A couple of years ago, Andrés Escala, PhD in Theoretical Astrophysics from Yale University, USA, made a foray into biology by correcting the mathematical formulation of the so-called "fire of life" law, which considers the minimum energy that living organisms must consume to exist. Today the professor of the University of Chile goes up a new step and presents a prediction related to the life expectancy of living organisms, according to their metabolism.

The reason why living beings age and eventually die is still a great mystery, but an explanation could be eventually reached according to this research where "I directly related life expectancy in all living organisms to their respiratory system. Although the idea that metabolism is related to aging has been around for a long time, there was no concrete and valid formula for all types of organisms, such as the one presented in this work and I propose evidence in favor of it", explained the researcher of the CATA, Center for Excellence in Astrophysics and Associated Technologies.

"The discovery - specifically - is that all living organisms, from the simplest ones such as amoebas, to large mammals such as elephants or the blue whale, consume throughout their lives approximately the same amount of energy per gram that constitutes it, but only after correcting this consumption by temperature and by the number of heartbeats in each respiratory cycle", indicates the scientist.

This implies, according to the formalism presented by Escala, that all species must live approximately the same in terms of their respiratory cycles (the time it takes to inhale and exhale in a human being, for example), so that the number of respiratory cycles that all living organisms have in common could be called "the number of life". "This contrasts with the fact that in terms of absolute time, life in the animal world on earth extends from less than a day (adult life of some flies such as the mayfly) to hundreds of years (certain tortoises such as the Galapagos tortoise)," adds Escala.

The relationship between metabolism and aging has traditionally been studied in terms of the so-called "free radical hypothesis", which, although it has presented problems in recent years, "there is no doubt that studying the exact relationship between the number of respiratory cycles throughout life and the by-products of the respiratory process should provide important clues about the origin of aging and the physical reason (at a molecular level) for natural death", commented the astrophysicist.

Energy consumption throughout life

In 2019, Andrés Escala published an article in the journal Theoretical Ecology where he corrected the mathematical formulation of the "fire of life" law, also known as Kleiber‘s law.

In this law, the Swiss chemist and biologist Max Kleiber proposed the minimum energy expenditure required by some species to stay alive. He stated that the basal metabolism of an animal (its blood circulation, respiratory system, among other processes) could be estimated by calculating its body weight to the 0.75 power. But subsequent measurements indicated that this power was not equally fulfilled in all species, there being notable differences between mammals and amphibians, to give an example. Escala demonstrated that the exceptions to Kleiber‘s Law were due to its poor mathematical formulation and not to the complexity of the problem per se.

According to this new study, based on Escala‘s corrected version of Kleiber‘s Law, throughout its life a living being must consume (at a temperature of 30°C) about 8000 ml (milliliters) of oxygen, that is, per gram that constitutes the organism and per heartbeat in each respiratory cycle, which in energetic terms is equivalent to each gram consuming approximately 160,000 Joule, or more simply, the energy needed to heat a bowl of tea or to keep a computer on for 10 minutes.

For a century it has been thought that organisms with a faster metabolism die younger, i.e. "live fast and die young" as the popular saying goes. However, in recent years this idea has been called into question by a series of experiments and contradictory data, but now with this work that provides a more correct estimate of the energy consumed, these problems that the evidence seems to contradict are now solved.

"One of the advantages of the formula found for the energy consumption of living beings throughout their existence is that it is possible to estimate how much the energy consumption of living organisms would increase as the earth‘s temperature rises, which is important in the context of current global warming. For example, in the case of "cold-blooded" organisms such as reptiles, insects or fish, their energy consumption would increase by 8.3% for each degree Celsius that the earth‘s temperature rises", indicates Escala.

Correcting the mathematical description in biology

Escala spent six months collecting data on the subject until he was able to formulate his new mathematical proposal. "The main mathematical tool or concept is dimensional homogeneity, which is based on the fact that only equivalent quantities (i.e. with the same units) can be compared. This concept is the basis for the metabolic law used in this work to calculate energy consumption throughout the life of organisms," explains the astrophysicist.

But his work does not end here, as he plans to continue this research line using the same postulates used in this work, to achieve new predictions for ontogenetic growth (development of the organism from birth to adulthood) and population growth, where he demonstrates how heart rate can determine other highly relevant biological times, such as the time of growth of an organism to adulthood, population growth, etc.

The results of this work appeared today in the article "Universal relation for life-span energy consumption in living organisms: Insights for the origin of aging" which appeared in the journal Scientific Reports.