DNA of First Settlers of Scandinavia Gleaned from Ancient Chewing Gums

DNA of First Settlers of Scandinavia Gleaned from Ancient Chewing Gums



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The first humans who settled in Scandinavia more than 10,000 years ago left their DNA behind in ancient chewing gums, which are masticated lumps made from birch bark pitch. This is shown in a new study conducted at Stockholm University and published in Communications Biology .

There are few human bones of this age, close to 10,000 years old, in Scandinavia, and not all of them have preserved enough DNA for archaeogenetic studies. In fact, the DNA from these newly examined chewing gums is the oldest human DNA sequenced from this area so far.

The DNA derived from three individuals, two females and one male, creates an exciting link between material culture and human genetics.

Piece of birch bark chewing gum containing oldest Scandinavian DNA (Image: Natalija Kashuba et al / Nature )

Alternative Scandinavian DNA Source

Previous DNA studies from the area were based on DNA derived from bones and teeth of seven individuals from the Norwegian Atlantic coast and the Baltic islands of Gotland and Stora Karlsö, dated to between 9,500-6000 years old, as reported in The Conversation. Colonization of Scandinavia is roughly dated to around 11,700 years ago and was one of the last parts of Europe to be populated when ice retreated in the area.

Ancient chewing gums are as of now an alternative source for human DNA and possibly a good proxy for human bones in archaeogenetic studies. The investigated pieces come from Huseby-Klev, an early Mesolithic hunter-fisher site on the Swedish west coast. The sites excavation was done in the early 1990's, but at this time it was not possible to analyze ancient human DNA at all, let alone from non-human tissue. The masticates were made out of birch bark tar and used as glue in tool production and other types of technology during the Stone Age.

This is an excavation of the Huseby-Klev site in the 1990's. (Per Persson/Stockholm University)

"When Per Persson and Mikael Maininen proposed to look for hunter-gatherer DNA in these chewing gums from Huseby Klev we were hesitant but really impressed that archaeologists took care during the excavations and preserved such fragile material," says Natalija Kashuba, who was affiliated to The Museum of Cultural History in Oslo when she performed the experiments in cooperation with Stockholm University.

"It took some work before the results overwhelmed us, as we understood that we stumbled into this almost 'forensic research', sequencing DNA from these mastic lumps, which were spat out at the site some 10,000 years ago!" says Natalija Kashuba. Today Natalija is a Ph.D. student at Uppsala University.

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The studied material and its origin. a One of the chewing gums from Huseby Klev, (Fynd 2037), with two plastelina casts for each side. b The location of the sites, genomes from which were used in this study. (Image: Natalija Kashuba et al / Nature )

Exciting link between material culture and human genetics

The results show that, genetically, the individuals whose DNA was found share close genetic affinity to other hunter-gatherers in Sweden and to early Mesolithic populations from Ice Age Europe. However, the tools produced at the site were a part of lithic technology brought to Scandinavia from the East European Plain, modern day Russia. This scenario of a culture and genetic influx into Scandinavia from two routes was proposed in earlier studies , and these ancient chewing gums provide an exciting link directly between the tools and materials used and human genetics.

Emrah Kirdök at Stockholm University conducted the computational analyses of the DNA. "Demography analysis suggests that the genetic composition of Huseby Klev individuals show more similarity to western hunter-gatherer populations than eastern hunter-gatherers," he says.

"DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights in their social relations, diseases and food," says Per Persson at the Museum of Cultural History in Oslo. "Much of our history is visible in the DNA we carry with us, so we try to look for DNA where ever we believe we can find it," says Anders Götherström, at the Archaeological Research Laboratory at Stockholm University, where the work was conducted. The study is published in Communications Biology .


Ancient ‘chewing gum’ reveals the oldest Scandinavian human DNA

The first humans to settle in Scandinavia over 10,000 years ago left their DNA behind in ancient chewing gums, which are masticated lumps of birch bark pitch.

There are only a few human bones of this age in Scandinavia, and most have not preserved enough DNA for genetic studies. In fact, the DNA from these newly examined chewing gums is the oldest human DNA sequenced from this area so far. The DNA derived from three individuals, two females and one male, creates an exciting link between material culture and human genetics. This new research was conducted at Stockholm University and published in Communications Biology.

