Scaling and universality in ontogenetic growth

Recently, West et al. claimed to derive a general quantitative model based on fundamental principles for the allocation of metabolic energy between maintenance of existing tissue and the production of new biomass, and in addition claimed to derive a single, parameterless universal curve that describes the growth of many species. They further claimed that their model of the 3/4 exponent for the allometric scaling of metabolism provides a novel version of the growth equations and use the goodness of fit of growth-curve data to these equations as support of this interpretation. Here, we show that the universal curve arises from general considerations that are independent of the specific allometric model used and that the data do not distinguish between the 3/4 or the 2/3 exponent for the metabolic rate mass scaling.