Transcriber's Note

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ANIMAL BEHAVIOUR

BY
C. LLOYD MORGAN, F.R.S.
AUTHOR OF “THE SPRINGS OF CONDUCT,” “HABIT AND INSTINCT,” “PSYCHOLOGY FOR TEACHERS,” ETC. ETC.

ILLUSTRATED

SECOND EDITION
THIRD IMPRESSION

LONDON
EDWARD ARNOLD
1920
(All rights reserved)

PREFACE TO THE FIRST EDITION

My book on “Animal Life and Intelligence” being out of print, I undertook to revise it for a new Edition. As the work of revision proceeded, however, it appeared that the amended treatment would not fall conveniently under the previous scheme of arrangement. I therefore decided to write a new book under the title of “Animal Behaviour.” A few passages from the older work have been introduced, and some of the observations and conclusions already published in greater detail in “Habit and Instinct” have been summarized. But it will be found that these occupy a relatively small space in the following pages.

C. Ll. M.

University College, Bristol,
October 1st, 1900.

CONTENTS

ILLUSTRATIONS

ANIMAL BEHAVIOUR

CHAPTER I
ORGANIC BEHAVIOUR

I.—Behaviour in General

We commonly use the word “behaviour” with a wide range of meaning. We speak of the behaviour of troops in the field, of the prisoner at the bar, of a dandy in the ball-room. But the chemist and the physicist often speak of the behaviour of atoms and molecules, or that of a gas under changing conditions of temperature and pressure. The geologist tells us that a glacier behaves in many respects like a river, and discusses how the crust of the earth behaves under the stresses to which it is subjected. Weather-wise people comment on the behaviour of the mercury in a barometer as a storm approaches. Instances of a similar usage need not be multiplied. Frequently employed with a moral significance, the word is at least occasionally used in a wider and more comprehensive sense. When Mary, the nurse, returns with the little Miss Smiths from Master Brown’s birthday party, she is narrowly questioned as to their behaviour; but meanwhile their father, the professor, has been discoursing to his students on the behaviour of iron filings in the magnetic field; and his son Jack, of H.M.S. Blunderer, entertains his elder sisters with a graphic description of the behaviour of a first-class battle-ship in a heavy sea.

The word will be employed in the following pages in a wide and comprehensive sense. We shall have to consider, not only the kind of animal behaviour which implies intelligence, sometimes of a high order; not only such behaviour as animal play and courtship, which suggests emotional attributes; but also forms of behaviour which, if not unconscious, seem to lack conscious guidance and control. We shall deal mainly with the behaviour of the animal as a whole, but also incidentally with that of its constituent particles, or cells; and we shall not hesitate to cite (in a parenthetic section) some episodes of plant life as examples of organic behaviour.

Thus broadly used, the term in all cases indicates and draws attention to the reaction of that which we speak of as behaving, in response to certain surrounding conditions or circumstances which evoke the behaviour. The middy would not talk of the behaviour of his ship as she lay at anchor in Portland harbour; the word is only applicable when there is action and reaction as the vessel ploughs through a heavy sea, or when she answers to the helm. Apart from gravitation the glacier and the river would not “behave in a similar manner.” Only under the conditions comprised under the term “magnetic field” do iron filings exhibit certain peculiarities of behaviour. And so, also, in other cases. The behaviour of cells is evoked under given organic or external conditions; instinctive, intelligent, and emotional behaviour are called forth in response to those circumstances which exercise a constraining influence at the moment of action.

It is therefore necessary, in a discussion of animal behaviour, that we should endeavour to realize, as far as possible, in every case, first, the nature of the animal under consideration; secondly, the conditions under which it is placed; thirdly, the manner in which the response is called forth by the circumstances, and fourthly, how far the behaviour adequately meets the essential conditions of the situation.

II.—Behaviour of Cells

From what has already been said it may be inferred that our use of the term “behaviour” neither implies nor excludes the presence of consciousness. Few are prepared to contend that the iron filings in a magnetic field consciously group themselves in definite and symmetrical patterns, or that sand grains on a vibrating plate assemble along certain nodal lines because they are conscious of the effects of the bow by which the plate is set in sounding vibration. But where organic response falls under our observation, no matter how simple and direct that response may be, there is a natural tendency to suppose that the behaviour is conscious; and where the response is less simple and more indirect, this tendency is so strengthened as to give rise to a state of mind bordering on, or actually reaching, conviction. Nor is this surprising: for, in the first place, organic responses, even the simplest, are less obviously and directly related to the interplay of surrounding circumstances; and, in the second place, they are more obviously in relation to some purpose in the sense that they directly or indirectly contribute to the maintenance of life or the furtherance of well-being. Now where behaviour is complex and subserves an end which we can note and name, there arises the supposition that it may well be of the same nature as our own complex and conscious behaviour.

Take for example the behaviour of the Slipper-animalcule, Paramecium, one of the minute creatures known to zoologists as Protozoa. The whole animal is constituted by a single cell, somewhat less than one-hundredth of an inch in length, the form and behaviour of which may be readily studied under the microscope. Thousands may be obtained from water in which some hay has been allowed to rot. The surface of the Paramecium is covered with waving hair-like cilia, by which it is propelled through the water, while stiffer hairs may be shot out from the surface at any point where there is a local source of irritation, as indicated at the top of the accompanying figure. Two little sacs expand and contract, and serve to drain off water and waste products from the substance of the cell. Food is taken in at the end of the funnel, shown in the lower part of the figure. The cilia here work in such manner as to drive the particles into and down the tube, and on reaching its inner end these particles burst through into the semi-fluid substance, and circulate therein. Just above the funnel there are two bean-like bodies, the larger of which is known as the macronucleus, the smaller as the micronucleus.

Fig. 1.—Paramecium.

The process of multiplication is by “fission,” or the division of each Paramecium into two similar animalcules. Not infrequently, however, two Paramecia may be seen to approach each other and come together, funnel to funnel; and in each the nuclei undergo curious changes. The macronucleus breaks up, and is scattered. The micronucleus in each divides into four portions, of which three break up and disappear; while the fourth again divides into two parts, one to be retained and the other to be exchanged for the similar micronuclear product of the other Paramecium. The retained portion and that received in exchange then unite to form a new micronucleus. M. Maupas concludes from his careful observations that, in the absence of such “conjugation” in the mid-period of life, Paramecia pass into a state of senility which ends in decrepitude and death. If this be so, conjugation is in them necessary for the continuance of a healthy race.

Here we have what a zoologist would describe as a specialized mode of behaviour of the nuclei; and we have also the behaviour of the minute creatures (which contain the nuclei) as they approach each other and come together in conjugation. Can one wonder that the latter, at any rate, has been regarded as an example of conscious procedure? In truth we do not know in what manner and by what subtle influences the Paramecia are drawn together in conjugation. But it is scarcely logical to base on such ignorance any positive assertion as to conscious attraction. It is better to confess that here is a piece of organic behaviour, the exact conditions of which are at present unexplained.

We may take from the writings[1] of Dr. H. S. Jennings, of Harvard, some account of other modes of behaviour among Paramecia. They largely feed upon clotted masses of bacteria. If a number are placed upon a glass slip, together with a small bacterial clot, they will be seen to congregate around the clot and to feed upon it. All apparently press in so as to reach it, or get as near it as possible. And if a number be placed on another slide without any clot, they soon collect in groups in one or more regions, as in Fig. 2, III. It appears as if they were actuated by some social impulse leading them to crowd together and shun isolated positions. Nay, more; it seems as if, after thus collecting and crowding in to some centre of interest, the attractive influence gradually waned; the group spreads, and the Paramecia are less densely packed; the assembly scatters more and more, but still seems to be retained by an invisible boundary beyond which the little creatures do not pass.

Fig. 2.—Behaviour of Paramecia (after Jennings).

Furthermore, if kept in a jar, the Paramecia crowd up towards the surface where the bacteria clots are floating; and if, beneath the cover glass of a slip on which they are under microscopic examination, a drop of liquid be introduced through a very fine tube, they will seem either to be attracted to it, as in Fig. 2, I., or repelled from it, as in Fig. 2, II., according to its nature. From alkaline liquids they are repelled; to slightly acid drops they are attracted, unless the acidity be too pungent. Heat and cold are alike repellent, and even a drop of pure distilled water forms an area into which the Paramecia do not enter.

With such facts before him, the incautious observer may be led to the conclusion that Paramecia are not only conscious, but endowed with intelligence and volition. Even M. Binet,[2] who occupies a position which should lead him to exercise more caution, tells us that there is not a single infusorian which cannot be frightened, and does not manifest its fear by rapid flight; he speaks of some of these unicellular animals as “endowed with memory and volition,” and possessed of “instinct of great precision;” and he describes the following stages:—

“(1) The perception of an external object;

“(2) The choice made between a number of objects;

“(3) The perception of their position in space;

“(4) Movements calculated either to approach the body and seize it, or to flee from it.”

But when we seem to have grasped his point of view, when we have catalogued the memory, fear, instinct, perception, choice and volition, the whole intelligent edifice crumbles; for we are told that “we are not in a position to determine whether these various acts are accompanied by consciousness, or whether they follow as simple physiological processes.” To most of us fear, memory, choice, volition, imply something more than simple physiological processes; they imply not only consciousness, but highly elaborated consciousness.

Dr. Jennings’s researches show that no such implication can be accepted unless we are prepared to cast aside the trammels of reasonable caution. In the first place, the whole matter of feeding appears to be referable to simple organic behaviour not necessarily involving consciousness. The cilia in the mouth-groove and funnel constantly wave in such a manner as to drive a current of water, together with any particles which float therein, towards the interior; and the particles are then engulphed, no matter what their composition may be. Digestible or indigestible, in they go. There is no selection of the one or rejection of the other. But, as we have seen, the Paramecia collect around a bacterial clot and feed upon it. Surely here there is selection of the nutritious! Apparently not. They collect in just the same way towards a piece of blotting-paper, cotton-wool, cloth, sponge, or other fibrous body, and remain assembled round such an innutritious centre just as long as round a bacterial clot. There seems to be no choice in the matter; contact with any substance gives rise, as an organic response, to the lessening or cessation of the regular movements in all the cilia except those of the mouth-groove and funnel. As the Paramecia swim hither and thither, first one, then another, then more, chance to come in contact with the bacterial clot, the blotting-paper, or other substance, and since the lashing of the cilia is then automatically lessened, there they stay; others find their way to the same spot in the course of their random movements, and they, too, stay; thus many soon collect.

But this does not account for the seemingly social assemblages of Paramecia where there is no such substance to arrest their progress. Dr. Jennings attributes this to the fact that a dilute solution of carbon-dioxide has, what we may call for the present, an attractive influence. If a bubble of air and a bubble of carbon dioxide be introduced into the water in which Paramecia are swimming beneath a cover-glass, the animalcules collect around the carbonic dioxide, but not around the air bubble. At first they press up close to the bubble of carbon dioxide, but gradually form a ring farther and farther from its limiting boundary. This is held to be due to the fact that it is only the dilute solution of carbonic acid that has the peculiar “attraction”—a stronger solution has a different effect. And, as the gas dissolves, the Paramecia collect in a ring just where the solution is sufficiently dilute.

Now carbon dioxide is a product of the organic waste of living substance; it is given off by active Paramecia. Where therefore many are collected together they form a centre of the production of this substance; and when other Paramecia come, in the course of their random movements, into such a centre they remain there and help to swell the numbers in the cluster. If Paramecia be placed in water to which a distinctly reddish tinge is given by mixing it with a small quantity of rosol—a substance which is decolourized by carbon dioxide, and is not injurious to Paramecia—it will be seen that, where the groups are collected, the reddish tinge fades and disappears. As the groups expand, and are less densely packed, the colourless area expands too: and the limits within which the group is circumscribed are also the limits of decolourization. Dr. Jennings considers it beyond question that the assembling of Paramecia is due to the presence in such assemblages of carbonic acid produced by the animals themselves. The first beginning of the crowd may be some small fragment of bacterial clot or other substance.

It would seem, then, that Paramecia are attracted by faintly acid solutions; and here at least there is, it may be urged, an element of choice. But even here, according to Dr. Jennings, there is not only no real choice, but not even any real attraction. What takes place, according to his observations, is briefly as follows. Suppose a faintly acid drop be inserted beneath the cover-glass. Paramecia may almost graze its boundary without being in any way affected by its presence. But in their random movements some, and eventually many, perhaps most, of the little animals chance to enter the faintly acid region; but there is no sign of reaction or response; they swim on across the drop until they reach its further margin. Here a reaction does take place. Instead of proceeding onwards, slowly revolving on its long axis, a Paramecium thus situated jerks backwards by a reversal of all the cilia, at the same time revolving on its axis in a direction opposite to that in which it was before turning. But the cilia of the mouth-groove resume their normal mode of working sooner than the others, and this causes the Paramecium to turn aside. It then goes ahead until it again reaches the boundary at another point, when the same behaviour is seen. The course of such a Paramecium is shown in Fig. 2, IV.

If, instead of a faintly acid drop, a little alkaline liquid be introduced beneath the cover-glass, the Paramecium similarly jerks backward and turns aside on reaching its outer boundary. The turning may carry it away from the alkali, as shown in Fig. 2, V.; but it just as often brings it again towards the drop, especially a large one. It seems to be a matter of chance which result follows. But eventually the little creature sails off, since each time it comes within the influence of the alkaline fluid it jerks back and turns. It appears, then, that when it is swimming in a normal solution a faintly acid liquid does not much modify its behaviour, but an alkaline fluid evokes a reversal of the cilia; and that when it is a slightly acid solution, not only does stronger acid cause reversal, but normal fluid produces a similar result. A reaction of essentially the same kind is in fact called forth by such different stimuli as chemical substances, water heated above the normal temperature, or cooled considerably below it, and fluids which cause changes of internal pressure within the substance of the cell. Nor does it matter where the stimulus is applied. If it be applied at the hinder end the infusorian still jerks backward, though this may drive it into a destructive solution and thus cause death. There is, however, some evidence of different behaviour in some infusorians according as the stimulus is here or there. In other words, the behaviour is to some extent related to the position of the part stimulated.

Furthermore, it may be gathered from Dr. Jennings’s account that there is nothing to lead us to suppose that such free living cells show any indication of what may be regarded as the keynote of intelligent behaviour. They do not profit by experience. They exhibit organic reactions which may be accompanied by some dim form of consciousness, but which do not seem to be under the guidance of such consciousness, if it exist.

One of the first lessons which the study of animal behaviour, in its organic aspect, should impress upon our minds is, that living cells may react to stimuli in a manner which we perceive to be subservient to a biological end, and yet react without conscious purpose—that is to say, automatically. The living cell assimilates food and absorbs oxygen, it grows and subdivides, it elaborates secretions, produces a skeletal framework or covering, rids itself of waste products, responds to stimuli in a definite fashion, moves hither and thither at random, its functional activities being stimulated or checked by many influences; and yet this varied life may give no evidence of a guiding consciousness: if purpose there be, it lies deeper than its protoplasm, deeper than the dim sentience which may be present or may be absent—we cannot tell which.

And when the cells are incorporated in the body of one of the higher animals, instead of each preserving a free and nomad existence; when they become the multitudinous constituents of an organic republic with unity of plan and unity of biological end, then the behaviour of each is limited in range but perfected within that range, in subservience to the requirements of the more complex unity. The muscle cell contracts, the gland-cell secretes, the rods and cones of the retina respond to the waves of light, and all the normal responses of the special cells go on with such orderly regularity that the term behaviour seems scarcely applicable to reactions so stereotyped. But the physiologist and the physician know well that such uniformity of response is dependent on uniformity of conditions. A little dose of some drug will profoundly modify and render abnormal the procedure which was before so mechanical in its exactitude; and we are thus led to see how dependent the orderly behaviour really is on the maintenance of certain surrounding conditions.

Moreover, the existence of every cell in the body corporate is the outcome of a process of division involving a special mode of behaviour in the nucleus, of which we are only beginning to guess the meaning and significance, and of which we seek in vain to find an explanation in mechanical terms. And when we trace these divisions back to their primary source in the fertilized ovum, we find changes and evolutions in the nuclear matter of which it can only be said that the more they are studied the more complex and varied do they appear.

The egg, or ovum, is a single cell produced by the female, and varying much in size, according to the amount of food-yolk with which it is supplied. Like other cells, it has a nucleus, and this undergoes changes which are definitely related to the fertilization of the ovum, which we describe as the biological end. Such preparatory changes for a future contingency are especially characteristic of organic behaviour. There is nothing like it in the mineral kingdom. The nucleus divides into two parts, one of which passes out of the ovum and is lost. The nucleus again divides, and again one part passes out and is lost. Thus only one quarter of the original amount of nuclear matter remains. Now, division of the nucleus occurs whenever an animal cell divides; but in this case (apart from details which would here be out of place) there is this difference. During the ordinary division of cells there are found in the nucleus a definite number of curved rods, and this number is constant for any given species; but in the nucleus which remains in the ovum after three parts of its substance are lost, the number of rods has been reduced to half that which is common to the species. The egg is now ready for fertilization. A minute active cell, which is produced by the male, and which also has only half the normal number of rods, enters the ovum. The two nuclei approach each other, and give rise to the single nucleus of the fertilized ovum, which thus has the full number of rods—half of them derived from one parent, half from the other parent. The sperm cell of the male adds little to the store of protoplasm in the ovum; but it introduces a minute body, which seems to initiate subsequent divisions of the cell. The nature of these divisions may be seen in the accompanying diagrammatic figure. In A the cell is just preparing to divide. Above the nucleus is the minute body (centrosome) just spoken of, which has already divided. In the nucleus the matter of which the rods will be constituted is net-like. In B this net-work has taken on the new form of a coiled thread, while the divided body above is associated with a spindle of delicate fibres. In C the membrane round the nucleus has disappeared, and the coiled thread has broken up into curved rods (chromosomes), four of which are shown. The two halves of the minute body form the centres of radiating stars. In D each curved rod has split along its length, and the two parts are being drawn asunder towards the centres of the two stars; the cell itself is beginning to divide. In E the process is carried a step further, while in F the cell has completely divided into two: the rods have disappeared as such, and are replaced by a net-work; a new nuclear membrane has been formed, and the minute body has again divided preparatory to the further division of the cell.

