It is common to distinguish between Africans and non-Africans, with the former being much more genetically diverse than the latter. But, the real "gap" in human origins seems to be between the really old Africans ("Paleoafricans") and the rest ("Afrasians").Now, a new paper has come along that provides further support for the ancient split among humans in Africa, and its more recent "healing".
The Paleoafrican element is entirely confined to Africa, while the Afrasian one is found in both Africa and Eurasia. Indeed, modern humans can be entirely split into two groups: (i) a group of "pure" Afrasians which includes all non-Africans, and (ii) a group of Afrasian-Paleoafricans which includes all non-Caucasoid Africans. Human groups of entirely Paleoafrican origin, unhybridized with the younger Afrasians are no longer in existence.
The Afrasians are a recent branch of humankind, and one which was for a great length of time separated reproductively from the Paleoafricans. This accounts for the reduced genetic diversity of Eurasians who are descended entirely from the Afrasian branch; by contrast, Sub-Saharan Africans and East Africans are the result of the intermixture of the Afrasians with the Paleoafricans, and this accounts for the high genetic diversity and antiquity of these populations.
The BBC has a story on this.
Ancient humans started down the path of evolving into two separate species before merging back into a single population, a genetic study suggests.The American Journal of Human Genetics doi:10.1016/j.ajhg.2008.04.002
The genetic split in Africa resulted in distinct populations that lived in isolation for as much as 100,000 years, the scientists say....
"We don't know how long it takes for hominids to fission off into separate species, but clearly they were separated for a very long time," said Dr Spencer Wells, director of the Genographic Project.
"They came back together again during the Late Stone Age - driven by population expansion."...
Dr Wells told BBC News: "Once this population reached southern Africa, it was cut off from the eastern African population by these drought events which were on the route between them."
Modern humans are often presumed to have originated in East Africa and then spread out to populate other areas. But the data could equally support an origin in southern Africa followed by a migration to East and West Africa.
The genetic data show that populations came back together as a single, pan-African population about 40,000 years ago.
This renewed contact appears to coincide with the development of more advanced stone tool technology and may have been helped by more favourable environmental conditions.
"[The mixing] was two-way to a certain extent, but the majority of mitochondrial lineages seem to have come from north-eastern Africa down to the south," said Spencer Wells.
The Dawn of Human Matrilineal Diversity
Doron M. Behar et al.
The quest to explain demographic history during the early part of human evolution has been limited because of the scarce paleoanthropological record from the Middle Stone Age. To shed light on the structure of the mitochondrial DNA (mtDNA) phylogeny at the dawn of Homo sapiens, we constructed a matrilineal tree composed of 624 complete mtDNA genomes from sub-Saharan Hg L lineages. We paid particular attention to the Khoi and San (Khoisan) people of South Africa because they are considered to be a unique relic of hunter-gatherer lifestyle and to carry paternal and maternal lineages belonging to the deepest clades known among modern humans. Both the tree phylogeny and coalescence calculations suggest that Khoisan matrilineal ancestry diverged from the rest of the human mtDNA pool 90,000-150,000 years before present (ybp) and that at least five additional, currently extant maternal lineages existed during this period in parallel. Furthermore, we estimate that a minimum of 40 other evolutionarily successful lineages flourished in sub-Saharan Africa during the period of modern human dispersal out of Africa approximately 60,00070,000 ybp. Only much later, at the beginning of the Late Stone Age, about 40,000 ybp, did introgression of additional lineages occur into the Khoisan mtDNA pool. This process was further accelerated during the recent Bantu expansions. Our results suggest that the early settlement of humans in Africa was already matrilineally structured and involved small, separately evolving isolated populations.