Teeth uncovered in Indonesia that are up to 25,000 years old show signs of the person having sucked on whole betel nuts, probably to release pain-relieving compounds. The finding represents the oldest archaeological evidence of habitual drug use in humans, dating back even further than the earliest-known beer-brewing.
āWe really donāt know much about the origins of our most widely used psychoactive substances, so to find that, up to 25,000 years ago, hunter-gatherers were already addicted to plants that alter human brain function, I think thatās fascinating,ā says at Griffith University in Brisbane, Australia.
About 10 years ago, Brumm and his colleagues were excavating a cave in Maros-Pangkep on the island of Sulawesi in Indonesia when they discovered a fragment of human jaw bone with three teeth. Dating methods revealed it to be 16,000 to 25,000 years old. āWhat really intrigued me was the presence of these bizarre grooves in the teeth,ā says Brumm. āWe sent images to some of the worldās leading experts in prehistoric dental wear and they hadnāt seen anything like it.ā
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The team then excavated a different cave site on the island and found another set of teeth, this time about 6000 to 8000 years old, with the same unusual grooves. These teeth were part of a more complete skull that appeared to have belonged to a middle-aged or older man.
The rounded grooves were consistent with repetitively moving a hard, spherical object back and forth inside the mouth, and probably sucking and gnawing on it. This must have been done on a regular basis, because the teeth were so worn down in some places that their nerve centres were exposed, which would have caused severe pain, says Brumm.
The damage reminded Brumm of 19th-century clay pipe smokers whose teeth also became badly worn down from clamping pipes in their mouths for long periods. This led him to speculate that the damage in the ancient teeth might also be related to a substance addiction.
One possibility was an addiction to betel nuts, since they are a popular stimulant in Indonesia and many other parts of Asia. However, the modern practice doesnāt leave rounded grooves in the teeth because the betel nuts, which are actually seeds from the fruits of areca palm trees, are sliced up and mixed with a substance called slaked lime. This enhances the release of stimulatory compounds, including one called arecoline. The mixture is then chewed, leaving different wear patterns on peopleās teeth.
Brumm wondered whether simply sucking on whole betel nuts was a precursor to this modern practice. As a preliminary test, he tried rolling a whole betel nut around inside his own mouth, gently sucking and gnawing on it. He found that āthere was a bitter, astringent taste that made my mouth go numbā.
The researchers then soaked whole betel nuts in artificial saliva and added the resulting liquid to cells engineered with human brain receptors. This confirmed that sucking on whole betel nuts would release enough arecoline to have physiological effects. They also found traces of arecoline on the ancient teeth, reinforcing their idea that the grooves were caused by sucking betel nuts.
Arecoline has both stimulatory and pain-relieving effects. Brumm believes that, in prehistoric times, people may have started sucking on betel nuts to relieve tooth pain, but then became addicted. Ultimately, this caused even more damage to their teeth because of the long-term impact of rolling the nuts around in their mouths.
Nowadays, betel nuts are the fourth most popular psychoactive substance in the world, behind alcohol, caffeine and nicotine. Chewing them with slaked lime produces feelings of euphoria and heightened alertness, but also stains teeth red and may increase the risk of and .
Previously, the most ancient examples of possible habitual drug use in humans included 13,000-year-old evidence of in Israel and 8000-year-old evidence of in Peru. But humans probably became addicted to plant substances much earlier than this, says Brumm. āItās just really hard to find archaeological evidence.ā
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