Saliva provides clues to early hominin sex.
Scientists at the University at Buffalo have found hints that a “ghost” species of archaic humans may have contributed genetic material to ancestors of people living in sub-Saharan Africa today.
The research adds to a growing body of evidence suggesting that sexual rendezvous between different archaic human species may not have been unusual.
Past studies have concluded that the forebears of modern humans in Asia and Europe interbred with other early hominin species, including Neanderthals and Denisovans. The new research is among more recent genetic analyses indicating that ancient Africans also had trysts with other early hominins.
“It seems that interbreeding between different early hominin species is not the exception—it’s the norm,” says Omer Gokcumen, an assistant professor of biological sciences at UB and a lead researcher of the study along with UB oral biology professor Stefan Ruhl.
The scientists came upon their findings while researching MUC7, a protein in saliva that contributes to its slimy consistency and binds to microbes, potentially helping to rid the body of disease-causing bacteria. “Saliva serves as an important gatekeeper in the mouth, shielding us from invading pathogenic microbes,” notes Ruhl, whose lab focuses on determining how genetically defined differences in saliva among different people make them more or less susceptible to disease. “In that regard, we can learn a lot from comparisons of salivary proteins and genes with those of closely related primate species and extinct hominid ancestors, as shown in this study.”
As part of their investigation, the team examined the MUC7 gene in more than 2,500 modern human genomes. The analysis yielded a surprise: A group of genomes from sub-Saharan Africa had a version of the gene that was wildly different from versions found in other modern humans.
The sub-Saharan variant was so distinctive that Neanderthal and Denisovan MUC7 genes matched more closely with those of other modern humans than the sub-Saharan outlier 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.”
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