Genetics: Ancient ‘chewing gum’ reveals human genome and oral microbiome

The entire genome of a 5,700 year-old human from Denmark has been obtained from a specimen of chewed birch pitch, reports a study published this week in Nature Communications. An analysis of plant, animal and microorganism DNA also contained within the pitch provides insights into the oral microbiome and potential sources of the individual’s diet.

Birch pitch is obtained by heating birch bark and has been used as an adhesive since the Middle Pleistocene (approximately 760,000 to 126,000 years ago). Small lumps of this material have been found at archaeological sites and have often included tooth imprints, which suggests that they were chewed.

By sequencing the human DNA contained within the birch pitch specimen, Hannes Schroeder and colleagues determined the individual’s sex as female and, based on genetic variation in several genes, find that she likely had dark hair, dark skin and blue eyes. The authors suggest that she was more closely related to western hunter-gatherers from continental Europe than hunter-gatherers from central Scandinavia. In an analysis of the non-human ancient DNA found in the birch pitch, the researchers detected bacterial species characteristic of the oral microbiome, some of which are known pathogens such as Porphyromonas gingivalis (implicated in gum disease). In addition, DNA sequences could be mapped to plant and animal species such as hazelnut and mallard, which the authors propose were left over from a recent meal.