Читать книгу Animal Behaviour - C. Lloyd Morgan - Страница 8

Table of Contents

The word “corporate” is here applied to the organic behaviour of cells when they are not independent and free, but are incorporated in the animal body, and act in relation to each other. If the behaviour of the individual cell during division impresses us with the subtle intricacy of organic processes, the behaviour of the growing cell-republic during the early stages of organic development must impress us no less forcibly. We place the fertilized egg of a hen in an incubator, and supply the requisite conditions of warmth, moisture, and fresh air. Before the egg is laid cell-division has begun. A small patch of closely similar cells has formed on the surface of the yolk. Further subdivision is then arrested until the warmth of incubation quickens again the patch into life. But when once thus quickened no subsequent temporary arrest is possible—life will not again lie dormant. If arrest there be it is that of death. And from that little patch of cells, which spreads further and further over the yolk, a chick is developed. Into the intricate technicalities of embryology this is not the place to enter. But it is a matter of common knowledge that, whereas we have to-day an egg such as we eat for breakfast, three weeks hence we shall have a bright active bird, a cunningly wrought piece of mechanism, and, more than that, a going machine. During this wonderful process the cellular constituents take on new forms and perform new functions, all in relationship to each other, all as part of one organic whole. Here bones are developed to form a skeletal framework, there muscles are constituted which shall render orderly movements possible; feathers, beak, and claws take shape as products of the skin; gut and glands prepare for future modes of nutrition; heart and blood-vessels undergo many changes, some reminiscent of bygone and ancestral gill-respiration, some in relation to the provisional respiration of the embryo by means of a temporary organ that spreads out beneath the shell, some preparatory to the future use of the lungs—some, again, related to the absorption of food from the yolk, others to subsequent means of digestion; nerve, brain, and sense-organs differentiate. A going machine in the egg, the chick is hatched, and forthwith enters on a wider field of behaviour. Few would think of attributing to the consciousness of the embryo chick any guiding influence on the development of its bodily structure, any control over the subtle changes and dispositions of its constituent cells. But no sooner does the chick, when it is hatched, begin to show wider modes of instinctive behaviour, than we invoke conscious intelligence for their explanation, seemingly forgetful of the fact that there is no logical ground for affirming that, while the marvellous delicacies of structure are of unconscious organic origin, the early modes of instinctive behaviour are due to the guidance of consciousness. Such modes of behaviour will, however, be considered in another chapter. Here we have to notice that the unquestionably organic behaviour of the incorporated republic of cells may attain to a high degree of complexity, and may serve a distinctly biological end.

Fig. 4.—Wapiti with antlers in velvet.

There is, perhaps, no more striking instance of rapid and vigorous growth than is afforded by the antlers of deer,[3] which are shed and renewed every year. In the early summer, when growing, they are covered over with a dark hairy skin, and are said to be “in velvet.” If you lay your hand on the growing antler, you will feel that it is hot with the nutrient blood that is coursing beneath it. It is, too, exceedingly sensitive and tender. An army of tens of thousands of busy living cells is at work beneath that velvet surface, building the bony antlers, preparing for the battles of autumn. Each minute cell, working for the general good, takes up from the nutrient blood the special materials it requires; elaborates the crude bone-stuff, at first soft as wax, but ere long to become hard as stone; and then, having done its work, having added its special morsel to the fabric of the antler, remains embedded and immured, buried beneath the bone-products of its successors or descendants. No hive of bees is busier or more replete with active life than the antler of a stag as it grows beneath the soft, warm velvet. And thus are built up in the course of a few weeks those splendid “beams,” with their “tynes” and “snags,” which, in the case of the wapiti, even in the confinement of our Zoological Gardens, may reach a weight of thirty-two pounds, and which, in the freedom of the Rocky Mountains, may reach such a size that a man may walk, without stooping, beneath the archway made by setting up upon their points the shed antlers. When the antler has reached its full size, a circular ridge makes its appearance at a short distance from the base. This is the “burr,” which divides the antler into a short “pedicel” next the skull, and the “beam” with its branches above. The circulation in the blood-vessels of the beam now begins to languish, and the velvet dies and peels off, leaving the hard, bony substance exposed. Then is the time for fighting, when the stags challenge each other to single combat, while the hinds stand timidly by. But when the period of battle is over, and the wars and loves of the year are past, the bone beneath the burr begins to be eaten away, through the activity of certain large bone-absorbing cells, and, the base of attachment being thus weakened, the antlers are shed; the scarred surface skins over and heals, and only the hair-covered pedicel of the antler is left.

Fig. 5.—Wapiti with velvet shredding off.

