Scientists have just discovered hints that a “ghost” species of archaic humans likely contributed genetic material to ancestors of people living in Sub-Saharan Africa today. The research is further evidence that sexual rendezvous between archaic human species was actually quite common.
Past studies have revealed that the forebears of modern humans in Asia and Europe interbred with other early hominin species, including both Neanderthals and Denisovans.
“It seems that interbreeding between different early hominin species is not the exception—it’s the norm,” says Omer Gokcumen, Ph.D. from the University of Buffalo.
“Our research traced the evolution of an important mucin protein called MUC7 that is found in saliva,” he said. “When we looked at the history of the gene that codes for the protein, we see the signature of archaic admixture in modern day Sub-Saharan African populations.”
The research was led by Gokcumen and Stefan Ruhl, a professor of oral biology in UB’s School of Dental Medicine. The scientists came upon their findings while researching the purpose and origins of the MUC7 protein, which helps give spit its slimy consistency and binds it to microbes, helping to rid the body of disease-causing bacteria.
As part of the investigation, the team examined the MUC7 gene in more than 2,500 modern human genomes. The analysis revealed that a group of genomes from Sub-Saharan Africa had a version of the gene that was very different than versions found in other modern humans. The variant was so distinctive that Neanderthal and Denisovan MUC7 genes matched more closely with those of other modern humans than the Sub-Saharan one did.
“Based on our analysis, the most plausible explanation for this extreme variation is archaic introgression — the introduction of genetic material from a ‘ghost’ species of ancient hominins,” Gokcumen says. “This unknown human relative could be a species that has been discovered, such as a subspecies of Homo erectus, or an undiscovered hominin. We call it a ‘ghost’ species because we don’t have the fossils.”
The team calculated that the ancestors of people who carry the Sub-Saharan MUC7 variant interbred with another ancient human species as recently as 150,000 years ago.