The Play of Animals
Chapter 1: The Surplus Energy Theory of Play
THE most influential theory of play explains it by means of the surplus energy principle. In what follows I shall attempt to demonstrate that this theory has not the scope usually attributed to it. It owes its development and extension principally to Herbert Spencer, but it is based on a principle of Schiller's, in whose philosophy, however, it holds but a subordinate place. It is necessary here in the beginning of the inquiry, to set Schiller's priority in the right light, as it does not seem to be generally known. Schiller's treatment of play and the play instinct is to be found in his excellent letters On the Aesthetic Education of Mankind. Later I shall enter more fully into their contents, confining myself here to the passage on which the theory of surplus energy is especially based. It is in the twenty-seventh letter, and reads as follows: "Nature has indeed granted, even to the creature devoid of reason, more than the mere necessities of existence, and into the darkness of animal life has alloyed a gleam of freedom to penetrate here and there. When hunger no longer torments the lion, and no beast of prey appears for him to fight, then his unemployed powers find another outlet. He fills the wilderness with his wild roars, and his
(2) exuberant strength spends itself in aimless activity. In the mere joy of existence, insects swarm in the sunshine, and it is certainly not always the cry of want that we hear in the melodious rhythm of bird-songs. There is evidently freedom in these manifestations, but not freedom from all necessity, only from a definite external necessity. The animal works when some want is the motive for his activity, and plays when a superabundance of energy forms this motive — when overflowing life itself urges him to action." I will not assert that in his choice of examples from animal life Schiller has here set forth particularly clear or unchallengeable cases, but that what he had to say about them is expressed with perfect clearness — namely, that the animal is impelled to serious work by an external want, but to play by his own superfluity of energy. Through the one he restores his depleted powers; by means of the other he gives vent to superfluous ones.
Jean Paul and J. E. Beneke express themselves much as Schiller does with reference to human play. " Play," says Jean Paul in Levana (§ 49), "is at first the expression of both mental and physical exuberance. Later, when school discipline has subjected all the passions to rule, the limbs alone give expression to the overflowing life by running, leaping, and exercising generally." And Beneke says, " The child directs his superfluous energy chiefly to play," and traces this tendency back to " conservation of original powers." 
Spencer gives a short account of his theory in the last chapter of the Principles of Psychology, which treats of the aesthetic feelings. "Many years ago," says he (§ 533), " I met with a quotation from a German author to the effect that the aesthetic sentiments originate from the play impulse. I do not remember the name of the author, and if any reasons were given for this statement, or any inferences drawn from it, I can not recall them. But the statement itself has remained with me, as being one which, if not literally true, is yet the adumbration of a truth." It is now well known to many readers of Spencer from what German work was derived this citation which made such a lasting impression on him. Many have publicly expressed themselves on the subject, as Sully, Grant Allen,  and myself in my Einleitung in die Aesthetik. The doctrine of the origination of the aesthetic feelings from play impulses is the cardinal point of Schiller's theory of the beautiful as it is revealed to us in these letters on aesthetic education. Schiller himself, not to speak of Kant, may have been influenced by Home, and so the idea merely found its way back to England when he in turn influenced Spencer. So far this indebtedness of Spencer to Schiller is pretty generally recognised in professional circles. But it is quite otherwise with the passage just quoted; it occurs in a part of the Aesthetics letters, comparatively unfamiliar, and therefore seemingly overlooked by most readers. " The theory " (of play impulse), says Wallaschek "remained unheeded, though committed to writing nearly a century ago. Put, in our times into
(4) scientific form by Mr. Herbert Spencer, it has nothing in common with its earlier presentment beyond the name, the grounds being quite different." Had the above-cited passage from Schiller's letters been known to Wallaschek, he could never have written this statement, for it sets forth in plain words the very "grounds" on which Mr. Spencer founded his theory—namely, the doctrine of superfluous energy as the cause of play. Moreover, Schiller is the forerunner of Spencer, not only in that he derives the aesthetic feelings from play impulses, but also in teaching that play impulse itself has its origin in superfluous energy. How far-reaching this correspondence is will be seen if I now let Spencer speak: "Inferior kinds of animals have in common the trait that all their forces are expended in fulfilling functions essential to the maintenance of life. They are unceasingly occupied in searching for food, in escaping from enemies, in forming places of shelter, and in making preparation for progeny. But as we ascend to animals of high types, having faculties more efficient and more numerous, we begin to find that time and strength are not wholly absorbed in providing for immediate needs. Better nutrition, gained by superiority, occasionally yields a surplus of vigour. The appetites being satisfied, there is no craving which directs the overflowing energies to the pursuit of more prey or to the satisfaction of some pressing want. The greater variety of faculty commonly joined with this greater efficiency of faculty has a kindred result. When there have been developed many powers adjusted to many requirements, they can not all act at once; now the circumstances call these into exercise and now those, and some of them occasionally remain unexercised for considerable periods. Thus it happens that in the more evolved creatures there
