A mysterious “ghost” of an ancient human species has been found in the genomes of modern west africans. The discovery suggests that early humans living in the region interbred with this unknown species to such an extent that they left their mark on modern humans, giving insight into a little-known area of human history.
Neanderthals and denisovans are known to be found in European and Asian DNA. These markers come from interbreeding between early modern humans and other ancient species, where their offspring inherited genes from both parents. Over time, more hybridization took place, and these genes eventually became embedded in modern humans. For example, some people in Papua New Guinea have up to 5 percent denisovan genes.
This is a process called “gene infiltration.” Neanderthals and denisovans interbred with modern humans who had left their birthplace in Africa. As a result, africans received fewer genetic inputs from denisovans and neanderthals. But scientists have little idea what kind of genetic variation it is and where it comes from.
Writing in the us journal science advances, arun dulvasula and sriram sankararaman of the university of California, Los Angeles, studied the genomes of four west African populations. The researchers then used computer models to compare the genomes with those of neanderthals and denisovans, which allowed them to study genetic variations that might have come from other ancient populations.
Their analysis revealed a “ghost” of an unknown species that contributed to genetic variation in modern west africans. They believe this contribution occurred before neanderthals separated from modern humans. They say a “simulation model” showing how this happens is at a low hybridization level “over a long period of time.”
What genes they might have passed on, and how this might have benefited early west African humans, is unclear. “A detailed understanding of ancient genetic infiltration and its role in adapting to a wide range of environmental conditions requires an analysis of existing and ancient genomes across the geographical range of Africa,” they conclude.
Yoo teixeira, of Australia’s centre for the study of ancient DNA, said their method of finding infiltration of ancient genes was “simple but very effective”.
Teixeira told newsweek: “their results strongly suggest that an ancient African species that separated from modern humans — before neanderthals and denisovans — about 600,000 years ago met and interbred with the ancestors of west africans. Interestingly, this may have occurred even before africans separated from non-africans, and human groups around the globe may have inherited the lineage of this “ghost race”.
“The results reveal complex patterns in human evolution that cannot be explained by simple narratives,” he said. The situation is only going to get more complicated, especially as more research is done in Africa, where we were born.”