Deeply worn teeth have preserved evidence of a psychoactive habit practiced by hunter-gatherers 25,000 years ago.
The discovery comes from the island of Sulawesi, in Indonesia. Researchers studied the remains of two people who lived long before agriculture reached the region. The oldest dates to between 25,000 and 16,000 years ago. The second lived between 7,600 and 6,300 years ago.
A peeled areca nut seed held in a hand.
Credit: Adam Brumm
Their teeth displayed deep, rounded grooves that were highly unusual. The team investigated what repeated action could have caused such wear. They concluded that these people regularly held and sucked whole areca nuts in their mouths. These are the seeds of the Areca catechu palm, still consumed today in several regions of Asia and the Pacific.
Why can this seed affect the brain? It contains arecoline, a substance that alters nervous system activity. Today, areca nut is generally prepared with lime, which strengthens and accelerates some of its effects. The prehistoric inhabitants of Sulawesi seem to have used a much simpler method: they sucked the seed directly.
The researchers verified that this action could actually release arecoline. Nuts were placed in artificial saliva, and the resulting liquid was then tested in the laboratory. The amount released was sufficient to act on proteins involved in nervous activity. Even more convincingly, analyses detected arecoline in the dental tissues of the people studied.
This practice was probably not without consequences. After remaining against the teeth, the hard, abrasive seeds wore away their surface. In some individuals, the wear could go as far as exposing the inner part of the tooth. This would have made eating painful and promoted infections.
A paradox could explain why the habit persisted despite this damage. Arecoline also has a pain-relieving effect, and the ancient populations of Sulawesi frequently suffered from dental problems. The researchers therefore suggest that the nut may have been used to relieve toothache. In the long term, however, its use could worsen the condition of the mouth.
This discovery significantly pushes back the known antiquity of regular areca nut use. Previous archaeological evidence generally placed the practice much later, particularly because seeds rarely survive for thousands of years. The teeth provide a durable physical trace of a behavior that would otherwise have disappeared.
It remains to be seen how far back this habit extends and how it spread. The researchers consider that it could be the oldest known evidence of the regular use of a psychoactive plant. Other human remains bearing the same dental wear could now be sought in archaeological collections from Southeast Asia.