Scientists Find Clues of 'Ghost' Human Ancestor in West Africa

Scientists find evidence of 'ghost population' of ancient humans

Homo sapiens first appeared a bit greater than 300,000 years in the past in Africa and later unfold worldwide, encountering different human species in Eurasia which have since gone extinct together with the Neanderthals and the lesser-recognized Denisovans.

With difficulties in obtaining a full fossil records and ancient DNA, scientists' understanding of the genetic diversity within West African populations has been poor. The authors call for more analysis of modern and ancient African genomes to reveal the nature of this complex history. What they found is the presence of DNA from "an archaic ghost population" in modern West African populations' genetic ancestry. The researchers also note that it's possible humans interbred with several waves of different hominids over thousands of years. And though humans eventually became established outside of Africa and began to separate and spread to populate the world, Europeans and Asians are nevertheless descended from a lucky few who managed to leave Africa and seed the rest of the planet.

Some data inferred that the unknown human population might have been present in Africa in the past, but the recent discovery is the conclusive form proof that confirms this theory. Now, by comparing 405 genomes of West Africans with Neanderthal and Denisovan genomes, Arun Durvasula and Sriram Sankararaman found differences that could be best explained by introgression by an unknown hominin whose ancestors split off from the human family tree before Neanderthals.

In ancient times the world was home to many related species or subspecies of human and when these groups came into contact, mating was not out of the question.

"They seem to have made a pretty substantial impact on the genomes of the present-day individuals we studied", Sankararaman said.

The study took four populations-two from Nigeria, one each from Sierre Leone and Gambia. The species of about 20,000 individuals eventually crossbred with the ancestors of modern west Africans in the last 124,000 years. The researchers tracked how new variants of genes arose in each branch of humans.

"It's very likely that the true picture is much more complicated", Sankararaman told the Guardian.

Ancestors of modern West Africans interbred with a yet-undiscovered species of archaic human, similar to how ancient Europeans mated with Neanderthals, researchers report.

"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", said John Hawks, an anthropologist at the University of Wisconsin-Madison, who was not involved in the research. "I think we're going to find more and more of these "ghost" populations coming up". It is tempting to speculate.

The unknown group "appears to have split off from the ancestors of modern humans a little before when Neanderthals split off from our ancestors", he says. "We haven't discovered enough fossils in most of Africa to say we know what was there".



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