New genetic research reveals that a small group of hunger-gatherers now living in Southern Africa once was so large that it comprised the majority of living humans during most of the past 150,000 years. Only during the last 22,000 years have the other African ethnicities, including the ones giving rise to Europeans and Asians, become vastly most numerous. Now the Khoisan (who sometimes call themselves Bushmen) number about 100,000 individuals, while the rest of humanity numbers 7 billion. Their lives and ways have remained unaltered for hundreds of generations, with only recent events endangering their hunter-gatherer lifestyles. The study's findings will be published in the journal Nature Communications on 4 December 2014.
By comparing nearly all the genes of these individuals -- their genomes -- with the genomes of 1,462 people from around the world, the researchers discovered that the inflow of new genes into the Khoisan peoples has been quite restricted the past 150,000 years, indicating that this large hunter-gatherer culture was physically isolated for most of its history and that its men typically did not take wives from outside the group.
"Khoisan hunter-gatherers in Southern Africa always have perceived themselves as the oldest people" said Stephan Schuster, a former Penn State University professor, now at Nanyang Technological University in Singapore and a leader of the research team, which includes scientists at Penn State and other research universities in the United States, Brazil, and Singapore. The Nature Communication paper analyzes five study participants from different tribes in Namibia. The study investigated 420,000 genetic variants across 1,462 genomes from 48 ethnic groups in populations worldwide. These analyses reveal that Southern African Khoisans are genetically distinct not only from Europeans and Asians, but also from all other Africans. The paper's first author Hie Lim Kim, formerly at Penn State and now at Nanyang Technological University, said "It is fascinating to unravel the population history of humankind over the last 150,000 years."
By conducting extensive computational analyses, the team demonstrated that two of the sequenced individuals showed no signs of having inherited any genetic material from members of other ethnic groups. Interestingly, these individuals are the oldest members of the Ju/'hoansi tribe, which still live in protected areas of Northwest Namibia. "This and previous studies show that the Khoisan peoples and the rest of modern humanity shared their most recent common ancestor approximately 150,000 years ago, so it was entirely unexpected to find that this group apparently did not intermarry with non-Khoisan neighbors for many thousand years," said Webb Miller, professor of Bioinformatics at Penn State and a member of the research team. "The current Khoisan culture and tradition, where marriage occurs either among Khoisan groups or results in female members leaving their tribes after marrying non-Khoisan men, appears to be long-standing."
The cultural and genetic persistence of the Ju/'hoansi tribe is intriguing, the researchers say, because genetic and genomic analysis of ancient hominid lineages such as the Neanderthals, as well as non-African humans, have shown that intermarrying does occur frequently in these groups and is traceable over the entire time span of 150,000 history during which anatomically modern humans have lived. "We also observed gene flow for some of the other Khoisan groups, as defined by their largely varying language, but a key finding of this study is that, even today, individuals without genes from other communities can be identified within the Ju/'hoansi population and possibly others," Schuster said.
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The damned important question is whether or not the Khoisan have the introgressed genes proposed to be Neandertal and Denisovan in origin. If they do and the conclusion the Khoisan have been genetically isolated for that long, it throws into question the recent admixture is really what it is.
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