The 'Ghost' of an Unknown Human Species Has Been Found in West Africans Living Today

The "ghost" of a mystery species of archaic human has been discovered in the genomes of modern West Africans. The discovery suggests early humans living in the region were interbreeding with this unknown species to such an extent that it left an imprint on modern populations, providing an insight into a little-understood area of human history.

It is well-known that people from Europe and Asia have traces of Neanderthals and Denisovans in their DNA. These are markers from where early modern humans interbred with other hominin species, producing children that inherited genes from both. As time went on, and more interbreeding took place, these genes eventually became embedded in modern humans. For example, some people in Papua New Guinea may be up to 5 percent Denisovan.

This is a process known as introgression. Neanderthals and Denisovans bred with modern humans that had already left Africa, the birthplace of modern man. As a result, people in Africa have less genetic input from Denisovans and Neanderthals. What genetic variation and where it comes from is not well known.

In a study published in Science Advances, Arun Durvasula and Sriram Sankararaman, from the University of California, Los Angeles, looked at the genomes of four populations of people from West Africa. These were then compared with Neanderthal and Denisovans using a computer model that allows them to look at genetic variation that could have come from other archaic hominin species.

In their analysis, they discovered the "ghost" of an unknown species of human that had contributed to the genetic variation of modern-day West Africans. They believe this contribution took place before Neanderthals split from modern humans. They say a "realistic model" of how this happened to be low levels of interbreeding "over an extended period of time."

What genes they may have passed on and how this may have benefited early humans in West Africa is unknown. "A detailed understanding of archaic introgression and its role in adapting to diverse environmental conditions will require analysis of genomes from extant and ancient genomes across the geographic range of Africa," they concluded.

João C. Teixeira, from the Australian Centre for Ancient DNA, who was not involved in the study, said their method to look for archaic introgression was "simple but very powerful."

"Their results strongly support that an African archaic (ghost) lineage that diverged from modern humans slightly before Neanderthals and Denisovans, perhaps 600,000 years ago, met and interbred with the ancestors of West African populations," he told Newsweek. "Interestingly, this might have happened even before the split between African and non-African populations, whereby global human groups might carry ancestry from this ghost lineage.

"This work sheds light on the complex patterns of human evolution, where a simple narrative does not conform to the data. The picture will only get more complex, especially when more work is done in Africa, the birthplace of humanity."

Representative image of a human skull. Researchers have found evidence of a mystery hominin species in the genomes of populations from West Africa. iStock