Stanley A. Cain, "Man and His Environment," in Michael Miklin, Ed., Population, Environment, and Social Organization: Current Issues in Human Ecology, The Dryden Press, 1973


Environment consists of all of the things, conditions, and forces to which living matter is sensitive and capable of reacting, including changes in the intensity and direction of stimuli. In simpler terms, if there is no response, there has been no effective stimulus, and anything in the surroundings that does not provide a stimulus is not a part of the environment of living oranisms. The rest of the surroundings, whatever they may be, have no significance for life because no stimulus to protoplasm is a consequence of their existence. They elicit no biological response.