Scientists uncover evidence of mysterious ‘ghost population’ of ancient humans who roamed half a million years ago

SCIENTISTS have discovered evidence of a mysterious "ghost population" of an extinct branch of humans who lived half a million years ago.
Researchers found traces of the unknown ancestor's DNA in the genomes of people living today in West Africa.
It's suspected the ancestors of modern west Africans interbred with the yet-to-be-discovered archaic humans tens of thousands of years ago.
Sriram Sankararaman, a computational biologist who led the research at the University of California in Los Angeles, said: "In the west Africans we looked at, all have ancestry from this unknown archaic population."
The discovery may shed light on human genetic diversity in Africa, which has been hard to chart until now because the fossil record is sparse.
GHOST POPULATION
Unlike today, the world had many related species or subspecies of human - and it wasn't uncommon for them to mate.
As a result, modern Europeans carry a small quantity of Neanderthal genes, while indigenous Australians, Polynesians and Melanesians carry genes from Denisovans, another group of archaic humans.
Previous studies have suggested that other ancient humans once roamed Africa, but a lack of fossils or DNA has made it tricky for researchers to delve deeper into the theory - until now.
RELATED
For the new study, Dr. Sankararaman and Mr. Durvasula carried out a large-scale comparison of genetic diversity in living humans, Neanderthals and Denisovans.
They studied how new variants of genes arose in each branch of humans.
Mostly, the information fit the current thinking about human evolution.
However, in a few populations in West Africa, such as the Yoruba of Nigeria and the Mende of Sierra Leone, some of the DNA contained variants not found in other living humans, or even in Neanderthals or Denisovans.
It is always interesting and useful to see researchers applying new methods to try to get a better idea of what ancient populations might have been like
John Hawks
Dr. Sankararaman concluded that the DNA had to come from an unknown branch of ancient humans.
He explained: "They seem to have made a pretty substantial impact on the genomes of the present day individuals we studied.
"They account for two to 19 per cent of their genetic ancestry."
The scientists reckon the ghost population split from the ancestors of Neanderthals and modern humans between 360,000 and one million years ago.
The group of an estimated 20,000 people then bred with the ancestors of modern west Africans at some point in the past 124,000 years, the research suggests.
However, Dr. Sankararaman said there are other possible explanations:
Most read in news
He said: "It’s very likely that the true picture is much more complicated."
The researchers, who published their findings in , now want to examine the ancient genes to see what they do.
John Hawks, an anthropologist at the University of Wisconsin-Madison, who was not involved in the study, said: "It is always interesting and useful to see researchers applying new methods to try to get a better idea of what ancient populations might have been like."