This properties of this baby's saliva evolved to help keep him healthy (Photo : Photo: Pereru - Own Work, CC BY-SA 4.0)

"Rapid evolution" of human and primate spit helped in the fight against harmful microbes.

A new study published on Thursday in Scientific Reports found that the salivary mucin-7 gene (MUC7) gave varying instructions regarding creation of salivary proteins to different primates. Scientists believe that the variation provides an evolutionary advantage by making the saliva stickier and slimier, thus more lubricative and better at trapping microbes.

Chewing, talking and swallowing rely on saliva lubricating the mouth well. Trapping microbes while still in the mouth is thought to prevent disease.

The research on MUC7's evolution was conducted by a team of scientists in the US and Greece. Differences in the evolution of MUC7 were found solely in primates -- other mammals have a version of MUC7 that does not give the same benefits people and other primates are experiencing.

In the studied versions of MUC7, short fragments of DNA are repeated multiple times. This repetition is called a tandem repeat.

"Tandem repeats may be a major way that many different genes in the genome quickly adapt to their environments," study coauthor and PhD student in biological sciences in the University of Buffalo College of Arts and Sciences Duo Xu said in a release.

Of the five species studied, gorillas's 4-5 tandem repeats were the fewest, humans were in the middle with 5-6, and African green monkeys' 11-12 tandem repeats were the most. It's possible that the specific adaption of MUC7 occurred in response to a harmful fungi.

The research team believes the variation of MUC7 is "fodder for rapid evolution." It's atypical to find a differing number of tandem repeats within a species.

"You don't always have to invent a new tool," study lead and assistant professor of biological sciences in UB College of Arts and Sciences Omer Gokcumen said in the same release.

"Sometimes, you just need to amplify the tool you already have."