Ancient human 'ghost' species revealed by saliva protein

A simple salivary protein has revealed a so-called 'ghost' species of ancient humans, a new study reveals, hinting at the existence of an archaic species that swapped genetic material with human ancestors. It is well known that ancient hominin species contributed to the rise of modern humans, not the least of which is the Neanderthals and lesser known Denisovans. Such rendezvous took place in Europe and Asia, but it seems similar encounters may have happened in ancient Africa, too.

The discovery was made thanks to a protein from saliva called MUC7 — it is the reason spit has its consistency and is a possible way the body gets rid of harmful bacteria. Researchers were studying this protein, particularly looking for its origins, and stumbled upon an interesting find: that some genomes from Sub-Saharan Africa possessed this gene, but a variety that is quite different from the gene found in other modern human genomes.

How different? According to the study, the MUC7 genes found in the Sub-Saharan sample were most closely related to Denisovan and Neanderthal genes versus than the other modern samples. This indicates an interbreeding between the ancestors of people with this unique MUC7 gene and a 'ghost' species — that is, one that is essentially unknown and nearly invisible to modern science. The mixing of the two could have taken place about 150,000 years ago.

The genes variant were found to have relation to different oral microbiomes, though other potential benefits from the genes isn't clear. We've seen previous studies that highlight benefits from genes like this, however, such as the Neanderthal contribution that helps protect humans from schizophrenia.

The discovery serves to expand a growing body of evidence suggesting that such encounters between ancient hominin species may not have been that unusual. Talking about this, University of Buffalo assistant professor of biological sciences Omer Gokcumen said:

It seems that interbreeding between different early hominin species is not the exception — it's the norm ... When we looked at the history of the gene that codes for the [MUC7] protein, we see the signature of archaic admixture in modern day Sub-Saharan Africa populations.

SOURCE: EurekAlert