Chapter VII: The Meaning of Evolution (2)

There were apparently two main types of structure by means of which this mobility and elasticity could be attained, the Arthropod type and the Vertebrate type. There seems little to choose between them if we had to select one of them in order to obtain a highly mobile organic mechanism. Arthropod and Vertebrate seem to be equally complex if we take account of difference in size and the additional bodily mechanism that great size must involve. Certainly the musculature of the Vertebrate is more complex than in the Arthropod. But greater weight must require larger and more powerful muscles if the same degree of mobility relative to the size of the animal is to be attained, and this more complex musculature must carry with it a more complex brain. It must also be concomitant with a more massive skeleton, for rigid supports for the muscles must be present in the mechanism. Why are there no great insects or crustaceans? Mr Wells has suggested in one of his novels the formidability of a wasp two feet long! Such a creature would indeed be more dreadful than any predatory bird that we know if its activity were also that of the wasps that we know, just as a Copepod as large as a shark would be a more formidable animal than the fish. It seems possible that the reason for the smaller size of the Vertebrate is to be found in the nature of the skeleton. Powerful muscles would require a very strong and thick carapace, and this would attain a mass in a very large insect or crustacean which would require too much energy for its rapid transport. A rigid exoskeleton like that of an Arthropod also means that growth must take place by a process of ecdysis, that is, the animal grows only during the periods when it casts its shell; and the necessity of this process of ecdysis must be a formidable disadvantage in the case of a very large animal, if indeed it would be possible at all. Thus the Arthropod developing an exoskeleton must remain small, and this smallness, fortunately for the Vertebrate, has made it the less formidable animal. It was an accident of evolution that the Arthropods developed an exoskeleton instead of an endoskeleton.

Undoubtedly the internal skeleton of the Vertebrates, with its light, hollow, cancellated bones, was mechanically the best means for the attachment of muscles. It made possible a greater degree of freedom of movement of the parts of the body, greater variety and plasticity of action, and it removed, to some extent, the limit of size and the embarrassing discontinuity of growth by ecdysis, with all the dangers that this involves. Above all, it led to the increased complexity of the central nervous system, since this became bound up with the increasing variety of bodily movement.

In the evolution of the dominant groups of organisms we see, then, the development of several tendencies. First, that tendency which seems to offer the greatest contrast to the universal tendency displayed in inorganic processes, the dissipation of energy. The plant organism is essentially a system in which energy is accumulated in the potential form. Then, in the animal kingdom we see that the main tendency of evolution has been the development of systems in which energy becomes expended in infinitely varied movements. It may seem, on superficial examination, that in the animal mode of metabolism energy is dissipated as it is in inorganic processes; and this is the conclusion that we should reach if we considered the actions, and the results of the actions, of the lower animals only, that is, animals lower than man. We return to this point later on, but in the meantime it is to be noted that the fundamental division of organisms is that founded upon their activities as energy-transformers, that is, into plants and animals. Within each of these kingdoms of organisms structural evolution has occurred: the unicellular green plant has evolved along very numerous lines, each of them characterised by a different type of morphological structure. The unicellular animal has also evolved in a similar way with the result that the present phyla have become established. Looking at these great groups of animals, we see that two of them have attained dominance by the development along different lines of a sensori-motor system. Here we see another fundamental difference between the plant and animal organism, but one which is a consequence of the difference that exists between the two kingdoms in respect of the energy-transformations carried out by them. The plant is characterised by immobility, the animal by mobility.

Immobility implies unconsciousness, mobility consciousness, and this physical difference is the third one which we can establish between the plant and the animal. Now few physiologists are likely to accept this distinction as one which has any real objective meaning. Consciousness is not a concept to be dealt with in any process of reasoning, it is not even something felt in the way in which we speak of the feelings of pain, or light, or hunger: these are all states of our consciousness. The difference in ourselves, says Ladd, when we are sunk in sound dreamless sleep, and when we are in full waking activity, _that_ is consciousness. If we reason about organisms and their activities as we do about inorganic things we have no right to speak about consciousness, for outside our own Ego it has no existence. The acting animal is only a body, or a system of bodies, moving in nature, and all its activities are to be described by a system of generalised force and position co-ordinates with reference to some arbitrarily chosen point of space. “This animal machine,” says a zoologist, writing about instinct, “which I call my wife, exhibits certain facial contortions and emits certain articulate sounds which correspond with those emitted by myself when I have a headache, but I have no right to say that she has a headache.” This kind of argument does not appear to be capable of refutation except, perhaps, by the domestic conflicts which it would usually evoke if applied in such cases as that quoted. In a description of nature by the methods and symbolism of science we see only systems of molecules in motion, and in those systems which we describe as organisms the motions are only more complex than they are in inorganic systems. Such is the method of science, as irrefutable in the study of the organism as we know that it is false. Valid in pure speculation according to the methods of the intellect it would nevertheless be absurd in the everyday affairs of common civilised life and the scientific man who applies it in his writing would nevertheless hesitate to apply it in the affairs of his own household.

