DNA from a type of “chewing gum” used by teenagers in Sweden 10,000 years ago is shedding new light on the stone age diet and oral health, according to research. The wads of gum are made from pieces of birch bark pitch, a tar-like black resin, and carry clearly visible teethmarks. They were found 30 years ago next to bones at the 9,700-year-old Huseby Klev archaeological site north of Gothenburg in western Sweden, one of the country’s oldest sites for human fossils. Hunter-gatherers probably chewed the resin “to be used as glue” to assemble tools and weapons, said Anders Götherström, the co-author of the study published in Scientific Reports. “This is a most-likely hypothesis – they could have been chewed just because they liked them or because they thought that they had some medicinal purpose,” he said. “There were several chewing gum [samples] and both males and females chewed them. Most of them seem to have been chewed by teenagers. There was some kind of age to it,” Götherström said. A previous 2019 study into the wads of gum mapped the genetic profile of the individuals who had chewed it. This time, Götherström and his team of paleontologists at Stockholm University were able to determine, again from the DNA found in the gum, that the teenagers’ stone age diet included deer, trout and hazelnuts. Traces of apple, duck and fox were also detected. “If we do a human bone then we’ll get human DNA. We can do teeth and then we’ll get a little bit more. But here we’ll get DNA from what they had been chewing previously,” Götherström said. “You cannot get that in any other way.” In addition, in one piece chewed by a teenage girl, researchers found a number of bacteria indicating a severe case of periodontitis, a severe gum infection. “She would probably start to lose her teeth shortly after chewing this gum. It must have hurt as well,” said Götherström. “You have the imprint from the teenager’s mouth who chewed it thousands of years ago. If you want to put some kind of a philosophical layer into it, for us it connects artefacts, the DNA and humans.”