Oldest human DNA found in 10,000-year-old chewing gum

The origins of cavemen who settled the North after the last Ice Age can be decoded from DNA left is spat out ancient chewing gum, a study found.

The first humans who colonised Scandinavia more than 10,000 years ago after the Ice Age used to chew birch bark pitch to make flint weapons and tools.

And both men, woman and children left their DNA or teeth marks behind in the discarded masticated lumps.

This is providing clues as to the origins of these ancient people and how they interacted with other groups as the Scandinavian Peninsula was settled as the ice retreated.

Few bones from this age remain and not all of them have preserved enough DNA for archaeogenetic studies.

But scientists who examined the old chewing gum managed to sequence DNA from two Stone Age females and one male.

Theirs is the oldest human DNA sequenced from this area so far and came from Huseby-Klev, an early Mesolithic hunter-fisher site on the Swedish west coast.

It was excavated in the early 1990's, but at this time it was not possible to analyse ancient human DNA at all, let alone from non-human tissue.

Associate Professor Per Persson in the Department of Archaeology at the Museum of Cultural History in Oslo said: "DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights in their social relations, diseases and food."

PhD student Natalija Kashuba added when it was first "proposed to look for hunter-gatherer DNA in these chewing gums from Huseby Klev we were hesitant but really impressed that archaeologists took care during the excavations and preserved such fragile material.

"It took some work before the results overwhelmed us, as we understood that we stumbled into this almost 'forensic research', sequencing DNA from these mastic lumps, which were spat out at the site some 10,000 years ago!"

Results showed genetically the three individuals shared close genetic affinity to other hunter-gatherers in Sweden and to early Mesolithic populations from Ice Age Europe.

However, the tools produced at the site were a part of lithic technology brought to Scandinavia from the East European Plain, modern day Russia.

This scenario of a culture and genetic influx into Scandinavia from two routes was proposed in earlier studies, and these ancient chewing gums provides an exciting link directly between the tools and materials used and human genetics.

Ms Kashuba added: "By combining genomic data and the archaeological dwelling site context, we are able to gain new insights into the Mesolithic society and discuss the social organisation of past populations.

"The fact that each of the studied mastic pieces was chewed only by single individuals, both male and female, and that the mastication of birch bark pitch was most likely connected to the process of tool-making and maintenance (an interpretation supported by the evidence of core processing, re-tooling, and hunting found at Huseby-Klev), allows for a discussion of gender roles within Mesolithic society.

"Combined with the fact that several mastics from the site have imprints of deciduous teeth, the new information allows us to discuss gender in childhood.

"The possible interpretations are that tool-production was not restricted to one sex, or, if the individuals examined were children, that gender roles did not yet apply to young individuals.

"When results from other dwelling sites besides Huseby Klev start to accumulate, we will be able to discuss the social organisation of past populations on a wider scale."

Dr Emrah Kird k at Stockholm University who conducted the computational analyses of the DNA said: "Demography analysis suggests that the genetic composition of Huseby Klev individuals show more similarity to western hunter-gatherer populations than eastern hunter-gatherers."

Professor in Molecular Archaeology Anders G therstr m, at the Archaeological Research Laboratory, Stockholm University, said: "Much of our history is visible in the DNA we carry with us, so we try to look for DNA where ever we believe we can find it."

The study is published in the journal Communications Biology.