Chimp's jaw, right. . In answers to question one and two, Aristotle reasons that since dividing comes before crushing, then the dividing teeth must come in first. As added proof, he offers that a smaller thing develops more quickly than a larger thing, even when they start growing at the same time. Since the front teeth are smaller than the grinders, they develop more quickly. That would be because the greater part, or larger part, of the jaw is in the back of the mouth where the grinders are, while the smaller part is in the front of the mouth.
More bone can hold more nutrients.
Therefore, there exists more nutritive substance in the back part than the front part, so the grinders are allowed to grow larger than the front part. Now onto questions three and four. Aristotle proposes that since what is sharp becomes dull with use, as with an ax or a knife, it becomes advantageous to replace the dull with the fresh and sharp. An ax or a knife can just be sharpened, but it would be rather painful to try sharpening your teeth. So, it is better that front teeth, dulled from use would come out allowing new and fresh teeth to come in and replace the old ones.