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Saturday, April 26, 2008

In the depths of the great-great-...-great-grandmother

A new study, by D.M. Behar et al., on the oldest human maternal lineages (mtDNA) has seen light at the AJHG (subscribers only - but will be open access in six months). As I have only access to the abstract and to the news published here and there, I can only comment so much but certainly it is great that mitochondrial genetics and specially old African ones (at the root of everyting else) are been given due attention.

The abstract is rather cryptic:

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 60,000-70,000 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.

But the news are written in a more spectacular style, suggesting that humankind was about to split in two separate species, one in southern and the other in equatorial Africa, due to isolation from each other. But later both groups came into contact again and the unity of the species was re-estabilished.

As far as I can tell this is related to the antiquity of L0, specific of Khoisan peoples of southern Africa.

Update: Science daily has an article with a maybe less dramatic approach to the same paper: Early Human Populations Evolved Separately For 100,000 Years. Here an excerpt:

Recent paleoclimatological data suggests that Eastern Africa went through a series of massive droughts between 135,000-90,000 years ago. It is possible that this climatological shift contributed to the population splits. What is surprising is the length of time the populations were separate - as much as half of our entire history as a species.

The timing of these events coincides with the onset of the Late Stone Age in Africa, a change in material culture that many archaeologists believe heralds the beginning of fully modern human behavior, including abstract thought and complex spoken language.

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