What is the evidence that growth is throughput limited?
West, Brown and Enquist (Science 276(5309):122-126, 1997) modelled biological growth as bounded by transport-network geometry. The exponent has been contested since (White and Seymour, PNAS 100(7):4046-4049, 2003; Kozlowski and Konarzewski, Functional Ecology 18(2):283-289, 2004), and the dispute is over which exponent, never over whether the transport network sets the limit. The programme needs the mechanism, not the number, and survives the dispute intact.
The premise is not the programme's; it belongs to West, Brown and Enquist, 'A General Model for the Origin of Allometric Scaling Laws in Biology', Science 276(5309):122-126, 1997. Nothing in the history of the universe has grown without bound. Every growth process that has run has terminated, and in every case the limit came from outside the growing thing: its supply ran down, its substrate was exhausted, or it destroyed the conditions of its own continuation. Not one stopped because it got better at regulating itself.
The premise is contested in its details, and the programme says so. White and Seymour reported basal metabolic rate proportional to mass to the two-thirds (PNAS 100(7):4046-4049, 2003). Kozlowski and Konarzewski asked in their title whether the WBE model is mathematically correct and biologically relevant (Functional Ecology 18(2):283-289, 2004). The dispute is over which exponent, never over whether the transport network sets the limit. Because the programme needs the mechanism and not the number, it survives the dispute intact.
The worked cases carry the shape at the strength they survived a specialist refutation round. Fission is the sharpest: fixing the geometry does not fix the multiplication factor; a prompt-supercritical assembly at fixed geometry grows exponentially until thermal expansion or hydrodynamic disassembly intervene. Tumours: bulk expansion is bounded by vascular throughput, but relieving the bound does not stop growth and restricting it selects for more invasive phenotypes; leukaemias face no diffusion limit at all. Epidemics: a closed population burns out below the herd-immunity threshold; replenished susceptibility gives an endemic equilibrium instead. Eddington is a luminosity ceiling, not a mass-throughput ceiling; ultraluminous X-ray sources sit above it. Cosmic inflation is excluded by scope (expansion of space, not growth on a substrate). Evolution is the nearest antecedent, with internal correctors of copy fidelity rather than of the phenotype-to-fitness map. In their surviving form: for everything before software, the terminal bound came from outside. Software is the first thing that keeps growing at fixed substrate without consuming the substrate to do it.