Ancient chewing gums are as of now an alternative source for human DNA and possibly a good proxy for human bones in archaeogenetic studies. The investigated pieces come from Huseby-Klev, an early Mesolithic hunter-fisher site on the Swedish west coast. The sites excavation was done in the early 1990’s, but at this time it was not possible to analyse ancient human DNA at all, let alone from non-human tissue. The masticates were made out of birch bark tar and used as glue in tool production and other types of technology during the Stone Age.

Natalija Kashuba/Stockholm University

“When Per Persson and Mikael Maininen proposed to look for hunter-gatherer DNA in these chewing gums from Huseby Klev we were hesitant but really impressed that archaeologists took care during the excavations and preserved such fragile material”, says Natalija Kashuba, who was affiliated to The Museum of Cultural History in Oslo when she performed the experiments in cooperation with Stockholm University.

“It took some work before the results overwhelmed us, as we understood that we stumbled into this almost ‘forensic research’, sequencing DNA from these mastic lumps, which were spat out at the site some 10 000 years ago!” says Natalija Kashuba. Today Natalija is a Ph.D. student at Uppsala University.


This Gum Has Held The DNA of The Ancient Humans Who Chewed It For 10,000 Years

They say a tree never forgets, and apparently, neither does its resin. For more than ten thousand years, an ancient chewing gum, made from the tar of a birch bark tree, has held the memory of Scandinavia's first human settlers.

Discovered in the 1990s, in a prehistoric hunter-fisher site on the Swedish coast, known as the Huseby Klev, the three pieces of roughed-up gum spent decades without scientists ever looking for their secrets.

A few years ago, researchers at last began testing the fragile material, and in December of last year, a pre-printed study claimed to have found ancient human DNA in the remains. Now, five months later, the team has published an updated, peer-reviewed paper, and it's every bit as juicy as a used piece of gum.

"It took some work before the results overwhelmed us, as we understood that we stumbled into this almost 'forensic research', sequencing DNA from these mastic lumps, which were spat out at the site some 10,000 years ago!" says co-author Natalija Kashuba, who was affiliated with The Museum of Cultural History in Oslo at the time of research.

Mashed up into the tooth-marked lumps, the team found remnants of Stone Age saliva. And from this they were able to sequence the oldest human DNA from this area.

Each lump, it seems, belonged to one individual: two females and one male. But unlike today, this was not just a hobby, the authors say. Surrounded by the shavings of raw material, the site was likely used for tool-making, and the sticky gum was part of the process.

"The material we use is made of birch bark pitch, which is known to have been used as an adhesive substance in lithic tool technology from the Middle Palaeolithic onward in many parts of Eurasia," the authors explain, "but also for recreational purposes, and as a cement for mending and sealing wood and ceramic vessels."

For the first time, the authors were able to link the tools these early humans produced to an ancient technology, brought to Sweden from Eastern Europe, or what is now modern day Russia.

Yet combing through genomic data, the authors show that these early humans were actually more genetically similar to western hunter-gatherers and individuals from Ice Age Europe.

In other words, both the site and these humans seem to be sitting right where the currents of western and eastern migration once collided.

"This scenario of a culture and genetic influx into Scandinavia from two routes was proposed in earlier studies, and these ancient chewing gums provides an exciting link directly between the tools and materials used and human genetics," says co-author Emrah Kirdök from Stockholm University, who conducted the computational analyses of the DNA.

They can also tell us quite a lot about the cultural history of the region. For instance, because the gum was connected to tool-making and maintenance, the authors think we might need to update our understanding of gender roles in Mesolithic societies.

"Combined with the fact that several mastics from the site have imprints of deciduous teeth, the new information allows us to discuss gender in childhood," the authors continue.

"The possible interpretations are that tool-production was not restricted to one sex, or, if the individuals examined were children, that gender roles did not yet apply to young individuals."

In a world where human bones and tools rarely survive the ages, perhaps there are other tree remnants out there that hold similar secrets.

"DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights in their social relations, diseases and food," says co-lead author Per Persson, a blank from the Museum of Cultural History in Oslo.


They came from Ice Age Europe, but used tools from Eastern Europe

Kashuba and her teammates found that the ancient humans in Huseby-Klev displayed close genetic affinity to other hunter-gatherer groups in what became modern-day Sweden. They were also closely related to early Mesolithic people from Europe during the Ice Age.

