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Tarlike birch bark pitch from Sweden preserved both clear tooth impressions and DNA for thousands of years.

N. Kashuba, et. al., bioRxiv 10.1101 (2018)/CC BY-NC-ND 4.0

This 8000-year-old ‘gum’ holds surprises about ancient toolmakers

Gum won’t really sit in your stomach for years, but it can preserve human DNA for millennia. Researchers have uncovered genetic material encased within 8000-year-old tarlike wads known as birch bark pitch, which Scandinavian hunter-gatherers chewed to make a glue for weapons and tools. Among other things, the DNA suggests these toolmakers were both male and female, and some may have been as young as 5 years old.

“It’s exciting … that you could get DNA from something people chewed thousands of years ago,” says Lisa Matisoo-Smith, a molecular anthropologist at the University of Otago in Dunedin, New Zealand. “I think there are lots of ways people will take this going forward.”

In the late 1980s, a team of Swedish archaeologists excavated a pit within an archaeological site called Huseby Klev in western Sweden. Here, they discovered more than 100 coal black, thumbprint-size lumps riddled with distinct toothmarks. Chemical analysis revealed these were pieces of pitch, an early adhesive derived from plant resin. Researchers already knew ancient toolmakers heated pitch distilled from birch trees over a fire to soften it, chewed bits of it into a pliable state, then used the sticky wad to fasten sharpened stones to wooden or bony shafts to make weapons and tools.

Natalija Kashuba, an archaeology Ph.D. student at Uppsala University in Sweden, and colleagues wondered whether any usable DNA from the chewers’ saliva remained inside the hardened resin. Kashuba, who did the work while a student at the University of Oslo, and the rest of the team took tiny samples from three wads, ground them to powder, and put them through an extremely sensitive DNA amplification process designed to locate ancient DNA, which is often highly degraded.

The researchers identified human DNA in all three pieces. Further analysis revealed each came from a different individual—two females and a male. Based on estimations of tooth size and wear taken from the toothmarks in the pitch, the researchers suspect the chewers were young, between 5 and 18 years old. Adult tooth impressions have also been found in pitch from the site, which could suggest an egalitarian toolmaking process involving all sexes and ages, the team reports this week on the bioRxiv preprint server.

The DNA also revealed these pitch chewers belonged to a genetic group known as Scandinavian hunter-gatherers, who hunted reindeer in what are today Sweden and Norway some 8000 years ago. That confirms what anthropologists suspected, says Torsten Günther, an evolutionary biologist at Uppsala University who wasn’t involved in the work. The study’s real value, he says, is highlighting the promise of studying ancient human populations even when you can’t find the humans themselves. “Even if human remains are found, it would be an opportunity to perform these genomic studies without destructive sampling of those human remains.”

Matisoo-Smith cautions that because the wads of pitch in the study weren’t found embedded in actual tools, we can’t be sure the chewers were toolmakers. They may have been children just chewing gum, she suggests. “Either way, it’s pretty cool.”