Danish scientists have extracted a DNA sample from a piece of birch pitch that is 5,700 years old and was used as chewing gum, a study revealed on Tuesday.
The Stone Age sample yielded enough information to determine the chewer's sex, what she had last eaten and the germs in her mouth. It also told them she probably had dark hair, dark skin and blue eyes.
The scientists said the woman was more closely related to hunter-gatherers from the mainland Europe than to those living in central Scandinavia at the time.
The ancient "chewing gum" is tar from a tree, which is a good DNA source, given the lack of human remains from the Stone Age period.
Hannes Schroeder, at the University of Copenhagen, said it was the first time that an entire ancient human genome had been extracted from anything other than human bones.
Mr Schroeder is co-author of the study, which was published in the review Nature Communications.
They found the DNA during an archaeological dig at Syltholm, in southern Denmark, said Tehis Jensen, one of the other authors.
"Syltholm is completely unique," Mr Jensen said. "Almost everything is sealed in mud, which means that the preservation of organic remains is absolutely phenomenal.
"It is the biggest Stone Age site in Denmark and the archaeological finds suggest that the people who occupied the site were heavily exploiting wild resources well into the Neolithic, which is the period when farming and domesticated animals were introduced into southern Scandinavia," Mr Jensen said.
The researchers also recovered traces of plant and animal DNA – hazelnut and duck – in the sample, which would probably have been part of the woman's diet.
But they were not sure why she chose to chew the bark: to turn it into a kind of glue; to clean her teeth; to stave off hunger; or simply as chewing gum.