of the Natural History Museum, London, is quoted by The Guardian as saying that “the immediate predecessors of modern humans probably arose in Africa about 500,000 years ago and evolved into separate populations”.*
It is still uncertain whether humans left Africa in two or more waves and when did they do so. Stephen Oppenheimer, who has written extensively on the subject, maintains that a single group of migrants were involved, around 80,000 years ago. He offers a number of papers on the Bradshaw Foundation website(d).
As I see it, dating the spread of humans remains unclear to a layman such as myself. Of particular interest is determining more accurately when man first crossed the Bering Strait from Asia into America.