Scientists examining the genomes of West Africans have found the latest evidence of humankind’s complicated genetic ancestry as they detected signs that a mysterious extinct human species interbred with our own species tens of thousands of years ago in Africa.
The study published in the journal Science Advances indicated that present-day West Africans trace some 2 to 19 per cent of their genetic ancestry to an extinct human species and the researchers have been calling it the “ghost population.”
While the transfer of genetic information from Neanderthals and Denisovans has been documented in modern humans outside Africa, not much has been known about the contribution of archaic hominins to the genetic variation of present-day Africans. However, the new study sheds some light over the issue.
“We estimate interbreeding occurred approximately 43,000 years ago, with large intervals of uncertainty,” said Sriram Sankararaman — the human genetics and computer science professor at the University of California, Los Angeles (UCLA) — who led the study.
Researchers believe that homo sapiens first appeared more than 300,000 years ago in Africa and later spread worldwide. They encountered with other human species in Eurasia and have since gone extinct along with the Neanderthals and the lesser-known Denisovans.
There is an ample fossil record of the Neanderthals and a few fossils of Denisovans. The previous genetic research showed that our species interbred with both the Neanderthals and Denisovans as the modern human populations outside of Africa still carry DNA from both. However, the newly identified “ghost population” is more enigmatic.
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For their research, the scientists examined genomic data from hundreds of West Africans including the Yoruba people of Nigeria and Benin and the Mende people of Sierra Leone. They compared this data that with Neanderthal and Denisovan genomes to find DNA segments in the West Africans that could best be explained by ancestral interbreeding with an unknown member of the human family tree that led to what is called genetic “introgression.”
The researchers do not know much about this population. Sankararaman said, “We don’t know where this population might have lived, whether it corresponds to known fossils, and what its ultimate fate was,” reported Reuters. Researchers believe that before the evolutionary split between the lineages that led to our species and to the Neanderthals, this extinct species seems to have diverged roughly 650,000 years ago from the evolutionary line that led to Homo sapiens.