Human DNA extracted from lumps of 10,000-year-old chewing gum is helping to unravel early settlement patterns in Scandinavia.
Discerning the migration routes of the earliest modern human settlers in the region has proved challenging, because few bones have ever been uncovered, and the DNA in those that have is degraded and therefore useless.
Artefacts arising at ancient occupation sites, however, have been found in considerable quantities. The style of stone tools unearthed points to an influx of people from the east, in what is now modern Russia – but DNA evidence to confirm this has been lacking.
At an early Mesolithic hunter-fisher site in Huseby-Klev on Sweden’s west coast, however, it was noted that the tool-makers sometimes combined, for instance, blades and handles by using a glue-like substance derived from birch bark.
The bark was converted into pitch by the simple expedient of masticating it – creating, in effect, chewing gum.
Although the Huseby-Klev site had been excavated since the early 1990s, no sources of human DNA had been found.
Recently, however, two researchers from Norway’s University of Oslo, Per Persson and Mikael Maininen, proposed analysing the birch bark material to see whether DNA from the saliva of the people who had originally chewed it could be retrieved.
The idea met a sceptical response, but nevertheless the pair were invited to join a research team led by Natalija Kashuba from Oslo’s Museum of Cultural History to do some tests.
“We were hesitant but really impressed that archaeologists took care during the excavations and preserved such fragile material,” recalls Kashuba.
“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!”
The results, published in the journal Communications Biology, are intriguing. The researchers were able to extract enough DNA to characterise three people – two female and one male. The samples represent the oldest human DNA ever found in the region.
And although the tools found at the site were Russian in style, the people who made them, it turns out, hailed from much further south, in Ice Age Europe.
The finding lends weight to earlier studies that had proposed two distinct lineages early Scandinavian settlement, based on tool and vessel style.
“Demography analysis suggests that the genetic composition of Huseby-Klev individuals show more similarity to western hunter-gatherer populations than eastern hunter-gatherers,” says co-author Emrah Kirdök from Stockholm University.
Per Persson, his idea now vindicated, sees the results as just the start of a new field of study.
“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,” he says.