Fig. 3.—Cell-division.

Such, stripped as far as possible of technicalities, are some of the facts concerning the behaviour of cells and their nuclei during the process of cell-multiplication. No good purpose would be subserved by pretending that we fully understand them. The splitting of the rods does indeed seem an efficient means to the end of securing a fair division of the nuclear substance, which, according to many biologists, is the organic bearer of hereditary qualities in the cells. But that is nearly all that we can say. Is the process accompanied by some form of sentience? We do not know. That it is controlled and guided by any consciousness in the cell is most improbable. But if it be a purely organic and unconscious process it should at least impress on our minds the fact that such organic behaviour may reach a high degree of delicacy and complexity.

III. Corporate Behaviour

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.

IV.—The Behaviour of Plants

A short parenthetic section on the behaviour of plants may serve further to illustrate the nature of organic behaviour. We have seen that Paramecium is apparently attracted by faintly acid solutions, and have briefly considered Dr. Jennings’s interpretation of the facts disclosed by careful observation. In the ferns the female element, or ovum, is contained in a minute flask-shaped structure (archegonium), in the neck and mouth of which mucilaginous matter, with a slightly acid reaction, is developed; and this is said to exercise an attractive influence on the freely swimming ciliated male elements, or spermatozoids, which are necessary for fertilization. “Now, it has been shown by experiment that the spermatozoids of ferns are attracted by certain chemical substances, and especially by malic acid. If artificial archegonia are prepared (consisting of tiny capillary glass-tubes) and filled with mucilage to which a small quantity of this acid has been added, they are found, when placed in water containing fern-spermatozoids, to exercise the same attraction upon them which the real archegonia exercise in nature. The malic acid gradually diffuses out into the water, and the spermatozoids are influenced by it, so that they move in the direction in which the substance is more concentrated, i.e. towards the tube. Although it cannot be proved that the archegonia themselves contain malic acid, as they are too small for a recognizable quantity to be obtained from them, yet there can be little doubt that the natural archegonia owe their attractive influence to the same chemical agent which has proved efficacious in experiment.”[5] In the light of Dr. Jennings’s observations, it is perhaps not improbable that this so-called attractive influence is similar to that seen in Paramecium; and that the spermatozoids enter the organic acid in the course of their random movements, and there remain. Be that as it may, the male elements collect in the mucilaginous mass, and pass down the neck of the flask until one reaches and coalesces with the female element, or ovum, and effects its fertilization. Here we have organic behaviour unmistakably directed to a biological end—behaviour which may indeed be accompanied by some dim form of consciousness, but which is due to a purely organic reaction. It is scarcely satisfactory to say that the spermatozoids “possess a certain power of perception, by which their movements are guided.”[6] If consciousness be present, it is probably merely an accompaniment of the response, and has no directive influence on its nature and character.

In the higher plants, as in the higher animals, the differentiation and the orderly marshalling of the cell-progeny arising from the coalescent male and female elements, afford, during development, examples of corporate organic behaviour which can be more readily described than explained, but which not less clearly subserve definite biological ends, and in many cases, such as the direction of growth in radicles and roots, the curling of tendrils, and the reaction to the influence of light and warmth, are related to and evoked by the environing conditions. More closely resembling familiar modes of behaviour in animals are such movements as are seen in the “tentacles” which project from the upper surface and margin of the Sun-dew leaf. Their knobbed ends secrete a sticky matter, which glistens in the sun, and to which small foreign bodies readily adhere. If particles of limestone, sand, or clay, such as may be blown by the wind, touch and stick to these knobs, there follows an exudation of acid liquid, but no marked and continuous change occurs in the position of the tentacles. But should an insect alight on the leaf, or a small piece of meat be placed upon the tentacles, not only is there a discharge of acid juice, but a ferment is also produced, which has a digestive action on the nitrogenous matter. Slowly the tentacle curves inwards and downwards, as one’s finger may bend towards the palm of one’s hand; neighbouring tentacles also turn towards and incline on to the stimulating substance; then others, further off, behave in a similar way, until all the tentacles, some two hundred in number, are inflected and converge upon the nitrogenous particle. Nay, more: “When two little bits of meat are placed simultaneously on the right and left halves of the same Sun-dew leaf, the two hundred tentacles divide into two groups, and each one of the groups directs its aim to one of the bits of meat.”[7]

Fig. 6.—Sun-dew (Drosera). Leaf (enlarged) with the tentacles on one side inflected over a bit of meat placed on the disc. (From Darwin’s “Insectivorous Plants.”)

The movements, though slow, are orderly, methodical, and effective, the secretions of many glands being brought to bear on just those substances which are capable of digestion and absorption by the plant. The seemingly concerted action is moreover due to an organic transmission of impulses from cell to cell—a transmission accompanied by visible changes in a purple substance contained within the cells. In the Sun-dew any tentacle may form the starting-point of the spreading wave of impulse. But in the Venus’s Fly-trap there are six delicate spines, the slightest touch on any one of which causes the two halves of the specially modified leaf-end to fold inwards on the midrib as a hinge. The transmission of impulse is more rapid, the trap closing in a few seconds; and electric currents have been observed to accompany the change. Tooth-like spines at the edge of the trap interlock, and serve to prevent the escape of small insects, while short-stalked purple glands secrete an acid digestive juice. Division of labour has been carried further; and organic behaviour, not less purposive, is carried out in a manner even more effective.

Fig. 7.—Venus’s Fly-trap (Dionæa). Leaf viewed laterally in its expanded state. (From Darwin’s “Insectivorous Plants.”)

In other plants adaptive movements are well known. “Few phenomena have such a peculiar appearance as the movements which occur in the sensitive Oxalis when rain comes on. Not only do the leaflets on which the finest rain-drops fall fold together in a downward direction, but all the neighbouring ones perform the same movement, although they have not themselves been shaken by the impact of the falling drops. The movement is continued to the common leaf-stalk bearing the numerous leaflets. This also bends down towards the ground. The rain-drops now slide over the bent leaf-stalk and down over the depressed leaflets, and not a drop remains behind on their delicate surfaces.”[8] The waves of impulse are said to be transmitted along definite lines, and to cause the expulsion of water from certain cells at the point of insertion of the leaflets or leaf-stalks, rendering them flaccid.

Fig. 8.—Flower of Valisneria.

Appealing even more strongly to the popular imagination, though probably not of deeper biological significance, is the behaviour of plants in relation to the essential process of fertilization. Only two examples can here be cited. Valisneria spiralis is an aquatic plant, with long submerged strap-like leaves, which grows in still water in Southern Europe. The female flower is enclosed in two translucent bracts, which form a protective bladder so long as the flower is beneath the surface of the water; but the flower-stalk continues to grow until the flower reaches the surface, when it becomes freely exposed by the splitting of the bracts. There are three boat-shaped sepals, which act as floats; three quite minute petals; and three large fringed stigmas, which project over the abortive petals in the space between the boat-like sepals. The flower is now ready for fertilization.

The male flowers, which are developed on different individuals from those which produce the female flowers, grow in bunches beneath an investing bladder. The stalk does not elongate, so that the bladder never rises far above the bottom, and remains completely submerged. Here the bladder bursts, and the male flowers, with short stalks, are detached. Each has three sepals, which enclose and protect the stamens. The separated flower now ascends to the surface, the sepals open and form three hollow boats, by means of which the flower floats freely, while the two functional stamens project upwards and somewhat obliquely into the air, exposing the large sticky pollen-cells. Blown hither and thither by the wind, these little flower-boats “accumulate in the neighbourhood of fixed bodies, especially in their recesses, where they rest like ships in harbour. When the little craft happen to get stranded in the recesses of a female Valisneria flower, they adhere to the tri-lobed stigma, and some of the pollen-cells are sure to be left sticking to the fringes on the margins of the stigmatic surface.”[9]

This is a good example of purely organic behaviour admirably adapted to secure a definite and important biological end. Few will be likely to contend that it is even accompanied by, still less under the guidance of, any conscious foresight on the part of the plant. And the lesson it should teach is that, in the study of organic behaviour, adaptation to the conditions of existence is not necessarily the outcome of conscious guidance.

It is well known that the orchids exhibit, in their mode of fertilization, remarkable adaptations by which the visits of insects are rendered subservient to the needs of the plant. In the Catasetums, for example, the male flower may be described as consisting of two parts—a lower part, the cup-like labellum (Fig. 9, l), which constitutes a landing-stage on which insects may alight; and an upper part, the column (Fig. 9, c), surrounded by the upper sepal and petals. In the upper part of the column the pollen-masses are borne at one end of an elastic pedicel, at the other end of which is an adhesive disc, and the rod is bent over a pad so as to be in a state of strain. The disc is retained in position by a membrane with which two long tubular horns (Figs. 9, h; 10, an) are continuous. These project over the labellum, where insects alight to gnaw its sweet fleshy walls, and if they be touched, even very lightly, they convey some stimulus to the membrane which surrounds and connects the disc with the adjoining surface, causing it instantly to rupture; and as soon as this happens, the disc is suddenly set free. The highly elastic pedicel then flirts the disc out of its chamber with such force that the whole is ejected, sometimes to a distance of two or three feet, bringing away with it the two pollen-masses. “The utility of so forcible an ejection is to drive the soft and viscid cushion of the disc against the hairy thorax of the large hymenopterous insects which frequent the flowers. When once attached to an insect, assuredly no force which the insect could exert would remove the disc and pedicel, but the caudicles [by which the pollen-masses are attached] are ruptured without much difficulty, and thus the balls of pollen might readily be left on the adhesive stigma of the female flower.”[10]

Fig. 9.—Flower of Catasetum; c, column; h, horns; l, labellum.

Here again we have adaptive behaviour of exquisite nicety, and we have the transmission of an impulse very rapidly along the cells of the irritable horns, followed by the sudden rupture of a membrane. Beautiful, however, as is the adaptation, effective as it is to a definite biological end, the organic behaviour does not afford any indication of the guidance of consciousness. Among plants we have many interesting and admirable examples of organic behaviour; but nowhere so much as a hint of that profiting by individual experience which is the criterion of the effective presence of conscious guidance and control.

Fig. 10.—Catasetum; C, diagram of column; a, anther; an, horn; d, adhesive disc; f, filament of anther; g, ovarium; ped, pedicel; D and E, pollinium; p, pollen-mass. (From Darwin’s “Orchids.”)

V.—Reflex Action

It is sometimes said that the tentacles of the Sun-dew leaf indicate a primitive kind of reflex action in plants, and that they afford evidence of discrimination. “It is,” says Romanes, “the stimulus supplied by continuous pressure that is so delicately perceived, while the stimulus supplied by impact is disregarded.”[11] And, comparing this with what is observed in the Venus’s Fly Trap, he says: “In these two plants the power of discriminating between these two kinds of stimuli has been developed to an equally astonishing extent, but in opposite directions.”[12] It is well, however, to avoid terms which carry with them so distinctively a conscious implication as “discrimination” and “perception” do for most of us. Just as the photographer’s film reacts differently according to the quality of light-rays, violet or red, which reach it, so do many organic substances react differently to stimuli of different quality, irrespective of their intensity. The “discrimination” of plants and of some of the lower animals is of this kind, and it is better to speak of it simply as differential reaction. There can then be no chance of its being confused with conscious choice.

Nor should the movements of the Sun-dew tentacles or of those of the Sea-anemone be termed in strictness reflex action. As originally employed by Marshall Hall, and, since that time, by common consent, reflex action involves a differentiated nervous system. There is, first, an afferent impulse from the point of stimulation passing inwards to a nerve-centre; secondly, certain little-understood changes within this centre; and thirdly, an efferent impulse from the centre to some organ or group of cells which are thus affected. In plants there is no indication of anything analogous to this specialized mode of response. The impulse passes directly from the point of stimulation to the part affected without the intervention of anything like a nerve-centre. In the sensitive Oxalis the impulse passes directly to the point of insertion of the leaflet or leaf-stalk; in Catasetum, from the horn to the retaining membrane; in the Sun-dew, from the affected tentacle to those in its neighbourhood. Even in the Sea-anemone, though there is a loosely diffused nervous system, the passage of the impulse from one part of the circlet of tentacles to other parts, seems to follow a direct rather than a reflex course, and there do not appear to be any specialized centres by which the impulses are received and then redistributed.

In all animals in which well-differentiated nervous systems are found, in which there are distinct nerve-fibres and nerve-centres, reflex actions, simple or more complicated, occur. They form the initial steps leading up to the highest types of organic behaviour. So long as the nervous arcs—afferent fibres, nerve-centre, and efferent fibres—remain intact reflex acts may be carried out with great precision and delicacy, even when the higher centres, which we believe to be those of conscious guidance and control, have been destroyed. When, for example, the whole of the brain of a frog has been extirpated and the animal is hung up by the lower jaw, if the left side be touched with a drop of acid the left leg is drawn up and begins to scratch at the irritated spot, and when this leg is held, the other hind leg is, with seemingly greater difficulty, brought to bear on the same spot. “This,” says Sir Michael Foster, “at first sight looks like an intelligent choice.... But a frog deprived of its brain so that the spinal cord only is left, makes no spontaneous movements at all. Such an entire absence of spontaneity is wholly inconsistent with the possession of intelligence.... We are therefore led to conclude that the phenomena must be explained in some other way than by being referred to the working of an intelligence.”[13] But if we concede that intelligence is absent, may there not at least be some consciousness? Sir Michael Foster’s reply to such a question goes as far as we have any justification for going, even when we give free rein to conjecture. “We may distinguish,” he says, “between an active continuous consciousness, such as we usually understand by the term, and a passing or momentary condition, which we may speak of as consciousness, but which is wholly discontinuous from an antecedent or from a subsequent similar momentary condition; and indeed we may suppose that the complete consciousness of ourselves, and the similarly complete consciousness which we infer to exist in many animals, has been evolved out of such a rudimentary consciousness. We may, on this view, suppose that every nervous action of a certain intensity or character is accompanied by some amount of consciousness which we may, in a way, compare to the light emitted when a combustion previously giving rise to invisible heat waxes fiercer. We may thus infer that when the brainless frog is stirred by some stimulus to a reflex act, the spinal cord is lit up by a momentary flash of consciousness coming out of the darkness and dying away into darkness again; and we may perhaps infer that such a passing consciousness is the better developed the larger the portion of the cord involved in the reflex act and the more complex the movement. But such a momentary flash, even if we admit its existence, is something very different from consciousness as ordinarily understood, is far removed from intelligence, and cannot be appealed to as explaining the ‘choice’ spoken of above.”[14]

These sentences indicate with sufficient clearness the distinction, more than once hinted at in the foregoing pages, between consciousness as an accompaniment, and consciousness as a guiding influence. We shall have more to say in this connection in subsequent chapters. The experiment with the frog shows, at any rate, that reflex actions, of a distinctly purposive nature, may be carried out when the centres, which are believed to exercise conscious control and guidance have been destroyed. It is said that in man, when, owing to injuries of the spine, the connection between the brain and the lower part of the spinal cord have been severed, tickling of the foot causes withdrawal of the limb without directly affecting the consciousness of the patient. But in all such cases we are dealing with a maimed creature. The living frog or man, healthy and intact, is, presumably in the one case, certainly in the other, conscious of these reflex actions, and can exercise some amount of guidance and control over them. In man this is unquestionably the case. But granting that the brain is the organ of conscious control, granting that it can receive impulses from and transmit impulses to the reflex centres, no more is here implied, and no more can be legitimately inferred, than that the kind of organic behaviour we call “reflex action” is in the higher animals in touch with the guiding centres. We have no ground for assuming that in reflex action there is any power of intelligent guidance independent of that which is exercised by the brain or analogous organ. In brief, reflex acts, in animals endowed with intelligence, may be regarded as specialized modes of organic behaviour; which are in themselves often characterized by much complexity; which subserve definite biological ends; which are effected by subordinate centres capable of transmitting impulses to, and receiving impulses from, the centres of intelligent guidance; and which, as responses confined to certain organs or parts of the body, form elements in the wider behaviour of the animal as a whole.

VI.—The Evolution of Organic Behaviour

The interpretation of organic behaviour in terms of evolution mainly depends on the answer we give to the question: Are acquired modes of behaviour inherited? A negative answer to this question is here provisionally accepted. But the premisses from which this conclusion is drawn are too technical for discussion in these pages. It must suffice to state as briefly as possible what this conclusion amounts to, and to indicate some of the consequences which follow from its acceptance.

The fertilized egg gives origin, as we have seen, to the multitude of cells which build up the body of one of the higher animals. There are, on the one hand, muscle-cells, gland-cells, nerve-cells, and other constituents of the various tissues; and there are, on the other hand, the reproductive cells—ova or sperms, as the case may be. Now, every cell in the developed animal is a direct descendant of the fertilized egg. But of all the varied host only the reproductive cells take any direct share in the continuity of the race. Hereditary transmission is therefore restricted to the germinal substance of these reproductive cells. Trace the ancestry of any cell in the adult body, say a nerve-cell, and you reach the fertilized ovum. Trace back the ancestral line yet further, and you follow a long sequence of reproductive cells, or, at least, of cells which have undergone but little differentiation; but never again will you find, in the course of a genealogy of bewildering length, a nerve-cell. Such a tissue-element is a descendant, but cannot become an ancestor; it dies without direct heirs.

