DNA from Stone Age woman obtained 6,000 years on

This is the face of a woman who lived 6,000 years ago in Scandinavia.

Thanks to the tooth marks she left in ancient "chewing gum", scientists were able to obtain DNA, which they used to decipher her genetic code.

This is the first time an entire ancient human genome has been extracted from anything other than human bone, said the researchers.

She likely had dark skin, dark brown hair and blue eyes.

Dr Hannes Schroeder from the University of Copenhagen said the "chewing gum" - actually tar from a tree - is a very valuable source of ancient DNA, especially for time periods where we have no human remains.

"It is amazing to have gotten a complete ancient human genome from anything other than bone,'' he said.

The woman's entire genetic code, or genome, was decoded and used to work out what she might have looked like. She was genetically more closely related to hunter-gatherers from mainland Europe than to those who lived in central Scandinavia at the time, and, like them, had dark skin, dark brown hair and blue eyes.

She was likely descended from a population of settlers that moved up from western Europe after the glaciers retreated.

Other traces of DNA gave clues to life at Syltholm on Lolland, an island of Denmark in the Baltic Sea. The DNA signatures of hazelnut and mallard duck were identified, showing these were part of the diet at the time.

"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 first introduced into southern Scandinavia," said Theis Jensen from the University of Copenhagen.

The researchers also extracted DNA from microbes trapped in the "chewing gum". They found pathogens that cause glandular fever and pneumonia, as well as many other viruses and bacteria that are naturally present in the mouth, but don't cause disease.

The DNA was stuck in a black-brown lump of birch pitch, produced by heating birch bark, which was used at that time to glue together stone tools.

The presences of tooth marks suggest the substance was chewed, perhaps to make it more malleable, or possibly to relieve toothache or other ailments.

The researchers said the information preserved in this way offers a snapshot of people's lives, providing information on ancestry, livelihood and health.

DNA extracted from the chewing gum also gives an insight into how human pathogens have evolved over the years.

"To be able to recover these types of ancient pathogen genomes from material like this is quite exciting because we can study how they evolved and how they are different to strains that are present nowadays," Dr Schroeder told the BBC. "And that tells us something about how they have spread and how they evolved."

The research is published in the journal Nature Communications.

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