allometry

In biology, a regular relationship between a given feature (for example, the size of an organ) and the size of the body as a whole, when this relationship is not a simple proportion of body size. Thus, an organ may increase in size proportionately faster, or slower, than body size does. For example, a human baby's head is much larger in relation to its body than is an adult's.

The best known allometric relationship is the surface area law: the ratio of body surface to total body volume decreases as body size gets larger. Large animals therefore lose less heat than small ones because they have proportionately less skin surface from which to radiate heat.