, in an organism, is an inferred condition (that is, a construct
—something inferred to exist and “constructed” from simpler, known elements) that arouses and directs it toward a specific goal. Motivational theories deal with and attempt to explain what instigates, directs, and maintains persistence in behavior. Many fields in psychology are concerned with motivation, and its study is approached from various perspectives, including the biological/physiological, the behavioral, the cognitive, and that based on a need hierarchy.
Biological/physiological approaches to motivation evolved from the work of Charles Darwin, who was interested in evolution and how species survived.
Instincts. Darwin explained survival of an organism, and consequently a species, as, in part, resulting from an instinct for survival. Other early attempts to explain motivation (by, for example, William James and William McDougall) also involved instincts, defined by some as unlearned patterns of behavior that aid in the survival of the organism. Explaining behavior in terms of instincts eventually fell out of favor, however, because of the indiscriminate labeling of all motivated behaviors as instincts (till they reached the thousands and included such things as instincts for rivalry, cleanliness, or parental love).
Ethology. Ethology, a branch of biology that studies evolution and the development and function of behavior, emerged in the 1930s and revived interest in instincts. Early theorists in the field include Konrad Lorenz, Nikolaas Tinbergen, and Irenaus Eibl‐Eibesfeldt. (Eibl‐Eibesfeldt investigated the possibility that certain human behaviors are universal, such as the display of facial expressions to express happiness or sadness.) The term instinct, as used by these theorists, has to do with unlearned behaviors and responses (for example, Tinbergen spoke of the reproductive instinct). Ethological theory became controversial, partly because it initially excluded certain known facts concerning nervous system functions and their effects on behavior. Although other approaches are now used more widely in the study of human motivation, ethology is still important in the study of animal behavior.
Sociobiology. Sociobiology, a contemporary discipline that evolved from instinct theories, is the study of the evolutionary and genetic foundations of social behavior in all species. Although the discipline is not universally accepted and its concepts have often been controversial because of the difficulty of verifying them through experimentation, sociobiology remains an active area of study.
Physiological regulation. In motivation theory, physiological regulation refers to the regulation of motivation by certain portions of the nervous system. Particular origins of such regulatory activity are proposed in what are known as local theories and central theories.
Local theories suggest that signals that regulate motivation come from the peripheral organs of the body (as opposed to the brain). But popular work (such as that by Walter Cannon and A. L. Washburn) in the early 1900s demonstrated that although the experience of hunger is related to hunger pangs (stomach activity), when the vagus nerve is severed, eliminating stomach contractions, hunger is still experienced. Such work led to decreased interest in local theories of regulation and subsequent focus on central regulation.
Central theories describe regulation of motivation by the brain, particularly by the hypothalamus. Motivations arising from hunger, thirst, and sexual appetite have been studied extensively from the central theory perspective.
Physiological regulation includes both short‐term and long‐term regulatory mechanisms.
Short‐term regulation refers to immediate physiological changes, such as those in blood‐sugar level when one eats.
Long‐term regulation refers to central nervous system mechanisms that function to maintain a steady state of physiological functioning, for example, maintenance of a relatively stable body weight. These regulatory systems are described in more detail in the following discussion of hunger, thirst, and sexual motivation.