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Nearly 6,000 years ago, a young woman spit out a lump of ancient chewing gum made from birch tar. It landed in a shallow lagoon near the coast of southern Denmark.
Recently, researchers spotted the gum among pieces of wood and wild animal bone during an excavation. They have reassembled her complete DNA from it and painted a general idea of what she looked like.
The strands of DNA saved in the gum suggest that she was a hunter-gatherer from continental Europe. The DNA indicates she had dark skin, dark hair and blue eyes. She lived near the lagoon. The young woman lived about 5,600 years ago, according to the information scientists analyzed on the birch tar.
Remains Of A Recent Meal
In addition to her DNA, the researchers also found genetic material (DNA) from duck and hazelnuts. These are probably the remains of a meal she had recently eaten. There were also at least 40 types of microbes.
Hannes Schroeder is a molecular anthropologist at the University of Copenhagen in Denmark. A molecular anthropologist studies links between modern and ancient humans through molecules in cells.
"This is the first time anyone has got a full ancient genome from anything other than bone or teeth," Schroeder said. "The preservation of the gum is quite extraordinary. We didn't expect to get the whole genome."
A genome is the complete DNA record of a person.
Lump Of Ancient Gum
The 2-centimeter-long lump of ancient gum was discovered during archaeological excavations on Lolland Island, Denmark. Also at the Stone Age site were piles of bones from cattle, deer, ox, wildcats, dogs and otters as well as the remnants of wooden fish traps over thousands of years.
"This was a place of special significance," said Theis Jensen, a researcher at the University of Copenhagen, and the main author of the study. "These people didn't live at the site, but probably on dry land a couple of hundred meters away."
Birch tar is made by heating the tree's bark. It has been used as a natural glue for hundreds of thousands of years. In the Stone Age, the material was removed from trees on a mass scale to attach arrowheads to arrows and provide handles for tools. It had other applications, too. Lumps of the tar found at archaeological sites often contain youth tooth marks. Given that it contains sanitizing substances, it may have been used as an ancient toothbrush.
Jensen and Schroeder wondered whether the chewed birch tar might contain ancient DNA. To find out, they washed pieces of the tar and removed what DNA they could find. Jensen said that there turned out to be a tremendous amount of DNA in it.
The scientists found they had enough ancient DNA to reconstruct a full human genome. It showed that the person was female and had dark skin, dark hair and blue eyes. She was also more closely related to hunter-gatherers from mainland Europe than those who lived in central Scandinavia at the time. It is impossible to know her age. However, given that children seemed to chew birch tar, the scientists suspect she was young.
Further DNA revealed her oral microbiome, which is the collection of microbes that live in the mouth. Three of the bacterial species found were linked to severe gum disease. A type of bacteria that often causes pneumonia was also found. The scientists spotted the Epstein-Barr virus, which is another illness. The young girl could have been sick, but she also could have been carrying the bacteria without being sick.
In May, a different team of scientists removed sections of human DNA from older chewed birch tar. Anders Götherström led the study. Both of these studies suggest that birch tar could be valuable for finding ancient human genomes from sites where no bones or teeth are ever found.
Substitute For Bones
"It's incredible because there are periods where we don't have any bones, but birch pitch survives very well," Jensen said. "It's a substitute for bones, and it's very intimate. You get so much information."
Götherström said the latest work was exciting. Chewing gum from trees could be a source of human DNA where there are limited amounts of other sources, such as bones.
"But even more exciting is the ancient microbial DNA," Götherström said. "The mouth is an exposed area of the body. It is possible that this type of material will outcompete bones when looking for DNA from ancient pathogens."