Scientists have made a surprising discovery while analyzing the DNA of modern-day African populations. The analysis revealed traces of an unknown, ghost human species previously unknown to science.

The ancestors of modern West Africans crossed paths with an undiscovered species of archaic humans, similar to how ancient Europeans mated with Neanderthals, a report suggests.

The new finding was reported in Science Advances by researchers at the University of California at Los Angeles (UCLA). It helps understand how archaic hominids added to the genetic variation of current Africans, which has been misunderstood, partly due to the limited fossil record in Africa and the difficulty of obtaining ancient DNA.

However, the new analysis of DNA present in modern-African populations has opened previously unseen doors leading to the better understanding of human origins and the variety of archaic humans that have existed in ancient times.

The new discovery adds to the mystery of human origins.

During the investigation, two scientists from the University of California School of Medicine in Los Angeles (USA), Arun Durvasula and Sriram Sankararaman, analyzed the genomes of more than 400 people from four populations in West Africa, including those from Yoruba and de Mende, in search of the segments of archaic descent.

“Using a method that can identify segments of archaic ancestry without the need for reference archaic genomes, we built genome-wide maps of archaic ancestry in the Yoruba and the Mende populations. Analyses of these maps reveal segments of archaic ancestry at high frequency in these populations that represent potential targets of adaptive introgression,” the researchers explain in the new paper.

Thanks to a computer modeling technique, which allows the identification of these segments without the need for archaic reference genomes, the researchers were able to find that between 2% and 19% of the genetic ancestry of these inhabitants was derived from an unknown source.

The scientists were of the opinion that the genes of these former hominids were introduced through an introgression process, a movement of genes between two populations that occurs when members of one pair with those of another and subsequently the resulting hybrids reproduce with members of the parental populations

“While introgression from Neanderthals and Denisovans has been documented in modern humans outside Africa, the contribution of archaic hominins to the genetic variation of present-day Africans remains poorly understood,” the researchers wrote in the study.

Not only did the new researcher reveal that this introgression did happen and there is an unknown ghost species we’ve yet to identify, but data suggests that it may have occurred relatively recent–around 35,000 years ago, according to fossil records.

This process may also have involved various archaic human species, pointing towards a complex and lasting interaction between anatomically modern humans and various different populations of ancient humans.

More data about this ghost species remains to elude experts. However, the researchers have pointed out that we could, in fact, be looking at a completely unknown species of ancient humans, which would have separated before the division between Neanderthals and modern humans.