Meanwhile, analysis of the tools found at the same site identified the artifacts as stone-based technology that came from the East European Plain. The plain belongs to Russia today.

Researchers earlier developed a theory that Scandinavia received cultural and genetic influences from two different directions. The ancient artifacts at Huseby-Klev supported the connection between human genes and material belongings.

“Demography analysis suggests that the genetic composition of Huseby Klev individuals show more similarity to western hunter-gatherer populations than eastern hunter-gatherers,” explained Stockholm researcher Emrah Kirdök, who ran the computer analyses of the genetic data.

KHM researcher Per Persson said that the genetic data in the ancient chewing gum showed the origin and movement of ancient humans during the Stone Age. It also shed light on their diet, diseases, and social relations.

Stockholm researcher Anders Götherström added that human DNA showed much of their history. Therefore, they look for genetic data wherever it might appear – such as ancient chewing gum.


Chewing gums reveal the oldest Scandinavian human DNA

This is shown in a new study conducted at Stockholm University and published in Communications Biology.

There are few human bones of this age, close to 10000 years old, in Scandinavia, and not all of them have preserved enough DNA for archaeogenetic studies. In fact, the DNA from these newly examined chewing gums is the oldest human DNA sequenced from this area so far. The DNA derived from three individuals, two females and one male, creates an exciting link between material culture and human genetics.

Ancient chewing gums are as of now an alternative source for human DNA and possibly a good proxy for human bones in archaeogenetic studies. The investigated pieces come from Huseby-Klev, an early Mesolithic hunter-fisher site on the Swedish west coast. The sites excavation was done in the early 1990’s, but at this time it was not possible to analyse ancient human DNA at all, let alone from non-human tissue. The masticates were made out of birch bark tar and used as glue in tool production and other types of technology during the Stone Age.

“When Per Persson and Mikael Maininen proposed to look for hunter-gatherer DNA in these chewing gums from Huseby Klev we were hesitant but really impressed that archaeologists took care during the excavations and preserved such fragile material”, says Natalija Kashuba, who was affiliated to The Museum of Cultural History in Oslo when she performed the experiments in cooperation with Stockholm University.

“It took some work before the results overwhelmed us, as we understood that we stumbled into this almost ‘forensic research’, sequencing DNA from these mastic lumps, which were spat out at the site some 10 000 years ago!” says Natalija Kashuba. Today Natalija is a Ph.D. student at Uppsala University.

Exciting link between material culture and human genetics

The results show that, genetically, the individuals whose DNA was found share close genetic affinity to other hunter-gatherers in Sweden and to early Mesolithic populations from Ice Age Europe. However, the tools produced at the site were a part of lithic technology brought to the site from the East European Plain, modern day Russia. This scenario of a culture and genetic influx into Scandinavia from two routes was proposed in earlier studies, and these ancient chewing gums provides an exciting link directly between the tools and materials used and human genetics.

Emrah Kırdök at Stockholm University conducted the computational analyses of the DNA. “Demography analysis suggests that the genetic composition of Huseby Klev individuals show more similarity to western hunter-gatherer populations than eastern hunter-gatherers”, he says.

“DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights in their social relations, diseases and food.”, says Per Persson at the Museum of Cultural History in Oslo. “Much of our history is visible in the DNA we carry with us, so we try to look for DNA where ever we believe we can find it”, says Anders Götherström, at the Archaeological Research Laboratory at Stockholm University, where the work was conducted. The study is published in Communications Biology.

Header Image – Masticate being examined, Photo: Natalija Kashuba/Stockholm University


DNA of First Settlers of Scandinavia Gleaned from Ancient Chewing Gums - History

Natalija Kashuba Et. Al/Stockholm University In the early Mesolithic Era, birch bark tar was commonly used as glue in tool production.

Researchers excavated a piece of 10,000-year-old birch bark in Sweden in the early 1990s in the hopes of uncovering a trove of DNA. Why would birch bark be full of human DNA? Well, the tree was used as an ancient form of chewing gum which could, in turn, shed some light on life in ancient Scandinavia.

Unfortunately, the technology to properly analyze the item’s DNA simply wasn’t available back then, and seeing as ancient human DNA in Scandinavia has been tremendously difficult to find, the potential behind these chewed bits of bark held great significance to researchers. According to Phys, times have at last changed and a new study conducted at Stockholm University has finally been able to unlock the ancient biological secrets within that birch bark.