(5) often occurs an energy somewhat in excess of immediate needs, and there comes also such rest, now of this faculty and now of that, as permits the bringing of it up to a state of high efficiency by the repair which follows waste." If we add to this the fact that such overflow of energy is explained by Spencer physiologically as a reintegration which more than balances the using up of brain cells, thus producing in the cells an " excessive readiness to decompose and discharge," we have become acquainted with the foundation of Spencer's theory of play. It is perfectly evident that it has more in common with Schiller's theory than the mere name; that, indeed, in its " grounds " it fully coincides with the passage cited from the Aesthetics letters. In one point only does Spencer go beyond Schiller's conception: he connects the idea of imitation with that of the overflow of energy. And it is exactly at this point that Spencer seems to me to have erred. I will return to his own text and endeavour to show that he can not substantiate his data. After he has given the foregoing physiological explanation of surplus energy, he goes on: " Every one of these mental powers then being subject to this law, that its organ, when dormant for an interval longer than ordinary, becomes unusually ready to act, unusually ready to have its correlative feelings aroused, giving an unusual readiness to enter upon all the correlative activities; it happens that a simulation of these activities is easily fallen into, where circumstances offer, in place of the real activities. Hence play of all kinds" "It is," says R. Wallaschek, in agreement
(6) with Spencer, "the surplus vigour in more highly developed organisms, exceeding what is required for immediate needs, in which play of all kinds takes its rise, manifesting itself by way of imitation or repetition of all those efforts and exertions which are essential to the maintenance of life." 
In review I may here enumerate the essential points so far made:
1. The higher animals being able to provide themselves with better nourishment than the lower, their time and strength are no longer exclusively occupied in their own maintenance, hence they acquire a superabundance of vigour.
2. The overflow of energy will be favoured in those cases where the higher animals have need for more diversified activities, for while they are occupied with one, the other special powers can find rest and reintegration.
3. When, in this manner, the overflow of energy has reached a certain pitch, it tends to discharge.
4. If there is no occasion at the moment for the correlative activity to be seriously exercised, simply imitative activity is substituted, and this is play.
There can be no doubt that the conception of play thus set forth is very plausible, but its inadequacy can easily be demonstrated. Should play indeed be universally considered as the imitation of serious activities, for which there may be inclination but no opportunity? There is, of course, no doubt that imitation is of the greatest importance in much play, and I shall often have occasion t0 refer in the sequel to the imitative impulses. Nevertheless it is true that the conception of
(7) imitation here set forth—namely, as the repetition of serious activities to which the individual has himself become accustomed—can not be applied directly to the primary phenomena of play—that is, to its first elementary manifestations, to the play of young animals and of children. For such plays, which must be explained at the very outset in order to get a satisfactory conception of the subject, are very often not imitations (Nachahmungen), but rather premonitions (Vorahmungen) of the serious occupations of the individual. The " experimenting " of little children and young animals, their movement, hunting, and fighting games, which are the most important elementary forms of play, are not imitative repetitions, but rather preparatory efforts. They come before any serious activity, and evidently aim at preparing the young creature for it and making him familiar with it. The tiny bird that tries its wings while still in the nest; the antelope that (as Dr. A. Seitz, director of the zoölogical gardens at Frankfort, tells me) attempts to practise leaping at the age of six weeks; the young monkey that playfully seizes anything within his reach, and is only quieted when he has caught his claws in the tufts of hair on his own body, and fettered them; the giraffe that is at home in its cage by the third day of life; the feline tribe that learn so early to cling by their claws; the dog which educates itself, by play, for fighting with other dogs, and for pursuing, seizing, shaking, and rending its prey; the infant that through continual practice in moving the fingers and toes, in kicking, creeping, arid Aising itself, in crowing and babbling, wins the mastery over his organs; the boy that romps with others, and "can no more help running after another boy who runs provokingly near him than a kitten can help
(8) running after a rolling ball—all these do not imitate serious action, whose organ has been dormant for an interval " longer than ordinary," but rather, impelled by irresistible impulse, they make their first preparations for such activities in this way.
