Betel nut use by Indonesian foragers dated to 25,000 years ago, study finds

Analysis of two exceptionally rare skeletons unearthed at separate sites on the island revealed deep, rounded grooves in the teeth of both adults, some of them worn so far down that the dental pulp would have been exposed. Traces of a psychoactive substance were found in the remaining tooth tissue. One individual was dated to about 7,000 years ago, the other to between 16,000 and 25,000 years ago.

"I was thinking, what the hell were these people doing? It's like someone had a drill head shaped like a gobstopper and wore away the inner part of the tooth," said Prof Adam Brumm of Griffith University's Australian Research Centre for Human Evolution in Brisbane, who led the work.

Betel nuts are the seeds of the Areca catechu palm, misnamed because they are commonly wrapped in betel vine leaves for chewing. They are the world's fourth most widely used psychoactive substance after alcohol, caffeine and nicotine, with an estimated tenth of the global population chewing the seeds. Today the nuts are typically chewed after being mixed with slaked lime, made by grinding burnt shells, to form a quid.

Brumm suspected the unusual wear pattern came from the foragers holding hard, round and abrasive objects in their mouths. "Imagine you kept a stone in your mouth and you moved it from one part of your mouth to another, and if you did that day after day, hour after hour. Eventually it would wear down your extremely hard dental tissue to form these grooves," he said.

The team proposed that the foragers sucked on betel nuts before people worked out that adding slaked lime releases more of the psychoactive drug and intensifies the high. Soaking betel nuts in artificial saliva, the researchers found, produced enough of the compound arecoline to induce a high, though a milder one than chewing delivers. Analysis of the foragers' teeth detected traces of arecoline in the tissues.

"I've sucked on a nut as an experiment and it's a really bitter, astringent taste. It makes your mouth go numb and I think that's what they were interested in," Brumm said. He added that while the habit might have started as a remedy for toothache, prolonged sucking wore teeth down so badly that it created worse dental pain over time. "These individuals were seemingly caught in a self-perpetuating cycle where they were continually sucking on the nuts to treat the tooth pain caused by this nut-sucking habit."

Humans are thought to have used mind-altering plants as soon as they encountered them, but the oldest known traditions of psychoactive drug use are dated to about 13,000 years ago, with fermented drinks such as barley beer.

Dr Elisa Guerra-Doce, an associate professor in European prehistory at the University of Valladolid in Spain, said the study provided "direct evidence of the antiquity of human drug use". "These findings not only represent the earliest known evidence to date of the use of psychoactive plants anywhere in the world, but also demonstrate that the consumption of Areca nuts is a millennia-old tradition dating back to prehistoric times," she said.