Genetics of African KhoeSan populationsmaps to Kalahari Desert geography6 September 2016

A Nama man is holding a whip outside his tent, whileherding sheep and goats in the Richtersveld, SouthAfrica. Credit: Justin Myrick.

Geography and ecology are key factors that haveinfluenced the genetic makeup of human groups insouthern Africa, according to new researchdiscussed in the journal Genetics, a publication ofthe Genetics Society of America. By investigatingthe ancestries of twenty-two KhoeSan groups,including new samples from the Nama and the?Khomani, researchers conclude that the genetic

clustering of southern African populations is closelytied to the ecogeography of the Kalahari Desertregion.

The name KhoeSan refers to several indigenouspopulations in southern Africa; KhoeSan peoplespeak "click" languages and include both hunter-gatherer groups and pastoralists. They aregenetically distinct and strikingly isolated from allother African populations, suggesting they wereamong the first groups to diverge from theancestors of all humans. Much scientific interesthas focused on the KhoeSan as researchers try toreconstruct this early divergence; however, little genetic material was collected until the pastdecade.

Brenna Henn, of Stony Brook University in NewYork, has been studying southern African population genetics for over a decade. She notesthat there is a tendency to lump all indigenoussouthern Africans into a single group - often called"Bushmen" - but in fact, the KhoeSan includesmany distinct populations. She and her team setout to explore genetic diversity in the area and tobetter understand the differences between theseKhoeSan groups.

"For the last twenty years or so, there has been alot of interest in understanding how genetic patternsare determined by geography in addition tolanguage," says Henn. The genetic differencesbetween human populations are strongly correlatedwith their linguistic histories, and both of thesefactors are also linked with geography. Hennargues that ecology and geography together arelikely a better explanation for the geneticdifferentiation between groups than either linguisticdifferences or method of subsistence (i.e.hunting/gathering or farming). However, much ofthe research on southern African populations hadpreviously focused on linguistics and subsistence,with little attention paid to ecogeography.

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A view of arid mountains at dusk in the RichtersveldCommunity Conservancy, South Africa. Credit: BrennaHenn

Henn and her colleagues analyzed geneticinformation from the KhoeSan. They collectedgenome-wide data from three south Africanpopulations: the Nama, the ?Khomani San, and theSouth African Coloured (SAC) group. Their analysisalso included samples from 19 other southernAfrican populations. It quickly became apparentthat the geography of the Kalahari Desert wasclosely tied to the population structure that theyuncovered. The outer rim of the Kalahari Desertpresented a barrier to genetic mixing, whilepopulations that live within the Kalahari basin mixedmore freely.

Their findings suggest a more complex history forthe KhoeSan populations than originally predicted.Previous work argued for a northern vs. southerndivergence pattern among the human groups, butthis new work identifies five primary ancestries inthe region, which points to a geographicallycomplex set of migration events responsible for theheterogeneity observed in the region.

Henn points out that there are more KhoeSanpopulations who were not sampled. Sampling in thearea is a significant challenge for a number ofreasons, including the complex politics of the region

in the post-Apartheid era. Most populations in SouthAfrica and Zimbabwe no longer identify asKhoeSan and have been absorbed into otherpopulations over the past 500 years. Still, theirfindings add to the body of knowledge surroundingthe history of southern African populations - whilealso complicating them.

"There are a lot of threads of information to bringtogether - linguistics, subsistence, geography,genetics, archaeology. They don't always reconcileeasily," says Henn.

Men traveling by donkey cart through the Khomani Sancommunity in the southern Kalahari Desert, South Africa.Credit: Brenna Henn.

The challenge continues to fascinate Henn and hercolleagues. She established a field site in 2005 andhas maintained and expanded it over the years asshe continues to research ancestry in the KhoeSan.

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She emphasizes that it is extremely important forinvestigators doing research in developingcountries to work closely with local collaborators asthey try to understand the genetic diversity of theregion.

"The first author on this paper, Caitlin Uren, is aSouth African student. I'm very proud of ourcollaboration and her excellent work," says Henn.

Much work remains to be done in understandingand uncovering the factors that contributed to theformation of southern African population structure.

"There is a huge amount of diversity in southernAfrica populations. These groups speak differently,look distinct, and have divergent genetic histories.They are not homogenous people, and the historicand prehistoric factors that led to their divergenceare still being explored. It's amazing how muchwork there is to do."

More information: C. Uren et al, Fine-ScaleHuman Population Structure in Southern AfricaReflects Ecogeographic Boundaries, Genetics(2016). DOI: 10.1534/genetics.116.187369

Provided by Genetics Society of AmericaAPA citation: Genetics of African KhoeSan populations maps to Kalahari Desert geography (2016,September 6) retrieved 6 June 2022 from https://phys.org/news/2016-09-genetics-african-khoesan-populations-kalahari.html

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