Today, the Sahara Desert is one of the most inhospitable places on our planet. But it wasn’t always this way.
Roll the clock back 7,000 years, and the Sahara was a lush, green savannah, teeming with wildlife, dotted with lakes – including one the size of modern-day Germany. It was, in other words, the perfect place for our ancient ancestors to settle.
But who were they? We might finally know.
Scientists have successfully analysed the DNA of two naturally mummified individuals from the Takarkori rock shelter, in what is now southwestern Libya. Their findings reveal something extraordinary: these ancient people belonged to a previously unknown branch of the human family tree.
The two women belonged to a so-called 'ghost population' – one that had only ever been glimpsed as faint genetic echoes in modern humans, but never found in the flesh.
“These samples come from some of the oldest mummies in the world,” Prof Johannes Krause, senior author of the new study, told BBC Science Focus. It is, he explained, remarkable that genome sequencing was possible at all, given hot conditions tend to degrade such information.
Genome sequencing is the process of reading the complete set of genetic instructions found in an organism’s DNA – a kind of biological blueprint.
Earlier studies had examined the mummies’ mitochondrial DNA, which is much more limited. It’s passed down only through the maternal line, and is far shorter than the full genome found in the cell nucleus.
“There are around 16,000 base pairs in mitochondrial DNA,” Krause said. “That might sound like a lot, but compared to the whole genome, which has 3.2 billion, it’s just a fraction."
So what did the team discover from this newly unlocked genetic treasure trove?
First, they found that this lost lineage split from the ancestors of sub-Saharan Africans around 50,000 years ago – about the same time other groups were beginning to migrate out of Africa.
Remarkably, this group then remained genetically isolated from other groups of humans for tens of thousands of years, all the way through to the time when these two women died around 7,000 years ago.
“It’s incredible,” Krause said. “At the time when they were alive, these people were almost like living fossils – like something that shouldn’t be there. If you’d told me these genomes were 40,000 years old, I would have believed it.”
This long-term isolation reveals two major insights. First, while the 'Green Sahara' – which lasted from 15,000 to 5,000 years ago – was a lush habitat for humans, it didn’t serve as a migration corridor between north and sub-Saharan Africa, as many scientists had previously assumed.
Second, there was some genetic mixing with populations to the North, including Neanderthals. But it was limited – far less than in non-African populations, which carry about ten times more Neanderthal DNA than the Takarkori people.
We know that these people were pastoralists, meaning that they kept livestock like cattle. However, their
genetic isolation suggests they adopted this lifestyle by exchanging knowledge and practices with neighbouring groups – rather than through migration and subsequent genetic mixing. Again, a surprise to the scientists.
Unsolved puzzle
The genome-wide sequencing of the mummies has revealed much about this lost human lineage. Still, many more mysteries remain.
“The greening of the Sahara only happened 15,000 years ago. Before that, it was a desert again,” Krause said. “So we actually don’t know where they were hanging out between 50,000 years ago – when they split from the southern African population – and 15,000 years ago.”
Wherever they went, they must have remained isolated for tens of thousands of years. A lost Eden perhaps? We may never know.
“It’s a real mystery,” Krause added.
Krause's study was published in Nature.
About our expert
Johannes Krause is the director of the Max Planck Institute for Evolutionary Anthropology in the Department of Archaeogenetics, Leipzig, Germany. He is also a professor of archaeogenetics at the Institute of Zoology and Evolutionary Research, Friedrich Schiller University Jena, Germany. Krause has authored more than 250 publications, mainly in peer-reviewed journals, including Nature, Science, Cell, Nature Reviews Genetics. In 2010, he was awarded the AAAS Newcomb Cleveland Prize and then the Thuringian Research Prize for Top Performance in Basic Research in 2017.
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