Animal Behaviour

by C. Lloyd Morgan

I.—The Nature of Intelligent Behaviour

Such an animal as a newly hatched bird or an insect just set free from the chrysalis is a going concern, a living creature. It is the bearer of wonderfully complex automatic machinery, capable, under the initiating influence of stimuli, of performing instinctive acts. But if this were all we should have no more than a cunningly wrought and self-developing automatic machine. What the creature does instinctively at first it would do always, perhaps a little more smoothly as the organic mechanism settled down to its work—just as a steam-engine goes more smoothly when it has been running for a while; but otherwise the action would continue unchanged. Instinctive behaviour would remain unmodified throughout life. The chick, however, or the imago insect is something more than this. It affords evidence of the accommodation of behaviour to varying circumstances. It so acts as to lead us to infer that there are centres of intelligent control through the action of which the automatic behaviour can be modified in accordance with the results of experience. When, for example, a young chick walks towards and pecks at a ladybird, the like of which he has never before seen, the behaviour may be purely instinctive; and so, too, when he similarly seizes a wasp-larva. Even when he rejects the ladybird or swallows the larva, this may be directly due to unpleasant stimulation in the one case, and pleasant in the other. But when, after a few trials, the chick leaves ladybirds unmolested while he seizes wasp-larvæ with increased energy, he affords evidence of selection based on individual experience. And such selection implies intelligence in almost its simplest expression. We may say, therefore, that, whereas instinctive behaviour is prior to individual experience, intelligent behaviour is the outcome and product of such experience. This distinction is presumably clear enough; and it is one that is based on the facts of observation. But we must not fail to notice that, though the logical distinction is quite clear, the acquired modifications of behaviour, which we speak of as intelligent, presuppose congenital modes of response which are guided to finer issues. We may say, then, that where these congenital modes of response take the form of instinctive behaviour, there is supplied a general plan of action which intelligence particularizes in such a manner as to produce accommodation to the conditions of existence.

We have already frankly admitted that, in the present state of our knowledge, we do not know with any definiteness how intelligent modification of behaviour is effected. But it seems probable that from all parts of the automatically working organic machine messages come in to the centres of conscious control, and that in accordance with the net result of all these messages, and the past experience which they recall, other messages go out to the automatic centres, and, by checking their action here and enforcing it there, give new direction to the resulting behaviour. If this be so, the consciousness associated with the control-centres is like the person who sits in a central office and guides the working of some organized system in accordance with the information he is constantly receiving; who sends messages to check activity in certain directions and to render it more efficient and vigorous in others.

It may be said, however, that intelligent guidance is, at any rate in such simple cases as the selection of a palatable grub and the rejection of a nauseous ladybird, itself determined by instinctive likes and dislikes. All young chicks apparently find wasp-larvæ palatable and ladybirds the reverse; and this is just as much the outcome of heredity as the instinctive act of pecking. Since, therefore, heredity determines what shall be selected and what rejected—since the likes and dislikes are themselves instinctive—any essential difference between congenital and acquired behaviour seems to be evanescent.

Now, if we apply to the affective qualities of mental states—the pleasurable tone or its opposite which characterize such states—the term “instinctive,” we do so in reference to the broader psychological conception of instinct, rather than in accordance with the narrower biological acceptation of the term. For the likes and dislikes constitute part of the conditions under which the behaviour occurs, and not elements in the co-ordinated response as such. Hence it is preferable to apply to these hereditary qualities the term innate, rather than the term instinctive. But, waiving this distinction, it is true that such pleasant or unpleasant qualities of the sensory results of stimuli are part of the animal’s hereditary outfit, and are not acquired in the course of individual experience. What, then, is acquired? What part does experience play in the development of intelligent behaviour? Let us consider the case of the chick and the ladybird, and see whether it helps us to answer these questions. The chick is stimulated to the instinctive pecking response by a small moving object. That is the first scene of the little drama. In the second scene the ladybird is seized, sensory centres are unpleasantly stimulated, and the insect is dropped or thrown on one side with signs of disgust. Let us grant that this aversion with its characteristic response is also instinctive. There is no hereditary connection between scene 1 and scene 2. After an interval the curtain rises on act ii. The characters are the same as in the first scene of the previous act. But the action of the drama is different. The chick does not seize the ladybird. Why? Because there is an acquired connection between scenes 1 and 2 of the previous act. The chick has gained experience of the nauseous character of the insect, and this experience influences and modifies his behaviour. The essentially new feature, therefore, is the establishment of a connection which is not provided through inheritance. To put the distinction in a brief form, we may say that instinct depends on how the nervous system is built through heredity; while intelligence depends upon how the nervous system is developed through use.

