[Functional evolution: origin and problems].

In the article the history of comparative and evolutionary physiology since the early XIX is given. The most substantial methods of evolutionary physiology are described. In the mid-50ies Orbely put forward the suggestion concerning two tasks facing evolutionary physiology, namely the study of evolution of functions and functional evolution. In the present work attention is given to the principles underlying evolution of functions on different levels of physiological systems. The main aspects of functional evolution are discussed.