Looking to saliva to gain insight on evolution

A baby gorilla. A new study looks to the genomes of several human and nonhuman primates for insights into evolution of saliva. Credit: Soumya Kuber

New research on slobber shows that adaptation isn’t just about creating new tools for survival — it’s also about tweaking the ones we have

“You don’t always have to invent a new tool. Sometimes, you just need to amplify the tool you already have. ”

BUFFALO, N.Y. — There’s no need to reinvent the genetic wheel.

That’s one lesson of a new study that looks to the saliva of humans, gorillas, orangutans, macaques and African green monkeys for insights into evolution.

The research, published on Aug. 25 in Scientific Reports, examined a gene called MUC7 that tells the body how to create a salivary protein of the same name. The protein, which is long and thin, forms the backbone of a bottlebrush-shaped molecule that helps to give spit its slimy, sticky consistency.

The study found that within the MUC7 gene, instructions for building important components of the bottlebrush were repeated multiple times in each of the five primate species studied. Gorillas had the fewest copies of this information (4-5), while African green monkeys had the most (11-12). Humans fell somewhere in between, with 5-6.

Through an in-depth analysis of MUC7’s evolutionary history, the researchers concluded that having numerous copies of the repeated instructions likely conferred an evolutionary advantage to primates — possibly by enhancing important traits of saliva such as its lubricity and, perhaps even more importantly, its ability to bind to microbes (a capability that may help curb disease).

The takeaway lesson?

Evolution can favor the expansion of tried-and-true genetic tools, in addition to the development of totally new ones, says University at Buffalo biologist Omer Gokcumen, who led the study together with Stefan Ruhl, a salivary researcher in UB’s oral biology department.

“You don’t always have to invent a new tool,” says Gokcumen, PhD, an assistant professor of biological sciences in UB's College of Arts and Sciences. “Sometimes, you just need to amplify the tool you already have.”

In the case of MUC7, repeating key genetic instructions over and over resulted in longer, denser proteins, which are likely better at performing two protective tasks: lubricating the mouth — which facilitates talking, chewing and other vital functions — and latching onto microbes, an action that’s thought to expedite the removal of disease-causing pathogens from the oral cavity.