On an autumn day about 9,700 years ago, a group of people were camping on the west coast of Scandinavia. They were hunter-gatherers who fished, hunted, and gathered resources in the area.
Some young people, both boys and girls, chewed resin to produce glue immediately after eating trout, deer, and hazelnuts. Due to severe gum infection (periodontitis), one of the teenagers had problems eating the chewable venison as well as preparing the resin by chewing it.
This snapshot of the Mesolithic period, just before Europeans began farming, comes from analysis of DNA left in chewed resin that we conducted and has now been published in Scientific Reports.
Its location is now known as Huseby Klev, north of Gothenburg (Göteborg), Sweden. Excavations by archaeologists in the early 1990s unearthed 1,849 flint artifacts and 115 pieces of resin (mastic). Radiocarbon dating at the site dated it to between 10,200 and 9,400 years ago, and one of the resin fragments was dated to 9,700 years ago.
There are teeth marks on some of the resin, indicating that children, actually teenagers, had chewed on it. It is not uncommon to find chewed pellets, often containing tooth marks, fingerprints, or both, in Mesolithic sites.
The resin pieces we examined were made of birch bark pitch, which is known to have been used as an adhesive in stone tool technology since the Middle Paleolithic Age. However, in traditional societies it was also chewed for recreational or medicinal purposes.
It is known that various substances with similar properties, such as resins obtained from coniferous trees, natural bitumen and other plant gums, are used in similar ways in many parts of the world.
The power of DNA
Half of the DNA extracted from part of the resin was of human origin. This is a lot compared to what we often find in ancient bones and teeth.
I represent some of the oldest human genomes from Scandinavia. There is a common ancestor profile among the Mesolithic hunter-gatherers who once lived there.
While some of the resin contains male human DNA, some of it contains female DNA. We think that young people of both genders prepared glue to use in making tools, such as attaching a stone ax to a wooden handle.
But what about the other half of DNA of non-human origin? Most of this DNA comes from organisms such as bacteria and fungi that have lived in the chewing gum since it was discarded 9,700 years ago. But some of this came from bacteria living in the human chewing it, along with the material the human chewed before putting the birch bark pitch into his mouth.
Analyzing all this DNA is a challenging task and breaks new ground. We needed to both adapt existing computing tools and develop some new analytical strategies. This study therefore became the starting point for developing a new workflow for this type of analysis.
This involves mining DNA using different strategies to characterize it, trying to break down short DNA fragments into longer ones, and using machine learning techniques to find which DNA fragments belong to pathogens (harmful microorganisms). It also involves comparing the data with what we see in the mouths of modern humans suffering from tooth decay (cavities) and periodontitis.
higher organisms
Naturally, we found the type of bacteria that would be expected in the oral microbiome, that is, the types of naturally occurring microorganisms found in the mouth. We also found traces of bacteria that play a role in conditions such as tooth decay or cavities (Streptococcus mutans) and systemic diseases such as Hib disease and endocarditis. There were also bacteria that could cause abscesses.
Although these pathogenic microorganisms were present at a high frequency, they were not clearly above the level expected for a healthy oral microbiome. Therefore, there is no conclusive evidence that members of the group suffer from diseases associated with these microorganisms.
However, we found a large number of bacteria associated with serious gum disease (periodontitis). When we applied a machine learning strategy (in this case, a technique called Random Forest modeling), we concluded that the girl who chewed on one of the resin pieces probably had periodontitis with a greater than 75% chance.
We also found DNA from organisms larger than bacteria. We found DNA for red deer, brown trout and hazelnuts. This DNA likely came from material the youngsters chewed before putting birch pitch into their mouths.
But we need to be a little careful, because exactly what we find also depends on the comparison data we have. Because the genomes of eukaryotic organisms (the group that includes plants and animals) are larger and more complex than the genomes of microorganisms, assembling a high-quality eukaryotic genome is more complex.
Resin samples contain fewer eukaryotic genomes and are of lower quality. This means that our brown trout, for example, may not actually be brown trout, but at least we know for sure that it is in the salmon family.
We also found a lot of fox DNA, but this is harder to interpret. Fox meat may have been part of the diet, but these juveniles may also have chewed the tendons and fur of foxes for use in textiles. Alternatively, fox DNA may even have resulted from territorial marking and became incorporated into the resin after being spat out.
But what we know for sure represents a major step forward in understanding these fascinating records of human culture from the Stone Age. As you analyze these, even more surprises may emerge.
This article is republished from The Conversation under a Creative Commons license. Read the original article.
Anders Götherström receives funding from: Swedish Research Council (2019-00849_VR), Riksbankens Jubileumsfond (P16-0553:1)
Emrah Kırdök does not work for, consult for, own shares in, or receive funding from any company or organization that may benefit from this article, and has disclosed no affiliations beyond his academic duties.