We must recognise that our knowledge that other beings like ourselves, as well as animals lower in organisation than ourselves, are consciously acting organisms is intuitive knowledge, attainable because of community of organisation: our intuitive knowledge of the behaviour and feelings of our own brothers and sisters is greater than our knowledge of other men and women; and we can, by intuition, place ourselves within the consciousness of an intelligent dog to a greater extent than in the case of other animals. This knowledge of the consciousness of other animals is not scientific knowledge and it is unattainable and unprovable by reasoning or methods of scientific observation. It is a conviction in itself incapable of analysis or proof, but yet a conviction on which we confidently base most of our dealings with our fellow-creatures, and which is justified by our experience.

It is nevertheless a scientific hypothesis of much the same validity as many other scientific hypotheses. We cannot bring ourselves to doubt that other men and women are consciously acting organisms, however impossible it may be to adduce scientific reason for the faith that is in us. We cannot doubt that a compass needle which “responds” by turning one or other of its poles towards us according as we push forwards one or other of the poles of a magnet is an unconscious piece of metal, though we find it impossible to say why this belief possesses such conviction. From this to the movements of the typical green plant is only a step. The turning of a green leaf towards the source of light, or the downward movement of a root into the soil, are responses to external stimuli which exhibit most of the inevitability of response of the magnet. They are “tropisms”: the plant leaf is obliged to turn towards the light so that the latter strikes against its surface perpendicularly, and the root must grow downwards because gravity acts along vertical lines. But suppose that reflex actions are tropistic: suppose, for instance, that the moth is bound to fly into the candle flame because the light stimulates both sides of its body equally and this orientates it and guides it towards the direction from which the stimulus proceeds. Complex actions, in the higher animal, on this view are chains of reflexes, and the acting must be unconscious and inevitable, just as the turning of the magnet or green leaf are unconscious movements. Therefore the actions of our fellow-creatures are unconscious and automatic, a conclusion toward which the whole tendency of mechanistic physiology forces us. Yet we know that the conclusion cannot be true.

Between the obligatory reaction of the compass needle to the magnet, or the analogous heliotropism and geotropism of the plant organism, and the infinitely variable responses of the higher animal toward changes in its environment, consciousness must come into existence. It is absent in the inorganic system and the typical green plant; it is dim in the sedentary sea-anemone or mollusc; it becomes brighter in the freely moving Arthropod or fish; and it is most intense in man. This, it must be admitted, is only a belief, but accepting it as such we may attempt to support it by showing a parallelism of stages of structural complexity and actions. The sensori-motor system is absent in the green plant; it is simple in the extreme in the sea-anemone; and it is rudimentary or vestigial in the sedentary mollusc. It becomes more complex in the Arthropod or fish, and it is developed to the greatest degree in ourselves. If we now examine our own mental states, with their corresponding conditions of bodily activity, we see as clearly as possible that our consciousness waxes and wanes with our activities. It is absent in normal sleep, when bodily activity in the real sense ceases almost absolutely, when the cerebral cortex becomes inactive, and when the only movements performed are those truly automatic ones of parts of the body which are analogous to the movements of the plant organism. Such movements are the rhythmic ones of the heart and lungs, the movements of the blood, and so on, in general the movements leading to constructive metabolism. Consciousness is most intense in difficult unfamiliar actions: the lad learning to row; the child learning scales on the piano, or the fingering of the violin; the engineer assembling together the parts of a new machine; or the artist engaged on a picture. In each of these cases the worker is acutely conscious, in a deliberative manner, of his own bodily actions. But with the habitual exercise of these movements, and with the ease and facility with which they are performed, consciousness that they are being performed fades towards nothingness.

