The teeth of ancient hominids commonly have curved grooves on their roots. It has been suggested that these marks were made by an implement used to pick teeth. But critics of this theory point out that the teeth of today's regular toothpick users have no such marks.
Resolving this conundrum has surprisingly wide implications. Similar grooves have been found on fossil teeth dating back 1.8 million years. If the individuals made them by using toothpicks, the habit would qualify as the oldest human custom yet recorded. It could also reveal details about ancient diets and oral health. To help settle the debate, palaeontologist Leslea Hlusko of the University of Illinois at Urbana-Champaign hit upon grass stalks as likely to have left the mystery grooves. Unlike wood, grass contains large numbers of hard, abrasive silica particles.
This may explain the grooves seen on ancient teeth. And grass stalks are the right size to leave the marks, between 1.5 to2.6 millimetres wide, that have been found on ancient teeth. Hlusko spent 8 hours grinding a piece of grass along a tooth taken from a baboon. She then replicated the experiment for 3 hours on a modern human tooth. In both, the grass left marks almost identical to those seen in scanning electron microscopic images of early hominid teeth (Current Anthropology,vol 44, p 738).
Author: Charles Choi
New Scientist issue: 8 November 2003
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