May 14, 2005

The mitochondrial time depth of humanity

The supplementary materials of the recent article on the Orang Asli of Malaysia, include a very useful table of the time depth of various human mtDNA clades.

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The most striking feature of these estimates is of course the close temporal agreement between the main Eurasian clades, N, M, and R at around 60-65ky, and their temporal proximity with L3, their parental clade at around 84ky.

The vast majority of living humans, including virtually all non-Africans are descended from L3. By contrast, the common ancestor of all humans has a time depth of 203ky, or almost 2.5 times more ancient.

This means, that e.g., an Australian, Korean, Indian, European, and many Africans have a common mitochondrial ancestor that lived 2.5 times later than the common ancestor of all humankind.

The situation with Y-DNA is similar, but the time depths are much shallower: most Africans and all non-Africans are descended from the M168 male, while all humans share an ancestry that is 1.5-2 times older.

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").

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 major human groups can then be described as follows:

Significantly Paleoafrican:

1. Sanids
2. Pygmids
3. Negrids

Afrasian-Paleoafrican:

4. Aethiopids

Entirely Afrasian:

5. Australasids
6. Europids
7. Mongolids

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