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. 2008 May;82(5):1130-40.
doi: 10.1016/j.ajhg.2008.04.002. Epub 2008 Apr 24.

The Dawn of Human Matrilineal Diversity

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The Dawn of Human Matrilineal Diversity

Doron M Behar et al. Am J Hum Genet. .
Free PMC article

Abstract

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 60,000-70,000 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.

Figures

Figure 1
Figure 1
Simplified Human mtDNA Phylogeny The L0 and L1′5 branches are highlighted in light green and tan, respectively. The branches are made up of haplogroups L0–L6 which, in their turn, are divided into clades. Khoisan and non-Khoisan clades are shown in blue and purple, respectively. Clades involved in the African exodus are shown in pink. A time scale is given on the left. Approximate time periods for the beginning of African LSA modernization, appearance of African LSA sites, and solidization of LSA throughout Africa are shown by increasing colors densities. For a more detailed phylogeny, see Figure S1.
Figure 2
Figure 2
Maternal Gene Flow within Africa The gradual maternal movements suggested by the first (A) and second (B) hypotheses are denoted by the ascending numerical labels. A gradient colorization system is used to illustrate the timing of the events. The temporal direction and timing of the arrows and expansion waves are general and should not be treated as firm migratory paths. (A) An initial prolonged colonization (brown) by anatomically modern humans (1) is followed by a dispersal wave (green) of a fracture of the population (2) and the localization of L0d and L0k to southern Africa (3). (B) An early Homo sapiens division in a hypothetical migration zone (1) resulted in two separately evolving populations (2) and the localization of L0 (green) in southern Africa and L1′5 (red) in eastern Africa. A subsequent dispersal event of the L0abf subset from the southern population and its mergence with the eastern population (brown) is suggested (3), resulting in the former population composed only of L0d and L0k and the latter composed of L1′5 and L0abf. Later dispersal waves from the eastern African population parallels the beginning of African LSA approximately 70,000 ybp (4). Rapid migrations during the LSA (5) brought descendants of the eastern African population into repeated contact with the southern population, peaking during the Bantu expansion (6).

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