A new analysis of Neolithic farmers’ dental plaque suggests milk has been a staple in humans’ diets for millennia. As researchers led by Sophy Charlton of England’s University of York report in the journal Archaeological and Anthropological Sciences, traces of beta lactoglobulin—a protein present in cow, sheep and goat milk—entombed in prehistoric Britons’ plaque represent the earliest direct evidence of milk consumption found to date.

According to Atlas Obscura’s Anne Ewbank, Charlton and her colleagues tested ten sets of teeth unearthed at three Neolithic sites across southern England: Hambledon Hill, Hazleton North and Banbury Lane. Using mass spectrometry analysis, the team identified peptides from the beta lactoglobulin protein in seven of these individuals’ calcified plaque. Although the exact type of milk consumed at each settlement remains unclear, certain peptides points toward Hambledon Hill’s predilection for goat milk and Hazelton North’s preference for cow or sheep milk. According to the study, however, zooarchaeological evidence recovered at the sites remains “most consistent” with cattle milk.

“The fact that we found this protein in the dental calculus of individuals from three different Neolithic sites may suggest that dairy consumption was a widespread dietary practice in the past,” Charlton says in a press release.

Crucially, Paul Rincon writes for BBC News, the majority of Neolithic Europeans—including the British farmers featured in the study—were lactose intolerant, making it difficult for them to drink milk without experiencing unpleasant side effects. The ability to break down lactose sugar in milk is a relatively modern one: As the study notes, just 5 to 10 percent of Europeans possessed the genetic mutation responsible for this process by the Bronze Age, which lasted from around 3,000 to 1,000 B.C. (In Britain, the preceding Neolithic period ran from 4,000 to 2,400 B.C. and saw the rise of such practices as farming, animal domestication and monument building.)

To cope with their lactose intolerance, early Britons may have imbibed small amounts of milk at a time or, in a more plausible scenario, processed the drink to reduce its lactose content. “If you process [milk] into a cheese, or a fermented milk product, or a yogurt, then it does decrease the lactose content so you [can] more easily digest it,” Charlton tells BBC News.

Dairy fats and milk residue discovered in Neolithic pottery across the European continent support this theory, offering evidence of heating and other forms of milk product processing. At Hambledon Hill specifically, the archaeologists write in the study, more than a quarter of pottery fragments recovered held traces of milk lipids.

Prior research has pinpointed the origins of milk consumption to thousands of years before these British farmers arrived on the scene. In 2016, for example, a study published in the Proceedings of the National Academy of Sciences drew on prehistoric pottery discovered in the northern Mediterranean to posit that the practice started as early as 9,000 years ago. Still, Atlas Obscura’s Ewbank explains, the new analysis is the first to draw on human remains to directly date milk consumption to the Neolithic period.

Moving forward, the researchers hope to assess whether members of prehistoric societies “consumed differential amounts of dairy products or dairy from different animals” on the basis of sex, gender, age or social standing. Additionally, Charlton says in the statement, “Identifying more ancient individuals with evidence of [the milk protein] in the future may … increase our understanding of how genetics and culture have interacted to produce lactase persistence.”