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‘Ghost’ ancestors: African DNA study detects mysterious human species

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'Ghost' ancestors: African DNA study detects mysterious human species

WASHINGTON (Reuters) – Scientists examining the genome of West Africans have detected signs that a mysterious and extinct human species crossed our species tens of thousands of years ago in Africa, the latest evidence of humanity's complicated genetic ancestry.

Photo: Yinka Sotomi stands atop Oluma Rock, a spiritual site for the Yoruba tribe, overlooking the city of Abeokuta in southern Nigeria on April 16, 2007. REUTERS / Finbarr O & # 39; Reilly / Photo by archive

The study indicated that today's West Africans trace a substantial proportion, from 2% to 19%, of their genetic ancestry to an extinct human species – what the researchers called the "ghost population".

"We estimate that the crossing occurred approximately 43,000 years ago, with wide ranges of uncertainty," said Professor of Human Genetics and Computer Science, University of California, Los Angeles (UCLA), Sriram Sankararaman, who led the study published this week. in Science Advances magazine.

Homo sapiens first appeared more than 300,000 years ago in Africa and then spread around the world, finding other human species in Eurasia that have since become extinct, including the lesser known Neanderthals and Denisovans.

Previous genetic research has shown that our species interbred with Neanderthals and Denisovans, with modern human populations outside Africa still carrying DNA from both. But while there is an ample fossil record of Neanderthals and some fossils of Denisovans, the newly identified "ghost population" is more enigmatic.

Asked what details are known about this population, Sankararaman said: "There is not much at this stage."

"We don't know where this population could have lived, whether it corresponds to known fossils and what their final destination was," added Sankararaman.

Sankararaman said that this extinct species appears to have diverged some 650,000 years ago from the evolutionary line that led to Homo sapiens, before the evolutionary division between the lineages that led to our species and the Neanderthals.

The researchers examined genomic data from hundreds of West Africans, including the Yoruba people of Nigeria and Benin and the Mende people of Sierra Leone, and then compared that with the Neanderthal and Denisovan genomes. They discovered segments of DNA in West Africans that could be better explained by ancestral crossing with an unknown member of the human family tree that led to what is called genetic "introgression".

It is not clear whether West Africans obtained genetic benefits from this gene flow a long time ago.

"We are beginning to learn more about the impact of the DNA of archaic hominins on human biology," said Sankararaman, using a term that refers to extinct human species. “Now we know that Neanderthal and Denisovan DNA were harmful in general, but there were some genes in which that DNA had an adaptive impact. For example, adaptation to altitude in Tibetans was probably facilitated by a denisovan introgressive gene. "

Reporting by Will Dunham; Editing by Sandra Maler

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