[BRIEF NOTE] On the early divergence of Khoisan peoples and the rest of humanity

[rfmcdonald]

Ian Steadman's Wired article reporting on a genetic study suggesting that the Khoisan peoples of southern Africa diverged genetically from the rest of the human species a hundred thousand years ago, before the great human migration from Africa, points to a remarkable finding about human history.

While homo sapiens evolved roughly 200,000 years ago, it appears that the Khoe-San people branched off and went their separate way around 100,000 years ago, according to research in the journal Science. That divergence, reports Live Science, comes far earlier than the human migration out of Africa, and also predates the migration into the area of other early human branches such as the Bantu or Pygmies who now live in the surrounding regions.

The geneticists, led by Carina M Schlebusch from Uppsala University, analysed around 2.3 million single-nucleotide polymorphisms (SNPs) from a sample of 220 southern Africans from 11 ethnic groups for genetic variations. The result was a noticeable split between the group who we now know as the Khoe-San and the rest of humanity dating back 100,000 years.

The Khoe-San (also spelled Khoisan, Khoesaan and Khoesan) live mainly in southern Africa, with their own distinct cultures, lifestyles and physical characteristics compared to the Bantu ethnic groups that surround them. The Khoe-San are largely divided into two groups — foragers and keepers of livestock — and their languages include distinctive click noises that aren’t found in the languages of their neighbours. Genetic adaptations were found among the Khoe-San DNA which are associated with skeletal development — a finding which may explain why they are noticeably taller than Bantu groups.

Any reasons why the split occurred are unknown. It is however likely that the harsh, dry climate and geography of Africa during that era played a part in forcing communities into isolation from one another.

GNXP's Razib Khan has made some posts on the subject with interesting discussion threads, here and here.

GenomeWeb goes into more detail.

Based on the SNP array results followed by data analysis, the researchers were able to identify what they claim is the oldest divergence event in human history. Additional statistical analysis did not localize the origin of modern humans to a single geographic region in Africa, but instead suggested a complex population history within the continent.

"We raise the possibility that modern humans emerged from a structured population, in contrast to emerging from a homogenous and possibly small population," said corresponding author Mattias Jakobsson.

Jakobsson told BioArray News that it is often suggested that early humans originated from a small, localized population in eastern or southern Africa. But according to his team's findings, the human population has actually been structured into different subpopulations "for a long time" and "it is possible that modern humans emerged from a non-homogeneous group."

Jakobsson's team's research focused on two ethnic groups indigenous to southern Africa, the Khoi and San, that share physical and linguistic characteristics and are commonly grouped together under the name "Khoisan" to distinguish them from the Bantu-speaking majority of the region. The Khoisan populations are concentrated in arid parts of the region, especially in South Africa's Kalahari Desert, and previous studies have shown that the groups are genetically diverse, and appear to have descended from a deeply divergent human lineage.

[. . .]

As the history of sub-Saharan Africa does not conform to a simple tree-like model, Jakobsson said the group's approach was designed to capture the major flow of ancestry over time, he said. Ultimately, the group was able to use a mathematical model to estimate population divergence times.

Based on these analyses, the team concluded that Khoisan populations diverged from the rest of early human populations more than 100,000 years ago, before the migration of modern humans out of Africa, which is estimated by some to have occurred about 70,000 years ago. This event also predated the divergence of central African Pygmies from other African groups, the next lineage to diverge about 50,000 years ago.

In addition, the team found stratification among Khoisan groups. For example, the researchers estimated that the San populations from northern Namibia and Angola separated from the Khoi and San populations living in South Africa between 25,000 and 40,000 years ago.