DNA that was so well preserved in a wad of 5700-year-old ‘chewing gum’ in Denmark has allowed researchers to build up a picture of the young girl who did the chewing. It was not exactly gum but a bit of birch bark, which the child chewed and then spat out. By analyzing this bark, researchers have been able to determine the entire genome of the young girl along with her DNA. They have also been able to ascertain what she had recently eaten.
The researchers, writing in the journal Nature Communications , said: “We have shown that pieces of chewed birch pitch are an excellent source of ancient human and non-human DNA. In the process of chewing, the DNA becomes trapped in the pitch where it is preserved due to the aseptic and hydrophobic properties of the pitch which both inhibits microbial and chemical decay.”
They discovered that the girl was genetically more closely related to western hunter-gatherers from mainland Europe than hunter-gatherers from central Scandinavia. They also found that she likely had dark skin, dark brown hair and blue eyes. Her most recent meal included duck and hazelnuts.
“It is amazing to have gotten a complete ancient human genome from anything other than bone”, said lead author Hannes Schroeder, an archaeologist at the University of Copenhagen.
Schroeder told the Guardian that: “the preservation of the gum is quite extraordinary. We didn’t expect to get the whole genome”.
Birch pitch is a black-brown substance obtained by heating birch bark and has been used as an adhesive as far back as the Middle Pleistocene. Small lumps of this material have been found at archaeological sites in Scandinavia and beyond, and have often included tooth imprints, which suggests that they were chewed. Freshly produced birch pitch hardens on cooling and it is thought that chewing was a means to make it pliable again before using it, such as for making composite stone tools. Medicinal uses have also been suggested as one of its main constituents, betulin, has antiseptic properties.
The lump of ancient gum, about ¾ of an inch long, was discovered during archaeological excavations on Lolland Island, prior to construction on a tunnel that will connect Denmark to Germany.
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 TZT Jensen, J Niemann, KH Iversen, et al. A 5700 year-old human genome and oral microbiome from chewed birch pitch. Nat Commun 2019;10:5520 doi:10.1038/s41467-019-13549-9