The purple nutsedge is one of the world's worst weeds, spreading stealthily underground and shrugging off herbicides as if they were soda water. But new research shows that for one ancient people, this noxious plant may have served as a tooth cleaner.

A new analysis of skeletons reveals that people who lived in Sudan 2,000 years ago were eating the purple nutsedge. Those people had surprisingly sound teeth—and the antibacterial properties of the weed may deserve the credit, scientists say in a study published in the journal PLOS ONE on Wednesday.

Early humans generally had relatively few cavities, thanks in part to meals that were heavy on the meat, light on the carbs.

Then humans invented farming and began eating more