Читать книгу Animal Behaviour - C. Lloyd Morgan - Страница 15

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We use the phrase “mental development” in its broadest acceptation as inclusive of, and applicable to, all phases of effective consciousness. We shall assume that throughout this development there is a concomitant development of nerve-centres and of their organic connections. And we shall further assume that experience, as such, is not inherited.

The nature of the grounds on which the latter assumption is based must first be briefly indicated. It is commonly asserted that fear of man, the inveterate hunter and sportsman, is inherited by many animals, as is also that of other natural enemies. This is, however, questioned, or even denied, by many careful observers. Mr. W. H. Hudson has an excellent chapter on “Fear in Birds” in his “Naturalist in La Plata,” and concludes that fear of particular enemies is, in nearly all cases, the result of experience individually acquired. I have found that pheasants, partridges, plovers, domestic chicks, and other young birds, hatched in an incubator, show no signs of fear in the presence of dog or cat, so long as the animal is not aggressive. It should be mentioned, however, that Miss M. Hunt[17] asserts that chicks do show inherited fear of the cat. Dr. Thorndike’s[18] observations, on the other hand, support my own, which I have since repeated with the same results. Neither birds nor small mammals show any signs of fear of stealthily moving snakes. My fox terrier smelt, nose to nose, a young lamb which was lying alone in a field. I was close at hand, and could detect no indication of alarm on the part of the lamb till the mother came running up in great excitement. Then the lamb ran off to her dam. Whenever opportunity has arisen, I have introduced young kittens to my fox terrier, and have never seen any sign of inherited fear. He was a great hunter of strange cats, but was trained to behave politely to all birds and beasts within the precincts of my study. It is true that he was on good terms, or at least terms of permissive neutrality, with the kittens’ mother. And it may be said that this was inherited; but such an argument cannot apply in the case of pheasant or lamb.

Here, as throughout our study of animal behaviour in its conscious aspect, we have not only to conduct observations with due care, but to draw inferences with due caution. Douglas Spalding described how newly hatched turkeys showed signs of alarm at the cry of a hawk; and he inferred that, since this sound was quite new to their individual experience, the alarm was due to the inheritance of ancestral experience of hawks. But since young birds show signs of alarm at any sudden and unaccustomed sound—a sneeze, the noise of a toy horn, a loud violin note, and so forth—the safer inference seems to be that they may be frightened by strange sounds of many kinds. But this does not imply the inheritance of experience, which is essentially a discriminating process. There is no sufficient evidence that a peculiar cry suggests the hawk, of which the progenitors have acquired bitter experience; nothing to justify the belief that the sound carries with it inherited meaning. And as with hearing, so with sight. Young birds may be frightened by many strange objects. I have seen a group of several species, filled with apparent alarm at a large white jug suddenly placed among them, at balls of paper tossed towards them, at a handkerchief dropped in their midst. It is, in fact, their inexperience which is often the condition of such fear. As Mr. Hudson says:[19] “A piece of newspaper carried accidentally by the wind is as great an object of terror to an inexperienced young bird as a buzzard sweeping down with death in its talons.”

Until recently it was commonly asserted that birds avoid gaudy but nauseous or harmful insects through the inheritance of experience gained by their ancestors through many generations. But here again the inference seems to have been incautiously drawn. Of the hundreds of young birds I have had under observation, not one has avoided the peculiarly distasteful cinnabar caterpillar, until it had gained for itself experience of its nauseous character. So too of wasps and bees. Only through experience are these avoided. It is true that chicks may shrink from them if they buzz or even walk rapidly towards them. But a large harmless fly will inspire just as much timidity. As the result of careful observations, Mr. Frank Finn[20] concludes “that each bird has to separately acquire its experience, and well remembers what it has learnt.” And with this conclusion my own observations are entirely in accord.

Such is some of the observational evidence on which is based the provisional hypothesis that experience, as such, is not inherited. What, then, is inherited? Clearly the organic conditions under which experience can be acquired. Since a young bird inherits a tendency to peck at small objects, especially, in the case of some birds such as plovers or partridges, at small moving objects, opportunities are afforded for discrimination in accordance with the results of experience. Since its inherited timidity leads the chick to shrink from many things seen or heard, a wide range of conscious data is supplied. Inheritance provides the raw material of organic behaviour for effective consciousness to deal with in accordance with the results which are its data.

