Ecology, bionomics and evolution of the torrential fauna: with special reference to the origins 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. This nice adjustment of an organism to the external conditions of its existence is the result of a series of gradual changes induced by the environment. New modifications arise and persist on account of their utility and their ultimate perfection is brought about through the agency of a process of selection exercised by nature in which the "fittest" survive in a "struggle for existence." "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 remaking of the characters and sometimes the changes effected are of such a totally different type that the genetic relations can hardly be discerned.