The term "instinct" in psychology was first used in 1870s by Wilhelm Wundt. By the close of the 19th century, most repeated behavior was considered instinctual. In a survey of the literature at that time, one researcher chronicled 4,000 human "instincts," having applied this label to any behavior that was repetitive. As research became more rigorous and terms better defined, instinct as an explanation for human behavior became less common. In a conference in 1960, chaired by Frank Beach, a pioneer in comparative psychology, and attended by luminaries in the field, the term was restricted in its application. During the 60's and 70's, textbooks still contained some discussion of instincts in reference to human behavior. By the year 2000, a survey of the 12 best selling textbooks in Introductory Psychology revealed only one reference to instincts, and that was in regard to Sigmund Freud's referral to the "id" instincts.. In this sense, instincts appeared to have become regarded as increasingly superfluous in trying to understand human psychological behavior.
Some Freudian Psychoanalysts have retained the term instinct to refer to human motivational forces (such as sex and aggression), sometimes represented as Eros - life instinct and Thanatos - death instinct. This use of the term motivational forces has been replaced by the term drives to correct the original error in the translation of |Freud's work.
Psychologist Abraham Maslow argued that humans no longer have instincts because we have the ability to override them in certain situations. He felt that what is called instinct is often imprecisely defined, and really amounts to strong drives. For Maslow, an instinct is something which cannot be overridden, and therefore while the term may applied to humans in the past, it no longer does.
The book Instinct (1961) established a number of criteria which distinguish instinctual from other kinds of behavior. To be considered instinctual, a behavior must: a) be automatic, b) be irresistible, c) occur at some point in development, d) be triggered by some event in the environment, e) occur in every member of the species, f) be unmodifiable, and g) govern behavior for which the organism needs no training (although the organism may profit from experience and to that degree the behavior is modifiable). 
Jean Henri Fabre, an entomologist, considered instinct to be any behavior which did not require cognition or consciousness to perform. Fabre's inspiration was his intense study of insects, some of whose behaviors he wrongly considered fixed and not subject to environmental influence. 
Instinct as a concept fell out of favor in the 1920s with the rise of behaviorism and such thinkers as B. F. Skinner, which held that most significant behavior is learned. These beliefs, like Fabre's belief that most behaviors were simply reflexive, also proved to be too simplistic to account for the complex emotional and social behavior of human beings.
An interest in innate behaviors arose again in the 1950s with Konrad Lorenz and Nikolaas Tinbergen, who made the distinction between instinct and learned behaviors. Our modern understanding of instinctual behavior in animals owes much to their work. For instance, in imprinting a bird has a sensitive period during which it learns who its mother is. Konrad Lorenz famously had a goose imprint on his boots. Thereafter the goose would follow whomever wore the boots. The identity of the goose's mother was learned, but the goose's behavior towards the boots was instinctive...