Ghostly Relative
The saliva protein indicated a human crossing with an unknown hominid
Scientists from Greece and the USA traced the evolution of a gene encoding one of the proteins of human saliva, and found that its appearance in the genome is associated with the crossing of the first people with an unknown hominid.
Drawing from the University at Buffalo press release
In saliva, clues to a ‘ghost’ species of ancient human – VM.
Human saliva contains a number of biological substances: enzymes that digest food, bactericidal compounds, as well as glycoprotein mucin, which gives saliva a characteristic gel-like structure. Mucin contains the MUC7 protein, which is encoded by the gene of the same name. It has long attracted the attention of genetic scientists. As previous studies have shown, the MUC7 gene carries several repetitions of key genetic instructions — the so-called tandem repeats. Moreover, different representatives of primates have a different number of them: monkeys can have 11-12, humans - 5-6. It was assumed that a version of the human MUC7 gene with five repeats protects the carrier from asthma.
In their new work, in order to more fully study the physiological function of the MUC7 protein and its evolutionary lineage, geneticists analyzed 251 genomes. They were randomly selected from representatives of modern European, African and Asian populations. Scientists have not found confirmation of an earlier assumption about the connection of one of the gene variants with asthma resistance. As the study showed, the structural variants of the gene greatly influenced the composition and number of bacteria living in the mouth. The MUC7 protein increased the ability of saliva to bind to microbes, helping to neutralize dangerous bacteria.
But, in addition, scientists found out that in people living in sub-Saharan Africa, the structure of the MUC7 gene contained characteristic features. And this made it so distinctive that even the Neanderthal and Denisovan MUC7 genes had more similarities with this gene in most people.
This fact allowed geneticists to assert that the ancient ancestors of Africans living in sub-Saharan Africa interbred once upon a time with hominids unknown to science. Scientists have called them a "ghostly" species of ancient hominids. And, as the analysis of mutations in the genome showed, the ingress of foreign genetic material into the human genome as a result of crossing people with a "ghost" species occurred about 150,000 years ago. At the same time, the evolutionary path of two species — humans and an unknown hominid — diverged about 1.5−2 million years ago.
The study is published in the journal Molecular Biology and Evolution (Xu et al., Archaic hominin introgression in Africa contributes to functional salivary MUC7 genetic variation).
Earlier, scientists learned that humans interbred with Neanderthals tens of thousands of years earlier than thought.
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25.07.2017