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Despite the enormous biological diversity on the planet- from bacteria to elephants, and algae to sapling trees- analysis of over three thousand species suggests that metabolism displays a striking degree of homeostasis across all of life.

This is the finding from a paper just published in the prestigious Proceedings of the National Academy of Science of the U.S.A., by an international team of authors led by Anastassia Makarieva from the Petersburg Nuclear Physics Institute, and including Steven Chown from the Centre for Invasion Biology at Stellenbosch University.

A brief look at living creatures reveals a dazzling diversity of ways to cope with the energetic demands of life. Green leaves photosynthesizing in the sunlight, cheetahs hunting their prey, spiders sit-and-waiting in their webs, butterflies flitting from flower to flower, fungi thriving on a rotten potato tuber, and a family enjoying Sunday lunch in the pizzeria. Is there any quantitative universality behind these numberless and picturesque ways of energy consumption by the living beings?

This work set out to answer what has come to be an intriguing and hugely significant question in biology. The authors analyzed a huge metabolic rate database, comprising over three thousand species that cover most of the taxonomic and size diversity on our planet, from vascular plants and tiny bacteria to insects and largest vertebrates. Instead of finding enormous size-related differences in the energetic demands of organisms from life's domains, as has for many years been assumed, the researchers discovered a striking similarity of mean metabolic rates per unit mass. These modestly ranged from 0.3 to 9 W/kg across taxonomic groups that comprise species differing by twenty orders of magnitude (i.e., by 100,000,000,000,000,000,000 times) in body mass. The observed narrow range of metabolic rates might be considered as the preferred, optimal range for the functioning of living matter, the researchers propose.

Viewed on a broader biological background, the observed approximate universality of energetic demands across the entire of life reminds one of the universality of the genetic code and of the biochemical universality of life in general. However, as the researchers point out, metabolic universality could not be given to all living beings once and for all — unlike the genetic code and protein composition, metabolic rate cannot be inherited from a common ancestor. Rather, a particular range of metabolic rates is maintained by natural selection. Species from different taxa have had to come up with diverse solutions to remain near the metabolic optimum, which the progressive evolutionary increase in body size (from prokaryotes to the largest vertebrates and plants) is continually leading organisms away from. Such seemingly unrelated, yet conspicuous features of nature, like the flat shape of green leaves and the mechanical breathing of animals, are examples of such complex adaptations.

The diversity of life has few known universalities, each being of paramount importance. Since the process of energy consumption from the environment is among the fundamental traits separating the animate and inanimate worlds, the proposed metabolic universality of living matter could potentially provide clues for understanding the cornerstones of life’s organization.


New Scientist