Genetic maps of African Khoesan populations at the geography of the Kalahari desert
Newswise – Geography and ecology are key factors that have influenced the genetic makeup of human groups in southern Africa, according to new research discussed in the journal GENETIC, a publication of the Genetics Society of America. By investigating the ancestors of twenty-two KhoeSan groups, including new samples from the Nama and Khomani, the researchers conclude that the genetic clustering of southern African populations is closely related to the ecogeography of the Kalahari Desert region. .
The name KhoeSan refers to several indigenous populations in southern Africa; KhoeSan people speak “click” languages and include both hunter-gatherer groups and pastoralists. They are genetically distinct and remarkably isolated from all other African populations, suggesting that they were among the first groups to diverge from the ancestors of all humans. Much scientific interest has focused on KhoeSan as researchers attempt to reconstruct this early divergence; however, little genetic material has been collected until the last decade.
Brenna Henn, of Stony Brook University in New York, has been studying the genetics of populations in southern Africa for more than a decade. She notes that there is a tendency to lump all the indigenous people of southern Africa into one group – often referred to as “Bushmen” – but in fact the KhoeSan include many distinct populations. She and her team set out to explore the genetic diversity in the region and better understand the differences between these KhoeSan groups.
“Over the past twenty years or so, there has been a lot of interest in understanding how genetic patterns are determined by geography in addition to language,” Henn explains. Genetic differences between human populations are strongly correlated with their linguistic histories, and these two factors are also linked to geography. Henn argues that ecology and geography together are probably a better explanation for genetic differentiation between groups than language differences or method of subsistence (i.e. hunting / gathering or farming). However, much of the research on populations in southern Africa had previously focused on linguistics and livelihoods, with little attention paid to ecogeography.
Henn and his colleagues analyzed the genetic information of KhoeSan. They collected genome-wide data from three South African populations: the Nama, the ≠ Khomani San and the South African Colored (SAC) group. Their analysis also included samples from 19 other populations in southern Africa. It quickly became apparent that the geography of the Kalahari Desert was closely tied to the population structure they discovered. The outer edge of the Kalahari Desert presented a barrier to genetic mixing, while populations that live in the Kalahari basin mixed more freely.
Their results suggest a more complex history for the populations of KhoeSan than originally anticipated. Previous work argued for a pattern of north-south divergence among human groups, but this new work identifies five primary ancestries in the region, indicating a geographically complex set of migratory events responsible for the heterogeneity observed in the region. the region.
Henn points out that there are more KhoeSan populations that have not been sampled. Sampling in the region is a significant challenge for a number of reasons, including the region’s complex politics in the post-apartheid era. Most of the populations of South Africa and Zimbabwe no longer identify as KhoeSan and have been absorbed by other populations over the past 500 years. Yet their findings add to the body of knowledge surrounding the history of the populations of southern Africa – while also complicating them.
“There are a lot of threads of information to put together – linguistics, livelihood, geography, genetics, archeology. They don’t always come together easily,” Henn explains.
The challenge continues to fascinate Henn and his colleagues. She established a field site in 2005 and has maintained and expanded it over the years as she continues her ancestry research in KhoeSan. She stresses that it is extremely important for researchers conducting research in developing countries to work closely with local collaborators as they attempt to understand the genetic diversity of the region.
“The first author of this article, Caitlin Uren, is a South African student. I am very proud of our collaboration and his excellent work, ”says Henn.
Much work remains to be done to understand and uncover the factors that have contributed to the formation of the population structure of Southern Africa.
“There is great diversity in the populations of southern Africa. These groups speak differently, look distinct and have divergent genetic histories. They are not homogeneous peoples, and the historical and prehistoric factors that led to their discrepancy are still being investigated. It’s amazing how much work there is to do. “
QUOTESmall-scale human population structure in southern Africa reflects ecogeographic boundaries Caitlin Uren, Minju Kim, Alicia R. Martin, Dean Bobo, Christopher R. Gignoux, Paul D. van Helden, Marlo Möller, Eileen G. Hoal, Brenna M. HennGENETIC Sep 2016 204: 303-314; doi: 10.1534 / genetics.116.187369http://www.genetics.org/content/204/1/303