Life, Death and Energy: What Does Nature Select?

Evolutionary biology is poised for a third major synthesis. The first presented Darwin's evidence from natural history. The second incorporated genetic mechanisms. The third will be based on energy and biophysical processes. It should include the equal fitness paradigm (EFP), which quantifies how organisms convert biomass into surviving offspring. Natural selection tends to maximise energetic fitness, (Formula presented.), where (Formula presented.) is mass-specific rate of cohort biomass production, (Formula presented.) is generation time, (Formula presented.) is fraction of cohort production that is passed to surviving offspring, and (Formula presented.) is energy density of biomas. At steady state, parents replace themselves with offspring of equal mass-specific energy content, (Formula presented.) ≈ 22.4 kJ/g, and biomass, (Formula presented.) ≈ 1 g/g. The EFP highlights: (i) the energetic basis of survival and reproduction; (ii) how natural selection acts directly on the parameters of (Formula presented.); (iii) why there is no inherent intrinsic fitness advantage for higher metabolic power, ontogenetic or population growth rate, fecundity, longevity, or resource use efficiency; and (iv) the role of energy in animals with a variety of life histories. Underlying the spectacular diversity of living things is pervasive similarity in how energy is acquired from the environment and used to leave descendants offspring in future generations.