Fossilized bones and teeth aren’t the only source of ancient human DNA.

The genetic material also sticks around in birch pitch “chewing gum,” which can hold enough DNA to piece together the genetic instruction books, or genomes, of long-dead people, researchers report December 17 in Nature Communications. By analyzing a 5,700-year-old chewed wad of pitch from Denmark, the team obtained the genome of an ancient woman, and determined that she probably had blue eyes, dark skin and dark hair.

Ancient humans likely chewed the pitch — made by heating birch bark — to make it pliable, working cells from the mouth deep into the sticky substance. Birch pitch is relatively resistant to bacteria and viruses as well as water, which would have protected the DNA from decay, the researchers say.

The team also recovered DNA from microbes that may have lived in the woman’s mouth, including from older versions of Epstein-Barr virus, which causes mononucleosis, and bacteria that can cause pneumonia or gum disease. Duck and hazelnut DNA were also identified, and may be remnants from a recent meal the woman ate before popping a piece of pitch into her mouth.

Scientists have gleaned information about ancient humans’ mouth microbes and diets (SN: 10/4/17) from dental plaque in fossilized teeth (SN: 3/8/17). “But that’s been built up over many years,” says study coauthor Hannes Schroeder, a geneticist at the University of Copenhagen. “With the chewing gum, it’s kind of like a snapshot of one moment in time.”