New DNA study shows humankind’s complex origins in Africa
Published 2012-09-20 | Anneli Waara
The Khoe and San peoples in southern Africa play an important role for our understanding of the evolutionary history of humans. These peoples are directly descended from the first branching of the genealogical tree of today’s humans. This is shown in a study led by Uppsala University researchers and being presented in the early online version of the journal Science today.
The study is based on an analysis of 2.3 million genetic variants from seven groups of the click-speaking Khoe and San peoples, a total of 220 individuals from southern Africa. The analysis is the largest genetic study ever of the Khoe and San peoples.
- Our study shows that most people who self-identify as Khoe or San are descendants of the earliest diversification of the human genealogical tree, says lead author Carina Schlebusch from South Africa, a postdoctoral fellow at Uppsala University.
These peoples belong to a branch that diverged from other peoples at least 100 000 years ago. This was long before modern human´s diaspora from Africa and even long before the evolutionary diversification of Pygmies in Central Africa and before the emergence of the hunters and gatherers of East Africa.
- The evolutionary history of humans in Africa is much more complex than we have believed so far. Our analyses show deep divergences among the various African peoples, with the deepest divergence involving the Khoe and San peoples, says Mattias Jakobsson, Uppsala University, who directed the study.
- When modern humans began to spread outside Africa 60-70 000 years ago, there were already clear stratification among African populations. Our data suggest that there was no single geographical origin but that several populations contributed genes to the ancestral population that lead to today’s humans.
The study also shows surprisingly great stratification among the groups. The San people from northern Namibia and Angola diverged from the Khoe and San in South Africa as early as 25 000-40 000 years ago. The study further illuminates how pastoralism spread to southern Africa. The Khoe people traditionally practise cattle-herding, unlike the San, who are hunters and gatherers. The genetic analyses show that the Khoe descend from southern San groups that potentially picked up cattle-herding from East African migrants that were assimilated into the Khoe people. The researchers were also able to demonstrate genetic changes in genes that are involved in the immune system, that regulates the structure of muscle and UV sensitivity, which may be adaptations to particular environmental conditions.
As the genetic data in the study comprise the deepest divergence among now living humans, the researchers developed a novel method to examine what genetic changes were underway when modern humans emerged more than 100 000 years ago. Among the top-five genes, there were three that regulate the structure of the skeleton, where, for example, mutations in one gene have been shown to lead to the prominent brow-ridges and rib forms reminiscent of Neanderthals.
One of the co-authors, Professor Himla Soodyall from the University of Witwatersrand, South Africa, has been studying the Khoe and San peoples for a long time. She is excited about the results and says that they clearly ascribe a prominent role to the Khoe and San peoples in the history of humankind.
Professor Soodyall, together with Mattias Jakobsson and Carina Schlebusch from Uppsala University, will be presenting the findings in South Africa, at the University of Witwatersrand in Johannesburg, and then on Heritage Day in Kalahari on 24 September, together with the San groups that took part in the study.
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