The results led the researchers to propose that by switching to a diet dominated by cultivated grains, Neolithic people effectively interrupted long-standing coevolutionary relationships between humans and the microbial communities living in their mouths, robbing themselves of diversity and, by extension, resilience against pathogenic bacteria. “Eating large amounts of soft carbohydrates, which get packed down around the base of your teeth, selects strongly for certain types of bacteria,” says Cooper, “so the ecosystem was swamped with bacterial species that can exploit this resource, and which have a negative impact on oral health.”