What does this mean but that degrees of consciousness are parallel to degrees of complexity of deliberated and purposeful bodily movements or actions? Or degrees of consciousness are also parallel to the attempt of the organism to perform these actions. What is pain, the most acutely felt of all our mental states? It is, Bergson says, the consciousness of the persistent and unsuccessful effort of the tissues to respond purposefully to a persistently renewed stimulus. But complex actions require for their performance systems of skeletal and muscular parts capable of moving in the most varied ways, and a system of afferent and efferent nerves with all their connections in the central nervous system: that is, a sensori-motor system. Therefore just as the sensori-motor system is more or less complex so, in general, is consciousness more or less acute.

Yet in the same organism consciousness is the more or less acute as the actions which it performs are more or less familiar. The pianist who plays scales as a matter of exercise carries out most complex movements of hands and wrists unconsciously and without effort, but to play an unfamiliar composition for the first time without error involves attention of the highest degree. A girl who counts the sheets of paper coming from a machine seizes a handful in one hand, and drops a separate sheet between every two fingers of the other hand, repeating this most difficult operation with great rapidity, and counting the handfuls of sheets accurately while thinking and talking deliberately about some other matter. At the beginning of her work these actions were clumsily performed and facility was only attained by sustained attention to the movements of the hands, yet with experience they become unconsciously performed. Complex movements of the body and limbs and digits, involving the co-ordinated activity of numerous muscles, nerves, and nerve centres, are performed at first only after a high degree of conscious effort, but with each repetition of the series of movements the animal ceases to be aware of them, or at least of their difficulty. In the higher animals there are, therefore, two categories of actions, (1) those unfamiliar actions which are _difficult_, and in the performance of which the animal becomes conscious of complex muscular activities; and (2) those habitual actions which have become _easy_ by dint of repetition, and the performance of which is unattended by conscious effort. Analysis of our own activities reveals these two categories of actions, and we have no doubt whatever that the higher animals have the same feelings of difficulty and effort in the one case, and of lack of conscious effort in the other.

The difference is one of those which separate instinctive from intelligent activities. Now we hesitate to attempt the discussion of this much-controverted question of the distinction between instinct and intelligence: after reading much that has been said as to the nature of this difference, one rises with the uncomfortable impression that the time is not yet ripe for its discussion, and that the problem is still one far more for the naturalist than for the psychologist. Reliable data are still urgently required. Yet it is a question which we cannot fail to consider. The typical plant differs from the typical animal in that a sensori-motor system has been evolved in the one but not in the other; and among the animals in which this system is developed to a high degree the activities which involve its exercise differ in their form. Actions of a stereotyped pattern characterise the behaviour of the higher Invertebrate, while in the higher Vertebrate all that we see indicates that the behaviour is the result of deliberation, and that the actions performed are not stereotyped but differ infinitely in their patterns. Just as clearly as differences in morphology differentiate Arthropod from Vertebrate, so also do differences in the mode of activity of the sensori-motor system mark divergent lines of evolution culminating in the Hymenopterous Insect on the one hand and in Man on the other.

What is the essential difference between an action performed instinctively and one performed intelligently? It is not that the animal is unaware of its activity in the first case and not in the second; however much we tend to “explain” organic activity in terms of inorganic reactions, we do not really believe that the instinctively acting wasp is a pure automaton, while admitting that the schoolgirl is acutely conscious of her own multifarious activities. It is not that the instinctive action displays a “finish,” or perfection of technique, that the deliberative action lacks: the comb built by the wasp is not more perfect in its way than is the doorway constructed by a skilled mason, or the “buttonholes” stitched by a seamstress. It is not that instinctive actions are so absolutely stereotyped, as is sometimes assumed, while intelligent actions grow more perfect in their result by repetition: the work of the insect or bird is often faulty and it is improved by practice. The most obvious difference is that the instinctive action is _effective_ the very first time it is performed, while the intelligent action only becomes effective after it has been attempted several times, or very many times, according to its difficulty. The flight of the young swallow is effective inasmuch as it sustains the bird in the air, but it is also an exceedingly difficult series of muscular efforts which is at first clumsily performed and which becomes more perfect by repetition. But the flight of an aeroplane, even now after years of experiment, is not always effective, and exhibits at its best all the imperfections of the flight of the young swallow. Yet can we doubt that in time it will exhibit all the ease and certainty and finish of the flight of the bird?

