Recently, a 5700-year-old piece of chewed birch pitch from Denmark was discovered by archaeologists during excavations east of Rødbyhavn in southern Denmark. Now, researchers from the University of Copenhagen have successfully extracted the complete human genome from ancient ‘chewing gum’. The incredible findings are presented in a new paper published on 17 December in Nature Communications (1).
The black-brown substance called birch pitch is produced by heating birch bark and dates back to palaeolithic times when it was commonly used as an all-purpose glue. However, pieces discovered with teeth imprints suggest the bark was also commonly chewed. Perhaps, to relieve toothache or other ailments since it has mild antiseptic properties. While other theories suggest birch bark may have been used as a toothbrush or chewing gum.
The discovery of well-preserved DNA samples dating back thousands of years have given rise to ‘ancient genomics’, a branch of research that is providing incredible insights into human prehistory. While ancient genomes have already been extracted from human bones, this is the first time a complete human genome has been extracted from something else. Discoveries like this are fast becoming a powerful resource for researchers and could shed light on time periods for which no human remains have been uncovered.
Associate Professor Hannes Schroeder from the Globe Institute at the University of Copenhagen, who led the study, said: ‘It is amazing to have gotten a complete ancient human genome from anything other than bone.’
‘Syltholm is completely unique. Almost everything is sealed in mud, which means that the preservation of organic remains is absolutely phenomenal,’ said Dr Theis Jensen, who worked on the study as part of his doctoral research and participated in the excavations.
No human remains were found at the site of Syltholm. So, instead, researchers used DNA extracted from the well-preserved gum to paint a picture of the girl who may have been chewing it. Incredibly, their genomic analysis revealed that the birch pitch was chewed by a female with dark skin, dark hair, and blue eyes. She was most likely related to the hunter-gatherers of mainland Europe and not the recently settled farmers of central Scandinavia. In addition, based on animal and plant DNA also found in the gum, they believe her diet may have included hazelnuts and duck.
The research team also isolated DNA from several oral microbes and important human pathogens — including DNA that could be assigned to Epstein-Barr Virus — as well as bacteria from the pitch itself. This bacterial DNA hints at the makeup of the ancient human microbiome. Schroeder said: ‘Our ancestors lived in a different environment and had a different lifestyle and diet, and it is therefore interesting to find out how this is reflected in their microbiome,’
Furthermore, ‘it can help us understand how pathogens have evolved and spread over time, and what makes them particularly virulent in a given environment. At the same time, it may help predict how a pathogen will behave in the future, and how it might be contained or eradicated’.
(1) Jensen, T.Z.T et al. A 5700 year-old human genome and oral microbiome from chewed birch pitch. Nature Communications, 2019; 10 (1) DOI: 10.1038/s41467-019-13549-9