Syltholm (Danemark): 5,700-year-old chewing gum still contains human DNA

Chris Melore

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Copenhagen gum 604x385The birch pitch found at Syltholm on Lolland. (Credit: Theis Jensen)

 Have you ever come across the black, sticky remains of chewing gum melted into the sidewalk? If so, you know it doesn’t dissolve fast once it leaves your mouth. What you may not know is that gum may keep a sample of your DNA locked inside it for centuries! Researchers in Denmark have discovered an ancient piece of “chewing gum” still containing the full human genome of its chewer. Remarkably, that ancient gum was last chewed on 5,700 years ago.

Archaeologists unearthed this wad of history during during excavations on the Danish island of Lolland in 2019. The fossil appears to be a piece of birch pitch, a tarry substance that comes from the birth tree.

A team from the University of Copenhagen successfully extracted the complete DNA history from the sample. Until this breakthrough, scientists have only recovered ancient genomes from human bone fragments.

“It is amazing to have gotten a complete ancient human genome from anything other than bone,” says Associate Professor Hannes Schroeder from Copenhagen’s Globe Institute in a university release.

“What is more, we also retrieved DNA from oral microbes and several important human pathogens, which makes this a very valuable source of ancient DNA, especially for time periods where we have no human remains.”

DNA reveals the ancient chewer’s identity

Genetic data in the pitch reveals so much about the chewer, scientists believe they even know what she looked like. First off, yes, the genome reveals this person was a female living in central Scandinavia at the time. Study authors add the genetic profile points to the woman being part of a group of hunter-gatherers in that region. The DNA also leads scientists to believe she had dark skin, dark hair, and blue eyes.

Lola gum 475x259Artistic reconstruction of the woman who chewed the birch pitch. She has been named Lola. (Illustration by Tom Björklund)

Scientists discovered the birch itself at Syltholm; a particularly important area for archaeologists in southern Denmark.

“Syltholm is completely unique. Almost everything is sealed in mud, which means that the preservation of organic remains is absolutely phenomenal,” explains researcher Theis Jensen.

“It is the biggest Stone Age site in Denmark and the archaeological finds suggest that the people who occupied the site were heavily exploiting wild resources well into the Neolithic, which is the period when farming and domesticated animals were first introduced into southern Scandinavia.”

The results also uncovered traces of plant and animal DNA in the pitch, specifically traces of hazelnuts and duck. Study authors add this may have been part of this prehistoric human’s diet.

Viruses locked away in ancient chewing gum?

Along with the female’s DNA, researchers also uncovered bacteria and viruses in the ancient gum.

“The preservation is incredibly good, and we managed to extract many different bacterial species that are characteristic of an oral microbiome. 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,” Schroeder reports.

Scientists say some of these genes may be part of Epstein-Barr Virus, which can cause infectious mononucleosis or glandular fever. Schroeder adds “chewing gums” like this have the potential to reveal how human pathogens have evolved throughout history. They also point to how the human microbiome has changed over the last few thousand years.

“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,” Schroeder concludes.

The findings were published in the journal Nature Communications in December 2019.