The groove worn by years of nut-sucking.

The arecoline absorbed into the tissue.

The marks of a behavior that was sustained long enough, and practiced often enough, to leave its signature in the hardest biological material the human body produces.

Brumm and his team found this evidence and knew what it meant.

They tested the hypothesis.

They confirmed it.

They published it.

And now the three teeth from Leang Bulu Bettue are the oldest known physical evidence for human drug use.