We finally have a way to connect archeological findings with genetic studies, using ancient chewing gum. In a new study published in Communications Biology, researchers from Stockholm University have found a way to extract DNA from saliva preserved in ancient chewing gum. This innovative technique could provide a source of DNA in excavation sites with no human remains, or when these are too damaged to study.
Birch bark pitch was used by Mesolithic societies as an adhesive substance in tool making, for example to attach a stone blade to a handle, to mend and seal wood and ceramics or even, as we do today, for recreational purposes. Over 100 such pieces of chewed gum were found at Huseby Klev, an excavation site in western Sweden, which dates to between 10,040 and 9,610 years ago. Each piece was usually only chewed by a single individual, and so could be used to retrieve their unadulterated DNA. Three pieces were used in this study, yielding the oldest DNA sequences from this area so far.
During the last Ice Age, around 20,000 years ago, humans retreated to small pockets of habitable land in Southern Europe. Once temperatures warmed, they slowly migrated out. The first hunter-gatherers reached Scandinavia around 10,000 years ago. From population genetic studies of ancient human remains, it appears that two groups migrated to Scandinavia: the Eastern Hunter-Gatherers (EHGs), who arrived from the North, and the Western Hunter-Gatherers (WHGs), who arrived from the South. These individuals met and merged in Scandinavia to form the Scandinavian Hunter-Gatherers (SHGs). Each group was thought to have used a different stone working technique. In particular, EHGs may have introduced a more advanced stone working technique to Scandinavia, but this connection remained unproven, because ancient human bones are often found without associated artefacts. Until now, researchers had no way of connecting genetic findings to the materials archeologists use to reconstruct the life of past societies.
The stone tools found at the Huseby Klev excavation site suggested that the individuals who lived there were using the methods introduced to Scandinavia by the EHGs. Unexpectedly, the DNA of SHG individuals in this study was more genetically similar to WHGs than to EHGs. This suggests that human settlement in Scandinavia may have followed a more complex sequence of events than anticipated, in which the new techniques were transmitted both with and without genetic intermingling.
The study also has cultural and anthropological implications. The chewed gum often still had imprints of teeth and fingers, and when 10 pieces from Huseby Klev were compared to modern parallels, they revealed that the chewers were between 5 and 18 years old. The gum would mainly have been used for tool making and maintenance, so the fact that both male and female DNA was found on the chewed gum suggests that gender roles may have been similar in these societies. Thus, studying chewed pitch sheds some light on the social organisation of such populations, and could also provide information about the environment, ecology and oral microbiome of the chewers. Per Persson, from the Museum of Cultural History in Oslo, concludes: “DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights into their social relations, diseases and food.”
This post was written by Helena Cornu and edited by Ella Mercer.