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Sunday, February 7, 2021

Scientists Reveal A Strange Ghost Lineage In The DNA of West Africans

Researchers find some indication that a group of unidentified human raise with our descendants.

(Inside Science)-A new study finds a strange extinct “ghost” human ancestry that was more distant relation than Neanderthals may have produced with the ancestors of the modern West Africans, suggestively contributing to their DNA.

Image: Zacarias Pereira da Mata/Shutterstock

While modern humans are now the only remaining raise of humanity, they believed that others once existed on earth. Some went to Africa before we did, together with the familiar Neanderthals in Eurasia and the recent Denisovan Lineages (genome derives from unidentified archaic hominin), indicating this species diverged from Neanderthals and humans million years ago) in Asia and Oceana. Although it is not clear whether these lineages would be considered species or subspecies, the groups had particular genetic dissimilarities. Previous work projected the families of modern humans separated about 700,000 years ago from the race that paved the way to the Neanderthals and Denisovans. The lines of Neanderthals and Denisovans differed from the others about 400,000 years ago.


The story is a bit more twisted than what the timeframe suggests. The genetic study of fossils of these lineages has shown that they once mated with modern humans. A union that may have endowed our ancestry with beneficial mutation as we started escalating across the globe about 194,000 years ago. Neanderthal DNA makes up to 1.8% to 2.6% of present humans’ genomes from outside Africa. While Denisovan DNA makes up 4% to 6% of current Melanesians.

These extinct human lineages that once existed in Africa may have mixed with present humans there as well. The remnants of the ancient human fossil record in Africa make it hard to detect DNA from such “ghost lineages” in present humans.

Image: Bob Wilder/University at Buffalo

Instead of looking for ancient human relics across Africa, the scientists hunted for genetic hints of ghost lineages in modern Africans. Researchers compared 405 genomes from present people from West Africa with ones from the fossils of Neanderthals and Denisovans, concentrating on DNA that emerged from the West African genomes approximately as much as Neanderthal and Denisovan DNA did from present human genomes in general.

The researchers identified statistical anomalies they suggested were explained by interbreeding between West Africans and an unidentified ancient human ancestor whose lineage separated from those recent humans. Before the riven among Neanderthals in south Nigeria, Gambians in western Gambi and Mende in Sierra Leone-may originate 2% to 19% of their DNA from a ghost lineage, said the researchers.


According to study senior author Sriram Sankararaman a computational geneticist at UCLA, “interbreeding among highly diverged human populations has been common through human evolution”.

Several ghost lineage genetic variants were prevalent in the Yoruba and Mende genomes, signifying they might discuss some evolutionary advantages. These comprised genes involved in tumor suppression, male reproduction and hormone regulation.

Some studies have also given some hints at interbreeding with ghost lineage in Africa, like 2011 research studying sub-Sahara Africa and January Paper investigating western Central Africa. According to Sankararaman, the ghost lineage tested in the January study “is likely the ghost lineage we are seeing.” “A broader question of the number of these ghost lineages that have survived into present-day Africans is fascinating, which we don’t have the answer to,” Sankararaman added.

Evolutionary genomicist Omer Gokcumen at the University at Buffalo in New York said that these findings highlighted how “it is not a question of whether our ancestors interacted with other hominins, but it is a question of when, where, who”. Gokcumen did not partake in this research. He also added that “I think we will need additional ancient genomes from Africa to more properly address these questions”.

Image: Georg Berg/Alamy

1.02 million years ago and interbred with the ancestors of present west Africans from 124 000 years ago; this is what the scientists estimated when the ghost lineage separated from Neanderthals and modern humans’ ancestors. Sankararaman also mentioned that “one limitation of our study is that we have mainly sampled present-day West African populations.” They don’t know yet how far the ghost lineage spread across Africa”, he said.

Scientists want to study people across Africa for some hints of ghost lineages. “We are beginning to understand some of the complexities of human history, but the true picture is almost certainly even more complicated,” Sankakaraman explained.

Discoveries are coming out; studies were being conducted, hints are all over us. These may resolve some of the most significant questions that hunted us for decades, leading to the answers even our ancestors cannot explain.
By  Kris De Vera Estrella, IFY Books

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