Assuming that an animal is capable of gaining experience and of acquiring new nervous connections in the course of individual experience, it follows that, as has already been indicated, instinctive behaviour in its logical purity is only presented in the first performance of any given co-ordinated act. For after this the animal has gained experience of its performance; and this can no longer conform to a definition of instinct, according to which it is characterized as “prior to experience.” On the other hand, intelligent behaviour cannot be presented on the first occurrence of any action, since there is no prior experience thereof in the light of which it may be guided. This logical distinction may be expressed by saying that instinctive behaviour is always prior to experience, while intelligent behaviour is always subsequent to experience. When, however, instinctive procedure continues throughout life practically unmodified or but little modified, we may still class it under instinct, since the hereditary connections are still the predominant factors. And where the latter part of an instinctive sequence is modified by the experience gained in the former part, we may still term the modification intelligent, however small may be the time-interval implied in the word “subsequent.” Sharp as the logical distinction is, the behaviour of animals is in the main a joint-product, and whether we term it instinctive or intelligent depends upon whether the hereditary or the acquired factor predominates.

Passing on now to consider some further characteristics of intelligent behaviour, we may first notice what Dr. Charles Mercier, in his work on “The Nervous System and the Mind,” terms the four criteria of intelligence. Intelligence is manifested, he says, first in the novelty of the adjustments to external circumstances; secondly, in the complexity; thirdly in the precision; and fourthly, in dealing with the circumstances in such a way as to extract from them the maximum of benefit.

Fig. 18.—Leaf-case of Birch-weevil.

If, however, we are to regard these severally as criteria of intelligence, each should serve to differentiate intelligent from instinctive behaviour. But this is not the case. The precision of the adjustment cannot be regarded as a criterion of intelligence, for many instinctive acts are remarkably precise. No grocer’s assistant rolls a paper funnel with more precision than is displayed by the birch-weevil (Rhynchites betulæ) in constructing the leaf-case in which her eggs are laid. Curved incisions of constant form are made on either side of the midrib, and are “of just the right shape to make the overlaps in the rolling, and to retain them rolled up with the least tendency to spring back,”[49] while the tip of the leaf is rolled into a second smaller funnel, which is tucked in to close the opening of the first, after the eggs have been deposited. “The eggs hatch in their dark place, each giving rise to an eyeless maggot, which ultimately leaves the funnel for the earth.... Hence the beetle cannot be considered to have ever seen a funnel, and certainly has never witnessed the construction of one, though, when disclosed, it almost immediately sets to work to make funnels on the complex and perfect system” characteristic of the species. This is but one example of instinctive precision out of the many which could be cited. We may say, then, that though, when an act is otherwise shown to be intelligent, the precision is a criterion of the level attained by the intelligence, still it cannot be said to be a criterion which serves to distinguish intelligent from instinctive behaviour.

Nor can we regard apparent prevision (which is sometimes advanced as a criterion of intelligence) as specially distinctive of intelligent acts regarded objectively in the study of animal behaviour. For, as we have had occasion to show, there are many instincts which display an astonishing amount of what may be termed “blind prevision”—instance the instinctive regard for the welfare of unborn offspring which the mother will never see, and the instinctive preparation for an unknown future existence in the case of insect larvæ.

Nor, again, is the complexity of the adjustment distinctive of intelligence as contrasted with instinct. We have cited examples which afford evidence of much complexity in instinctive behaviour. The construction and storage of the nest among solitary wasps, and their methods of capturing and conveying the insects or spiders on which they prey, are sufficiently complex. So, too, is the behaviour of the Sitaris larva which attaches itself to the male bee, passes to the female, and then slips on to the eggs she lays; and so, again, is that of the Yucca moth, which collects pollen from the anthers, conveys it to the stigma, and then lays her eggs among the ovules. These cases show, too, that the circumstances may be dealt with in such a way as to extract from them the maximum of benefit. It would be difficult intelligently to improve upon the manner of dealing with the circumstances displayed in many familiar modes of instinctive procedure.

There remain the novelty of the adjustment and the individuality displayed. And here we seem to have valid criteria of intelligent behaviour. The ability to perform acts in special adaptation to new circumstances, and the individuality manifested in dealing with the complex conditions of a variable environment,—these seem to be distinctive features of intelligence. On the other hand, in instinctive behaviour there seems to be no choice; the animal is impelled to their stereotyped performance through impulse, as by a stern necessity; they are so far from novel that they are performed by every like individual of the species, and have been so performed by their ancestors for generations; and in performing the instinctive act, the animal seems to have no more individuality or originality than a piece of adequately wound clockwork.

Granting, then, that behaviour is shown to be intelligent by the fact that there is evidence of profiting by experience, we may say that the level attained by the intelligence is indicated by the complexity of the adjustment, its precision, the individuality shown, the amount of prevision disclosed, and in its being such as to extract from the circumstances the maximum of benefit. Many of these points, however, serve equally well to mark the level of instinctive procedure.