A University at Buffalo study has revealed that our diet has significantly changed our saliva in comparison to that of other primates.
Researchers at the university's School of Dental Medicine found that the human diet - and our increased consumption of meat, how we cook our food and even how we grow what we eat - has changed the makeup of our saliva.
The research also suggests that these changes have shifted human development further away from other species of great apes on the evolutionary chart.
How Is It Different?
The researchers found that human saliva is different from the saliva found in the other members of the great ape family, like chimpanzees and gorillas, because it's waterier and is made up of a different combination of proteins.
The findings came as a big surprise to the UB researchers, as it was assumed that saliva makeup among the great apes would be similar due to genetic links between species.
The study is of great interest to researchers from the team because scientists have long known that the way earlier species of humans adapted their diets to survive affected their jaws, teeth and the overall oral microbiome.
The discovery shows these changes had a pathogenic effect on saliva, too - and these changes may be linked to species survival.
'Saliva is critical to the body,' said Dr. Sean Endsley, a Waco, Texas, dentist.
Saliva's role is so crucial that, without it, eating may be difficult or impossible. Saliva helps to digest food and makes swallowing easier.
Saliva also plays a role in speech and tasting food.
'Saliva helps to protect tooth enamel against tooth-decay-causing bacteria and helps fight against illness-causing pathogens,' Endsley said.
The benefits of saliva are credited to proteome, the thousands of proteins found in the secretion.
Proteomes were the Buffalo team's focus of research, and the scientists compared the salivary proteins of humans to those of gorillas and chimpanzees. The team also examined the differences between human saliva and that of macaques.
Macaques are a 23-species group of Old World monkeys that shares a common but more distant ancestor with humans and great apes.
What they found in their comparison was that human saliva was waterier than the saliva of the other great apes. They also found that the protein content in human saliva was less than half that found in the other species they analyzed.
They also found higher levels of amylase, an essential protein in breaking down starches and sugars, in human saliva.
The researchers also found more carbonic anhydrase VI, an enzyme involved in taste perception, in humans than the other great apes.
The saliva of humans had the same levels of zinc-alpha-2-glycoprotein as chimpanzees and gorillas. Zinc-alpha-2-glycoprotein is necessary for breaking down and metabolizing fats.
Another finding after comparing the saliva of humans and great apes was that the saliva of gorillas contained latherin, a detergent-like protein that helps fluids become frothy; this protein was not present in chimpanzees or humans.
The researchers believe that this finding is connected to the fact that humans no longer have fur coats or groom themselves socially.
The Buffalo researchers considered the fact that saliva contained more water in humans because our food is softer from cooking, and we chew less than our great ape counterparts who chew raw food for long periods.
The researchers hope that their findings help spur on future studies to determine if differences between human saliva and the saliva of other great apes are connected to evolutionary adaptations.
The research was published on Oct. 15 in Molecular Biology and Evolution and was supported by the National Institute of Dental and Craniofacial Research, the National Cancer Institute and the Roswell Park Comprehensive Cancer Center.
Source: University of Buffalo News Center. A secret in our saliva: Food and germs helped humans evolve into unique member of great apes. 16 October 2019.