Having thus cleared the ground and laid bare some at least of the assumptions which we accept as foundations on which to build, we may now follow up the line of treatment which was suggested in the first section of this chapter. Remembering that our aim is to understand the influence of consciousness on behaviour—or, in more accurate, if more cumbrous phraseology, the influence of certain nerve-centres which have for their concomitant what we have termed effective consciousness—the questions which present themselves in any given case are: What is the conscious situation which is effective in guidance? what elements enter into the situation, whence are they derived, and how were they introduced? how do they take effect in behaviour?

If it be true that, in many of the lower forms of life, consciousness or sentience, though presumably present in some dim form, is merely an accompaniment of organic behaviour without reaching the level of recognizable effectiveness; and if, during the development of one of the higher animals from the fertilized ovum, the early stages of organic behaviour are in like manner merely sentient; it follows that, when effective consciousness enters upon the scene (who can say at what exact stage of evolution?), it finds itself a partner in a going concern. Much organic business is being transacted with orderly regularity; preparations have been made for more extensive operations; and energies lying dormant, or expending themselves aimlessly in starts and twitches, await the guidance which shall direct them to higher and wider biological ends. Or, to vary the analogy, consciousness is the heir to a wide estate, over which he has no control until he comes of age. Up to that time the estate is managed in strict accordance with the dictates of the hereditary bequest. He may be aware of what is going on, but merely as a spectator without power of interference. And when he comes into possession his first business is to gather up the threads. He must learn bit by bit how the estate is being managed, that he may have data for the guidance of his own management within the wise limits of the hereditary entail.

Now, when a mammal is born, a bird is hatched, an insect emerges from the chrysalis, we have, if not the beginning, at any rate a great and sudden extension of the range of effective consciousness. In the case of the mammal and bird the experience gained in the womb or within the egg-shell is presumably of little value for the wider life upon which an entrance is made. It is true that an insect has passed through a previous stage of active and no doubt consciously guided existence as a caterpillar. But we do not know whether the experience thus acquired is effectual for use in the later imago stage. And we may perhaps infer from the extensive remodelling of the nervous system, which occurs during the chrysalis sleep, that this itself serves to break the continuity of experience. In any case the newly hatched chick, if it inherit no experience, and can have gained little of guiding value in the egg, enters upon a situation which from the number and variety of the data supplied may well seem to us bewildering. If we picture ourselves in such a position, with sights, sounds, motor sensations, touches, and pressures raining in upon a virgin experience, we wonder how we should make a beginning; how we could possibly decide on the first step towards reducing this multiplicity and diversity to something like unity and order. And perhaps we wonder how we ourselves made a beginning when we were pink newly born babies.

If it may be said without paradox, we never did make a beginning. The beginning was made for us. For we habitually associate ourselves with the control centres, and regard our bodies, like our watches, as ours and not us. We wind the bodily watch, and set its hands from time to time; but we did not make it, and it was already going when heredity handed it to us over the counter of birth. The first step towards reducing the seeming chaos of sensory experience to something like order is not due to the selection by consciousness of this or that element for prominence among the rest, but to the thrusting forward of certain modes of behaviour by the conditions of organic life. The differentiation of the field of vision in the chick is not effected by any conscious determination to fix the attention on that wriggling maggot, but through the congenital response it calls forth. This serves not only to make the grub stand out clearly amid its surroundings, but also to emphasize a motor group, called into vigorous action in the midst of other motor sensations, and, in rapid sequence, to lay stress on a sensation of taste suddenly called into prominence.

Nor, as we have seen, do the organic effects cease here. The functional action of three sensory centres is thus called into play. But they are constituent parts of one nervous system. The direct stimulation of each by nerve impulses from eye, motor organs, and beak, gives temporary predominance to certain sensory data which are termed presentative. But the several centres are connected with each other. And thenceforward, in subsequent stages of experience, the direct stimulation of the visual centre indirectly calls into play the other two, so that the presentation through sight evolves re-presentations of the motor group, and of taste. Hence sentience is not sufficient for guidance; there must be consentience involving the presence of several elements. But these elements must not be regarded as separate save in our analysis; they form constituent parts of the coalescent situation as a whole, of which alone the chick is presumably conscious, without analysis of detail.

