Causation of Instinctive Behaviour

Starting and Stopping: Classes of Causal Factor

At the present stage of exposition an adult animal is pictured as possessing an elaborate behavioural equipment that comprises a very large but finite number of behavioural systems that are organised in chains or hierarchies, or a mixture of the two, and that, when activated, lead to behavioural sequences of greater or less complexity each of which commonly promotes survival of individual and/or species. The precise forms the systems take in a particular individual are, as always, a product of gene action and environment; and, dependent on species and system, the forms they take are more or less stable environmentally. In addition to the more stable behavioural systems responsible for instinctive behaviour, animals are equipped with many others that are environmentally labile and in the development of which learning plays a very large part (though they are not our concern here). Given this varied equipment, then, the question that confronts us is why one part of it is in action at one time and another part at another.

The first thing to recognise is that, so long as an animal is alive, one or another part of its behavioural equipment is bound to be in action. Animal life is behaviour, even if it is only the behaviour of sleep. Since our task as psychologists is not that of solving the riddle of life, we are not called upon to explain why an animal behaves but only why at any one time it behaves in this way rather than that, and why, when it is behaving in any particular way, it does so more intensely at some times than at others.

One approach to the problem is to consider the activity of physiological systems. Most physiological systems are in constant simultaneous activity. The cardiovascular system, the respiratory, the excretory, are permanently at work; and, whilst the digestive and the reproductive are more episodic in their operation, their activities are not usually