For the Ice Age foragers of Sulawesi, the question of why they first began using the betel nut is not answered by the study.

The initial motivation might have been anything: the discovery that chewing or holding the nut produced a pleasant or useful effect, the observation that someone with a toothache experienced relief from chewing on the nut (arecoline has analgesic properties), or social transmission of a behavior that was already established in the community.

What the study establishes is that once the use began, it continued — consistently enough, over enough years, to wear distinctive grooves into the teeth and leave detectable chemical traces in the dental tissue.

That persistence is the signature of habitual use, and the study uses that word deliberately: “habitual.” Not casual, not occasional, not opportunistic.