ABSTRACT
Although the role of biological factors in individual functioning was emphasized early (cf., Angell 1907), until very recently one of the main characteristics of psychological research has been its neglect of such factors. This circumstance has considerably limited the effectiveness of research, the purpose of which is to understand why individuals think, feel, act, and react as they do in real life, which is the ultimate goal of psychology as a scientific discipline (Magnusson 1988).
