Instinct and the Unconscious. W.H.R.Rivers
difficult to analyse human behaviour into its innate and acquired components.
One other point about this mode of distinguishing instinct and intelligence may be mentioned. The distinction belongs to the field of biology rather than of psychology. If we were able [p. 43] to analyse every case of behaviour, whether human or animal, into its innate and acquired elements, we should still be little, if at all, nearer the solution of the psychological as opposed to the biological problem. We should not yet have begun to understand the place of consciousness in relation to behaviour, which, whatever may be our interest in the unconscious, must still remain the special task of psychology.
So long as we are considering the subject biologically we may be content with distinctions which depend on whether behaviour is exhibited by Man or animal, whether it is dependent on, or independent of, acquired experience, and on the locality of the physiological processes with which the behaviour is correlated. These modes of distinction, however, will not, or should not, satisfy the psychologist who requires something in the nature of the behaviour itself by means of which he may distinguish the instinctive from the intelligent. Nevertheless in the present state of the subject I believe we shall do best to take as the distinguishing mark of instinct its innate character, even though this character be biological rather than psychological. We shall do best if we devote our inquiries to the attempt to distinguish different kinds of instinct according to their psychological character. It should be our task to analyse the general group of instincts into its component parts just as it has been the main task of psychologists hitherto to analyse the different forms of intelligent behaviour.
In seeking for a criterion by which to distinguish different varieties of instinct, I propose to turn away for a time from the behaviour of insects or other invertebrate animals which are usually taken as our patterns of the instinctive. These animals differ so enormously from ourselves that it is too great an adventure into the unknown to base any distinction on differences between their behaviour and ours. Let us look rather to the behaviour of Man as compared with the animals to which he is more nearly related, and to the behaviour of adult man as compared with the infant, for our clue to the nature of the differences which will enable us to distinguish different classes of instinctive behaviour. [p. 44]
I will begin with a difference taken from the comparison of the human adult with the infant and the animal. An animal or child exposed to danger, which is so recognised as danger that it produces a reaction, tends to give itself to the reaction fully. If it runs away, it tends to run with every particle of the energy which it is capable of putting forth; if it cries, screams, or utters other sound, it tends to do so with all the vigour at its command. In these cases there is no discrimination of the degree of danger. The reaction by flight or cry is the same whether the danger be great or small. In the case of the animal the movement of a shadow thrown by a falling leaf may produce as strong a reaction as the full sight of its deadliest enemy. The child may scream as vigorously after some trivial touch as it does with the pain of a cut or burn. With no discrimination of the degee of danger, there may be complete absence of graduation of the reaction to the nature of the stimulus which occurs even in the animal in its more intelligent behaviour, and is characteristic of the behaviour of the adult man when danger threatens. If the danger is sufficiently great, or if certain lines of behaviour by which the danger would normally be met are frustrated, even the adult man will fail to discriminate the nature of the danger and to graduate his movements accordingly. He will devote every particle of his energy to flight or other form of primitive or instinctive behaviour. Thus, if he becomes angry and assumes an aggressive attitude, his anger and aggression will go far beyond those called for by the needs of the situation. If he flees, his flight may continue long after it has removed him to a safe distance from the source of danger.
In what I have just said I have spoken of the child as tending to scream and of the animal as tending to run away with all the force at their command, because I wish to make clear that the child or animal does not always behave in this thoroughgoing manner. All I wish to imply is that when these reactions take place in their most characteristic manner, they show a complete absence of proportionality between the behaviour and the conditions which call it forth. I assume that when the child and animal are so behaving, they are acting [p. 45] in a manner ill which they would act if their instinctive behaviour had not been modified by experience.
In the last chapter I have adopted the current view that such emotions as fear or anger, with the reactions characteristic of them, are expressions of instinct. When they occur in Man, these reactions are prominent, even the most prominent, elements in that part of his behaviour which can be ascribed to instinct. We have now seen that these reactions, when occurring in their most characteristic form, have the special feature that there is an absence of graduation according to the nature of the conditions by which the behaviour is produced. If they take place at all, they tend to occur in their full strength. This form of reaction is known in physiology as the "all-or-none" reaction,[4] and I propose to adopt this term for the special kind of behaviour I am now supposing to be characteristic of certain forms of instinct.
It may help us to understand this reaction if I give a brief account of its nature in physiology. For this purpose I will begin with the instance in which the principle was discovered by Keith Lucas and Adrian. I will not describe the somewhat complex experimental procedures which were needed to demonstrate the principle, and will give only the essential facts. When a weak electrical stimulus is applied to isolated nerve-fibre, and the impulse which in consequence travels along the nerve is measured, it is found that if the stimulus is weak there is no impulse at all, or more correctly, the electrical behaviour of the nerve gives no evidence of any impulse. If strength of the electrical stimulus is gradually increased, a point is reached when the nerve gives the response normally associated with an impulse passing along its length. If now strength of the stimulus is increased, there is no corresponding increase in the response, and this remains so, however great the increase of the stimulus. If the isolated nerve-fibre is set action at all, it reads with its full strength and produces all effect of which it is capable. [p. 46]
In previous chapters I have cited the work of Head as giving good examples of the process of suppression, and protopathic sensibility as a characteristic example of the content of the unconscious. It will greatly strengthen my argument and help to show that I am dealing with a real character of certain forms of instinct if protopathic sensibility should be subject to the "all-or-none" principle. As a matter of fact this is practically, though not completely, the case. When a region of the skin which is endowed only with protopathic sensibility is stimulated with cold, the intensity of the cold sensation is roughly the same whether the temperature of the stimulating surface is zero or 20°C., i.e., whether it is the temperature of ice or about the temperature of a summer day. The sensation due to the colder stimulus radiates over a larger area, which makes it difficult to be absolutely confident that there is no difference in the intensity of the sensation of cold, but we can be confident that when protopathic sensibility reacts to cold, it does so with appropriately or altogether the same strength so far as this can be tested by sensory experience,
The principle also holds good of certain forms of reflex action. Thus, the nature of the reflex known as the "extensor thrust" led Sherrington to think that the strength of the stimulus had no influence upon the amount of the response, and that the reflex occurred either not at all or fully.[5] The mass-reflex recently observed by Head and Riddoch, of which I gave an account in Chapter IV, also obeys the "all-or-none" principle fairly completely. Still more significant is the fact that the heart-muscle responds to stimulation either not at all or fully, this mode of reaction being of especial importance owing to the close relation between the heart and those affective disturbances which are closely connected with instinct.
Thus, the isolated nerve-fibre, the heart, certain forms of reflex action, and the protopathic sensibility of the skin all agree in having characters which only appear in the more complex behaviour of man or animal under conditions which bring instinctive processes into activity. [p. 47]
The "all-or-none" principle may be regarded as only a special case of a wider law holding good of the relation between stimulus and sensation, or between stimulus and reaction. Except at the limits of the range of intensities the normal sensibility of the skin or other sense-organs shows definite proportionality between stimulus and reaction, of which the most exact