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Scientists have recently discovered traces of DNA belonging to a group of unknown hominins in West Africa. This, they say, is evidence that some 50,000 years ago, prehistoric humans had procreated with another group of ancient humans that scientists did not know existed.

While there are no bones or ancient DNA to prove the theory, researchers say that the evidence would be in the genes of modern West Africans. By analyzing the genetic material of hundreds of people from Nigeria and Sierra Leone, they found signals of what they would call the “ghost” DNA of an unknown human ancestor.

The Homo sapiens had lived along other ancient hominin groups and there is plenty of evidence that early humans had sex with other hominins such as the Neanderthals. This is why Neanderthal genes are present in modern humans, particularly those of European and Asian descent. Early humans also mated with the Denisovans, as evidenced by the genes found in people from Oceania.

Unknown Ghost DNA

The picture of how Homo sapiens evolved away from other early human ancestors became more complicated with the discovery of the unknown ghost DNA.

Sriram Sankararaman, a computational biologist at UCLA, and his team analyzed the genomes of 405 West Africans using a statistical model to flag parts of the DNA. it pulls out chunks of DNA from the person’s genome that are likely to have come from a population different from the modern human.

While it is common knowledge that early humans had procreated with Neanderthals and Denisovans, the unusual DNA found in West Africa is not associated with either group. Sankararaman and his co-author, Arun Durvasula, believes it comes from another yet to be unnamed group.

According to Sankararaman, the term they use is “ghost” because there is no clear identity established for the archaic group yet. It is also not closely related to the known groups from which genome sequences have been pulled.

The researchers believe that the interbreeding happened around 50,000 years ago, which was around the same time modern humans were breeding with Neanderthals in other parts of the world. It is also unclear whether it was a single interbreeding event or something that had occurred over a long period of time.

Sankararaman adds that the unknown group appears to have split off from the modern human ancestors before Neanderthals split off from similar ancestors.

Biostatistics professor Sharon Browning from the University of Washington believes that the scenario at hand is realistic. In fact, she notes that the ghost DNA has appeared frequently in the genetic material, proving that the archaic populations had some DNA that might also prove to be useful to modern humans.

However, Sankararaman claims that it is not possible to know at the moment the role these genetic materials have for modern humans who have them, such as adaptive benefits or damaging consequences. He adds that it is likely to find other evidence of ghost DNA in modern humans from other parts of the world. There is always the possibility of discovering more ghost populations as genome sequences from different parts of the world are extracted.

Browning believes that it is possible that the current ghost DNA in the study might have come from multiple groups. Although it tells us of possible integration, the study does not tell how many archaic groups might have been involved.

Neanderthals have abundant DNA fossil evidence, but physical DNA samples are more challenging to get in Africa because of the climate on the continent. In order to recover DNA, the fossils should not totally disintegrate. While there have been a lot of archaic bones and fossils found in Africa, no DNA has been recovered yet, but the technology is continuing to improve.

As for the ghost population in West Africa, it is possible that they had either died off or been completely absorbed into the modern human population.

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