Why people do the things they do is an age-old question. However, psychology — the science concerned with behavior, in both human and nonhuman animals — first appeared in the 1870s. Despite its youth, it is a broad discipline, essentially spanning subject matter from biology to sociology. Psychologists have doctoral degrees. They study the intersection of two critical relationships: one between brain function and behavior; and another between the environment and behavior. As scientists, psychologists follow scientific methods, using careful observation, experimentation and analysis. But psychologists also need to be creative in the way they apply scientific findings.