Approximately 10,000 years ago, teenagers in what is now western Sweden chewed wads of birch bark pitch and spat them out, and the saliva preserved in the wads contained enough human and microbial DNA that scientists have since sequenced the chewers’ complete genomes, identified the food they had eaten that day, and detected the bacterial signature of their gum disease.

The site is called Huseby Klev. It sits on the island of Orust on the western coast of Sweden, about an hour’s drive north of Gothenburg. Approximately ten thousand years ago, when sea levels were higher and the coastline ran further inland, Huseby Klev was a coastal fishing camp at the end of a narrow [...] The post Approximately 10,000 years ago, teenagers in what is now western Sweden chewed wads of birch bark pitch and spat them out, and the saliva preserved in the wads contained enough huma