The research was published in the journal, Communications Biology and emphasizes the regional scarcity of human bones from the Stone Age. The bones that have been found contain only poorly preserved DNA and has consequently left the scientific community with a notable void. It may have taken science a few decades to catch up, but the excavated item — found at a site called Huseby Klev on the west coast — has finally become an informative source of data.

“Much of our history is visible in the DNA we carry with us, so we try to look for DNA where ever we believe we can find it,” said Anders Götherström, who works in the Archaeological Research Laboratory at Stockholm University.

This early form of gum is now officially the oldest human DNA ever sequenced from this part of the world, but masticated birch bark itself was actually not a shocking find as Stone Age peoples commonly used its tar as glue to build tools.

Per Persson/Stockholm University Though the gum was excavated at Huseby Klev decades ago, science had to catch up in order to properly analyze it for DNA.

As such, discovering this in an early Mesolithic hunting and fishing site wasn’t abnormal. For the first time since its unearthing, however, scientists are able to make informed deductions from the item. These span across food, disease, and social habits of the region during that time. Indeed, researchers have even now revealed that the DNA on the bark belonged to two females and one male.

“When Per Persson and Mikael Maininen proposed to look for hunter-gatherer DNA in these chewing gums from Huseby Klev we were hesitant, but really impressed that archaeologists took care during the excavations and preserved such fragile material,” said Natalija Kashuba of the Museum of Cultural History in Oslo.

“It took some work before the results overwhelmed us, as we understood that we stumbled into this almost ‘forensic research,’ sequencing DNA from these mastic lumps, which were spat out at the site some 10,000 years ago,” Kashuba added.

Natalija Kashuba Et. Al/Stockholm University The two casts (left and right) clearly show teeth marks. It’s likely the early peoples of Scandinavia chewed on the bark in their downtime or during tool production.

The overwhelming results she referenced largely regard potential migratory and trade patterns of the time. Earlier studies have proposed that Scandinavia saw a cultural and genetic influx from two routes along the East European Plain (modern-day Russia) and from Ice Age Europe. Indeed, the DNA results from this gum showed that three individuals were closely genetically related to Mesolithic populations from Ice Age Europe — while the tools produced at the site were brought to Scandinavia from Russia.

As such, this piece of chewed up bark directly supports this previous theory. For Kashuba’s colleague, Per Persson of the Museum of Cultural History in Oslo, there’s still an untapped wealth of information in that small piece of chewed tree bark.

“DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights in their social relations, diseases, and food,” he said.


5,700-year-old chewing gum still contains human DNA from prehistoric woman

COPENHAGEN, Denmark — 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.

Artistic 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.


Chewing Gums Reveal the Oldest Scandinavian Human DNA

This is an excavation of the site in the 1990's. Per Persson/Stockholm University The first humans who settled in Scandinavia more than 10,000 years ago left their DNA behind in ancient chewing gums, which are masticated lumps made from birch bark pitch. This is shown in a new study conducted at Stockholm University and published in Communications Biology.

There are few human bones of this age, close to 10 000 years old, in Scandinavia, and not all of them have preserved enough DNA for archaeogenetic studies. In fact, the DNA from these newly examined chewing gums is the oldest human DNA sequenced from this area so far. The DNA derived from three individuals, two females and one male, creates an exciting link between material culture and human genetics.

Ancient chewing gums are as of now an alternative source for human DNA and possibly a good proxy for human bones in archaeogenetic studies. The investigated pieces come from Huseby-Klev, an early Mesolithic hunter-fisher site on the Swedish west coast. The sites excavation was done in the early 1990's, but at this time it was not possible to analyse ancient human DNA at all, let alone from non-human tissue. The masticates were made out of birch bark tar and used as glue in tool production and other types of technology during the Stone Age.

"When Per Persson and Mikael Maininen proposed to look for hunter-gatherer DNA in these chewing gums from Huseby Klev we were hesitant but really impressed that archaeologists took care during the excavations and preserved such fragile material", says Natalija Kashuba, who was affiliated to The Museum of Cultural History in Oslo when she performed the experiments in cooperation with Stockholm University.

