Neolithic Birch Tar Chewing Gum Reveals Ancient DNA

Neolithic people appear to have relished chewing gum as much as a child bored in a calculus lesson. The wads they left behind are now yielding unexpected evidence about human life as long as 6,000 years ago.

Neolithic birch tar and the earliest chewing gum

Birch-bark tar is the oldest synthetic material known in the world. In the European Alps, Neolithic communities used this pliable, sticky material to fasten handles to stone blades, mend pottery and chew as they went about their work.

"The precise reason for chewing tar remains unclear, but it has been suggested that it was chewed for medicinal purposes as it contains natural compounds with antimicrobial properties," write a team of archaeologists led by Anna White from the University of Copenhagen.

The researchers examined 30 birch-tar artefacts from nine Alpine sites, mainly lake settlements dating back as far as 6,300 years. Twelve pieces were separate wads of tar, with many showing the clear marks of chewing.

Adhesives are particularly useful archaeological materials because they can gather a wide variety of substances from their surroundings, whether by chance or through deliberate addition. Materials detected in preserved tar, including pine resin, may have been intentionally mixed in to alter birch tar's physical properties.

When tar is chewed, traces of the human oral microbiome can become embedded in it, alongside food and other material caught between the chewer's teeth. DNA from linseed (Linum usitatissimum) and poppy seeds (Papaver somniferum) appeared in some pieces, although it is not known whether the latter was consumed as food or for its opioid effects.

Ancient human DNA survived well enough in 19 samples for the team, in certain instances, to establish the sex of the person who had chewed the tar.

"The presence of human and oral microbial DNA in some of the samples suggests the tar was chewed, in some cases by multiple individuals," the authors write.

"The human DNA also enables us to determine the sex of those who chewed the tar, offering insights into gendered practices in the past, while plant and animal DNA shed light on past diets and the possible use of additives."

DNA evidence from chewed tar

Study of the organic residue and ancient DNA preserved in the tar found male DNA on the 10 stone tools for which tar had served as an adhesive. Female DNA, meanwhile, was identified in the tar used to repair each of the three pottery objects investigated.

Chewing may have played a significant role in preparing tar for adhesive work. The material becomes hard as it cools, whereas chewing would have made it softer and easier to use.

However, saliva generally weakens tar's adhesive qualities, which are restored only after the material has been reheated.

"[This] may explain why we find less oral microbial DNA in the hafted samples and the ceramic tars than in some of the 'chewed' pieces," the authors note.

Human remains from this period are limited, so this ancient chewing gum provides an unusual means of investigating prehistory that might otherwise have disappeared with time.

So dispose of your next piece of chewing gum carefully: it may preserve your DNA, and evidence of your dinner, for thousands of years.

The research was published in Proceedings of the Royal Society B.