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Wherever we look, the diversity of life is stunning. However, if biologists tend to focus on the multitude of forms and lifestyles of species, what unites species can sometimes be more interesting than what distinguishes them. In the era of Big Data, we can now see this diversity in its totality, revealing universal properties common to all creatures, large and small.

The laws of scales that link the main demographic and functional characteristics of species to their body mass are among the most universal quantitative patterns in biology. Within the major taxonomic groups of life, the four key ecological variables - metabolism, abundance, growth and mortality - are often related to body mass by a power law whose exponent revolves around ¾. The main existing theories attribute this relationship to biophysical constraints on metabolism. Nevertheless, these theories remain controversial, and the links between the four above variables have never been studied systematically on the whole spectrum of living organisms.

Researchers from the Autonomous University of Barcelona and the Station of Theoretical and Experimental Ecology (Univ Toulouse Paul Sabatier / CNRS) have collected data from several thousand studies on the whole spectrum of living organisms. Their results confirm that, despite the great diversity of life, many of the most important characteristics of species follow universal laws that link them to their body mass, from the smallest protists to the largest blue whale. "These simple relationships are surprisingly strong and reveal unexpected links between traits that have not been fully appreciated before," says Ian Hatton, lead author of the study, currently a researcher at the Autonomous University of Barcelona.

If they do confirm and generalize universal laws that have been already demonstrated or foreshadowed in the past, the results of this study radically challenge one of the most prominent theories of ecology, known as "Metabolic Theory of Ecology". This theory that provided ecologists with powerful frameworks for understanding the links between key demographic and functional characteristics and their body mass is based on the idea that the metabolic rate is the main limitation of many other essential traits, including its growth rate.

"One of our main conclusions is that, surprisingly, the growth rate of an organism seems to control the metabolism, not the other way around." Says Michel Loreau, co-author of the study "Our study puts growth at the center of the biological constraints that govern the patterns of life on a large scale."

Since growth is at the root of all biological and ecological processes, from ontogenetic development to cancer, impacting resource production and the global carbon cycle, understanding the factors that determine the growth of living systems, thus appears as central to the study of all ecological processes.

"What is amazing is that no matter where you look, no matter what kind of living system you're looking at, everything seems to follow the same law of growth," explained Ian Hatton. "We cannot explain everything yet, but we know that this has very important implications.” Thus, beyond the fact that this article turns the usual questioning on its head, it offers a new perspective on the most basic characteristics of life and the extraordinary unity that permeates the diversity of life.