It is a remarkable and puzzling fact that, for over a century, psychological and biological research have been exploring the development and functional characterization of brain/mind activity in almost totally separate and non-interactive ways. It cannot be denied, however, that the human brain is the result of evolution in the brains of other mammals. The subcortical structures of mammals present anatomical, neurochemical and functional homologies, and these suggest largely similar mechanisms for emotion, perception and action. One of the reasons for the lack of concern by experimental psychologists with biological issues may derive from a premature, and thus largely sterile, nature-nurture controversy. While it was difficult in the recent past to understand how genes might interact with the environment in expressing themselves, the notion of epigenetic development is now better understood in its precise mechanisms, although much remains to be discovered. The nature-nurture controversy, however, has overshadowed other important points. Even if it is recognized that human behavior largely results from individual and socio-historical interaction with the environment, such interactions can hardly be understood if the general constraints that the species confronts, given its bodily structure, general needs, and physical-social environment, fail to be grasped.