Allometry

Allometry is the science studying the differential growth rates of the parts of a living organism's body part or process. This can be especially dramatic in various insect species (e.g., the Hercules Beetle), where a small change in overall body size can lead to an enormous and disproportionate increase in the dimensions of appendages such as legs, antennae, or horns.

It also refers to change in proportion of body size (mass and volume) relative to body area.