Mesolithic hunter-gatherers living on a meat-dominated, grain-free diet had much healthier mouths that we have today, with almost no cavities and gum disease-associated bacteria, a genetic study of ancient dental plaque has revealed. The international team of researchers, led by a group at the Australian Center for Ancient DNA, University of Adelaide, publish their findings in today’s Nature Genetics. The researchers extracted DNA from dental plaque from 34 prehistoric northern European human skeletons, and traced the changes in the nature of oral bacteria from the last hunter-gatherers to Neolithic and medieval farmers and modern individuals. “Dental plaque represents the only easily accessible source of preserved human bacteria,” said lead author Dr. Christina Adler, now associate lecturer in dentistry at the University of Sydney. The researchers found that the composition of bacteria changed with the introduction of farming and again 150 years ago, during the Industrial Revolution.