This informative film illustrates American physician Dr. Paul MacLean's theory of human brain structure and evolution--the triune brain. The human brain, he theorizes, functions through the interaction of three cerebral formations: the reptilian complex, the limbic system, and the neocortex. These control instinct, emotions, and intellect, respectively. Using computer animation to explain the development of these formations, the film documents our current knowledge about this most complex of human organs.