Published: Fri, February 14, 2020
Sci-tech | By Patricia Wade

'Ghost' of mysterious hominin found in West African genomes

'Ghost' of mysterious hominin found in West African genomes

Based on this finding, they arrived at the idea that aeons ago, west Africans must have interbred with a population of archaic human we are yet to learn about.

Scientists say they have found evidence of a new population of humans that lived about half a million years ago.

Sankararaman and Arun Durvasula, a UCLA graduate student studying human genetics, used two new statistical methods that look for patterns in the genome that could reveal the presence of DNA from a distantly related unknown archaic population. Hidden deep in the DNA code of present-day humans is evidence of an extinct human species, detectable only by a few tell-tale genetic markers lingering in their ancestors. They analyzed genetic material from hundreds of people from Nigeria and Sierra Leone and found signals of what they call "ghost" DNA from an unknown ancestor. The researchers also added that the genes of this "ghost population" live on in people even today.

With difficulties in obtaining a full fossil records and ancient DNA, scientists' understanding of the genetic diversity within West African populations has been poor. Denisovan DNA seems to be mostly found in Oceanian and some East-Asian populations, but basically everyone except sub-Saharan Africans has some Neanderthal DNA lingering in their cells, around 4 percent on average.

Homo sapiens first appeared a bit more than 300,000 years ago in Africa and later spread worldwide, encountering other human species in Eurasia that have since gone extinct including the Neanderthals and the lesser-known Denisovans.

But our understanding of the relationship between ancient human ancestors within Africa, and their connection with archaic humans, is beginning to deepen.

The study published in the journal "Science Advances" mentions that this ancient "ghost population" possibly diverged from modern humans much before the Neanderthals disbanded. Recent studies have shown that, though modern West Africans do not have Neanderthal or Denisovan ancestry, there may have been introgression by other ancient hominins in their past.

The Neanderthals

Researchers recommend DNA from this team comprises in between 2% and also 19% of contemporary West Africans' hereditary origins.

The scientists are now excited to dive into the ancient genes and work out what they do.

However, the study authors admit its unknown what role the ghost genes play in humans who carry them.

"There may have been multiple waves of mating over many thousands of years". One prospect is that west Africans kept the DNA because it helped them survive and hybridize. "It's very likely that the true picture is much more complicated", he said.

Well-established research, the study says, has established the existence of Neanderthal DNA in modern European populations, and Denisovan DNA in Oceanic populations. This showed that the history of African populations was complex.

We still think that most - anywhere between about 92% and 98.5% - of the ancestry in people not living in Africa today does indeed derive from the out-of-Africa expansion.

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