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

James Marshall
February 14, 2020

John Hawks, an anthropologist at the University of Wisconsin-Madison, told the newspaper that studies like this one, "Open a window showing us that there is much more than we thought to learn about our ancestors".

Scientists have found evidence for a mysterious "ghost population" of ancient humans that lived in Africa about half a million years ago and whose genes live on in people today.

By comparing the genomes from African populations that looked different than modern human DNA with genes from Neanderthals and Denisovans, the researchers have determined that the DNA belonged to an unknown group of ancient humans.

It cast doubt on the widely held "out of Africa" theory of human migration, meaning that modern humans originated in Africa and dispersed to the rest of the world in a single wave between 60,000 and 80,000 years ago.

According to reports, the scientists believe that the ancestors of modern west Africans at some point interbred with the yet-to-be-discovered "ghost population". They found 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".

Sriram Sankararaman, a computational biologist at UCLA and one of the study's authors, said: 'It's nearly certainly the case that the story is incredibly complex and complicated and we have kind of these initial hints about the complexity'.

Sharon Browning, a biostatistics professor at University of Washington who has studied the mixing of Denisovans and humans, says "the scenario that they are discovering here is one that seems realistic".

Their data indicated that a wave of modern humans left Africa for Europe about 200,000 years ago and interbred with Neanderthals, before migrating back to Africa.

By employing statistical techniques, the researchers looked for markers of interbreeding that may have occurred in the distant past - turns out it did.

They discovered signals of what they have termed "ghost DNA", which they believe comes from a group of humans that were previously unknown. This allowed them to pull out sequences that most probably came from an ancient relative. We haven't found their fossils, but their genes are still very much etched in the genomes of certain west African populations. "Are they just randomly floating in our genomes?" But far from making them a uniform or an inbred population, they are in fact by far the most genetically diverse peoples on Earth.

The four groups analyzed came from three countries: two from Nigeria, one from Sierra Leone, and one from Gambia. Next, the researchers plan to focus on some of these genes in order to tease out what they do.

"Actually knowing who those ancestors were, how they interacted, and where they existed is going to take fieldwork to find their fossil and archaeological remains", he told the Guardian.

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.

Other reports by Click Lancashire

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