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Comparative physiology is a branch of science that explores the similarities and differences between living things and how they function. As an area of research, comparative physiology is a subclass of physiology: the study of the functional processes of living organisms. The discipline itself incorporates many divergent scientific arenas, including evolution, environmental studies, and archaeology.
A combination of necessity and curiosity gave rise to comparative physiology. Physicians needed new ways to treat human patients, so animals that shared many characteristics with humans were a ripe area for research. Thus came the Krogh Principle, which dictates the use of readily accessible living things to answer scientific or medical inquiries. Eventually, this practical use for comparisons blossomed into an overall scientific curiosity concerning the likenesses and divergences among various animal species.
Comparative physiologists study and compare a wide range of functions in organisms. Almost any part of an organism’s body serves some important use, and nearly all living organisms share basic needs like food, breathing, internal temperature control, and heart sustenance. By studying the processes that drive these needs — such as cell-based exchanges and blood circulation — researchers can gather a vast amount of comparative information.
In a sense, relationships define comparative physiology. At the most basic level, this field is a study of the relationship between a living creature and its own body. Proper comparisons can only be achieved when the scientist understands how each organism’s physical body allows it to carry out the actions essential for day-to-day living. The physiological component of comparative physiology may therefore range from studying how organisms use limbs or other appendages to move to how organisms breathe.
Another important aspect of comparative physiology is the relationship between organisms and their environment, or ecophysiology. The same physical setting may exercise very different effects on divergent organisms. A fish, for example, will have a much bleaker outcome in a desert environment than in its home habitat of water. In contrast, a land-dwelling lizard acclimated to harsher climates would be ill-equipped to deal with an aquatic setting due to its anatomical makeup. As such, ecophysiology and its study of aspects of adaptation can offer enhanced understanding of all animal groups in comparative physiology.
One particular area of comparative physiology has received increased attention over time: the use of phylogenic comparative methods. Scientists utilize these methods to examine potential evolutionary relationships between diverse living organisms and to document any significant changes a particular animal group may have undergone since its inception. Researchers may study the physical resemblances between certain organisms or how certain organisms have developed similar functional parts, like lungs or gills for breathing purposes. As a result, the study may uncover common ancestors among different species and solidify an evolutionary link. Examination of fossil remains and other archaeological evidence may also help comparative physiologists understand how an animal group has changed and adapted from ancient times until the present era.