Evolution of Human Psychology

How do humans and animals think and act?
The origins of scientific psychology are usually traced to the work of the German physicist Hermann von Helmholtz and his student Wilhelm Wundt Helmholtz applied the scientific method to the study human vision, and his Handbook of Physiological Optics is even now described as "the single most important treatise on the physics and physiology of human vision". In 1879, Wundt opened the first laboratory of experimental psychology at the University of Leipzig. Wundt inside on carefully controlled experimental in which his workers would perform a perceptual or associative task while introspecting on their thought processes. The careful controls went a long way toward masking psychology a science, but the subject nature of the data made it unlikely that an experimenter would ever disconfirm his or her own theories.
Biologists studying animal behavior, on the other hand, lacked introspective data and developed an objective methodology, as described by H.S. Jennings in his influential work Behavior of the Lower Organisms. Applying this viewpoint to humans, the behaviorism movement, led by John Watson, rejected any theory involving mental processes on the grounds that introspection could not provide reliable evidence. Behaviorists insisted on studying only objective measures of the percepts given to an animal and its resulting actions. Mental contracts such as knowledge, beliefs, and goal and reasoning steps were dismissed as unscientific "folk psychology".
Behaviorism discovered a lot about rats and pigeons, but had less success at understanding humans. Nevertheless, it exerted a strong hold on psychology from about 1920 to 1960.