The typical intelligently performed action is the action of a _tool_, or of a part of the body which is used for some other purpose than that which is indicated by its immediate evolutionary history, or by its previous use. The typical instinctively performed action is always the action of a bodily organ, the structure and immediate evolutionary history of which indicates that it originated as an adaptation for the performance of these particular actions, or category of actions. Here it seems to us that we find the distinction between the two kinds of bodily activity; and the distinction is one which depends for its validity on our notions as to what a tool is. An implement made by man is a piece of inert matter fashioned in order that it may be used for a definite preconceived purpose. It has an existence as a definite specific object _apart from its use_; and its exercise by the man who made it and its existence in nature are two different things. Its use must be _learned_, and the results obtained by its employment become more perfect with every repetition of its use. But the mandibles of an insect are implements purposefully adapted for some action or series of actions, just as the pincers of the blacksmith are so adapted. They are, however, implements which are part of the organisation of the animal using them--organised tools--and it does not seem as if we ought to think of them, and of their shape and nature, as something apart from their exercise. Must we think of an animal as having to _learn_ how to use any part of its body? If so, then the problem of instinct remains with us in all its historic obscurity. But if we think of the existence of a bodily tool as something inseparable from the functioning of the tool, the problem becomes less obscure, or at least it can be stated in terms of some other problems which we have already considered.

We do actually think of bodily parts or organs as material structures quite apart from the consideration of their functions: it is the distinction between morphology and physiology--an altogether artificial one. An animal, for the morphologist, is a complex of skeleton, muscles, nerves, glands, and so on; and it does not matter whether it is contained in a jar of methylated spirit or is running about in a cage. For the physiologist it is “something happening”; but is it not really both things, and are not the structure and the functioning only two convenient, but arbitrary, aspects from which we consider the organism? We ought not to think of diaphragm and lungs apart from the movements of these organs, and we do not say that the first breath drawn by the newly-born mammal is an instinctive action, involving the use of inborn bodily tools--the diaphragm, lungs, etc. We ought not to think of the lips and mouth and pharynx of the young baby apart from the actions of suckling the mammæ of its mother, but usually we say that this action is an instinctive one. Where does the ordinary functioning of an organ end and its instinctive functioning begin? Are the muscular actions of the lobster when it frees its body and appendages from the carapace during the act of ecdysis instinctive ones? Most zoologists would say that they are not, any more than the movements of the maxillipedes in respiration are instinctive ones, yet they probably would not hesitate to say that the action of the “soft” lobster in creeping into a rock crevice is instinctive. Does a young child really “learn” to walk? It is more likely that the actions of walking are potential in its limbs and that they become actual when all the connections of nerve tracts and centres in its brain and spinal cord become established. What is the difference between the acquirement of the ability to walk and to write? The latter series of actions are unfamiliar combinations of nervous and muscular activities which are no part of the organisation of the young child; while the former are simply the result of the complete functional development of certain nervous and muscular apparatus.

It seems difficult, then, to express clearly what is the essential difference between instinctive and intelligent behaviour; and it is doubtless the case that reasoned experiments and observations are still too few to enable us to make sound deductions. But it certainly seems as if we ought to think of instinctive actions as having evolved concomitantly with the structure of the organs which effect them: they are those _inheritable adaptations of behaviour_ which are bound up with--are indeed the same things as--inheritable adaptations of structure. In performing them the instinctively acting animal is doubtless aware of its own activity, but we must think of this awareness as being of much the same nature as our consciousness of the automatic activities of our own bodies--the rhythmic activities of the heart and respiratory organs, or the actions of our arms and legs in walking, for instance. It is knowledge of the inborn ability of the organisms to use an inborn bodily tool.

In the intelligent action we certainly see something different from this. The organ or organ-system which carries out such an action functions in a manner which is different from that for which it was evolved: the action is the conscious adaptation of the organ for some form of activity new to it, and this acquirement of activity seems to be non-inheritable--at least it is non-inheritable in the sense in which we speak of acquired characters being non-inherited. It is accompanied, while it is being acquired, by a consciousness which is deliberative, and is different from that awareness of its own activity which accompanies the acting of the instinctive animal--the knowledge that it is acting in an effective manner. It does not seem as if the animal in so acting is aware of the relation of the bodily tool to the object on which it is acting. But intelligence seems to imply more than this: it implies the knowledge of the organism that some parts of its body bear certain relations to the parts of the environment on which they are acting, and that these relations are variable ones and may be the objects of conscious choice.