The genetics of African KhoeSan populations match the geography of the Kalahari Desert
(Click to enlarge)
Photo courtesy of Justin Myrick.
Photo courtesy of Brenna Henn.
Geography and ecology are key factors that have influenced the genetic composition of human groups in southern Africa, according to new research discussed in the journal GENETIC, a publication of the Genetics Society of America. 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 linked to the ecogeography of the desert region of Kalahari. The name KhoeSan refers to several indigenous populations of southern Africa; The KhoeSan speak “click” languages and include both hunter-gatherer and herder groups. They are genetically distinct and remarkably isolated from all other African populations, suggesting that they were among the first groups to diverge from the ancestry of all humans. Much scientific interest has focused on the 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 studied the genetics of southern African populations for more than a decade. She notes that there is a tendency to group all the natives of southern Africa into one group – often referred to as “Bushmen” – but in fact the KhoeSan comprises 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,” says Henn. Genetic differences between human populations are strongly correlated with their linguistic histories, and both of these factors are also related to geography. Henn argues that ecology and geography together are probably a better explanation of genetic differentiation between groups than linguistic differences or subsistence method (i.e. hunting/gathering or farming). However, much of the research on southern African populations had previously focused on linguistics and subsistence, with little attention given to ecogeography.
Henn and his colleagues analyzed the genetic information of the KhoeSan. They collected genome-wide data from three South African populations: the Nama, the ≠Khomani San and the South African Color Groups (SAC). Their analysis also included samples from 19 other southern African populations. It quickly became apparent that the geography of the Kalahari Desert was closely tied to the population structure they discovered. The outer rim 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 KhoeSan populations than originally expected. Previous work has argued for a pattern of north-south divergence among human groups, but this new work identifies five primary ancestors in the region, indicating a geographically complex set of migration events responsible for heterogeneity. observed in 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 complex politics of the region in the post-apartheid era. Most populations in South Africa and Zimbabwe no longer identify as KhoeSan and have been absorbed into other populations over the past 500 years. Yet their findings add to the body of knowledge surrounding the history of southern African people – while complicating it.
“There are a lot of threads of information to pull together — linguistics, subsistence, geography, genetics, archaeology. They don’t always come together easily,” says Henn.
The challenge continues to fascinate Henn and his colleagues. She established a field site in 2005 and has maintained and developed it over the years while continuing to research ancestry 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 student from South Africa. I am very proud of our collaboration and her excellent work,” says Henn.
Much 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 enormous diversity in the populations of southern Africa. These groups speak differently, appear distinct and have divergent genetic histories. They are not homogeneous people, and the historical and prehistoric factors that led to their divergence are still being explored. It’s amazing how much work there is to do.”