Birch bark tar found at a site in southwestern Estonia has led to researchers for the first time extracting human DNA, offering a fascinating new insight into the region's more distant past.
The pieces found at the Pulli site, which is in Pärnu County and is Estonia's oldest known settlement, date back roughly 10,500 years B.P., near the end of the Upper Paleolithic era.
The DNA fragments extracted so far represent the oldest finds of human genetic material in Estonia, and also rank alongside the world's oldest snippets of human genetic material ever recovered from tar, made from tree sap, of any kind.
Tar finds containing human genetic material like this are particularly special as knowledge about ancient peoples from places and periods where no other human remains have been found can be obtained. The fragments also tell us the story of prehistoric materials technology and, for instance, may reveal illnesses prevalent at the time, dietary habits, or even the background to artistic and cultural practices.
Professor of laboratory archaeology Aivar Kriiska, who has been studying ancient tar for over 10 years now, explained how the tar was used by prehistoric people.
Birch bark tar, as its name suggests, was obtained by heating the bark of the tree, widely found in the region, and was likely first created by Neanderthals, an extinct group of archaic humans who lived until around 40,000 B.P. "The oldest known finds go back more than 200,000 years," Kriiska noted.
Tar had multiple uses for early humans, including as an adhesive for various tools, for repairing pottery, coating the hulls of wooden boats, and as decorations, either to embellish other items or by fashioning ornaments themselves out of the malleable substance.
This and the fact that tar was perhaps also suitable as a type of early chewing gum reveal how and why traces of human DNA could become infused into tar fragments.
Tooth marks and oral microbiomes on some tar finds certainly suggest this, but Kriiska says this is just an assumption, which has no foundation based on the empirical evidence. "If it had been chewed systematically as chewing gum is today, the sites would be full of it. Yet tar finds are rather rare. The scarcity of finds and the forms of the pieces point primarily to their adhesive use. Tar was usually chewed so as to soften hardened pieces in the mouth," Kriiska explained.
At the same time, considering tar's antiseptic properties, it cannot be ruled out that it was also used for medicinal or dental purposes.
The experts also tried recreating the prehistoric making and use of tar for themselves.
"We tried to obtain tar from birch bark by heating it," Professor of Evolutionary Genomics Mait Metspalu related.
Meanwhile, archaeology researcher Irina Khrustaleva led experiments, including to find out if the birch bark tar they were able to make could be chewed by the researchers themselves. They confirmed that chewing and oral warmth restore the plasticity and adhesive qualities of even dried tar pieces.
Although the genetic traces found in the tar are highly fragmented, the initial results, according to Metspalu, indicate that at least one tar piece from the Pulli site was chewed by two different people, one male and one female.
A tooth impression backs this up: Though the gender of the chewer in this case cannot be ascertained, their age can - the bite mark is from a child or teenager.
Genetic analysis suggests that the handler(s) had dark eyes and dark hair, typical for the era.
"The reason why we find specifically the genetic material of children and adolescents on tar pieces is very easy to explain, if half-jokingly -- they had teeth. One can imagine that older Stone Age people already had serious dental issues, so softening the tar was a task for the young," Kriiska explained.
The research is a part of an Estonian Research Council-funded project, overseen by Metspalu and carried out in cooperation between archaeologists, geneticists, and archaeochemists at the University of Tartu and the Estonian Academy of Arts (EKA).
More detailed results are due to be published next year.