V. Ecology, bionomics and evolution of the torrential fauna, with special reference to the organs of attachment

Abstract

In studying the life and characters of the animals inhabiting the torrential streams of India and elsewhere, one thing has become quite clear to me—that evolution is no more than the adaptation of organisms to environment. "Adaptation" signifies correlation of an animal with its habitat, and therefore the study of animal organisation, however detailed, cannot by itself lead to the proper understanding of this phenomenon. Environment with its unlimited gradations plays an important part in the making and re-making of the characters, and sometimes the resultant forms are of such totally different types that genetic relations can hardly be discerned ( vide infra , pp. 190, 237, 246). This fine adjustment of an organism to the external conditions of its existence is the result of a series of gradual changes induced by the environment.