DNA Research Reveals Complicated Human Origins in Africa

These people are directly descended from the first branching of the genealogic tree of modern-day humans.

The study was led by Uppsala University (Sweden) researchers and the findings were published in the early online version of the journal Science September 20, 2012. The study is based on an analysis of 2.3 million genetic variants from seven groups of the 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.

The study demonstrated that most people who self-identify as Khoe or San are descendants of the first diversification of the human genealogic tree, according to lead author Dr. 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.

Human evolutionary history in Africa is much more complex than once thought. The analyses show great divergences among the various African peoples, with the deepest divergence involving the Khoe and San peoples, reported Dr. Mattias Jakobsson, who directed the study.

When modern humans began to travel outside Africa 60-70,000 years ago, there were already distinct stratification among African populations. These data suggest that there was no single geographic origin but that several populations contributed genes to the ancestral population that lead to modern humans.

The study also shows amazingly 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 additionally clarifies how pastoralism spread to southern Africa. The Khoe people traditionally practice cattle herding, unlike the San, who are hunters and gatherers.

The genetic analyses demonstrated 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 alterations in genes that are involved in the immune system, that regulate the structure of muscle and ultraviolet (UV) sensitivity, which may be adaptations to particular environmental conditions.

As the genetic data in the study make up the greatest divergence among now living humans, the researchers developed a novel method to assess what genetic changes were underway when modern humans emerged more than 100 000 years ago. Among the top-five genes, three 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 suggestive of Neanderthals.

One of the co-authors, Prof. Himla Soodyall, from the University of Witwatersrand (Johannesburg, South Africa), has been studying the Khoe and San peoples for a long time. She is excited about the results and noted that they distinctly assign a prominent role to the Khoe and San peoples in the evolution of humankind.

Prof. Soodyall, together with Mattias Jakobsson and Carina Schlebusch from Uppsala University, presented the findings at the University of Witwatersrand on September 24, 2012.

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Uppsala University
University of Witwatersrand