It is universally admitted that the bodily structures are subject to what is termed modification under the stress of environing circumstances. The muscles may acquire unusual strength by use and exercise; the nerve-centres may learn certain tricks of behaviour in the course of individual life; and other structures may be similarly accommodated to the conditions which affect them. To such modifications of structure or function in the organs or parts the term acquired is primarily applied. The tissues have thus a certain amount of organic plasticity, through which they are adjusted to a range of circumstances varying in extent. They are able to acquire new modes of behaviour. But the cells of which they are composed are off the line of racial descent. They leave no direct heirs. When the body dies the modifications of behaviour acquired by its parts perish with it. Only if in some way they exercise what we may term a homœopathic influence on the germinal substance can the accommodation they have learnt be transmitted in inheritance. By a homœopathic influence is here meant one that is of such a nature as to communicate to the germinal substance, the seeds of similar changes of structure or function. And of the occurrence of any such homœopathic influence there is no convincing evidence.

Logically contrasted with the modifications of the tissues, dependent on organic plasticity, are the variations which arise from the nature and constitution of the reproductive cells. How they arise cannot here be discussed. But they are, it is believed, subject to the influence of natural selection, which has guided them, throughout the ages of organic evolution, in the directions they have taken; disadvantageous variations having been eliminated, and favourable variations surviving in the struggle for existence. Such modes of behaviour as are congenital and are due to hereditary transmission are therefore the outcome of variations which have been selected generation after generation. And the fit adjustment of this congenital behaviour to the needs of life is termed adaptation. It is here assumed that modifications of behaviour in one generation are not inherited, and therefore contribute nothing to the store of adaptive behaviour in the next generation.

It must not, however, be supposed that the provisional acceptance of this conclusion involves the denial of all connection of any sort between accommodation and adaptation. When we remember that plastic modification and germinal variation have been working together, in close association, all along the line of organic evolution to reach the common goal of adjustment to the circumstances of life, it is difficult to believe that they have been throughout the whole process altogether independent of each other. Granted that acquired modifications, as such, are not directly inherited, they may none the less afford the conditions under which coincident variations escape elimination. By coincident variations I mean those the direction of which coincides with that taken by modification. The survival of an animal depends on its adjustment to the circumstances of its life, no matter how this adjustment is secured. And this survival would in the long run be better secured, we may suppose, where the two methods of adjustment were coincident and not conflicting;[15] just as a man who not only acquires by his own exertions a fortune but also inherits one, is better off than his neighbour, of equal business capacity, who is entirely dependent on his own exertions. The inheritance of a small capital may, indeed, make just the difference between success and failure. Even with it, if he had no power of acquiring more, he might remain a poor man. Inheritance and acquisition combined may best lead to survival in competition. Thus modification may supply the conditions under which coincident variations are favoured, and, given time, to reach step by step, through natural selection, a fully adaptive level. If this be so we may accept many of the facts adduced by the transmissionist in favour of the direct inheritance of acquired characters, and at the same time interpret them on selectionist principles.

If, however, acquired characters are not hereditary the method of natural selection in racial progress is curiously indirect. Apart from the preservation of their fecundity, the cells on which the continuity of life, in all the higher animals, depends, have themselves taken little part in the struggle for existence. Just as in the forest tree, the firmly implanted roots, the sturdy stem, and the strong branches have to bear the stress of the winter storm, that the flowers of spring may ripen the seeds which contain the potentiality of all this strength; so do muscle, sinew, and brain secure the survival of the animal, that his descendants may carry on the struggle. One may liken the cellular constituents of the animal to a hive of bees with fertile drones and queen, and sterile workers. It is on the exertions of the latter that, in the struggle for existence, the continued existence of the swarm depends, while it is by the pairing of the fertile drone and queen that the continuity of the race is secured. No worker can transmit the qualities which are so essential to the well-being of the community. But in the eggs of their sister the queen-mother these qualities lie dormant. And since the race is one race, the workers by their exertions contribute indirectly to the maintenance of those hereditary aptitudes to which they are unable to contribute directly. For it is essential to bear in mind that they not only work for their own generation, but they determine the course of heredity. Picture two such communities set in an environment which intensifies the struggle for existence. The one is strong, healthy, and vigorous; the other in all respects the reverse. The incidence of the battle of life falls mainly on the workers. If they succumb in the one group their fertile queen either perishes, or gives rise to a poor stock, certain in the long run to be eliminated. But the vigorous workers in the other group survive and secure, too, the survival of their queen, who, since she is also their sister, bears, in her ovaries, the good seed from which a new generation of vigorous workers shall be developed. Thus though the sterile bees contribute nothing directly to the heredity of the race, they indirectly determine the direction which that heredity shall take. So, too, in the higher animals, the reproductive cells are the fertile sisters of a host of sterile body cells, on which the main incidence of the struggle for existence falls. Their sterility precludes their directly contributing to the success of future cell-generations; but in protecting their fertile sisters, the reproductive cells, they are really determining the lines along which the evolution of the race shall continue.

Acquired characters may thus be regarded as the results of those accidents, fortunate or the reverse as the case may be, which happen to the body, and more or less modify its outward form or hidden structure, and its modes of organic behaviour; but which, as such, have no direct effects for better or worse on the germinal substance. All that the plant or animal can be is due to heredity; all that it is, to heredity and circumstance. Even the ability to yield to circumstance is part of heredity’s dower. Fortunate, then, the plant or animal that inherits such definiteness of structure and behaviour as may fit it to its station, together with such plasticity as may enable it to accommodate itself to those changes of environing conditions which may fall to its lot.

One more point must be noticed in connection with this difficult and puzzling subject. The acceptance of the conclusion that acquired modes of behaviour are not hereditary nowise commits us to the belief that heredity has nothing whatever to do with them. Though what is acquired may not be transmitted, what one may term the acquisitiveness is unquestionably inherited. Though this, that, or the other acquired mode of behaviour may have no direct descendants, the power of acquiring any one of them under the appropriate circumstances is handed on as an invaluable legacy. Just as the mirror which has reflected a fleeting scene retains no lasting image of the bygone events, so heredity may retain no impress of acquired characters; but just as the mirror keeps its power of reflecting such scenes, so does heredity transmit the power of acquiring such characters. As the leaves of the oak are renewed each successive spring, so may acquired modes of behaviour be repeated in each successive generation if only the requisite conditions recur in due season.

From what has preceded it may, therefore, be inferred that organic behaviour may arise either through modifications occurring in the plastic tissues, or through variations having their origin in the germinal substance. Broadly speaking, however, we may regard as predominantly due to adaptation those congenital modes of behaviour and those organic responses which on their first occurrence are relatively definite in character, and which are directed to a biological end, for whose attainment the tissues have had no preparatory training; and we may regard as predominantly due to accommodation those responses which are, so to speak, learnt by the tissues in the course of individual life. Both are dependent on heredity, but in different ways. What the animal owes to heredity may, indeed, as I have elsewhere said,[16] be classified under two heads. Under the first will fall those relatively definite modes of behaviour which fit the animal to deal at once, on their first occurrence, with certain essential or frequently recurring conditions of the environment. Under the second head will fall the power of dealing with special circumstances as they arise in the course of a varied life. The former may be likened to the inheritance of specific drafts for definite needs which are sure to arise in the conduct of life; the latter to the inheritance of a legacy which may be drawn upon for any purpose as occasion may demand. If the need becomes habitual the animal may, so to speak, instruct his banker to set aside a specific sum to meet it as it arises. But this arrangement is a purely individual matter, dictated by experience, and in no wise enjoined by the original terms of the bequest. And both types are fostered by natural selection which develops (a) such congenital definiteness of response, and (b) such innate plasticity, as are advantageous under the conditions of existence; uniform conditions tending to emphasize the former, variable conditions the latter.

Difficult as it may be to earmark the items of the organic bequest—to say that, of the sum of energy expended in any given case of organic behaviour, so much is due to a specific draft definitely assigned in heredity for this particular purpose, and so much is contributed from the general legacy of innate plasticity,—it none the less conduces to clear thinking to emphasize the logical distinction between them, so long as it is steadily borne in mind that logical distinction does not imply biological separation. The animal, with all its varied modes of behaviour, is an organic whole, and as an organic whole it has been developed from the fertilized egg. The very same tissues which exhibit congenital modes of behaviour are capable also of acquiring new responses and playing their part in accommodation. We have not one set of organs which are the products of variation and another set which result from modification. Our study would no doubt be simplified if this were the case; but it is not so. And we must take the animal as we find it, presenting varied behaviour of complex origin. Even the reflex nervous centres, which are concerned in responses so automatic as to suggest a stereotyped structure of distinctively germinal origin, are also, as we saw at the close of the last section, in close touch with those centres of control which are associated with the supreme power of accommodation arising from the possession of consciousness.

CHAPTER II
CONSCIOUSNESS

I.—The Conscious Accompaniments of Certain Organic Changes

It is possible that all organic behaviour is accompanied by consciousness. But there is no direct means of ascertaining whether it is so or not. This is, and must remain, a matter of more or less plausible conjecture. We have, indeed, no direct knowledge of any consciousness save our own. Undue stress should not, however, be laid on this fundamental isolation of the individual mind. We confidently infer that our fellow-men are conscious, because they are in all essential respects like us, and because they behave just as we do when we act under its guiding influence. And on similar grounds we believe not less confidently that many animals are also conscious. But how far we are justified in extending this inference it is difficult to say. Probably our safest criterion is afforded by circumstantial evidence that the animal in question profits by experience. If, as we watch any given creature during its life-history, we see at first a number of congenital or acquired modes of behaviour, we may not be able to say whether they are accompanied by consciousness or not; but if we find that some of these are subsequently carried out more vigorously while others are checked, we seem justified in the inference that pleasurable consciousness was associated with the results of the former, and disagreeable consciousness with those of the latter. When we see that a chick, for example, pecks at first at any small object, it is difficult to say, on these grounds, whether it is a sentient animal or only an unconscious automaton; and if it continued to behave in a similar fashion throughout life, our difficulty would still remain. But when we see that some objects are rejected while others are selected, we infer that consciousness in some way guides its behaviour. The chick has profited by experience. But even this is clearly only a criterion of what we may term effective consciousness. There may be sentience which is merely an accompaniment of organic action without any guiding influence on subsequent modes of behaviour. In that case it is not effective; and whether it is present or not we have no means of ascertaining.

We seem also to be led to the conclusion, both from a priori considerations and from the results of observation, that effective consciousness is associated with a nervous system. Its fundamental characteristic is control over the actions, so that some kinds of behaviour may be carried out with increased vigour, and others checked. And it is difficult to see how this can take place unless the centres of control are different from those over which they exercise this influence. If we are to understand anything definite by the guidance of consciousness, we must conceive it as standing apart from and exercising an overruling influence over that which it guides. This is unquestionably an essential characteristic of consciousness, as generally understood by those who take the trouble to consider its relation to behaviour; and though some would seek to persuade us that a mere accompaniment of consciousness can somehow determine the continuance or discontinuance of organic behaviour, it is difficult to see how this can be the case. The accompaniment of air-tremors can no more influence the vibrations of a sounding string than an accompaniment of consciousness can affect the nature of the organic changes in the tentacles of the Sun-dew leaf.

And if, instead of trusting to such general a priori considerations, we study with attention the conditions under which an animal so behaves as to lead us to infer that it profits by experience, we find that it is not the consciousness that accompanies the behaviour which leads to future guidance, but the consciousness that arises from the results of the behaviour. Let us willingly grant that the newly hatched, and as yet inexperienced chick, when it pecks at a small object is conscious of a visual impression, and is conscious also of movements of its neck and beak. These do not constitute the experience by which it profits. This is provided by the results of the pecking, according as the morsel seized is nice or nasty. We may say, in popular language, that the little bird remembers when it sees a similar object that the former results were pleasant or distasteful, as the case may be; and that it is through this remembrance that future guidance is rendered possible. But all the evidence that we possess goes to show that the sensory centres, stimulated by what we will assume to be the taste of the morsel, are different from those which are affected by sight, and the movements concerned in pecking. So that the consciousness which is effective in guiding future action is an accompaniment of the stimulation of centres that are different from those concerned in the behaviour over which guidance is exercised. And if this interpretation of the observed facts be correct, it supports the conclusions reached from a priori considerations. It seems further to show that, not only is a nervous system necessary for the occurrence of controlled behaviour, but that no little complexity in its intercommunications is essential.

It may be urged that the chick’s behaviour which has been selected for purposes of illustration, and the interpretation we have put upon it, throws too much stress on remembrance, so called, and further gives the false impression that all experience must be for future guidance. There are surely numberless cases, it will be said, in which nothing of the nature of distinct memory is involved, and in which the guidance of consciousness is exercised at once over present behaviour, without any postponement to the future. Even omitting for the present the former point, the formula implied—that present experience is for future guidance—cannot be accepted in view of the familiar fact that present experience is constantly influencing present behaviour. Practically speaking, this is perfectly true: because, practically, under the term present we include quite an appreciable period of time—say, a few seconds, or even minutes. If we narrow our conception of the present, as is commonly done in philosophical discussions, to the boundary line between past and future, then it will be seen that even the guidance of what in popular speech is called present behaviour is really exercised on the subsequent phases of that behaviour. At the risk of some technicality our position must be explained a little more fully. It is assumed that the data of consciousness are afforded by afferent impulses coursing inwards from the organs of special sense, or those concerned in responsive movements. This conclusion rests on such a wide body of psychological inference that it may be accepted without discussion, at any rate for our immediate purpose. The efferent impulses, those which effect the orderly contraction of the muscles, are unconscious; but when the movement is produced afferent impulses course inwards from the parts concerned in the behaviour, and these may then contribute data to consciousness.

Now let us suppose that a chick, which has been hatched in an incubator, be removed some twelve hours after birth, held in the hands for a few minutes until its eyes have grown accustomed to the light, and placed on a table near some small pieces of hard-boiled egg. Let us watch its behaviour and endeavour to interpret it. We shall have occasion to consider hereafter whether the conscious experience of parents and ancestors is inherited as such; for the present we will assume that it is not. The chick has to acquire for itself its own experience. A piece of egg catches the eye of the little bird, which then pecks at it, and just fails to seize it. Here is a piece of congenital organic behaviour. Taken by itself one might find it difficult to say whether it is accompanied by consciousness or not, just as one finds it difficult to say whether the closure of the Venus’s Fly-trap is conscious. But the subsequent behaviour of the chick leads us to infer that it is a sentient animal; and we may, therefore, fairly assume that it is sentient from the first. Dividing the course of the observed behaviour into stages, we may say that the first stage is that in which the chick receives a visual stimulus accompanied by a sensation of sight. Upon this there rapidly follows the second stage, when the bird pecks, and its experience is widened by new data of consciousness derived from a group of motor sensations; and upon this, again, there follows the third stage, when sensations come in from the morsel of egg which the chick touched but just failed to seize. After a pause the chick strikes again. But we have not a mere repetition of the former sequence of stages. The visual stimulus at first fell upon the eye of a wholly inexperienced bird; now it falls upon the eye of one that has gained experience of pecking and tasting. What we may call the conscious situation has completely changed, at all events if we assume that the items of consciousness, including as essential the consciousness of behaviour, do not remain separate and isolated, but have coalesced into a group through association. And in this group the consciousness of behaving is perhaps the most important element in the situation, making it of practical value. What psychologists term the presentative visual stimulus, now calls up re-presentative elements, motor and gustatory; and these place the situation in a wholly new aspect. They give it what Dr. Stout terms “meaning.” On the second or third attempt the chick seizes and swallows the morsel of egg. Its experience is yet further widened; and thereafter the situation has other new elements. Later it pecks at some nasty grub; shakes its head, and wipes its bill on the ground. The conscious situation has for the future become more complex, and the behaviour is henceforth differentiated into that of acceptance and that of rejection, in each case determined by the acquired meaning in the coalescent conscious situation: the sight of a nice piece of egg being one situation, that of a nasty caterpillar another, each associated with its specific behaviour-consciousness. We need not carry the illustration further on these lines: the essential feature is that experience grows by the coalescence of successive increments, and that each increment modifies the situation which takes effect on the succeeding phases of behaviour, even if they succeed within the fraction of a second. That is what is meant by saying that present experience is for future guidance. The future need not be remote, but may be so immediate that in popular speech we may say that it is not future but present guidance which is rendered possible.

We may now turn for a moment to the criticism that there are numberless cases in which nothing of the nature of distinct memory is involved. We may now substitute for the word remembrance, which was used above, the more technical term re-presentation. Profiting by experience, regarded as a criterion of the presence of effective consciousness, involves re-presentative elements in the conscious situation which carry with them meaning. Let us for the moment assume an ultra-sceptical attitude with regard to any conscious accompaniment. The chick when it pecks, let us say, is an unconscious automaton. It seizes a piece of egg; this affords an unconscious stimulus, which sets agoing unconscious acts of swallowing; or it seizes a piece of meal soaked in quinine, which sets agoing unconscious acts of rejection and touches the hidden springs which make the automaton wipe its bill. So far we find no great difficulty. It is when we have to consider subsequent behaviour that a severe strain is felt on this method of interpretation. One can understand an automatic action repeated again and again as often as the stimulus is repeated. But the chick may shake its head and wipe its bill on the mere sight of the quinine-soaked meal, which, on the hypothesis of conscious experience, has already proved distasteful. So that if we accept the unconscious automaton theory we must assume an organic association which closely simulates the conscious association to which our own experience testifies. But the associations which take part in the guidance of behaviour in the chick are so varied and delicate, so closely resemble those which in ourselves imply conscious guidance, that a sceptical attitude throws more strain upon our credulity than the acceptance of the current belief in conscious control. We shall therefore assume that evidence for such coalescent association is also evidence of the presence of effective consciousness.

It may still be said, however, that in selecting an example from so highly organized an animal as a bird, we are taking for granted that a complex case of controlled behaviour may fairly be accepted as a type of more simple cases. Unfortunately the only being with whose power of conscious control we have any first-hand acquaintance is possessed of a nervous system even more complex than that of the chick. Our psychological interpretations are inevitably anthropomorphic. All we can hope to do is to reduce our anthropomorphic conclusions to their simplest expression. The irreducible residuum seems to be that wherever an animal, no matter how lowly its station in the scale of life, profits by experience, and gives evidence of association, it must have some dim remembrance, or, let us now say, some re-presentation, of the results of previous behaviour which enters into and remodels the conscious situation; that through the re-presentative elements behaviour is somehow guided; and, further, that the centre of conscious control is different from the centre of response over which the control is exercised.

