Portrait by gum
The ancient blue-eyed hunter-gatherer was identified by a gum made of birch tar
Danish scientists have compiled a portrait of an ancient man and microbes from his mouth from the remains of DNA in a petrified gum made of birch tar.
It turned out to be a dark-skinned and blue-eyed woman who lived 5700 years ago and was a hunter-gatherer. She ate both animal and vegetable food, and in her mouth lived approximately the same types of bacteria and viruses as in modern humans, including pathogenic ones. The study is published in the journal Nature Communications (Jensen et al., A 5,700 year-old human genome and oral microbiome from chewed birch pitch).
Artistic reconstruction of a woman who chewed birch resin. She was named Lola. A drawing from the press release of Ancient “Chewing Gum” Yields Insights into People and Bacteria of the Past.
In the parking lots of ancient people from the late Mesolithic and Early Neolithic times, lumps of birch tar are found every now and then. Apparently, tar was used as glue, but from time to time it is possible to see teeth marks on the lumps. Perhaps ancient people chewed tar to soften it and reuse it. Or they used it as a medicine – at least, such recipes are found in traditional medicine.
Not so long ago, scientists discovered traces of human DNA in such a lump, and a group of researchers led by Hannes Schroeder from the University of Copenhagen decided to check what could be learned from another lump of tar that was found during excavations in Siltholm, in southern Denmark. Judging by the results of radiocarbon analysis, this tar was chewed 5858-5661 a year ago.
DNA was extracted from the sample, about a third of which turned out to be reliably human – about the same amount is found in well-preserved teeth and bones. The authors of the work collected from this DNA an approximate nuclear and mitochondrial genome of its host. It turned out that it was most likely a woman with dark skin, dark brown hair and blue eyes.
The researchers also found out that she had lactose intolerance: in adulthood, a woman could not digest milk, like many ancient and some modern people. The genome was also compared with the genomes of thousands of Eurasians and hundreds of ancient people to determine the approximate origin. Apparently, she was a native of Western European hunter-gatherers.
Then the scientists took up the analysis of other DNA fragments from ancient gum. They found a lot of bacterial DNA in the sample, which resembles the DNA of microbes from the oral cavity of modern humans. Among these bacteria were both representatives of the healthy microbiota of the mouth, like Neisseria subflava, and pathogenic groups – for example, Streptococcus pneumoniae and Porphyromonas gingivalis, the causative agent of periodontitis and suspected in the development of Alzheimer's disease. Viral DNA resembling the Epstein-Barr virus was also found in this sample.
Finally, the researchers tested the gum for the presence of animal and plant DNA. In addition to the DNA of the birch itself, they found in it the DNA of a hazelnut and a wild duck – probably the remains of a woman's food that stuck to the lump.
Thus, scientists have demonstrated that chewing gum can be a valuable source of information not only about ancient people, but also about their diet and microscopic symbionts. Previously, this information could be obtained in some form from tartar, but DNA samples were not stored in it for so long. Thanks to the antiseptic and hydrophobic properties of tar, information about the microbes inhabiting it can be obtained even after several thousand years.
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