Instinct is the inherent disposition of a living organism toward a particular behavior. Instincts are unlearned, inherited fixed action patterns of responses or reactions to certain kinds of stimuli. Examples of instinctual fixed action patterns can be observed in the behavior of animals, which perform various activities (sometimes complex) that are not based upon prior experience and do not depend on emotion or learning, such as reproduction, and feeding among insects. Other examples include animal fighting, animal courtship behavior, internal escape functions, and building of nests.

Instinctual actions - in contrast to actions based on learning which is served by memory and which provides individually stored successful reactions built upon experience - have no learning curve, they are hard-wired and ready to use without learning, but do depend on maturational processes to appear.

Biological predispositions are innate biologically vectored behaviors that can be easily learned. For example in one hour a baby colt can learn to stand, walk, and run with the herd of horses. Learning is required to fine tune the neurological wiring reflex like behavior. True reflexes can be distinguished from instincts by their seat in the nervous system; reflexes are controlled by spinal or other peripheral ganglion, but instincts are the province of the brain.

Overview

Technically speaking, any event that initiates an instinctive behavior is termed a key stimulus (KS) or a releasing stimulus. Key stimuli in turn lead to innate releasing mechanisms (IRM), which in turn produce fixed action patterns (FAP). More than one key stimulus may be needed to trigger a FAP. Sensory receptor cells are critical in determining the type of FAP which is initiated. For instance, the reception of pheromones through nasal sensory receptor cells may trigger a sexual response, while the reception of a "frightening sound" through auditory sensory receptor cells may trigger a fight or flight response. The neural networks of these different sensory cells assist in integrating the signal from many receptors to determine the degree of the KS and therefore produce an appropriate degree of response. Several of these responses are determined by carefully regulated chemical messengers called hormones. The endocrine system, which is responsible for the production and transport of hormones throughout the body, is made up of many secretory glands that produce hormones and release them for transport to target organs. Specifically in vertebrates, neural control of this system is funneled through the hypothalamus to the anterior and posterior pituitary gland. Whether or not the behavioral response to a given key stimuli is either learned, genetic, or both is the center of study in the field of behavioural genetics. Researchers use techniques such as inbreeding and knockout studies to separate learning and environment from genetic determination of behavioral traits. The definitions of what constitutes instinct in humans beyond infancy is conjectural. It could be said that as well as obvious instincts such as breathing, sex-drive, desire to communicate, etc., humans also have an instinct toward knowledgeFact: date=September 2008. The will to invent solutions to requirements, to present self and possessions aesthetically and to be organised economically, culturally, religiously and politically could be described as instincts to promote survival, which are further enhanced by learning which is not instinctive.