The inborn tendency of every member of a certain species to behave in the same way given the same situation or set of stimuli.
Behavior is considered instinctive only if it occurs in the same form in all members of a species. Instincts must be unlearned and characteristic of a specific species. Animals provide the best examples of instinctive behavior. Birds naturally build nests without being taught and feed and protect their young in the exact same ways. Other animals, such as squirrels or dogs, behave in manners characteristic of only squirrels or dogs. Ethologists, scientists who study animals in their natural environments, devote much of their efforts to the observation of instinctive behavior.
Throughout history, theorists have speculated on the role of instinct in determining human behavior. While it has been widely accepted that animal behavior is governed largely by innate, unconscious tendencies, the presence and power of instincts in humans have been a source of controversy. Early Christian theorists believed that only animals were guided by instincts, asserting that the absence of instinct-governed behavior and the presence of a moral code provided the major distinction between humans and animals. Instinct assumed a more prominent place in behavior theory in later years. In the late 1800s, William James proposed that human behavior is determined largely by instinct, and that people have even more instinctual urges than less complex animals. James believed that certain biological instincts are shared with animals, while human social instincts like sympathy, love, and modesty also provide powerful behavioral forces.
Sigmund Freud considered instincts to be basic building blocks of human behavior and play a central role in his drive theory, which postulates that human behavior is motivated by the desire to reduce the tension caused by unfulfilled instinctive urges or drives. For instance, people eat when they are hungry because unsatiated hunger causes tension, which is reduced by eating. For Freud, the life instinct (Eros) and its components motivate people to stay alive and reproduce. The death instinct (Thanatos) represents the negative forces of nature. Another theorist, William McDougall, described instincts simply as "inherited dispositions."
The debate continues today over the role of instinct in human behavior, as the balance between learned behavior and innate urges remains a subject ripe for continued research and discussion. It is useful to note a nonscientific use of the term instinct. In casual conversation, a person may use instinct to mean "natural" or "automatic—in describing a baseball player's instinct for batting, for example. This use of the term would not meet the scientist's criteria for instinct.
See also Drive reduction theory
Atkinson, Rita L.; Richard C. Atkinson; Edward E. Smith; and Ernest R. Hilgard. Introduction to Psychology. 9th ed. San Diego: Harcourt Brace Jovanovich, 1987.
Zimbardo, Philip G. Psychology and Life. 12th ed. Glenview, IL: Scott, Foresman, 1988.