When hunter-gatherers living in what is now southern Denmark broke down pieces of birch bark into sticky, black tar about 5,700 years ago, they almost certainly didn’t realize that they were leaving future scientists their entire DNA.
Ancient people used the gooey birch pitch to fix arrowheads onto arrows and to repair a variety of stone tools. When it started to solidify, they rolled the pitch in their mouths and chewed on it, like some sort of primitive bubble gum. Chewing on birch pitch would have made it pliable again for using on tools.
It might have also relieved toothaches because of the antiseptic oils in the gum. It’s possible that children also used it recreationally, much like modern humans do today. When they spat the gum out, the same antiseptic properties helped preserve the DNA in their saliva.
The ancient DNA, described in a paper published Tuesday in Nature Communications, is especially valuable because few human bones from the Mesolithic and Neolithic Stone Ages have been found in Scandinavia. DNA from the chewed-up gum provides clues about the people who settled in the area, the kind of food they ate and even the type of bacteria they carried on their teeth.
“It is very exciting to be able to extract a full human genome from anything other than bone,’’ said Hannes Schroeder, an archaeologist at the University of Copenhagen, who led the research. “This sample had lots of microbial DNA preserved as well.”
Researchers uncovered the wad of gum last year from the site of the Fehmarn Belt Fixed Link tunnel. Planned construction of the underwater tunnel, which will connect the Danish island of Lolland with the German island of Fehrman, has forced archaeologists to rush to collect artifacts and fossil evidence before they are lost forever.
Findings from the site suggest that people living in the area relied heavily on fishing, hunting and the gathering of wild nuts and berries for their survival, even as other Scandinavian populations started farming and domesticating animals, Dr. Schroeder said.
When researchers analyzed human DNA preserved in the 5,700-year-old birch pitch, they found that the individual who chewed on it was a female, who was more closely related to hunter-gatherers from continental Europe than those from central Scandinavia. They named her Lola.
Her genes suggest she likely had a striking combination of dark skin, dark hair and blue eyes. She also probably couldn’t digest milk. But these characteristics are not surprising. They have been noted in reconstructions of a 10,000-year-old British skeleton called the Cheddar Man, as well as other European hunter-gatherers. (Experts believe Northern Europeans evolved lighter skin and hair to adapt to the lower light conditions in regions where they lived much later on, and the genetic mutation for digesting milk came around once they became more dependent on livestock for food.)
Lola, however, had been eating duck and hazelnuts before she started chewing on birch pitch, based on additional DNA found in the birch sample.
“This is a snapshot of a real person in real time,” said Natalija Kashuba, an archaeologist at Uppsala University in Sweden, who also studies birch pitch samples but was not involved in the latest research. “It’s as close as we’ll ever come to standing face to face with an individual from the Stone Age of Scandinavia.”
Researchers also detected DNA from bacteria and viruses in the birch resin, providing a snapshot of the ancient oral microbiome that scientists had never seen before. “That changes the game,” Dr. Kashuba said.
Studying ancient oral microbiomes could reveal larger truths about how bacteria interact with one another, how they change over time or with the type food a person eats, as well as how they may be implicated in health and disease — questions that also interest scientists studying the modern microbiome.
The Danish team identified several species of bacteria that were similar to those hiding in people’s plaque and on the tips of their tongues today. Some included bacteria known to cause gum disease, such as Porphyromonas gingivalis. The birch pitch sample also had traces of Streptococcus pneumoniae bacteria and Epstein-Barr virus, which provide clues to Lola’s health.
For the wealth of information the small piece of pitch provides, it raises just as many questions, Dr. Kashuba said. Scientists are unable to glean an individual’s age from the DNA stored in the sample. They’re also unsure exactly why some individuals chewed it. But because people chewed gums made of pitch and other substances all around the world, we could be left with a trove of already-been-chewed treasure for tracing people, activities and bacteria of the past.