II.—The Early Stages of Mental Development

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.

III.—Later Phases in Mental Development

Some surprise may be felt that in our brief discussion of the early stages of mental development nothing has been said of percepts and concepts, nothing of abstraction or generalization. The omission is not only due to a desire to avoid the subtle technicalities of psychological nomenclature. It is partly due to the wish not to forejudge a difficult question of interpretation. Spirited passages of arms from time to time take place between psychologists in opposing camps, as to whether animals are or are not capable of forming abstract and general ideas; and untrained camp followers hang on the skirts of the fray, making a good deal of noise with blank-cartridge. The question at issue turns partly on the definitions of technical terms; partly, when there is agreement on this point, on the interpretation to be put on certain modes of behaviour. Nothing seems at first sight much easier than to say what we mean by an abstract idea or by a general idea. We are thinking about colour, which is both abstract and general—abstract, because in itself it is a special quality of visible objects floated off, so to speak, from other qualities, such as hardness and weight, shape and size; general, because it includes many different colours in one group. Looking up at the bookshelves, we see a volume with a red back. We neglect the shape, the contents, the lettering; it is the colour with which we are immediately concerned, which forms an important feature in the present thought-situation; and this is, in virtue of that situation, abstracted from the rest. But a chick a few days old may have acquired experience of several kinds of caterpillars much alike in shape and size; of which, one kind is ringed with orange and black. And while the others are eagerly seized, caterpillars of this kind are left untouched. It is not the size or the shape which is an effective element in the situation; it is the peculiar coloration of the cinnabar caterpillars. Now, does the effectiveness of this quality in the stimulus justify the inference that the chick forms an abstract idea of colour? That clearly depends on our definition of abstract idea, and on our inferences concerning the nature of the chick’s mind.

A dog lies dozing upon the mat, and hears a step in the porch without. His behaviour at once shows that this enters into the conscious situation. There is, moreover, a marked difference according as the step has the familiar fall of the master’s tread, the well-known shuffle of the irrepressible butcher’s lad, or an unfamiliar sound. These several situations are, without question, nicely distinguished. Let us suppose the situation of the moment is introduced by a strange footfall. It seems to suggest man; but this cannot be any particular man, since he is as yet invisible and is a stranger. Does the dog, then, frame a general idea of man? Does the chamois do so when, bounding across the snow field, he stops suddenly on scenting the distant footprints of a mountaineer? Do you do so when you hear the bleating of an invisible lamb in the meadow behind yonder wall? Here, again, the answers we give to these questions depend partly on the exact meaning of the term “general idea;” partly on our interpretation of what passes through the mind of the being concerned. We have sought, so far, rather to avoid than to answer these questions. We seem to be on safe ground so long as we content ourselves with saying that the orange and black of the cinnabar caterpillar, the strange footfall, or the trail of the mountaineer, enter as effective elements into the immediate conscious situation.

But when we pass to the higher phases of mental development we can no longer wholly ignore such questions. When we are dealing with intellectual human beings, there can be no doubt that they at least are capable of framing, with definite intention, and of set purpose, both general and abstract conceptions. And how do they reach these conceptions? By reviewing a number of past situations, analyzing them, intentionally disentangling and isolating for the purposes of their thought certain elements which they contain, and classifying these abstracts under genera and species—that is to say, into broader and narrower groups. The primary and proximate object of this process is to reach a scheme of thought by which the scheme of nature, as given in experience, can be explained. And, no doubt, underlying this primary object is the purpose of guiding future behaviour in accordance with the rational scheme which is thus attained. Man is sometimes described as par excellence the being who looks before and after. All his greatest achievements are due to his powers of reflection and foresight.

What share the symbolism of speech takes in the process briefly indicated in the last paragraph is the subject of much discussion. Without going so far as to urge that the very beginnings of reflective thought are inexplicable without its aid, it may be accepted as obviously true that words are a great assistance. They may be regarded as intellectual pegs upon which we hang the results of abstraction and generalization. It may be said that we often think in pictures or images, and not in words, but the more abstract and general our thought, the more it is dependent on the symbolic elements.

We may say, then, that the higher phases of mental development are characterized by the fact that the situations contain the products of reflective thought, presumably absent in the earlier stages; they are further characterized by a new purpose or end of consciousness, namely, to explain the situations hitherto merely accepted as they are given in presentation or re-presentation; they require deliberate attention to the relationships which hold good among the several elements of successive situations; and they involve, so far as behaviour is concerned, the intentional application of an ideal scheme with the object of rational guidance. We shall follow Dr. Stout in terming this later stage of mental development the ideational stage; and in speaking of the simpler situations considered in the preceding section as belonging to the perceptual stage.

It should be observed that we are not attempting to determine just where, in the scale of organic existence, the line between the perceptual and the ideational stages of mental development is to be drawn. We are certainly very far from asserting that the one does not give rise to the other in the course of an evolution which is orderly and progressive. We are merely contrasting the rational guidance of effective consciousness at its best with the earlier embryonic condition out of which it has arisen by natural genesis. In doing this we have been forced to make some reference to the difficulties of technical nomenclature. And some further reference is necessary lest our point of view be misunderstood.

We shall regard these abstract and general ideas as the products of an intentional purpose directed to the special end of isolating the one and of classifying the other; we shall reserve the term rational for the conduct which is guided in accordance with an ideal scheme or deliberate plan of action; while for behaviour to the guidance of which no such reflection and deliberation seems to have contributed we shall reserve the term intelligent. If, for example, the rejection of a cinnabar caterpillar by the chick is the direct result of experience through the re-presentation in the new situation of certain elements introduced during the development of a like situation, we shall call it an intelligent act. But if we have grounds for supposing that the situation is reflectively considered by the chick in relation to an ideal and more or less definitely conceived plan of action which is (perhaps dimly) taking form in its mind, we shall regard it as so far rational. And so, too, in other cases of animal behaviour. Now, with regard to the control through which consciousness is effective in the guidance of behaviour, it is necessary, in view of these considerations, to distinguish its intelligent from its rational exercise. And this is of importance since we generally speak of control in the latter sense in reference to human conduct. Intelligent control (on the perceptual plane) is due to the direct operation of the results of experience without the intervention of any generalized conception or ideal. In rational control (on the ideational plane), such conceptions and ideals exert a controlling influence. If, to prevent a boy sucking his thumb we administer bitter aloes, we trust to intelligent control through the immediate effects of experience; but if he be induced to give up the habit because it is babyish, he so far exercises rational control. What we call self-control is of this type. Only one more distinction need be drawn. Intelligent behaviour, founded on direct association gained through previous experience, we shall attribute to impulse; but for rational conduct, the outcome of reflection and deliberation, we seek to ascertain the motive. In human affairs our motives are referred to certain categories each of which presupposes an ideal scheme, prudential, æsthetic, ethical, or other. To act from motive and not from impulse is to act deliberately, because we judge the action to be expedient, seemly, or right, as the case may be. If, then, we contrast the lower perceptual stages of mental evolution with the higher ideational phases, the former includes behaviour due to impulse; but from it conduct due to motive is excluded.

IV.—The Evolution of Consciousness

The origin of consciousness, like that of matter or energy, appears to be beyond the pale of scientific discussion. The appearance of effective consciousness on the scene of life does indeed seem to justify the belief in the prior existence of sentience as the mere accompaniment of organic behaviour. Ex nihilo nihil fit. And since effective consciousness must, on this principle, be developed from something, it is reasonable to assume that this something is pre-existing sentience. Again, we may assume that this sentience is a concomitant of all life-processes, or only of some. But we have no criterion by which we can hope to determine which of these alternatives is the more probable.

We appear, however, at all events to have evidence that when effective consciousness does enter on the scene and play its part in the guidance of behaviour, its progress is, in technical phraseology, marked by that differentiation of conscious elements, and that integration of these differentiated items, which are seemingly the correlatives of the differentiation and integration of nervous systems. There is thus, presumably, a progressive development of orderly complexity in the conscious situations of which controlled or guided behaviour is the outcome. And when this has reached a certain stage—what stage it is most difficult to determine—the relationships, at first implicit in the conscious situations, as they naturally arise in the course of experience, begin to be rendered explicit with the dawn of reflection. Intentional abstraction and generalization to which data are afforded by the reiterated emphasis in experience of the salient features in successive situations, supply new elements to the more highly developed situations of rational life. Ideal schemes and plans of action, the products of reflection and foresight, take form in the mind and enter into the conscious situation. And the intelligent animal, hitherto the creature of impulse, guided only by the pleasurable or painful tone which gives colour to experience, becomes a rational being, capable of judging how far his own behaviour and that of others is conformable to an ideal.

If, then, we were asked to characterize in the briefest possible terms the stages of conscious evolution, we should say that in the first stage we have consciousness as accompaniment; in the second, consciousness as guide; in the third, consciousness as judge. And if we were pressed to apply distinctive terms to these three, we should adopt St. George Mivart’s term consentience for the mid-phase, and speak of mere sentience in the first stage; consentience in the second; and consciousness, with restricted signification, in the third and highest stage. Such a distinction in terms is, however, a counsel of perfection, and we shall not attempt to preserve it in the following pages, in which the word “consciousness” will be used in a comprehensive sense.

Ever since the publication of Darwin’s “Origin of Species,” evolutionists have been divided into two sections where consciousness in the narrower sense is under discussion. The members of the one have contended that, though the physical and perhaps the lower mental nature of man is the outcome of evolutionary process, his higher mental attributes are of other origin. The members of the second section have urged that the higher not less than the lower characteristics of the mind of man have been evolved. It is somewhat strange that naturalists who accept the latter position are not infrequently impatient when any serious attempt is made to discuss it from the standpoint of psychology. It is, however, becoming more and more clearly evident that the discussion of the relation of the animal to the human mind, if it is to be made a subject of scientific inquiry, must be conducted on psychological lines by those who have devoted years of study to the subject. In this work such a discussion will be attempted, and animal behaviour will be treated as the precursor of human conduct, and as affording evidence of the germs from which the distinctively human mental attributes may have been evolved.

CHAPTER III
INSTINCTIVE BEHAVIOUR

I.—Definition of Instinctive Behaviour

There are probably few subjects which have afforded more material for wonder and pious admiration than the instinctive endowments of animals. “I look upon instinct,” wrote Addison in one of his graceful essays, “as upon the principle of gravitation in bodies, which is not to be explained by any known qualities inherent in the bodies themselves, nor from any laws of mechanism, but as an immediate impression from the first Mover and the Divine Energy acting in the creatures.”[21] In like manner Spence said: “We may call the instincts of animals those faculties implanted in them by the Creator, by which, independent of instruction, observation or experience, and without a knowledge of the end in view, they are all alike impelled to the performance of certain actions tending to the well-being of the individual and the preservation of the species.”[22] According to such views, instinct is an ultimate principle the natural genesis of which is beyond the pale of explanation. But similar views were, at the time these passages were written, held to apply, not only to animal behaviour, but also to animal structure. The development of the stag’s antler, or of the insect’s wing, was also regarded as “an immediate impression from the first Mover and the Divine Energy acting in the creatures.” This view, however, is, neither in the case of structure nor in the case of behaviour, that entertained by modern science. It is indeed an expression of opinion concerning the metaphysics of instinct. Leaving the question of ultimate origin precisely where it stood in the times of Addison and of Spence, modern science seeks to trace the natural antecedents of all natural phenomena, and regards structure and behaviour alike as the products of evolution, endeavouring to explain the manner of their genetic origin in terms of progressive heredity.

Omitting, therefore, all reference to problems which, however important, are beyond the limits of scientific inquiry,[23] we may take as a basis for further discussion Spence’s definition, according to which the instincts of animals are those faculties by which, independent of instruction, observation, or experience, and without a knowledge of the end in view, they are all alike impelled to the performance of certain actions tending to their own well-being and the preservation of the species.

Let us first consider the reference of instinctive actions to a faculty by which animals are said to be impelled to their performance. Paley also defined instinct as “a propensity prior to experience.” And unquestionably in the popular conception it is usual to attribute instinctive acts to some such conscious cause. But it will be more convenient, for the present, to consider instinctive behaviour from the objective point of view, as it is presented to our observation; we may then proceed to the further consideration of the conscious concomitants which may be inferred. From the objective point of view, therefore, we may agree with Professor Groos, who says[24] that “the idea of consciousness must be rigidly excluded from any definition of instinct which is to be of practical utility,” since “it is always hazardous in scientific investigation to allow an hypothesis which cannot be tested empirically.” In this we have the support of Dr. and Mrs. Peckham, whose studies of the life-histories of spiders and wasps are models of careful and patient investigation. “Under the term Instinct,” they say, “we place all complex acts which are performed previous to experience, and in a similar manner by all members of the same sex and race, leaving out as non-essential, at this time, the question of whether they are or are not accompanied by consciousness.”[25]

It may be said, however, that some reference to the conscious aspect of instinctive behaviour is implied by saying that the acts are performed without instruction or experience. But the reference at present is wholly negative. We may say, as the result of observation, that instinctive acts are performed under such circumstances as exclude the possibility of guidance in the light of individual experience, and render it in the highest degree improbable that there exists any idea of the end to be attained. But this is a very different position from that of asserting the presence of a positive faculty or propensity which impels an animal to the performance of certain actions. This it is which, from the observational point of view, is unnecessary. For the reference of a given type of observed behaviour to a “propensity” so to behave or to a “faculty” of thus behaving, is no more helpful than the reference of the development of any given type of structure to a “potentiality” so to develop. We may, therefore, without loss of precision, simplify Spence’s definition by stating that instinctive behaviour is independent of instruction and experience, and tends to the well-being of the individual and the preservation of the species.

Let us next consider the clause which affirms that instinctive behaviour is prior to experience. This is well in line with the distinction now drawn by biologists between congenital and acquired characters. It refers them to the former category, and implies that the organic mechanism by which they are rendered possible is of germinal origin. This is not, however, universally admitted. Professor Wundt, for example, approaching the subject from the point of view afforded by the study of man and the higher animals, gives to the term a wider meaning, and so defines instinct as to include acquired habits. “Movements,” he says,[26] “which originally followed upon simple or compound voluntary acts, but which have become wholly or partly mechanized in the course of individual life, or of generic evolution, we term instinctive actions.” In accordance with this definition, instincts fall into two groups. Those “which, so far as we can tell, have been developed during the life of the individual, and in the absence of definite individual influences might have remained wholly undeveloped, may be called acquired instincts.” They have become instinctive through repetition. “To be distinguished from these acquired human instincts are others which are connate.” Now, there can be no question that behaviour which has become habitual through frequent repetition is frequently, in popular speech, described as instinctive. We hear it said that the experienced cyclist guides his machine instinctively. And the word is similarly used in many like cases. But we shall find it conducive to precision and clearness of thought to emphasize the distinction between what is acquired in the course of life and what is congenital in the race. And to this end we shall regard behaviour which has “become mechanized in the course of individual life” as due to acquired habit, reserving the term instinctive for such behaviour as is independent of individual experience. We shall, in short, so far accept Spence’s definition.

In this definition, as in those of the majority of naturalists, it seems to be further implied that instinctive behaviour is of a relatively definite kind, though it is no doubt subject to such variation as is found in animal structure and organization. Mr. Rutgers Marshall, however, in a recent work,[27] protests against any such implication, and urges that “this variableness is so wide that definiteness of reaction cannot for a moment be used as a differentia in relation to instinct without narrowing our conception of the bounds of instinct in a manner to be deplored.” “The actions,” he says, “connected with the preparation for self-defence, those connected with protection of the young, with nest-building, with migration, etc., these actions are surely to be classed as instinctive; and yet they are exceedingly variable and unpredictable in detail; all that we can predict is the general trend of the varying actions which result from varying stimuli under varying conditions, and which function to some determinate biological end.”

Mr. Marshall then proceeds to argue that we are “warranted in speaking of the ethical instincts, of the patriotic instincts, of the benevolent instincts, and of the artistic instincts;” and thus leads up to the position, to be further elaborated in his work, that there exists in man a religious instinct which has fulfilled a function of biological value in the development of our race. Now, here again there is much in popular usage of the words instinct and instinctive which lends support, for what it is worth, to Mr. Marshall’s very broad conception of the range of instinct. Again and again we hear, in the pulpit and elsewhere, of the religious instinct; we hear, too, of the benevolent, patriotic, and artistic instincts, and more besides. But what we are endeavouring to define is a type of behaviour which, as such, is prior to instruction and experience. Can we affirm that patriotic and religious behaviour conforms to such a type? Is it unquestionably congenital and not acquired? If we are forced to give negative answers to these questions we must regard Mr. Marshall’s conception of instinct (one inclusive of multifarious tendencies which have a biological value) as too broad and too vague to be of any service to us at this stage of our study of animal behaviour.

What, then, shall we understand by Spence’s phrase that instinct involves the performance of “certain actions”? And how far shall we accept it? We shall take it as implying so much definiteness of behaviour as renders instinctive acts susceptible of scientific investigation, and in this sense shall accept it with some modification of phraseology. We shall freely admit, however, the existence of variations of instinctive behaviour analogous to variations in animal structure. It is the occurrence of such variations that renders the natural selection of instinctive modes of behaviour conceivable. We shall also admit some, nay much, variation in detail. Take, for example, two of the cases which Mr. Marshall cites—nest-building and migration. Both involve, not merely a simple response to a given stimulus, but a complex sequence of actions. In detail there may be much variation even among members of the same species. And yet, can it be questioned that the behaviour as a whole is in each case relatively definite? May we not even say that it is remarkably definite? May we not even go further, and assert that only on the assumption that any given instinctive act is relatively definite, can we regard it as a subject for scientific investigation, and can we hope to distinguish it from other modes of behaviour?

