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Updated Feb 14, 2020

Scientists may have discovered what they describe as a “ghost population” of ancient humans who lived more than 500,000 years ago after sequencing the genomes of several West African populations. Up to a fifth of the sequenced individuals’ DNA contained genes that could be traced back to this missing human subspecies. Arun Durvasula and Sriram Sankararaman, two computational geneticists at the University of California in Los Angeles (UCLA), gathered 405 genomes from four West African populations. They used statistical techniques to determine if an influx of genes possibly occurred in the ancient past, with the results supporting this theory in every case.
For millennia, various species and subspecies of humans wandered the planet and interbred. This is why Europeans to this day hold trace genetic material from our Neanderthal cousins, whereas indigenous Australians, Polynesians, and Melanesians carry genes from a separate group of ancient humans known as Denisovans. Prior research suggested that a similar distinct subspecies of human existed in Africa, but without any fossil evidence or surviving DNA to study, the theory remained a weak one until now.
Durvasula and Sankararaman pored over the genetic sequences before them to find any portions of DNA that differed from those of modern humans. Their preliminary results showed that this “ghost population” left a sizable genetic imprint on their tested group, comprised of two communities from Nigeria, one from Sierra Leone, and one from The Gambia. Their study is far from conclusive, but Sankararaman told The Guardian that two theories emerge as to what happened: the ghost population split from the Neanderthals between 360,000 and 1 million years ago, whereupon 20,000 individuals interbred with the ancestors of modern-day West Africans some 124,000 years ago. Alternatively, there could have been multiple waves of mating over thousands of years, or there could have been an as-yet-unknown number of other ancient human subspecies who lived in the region.
The UCLA research is only the beginning and Sankararaman expects the full picture to be vastly more complicated. Their research will have to expand into the fields of archaeology and anthropology to find the remains of these ancient humans and discern how they lived. Further details of the study can be read in the Science Advances journal.

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