These bacteria produce acid as a byproduct of breaking down sugars. This acid then attacks tooth enamel and leads to cavities, Peter S. Ungar, an anthropologist at the University of Arkansas who was not involved in the study, wrote in an email.
Most scientists believe that hunter-gatherers ate a diet low in carbohydrates and rich in protein, and that it was only during the agricultural revolution that carbohydrate consumption increased.
But the new findings suggest humanity's sweet tooth may be much older than that.
For instance, new evidence has revealed that other Paleolithic communities "ate a range of starchy and fat-rich seeds and nuts, as well as berries," Marijke van der Veen, an archaeologist at the University of Leicester who was not involved in the study, wrote in an email to LiveScience.
Still, the carb-loading cave dwellers were probably the exception, not the rule.
"While about 90 percent of adults in the U.S. suffer from cavities, little more than a handful of early human ancestor teeth have them," Ungar told LiveScience. In contrast, less than 2 percent of Stone Age foragers had cavities, he said.
"This study, and others like it, make clear the fact that our oral environments are not those to which our teeth initially evolved," Ungar said.
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This story originally appeared on LiveScience.