Final answer:
Introspection was considered subjective, leading William James to introduce functionalism, which emphasized the adaptive functions of mental activities. Behaviorism, founded by John B. Watson, focused exclusively on observable behavior.
Step-by-step explanation:
Introspection proved to be subjective, and psychologist William James introduced the school of functionalism, which focused on how mental and behavioral processes enable the organism to adapt, survive, and flourish. Functionalism was influenced by Darwin's theory of evolution and natural selection, emphasizing that mental activities served as adaptive responses to an organism's environment. Contrasting with structuralism, which was more concerned with the individual parts of the mind, functionalism focused on the operational whole of mental processes. Behaviorism, later introduced by John B. Watson, shifted the focus further by studying observable behavior and disregarding unobservable mental processes, emphasizing objective analysis over introspection.