By Cecelie Krabbe
The researchers believe it marks the first time that anyone has extracted an entire ancient human genome from anything other than human bones.
“It is amazing to have gotten a complete ancient human genome from anything other than bone,” says Hannes Schroeder, associate professor from the Globe Institute at the University of Copenhagen.
“What is more, we also retrieved DNA from oral microbes and several important human pathogens, which makes this a very valuable source of ancient DNA, especially for time periods where we have no human remains.”
What Is Birch Pitch?
Birch pitch is a black-brown substance that is produced by heating birch bark. It was commonly used in prehistory for hafting stone tools as an all-purpose glue. The earliest known use of birch pitch dates back to the Palaeolithic.
Scientists often find pieces of birch pitch with tooth imprints suggesting that people chewed them. As the pitch solidifies on cooling, scientists have suggested that people chewed to make it malleable again before using it for hafting.
Scientists have also suggested other uses for birch pitch. For example, one theory suggests that birch pitch could have been used to relieve toothache or other ailments as it is mildly antiseptic. Other theories suggest, people may have used it as a kind of prehistoric tooth brush, to suppress hunger, or just for fun as a chewing gum.
Sealed in the Mud
Based on the ancient human genome, the researchers could tell that a female chewed the birch pitch. She was genetically more closely related to hunter-gatherers from the mainland Europe than to those who lived in central Scandinavia at the time. They also discovered she probably had dark skin, dark hair, and blue eyes.
Archeologists found the birch pitch during excavations at Syltholm, east of Rødbyhavn in southern Denmark. The Museum Lolland-Falster is conducting the excavations in connection with the construction of the Fehmarn tunnel.
“Syltholm is completely unique. Almost everything is sealed in mud, which means that the preservation of organic remains is absolutely phenomenal,” says Theis Jensen, a postdoc at the Globe Institute, who worked on the study for his PhD and also participated in the excavations at Syltholm.
“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,” he says.
The DNA results reflect this, as the researchers also identified traces of plant and animal DNA in the pitch—specifically hazelnuts and duck—which may have been part of the individual’s diet.
Secrets of Ancient Gum
Further, the researchers extracted DNA from several oral microbiota from the pitch, including many commensal species and opportunistic pathogens.
“The preservation is incredibly good, and we managed to extract many different bacterial species that are characteristic of an oral microbiome,” Schroeder says. “Our ancestors lived in a different environment and had a different lifestyle and diet, and it is therefore interesting to find out how this is reflected in their microbiome.
The researchers also found DNA they could assign to Epstein-Barr virus, known to cause infectious mononucleosis or glandular fever. Ancient “chewing gums” have great potential for researchers investigating the composition of our ancestral microbiome and the evolution of important human pathogens, according to Schroeder.
“It can help us understand how pathogens have evolved and spread over time, and what makes them particularly virulent in a given environment. At the same time, it may help predict how a pathogen will behave in the future, and how it might be contained or eradicated.”
The research appears in Nature Communications. The Villum Foundation and the EU’s research program Horizon 2020 through the Marie Curie Actions funded the work.