the branch of psychology concerned with the changes in cognitive, motivational, psychophysiological, and social functioning that occur throughout the human life span. During the 19th and early 20th centuries, developmental psychologists were concerned primarily with child psychology. In the 1950s, however, they became interested in the relationship between personality variables and child rearing, and the behavioral theories of B.F. Skinner and the cognitive theories of Jean Piaget were concerned with the growth and development of children through adolescence. At the same time, the German psychologist Erik Erikson insisted that there are meaningful stages of adult psychology that have to be considered in addition to child development. Psychologists also began to consider the processes that underlie the development of behaviour in the total person from birth to death, including various aspects of the physical-chemical environment that can affect the individual during the intrauterine period and at birth. By the latter part of the 20th century, developmental psychologists had become interested in many broad issues dealing with the psychological process throughout life, including the relation of heredity and environment, continuity and discontinuity in development, and behavioral and cognitive elements in the development of the total person. See also child psychology; psychological development.