You're probably not too interested in what some people call ABC gum - already been chewed. But for archaeologists, such gum - as long as it's really old - is a genetic gold mine. "It's a bit like Jurassic Park." Natalija Kashuba, a graduate student in archaeology at Uppsala University in Sweden. She's referring to that famous clip from the movie, about how Jurassic Park scientists extract blood from a mosquito trapped in amber, "and bingo, dino DNA."
Except in this case it's human DNA, and it's trapped not in amber, but in exceptionally old chewing gums found at the site of an ancient hunting and fishing village on the west coast of Sweden. The samples look just like chewed-up wads of modern-day gum. But don't think Wrigley's - his detritus is black, sticky tar distilled from birch bark. Kashuba has tasted modern-day versions and isn't eager to try it again. "Not unless I'm paid for it."
So why chew something so unpleasant? Maybe because their gum wasn't for fresh breath. "You could use it to seal your boat, or like seal your pots, so it's an everyday-use type of substance." Many of the gums have teeth marks, too, so perhaps they chewed it to help shape it and in turn developed a habit, despite the taste, that today's tobacco chewers might relate to.
Kashuba's team extracted and sequenced DNA from the ancient gum, and they found genetic evidence of three different gum chewers - two women and a man. It's the oldest human DNA found in Scandinavia, dating to about 8,000 B.C. And because it more closely resembles the DNA of hunter-gatherers from western Europe than from eastern Europe, it also provides hints about how people ended up in what's now Sweden. The results are in the journal Communications Biology.
The gum could still hold other clues about ancient diets or the bacteria these people had in their mouths. Given that we can learn so much from chewing gum, is it really so bad to stick it to the bottom of chairs and tables? You know, for the benefit of future archaeologists? "I think you should definitely throw it in the bin. But I won't blame these guys who spat it out 10,000 years ago. They did a good job then."