At the end of the nineteenth century, the question of man's place in the natural order was paramount. Evolutionary thinking had revolutionalized long-standing conceptions concerning the origin of species and their interrelation. In so doing, man's relation to his ancestry appeared in a new light. Questions concerning the nature of inheritance, memory, instincts, life, and energy were critical issues in the sciences of the body – biology, ethology, physiology, zoology – as well as in the attempts to form a new scientific psychology.

Proponents of the new scientific psychology called their field “physiological psychology” to differentiate it from the older philosophical psychology, and to associate it with the contemporary revolutions in the sciences of the body. They sought to replace the static mind of the philosophical tradition with a mind that had evolved, and was adapted to the environment. For psychologists, the critical issue was one of linking their field with developments in the sciences of the body, while maintaining the disciplinary autonomy of psychology.

One means by which this was effected was through the concept of the unconscious. This provided a new formulation of the relation between the soul and the body. Conceptions of life, memory, and instincts became transfigured by the unconscious. This in turn became a new touchstone of self-knowledge, which came to signify knowledge of what was unconscious, in some shape or form, to the self.