Every living organism, by virtue of its biologic structure, reacts to certain stimuli from within and without. In the course of its development as an individual, the organism tends to fit the contours of its environment, i. e., to adapt. One can see this process in the infant as (through the developing nervous system) he meets his environment for the first time and in the adult when he encounters a new situation. This fitting into the milieu, or adaptation, seems to be a property of all living organisms. As one passes from lower to higher forms of life, the adaptation of the organism as a whole is carried out by successively more highly differentiated and specialized tissues, until in the highest vertebrates adaptation is accomplished chiefly by the cerebral cortex.
In the process of adaptation the organism begins to react to substitutes, or signals, for stimuli having congenital connections—to natural
GANTT WH. A METHOD OF TESTING CORTICAL FUNCTION AND SENSITIVITY OF THE SKINAN AID IN DIFFERENTIATING ORGANOGENIC AND PSYCHOGENIC DISTURBANCES. Arch NeurPsych. 1938;40(1):79-85. doi:10.1001/archneurpsyc.1938.02270070089007