"It took some work before the results overwhelmed us, as we understood that we stumbled into this almost 'forensic research', sequencing DNA from these mastic lumps, which were spat out at the site some 10 000 years ago!" says Natalija Kashuba. Today Natalija is a Ph.D. student at Uppsala University.

Exciting link between material culture and human genetics

The results show that, genetically, the individuals whose DNA was found share close genetic affinity to other hunter-gatherers in Sweden and to early Mesolithic populations from Ice Age Europe. However, the tools produced at the site were a part of lithic technology brought to Scandinavia from the East European Plain, modern day Russia. This scenario of a culture and genetic influx into Scandinavia from two routes was proposed in earlier studies, and these ancient chewing gums provides an exciting link directly between the tools and materials used and human genetics.

Emrah Kirdök at Stockholm University conducted the computational analyses of the DNA. "Demography analysis suggests that the genetic composition of Huseby Klev individuals show more similarity to western hunter-gatherer populations than eastern hunter-gatherers", he says.

"DNA from these ancient chewing gums have an enormous potential not only for tracing the origin and movement of peoples long time ago, but also for providing insights in their social relations, diseases and food.", says Per Persson at the Museum of Cultural History in Oslo. "Much of our history is visible in the DNA we carry with us, so we try to look for DNA where ever we believe we can find it", says Anders Götherström, at the Archaeological Research Laboratory at Stockholm University, where the work was conducted. The study is published in Communications Biology.


Human Genome Recovered From 5,700-Year-Old Chewing Gum

Modern chewing gums, which often contain polyethylene plastic, could stick around for tens or even hundreds of years, and perhaps much longer in the right conditions. Some of the first chewing gums, made of birch tar and other natural substances, have been preserved for thousands of years, including a 5,700-year-old piece of Stone Age gum unearthed in Denmark.

For archaeologists, the sticky stuff’s longevity can help piece together the lives of ancient peoples who masticated on the chewy tar. The ancient birch gum in Scandinavia preserved enough DNA to reconstruct the full human genome of its ancient chewer, identify the microbes that lived in her mouth, and even reveal the menu of a prehistoric meal.

“These birch pitch chewing gums are kind of special in terms of how well the DNA is preserved. It surprised us,” says co-author Hannes Schroeder, a molecular anthropologist at the University of Copenhagen, Denmark. “It’s as well-preserved as some of the best petrous [skull] bones that we’ve analyzed, and they are kind of the holy grail when it comes to ancient DNA preservation.”

Birch pitch, made by heating the tree’s bark, was commonly used across Scandinavia as a prehistoric glue for attaching stone tools to handles. When found, it commonly contains toothmarks. Scientists suspect several reasons why people would have chewed it: to make it malleable once again after it cooled, to ease toothaches because it’s mildly antiseptic, to clean teeth, to ease hunger pains, or simply because they enjoyed it.

The gum’s water-resistant properties helped to preserve the DNA within, as did its mild antiseptic properties which helped to prevent microbial decay. But the find was also made possible by the conditions at the site, named Syltholm, on an island in southern Denmark, where thick mud has perfectly preserved a wide range of unique Stone Age artifacts. Excavations began at the site in 2012 in preparation for the construction of a tunnel, affording the Museum Lolland-Falster a unique chance for archaeological field work.

No human remains have yet been found at Syltholm—unless you count the tiny strands of DNA preserved in the ancient gum Schroeder and colleagues described today in Nature Communications.

The discarded gum yielded a surprising amount of information about its 5,700-year-old chewer. She was a female, and while her age is unknown, she may have been a child considering similar birch pitch gums of the era often feature the imprints of children’s teeth.

From the DNA, researchers can start to piece together some of the ancient woman’s physical traits and make some inferences about the world she lived in. “We determined that she had this striking combination of dark skin, dark hair, and blue eyes,” Schroeder says. “It’s interesting because it’s the same combination of physical traits that apparently was very common in Mesolithic Europe. So all these other ancient [European] genomes that we know about, like La Braña in Spain, they all have this combination of physical traits that of course today in Europe is not so common. Indigenous Europeans have lighter skin color now but that was apparently not the case 5,000 to 10,000 years ago.”

An artist's illustration of what the Scandinavian person who chewed the ancient piece of gum may have looked like. (Tom Björklund)

The gum-chewers’ family ties may also help to map the movement of peoples as they settled Scandinavia.

