英语时差：智齿的演变（上）

As we all learned in health class, human beings have 32 teeth. Twenty-eight of them come in before puberty, but the last four teeth, our “third molars,” usually come in during our late teens or early twenties, when we’re presumably older and wiser hence their nickname, “Wisdom Teeth.” These extra molars probably helped our early ancestors to chew and digest their rough diet of tough meats, fibers, and seeds. These wisdom teeth would have helped early humans to eat better, and in turn, live longer in better health. According to the logic of evolution, the teeth would have given our ancestors an edge in surviving long enough to reproduce, so evolution has passed them along to modern humans.