allometry

Disproportionate growth of a part of a living organism in relation to the whole.

Some organs may grow faster than the rest of the body so that their size increases not only in absolute terms, but also relatively to the rest of the body, which is positive allometry; or they may grow more slowly than the rest of the body, and so decrease in relative size, which is negative allometry.

The science studying the differential growth rates of the parts of a living organism.