INSTINCT

an involuntary response by an animal to an external stimulus, resulting in a predictable and relatively fixed behaviour pattern. Instinctive behaviour is an inherited, adaptive mechanism that serves to promote the survival of an animal or species. It is most apparent in fighting and sexual activity. Certain animal behaviour, such as exploring and play, can be modified, but, in general, inherited behaviour is a sequence of acts that is internally motivated; it may be triggered by external conditions but is only secondarily influenced by them. The simplest form of instinctive behaviour is the reflex action, or the response of a single organ to a stimulus. Some lower animals are governed by chain reflexes; in millipedes, for example, the motion of one leg stimulates the motion of another. Most animals, however, are capable of fixed action patterns in which several body systems participate. A number of these fixed patterns lead to one goal, but others may have several functions, such as the distinctive display actions of courtship. Patterns of motor behaviour, such as gesturing and dancing, are also used by insects, birds, and fish to communicate and enable a species to distinguish its signals from those of any other. Among the fixed action patterns that may be modified by learning processes in some species is nest-building behaviour. Jackdaws, for example, learn how to select appropriate materials through trial and error, but canaries, even ones that have been reared in man-made cloth nests, have an innate ability to choose the right materials and to line the nest with feathers. All animals have instinct. In general, the higher the animal form, the more flexible the behaviour. Among mammals, learned behaviour often prevails eventually over fixed action patterns, as when a young rat learns through experience to adjust its instinctive heaping and smoothing motions to the appropriate stage of nest building. In humans, behaviour is heavily influenced by the socialization process, and the issue of heredity versus environment continues to be a controversial subject. involuntary response by an animal to an external stimulus. The concept has come to refer to complex unlearned behaviour that is recognizable and predictable in at least one sex of a species. Additional reading Niko Tinbergen, The Study of Instinct (1951, reissued 1989), is a wide-ranging survey of instinctive behaviour. Papers and books devoted to special aspects of instinctive behaviour are T.H. Bullock, The Origins of Patterned Nervous Discharge, Behaviour, 17:4859 (1961); Society for Experimental Biology (Great Britain), Nervous and Hormonal Mechanisms of Integration (1966), symposium papers; Robert A. Hinde (ed.), Bird Vocalizations: Their Relation to Current Problems in Biology and Psychology (1969), and Non-Verbal Communication (1972); Konrad Lorenz, The Innate Bases of Learning, in Karl H. Pribram (ed.), On the Biology of Learning (1969); and Ronald J. Schusterman, Jeanette A. Thomas, and Forrest G. Wood (eds.), Dolphin Cognition and Behavior: A Comparative Approach (1986). The works by Peter Marler and William J. Hamilton III, Mechanisms of Animal Behavior (1968); and W.H. Thorpe, Learning and Instinct in Animals, new ed. (1969), are also of interest.