The life histories of organisms and the trophic dynamics of ecosystems are shaped by taxes paid in the form of dead offspring. No organism is exempt from the tax because mortality is ubiquitous in the struggle of life. New theory and data highlight how the tax: i) reflects the proportion of the biomass produced over a life cycle that is lost to mortality and consumed in the ecosystem, ii) is predicted by the number and relative size of offspring, iii) varies widely across species from <50% to >99.9%, depending on fecundity and parental care, and iv) supplies energy and nutrition to other organisms in the ecosystem. Taxes levied on individuals and populations support the maintenance, infrastructure and functioning of ecosystems and human economies alike.

Here we review and extend the equal fitness paradigm (EFP) as an important step in developing and testing a synthetic theory of ecology and evolution based on energy and metabolism. The EFP states that all organisms are equally fit at steady state, because they allocate the same quantity of energy, ~22.4 kJ/g/generation to production of offspring. On the one hand, the EFP may seem tautological, because equal fitness is necessary for the origin and persistence of biodiversity. On the other hand, the EFP reflects universal laws of life: how biological metabolism – the uptake, transformation and allocation of energy – links ecological and evolutionary patterns and processes across levels of organization from: i) structure and function of individual organisms, ii) life history and dynamics of populations, iii) interactions and coevolution of species in ecosystems. The physics and biology of metabolism have facilitated the evolution of millions of species with idiosyncratic anatomy, physiology, behavior and ecology but also with many shared traits and tradeoffs that reflect the single origin and universal rules of life.