We have no reason to suppose that this corporate cellular behaviour, involving the nicely adjusted co-operation of so vast an army of organic units, is under the conscious guidance of the stag. And yet how orderly the procedure! how admirable the result! Nor is there an organ or structural part of the stag or any other animal that does not tell the same tale. This is but one paragraph of the volume in which is inscribed the varied and wonderful history of organic behaviour in its corporate aspect. Is it a matter for wonder that the cause of such phenomena has been regarded as “a mystery transcending naturalistic conception; as an alien influx into nature, baffling scientific interpretation”? And yet, though not surprising, this attitude of mind, in face of organic phenomena, is illogical, and is due partly to a misconception of the function of scientific interpretation, partly to influences arising from the course pursued by the historical development of scientific knowledge. The function of biological science is to formulate and to express in generalized terms the related antecedences and sequences which are observed to occur in animals and plants. This can already be done with some approach to precision. But the underlying cause of the observed phenomena does not fall within the purview of natural science; it involves metaphysical conceptions. It is no more (and no less) a “mystery” than all causation in its last resort—as the raison d’être of observed phenomena—is a mystery. Gravitation, chemical affinity, crystalline force—these are all “mysteries.”

If the mystery of life, lying beneath and behind organic behaviour, be said to baffle scientific interpretation, this is because it suggests ultimate problems with which science as such should not attempt to deal. The final causes of vital phenomena (as of other phenomena) lie deeper than the probe of science can reach. But why is this sense of mystery especially evoked in some minds by the contemplation of organic behaviour, by the study of life? Partly, no doubt, because the scientific interpretation of organic processes is but recent, and in many respects incomplete. People have grown so accustomed to the metaphysical assumptions employed by physicists and chemists when they speak of the play of crystalline forces and the selective affinities of atoms, they have been wont for so long to accept the “mysteries” of crystallization and of chemical union, that these assumptions have coalesced with the descriptions and explanations of science; and the joint products are now, through custom, cheerfully accepted as natural. Where the phenomena of organic behaviour are in question, this coalescence has not yet taken place; the metaphysical element is on the one hand proclaimed as inexplicable by natural science, and on the other hand denied even by those who talk glibly of physical forces as the final cause of the phenomena of the inorganic world.

So much reference to the problems which underlie the problems of science seems necessary. It is here assumed that the phenomena of organic behaviour are susceptible of scientific discussion and elucidation. But even assuming that an adequate explanation in terms of antecedence and sequence shall be thus attained by the science of the future, this will not then satisfy, any more than our inadequate explanations now satisfy, those who seek to know the ultimate meaning and reason of it all: What makes organic matter behave as we see it behave? what drives the wheels of life, as it drives the planets in their courses? what impels the egg to go through its series of developmental changes? what guides the cells along the divergent course of their life-history? These are questions the ultimate answers to which lie beyond the sphere of science—questions which man (who is a metaphysical being) always does and always will ask, even if he rests content with the answer of agnosticism; but questions to which natural science never will be able, and should never so much as attempt, to give an answer.

Enough has now been said to show that organic behaviour is a thing sui generis, carrying its own peculiar marks of distinction: and further, that, for science, this is just part of the constitution of nature, neither more nor less mysterious than, let us say, crystallization or chemical combination. But associated and closely interwoven with all that is distinctively organic there is much which can to some extent be interpreted in terms of physics and chemistry.

The animal[4] has sometimes been likened to a steam-engine, in which the food is the fuel which enters into combustion with the oxygen taken in through the lungs. It may be worth while to modify and modernize this analogy—always remembering, however, that such an analogy must not be pushed too far.

In the ordinary steam-engine the fuel is placed in the fire-box, to which the oxygen of the air gains access; the heat produced by the combustion converts the water in the boiler into steam, which is made to act upon the piston, and thus set the machinery in motion. But there is another kind of engine, now extensively used, which works on a different principle. In the gas-engine the fuel is gaseous, and it can thus be introduced in a state of intimate mixture with the oxygen with which it is to unite in combustion. This is a great advantage. The two can unite rapidly and explosively. In gunpowder the same end is effected by mixing the carbon and sulphur with nitre, which contains the oxygen necessary for their explosive combustion. And this is carried still further in dynamite and gun-cotton, where the elements necessary for explosive combustion are not merely mechanically mixed, but are chemically combined in a highly unstable compound.

But in the gas-engine, not only are the fuel and the oxygen thus intimately mixed, but the controlled explosions are caused to act directly on the piston, and not through the intervention of water in a boiler. Whereas, therefore, in the steam-engine the combustion is to some extent external to the working of the machine, in the gas-engine it is to a large extent internal and direct.

Now, instead of likening the animal as a whole to a steam-engine, it is more satisfactory to liken each cell to an automatic gas-engine which manufactures its own explosive. During the period of repose which intervenes between periods of activity, its protoplasm is busy in construction, taking from the blood-discs oxygen, and from the blood-fluid carbonaceous and nitrogenous materials, and knitting these together into relatively unstable explosive compounds, which play the part of the mixed air and gas of the gas-engine. A resting muscle may be likened to a complex and well-organized battery of gas-engines. On the stimulus supplied through a nerve-channel a series of co-ordinated explosions takes place: the gas-engines are set to work; the muscular fibres contract; the products of the silent explosions are taken up and hurried away by the blood-stream; and the protoplasm prepares a fresh supply of explosive material. Long before the invention of the gas-engine, long before gun-cotton or dynamite were dreamt of, long before some Chinese or other inventor first mixed the ingredients of gunpowder, organic nature had utilized the principle of controlled explosions in the protoplasmic cell, and thus rendered animal behaviour possible.

