Instinct is an innate or typically fixed, inherently characteristic natural pattern of behavior in response to physical stimuli in the environment.
Instincts are inborn complex patterns of behavior that exist in most members of a species, and should be distinguished from reflexes, which are simple responses of an organism to a specific stimulus, such as the contraction of the pupil in response to bright light or the spasmodic movement of the lower leg when the knee is tapped.
Any behavior is instinctive if it is performed without being based upon prior experience (that is, in the absence of learning), as an expression of innate biological factors. Though an instinct is defined by its invariant innate characteristics, details of performance can be changed by experience; for example, some animals can improve their fighting skills by practice.
The absence of volitional capacity must not be confused with an inability to modify fixed action patterns. Healthy people are able to modify a stimulated fixed action pattern by consciously recognizing, from personal observation or education offered by others, the point of its activation and simply stop doing it through a choice of their free will, whereas animals without a sufficiently strong volitional capacity may not be able to disengage from their fixed action patterns, once activated.
- voluntarily, with awareness, consent and cooperation, and
- involuntarily, induced without awareness or consent.
The term "instinct" in psychology was first used in the 1870s by Wilhelm Wundt. By the close of the 19th century, most repeated behavior was considered instinctual. Sigmund Freud considered that mental images of bodily needs, expressed in the form of desires, are called instincts. 
William McDougall held that many instincts have their respective associated specific emotions. As research became more rigorous and terms better defined, instinct as an explanation for human behavior became less common. In 1932, McDougall argued that the word 'instinct' is more suitable for describing animal behaviour, while he recommended the word 'propensity' for goal directed combinations of the many innate human abilities, which are loosely and variably linked, in a way that shows strong plasticity. During the 1960s and 1970s, textbooks still contained some discussion of instincts in reference to human behavior.
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 have applied to humans in the past, it no longer does.
The book Instinct: an enduring problem in psychology (1961) selected a range of writings about the topic.
F.B. Mandal proposed a set of criteria by which a behavior might be considered instinctual: 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).
In a classic paper published in 1972, the psychologist Richard Herrnstein wrote: "A comparison of McDougall's theory of instinct and Skinner's reinforcement theory — representing nature and nurture — shows remarkable, and largely unrecognized, similarities between the contending sides in the nature-nurture dispute as applied to the analysis of behavior."
By the year 2000, the term 'instinct' appeared to have become outmoded for introductory textbooks on human psychology.
In Information behavior: An Evolutionary Instinct (2010, pp. 35–42), Amanda Spink notes that "currently in the behavioral sciences instinct is generally understood as the innate part of behavior that emerges without any training or education in humans." She claims that the viewpoint that information behavior has an instinctive basis is grounded in the latest thinking on human behavior. Furthermore, she notes that "behaviors such as cooperation, sexual behavior, child rearing and aesthetics are [also] seen as 'evolved psychological mechanisms' with an instinctive basis." Spink adds that Steven Pinker similarly asserts that language acquisition is instinctive in humans in his book The Language Instinct (1994). Spink's book does not mention William McDougall's 1908 work about the "instinct of curiosity" and its associated "emotion of wonder"
M.S. Blumberg in 2017 examined the use of the word instinct, and found it varied significantly.
The complex response called "imprinting" may involve visual, auditory, and olfactory cues in the environment surrounding an organism. In some cases, imprinting attaches an offspring to its parent, which is a reproductive benefit to offspring survival. If an offspring has attachment to a parent, it is more likely to stay nearby under parental protection. Attached offspring are also more likely to learn from a parental figure when interacting closely. (Reproductive benefits are a driving force behind natural selection.)
Environment is an important factor in how innate behavior has evolved. From a more biological standpoint, the brain's limbic system operates as the main control-area for response to certain stimuli, including a variety of instinctual behavior. The limbic system processes external stimuli related to emotions, social activity, and motivation, which propagates a behavioral response. Some behaviors include maternal care, aggression, defense, and social hierarchy. These behaviors are influenced by sensory input—sight, sound, touch, and smell.
