Public release date: 5-Nov-2003 Contact: Claire Bowles claire.bowles@rbi.co.uk 44-207-331-2751 New Scientist Oldest human custom EVEN early humans knew a thing or two about dental hygiene. Our ancestors used grass stalks as tooth picks, experimental findings suggest. 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...