O "ghost population”- a group of ancient humans thought to have lived in Africa about half a million years ago – had their genes found by scientists in modern humans. Traces of the unknown ancestor emerged when researchers analyzed genomes of West African populations and found up to a fifth of their DNA it seemed to have come from missing relatives.
Published in Science Advances, geneticists explain how they think that the ancestors of modern Western Africans crossed with archaic humans hitherto unknown tens of thousands of years ago.
If so, it would prove to be similar to the mating of ancient Europeans with Neanderthals.
Sriram Sankararaman, a computational biologist who led the research at the University of California at Los Angeles, revealed the extent of the unknown DNA.
He said: "In the West Africans we look at, everyone has ancestry from this unknown archaic population."
The world was once home to many human related species and subspecies.
When these different species intersected, they sometimes mated.
As a result, many modern Europeans carry a handful of Neanderthal genes.
Meanwhile, Australians, Polynesians and indigenous Melanesians carry genes from Denisovans, another group of archaic humans.
The analysis suggested that it had in all cases.
The scientists then scanned African genomes for pieces of DNA that looked different from modern human genes.
This allowed them to extract strings that probably came from an old relative.
So, comparing them to Neanderthal and Denisovan genes, the scientists concluded that the DNA had come from an unknown group of archaic humans.
Sankararaman said: "They appear to have had a substantial impact on the genomes of the current individuals we studied – they represent 2% to 19% of their genetic ancestry".
Of the four populations studied, two came from Nigeria and one from Sierra Leone and The Gambia.
Although the conclusions are far from definitive, the scientist's best estimates suggest that the "phantom population" separated from the ancestors of Neanderthals and modern humans between 360,000 and a million years ago.
A group of perhaps 20,000 individuals was created with the ancestors of modern West Africa at some point in the past 124,000 years.
Some other explanations are possible, according to Sankararaman, for example, there may be several mating waves over thousands of years – or even a number of populations yet to be discovered by archaic human relatives.
He said, "It is very likely that the real picture will be much more complicated."