Revealed: first DNA profiles of ancient people who roamed a lush Sahara
Baku, April 4, AZERTAC
Ancient DNA extracted from two women who died in what is now Libya around 7,000 years ago is now helping researchers to reconstruct the origins of these early Saharans. The women’s DNA profiles, described in a study published on 2 April in Nature, represent the first full Saharan genomes from the African Humid Period — and reveal that the people were remarkably isolated from other African populations.
“The prehistory of North Africa is a big puzzle, and we only have a few pieces available,” says Rosa Fregel, a geneticist at the University of La Laguna in San Cristobal, Spain, who was not involved in the research. The work is “a significant contribution to the palaeogenomics of North Africa”, she says.
Ancient genomes from North Africa are hard to come by. Almost all palaeogenetic work is concentrated in Europe and Asia. Ancient DNA is especially rare in the Sahara, where high temperatures and strong ultraviolet light quickly degrade genetic material in remains.
That’s why it’s important to explore sites that are protected from the elements, says Nada Salem, an archaeologist at the Max Plank Institute for Evolutionary Anthropology in Leipzig, Germany.
One such site is the Takarkori rock shelter in southwestern Libya. Between 2003 and 2007, archaeologists uncovered the remains of 15 people who were buried between 8,900 and 4,800 years ago at Takarkori. Two of the corpses — both belonging to women who lived between 7,000 and 6,000 years ago — had naturally mummified.
Archaeological evidence at the site suggested that the Takarkori women belonged to a group of herders who appeared in the region around 8,000 years ago. This marked a major transition in the way of life of early Saharans, who had previously all been hunter-gatherers. Some researchers have suggested that Saharans learnt herding by intermarrying with people who were migrating into North Africa from the Levant.
To test this, Salem and her colleagues sequenced the Takarkori genomes and compared the DNA to that of around 800 modern humans and 117 ancient genomes from around Africa, southern Europe and the Middle East. The team found that the Takarkori women had only small traces of Levant ancestry — suggesting that any intermingling had happened long before the advent of herding in the region.
What’s more, the analysis struggled to connect these early Saharans to any other ancient group. “This was puzzling for us. How is it that this lineage has not spread either to the east or the west or to the south?” says Salem.
The latest research is the first genome-wide analysis of the Takarkori women. But a 2019 study reported the sequence of mitochondrial DNA from these remains. This revealed that the women belonged to a population that broke off from sub-Saharan Africans 60,000 years ago, around the same time as the ancestors of all modern humans who settled outside Africa. This hinted that ancient North Africans remained genetically isolated from almost all other Africans for most of prehistory.
Salem and her colleagues could make only one strong connection between the Takarkori genomes and other ancient Africans: the women shared ancestry with hunter-gatherers who lived in Morocco around 15,000 years ago. The analysis further suggested that the Takarkori women were more closely related to a person who died 45,000 years ago in what is now the Czech Republic than to a person whose 4,500-year-old remains were found in East Africa.
This means that herding probably arrived as a result of cultural adoption rather than through migration, says Salem. More ancient DNA will need to be found in other Saharan sites to confirm this trend for other Saharans living during the African Humid Period, says Fregel.
The return of the desert probably cut people off as water sources became scarcer. But the genetic isolation of the Takarkori women suggests that even when the Sahara was lush, it was still a barrier to travel. “It’s not easy for us to believe,” says Salem. “But this is what we found.”
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