Scientists believe they have found the earliest known human use of psychoactive drugs among foragers who lived 25,000 years ago.

Two skeletons discovered on the island of Sulawesi, Indonesia, show signs that their owners routinely sucked on betel nuts, used in some parts of the world today as a recreational drug.

The rare remains belonged to pre-agricultural foragers found at two separate archaeological sites.

One lived about 7,000 years ago, but the other dates to between 16,000 and 25,000 years ago – putting their use of betel nuts long before the first human use of alcohol or other substances.

Both had unusually deep, rounded grooves in their teeth, with the wear exposing the dental pulp. They also found traces of arecoline, the psychoactive compound found in betel nuts, in the teeth.

Writing in Science Advances, led by Adam Brumm and his team from the Australian Research Centre for Human Evolution, Griffith University, Brisbane, suggest this was likely caused by repeatedly sucking on the nuts.

‘With the earliest forager dating to 25 to 16 thousand years ago, our findings suggest the use of betel nut as a drug has more ancient origins than previously supposed,’ he said.

They say that unlike users today, who chew processed nuts, our ancestors sucked the nuts whole to release the psychoactive compounds contained within.

The modern custom of chewing betel nuts is practised by around 1 in 10 people worldwide.

Betel nuts are actually the seeds of the Areca catechu palm. They are commonly called betel nuts because they are traditionally wrapped in leaves of the betel vine before being chewed.

The researchers wondered whether people may have used betel nuts in a simpler form before discovering that adding slaked lime released more of the psychoactive compound and produced a stronger effect.

To put this to the test, they soaked betel nuts in artificial saliva. The liquid quickly accumulated enough arecoline to produce a psychoactive effect, although the researchers say it would have been weaker than that produced by chewing processed nuts.

The findings could push back the known history of deliberate drug use by thousands of years.

Humans are likely to have experimented with mind-altering plants long back into prehistory, but the oldest known instances of psychoactive substance use have until now been associated with fermented drinks.

The Sulawesi discoveries suggest that the search for altered states of consciousness may have begun much earlier, among hunter-gatherer communities experimenting with naturally occurring plants long before the development of agriculture allowed them to cultivate and process plants with that effect more easily.

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