The next point for consideration in Spence’s definition, which we have taken as our text, is his characterization of instinctive acts as “tending to the well-being of the individual and the preservation of the species.” Here we have Mr. Marshall with us, for he too lays stress on the fact that instinctive behaviour has reference to a definite biological end. But in saying that the biological end is the objective mark of an instinct,[28] he seems to be in error. Because, in the first place, there are other “objective marks,” and because, in the second place, this objective mark is not restricted to instinctive behaviour. According to Spence, a further characteristic of instinctive acts is that they are independent of instruction or experience; and this serves to differentiate them from other modes of behaviour which are also subservient to a biological end. Intelligent behaviour, not less than that which we term instinctive, has reference to a biological end. Many intelligent acts, for example, have for their object the well-being of the individual; many subserve race preservation; these bear, every whit as much as instinctive acts, the “objective mark” which Mr. Marshall regards as characteristic of instinct. And if we turn to his subjective criterion—the absence of any conception of the biological end which the behaviour subserves—Mr. Marshall’s position is equally untenable. There are thousands of acquired modes of behaviour, dependent on instruction or experience, in which there is, on the subjective side, so far as we can judge, no conception of the biological end to be attained. What can the animal in the early stages of intelligence know of biological ends? Mr. Marshall’s subjective criterion applies just as much to a wide range of intelligent behaviour as it does to instinctive actions.

In accepting, therefore, Spence’s statement that when animals behave instinctively they perform, without a knowledge of the end in view, certain actions tending to their own well-being and the preservation of the species, we must take it in connection with the preceding limitation, remembering that they are also performed without instruction and experience.

A further point for very brief consideration is suggested by the phrase in which Spence says that animals are all alike impelled to the performance of certain actions. As it stands it is too sweeping and general. Still, we do require some explicit statement of the facts which he had in mind when he wrote the words “all alike.” And we find it with sufficient exactness in Dr. Peckham’s definition, where he comprises under the category of instinctive behaviour “all complex acts which are performed previous to experience, and in a similar manner by all members of the same sex and race.” This places congenital behaviour in line with morphological structure as a subject for comparative treatment.

One more question remains. What shall we understand by “complex acts”? In the first place, it is well to restrict the term instinctive to co-ordinated actions; and this implies the presence of nerve-centres by which the co-ordination is effected. We thus exclude the organic behaviour of plants, since there is no evidence in the vegetable kingdom of co-ordinating centres. In the second place, the co-ordination is, as we have seen, congenital, and not acquired in the course of individual experience. Young water-birds, and indeed young chicks, as soon as they are born, and have recovered from the shock of birth, can swim with definite co-ordination of leg movements. Here the definiteness is not only congenital, but connate, if we use the latter term for an instinctive activity which is performed at or very shortly after birth. On the other hand, young swallows cannot fly at birth; they are then too immature, and their wings are not sufficiently developed. But when they are some three weeks old, and the wings have attained functional size and power, little swallows can fly with considerable if not perfect skill. The co-ordination is congenital, for it is not acquired in the course of individual experience; but it is not connate, since it is not exhibited at or shortly after birth. The term deferred may be applied to such congenital activities as are thus carried out when the animal has undergone a certain amount of further development after birth.

In the third place, it is customary to distinguish between such reflex actions as have already been briefly exemplified,[29] and instinctive behaviour. It is, however, by no means easy, if indeed it be possible, to draw any sharp and decisive line of demarcation. Instinct has indeed been well described by Mr. Herbert Spencer as compound reflex action; hence the distinction between instinctive and reflex behaviour turns in large degree on their relative complexity. It would seem, however, that whereas a reflex act—such as the withdrawal of the foot of a sleeping child when the sole is tickled—is a restricted and localized response, involving a particular organ or a definite group of muscles, and is initiated by a more or less specialized external stimulus; instinctive behaviour is a response of the animal as a whole, and involves the co-operation of several organs and of many groups of muscles. Partly initiated by an external stimulus or group of stimuli, it is also, seemingly, determined in part, in a greater degree than reflex action, by internal factors which cause uneasiness or distress, more or less marked, if they do not find their normal instinctive satisfaction. This point, however, may be more profitably discussed in connection with the conscious aspect of instinct. If, then, we say that reflex acts are local responses of the congenital type due to specialized stimuli, while instinctive activities are matters of more general behaviour, usually involving a larger measure of central (as opposed to local or ganglionic) co-ordination, and due to the more widely-spread effects of stimuli in which both external and internal factors co-operate, we shall probably get as near as is possible to the distinction of which we are in search. But it must be remembered that there are cases in which the distinction can hardly be maintained.

We are now in a position to define instinctive behaviour as comprising those complex groups of co-ordinated acts which are, on their first occurrence, independent of experience; which tend to the well-being of the individual and the preservation of the race; which are due to the co-operation of external and internal stimuli; which are similarly performed by all the members of the same more or less restricted group of animals; but which are subject to variation, and to subsequent modification under the guidance of experience.

II.—Instinctive Behaviour in Insects

Since instinctive behaviour is, by definition, independent of experience, and since the animals which act instinctively are also, in many cases, able to act intelligently, it is clear that, apart from hereditary variations, we must expect to find acquired modifications of instinct. As Huber said of bees, their instinctive procedure often indicates “a little dose of judgment.” It is, indeed, exceedingly difficult, as a matter of observation, to distinguish between hereditary variation and acquired modification. For the rôle played by these two factors in any given behaviour can only be determined if the whole life-history of the individual be known, and if there be opportunities for comparing it with the complete life-histories of other members of its race. And this is seldom possible.

These considerations must be borne in mind as we proceed to a brief study of some of the instinctive modes of behaviour in insects.

Dr. and Mrs. Peckham’s investigations on the instincts and habits of the solitary wasps have been described in a volume[30] worthy to be placed by the side of Fabre’s “Souvenirs.” Their descriptions seem to glow with the warm sunshine, and are redolent of the fresh air which afforded the conditions under which the observations were conducted. We can but regret that, in extracting from their bright pages some of the salient facts, the natural delicacy and grace of their treatment must be lost. For we can only give the dry skeleton which they have clothed with the flesh of lively detail. They enumerate the following primary modes of instinctive behaviour:—

1. Stinging.

2. Taking a particular kind of food.

3. Method of attacking and capturing prey.

4. Method of carrying prey.

5. Preparing nest, and then capturing prey, or the reverse.

6. The mode of taking prey into the nest.

7. The general style and locality of the nest.

8. The spinning or not spinning of a cocoon, and its specific form when one is made.

When the young Pelopœus emerges from the pupa-case and gnaws its way out of the mud cell, with limp and flaccid wings, it responds to a touch by well-directed movements of the abdomen with thrusts of the sting, as perfect as those of the adult. There is clearly no opportunity here for either instruction or experience to afford any intelligent guidance. Stinging is an instinctive act. And it is an act of which great use is made in the capture of prey which shall serve for food to the young—it has a biological end. But the wasps of different species do not have to learn by experience what prey to attack. It is by instinct, too, that they take their proper food-supply, one caterpillars, another spiders, a third flies or beetles. So deeply seated, indeed, is the hereditary preference, that no fly-robber ever takes spiders, nor will the capturer of spiders change to caterpillars or beetles. Some keep to a few species or genera, while Philanthus punctatus preys chiefly or entirely on bees of the genus Halictus.

Romanes[31] thought that the manner of stinging and paralyzing their prey might “be justly deemed the most remarkable instinct in the world.” Spiders, insects, and caterpillars are stung, he says, “in their chief nerve-centres, in consequence of which the victims are not killed outright, but rendered motionless; they are then conveyed to a burrow and, continuing to live in their paralyzed condition for several weeks, are then available as food for the larvæ when these are hatched. Of course the extraordinary fact which stands to be explained is that of the precise anatomical, not to say also physiological knowledge which appears to be displayed by the insect in stinging only the nerve-centres of its prey.” Eimer[32] thought that it “is absolutely impossible that the animal has arrived at its habit otherwise than by reflection upon the facts of experience.” “At the beginning,” he says, “she probably killed larvæ by stinging them anywhere, and then placed them in the cell. The bad results of this showed themselves; the larvæ putrified before they could serve as food for the larval wasps. In the mean time the mother wasp discovered that those larvæ which she had stung in particular parts of the body were motionless but still alive, and then she concluded that larvæ stung in this particular way could be kept for a longer time unchanged as living motionless food.”

Now, since these wasps, when they have stored their nests and laid an egg on one of the victims, close it up once and for all, and take no further interest in it or its contents, there seems no opportunity, at any rate in the existing state of matters, for the acquisition of that experience on which Eimer relied. But both his explanation and Romanes’s difficulty are based on the following assumptions: first, that the victims are instinctively or habitually stung in the chief nerve-centres; secondly, that when thus stung they are not killed but remain paralyzed for weeks; and thirdly, that the marvellously definite and delicate instinctive behaviour is in direct relation to the uniform result of prolonged paralysis and consequent preservation of the food in the fresh state. But Dr. Peckham’s careful observations and experiments show that, with the American wasps, the victims stored in the nests are quite as often dead as alive; that those which are only paralyzed live for a varying number of days, some more, some less; that wasp larvæ thrive just as well on dead victims, sometimes dried-up, sometimes undergoing decomposition, as on living and paralyzed prey; that the nerve-centres are not stung with the supposed uniformity; and that in some cases paralysis, in others death, follows when the victims are stung in parts far removed from any nerve-centre. “We believe,” he says, “that the primary purpose of the stinging is to overcome resistance, and to prevent the escape of the victims, and that incidentally some of them are killed and others are paralyzed.”

If, therefore, as will probably be shown to be the case, these conclusions are found to be generally true for this interesting group of insects, the mystery of “the precise anatomical, not to say also physiological knowledge which appears to be displayed” by these wasps turns out to be one of our own fabrication. It melts away in the light of fuller and more searching investigation.

Fig. 11.—Solitary Wasp stinging Caterpillar (after Peckham).

It must not be supposed, however, from what has been said, that the behaviour in the act of stinging is altogether indefinite. On the contrary, each species proceeds in a relatively definite manner with some variation or modification of method. Philanthus punctatus, for example, stings the bees, on which she preys, under the neck, and the thrust is at once fatal. Dr. Peckham further notes that he was only successful in getting the wasps to sting when they were hunting; those that had not yet begun to store the nests paid no attention to the bees. This is an example of that internal factor to which reference was made in the last section. Marchal observed that Cerceris ornata runs the end of her abdomen along the under surface of the thorax of the bee, and delivers her thrust at the division of the segments—that is, where the sting can enter. The action does not imply any physiological knowledge. In general she begins at the neck. Spiders are usually, but not always, stung on the ventral surface. To give but one more example, Dr. Peckham observed in three cases the procedure of Ammophila urnaria which preys on caterpillars, and often, after stinging, bites the neck in several places, this process being termed malaxation. In three observed captures, all the caterpillars being of the same species and alike in size, the thrusts were given on the ventral surface near the middle line, between the segments. In the first, seven stings were given at the extremities (there being thirteen segments), the middle segments being left untouched, and no malaxation was practised. In the second, seven stings were again given, but in the anterior and middle segments, followed by slight malaxation. In both these cases the first three thrusts were in definite order, behind the third, the second, and the first segments successively. In the case of the third caterpillar, only one thrust was given, between the third and fourth segments—that is to say, in the position of the first stab in the other cases,—and after this one thrust there was prolonged malaxation. Of fifteen stored caterpillars examined, some lived only three days, others a little longer, while a few showed signs of life at the end of a fortnight. In more than one instance the second of the two caterpillars stored in each nest died and became discoloured before the first one was entirely eaten. The larva under such circumstances ate it with good appetite, and then spun its cocoon as if nothing unpleasant had occurred.

Fig. 12.—Solitary Wasp dragging a Caterpillar to its Nest (after Peckham).

The mode of carrying their booty is in these wasps instinctive, and relatively uniform. Ammophila urnaria grasps the caterpillar, near the anterior end, in her mandibles, and carries or drags it beneath her legs, walking forwards. It is generally but not always with the ventral surface uppermost. Pompilus takes hold of her spider anywhere, but always drags it over the ground, walking backwards. Oxybelus clasps her fly with her hind legs; Bembex with the second pair. Each works after her own fashion in a way that is relatively uniform for each species.

The general style of the nest, its mode of construction, and its method of closure, are always performed, says Dr. Peckham, by each species in a similar manner, not indeed in circumstantial detail, but quite in the same way in a broad sense. Variation or modification is always present, but the tendency to depart from a nest of a given type is not excessive. Some dig in the ground curved tunnels, with or without one or more chambers. Others bore into decaying wood; others use straws, or make tunnels in bramble stems; while the mud-daubers build cells in which to store the food and lay the egg. This is sometimes deposited on the first, sometimes on the last, sometimes on some intermediate victim, but generally in much the same place and position. Ammophila, for instance, lays it on the side of the sixth or seventh segment—that is to say, in about the mid position.

Some species first capture their prey, and then make the nest in which it is to be entombed. Others first prepare the nest, and then carry or drag their prey to it—often from considerable distances—quite irrespective of what seems to us the more appropriate method of the two under the particular circumstances of the case. And the way in which the victim is dragged into the nest is similarly a matter of inheritance. Each way is characteristic of the species concerned, and would be an important part of any definition of the animal based upon its modes of behaviour. For example, a Sphex places her grasshopper just at the entrance of the nest, which she then enters herself before dragging in her prey by the antennæ. When the wasp was in the hole, Fabre moved the victim a little way off; the wasp came out, brought the grasshopper to the entrance as before, and went in a second time. This was repeated about forty times, each time with the same result, until the patience of the naturalist was exhausted, and the persistent wasp took her booty in after her appropriate fashion. She must place the grasshopper close to the opening; she must then descend and examine the nest, and, after that, must drag it down. Nothing less than the performance of these acts in a certain order satisfies her instinctive impulse.

In a private letter, from which he kindly allows me to quote, Dr. Peckham says: “We have recently made some experiments on this wasp (Sphex ichneumonea). First we allow her to carry in her prey undisturbed, to see how far she was faithful to the traditions of her ancestors, and to observe her normal methods. On the next day, when she had placed her grasshopper just at the opening of the nest, and while she was below, we drew it back to a little distance. She came out, and we both repeated our operations four times—she running down into the nest, always after getting the grasshopper into position, and we as regularly drawing it away. The fifth time she changed her plan, seized it by the head and backed into the nest with it. The next day, at the fourth trial, she straddled it and walked head first into the nest with it; and on the fourth day, at the eighth trial, she backed in with it as on the second day.” These interesting observations show that the wasp has sufficient intelligence to modify her procedure in accordance with an unwonted situation. The “consecutive necessity,” as it has been termed, has a potent influence, but is not absolute.

Fabre notes a case of similar consecutive necessity in the case of the mason bee, Chalicodoma. If while a bee is provisioning its nest with honey and pollen the structure be destroyed, she sometimes breaks open a completed cell, and, having done so, goes on bringing more provision, though the cell already contains a sufficient store of food; and only when she has completed the superfluous storing does she deposit her egg and seal up the cell. So, too, when the cell is removed in an early stage of construction, and another completed cell already partially stored is substituted, the bee, instead of simply adopting the new cell, goes on building until the cell is as much as one-third beyond the usual height; then, and not till then, does she proceed in due course to the next stage of the instinctive procedure, the provisioning of the cell.

From our general knowledge of animal nature, we should expect to find parasitic forms ready to take advantage of the material stored by such insects as the solitary wasps and the mason bees. It is said that Chalicodoma provides nourishment to the larvæ of some sixteen unbidden guests. A parasitic bee (Stelis nasuta) breaks open a closed cell, and, after depositing its eggs, seals it up again with mortar. Since her eggs and larvæ develop more rapidly than those of the mason bee, they are first served with the store of provision, while the rightful owner is done out of its inheritance. By a curious act, of what appears to us like retributive justice, these parasitic larvæ sometimes fall a prey to another parasite, also a hymenopterous insect named Monodontomerus, the larvæ of which prey on the young of both bees. Another genus of the same family, Leucopsis (Fig. 13, F), also succeeds in piercing with its ovipositor, at a suitable spot, the walls of the Chalicodoma cell, and suspends its curious hooked egg (Fig. 13, G) on the delicate cocoon within which the chrysalis lies. Fabre found in some cases as many as five of these parasitic eggs on a single cocoon. But he never found more than one larva in any cell that he examined. The following is an epitome of his conclusions and inferences. From the parasitic egg is hatched a minute arched grub, with relatively large head and mandibles, and provided with a number of bristles, which aid it in progression (Fig. 13, H). It does not, however, at once attack the bee larva, but makes a series of excursions, the object of which is to reach and destroy any other parasitic eggs. This was not actually observed, but the eggs were found to have been destroyed, and there was seemingly no other means of destruction under the conditions maintained. The larva, this done, changes its skin and takes on a new form, destitute of bristles, with a very small head and minute mandibles (Fig. 13, I). In this new form it attacks the Chalicodoma larva, making a very small incision, through which the juices of the host are transferred to the guest without further injury to the grub. It is interesting to note that, if the facts are accurately described and the inferences are correct, there are associated with two types of instinctive behaviour two distinct types of structure. The creature can have no conscious control over its structural development, and there is no ground for assuming that it has any control over its instinctive behaviour.

Fig. 13.—Insect Larvæ. A, B, of Sitaris; C, D, E, of Argyromœba; G, H, I, of Leucopsis; F, imago of Leucopsis (after Fabre).