Certain cells are, however, more delicately explosive than others. Those, for example, on or near the external surface of the body—those, that is to say, which constitute the end-organs of the special senses—contain explosive material which may be fired by a touch, a sound, an odour, the contact with a sapid fluid or a ray of light. The effects of the explosions in these delicate cells, reinforced in certain neighbouring nerve-batteries, are transmitted down the nerves as waves of subtle chemical or electrolytic change, and thus reach that wonderful aggregation of organized and co-ordinated explosive cells, the brain. Here it is again reinforced and directed (who, at present, can say how?) along fresh nerve-channels to muscles, or glands, or other organized groups of explosives. And in the brain, somehow associated with the explosion of its cells, consciousness, the mind-element, emerges; of which we need only notice here that it belongs to a wholly different order of being from the physical activities and products with which we are at present concerned.

We must not press the explosion analogy too far. The essential thing seems to be that the protoplasm of the cell has the power of building up complex and unstable chemical compounds, which are perhaps stored in its spongy substance; and that these unstable compounds, under the influence of a stimulus (or, possibly, sometimes spontaneously), break down into simpler and more stable compounds. In the case of muscle-cells, this latter change is accompanied by an alteration in length of the fibres, and consequent movements in the animal, the products of the disruptive change being useless or harmful, and being, therefore, removed as soon as possible. But very frequently the products of explosive activity are made use of. In the case of bone-cells, one of the products of disruption is of permanent use to the organism, and constitutes the solid framework of the skeleton. In the case of the secreting cells in the salivary and other digestive glands, some of the disruptive products are of temporary value for the preparation of the food. It is probable that these useful products of disruption, permanent or temporary, took their origin in waste products for which natural selection has found a use, and which have been gradually rendered more and more efficacious in modes of organic behaviour increasingly complex.

In the busy hive of cells which constitutes what we call the animal body, there is thus ceaseless activity. During periods of apparent rest the protoplasm is engaged in constructive work, building up fresh supplies of unstable materials, which, during periods of apparent activity, break up into simpler and more stable substances, some of which are useful to the organism, while others must be got rid of as soon as possible. From another point of view, the cells during apparent rest are storing up energy to be utilized by the animal during its periods of activity. The storing up of available energy may be likened to the winding up of a watch or clock; it is when an organ is at rest that the cells are winding themselves up; and thus we have the apparent paradox that the cell is most active and doing most work when the organ of which it forms a part is at rest. During the repose of an organ, in fact, the cells are busily working in preparation for the manifestation of energetic action that is to follow. Just as the brilliant display of intellectual activity in a great orator is the result of the silent work of a lifetime, so is the physical manifestation of muscular power the result of the silent preparatory work of the muscle-cells.

It may, perhaps, seem strange that the products of cellular life should be reached by the roundabout process of first producing unstable compounds, from which are then formed more stable substances, useful for permanent purposes as in bone, or temporary purposes as in the digestive fluids. It seems a waste of power to build up substances unnecessarily complex and stored with an unnecessarily abundant supply of energy. But only thus could the organs be enabled to act under the influence of stimuli, and afford examples of corporate behaviour. They are like charged batteries ready to discharge under the influence of the slightest organic touch. In this way, too, is afforded a means by which the organ is not dependent only upon the products of the immediate activity of the protoplasm at the time of action, but can utilize the store laid up during preceding periods of rest.

Sufficient has now been said to illustrate the nature of some of the physical processes which accompany organic behaviour in its corporate aspect. The fact that should stand out clearly is that the animal body is stored with large quantities of available energy resident in highly complex and unstable chemical compounds, elaborated by the constituent cells. These unstable compounds, eminently explosive according to our analogy, are built up of materials derived from two different sources—from the nutritive matter (containing carbon, hydrogen, and nitrogen) absorbed during digestion, and from oxygen taken up from the air during respiration. The cells thus become charged with energy that can be set free on the application of the appropriate stimulus, which may be likened to the spark that fires the explosive.

Let us note, in conclusion, that it is through the blood-system, ramifying to all parts of the body, and the nerve-system, the ramifications of which are not less perfect, that one of the larger and higher animals is knit together into an organic whole. The former carries to the cell the raw materials for the elaboration of its explosive products, and, after the explosions, carries off the waste products which result therefrom. The nerve-fibres carry the stimuli by which the explosive is fired, while the central nervous system organizes, co-ordinates, and controls the explosions, and initiates the elaboration of the explosive compounds. Blood and nerves co-operate to render corporate behaviour possible.