It is upon the projected surface of biology that man appears as a being possessing functions receiving stimuli (physiological ones, but also social, interhuman, and cultural ones), reacting to them, adapting himself, evolving, submitting to the demands of an environment, coming to terms with the modifications it imposes, seeking to erase imbalances, acting in accordance with regularities, having, in short, conditions of existence and the possibility of finding average norms of adjustment which permit him to perform his functions.