sciencehabit writes: The most tedious part of a chimpanzee's life is chewing. Our primate cousins spend six hours a day gnashing fruits and the occasional monkey carcass — all made possible by the same type of big teeth and large jaws our early ancestors had. So why are our own teeth and jaws so much smaller? A new study credits the advent of simple stone tools to slice meat and pound root vegetables, which could have dramatically reduced the time and force needed to chew, thus allowing our more immediate ancestors to evolve the physical features required for speech. The abstract for the (paywalled) article is more informative than many.