Anthropology is the scientific study of the origin, development, and varieties of human beings and their societies, particularly so-called primitive societies while psychology is the science dealing with mental phenomena and processes. Psychologists study emotions, perception, intelligence, consciousness, and the relationship between these phenomena and processes and the work of the glands and muscles. Psychologists are also interested in diseased or disordered mental states, and some psychologists provide therapy for individuals. In the United States, however, psychologists, unlike psychiatrists, are not medical doctors.