What a 5,700-Year-Old Piece of Gum Reveals About Its Chewer

Nearly 6,000 years ago, in a seaside marshland in what is now southern Denmark, a woman with blue eyes and dark hair and skin popped a piece of chewing gum in her mouth. Not spearmint gum, mind you, but a decidedly less palatable chunk of black-brown pitch, boiled down from the bark of the birch tree. An indispensable tool in her time, birch pitch would solidify as it cooled, so the woman and her comrades would have had to chew it before using it as a sort of superglue for, say, making tools. Our ancient subject may have even chewed it for its antiseptic properties, perhaps to ease the pain of an infected tooth.

Eventually she spit out the gum, and six millennia later, scientists found it and ran the blob through a battery of genetic tests. They not only found the chewer’s full genome and determined her sex and likely skin and hair and eye color, they also revealed her oral microbiome—the bacteria and viruses that pack the human mouth—as well as finding the DNA of hazelnut and duck she may have recently consumed. All told, from a chunk of birch pitch less than an inch long, the researchers have painted a remarkably detailed portrait of the biology and behavior of an ancient human.

Photograph: Theis Jensen

When that birch pitch hit the ground 5,700 years ago, the European continent was playing host to a full-tilt transformation of its human residents. Agriculture was spreading north from the Middle East, and humans were literally and figuratively planting roots—if you’re looking after crops, you’re staying put and building up infrastructure to support your efforts, not following around herds of wild game.

But several converging lines of evidence indicate that this gum-chewing woman actually was a hunter-gatherer, thousands of years after the invention of agriculture. For one, previous analyses have allowed scientists to associate certain genes with either agricultural or hunter-gatherer lifestyles. They did this by matching DNA samples with archaeological evidence for those people—farming tools versus hunting tools, for instance.

Illustration: Tom Björklund

The genetics of this ancient woman point to the hunter-gatherer way of life, matched with contemporaneous archeological evidence from the area. “You find lots of fish traps and eel-catching prongs and spears,” says University of Copenhagen geneticist Hannes Schroeder, coauthor on a new paper in Nature Communications describing the findings. Evidence of a more settled lifestyle at the site only came later in history.

This is further bolstered by the duck and hazelnut DNA the researchers found in the birch pitch, which are staple foods in that hunter-gatherer diet. But it’s also possible that those hazelnut genes came from hazelnut bark she mixed in with the birch when she made the pitch. And just because she may have been noshing on duck before she chewed the birch pitch, doesn’t mean she wasn’t eating cultivated crops too.

“There’s actually nothing to tell us that on a Thursday she didn’t do farming, and was eating duck on the weekend,” says Schroeder. “But what we can go on is that we know, genetically, she looks like a Western hunter-gatherer.” That and where she was chewing pitch was likely a seaside marshland, not the greatest of places to homestead.

One more fascinating bit of evidence to suggest she wasn’t a farmer: Her genes indicate lactose intolerance. The ability to digest milk in adulthood without severe gastrointestinal distress (babies, of course, need to be able to process milk) only came with the arrival of farming.

So here we have what was clearly a hunter-gatherer, exploiting natural resources as the world around her converted to agriculture. You see, the transition from the hunter-gatherer lifestyle to sedentary one was a stepwise process, not a sudden transformation of the whole of Europe into an industrialized food economy. “However, this transition is still not well known and it is being consistently studied,” says Emrah Kırdök, a paleogeneticist at Mersin University, who wasn’t involved in this work. “So according to our knowledge, farming was introduced to different parts of the world progressively, and some cultures could have remained as a hunter-gatherer society for some time.” Our gum chewer was one such holdout.

Now, about that mouth microbiome. Here we have the tricky matter of bacteria and viruses drifting all over a given environment, so some of the microbes could have landed on the pitch after she spit it out. Luckily, scientists have built a database of known species compositions of microbiomes around the body, including gut, skin, and mouth. The pitch-chewer, these researchers found, had an oral microbiome not all that different from our own. They even found standouts types, like the bacteria Streptococcus pneumoniae, which can lead to pneumonia, and Epstein-Barr virus, a variety of herpes and one of the more common human viruses. Same woes, different millennium, it seems.

Also intriguing is the woman’s phenotype, or physical characteristics, as suggested by her genome. In recent history, the European north has been populated by a lot of folks with lighter hair and skin and blue eyes—the idea being that from an evolutionary perspective, fairer skin would help humans in colder, darker climes manufacture enough vitamin D, whereas in hotter climes peoples would need more dark melanin to protect them from the sun. But while this woman had blue eyes, her genes suggest she had darker hair and skin. “That means that this combination of phenotypic traits was probably fairly common until recently,” says Schroeder. “That’s only really evolved in Europe in the last 5,000 years, which is interesting.”

So a tiny piece of chewed-up pitch reveals not only a heap of information about this ancient woman, but also adds a layer to the larger story of human evolution. Something to chew on, for sure.

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