While anatomy is the study of the structures of an organism, physiology is the science dealing with the study of the function of an organism's component structures. However, it often is not enough to know what an organ, tissue, or other structure does. Physiologists want to know how something functions. For example, physiological questions might ask: What is the function of human lung tissue? How can a seal survive under water without breathing for over ten minutes? How do camels survive so long without water? How do insects see ultraviolet light? Physiology examines functional aspects at many levels of organization, from molecules, to cells, to tissues, to organs, to organ systems, to an entire organism. It is the branch of biology that investigates the operations and vital processes of living organisms that enable life to exist.

Comparative physiology, then, is the comparison of physiological adaptations among...