It is just because the chick is a going concern when consciousness comes of age and begins to assume control—just because a wide range of congenital behaviour is part of the organic heritage—that the early stages of the acquisition of experience proceed so rapidly and so smoothly. The animal has not to make and fashion the early conscious situations; it has only to accept them. It has not at first to enforce order on the multiplicity of sensory data raining in upon the conscious centres; it has only to take note of the existing order among them. It has not painfully to learn how to co-ordinate the efferent impulses proceeding to the many muscles concerned in some simple response; it has only to be sensitive to the response as a whole. It has not to select the association of this, that, and the other group of data within a coalescent situation; organic behaviour provides it with predetermined sequences ready made—sequences which have for generations received the emphatic sanction of natural selection. Congenital tendencies which it has inherited but not acquired determine all its earliest behaviour, determine what elements in the sensory complex shall be thrust into conscious prominence, determine in what manner these data shall be associated; determine, in fact, what salient points in the developing situations shall stand out clearly from the rest, and how these salient points shall be grouped and linked by the connecting threads of association and shall coalesce into effective wholes.

And if in the comparatively helpless human infant the congenital modes of response seem less organized than those of the chick, if there is a larger percentage of random and apparently aimless movements, if the organic management of the bodily estate is less definitely ordered by the terms of the hereditary bequest, if there is more of maternal guidance and fosterage; still the data are provided in a substantially similar way. The situations are indeed destined to become more complex, the distinctions which arise in consciousness are more numerous, the coalescence and association include a wider range and succession of salient points; a longer time is required to become acquainted with the transactions of a business conducted in a far greater number of centres: but, at least in the early stages, the data are of the same kind, and are emphasized in the same way. Presentation and re-presentation play a similar rôle; and the chief difference lies in the fact that less stereotyped congenital behaviour is supplemented by some guidance, probably far less than is generally supposed, from those who lovingly minister to the course of infant development.

No attempt can here be made to trace even in outline (an outline which must in any case be imaginary and conjectural) the sequence of situations which marks the course of mental development in its earlier stages. An example may, however, serve to show how the exercise of congenital tendencies may give rise to a new situation, and lead to a further development of behaviour.

I kept some young chicks in my study in an improvised pen floored with newspaper, the edges of which were turned up and supported, to form frail but sufficient retaining walls. One of the little birds, a week old, stood near the corner of the pen, pecking vigorously and persistently at something, which proved to be the number on the page of the turned-up newspaper. He then transferred his attention and his efforts to the corner of the paper just within his reach. Seizing this, he pulled at it, bending the newspaper down, and thus making a breach in the wall of the pen. Through this he stepped forth into the wider world of my study. I restored the paper as before, caught the bird, and replaced him near the scene of his former efforts. He again pecked at the corner of the paper, pulled it down, and escaped. I then put him back as far as possible from the spot. Presently he came round to the same corner, repeated his previous behaviour, and again made his escape.

Now, here the inherited tendency to peck at small objects led, through the drawing down of the paper, to a new situation, of which advantage was taken. The little drama consisted of two scenes, which may be sufficiently described as “the corner of the pen,” and “the open way,” this being the sequence in experience. Subsequently the first scene was again enacted in presentative terms, and there followed first a re-presentation of scene ii., with its associated behaviour, and then the presentative repetition of this scene. We may take this as a sample of the nature of a conscious situation which is effective in guidance. We have seen the nature of the elements (sensory data, including as essential those supplied by the behaviour itself, with a pleasurable or painful tone) which enter into such a situation; we have seen that they owe their primary origin to direct presentation, but that they may be subsequently introduced indirectly in re-presentative form; we have seen that the situation as a whole results from the coalescence of the data. There only remains the question how the felt situation takes effect on behaviour. And to this question, unfortunately, we can give but a meagre and incomplete reply. All we can say is, that connections seem to be in some way established between the centres of conscious control and the centres of congenital response; and that through these channels the responsive behaviour may be either checked or augmented (as a whole or in part), according to the tone, disagreeable or pleasant, that suffuses the situation. How this is effected we do not fully know.