Scientists Find a Mysterious ‘Ghost Lineage’ In the DNA of West Africans
(Inside Science) — A mysterious extinct “ghost” human lineage that was an much more distant relation than Neanderthals might have interbred with the ancestors of trendy West Africans, considerably contributing to their gene pool, a new research finds.
Although trendy people at the moment are the solely surviving lineage of humanity, others as soon as lived on Earth. Some made their approach out of Africa earlier than we did, together with the acquainted Neanderthals in Eurasia and the newfound Denisovan lineages in Asia and Oceania. It is not fully clear whether or not these lineages can be thought of species or subspecies, however the teams had identifiable genetic variations. Prior work estimated the ancestors of trendy people cut up about 700,000 years in the past from the lineage that gave rise to Neanderthals and Denisovans, and the ancestors of Neanderthals and Denisovans diverged from each other about 400,000 years in the past.
The story is a bit extra tangled than the timeline suggests, as genetic evaluation of fossils of these extinct lineages has revealed they as soon as interbred with trendy people, unions that will have endowed our lineage with useful mutations as we started increasing throughout the world about 194,000 years in the past. Neanderthal DNA makes up roughly 1.eight% to 2.6% of the genomes of trendy people from exterior Africa, whereas Denisovan DNA makes up four% to six% of trendy Melanesians.
Any quantity of now-extinct human lineages that when existed inside Africa might have hybridized with trendy people there as effectively. However, the sparse nature of the historical human fossil file in Africa makes it tough to determine DNA from such “ghost lineages” in trendy people.
Instead of looking for historical human fossils throughout Africa, the scientists regarded for genetic traces of ghost lineages in trendy Africans. They in contrast 405 genomes from trendy folks from West Africa with ones from fossils of Neanderthals and Denisovans, specializing in DNA that stood out from the West African genomes roughly as a lot as Neanderthal and Denisovan DNA did from trendy human genomes general.
The researchers detected statistical anomalies they prompt have been greatest defined by interbreeding between West Africans and an unknown historical human lineage whose ancestors diverged from these of trendy people earlier than the cut up between Neanderthals and trendy people. Four West African teams — Yoruba in southwestern Nigeria, Esan in southern Nigeria, Gambians in western Gambia, and Mende in Sierra Leone — might derive 2% to 19% of their DNA from a ghost lineage, the researchers mentioned.
“Interbreeding among highly diverged human populations has been common through human evolution,” mentioned research senior creator Sriram Sankararaman, a computational geneticist at UCLA.
A quantity of ghost lineage genetic variants have been unusually frequent in the Yoruba and Mende genomes, suggesting they could confer some evolutionary benefits. These included genes concerned in tumor suppression, male copy and hormone regulation.
Previous analysis additionally hinted at interbreeding with ghost lineages in Africa, reminiscent of a 2011 research inspecting sub-Saharan Africa and a January paper investigating western Central Africa. The ghost lineage examined in the January research “is likely the ghost lineage we are seeing,” Sankararaman mentioned. “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 answers to.”
These findings underscore how “it is not a question of whether our ancestors interacted with other hominins, but it is a question of when, where, who,” mentioned evolutionary genomicist Omer Gokcumen at the University at Buffalo in New York, who didn’t participate on this analysis. “I think we will need additional ancient genomes from Africa to more properly address these questions.”
The scientists estimated this ghost lineage diverged from the ancestors of Neanderthals and trendy people as much as 1.02 million years in the past and interbred with the ancestors of trendy West Africans from 124,000 years in the past as much as the current day. “One limitation of our study is that we have mainly sampled present-day West African populations,” Sankararaman mentioned. They do not know but how far the ghost lineage unfold throughout Africa, he mentioned.
The scientists intention to investigate folks throughout Africa for indicators 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,” Sankararaman mentioned.
The researchers detailed their findings on-line Feb. 12 in the journal Science Advances.
This article initially appeared in Inside Science. Read the authentic right here