A study of the teeth of ancient hunter-gatherers shows they sucked on betel nuts, evidence that humans used mind-altering drugs much earlier than previously thought, scientists say.

The Griffith University study, led by Professor Adam Brumm, examined teeth from two skeletons found on the Indonesian island of Sulawesi.

One dated from 16,000 to 25,000 years ago and the other from 6,300 to 7,600 years ago.

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