Is there anything more annoying than having something stuck in your teeth? It looks like our oldest human ancestors may have been bothered by the exact same feeling. Paleontologists have been puzzled by the tiny grooves discovered on fossilized hominid teeth, some specimens dating back 1.8 million years. It’s been speculated that the curved marks, found at the roots of the teeth, could have been made by some kind of toothpicklike implement, but critics note that modern toothpick users show no such distinctive grooves.
Now, as New Scientist reported last week, Leslea Hlusko of the University of Illinois at Urbana-Champaign may have solved the mystery. She believes that early humans may have used grass stalks to clean their teeth and that the stalks created the grooves. Grass, in contrast to wood, contains hard, abrasive silica particles. The stalks are also the right size to leave the marks, which are up to a 10th-of-an-inch wide.
To test her theory, Hlusko ground a piece of grass along a baboon tooth for a few hours. She then repeated the experiment on a modern human tooth. In both cases, the marks obtained were almost identical to those found on the ancient teeth. If Hlusko is right, and the grooves were formed by grass-stalk toothpicks, picking your teeth would qualify as the oldest human custom yet recorded.