A sticky lump of birch pitch, chewed and discarded nearly 6,000 years ago in southern Denmark, has yielded a complete human genome for the first time from a source other than bone. This remarkable scientific achievement provides an unprecedentedly intimate snapshot of a person from the Neolithic era, revealing her physical appearance, her genetic ancestry, and even the microbes that lived in her mouth. The analysis of this ancient “chewing gum,” along with similar finds in Sweden, is opening a new, untapped reservoir of genetic data, offering profound insights into the diet, health, and lifestyle of Stone Age communities.
The breakthrough demonstrates that birch pitch, a tar-like substance created by heating birch bark, can preserve a wealth of biological information that is often lost from skeletal remains. Researchers can now reconstruct detailed profiles of individuals from periods with scarce human fossils, painting a richer picture of populations in transition. Analysis of these chewed resins not only uncovers the genetic makeup of the chewer but also captures DNA from recent meals and a startling array of oral bacteria and viruses, some of which are linked to diseases that still affect humans today. This offers a powerful tool for understanding the evolution of human health and the microbiomes of our ancestors.
An Unprecedented Genetic Portrait
The most complete genetic sample came from a 5,700-year-old piece of birch pitch discovered at Syltholm on the Danish island of Lolland. Scientists from the University of Copenhagen successfully extracted enough DNA to reconstruct the entire genome of the individual who chewed it. The analysis revealed the person was a female, and based on her genetic markers, she likely had a striking combination of dark skin, dark hair, and blue eyes. This combination of features was relatively common among hunter-gatherers in Mesolithic Europe.
Further genetic sequencing showed that she was more closely related to hunter-gatherer groups from mainland Europe than to those who resided in Scandinavia at the time. This finding provides crucial evidence about population movements and interactions during the Neolithic period, a time when farming practices were beginning to spread into southern Scandinavia. The site at Syltholm, described as “completely unique” due to its phenomenal preservation in mud, suggests that local communities continued to heavily exploit wild resources well into the era of agriculture.
Diet and Daily Life in the Stone Age
The genetic material trapped in the ancient gum also contained traces of the woman’s recent diet. Scientists identified DNA from hazelnuts and duck, indicating these were likely components of her last meal before she discarded the pitch. This aligns with archaeological evidence from the site suggesting a reliance on wild food sources. Similar discoveries were made at a 9,700-year-old site called Huseby Klev in Sweden, where DNA from chewed birch resin revealed a diet consisting of deer, trout, and hazelnuts. Traces of other foods, including apple, duck, and fox, were also detected in the Swedish samples.
Analysis of the Swedish artifacts, which were found around 30 years ago, showed they were chewed by both males and females, many of whom appeared to be teenagers. This suggests the practice was common among various members of the community. While the primary purpose of chewing the pitch was likely practical, it may have served other functions as well. The act of chewing softened the tar, making it a more effective adhesive for hafting stone points onto spear shafts or arrows. However, researchers speculate it could also have been used for medicinal purposes, such as soothing a toothache with its antiseptic compounds, or simply for recreation.
A Window into Prehistoric Health
Oral Microbiome Evidence
Beyond the human genome, the birch pitch preserved a remarkable record of the oral microbiome of its chewers. In the 5,700-year-old Danish sample, researchers identified genetic material from at least 40 types of microbes. Many of these are common, harmless bacteria found in a healthy mouth, but the sample also contained DNA from pathogens. This included Streptococcus pneumoniae, a bacterium that can cause pneumonia, and the Epstein-Barr virus, which is responsible for infectious mononucleosis. While the presence of these microbes does not prove the woman was ill, it offers direct evidence of the pathogens carried by ancient populations.
Signs of Ancient Disease
The older samples from Sweden provided even more dramatic evidence of prehistoric health challenges. In one piece of resin chewed by a teenage girl approximately 10,000 years ago, scientists found high concentrations of bacteria associated with severe periodontitis, a serious gum infection that leads to tooth loss. According to researchers, the girl would have likely started losing her teeth shortly after chewing the gum, and the condition must have caused her considerable pain. These findings give scientists a direct line of sight into the specific diseases and health burdens faced by Stone Age hunter-gatherers, something that cannot be easily determined from bones alone.
The Science of Birch Pitch
Birch pitch is a black, sticky substance produced by heating the bark of birch trees in an environment with little to no oxygen. This process makes it one of the earliest synthetic materials deliberately created by humans. Its primary and most well-documented use was as a powerful adhesive for constructing tools and weapons. Small lumps of the material, often bearing clear tooth impressions, have been found at archaeological sites across Europe.
The unique properties that made birch pitch an excellent glue also make it an extraordinary vessel for preserving DNA. Its hydrophobic nature repels water, creating a sealed, anaerobic environment that protects genetic material from the rapid degradation it would normally undergo. This allows it to survive for millennia, trapping not only the DNA of the person who chewed it but also a comprehensive sample of the microscopic life within their mouth and remnants of their last meal. The success of these studies suggests that caches of chewed birch pitch could become a vital resource for understanding ancient human genomes, especially in regions or time periods where skeletal remains are rare.