While they confirm and generalise universal laws that had already been demonstrated or foreseen in the past, the results of our study also pose a strong challenge to one of the most eminent theories of ecology, called the “metabolic theory of ecology”. This conjecture has provided experts with one of the most basic frameworks for understanding the links between a species’ main demographic and functional characteristics and its body mass. It is founded on the idea that an organism’s metabolic rate is determined by the acquisition and use of available resources, which thus constitutes the primary limit of many other essential features, including the speed at which the organism can grow and develop.
Yet one of the main conclusions of our study is that actually, the opposite is true: an organism’s growth rate seems to control its metabolism. Indeed, growth rate is linked to body mass by a scaling law with an exponent of ¾, and this relation is remarkably constant across all taxonomic groups. On the other hand, metabolic rates comply with this law only within each major group — and not in the case of individuals from different taxonomic groups. Ultimately, it seems that growth, and not metabolism, is the key biological constraint governing the large-scale patterns of life.

Given that growth forms the basis of all biological and ecological processes, from the development of cancerous tumours to the production of our biological resources, the global carbon cycle and the dynamics of populations, understanding the factors that determine the growth of living systems could be of vital importance.

Everywhere you look, whatever type of living system you think of, they all seem to comply with the same law of growth. While we do not yet know which biological constraints underlie this universal law, we do know that it has far-reaching implications. It offers a new perspective on the most fundamental characteristics of life, and on the extraordinary unity that permeates the diversity of living organisms.