Modelling universality and scaling

Understanding the allocation of metabolic energy between the sustenance of an organism and its growth is an important issue in ecology. West et al.1 have built on their earlier attempts to explain the exponent for the allometric scaling of metabolism and have derived a single, parameterless universal curve that describes the growth of many species. Here we show that the universal curve arises from general considerations that are independent of the specific allometric model used by West et al. and that the data do not distinguish between a 3/4 or 2/3 exponent in the relationship between metabolic rate and mass scaling.