For decades, small grooves on ancient human teeth were thought to be evidence of deliberate tool use – people cleaning their teeth with sticks or fibres, or easing gum pain with makeshift "toothpicks". Some researchers even called it the oldest human habit . But our new findings, published in the American Journal of Biological Anthropology , challenge this long-held idea about human evolution. We found these grooves also appear naturally in wild primates, with little support for tooth-picking