That’s right—rats may be the culprit behind dental decay. Not a very pleasant thought to have at the dentist’s office is it? But according to a study coming out of the Stanford School of Medicine, it may be an unfortunate side-effect of the rise of civilization and, most importantly, agriculture.
The study analyzed the genomes of several strains of prevalent decay-causing bacterium, Streptococcus mutans, to discover when new genes evolved in the species and its close relatives. The analysis suggests that the bacteria’s population began expanding rapidly about 10,000 years ago—right around the time when agriculture was born.
According to Omar Eduardo Cornejo Ordaz, the leader of the Stanford research team, as humans began to live in greater proximity to one another due to the demands of farming, they also began to live in closer proximity to rats. The closest relative of Streptococcus mutans, he says, is the appropriately named Streptococcus ratti, whose natural environment is probably in a rat’s mouth. As humans and rats became “closer” it’s likely that S. ratti shifted to human mouths and became the new species S. mutans.
Other researchers agree with Cornejo Ordaz’s conclusion that the dental decay epidemic began around the birth of agriculture. George Armelagos of Emory University studied the teeth in 39 fossil skeletons found in Wadi Halfa, Sudan, estimated to be between 8,000 and 11,000 years old. His team’s findings suggest that when the people of that region switched to intensive agriculture, the incidence of dental caries jumped from 0.8 percent to nearly 20 percent.
The debate is ongoing, however. A large body of research also suggests that modern dental decay is largely due to our diet which contains much more sugar than the diets of our ancestors. According to Peter Brown, a paleontologist from the University of New England in Australia, dental caries didn’t appear in Australia’s Aboriginal communities until the introduction of sugar and flour. Rats had nothing to do with it.
Want to learn more about the rise of dental decay? Check out the Scientific American article we used as a source for this post.