The descendents of the first tool-using upright apes, some of whom were ancestors of modern humans, left Africa millions of years ago. Arguably the most storied of these populations of humans are the Neanderthals, who have haunted our imaginations for over a century. Modern archaeology and genetic science tells us that their path separated irrevocably from that of African humans, the ancestors of modern groups, at least 650,000 years ago. For over 600,000 years, up until about 40,000 years ago, Europe and much of northern Asia was the domain of the Neanderthals. And then they went extinct forever.
Or did they? Modern genetics and archaeology tells us that our ancestors left Africa about 50,000 years ago. Looking at the ancient genomes of Neanderthals and comparing them to modern humans researchers have discovered that a few percent of the ancestry of all humans outside of Africa match Neanderthals far better than Africans. In other words, Neanderthals and modern humans mixed their genes. But this is not true for all humans. Neanderthals did not exist within Africa. Human populations that arose within the continent, and remained within its boundaries, have no Neanderthal ancestry because there were no Neanderthals for them to mix their genes with. Research indicates that Neanderthals never crossed water into the African continent from Europe and Northern Asia.