The specialization of structure and of instinctive behaviour, in accordance with a definite sequence of life-conditions, is even more remarkable in another of the many parasites which Chalicodoma unwittingly labours to nourish. This time it is a fly (Argyromœba), which lays a minute egg on the outside of the cell. From this egg is hatched a slender threadlike worm, barely one-twentieth of an inch in length (Fig. 13, C). It has three pairs of longish bristles near the anterior end, and a single yet longer pair at the hinder extremity. These aid it in creeping over the wall of the cell. Its small head is armed with short, stiff bristles. For many days it wanders over the surface of the cell, inserting its bristly head into each minute cranny and crack. Throughout this long period it has never a bite nor sup. Probably many of them never succeed in finding a crevice by which they can effect an entrance, but those that do manage to wriggle in undergo a change, lose their bristles, and develop a minute suctorial mouth, through which the contents of the larva are absorbed into their swelling bodies (Fig. 13, D). When fully grown they are quite helpless, and unable to get out from the cell in which they are now imprisoned. For months they lie quiescent, but in the succeeding spring they pass into a pupal condition very different from that of most flies. The relatively large head is armed with strong spines; the middle region bears bristles directed backwards; the posterior end has short spines (Fig. 13, E). Fixing itself to the interior of the cell by the latter, it strikes with its armoured head repeated blows on the walls of its prison until a breach is at last made, and sufficiently enlarged to form a suitable exit. Then the pupa-skin bursts, and the imago insect emerges and flies off. At each stage of life there is the closest relation between structure and behaviour, and each is equally adapted to a biological end of which the creature has never had an opportunity of gaining any experience.

Exceedingly multifarious are the ways in which insects thus provide for the future of young they will never see. Antherophagus lives in flowers, and is believed to seize with its mandibles humble bees, which then unwittingly bear the parasitic beetle to the nests in which alone the larvæ have been found. The larvæ of our common oil-beetle (Meloë) are parasitic on the bee, Anthophora. It deposits its ten thousand eggs without observable discrimination; but the active young larva instinctively seizes and attaches itself to any hairy object. Thousands must go astray. They have been found on hairy beetles, flies, and bees of the wrong genus. Some, however, become thus attached to the one suitable species, and are conveyed by the Anthophora to her nest, where they promptly eat the egg she lays. It is not difficult to picture to one’s self how this incompletely evolved instinct might be further perfected by natural selection, through the survival of those females which laid their eggs in the haunts of the bee-host. And such an advance in instinctive behaviour is seen in another and rarer beetle—Sitaris. Her eggs are laid in August near the entrance to a nest of the Anthophora. In September they hatch to form larvæ, which hibernate in groups till the following spring. Then they become active (Fig. 13, A), and attach themselves to hairy objects. Being near the Anthophora nest, there is an increased chance of their fastening upon this bee. The chance is still far from good, for if this were so, we should not find that the Sitaris laid as many as two thousand eggs. Still, on these grounds, we may presume that its chance of survival is about five times as good as that of Meloë, which lays ten thousand eggs. The larva is said generally to attach itself to a male bee, which is hatched earlier than his mate, and to pass on to the female at the nuptial period; but in any case it eventually slips on to the egg that she lays. This forms the food of the larva during the remainder of this stage of its existence. It then moults and assumes a new form, capable of feeding on the honey (Fig. 13, B); and, after further changes, becomes a pupa, and then assumes the imago condition.

In these cases the advantage is wholly on the side of the parasite. But there are cases of close relationship between insects and flowering plants where the instinctive behaviour gives rise to reciprocal benefit. The Yucca is a genus of American Liliaceous plants, with large pale sweet-smelling flowers; and these are dependent for fertilization on the instinctive behaviour of a small straw-coloured moth of the genus Pronuba. Just when the Yucca plant blossoms in the summer, the moths emerge from their chrysalis cases. They mate; and the female then flies to a flower, collects a pellet of pollen from the anthers, proceeds to another flower, pierces the pistil with her sharp ovipositor, lays her eggs among the ovules, and finally darting to the stigma stuffs the pollen pellet into its funnel-shaped extremity (Fig. 14). If the flower be not thus fertilized the ovules do not develop; and if the ovules do not develop the grubs which are hatched from the moth’s eggs die of starvation. There are enough ovules to supply food to the grubs, and leave a balance to continue the race of Yuccas.

Fig. 14.—Yucca Flower and Moth.

Whether the female moth is attracted to the flower by sight or smell, we do not know. And whether the male finds the female, in the case of the Yucca moth, through scent, we are not in a position to state with certainty. It has, however, been shown that in certain moths[33] some odour emitted by the female is the attractive stimulus, affecting sense-organs situated on the antennæ of the male. To females confined in an opaque vessel over the mouth of which gauze was tied, the males came in numbers; but when a clear glass vessel was inverted, and sand was packed round the mouth, so as to prevent the escape of air from the interior, no males came, though the imprisoned females were clearly visible. If the antennæ of the males were either removed or coated with shellac the moths failed to notice the females even when close to them. In what way the intact male is made aware of the direction from which the scent comes, we do not know—possibly by differential stimulation in the antennæ, the moth instinctively turning in the direction of greater stimulation. It will be seen, therefore, that in the case of the behaviour of the Yucca moth—behaviour which is essential to the biological end of reproduction—there is much detail concerning which we are ignorant. But for our present purpose the important point to notice is that the procedure of the female cannot be due to imitation; nor can it be the outcome of individually acquired experience; for the method of procedure is not gradually learnt, but is carried out without apparent hesitation the first and only time the appropriate occasion presents itself. Not only does the moth take no heed of her grubs, but they are so placed that she could not in any case ascertain by observation that only if the ovules are fertilized do her offspring thrive. She cannot possibly know what effect the stuffing of the pollen on to the stigma exercises, or indeed whether it have any effect at all. And yet generation after generation these moths collect the pollen from the anthers and bear it to the stigma. Spence’s words “without knowledge of the end in view” are amply justified in this case, as in other cases of typically instinctive behaviour.

III.—The Instinctive Behaviour of Young Birds

Since it is easy to hatch birds of many species in an incubator, and to rear them under conditions which not only afford facilities for observation but exclude parental influence, their study has special advantages. One can with some approach to accuracy distinguish the instinctive from the acquired factors in their behaviour.[34]

Fig. 15.—Newly-hatched Chick swimming.

The callow young of such birds as pigeons, jays, and thrushes are hatched in a helpless condition, and require constant and assiduous ministration to their elementary organic needs. Most of their instincts are of the deferred type. But pheasants, plovers, moor-hens, domestic chicks, and ducklings, with many others, are active soon after birth, and exhibit powers of complex co-ordination, with little or no practice of the necessary limb-movements. They walk and balance the body so soon and so well as to show us that this mode of procedure is congenital, and has not to be gradually acquired through the guidance of experience. Young water-birds swim with neat and orderly strokes the very first time they are gently placed in water. Even little chicks a day or two old can swim well. Dr. Thorndike, who draws attention to this fact,[35] appears to accept the view, suggested by Dr. Bashford Dean, that the movements are not those of swimming but only of running. I have carefully watched the action through the glass walls of a tank and compared it with that of a young moor-hen. In the two cases it is quite similar in type, and the type appears to be different from that of running, though it is perhaps hard to distinguish the two. In any case, the hand over hand action is well co-ordinated, and is very different from a mere excited struggle. Chicks twenty-six hours old taken straight from the incubator drawer, before they had taken food, made directly for the side of the tank and tried to scramble out. They gradually sank deeper through the wetting of the down, but could keep afloat for from two to three minutes. I have made observations on chicks of various ages from twenty-four hours to a month, and find in all cases similar results; but with the older birds the flapping of the wings and more vigorous action cause them to get water-logged more rapidly. There is some apparent distress with cries; but less than one might expect under the circumstances. For the purposes of the above illustration Mr. Charles Whymper had before him a sketch I made of the leg-action, and instantaneous photographs of the chicks swimming for which I am indebted to my colleague Mr. George Brebner. I have not observed the behaviour of an adult hen when placed in the water. Dr. Thorndike says, “there is no vigorous instinct to strike out toward the shore,” she “will float about aimlessly for awhile and only very slowly reach the shore.” But Mrs. Foster Wood informs me that she has seen a hen leap into a pond after her brood of ducklings and swim to the other side, a distance of twenty feet.

Diving, in water-birds, is also an instinctive mode of behaviour; and this is obviously a more difficult procedure than swimming, one further removed from reflex action. And careful observations have placed beyond question the fact that flight is also instinctive. A swallow, for example, taken from the nest under conditions which made it practically certain that it had never yet taken wing, exhibited guided flight, and attempted to alight on a suitable ledge. Of course flight is generally a deferred instinct, and is not performed until the wings have reached a suitable state of development. An instinctive response, which may perhaps be regarded as one of its initial stages, is seen in quite young chicks. If placed in a basket, and rapidly lowered therein through a foot or two, the chick will extend its skinny and scarcely feathered wings. But though, from the usual conditions of development, flight in birds is a deferred instinct, yet in exceptional cases it may be connate. The mound-builders (Megapodes) of the Australian region are hatched from large eggs in warm earth or sand, and are not tended by the parents. So well fledged are these birds that they can fly the day they emerge from the egg. Dr. Worcester, while digging in one of their mounds, made an unsuccessful attempt to seize one which was newly hatched; but it flew several rods into thick brush, and this notwithstanding the fact that it had probably never before seen the light of day.

Fig. 16.—Nestling Megapode, to show the well-developed wings. (From Dr. R. Bowdler Sharpe’s “Wonders of the Bird World.”)

It must not be supposed that, in adducing flight as an example of instinctive behaviour in birds, we are contending that it is this and nothing more throughout life. The inference to be drawn from the facts of observation is rather that instinct provides a general ground plan of behaviour which intelligent acquisition, by enforcing here and checking there, perfects and guides to finer issues. Few would contend that the consummate skill evinced in fully developed flight at its best, the hurtling swoop of the falcon, the hovering of the kestrel, the wheeling of swifts in the summer air, the rapid dart and sudden poise of the humming bird, the easy sweep of the sea-gull, the downward glide of the stork—that these are, in all their exquisite perfection, instinctive. A rough but sufficient outline of action is hereditary; but the manifold graces and delicacies of perfected flight are due to intelligent skill begotten of practice and experience.

There are many little idiosyncracies and special traits of flight which are probably instinctive—such as enable an ornithologist or a sportsman to recognize a flying bird from a distance. And the same is true of other modes of behaviour. The observer of young birds cannot fail to note and to be impressed by many of these. The way in which a little moor-hen uses its wings in scrambling up any rough surface is very characteristic; so, too, is the manner in which a guinea-chick runs backwards and then sideways at a right angle when one attempts to catch him. If suddenly startled, moor-hens and chicks scatter and hide; plovers drop and crouch with their chins on the ground; pheasants stand motionless and silent. Knowledge of the ways of birds enables one to predict with tolerable accuracy how each kind will behave under given circumstances. That the actions are always precisely alike cannot be said with truth; but that the behaviour is so relatively definite as to be readily recognizable can be confidently asserted. That a moor-hen will flick its tail, that a chick will dust itself in the sand, that pheasants and partridges will scratch the ground, that a jay will go through certain actions in the bath, that the preening of the down will be carried out in particular ways—moor-hens, for example, wringing out the water in a peculiar manner,—and that all these, and many other modes of behaviour, will be presented in relatively definite ways: all these are, to borrow a phrase of Dr. Peckham’s, so characteristic of the several groups of birds, that they would be an important part of any definition based upon behaviour. And there can be no question that they are instinctive. They may indeed seem trivial and commonplace, scarcely worthy of special note; but they serve to show in how many details organic heredity lays the foundation for future behaviour, and affords groups of data for effective consciousness to utilize.

To show the instinctive nature of such behaviour, the following examples will suffice. One of a batch of moor-hen chicks showed once, and once only, when a week old, an incipient tendency to bathe in the shallow tin of water which was placed in their run, but soon desisted; nor was the action repeated, though he and the others enjoyed standing in the water. Five weeks later one of the batch was taken to a beck. He walked quietly through the comparatively still water near the edge; but when he reached the part of the stream where it ran swiftly and broke over the pebbles, he stopped, ducked, and took an elaborate bath, dipping his head well under, flicking the water over his back, ruffling his feathers, and behaving in a most characteristic manner. Each day thereafter he did the same, with a vigour that increased up to the third morning, and then remained constant. The same bird some weeks later was swimming in a narrow part of the stream, with steep banks on either side, when he was frightened by a rough-haired pup. Down he dived, for the first time in his life; and after a few seconds his head was seen to appear, just peeping above the water beneath the bank.

Ten days after receiving two nestling jays I placed in their cage a shallow tin of water. They took no notice of it, having never seen water before; for they were fed chiefly on sopped food. Presently one of them hopped into it, whether attracted by the water or by accident it is difficult to say, squatted in it bending his legs, and at once fluttered his feathers, as such birds do when they bathe, though his breast scarcely touched the water. The other seized the tin in his bill, and then pecked at the water, thus wetting his beak. He, too, fluttered his feathers in a similar fashion, though he was outside the tin and not in the water at all. A little later the first again entered the tin, and dipped his breast well into the water; this was followed by much fluttering and splashing. The bird took a good bath, as did the other shortly afterwards, and then spent half an hour in a thorough grooming, with much fluttering of the wings, the crest feathers being constantly raised and lowered, expressive of an emotional state.

Now, in these cases it would be impossible to say whether the behaviour was carried out in the manner characteristic of the species, prior to experience and independent of imitation, on the basis of mere casual and chance observation. But in these cases the whole life-history of the individuals concerned was known; and it can be asserted with confidence that the behaviour was hereditary, and not acquired by any gradual process of learning. Moreover, in each case there seemed to be such evidence as observation can afford, that internal emotional factors co-operated with the direct external stimuli in determining the nature of the behaviour. Whether such actions so far contribute to the well-being of the individual as to be of decisive advantage it is difficult to say. Some would contend that bathing is practised by birds merely for the pleasure it seemingly affords; others would urge that it is a means of getting rid of troublesome and presumably hurtful parasites, to the attacks of which birds are peculiarly subject.

Fig. 17.—Young Cuckoo ejecting nestling Meadow Pipit. (From Mrs. Hugh Blackburn’s sketch in “Birds from Moidart.”)

One of the most remarkable instincts of young birds is that of the cuckoo, which ejects eggs and nestlings from the home of its foster-parent. Mrs. Hugh Blackburn found a nest which contained two meadow-pipits’ eggs, besides that of a cuckoo. On a later visit “the pipits were found to be hatched, but not the cuckoo. At the next visit, which was after an interval of forty-eight hours, we found the young cuckoo alone in the nest, and both the young pipits lying down the bank, about ten inches from the margin of the nest, but quite lively after being warmed in the hand. They were replaced in the nest beside the cuckoo, which struggled about until it got its back under one of them, when it climbed backwards directly up the open side of the nest, and hitched the pipit from its back on to the edge. It then stood quite upright on its legs, which were straddled wide apart, with the claws firmly fixed halfway down the inside of the nest, among the interlacing fibres of which the nest was woven, and, stretching its wings apart and backwards, it elbowed the pipit fairly over the margin, so far that its struggles took it down the bank instead of back into the nest. As it was getting late, and the cuckoo did not immediately set to work on the other nestling, I replaced the ejected one and went home. On returning next day, both nestlings were found dead and cold, out of the nest.”[36] Here we have a definite account by an eye-witness, who sketched the young cuckoo, which was naked, blind, and could scarcely hold up its head. And her account, itself confirmatory of that given by Jenner in 1778, is confirmed by that of Dr. John Hancock,[37] who witnessed the ejection of a fledgling hedge-sparrow, which “was put over the edge of the nest exactly as illustrated by Mrs. Blackburn.” The procedure is unquestionably instinctive.

The sounds uttered by young birds are sufficiently definite to be readily recognized and are susceptible of classification. In domestic chicks at least six notes may be distinguished. First the gentle “peeping” note, expressive of contentment. A further low note, a double sound, seems to indicate extreme satisfaction and pleasure. Very characteristic and distinct is the danger-note—a sound difficult to describe, but readily recognized. If a humble-bee, a black-beetle, a big worm, a lump of sugar—anything strange and largish—be thrown to the chicks, this danger-note is at once heard; and it serves to place others on the alert, though this is perhaps the outcome of experience. Then there is the cheeping sound, expressive apparently of a state of mild dissatisfaction with the present state of affairs. It generally ceases when one throws some grain, or even stands near them. Extreme dissatisfaction is marked by a sharper, shriller squeak, when one seizes them against their inclination. Lastly, there is the shrill cry of greater distress, when, for example, their swimming powers are subjected to critical examination. With pheasants a gentle, “peeping” note of contentment, a shriller cry of distress, and a danger-note, generically like, but specifically distinct from, that of the chick, are early differentiated. The complaining note of the partridge is uttered six or seven times in quick succession, followed by a pause. The note of the plover is high-pitched, and much like the familiar cry of the adult bird, to which it owes its popular name of “peewit.” So, too, the guinea-fowl in down utters from the first notes quite characteristic of its kind, while its danger-note is not unlike that of the chick or pheasant. The piping of ducklings is comparatively monotonous, and there does not seem to be a definite danger-note. With moor-hen chicks, even on the first day, two notes are well-marked—a call-note, lower in pitch than that of the chick, and rather harsh and raucous, and a “tweet, tweet” of pleasure, something like the contented note of a canary. Later, five or six notes are differentiated, the most characteristic of which is the harsh “crek, crek,” when the little bird is from any cause excited. It is uttered in a crouching attitude, with head thrown back and wings held outwards and forwards, waving to and fro in a very characteristic manner. That this has suggestive value for other moor-hen chicks is shown by its distinctly infectious effect; if one bird has cause to utter the note and strike the attitude others follow suit. While clearly instinctive in their mode of occurrence, while they seem to show well the co-operation of an internal emotional factor, their biological value seems to lie in their suggestive effect on other members of the brood. They form an elementary but sufficient social bond.

