Allometry

From EvoWiki

Allometry is the study of differential growth rates of different parts of an organism's body or behavior. Allometric relationships are often expressed in power-law form,

y = x^a

or else

log(y) = a*log(x)

where x and y are values of traits under consideration, and where a is the allometric coefficent. Where a = 1, growth is considered isometric. Where a > 1, growth is considered positively allometric, and where a < 1, growth is considered negatively allometric.

One of the first to consider allometry was Galileo, who noted that large animals have limb bones that are proportinately thicker than small ones. He explained this by the square-cube law. Weight grows as the cube of the size, while surface area grows as the square of the size. The ratio of these quantities gives a typical value for the weight-induced stress, which thus scales as the size.

Allometric relationships have been found in various circumstances, and they have been explained with varying success, often as a result of physical constraints.

Nice article on allometric scaling: Kleiber Rules (How to run faster, live longer and anaesthetise an elephant)