Fig. 6. The universality of growth is illustrated by plotting the dimensionless mass ratio (m/M)^1/4 against a dimensionless time variable, as shown. When data for mammals, birds, fish and crustacea are plotted this way, they are predicted to lie on a single universal curve; m is the mass of the organism at age t, m₀ its birth mass, M_b its mature mass, and a a parameter determined by theory in terms of basic cellular properties that can be measured independently of growth data. Figure taken from West et al. (2001) with permission.