If these notes afford evidence of an incipient social factor, the instinct of pecking is distinctively individualistic. Chicks peck with considerable but not complete accuracy of aim at practically anything of suitable size at suitable distance; but it is through experience that they learn what to select for food and what to reject or leave untouched. Moving objects, however, are more readily pecked at than those which are still; and the instinctive response seems to be stimulated if one tap on the ground near the object, or move it with a pencil, thus simulating the action of the hen. And this is even more marked with pheasants and partridges. Plovers seize small worms with an avidity which looks like an inherited response to the sight of natural food. Pheasants and partridges also appear to be specially affected by worms, and when one of them seizes a worm for the first time, he shakes it and dashes it against the ground. Chicks, a week or ten days old, also seize a largish fly or bee with a dash, and maul it on the ground, throwing it on one side before again approaching it. And such birds seem to show an instinctive tendency to bolt with such treasures as caterpillars or small worms. Moor-hens cannot at first be induced to take food from the ground. It has to be held above them, whereupon they crouch down, with head and neck held back, opening their beaks more like the callow young of nursling birds; but they also strike upwards at the object—these modes of behaviour being, no doubt, correlated with the manner in which the mother moor-hen normally feeds her young from her beak during the early days of life. Callow fledglings, such as young jays, simply open their mouths, gaping widely to be fed. And many will respond in this way to such a note as a low whistle, as may readily be seen with swallows. But at a later age such birds show instinctive modes of reaction of a more complex type. A jay, for example, was offered a summer chafer or June bug, seized it at once in his bill, and tried to place his foot on it. Then he hopped down on to the floor of his cage, dropped the beetle, seized it again as it crawled off, and after two or three attempts swallowed it, tossing it back from the point of his bill into the throat. This was the first time he took food from the ground or swallowed it in this manner.

On the whole, there seems to be much inherited definiteness of co-ordination, and some tendency to respond in a definite manner to specific stimuli. That there should not be more differentiation in this respect than observation discloses is probably due to the fact that the parent birds afford, under natural conditions, much guidance in the selection of food. Since the solitary wasp unerringly seizes its appropriate food, since it responds instinctively to specific stimuli, there would seem no reason why birds should not show similar instinctive differentiation. But one must remember that in the case of the wasp there is no parental guidance; the insect is more completely dependent on instinct than is the bird to whose needs the hen assiduously ministers.

It is at first sight surprising that such birds as chicks and pheasants do not peck instinctively at still water. When a shallow vessel containing water was placed among some little chicks, several of them ran repeatedly through the water, but took no heed of it. Then, after about an hour, one of them standing in the vessel pecked at his toes, and at once lifted his head and drank freely with characteristic action. Another subsequently pecked at a bubble near the edge, and then he too drank. In fact, the best way of inducing them to drink is to scatter some grains of food in the tin; they peck at the grains, which catch their eye, and incidentally find the water, and the touch of water in the bill at once leads to the characteristic response and congenitally definite behaviour. That the sight of a still surface does not itself suffice to evoke this behaviour is probably again due to the fact that under nature the hen guides them and pecks at the water, when they follow her lead.

One fact which must be constantly borne in mind is that what is inherited is instinctive co-ordination, often related to a definite stimulus, not instinctive knowledge. A chick pecks at a grain when it is at a suitable distance, not because instinct provides him with the knowledge that this is something to be seized and tested, but because he cannot help doing so. He is so organized that this stimulus produces that result through an organic co-ordination that is independent of conscious knowledge or experience. How definite is the inherited co-ordination is shown by many observations. A young pheasant, only a few hours old, was taken from the incubator drawer, and held snugly while a piece of egg-yolk was moved before his eyes with the aid of fine forceps. He did not peck at it, but followed with movements of his head every motion of the object in a narrow circle. Simple as this action seems, it presents a striking example of co-ordinated movements accurately related to movements in the visual field, the whole performed without any opportunity for learning or practice, and less than half an hour after the bird was taken from the drawer of the incubator and first saw daylight. Psychologists sometimes puzzle their heads over the question how and by what steps the field of vision and the field of movement are brought into relation with each other; but in such a case as this, the problem ceases to be primarily psychological. The relation is purely organic; the conscious data are grouped from the outset. With young jays there was no such co-ordination at first; and when they began after a few days (about twelve or fourteen) to follow an object with the head and eye, the movements were at first jerky. But a week later, when I swept the food through a circle a foot in diameter in front of their cage, it was followed smoothly and evenly. Here a certain amount of learning and practice, absent in the case of the pheasant, was required. And it is difficult to say what proportion of the final result was acquired, what proportion hereditary; but probably the behaviour is in the main instinctive, though somewhat deferred.

One more example, perhaps even more trivial in the eyes of some people, may be given. A duckling a few hours old will scratch the side of his head. It is true he may topple over in the process, through insufficient powers of balance, for the simultaneous performance of poising on one leg and having a good scratch with the other is no easy matter. But let not either our familiarity with such behaviour, nor some observed and laughable failure on the part of the duckling, blind us to the fact that this is a congenital activity, and one of no little complexity, indicating a definite organic nexus. A local irritation sets agoing movements of the hind limb of that side through which just that particular spot is scratched in the absence of any previous practice, any learning to localize the spot. There can be no question that such inherited co-ordinations, whether perfect from the first, or with deferred perfection and some aid from acquisition, afford ready-made data to consciousness, which are of the utmost service in the guidance of subsequent behaviour. The two-days-old chick, with the aid of this instinctive co-ordination, performs well a number of actions, which, had she to consciously learn them all, would probably be still but half mastered when she was a skinny old hen.

Our whole treatment of instinctive behaviour has been based on the assumption, already to some extent justified, that experience is not inherited. If it be hereditary, how comes it that chicks show no recognition of still water, which must have been familiar to the experience of generation after generation of birds? How comes it that they do not even seem to recognize their natural parent and protector, the hen? Two chicks ten days old were taken to the yard whence were derived the eggs from which they were hatched, and were placed about two yards from a hen which was clucking to her brood. They were not in a frightened condition, for they stood on my hand and ate grain from it, scratching at the palm. But of the clucking of the hen they took no notice whatever. The same results were obtained with other chicks thirteen days old. Was this due, as Spalding suggested, to loss of the instinctive response which was perhaps present at an earlier age? Seemingly not. For a chick was taken at the age of two and a half days to its own mother, which had three chicks. These followed her about, and ran at once to her when she clucked and pecked on the ground. The little stranger, however, took no notice, nor did he show any tendency either to go to the hen or to follow the three chicks, having been purposely brought up alone. When the hen took her little brood under her wing, the stranger was placed close to her. She clucked, and seemed anxious to entice and welcome the little fellow, seizing an oat-husk and dropping it before him; but he remained indifferent, walking away and standing in the sunshine. After about forty minutes he seemed more inclined to go with the other chicks, but still ignored the existence of the hen. The natural instinctive tendency seems to be from the first to nestle under anything; and there is the hen provided by nature for the purpose. By experience the chicks grow accustomed to her fussy ways, as they grow accustomed to the ways of such a foster-parent as the writer of these pages. Still, though there is, apparently, no instinctive knowledge of the hen as their natural protector, and though I have seen no observable response to the clucking sound, this must not be taken as necessarily implying that there is no instinctive response to any of her modes of behaviour. There is such a response to her pecking on the ground; there is probably such a response to her danger-note; and there may be many other such instinctive modes of behaviour related to her actions. How far they extend can only be ascertained by patient observation; and such responsive behaviour need not imply any instinctive knowledge begotten of inherited experience.

We may now summarize some of the general conclusions which may be drawn from observations of instinctive behaviour in young birds.

1. That which is inherited is essentially a motor response or train of such responses. Mr. Herbert Spencer’s description of instinct as compound reflex action is thus justified.

2. These often show very accurate and nicely-adjusted hereditary co-ordinations.

3. They are evoked by stimuli, the general type of which is fairly definite, and may in some cases be in response to particular objects.

4. They are also generally shown under conditions which lead us to infer the presence of an internal factor, emotional or other.

5. There does not seem to be any evidence of inherited knowledge or experience.

IV.—The Conscious Aspect of Instinctive Behaviour

In our definition of instinctive behaviour all positive reference to the presence of conscious states was omitted. By some writers, however, the fact that it is accompanied by consciousness is regarded as a distinguishing feature of instinct. Romanes introduced his definition with the words:[38] “Instinct is reflex action into which there is imported the element of consciousness.” And he emphasized the conscious aspect when he said: “The term comprises all those faculties of mind which are concerned with conscious and adaptive action, antecedent to individual experience.” Professor Wundt also lays some stress on the conscious accompaniments of instinctive activities which, he says,[39] “differ from the reflexes proper in this, that they are accompanied by emotions in the mind, and that their performance is regulated by these emotions.” The definitions of other writers express or imply the presence of consciousness in differing modes and degrees, culminating in the hypothesis of inherited knowledge. Douglas Spalding, for example, said[40] that “animals can forget the instinctive knowledge which they never learned!”

Now, the exclusion from our definition of direct reference to the conscious aspect must not be taken to imply that instinctive behaviour is a mere matter of unconscious automatism; nor even that it is unprofitable to discuss how much consciousness there may be, of what sort, and how distributed. All that it does imply is, that the amount, nature, and distribution of consciousness cannot well be introduced into a definition the object of which is to help us to distinguish certain observable types of behaviour from others. In a word, the definition given is biological and objective, and is to be accepted or rejected without prejudice to such psychological considerations as those upon which we have now briefly to enter.

The first thing we have to decide is how much we are to include, from the psychological standpoint, under instinct. For we may take either a broader or a narrower view of the matter; and which of these we adopt will make much difference in our conclusions. Let us first deal with the narrower. We have said above that what is hereditary in instinctive behaviour is the co-ordination. Now, such co-ordination of movements into a finished and appropriate act is due to a nicely graded distribution of efferent nerve-waves to the several muscles concerned, so that these muscles may be caused to contract in due order, and each to just the right extent. But efferent nerve-waves as such, and their mode of distribution by the nerve-centres, are in all probability unconscious, while the contraction of the muscles is a purely organic matter. If, therefore, we narrow our conception of instinct so as to include only the co-ordinated act by itself, excluding all reference both to the stimuli which are its antecedents, and to the effects in consciousness which its performance may produce; and if the data for consciousness are in all cases supplied through afferent channels; then there seems to be no escape from the conclusion that instinctive behaviour as such may be, and probably is, altogether outside the individual consciousness. It should be noted, however, that on this view only the instinctive co-ordination in itself can be fairly regarded as independent of the stream of experience.

Now, in the first place it is convenient so far to broaden our conception as to include under the head of instinctive behaviour, in its conscious aspect, not only the co-ordinated act but the data which its performance affords to consciousness. It may indeed seem that we are here trying to draw a distinction where no real difference exists. The physiological distinction is, however, not only clear and undeniable, but quite easily understood. For the sake of illustration let us take the case of an intentional action, such as glancing up from the words we are reading to the clock. Efferent waves course along several motor nerves to the six muscles by which each eye is moved, and to the muscles of accommodation within the eye. These muscles are called into duly co-ordinated activity, by which our vision is focussed upon the clock-face. This is one part of the physiological procedure—that by which the intended result is attained. But there is a second part readily distinguishable from the former. As the eyes move, afferent messages course inwards from the muscles or the eye-sockets and their neighbourhood; and it is these incoming waves which afford data to consciousness, telling us that the movements are in progress or have been effected. The nerves involved in the latter part are quite different from those concerned in the former part, and they proceed to areas of the brain differently situated from those whence the efferent waves issued. Thus it is in all cases of movement; the efferent nerves call the muscles into play; the afferent nerves bring information that the movements are carried out. It is through the latter that data are unquestionably afforded to consciousness.

But in the case of any complex action—and, as we have seen, instinctive behaviour is often remarkably complex—the information that the action has begun comes in before the behaviour is completed. Practically we may say that any given stage of performance and the consciousness it evokes are simultaneous; for though in strictness the one lags just a little behind the other, yet they are so nearly coincident in time that we may disregard the interval between them. Such being the case, therefore, we may fairly regard the felt performance of the instinctive act as capable of introducing important elements into the conscious situation.

But not only does instinctive behaviour thus introduce important elements into the conscious situation, it is also called forth by stimuli which themselves afford not less important elements. To exclude these from any consideration of instinct, in its conscious aspect, would render the treatment of the problem so incomplete as to be wholly unsatisfactory from a psychological point of view. Can we believe that when the moor-hen dived, as it never had dived before, at the sight of the rough-haired pup, the vivid experience of that strange and disquieting intruder did not enter into, and form a prominent feature in, the conscious situation? If we are to consider the conscious aspect at all, we must try and grasp the situation as a whole. And on these grounds we may yet further broaden our conception so as to include, from the psychological point of view, not only the behaviour itself, and its effects in consciousness, but also the stimulating conditions under which it is called into play. If, then, we accept this position, and agree to use the term “instinct” for our present purpose in a comprehensive sense, we may now proceed to consider very briefly the nature of the elements which enter into the instinctive situation.

First, there are the external stimuli affecting one or more of the sense organs, and thus evoking consciousness; and secondly, there are internal factors, having their source in the condition of the body, or its parts and organs. It is convenient to take these two together, so that we may see what relationship they bear to each other. Both seem to be present, and to co-operate in a great number of instinctive acts. In the behaviour connected with feeding, for example, an internal element of hunger co-operates with the external presentation of the appropriate food or prey. So, too, with the instincts concerned in the propagation of the race. Looking at the matter generally, we may regard the internal factors of the kind with which we are now dealing, as giving rise to a want or need, passing in some cases into a state of craving. In themselves such conscious states are in their inception exceedingly indefinite; for a want can only be rendered definite in experience by its appropriate satisfaction. In many cases of instinctive behaviour the indefinite want and the particular and duly related stimulus seem to lead, without prevision and by a blind impulse, to the performance of those acts which will afford the unforeseen satisfaction. And when once this satisfaction has been attained, subsequent wants or needs of like character will no longer be indefinite; nor will future behaviour of the same kind be thereafter wholly instinctive, for it can never again be prior to, or independent of, experience.

Granted, however, that a felt need of some kind, indefinite at first but none the less real, is present in many cases as a spur to instinctive behaviour; is it in all cases a necessary factor? May we say that this distinguishes instinctive from merely reflex action? The question is, from the nature of the case, exceedingly difficult to answer. But without going so far as to say that reflex action may be unerringly distinguished from instinctive behaviour by the absence of any such internal factors, we may perhaps, at any rate, go so far as to give provisional acceptance to the view that in instinct these wants and felt needs enter into the conscious situation in a manner and to a degree that are so far distinctive—which seems to be the position adopted by Professor Wundt.

There is, however, a further relation between the external stimulus and these internal factors which is presumably of no little importance. The stimulus intensifies the want, or may in some cases call it into existence. Just as a whiff from the kitchen may lead us to realize that we need the satisfaction that will erelong be presented at table, so may the sight of his mate in the spring evoke in the breast of the yearling sparrow a need, having its source in morphological and physiological changes, that spurs him on to the courtship that shall lead to its due satisfaction. Popular attention has, indeed, been so naturally drawn to the internal needs or wants with which we are now dealing, as to give them an almost exclusive monopoly of the term “instinct,” which thus often comes to be regarded as a connecting link between the stimulus and the act. The sight of a mouse, for example, is said to call forth the instinct of the cat, which is satisfied by her pouncing upon it. And so it comes about that, while the biologist fixes upon the instinctive act as the essential feature, the psychologist is apt to regard the impulse[41] which prompts to action as the more central and characteristic element. We are here endeavouring to combine both these points of view.

To come to closer quarters with the relationship which holds good between the external and internal elements, it appears that, when the stimulus evokes or intensifies the want or need, this is probably effected by efferent waves which call the organs or parts into tonic action, of which the animal becomes conscious through the afferent messages which come in from them to the sensory centres; in much the same way as the whiff from the kitchen takes effect on the salivary and other glands, and throws the organs of digestion into a felt preparedness for the fulfilment of their functions. But it may have other and more indirect consequences. When the moor-hen dived to escape from the obtrusive puppy, his heart-beat was probably affected; he had, perhaps, an uncomfortable sinking in his gizzard; his breathing was short and laboured; and he experienced creepy sensations in the skin and around the feather-roots. Such we may suppose were the accompaniments or sources of the emotional state of fear or alarm. And they presumably entered with no little vividness into the conscious situation at the moment of instinctive action. In all those cases in which the behaviour is associated with such an emotional state as anger or fear, the external stimulus seems to produce widely-spread effects on the glands, respiratory organs, heart and blood-vessels, skin and other parts, as well as the more direct response in productive action. And all this must enter into the conscious situation, contributing largely, as we shall hereafter see, to the emotions in their instinctive origin.

Enough has now been said to indicate with sufficient clearness the kind of co-operation and mutual relationship which subsists between the external and the internal factors in the conscious situation which leads to instinctive behaviour. We have seen that, not improbably, some organic prompting is always present in greater or less degree. But the question still remains whether anything like a definite and particular external stimulus is in all cases a necessary factor.

When the predaceous larva of the water-beetle, Dytiscus, ceases to feed, and, creeping into the moist earth near the pond’s edge, makes a hollow cell in which to enter upon its pupal sleep, there does not seem to be any well-defined stimulus from the outer world which can be said to initiate the behaviour of whose purport the larva can have no idea. Some inner need seems to impel the creature to this necessary but as yet unknown course of action; and this appears to constitute, if not the sole, at least the preponderant element in the conscious situation. In healthy young birds and other animals there is after the rest of sleep a certain exhilaration and exuberance of spirits which seemingly leads to characteristic action; dancing, flapping of the wings, running hither and thither in short quick spurts, and so forth. No doubt in such cases external stimuli are present, and contribute in some degree to the effects produced; but they do not seem to be particularized so that one can say that just this or that well-defined stimulus is necessary to give rise to the observed behaviour. In the case of migration, too, an internal factor—the nature of which we do not know—is probably as strong as if not stronger than any influence from without. While, therefore, we may say that some external factors are frequently, not improbably always, contributory, we must add that observation does not enable us in all cases to define them with any approach to accuracy; and, further, that promptings from within seem in some instinctive acts to be the most important elements in the conscious situation.

