DNA found in 5,700 year old chewing gum

Around 5,700 years, during the beginning of the Neolithic period in Denmark, ago a dark-skinned, blue-eyed girl chewed a piece of gum made of birch tar resin after eating some duck and hazelnuts. The piece of ‘gum’ (birch tar), was found during archeological excavation on the Island of Lolland, Denmark. 

The ancient DNA is particularly valuable because few traces of DNA from the Mesolithic and Neolithic Stone Ages have been found in Scandinavia. The DNA did show that it is more likely that the owner of the gum was more closely related to the hunter-gatherers of continental Europe than central Scandinavia. The researchers named the gum chewer Lola. 

Alongside the DNA of Lola, scientists found genetic material from a mallard duck and hazelnuts, thought to have been consumed by the girl before chewing the gum.

The DNA revealed that Lola probably suffered from severe periodontitis (gum infection) and chewed the piece of birch tar resin to relieve the pain that she is likely to have had in her mouth. 

Birch tar is a black-brown substance that is obtained by heating the bark of this tree. It is thought that prehistoric people used it primarily as a glue. It is now understood that is glue like substance is likely to have also been used as gum, as it is not the first time birch tar has been found with teeth like impressions.

Researchers, led by Associate Professor Hannes Schroeder of the Globe Institute at the University of Copenhagen, successfully extracted a complete human genome (an organism’s complete set of DNA, including all of its genes) from the 2cm piece of gum. According to the scientists, it is a new, untapped source of ancient DNA, as it is the first time that an entire ancient human genome has been obtained from something other than bone.

By studying Lola's genome, the scientists found that the DNA included alleles associated with  ‘lactase non-persistence’, meaning that Lola was lactose intolerant (not able to drink cow’s milk). The DNA also shows that Lola had none of the genetic markers associated with the new farming populations (Neolithic populations) entering northern Europe. This strengthens arguments that genetically distinct hunter-gatherer populations in the region survived for longer than previously thought.  

Researchers also detected DNA from bacteria and viruses in the resin, which provided a snapshot of ancient oral microbiome - something that has never been seen before. 

Studying oral microbiomes could provide a greater understanding of how bacteria interact with each other, how they change over time and how they react with different food and how this may impact disease. The birch tar resin sample also had traces of Streptococcus pneumoniae bacteria and Epstein-Barr virus, which gives the researchers an indication of Lola’s health. Streptococcus pneumoniae is a type of bacterium that can cause pneumonia, otitis media (middle ear infections) and is an important factor in the development of bacterial meningitis.

The finding "may help us understand how viruses have evolved and spread over time, and what makes them particularly harmful in a given environment. At the same time, it can help predict how a virus will behave in the future, and how it might be contained or eradicated," said Hannes Schroeder.

Reference: Jensen, T.Z.T., Niemann, J., Iversen, K.H. et al. A 5700 year-old human genome and oral microbiome from chewed birch pitch. Nat Commun 10, 5520 (2019). DOI: https://doi.org/10.1038/s41467-019-13549-9