“The fact that she was more closely related genetically to people from Belgium and Spain than to people from Sweden, which is just a few hundred kilometers farther north, tells us something about how southern Scandinavia was first populated,” Schroeder says. “And it looks like it was from the continent.” This interpretation would support studies suggesting that two different waves of people colonized Scandinavia after the ice sheets retreated 12,000 to 11,000 years ago, via a southern route and a northeastern route along today’s Norwegian coast.

The individual was part of a world that was constantly changing as groups migrated across the northern regions of Europe. “We may expect this process, especially at this late stage of the Mesolithic, to have been complex with different groups, from south, west or even east, moving at different times and sometimes intermingling while perhaps other times staying isolated,” Jan Storå, an osteoarchaeologist at Stockholm University, says via email.

Additional archaeological work has shown that the era was one of transition. Flaked stone tools and T-shaped antler axes gave way to polished flint artifacts, pottery and domesticated plants and animals. Whether the region’s turn to farming was a lifestyle change among local hunter-gatherers, or spurred by the arrival of farming migrants, remains a matter of debate.

“This is supposed to be a time when farming has already arrived, with changing lifestyles, but we find no trace of farmer ancestry in her genome, which is fairly easy to establish because it originated in the Near East. So even as late as 5,700 years ago, when other parts of Europe like Germany already had farming populations with this other type of ancestry present, she still looked like essentially western hunter-gatherers, like people looked in the thousands of years before then,” Schroeder says.

“The ‘lack’ of Neolithic farmer gene flow, at this date, is very interesting,” adds Storå, who wasn’t involved in the research. “The farming groups would probably have been present in the area, and they would have interacted with the hunter-gatherer groups.”

The era’s poor oral hygiene has helped add even more evidence to this line of investigation, as genetic bits of foodstuffs were also identifiable in the gum.

Presumably not long before discarding the gum, the woman feasted on hazel nuts and duck, which left their own DNA sequences behind. “The dietary evidence, the duck and the hazel nuts, would also support this idea that she was a hunter-gatherer and subsisted on wild resources,” Schroeder says, noting that the site is littered with physical remains which show reliance on wild resources like fish, rather than domesticated plants or animals.

“It looks like in these parts maybe you have pockets of hunter-gatherers still surviving, or living side-by-side with farmers for hundreds of years,” he says.

Scientists also found traces of the countless microbes that lived in the woman’s mouth. Ancient DNA samples always include microbial genes, but they are typically from the environment. The team compared the taxonomic composition of the well-preserved microbes to those found in modern human mouths and found them very similar.

Satisfied that genetic signatures of ancient oral microbes were preserved in the woman’s gum, the researchers investigated the specific species of bacteria and other microbes. Most were run-of-the-mill microflora like those still found in most human mouths. Others stood out, including bacterial evidence for gum disease and Streptococcus pneumoniae, which can cause pneumonia today and is responsible for a million or more infant deaths each year.

Epstein-Barr virus, which more than 90 percent of living humans carry, was also present in the woman’s mouth. Usually benign, the virus can be associated with serious diseases like infectious mononucleosis, Hodgkin’s lymphoma and multiple sclerosis. Ancient examples of such pathogens could help scientists reconstruct the origins of certain diseases and track their evolution over time, including what factors might conspire to make them more dangerous.

“What I really find interesting with this study is the microbial DNA,” Anders Götherström, a molecular archaeologist at Stockholm University, says in an email. “DNA from ancient pathogens holds great promise, and this type of mastics may be a much better source for such data than ancient bones or teeth.”

Natalija Kashuba, an archaeologist at Uppsala University in Sweden, and colleagues have also extracted human DNA from ancient birch gum, from several individuals at a 10,000-year-old site on Sweden’s west coast. “It’s really interesting that we can start working on this material, because there’s a lot of it scattered around Scandinavia from the Stone Age to the Iron Age,” she says, adding that gums may survive wherever birches were prevalent—including eastward toward Russia, where one wave of Scandinavian migration is thought to have originated.

The fact that the discarded artifact survived to reveal so much information about the past isn’t entirely due to luck, Kashuba says. “I think we have to thank the archaeologists who not only preserved these gums but suggested maybe we should try to process them,” she says. “If it hadn’t been for them, I’m not sure most geneticists would have bothered with this kind of material.”