The quantification of biological scaling relationships between two measured quantities. The scaling may be applied to morphological traits (e.g. the relationship between brain size and body size among adult humans), physiological traits (e.g. the relationship between metabolic rate and body size among mammal species) or ecological traits (e.g. the relationship between wing size and flight performance in birds) (Shingleton 2010). For example, the dependence of a biological variable (Y ) on body mass (m ) is often characterised by an allometric scaling law of:
is the scaling exponent
is a constant that is characteristic of the kind of organism (West et al. 1997).