It now only remains to draw attention to the fact that the effects of the behaviour, as the animal becomes conscious of the performance of the acts concerned, serve to complete and render definite the conscious situation. Consciousness, however, probably receives information of the net results of the progress of behaviour, and not of the minute and separate details of muscular contraction. These net results, having thus entered presentatively into the situation, are subsequently susceptible of re-presentative recall, when the recurrence of certain salient elements serve to reproduce the essential features of the situation of which experience has been gained on a former occasion. Hence, as has already been noted, it is only the first performance of an instinctive action which can be described as prior to experience. The second time the deed is done it is done by an animal which has had opportunity of gaining experience on the foregoing occasion. And then it may be done with a difference, with some acquired modification of performance. By the repetition of the slightly modified behaviour the effects of habit are introduced, and thus acquired peculiarities of action are established as individual traits. We must not forget that, in a large number of cases, so-called instinctive behaviour, as presented to observation, has lost through modified repetition its original purity of type. The acts we see are often the joint products of heredity and individual acquisition, the inherited co-ordination having been supplemented or otherwise altered through experience.

Even in the case of the very first exhibition of such a deferred instinct as the moor-hen’s dive, although that organized sequence of acts which constituted the behaviour as a whole had never before occurred, although there was no gradual learning how to dip beneath the surface, and to swim under water, still many of the constituent acts had been often repeated; experience had already been gained of much of the detail then for the first time combined in an instinctive sequence. So that if we distinguish between instinct as congenital and habit as acquired, we must not lose sight of the fact that there is continual interaction, in a great number of cases, between instinct and habit, and that the first performance of a deferred instinct may be carried out in close and inextricable association with the habits which, at the period of life in question, have already been acquired. Instinct supplies an outline sketch of behaviour, to which experience adds colour and shading. Which predominates in the finished picture depends on the status of the animal. In the lower and less intelligent types the outline stands out clearly, there being but little shading to divert our attention from the clear firm lines inscribed by heredity; but in the higher and more intelligent animals, the deft pencil of experience has added so much detail and has interwoven with the fainter outline so many new and skilfully introduced touches, that the original sketch is scarcely distinguishable unless we have carefully watched from the beginning the gradual development of the picture.

V.—The Evolution of Instinctive Behaviour

It may be assumed that the fact of evolution is generally admitted. The question of its method is, however, still open to discussion. It is possible that, as some biologists contend, there is an inherent tendency in organic beings to evolve in certain definite directions independently of their relation to the environment. But it is scarcely probable that instinctive behaviour is mainly due to any such inherent tendency—of the nature of which in any case we know but little. Setting this on one side, therefore, we have two hypotheses: first, that instincts are the result of natural selection; secondly, that they are due to the inheritance of acquired habits. These two views we will now proceed to consider.

We have seen that Professor Wundt distinguishes two classes of instinctive acts: first, those which are acquired or have become wholly or partly mechanized in the course of individual life; secondly, those which are connate or have been mechanized in the course of generic evolution. “The laws of practice,” he says,[42] “suffice for the explanation of the acquired instincts. The occurrence of connate instincts renders a subsidiary hypothesis necessary. We must suppose that the physical changes which the nervous elements undergo can be transmitted from father to son.... The assumption of the inheritance of acquired dispositions or tendencies is inevitable if there is to be any continuity of evolution at all. We may be in doubt as to the extent of this inheritance; we cannot question the fact itself.”

Now, the application of the term “instinct,” both to acquired and to connate behaviour, seems to prejudge the question of their genetic connection. And since we have the well-recognized term habits for actions the performance of which becomes automatic through frequency of repetition, we may substitute this term, or the phrase habitual acts, for the “acquired instincts” of Professor Wundt. Modifying, therefore, his statement in accordance with this usage, the fact which, he says, we cannot question is that acquired habits are inherited as congenital instincts. This opinion has long been held: G. H. Lewes regarded instinctive actions as transmitted habits from which the intelligence, through which they were originally acquired, had lapsed. Darwin believed that such inheritance was a factor in the evolution of instinctive behaviour. Romanes distinguished instincts due to this mode of origin as “secondary;” reserving the term “primary” for those attributable to natural selection, and describing those in which both factors co-operate as “instincts of blended origin.” The late Professor Eimer, of Tübingen, going further than either Darwin or Romanes, reverted almost entirely to what we may term the Lamarckian interpretation. “I describe as automatic actions,” he says,[43] “those which, originally performed consciously and voluntarily, in consequence of frequent practice come to be performed unconsciously and involuntarily.... Such acquired automatic actions can be inherited. Instinct is inherited faculty, especially is inherited habit.” In his discussion of the subject Eimer makes no express allusion to primary instincts; but he attributes to lapsed intelligence some of those which were classed by Romanes as primary, and his tendency is to refer all instincts to the same source. “Every bird,” he says, “must, from the first time it hatches its eggs, draw the conclusion that young will also be produced from the eggs which it lays afterwards, and this experience must have been inherited as instinct.” Why, in the first instance, it must draw the conclusion from observation if it inherit instinctive knowledge, is not made clear. But our present purpose is to indicate, not to criticize, Eimer’s position. He claims that “the original progenitors of the cuckoo, when they began to lay their eggs in other nests, acted by reflection and design.” Of the behaviour of mason wasps and their allies, which provide their young with paralyzed but living prey, he exclaims, “What a wonderful contrivance! What calculation on the part of the animal must have been necessary to discover it!” Of the instincts of neuter bees he remarks, “Selection cannot here have had much influence, since the workers do not reproduce. In order to make these favourable conditions constant, insight and reflection on the part of the animals, and the inheritance of these faculties were necessary.” And he concludes, “Thus, according to the preceding considerations, automatic action may be described as habitual voluntary action; instinct, as inherited habitual voluntary action, or the capacity for such action.”

Turning now to the opposite end of the scale of opinion, we find that Professor Weismann, commenting on the supposed inheritance of acquired habit, says,[44] “I believe that this is an entirely erroneous view, and I hold that all instinct is entirely due to the operation of natural selection, and has its foundation, not upon inherited experiences, but upon variation of the germ.” Ziegler and Groos in Germany, Whitman and Baldwin in America, Poulton and Wallace in England, either deny the existence of secondary instincts, due to the inheritance of acquired habits, or question the sufficiency of the evidence adduced in support of such transmission. In their explanation of the manner in which that inherited co-ordination, which is biologically the central fact in instinctive behaviour, has been evolved they rely mainly or entirely on the principle of natural selection.

What, then, were the facts which appeared to Romanes sufficient to justify a belief in the existence of a class of instincts dependent on inherited habit for their origin? He tells us that he only gives a few examples “amongst almost any number” that he could quote. It is certainly unfortunate that, out of more than one hundred and fifty pages devoted to instinct in his work on “Mental Evolution in Animals,” only three[45] are assigned to secondary instincts; or six, if we include one dealing with inherited peculiarities of hand-writing in man, and two showing the force of heredity in the domain of instinct, “whether of the primary or secondary class.” It is true that many pages are devoted to instincts of blended origin, but the co-operation of the Lamarckian factor is here rather assumed than proved. We must, however, be content to take the few examples that are actually given. They are four in number. First, that ponies in Norway are used without bridles, and are trained to obey the voice; and that, as a consequence, a race-peculiarity has been established, for Andrew Knight says that it is impossible to give them what is called “a mouth.” No details are given, and Romanes does not further discuss the evidence. Secondly, Mr. Lawson Tait had a cat which was taught to beg for food like a terrier. All her kittens adopted the same habit under circumstances which precluded the possibility of imitation. Supposing the facts to be correctly reported, and granting that the owners of the kittens, presumably aware of the maternal propensity, did not take some pains to teach the offspring of such a parent to beg (and this does not present much difficulty), one can hardly found a scientific conclusion on so slight an anecdotal basis. Thirdly, instinctive fear is said to be an inherited acquisition; which, fourthly, is lost by disuse. But, as we have already seen, modern investigation has placed this matter of so-called hereditary fear of natural enemies on a different footing. Pheasants, partridges, moor-hens, and wild duck show no fear of a quiet dog. If approached gently, in the absence of their parents, callow wild birds in their nest exhibit little alarm at the slow and gentle approach of man. Mr. Hudson’s opinion has already been quoted, but will bear repetition; it is, “that fear of particular enemies is in nearly all cases the result of experience.” And there is no evidence to show that, in those cases in which it is truly instinctive and not the result of experience, the instinctive behaviour is necessarily due to inherited habit and not to natural selection.

It cannot be said that the evidence for the supposed mode of origin of secondary instincts is sufficiently varied and cogent to carry conviction. On the other hand, there does seem some evidence which points to a different conclusion. When instinctive behaviour follows on a sensory impression, not only is the co-ordination hereditary, but there is an inherited linkage of stimulus and response. Thus in the solitary wasps the sight of the natural prey is followed by the appropriate modes of attack. The Meloë larva springs upon anything hairy. In chicks the sight of a small object at a certain distance initiates the act of pecking. In moor-hens and ducklings the stimulus of water produces the movements concerned in swimming. And so, too, in many other examples of instinctive behaviour, we infer from the observed facts that stimulus and response have an organic connection founded on hereditary links in the nervous system. Now, if such connection were due to inherited habit, we should expect them to be established wherever the experience to which they are related has been constant through many generations. How comes it, then, that the chick does not instinctively respond by appropriate behaviour to the sight of water? How comes it that young birds do not instinctively avoid bees, and wasps, and nauseous caterpillars? If the effects of ancestral experience be hereditary, one would surely expect that in these cases the connection between stimulus and response—a connection which passes into acquired habit—would have become congenital; that the habitual behaviour would have long ago become instinctive. But this does not appear to be the case. And with regard to disuse causing the loss of instinct, how comes it that young chicks swim with well-ordered leg-movements, though swimming is not an act that is habitually performed by the members of their race?

What, then, has the alternative hypothesis of natural selection to advance in explanation of these facts? On this hypothesis instinctive acts have biological value in such degree that they have become congenital through the preservation of adaptive variations. But if this be so, why does not the chick respond instinctively to the sight of that which is so essential to its existence as water to drink? In reply to this question it may be suggested that, under natural conditions, the hen teaches all her chickens to peck at the water, and thus shields them from the eliminating influence which gives rise to natural selection, in the absence of which the habit of drinking in response to the sight of water, though acquired by each succeeding generation of birds, has not become instinctive and congenital. Or, to put the matter from a slightly different point of view, the maternal instincts of the hen protect her chicks from any elimination in this respect; and in the absence of such elimination the habit has not been inherited as instinct. But though the hen can lead her young to peck at the water, she cannot teach them how to perform the complex movements of the mouth, throat, and head in actual drinking. In this matter, therefore, her own instinctive procedure does not shield them from the incidence of that elimination which leads to survival under natural selection. Those chicks would be eliminated which, on pecking the water, failed to respond to the stimulus by the complex behaviour involved in drinking, leaving those to survive in which the response had been congenitally established. Thus it would seem that, when natural selection is excluded, the habit has not become congenitally linked with a visual stimulus; but when natural selection is in operation, the response has been thus linked with the stimulus of water in the bill. Whence we may infer that the co-operation of natural selection is an essential factor in the evolution of instinctive behaviour.

There are, however, cases of instinctive behaviour which may seem too trivial and unimportant to be subject to the sway of natural selection. There are numberless little idiosyncracies of behaviour which seem to be truly instinctive, which are readily recognizable as distinctive traits, but which can hardly be regarded as of sufficient biological value to determine whether the creatures in which they are developed should survive or be eliminated in the struggle for existence. In many cases, however, these serve rather to distinguish the detailed manner of behaviour than its biological end or purpose. In different species natural selection may determine the survival of those whose instinctive behaviour meets a biological need. The relatively unimportant details, differing slightly in each species, are mere adjuncts; and since natural selection deals with each species or inter-generating group separately, the essential behaviour may in each case carry with it the associated differences of manner. We must remember, too, that, as in the matter of structure so in that of behaviour, it is the animal as a whole that is selected for survival; and so long as the whole is adapted to the circumstances of life, the associated differences of form or manner may share in, without doing much to determine, survival. In any case these little instinctive traits, if they are so trivial as to seem of small value from the biological point of view, appear to be too unimportant to have been intelligently acquired as habits.

Let us now consider one or two cases of instinctive behaviour which would fall under Romanes’s category of instincts of blended origin partly due to natural selection, partly to the inheritance of acquired habit. It is the custom of the house martin to build beneath the eaves. Forsaking the ancestral rocky haunts, it has been led to utilize the houses that man has built. This has all the appearance of being due to an intelligent modification of the ancestral instinct; but how far the modification has become through heredity a congenital variation, we do not know. The intelligence which is said to have enabled the martin of the past to adopt this method of nidification is still operative. The nestlings brought up under the eaves would have opportunities for acquiring experience which might lead them to build under similar circumstances. Nest and eaves would be associated in the conscious situation. Nor would the effects of natural selection be necessarily excluded. One may suppose that in the open country, far from rock-shelters, those martins in which there was a congenital tendency to build in house-shelters would bring up their broods and transmit this tendency; while those in which it was absent would either go elsewhere or fail to bring up broods at all. In the absence of fuller knowledge as to the truly instinctive nature of the behaviour, and as to its mode of genesis, we are in large degree at the mercy of conjecture. But in any case the incidence of elimination is not necessarily excluded, and there are, therefore, no grounds for denying that natural selection has been a co-operating factor in the evolution of the instinctive behaviour, if such it be.

It is well known that the lapwing will apparently simulate the actions of a wounded bird, with the object, as it seems, of drawing intruders away from her nest. And such tactics are not restricted to this bird, nor even to one or two species. They are common, no doubt with diversities of detail, to such different birds as grouse, pigeons, plovers, rails, avocets, ducks, pipits, buntings, and warblers. Granting that the behaviour is truly instinctive, it forms a very pretty subject for transmissionists and their critics to quarrel over. “If we seek, as an example,” the transmissionist may exclaim, “an instinct which bears the marks of its intelligent, and therefore acquired origin, this of feigning wounded provides all that we can possibly demand.” “What mode of instinctive behaviour,” the selectionist may ask, “can be adduced which is more obviously useful to the species? Is not this just the kind of procedure which natural selection, if it be a factor at all, must fix upon and perpetuate through the elimination of failures? Those birds which, through congenital variation of behaviour, acted in this way would certainly enable their offspring to escape destruction by enemies, and these would survive to perpetuate the instinct.”

Let us expand the transmissionist position a little further. An extremist, of the type presented by Eimer, would perhaps urge that the lapwing reasons thus: “If I pretend to be wounded, trail my wing, and flutter along the ground, instead of flying off, I shall draw upon myself the intruder’s attention, and lead him to suppose that I shall be easily caught; and if I thus entice him away, my little ones will be saved, and my end gained.” Thus, it may be said, might the bird argue, and then give practical effect to its reasoning. But are we not here attributing to the lapwing powers of ratiocination beyond the capacity of the most intelligent of birds? Are we not assuming a histrionic power, and a realization of the effects on others of its display, which many a human actor might well covet?

“But may not the bird,” it may be urged in reply, “have found by experience, without any elaborate process of abstract reasoning, that the trick is effectual?” In any case it would be experience perilously acquired. Granting that the bird has the wit to try the trick, a little over-acting, a little too much lameness of wing, and she is herself seized and killed; a little under-acting, and the trick fails—her brood is found and destroyed. Does it not seem probable that such experience would be dearly bought, that failure would mean either death to the parent or death to the offspring? And is it not clear that natural selection is thus introduced in any case? And may not the selectionist pertinently ask: “If natural selection is thus introduced as a factor, why halt midway between two hypotheses? Why not take the further step—one by which all the difficulties attending the intelligent acquisition and the biological transmission are alike avoided—of allowing that natural selection exercises, throughout, its influence on congenital variations, and not on acquired modifications of behaviour?”

There is, however, a way in which, when natural selection is operative, intelligence may serve to foster congenital variations of the required nature and direction. We must remember that acquired habits on the one hand, and congenital variations of instinctive behaviour on the other hand, are both working, in their different spheres, towards the same end, that of adjustment to the conditions of life. If, then, acquired accommodation and congenital adaptation reach this end by different methods, survival may be best secured by their co-operation. And the more thorough-going the co-operation the better the chance of survival. There would be a distinct advantage in the struggle for existence when inherited tendencies of independent origin coincided in direction with acquired modifications of behaviour; a distinct disadvantage when such inherited tendencies were of such a character as to thwart or divert the action of intelligence. Thus any hereditary variations which coincide in direction with modifications of behaviour due to acquired habit would be favoured and fostered; while such variations as occurred on other and divergent lines would tend to be weeded out. Professor Mark Baldwin,[46] who has independently suggested such relation between modification and variation, has applied to the process the term “Organic Selection;” but it may also be described as the natural selection of coincident variations.

It may be urged, therefore, that if natural selection be accepted as a potent factor in organic evolution, and unless good cases can be adduced in which natural selection can play no part and yet habit has become instinctive, we may adopt some such view as the foregoing. While still believing that there is some connection between habit and instinct, we may regard the connection as indirect and permissive rather than direct and transmissive. We may look upon some habits as the acquired modifications which foster those variations which are coincident in direction, and which go to the making of instinct.

The net result of a study of instinctive behaviour is to lead us to the conclusion that its evolution runs parallel with the evolution of animal structure. This is perhaps best seen in the case of those insects in which typical instinctive acts are performed by larvæ of wholly different form and structure, though they are stages in the development of the same species. This is exemplified in the cases of Sitaris, Argyromœba, and Leucopsis which have been briefly described. It is probable that in all cases of instinctive action natural selection has been a co-operating factor. Without going so far as to assert with Professor Weismann the “all-sufficiency of natural selection,” we may echo the words of Professor Groos,[47] and say: “Nevertheless, we know no principle except that of selection, and we must go as far as that will take us. Absolute knowledge of such phenomena is unattainable.” And in this conclusion we have the support of Dr. Peckham, who says,[48] “We have found them [the instinctive acts of solitary wasps] in all stages of their development, and are convinced that they have passed through many degrees from the simple to the complex, by the action of natural selection. Indeed, we find in them beautiful examples of the survival of the fittest.”

CHAPTER IV
INTELLIGENT BEHAVIOUR

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.