The relationship of the growth of one part of an organism to the growth of another part or the growth of the whole organism is called allometry. The term also applies to the measure and study of such growth relationships. Allometry comes from the Greek word allos, which means "other," so allometric means "other than metric." Isometric growth, where the various parts of an organism grow in one-to-one proportion, is rare in living organisms. If organisms grew isometrically, young would look just like adults, only smaller. In contrast, most organisms grow non-isometrically; the various parts and organisms do not increase in size in a one-to-one ratio. One of the best known examples of non-isometric growth is human growth. The relative proportions of a human body change dramatically as the human grows. Medieval and earlier painters sometimes did not realize this and drew children as tiny adults. But the...