Evolutionists assert that within the "circuitry" of the limbic system, there are various places where evolution could have taken place, or could take place in the future. For example, many rodents have receptors in the vomeronasal organ that respond explicitly to predator stimuli that specifically relate to that individual species of rodent. The reception of a predatory stimulus usually creates a response of defense or fear. Mating in rats follows a similar mechanism. The vomeronasal organ and the main olfactory epithelium, together called the olfactory system, detect pheromones from the opposite sex. These signals then travel to the medial amygdala, which disperses the signal to a variety of brain parts. The pathways involved with innate circuitry are extremely specialized and specific. Various organs and sensory receptors play parts in this complex process.
Instinct is a phenomenon that can be investigated from a variety of research disciplines and approaches: genetics, limbic system, nervous pathways, and environment. Researchers can study levels of instincts, from molecular behavior to groups of individuals. Extremely specialized systems have evolved, resulting in individuals which exhibit behaviors without learning them.
- Philosophical naturalism
- Training and conditioning
- Free will
- Lorenz, Konrad (1977). Behind the Mirror: A Search for a Natural History of Human Knowledge. New York: Harcourt Brace Jovanovich. ISBN 978-0-15-111699-7.
- Hjelle, Larry (1981). Personality Theories: Basic Assumptions, Research, and Applications. McGraw-Hill. ISBN 9780070290631.
- McDougall, W. (1928). An Introduction to Social Psychology, 21st edition, Methuen & Co. Ltd, London, p. xxii.
- McDougall, W. (1928). An Introduction to Social Psychology, 21st edition, Methuen & Co. Ltd, London, p. vii.
- McDougall, W. (1932). The Energies of Men: a Study of the Fundamentals of Dynamic Psychology, second edition, Methuen & Co. Ltd, London, p. 99.
- Maslow, Abraham H. (1954). "Instinct Theory Reexamined", Motivation and Personality. New York: Harper & Row.
- Birney, R.C., Teevan, R.C. (1961). Instinct: an enduring problem in psychology, Van Nostrand, Princeton NJ.Template:Pn
- Mandal, F. B. (2010). Textbook of Animal Behaviour. PHI Learning. ISBN 978-81-203-4035-0.
- Herrnstein, R. J. (1972). "Nature as Nurture: Behaviorism and the Instinct Doctrine". Behaviorism 1 (1): 23–52.
- Buss, D. (2008). Evolutionary psychology: The new science of the mind, 3rd, Boston: Allyn & Bacon.
- Dickens, W. T. (2003). Instinct and choice: A framework for analysis. In C. Garcia Coll (Ed.), Nature and nurture: The complex interplay of genetic and environmental influences on human behavior and development.. Mahwah, NJ: Erlbaum.
- Geary, D. C. (2004). The origin of mind: Evolution of brain, cognition, and general intelligence.. Washington, DC: American Psychological Association.
- Basic Instinct: The Genesis Of Behavior By Mark S. Blumberg, 9 pages
- Jaynes, Julian (1957). "Imprinting: The interaction of learned and innate behavior: II. The critical period". Journal of Comparative and Physiological Psychology 50 (1): 6–10. doi:10.1037/h0044716. PMID 13406129.
- Kim, Young-Joon; Žitňan, Dušan; Galizia, C. Giovanni; Cho, Kook-Ho; Adams, Michael E. (2006). "A Command Chemical Triggers an Innate Behavior by Sequential Activation of Multiple Peptidergic Ensembles". Current Biology 16 (14): 1395–1407. doi:10.1016/j.cub.2006.06.027. PMID 16860738.
- Sokolowski & Corbin 2012, "Wired for behaviors: from development to function of innate limbic system circuitry"
instinct definition (bing.com) online listing of online resources offering definitions and discussions of instinct
Wired for behaviors: from development to function of innate limbic system circuitry, Katie Sokolowski and Joshua G. Corbin, Children's National Medical Center, Center for Neuroscience Research, Children's Research Institute, Washington, D.C., USA - frontiers in MOLECULAR NEUROSCIENCE Review article