Evolutionary physiology

Evolution, a “process of heritable change in populations of organisms over multiple generations […] through mechanisms including natural selection, sexual selection and genetic drift,”¹ is the unifying framework that explains the diversity of life, guiding our understanding of biological processes, species interactions, and the development of new medical and biotechnological innovations. Evolutionary physiology is a multidisciplinary field that explores how organisms adapt their physiological functions to changing environmental conditions. Some authors attribute the development or emergence of evolutionary physiology as a subspecialty to the late 1980s² as a field which integrates perspectives from genetics, ecology, and evolutionary biology to understand the origins, adaptability and maintenance of physiological diversity. Svante Pääbo, so-called “reader of the Neanderthal genome,”³ may be seen as a prime example who opened the door to ancient genomics. However, for a study to touch upon evolutionary physiology, it does not necessarily have to focus primarily on elucidating developments from eons past. In this paper, we take a closer look at recent publications, which aim to investigate the physiological adaptations and trade-offs that have arisen through natural selection, shedding light on evolutionary pathways, outcomes and perspectives.

Recent developments, including climate change, are increasingly recognized as significant drivers of evolutionary processes in various species. These environmental changes create new selective pressures, leading to adaptations that can alter genetic diversity and influence species' survival and reproduction.⁴ The study by Sokolova et al. sheds light on the impact of environmental temperature changes on energy metabolism and thus on the mitochondrial function.

Mitochondria, usually introduced in Bio 101 classes as cellular power plants, are in themselves almost bizarre examples of evolutionary development. Other entities within the mammalian organism are also of questionable descent, such as retrovirus-like Gag Protein Arc1, which—and we do not know why—bears a domain which resembles retroviral/retrotransposon -like proteins, which multimerize into a capsid that packages viral RNA.⁵ Most likely, once upon a time, mitochondria started out as α-Proteobacteria. Until recently, the most common theory was an endosymbiont hypothesis, that is, an incorporation of bacterial cell compounds into eukaryotic cells. Recently, however, evidence has emerged which prompts the question of whether the mitochondrion really emerged after the eukaryotic cell, or if this organelle even originated simultaneously with the cell that contains it.⁶ Nevertheless, mitochondrial bacterial characteristics, such as cytosine-phosphate-guanosine, the membrane lipid cardiolipin, N-formylated peptides and circular double-stranded DNA may be responsible for inducing or perpetuating inflammatory processes following mitochondrial damage.⁷

Human energy metabolism is in itself a focus topic touching heavily on evolutionary physiology: Brown adipose tissue (BAT) expresses thermogenic uncoupling protein 1 (UCP1), enabling humans to maintain their body temperatures during cold stress.

As it has recently emerged how adults retain BAT, which may play a role in non-shivering thermogenesis, it has been hypothesized that BAT plasticity was a main factor in allowing human populations expansion into circumpolar regions.⁸ Recently developed UCP-1 deficient animal models allow a closer look at non-shivering thermogenesis⁹ and thermogenic adaptation to cold challenges,¹⁰ and further insights into the evolution of mammalian brown fat (non-shivering) thermogenesis,¹¹ 50 years after the identification and description of UCP-1.¹²

Also, mitochondria seem to be critically involved in the evolutionary adaptation of vertebrates to hypoxic or even anoxic environments,¹³ comprising mainly cardiorespiratory^{14, 15} as well as neuromuscular¹⁶ adaptations.

During mammalian evolution, the utilization of oxygen and nutrients, as exemplified above, was adapted, as was the excretion of metabolic waste. In Book XXXI of his Natural History, Pliny the Elder mentioned a salt he named “hammoniacum,” which is thought to have derived its name from its proximity to the Temple of Jupiter Amun (Ἄμμων Ammon in Greek), which was located in the Roman province of Cyrenaica.¹⁷ The precise nature of this salt remains uncertain; however, it is the etymological origin of the names for ammonia and ammonium compounds. Ammonia is one of the so-called “nitrogen wastes,” which, together with urea, uric acid, and creatinine result from mammalian protein metabolism and must be excreted to avoid toxicity, processes whose evolutionary origins and development have recently been elucidated in intriguing detail.^18-20

The evolution of another characterizing function of most higher organisms, circadian rhythm, is thought to have provided organisms with a survival advantage by synchronizing physiological processes and behavior with the predictable cycles of the environment, such as day and night. Circadian clocks are present in most light-sensitive organisms, from simple unicellular entities to humans, and probably provide an evolutionary advantage by enabling organisms to anticipate and proactively respond to challenges arising from their cyclic environment.²¹ Modern environments, mostly indirect results of human evolution, with artificial lighting and irregular schedules, can disrupt natural circadian rhythms, leading to potential behavioral and health-related consequences.²²

In summary, these studies highlight the intricate relationship between physiology and evolution, demonstrating how organisms adapt to their environments through physiological modifications. By examining the evolutionary pathways and trade-offs that shape physiological traits, we gain a deeper understanding of the mechanisms underlying physiological diversity. These findings underscore the importance of considering evolutionary history in physiological studies and provide a foundation for future research in this dynamic and integrative field. As we continue to explore the complexities of evolutionary physiology, we can better appreciate the adaptive strategies that enable species to thrive in a constantly changing world.

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