Spencer's theory of play is therefore unsatisfactory, so far, as concerns the adequacy of its explanation of the problem by means of the principle of imitation of previously accomplished serious activities of the individual. And since in all the cases cited there is really no imitation of other individuals—that is, no "dramatization of the acts of adults " of which Spencer elsewhere treats —it appears that this principle of imitation can not be taken as a universal explanation of play. Nor can I agree with Professor Wundt when he says, in his Lectures on Human and Animal Psychology: "We regard certain actions of the higher animals as play when they appear to be imitations of voluntary acts. But they can be recognised as imitations because the result striven for only appears to be such, while the real end is the production of certain pleasurable effects, which are connected, though as mere accompaniments only, with real voluntary action. This is as much as to say that animal play is in general terms identical with that of the human being. For this is, at least in its simpler form, and especially as it appears in the play of children, 'imitation of the business of practical life' stripped of its original aim and having a pleasurable mental effect." Wundt, in his
(9) Ethik, in which he is evidently influenced by Spencer, sets forth this idea perhaps more clearly. "Play," he says there, "is the child of work. There is no kind of play that does not find its prototype in some form of serious activity which naturally precedes it."
It is, of course, undeniable that many plays originate in such imitation, but a glance over the passages cited above is sufficient to show that the most important and elementary kinds of play can be attributed neither to imitative repetition of the individual's former acts, nor to imitation of the performances of others.
If, then, Spencer's theory becomes so far untenable through the deviation of its imitative principle from Schiller's, our next step is evidently to inquire whether Schiller's idea alone would be satisfactory. Can it be admitted that accumulated superabundance of energy alone suffices to explain all the phenomena of play in animals? In order to get at the full meaning of this conception we must consider the psychological aspect of the surplus energy theory, as well as its merely physiological side. No doubt superabundant physical activity may often be considered as the psychological expression of exuberant spirits. This comes very near the idea that the play of animals and human beings originates in such physically conditioned dispositions; it is only necessary to instance the great influence good weather and comfortable temperature have on animals and men. Karl Müller notices this in an article on The Mental Life of Higher Animals in connection with the great influence the weather hag on bird-songs, and says further: "Does this belong to the sexual instinct? Or has not rather the sense of comfort and well-being the
(10) most influential part in it? Look at the healthy boy as he runs outdoors with his bread and butter. We often see him break forth into the most childish expressions of delight over the joy-bringer in his hand, and this delight in the thought of eating will show itself in leaping and running, and often in singing, the more excessively the more feeling or temperament controls him. And though the more advanced adult may not express his pleasurable excitement in singing, he does by whistling." Th. Ziegler makes use of the same idea: " Joy in life, consciousness of strength, and the feeling of power—in short, the feeling of pleasure as such, is in its primitive and original meaning the beginning and the end of play for children."  And W. H. Hudson says in his wonderful book, The Naturalist in La Plata:  " My experience is that mammals and birds, with few exceptions—probably there are really no exceptions—possess the habit of indulging frequently in more or less regular or set performances, with or without sound, or composed of sound exclusively, and that these performances, which in many animals are only discordant cries and choruses, and uncouth, irregular motions, in the more aërial, graceful and melodious kinds take immeasurably higher, more complex, and more beautiful forms."  " We see that the inferior animals, when the conditions of life are favourable, are subject to periodical fits of gladness, affecting them powerfully, and standing out in vivid contrast to their ordinary temper. And we
(11) know what this feeling is—this periodic intense elation which even civilized man occasionally experiences when in perfect health, more especially when young. There are moments when he is mad with joy, when he can not keep still, when his impulse is to sing and shout aloud and laugh at nothing, to run and leap and exert himself in some extravagant way. Among the heavier mammalians the feeling is manifested in loud noises, bellowings, and screamings, and in lumbering, uncouth motions—throwing up of heels, pretended panics, and ponderous mock battles. In smaller and livelier animals, with greater celerity and certitude in their motions, the feeling shows itself in more regular and often in more complex movements. Thus Felidoe, when young, and very agile, sprightly species like the puma, throughout life simulate all the actions of an animal hunting its prey . . . . Birds are more subject to this universal joyous instinct than mammals, more buoyant and graceful in action, more loquacious, and have voices so much finer, their gladness shows itself in a greater variety of ways, with more regular and beautiful motions, and with melody."
There is certainly no question that from the conception of physical and mental overflow of energy as it is laid before us in this series of pictures, a knowledge of one of the most important characteristics of the play condition is obtained. The physiological impulse that impels the latent powers to activity, and that mental joyousness whose highest point of development Schiller lifts justly recognised as the feeling of liberty, Certainly form one of the most obvious characteristics of play. But it is quite as certain that the question whether by
(12) it a full comprehension of human and animal play can be obtained, must receive a negative answer; for, while simple overflow of energy explains quite well that the individual who finds himself in a condition of overflowing energy is ready to do something, it does not explain how it happens that all the individuals of a species manifest exactly the specific kind of play expression which prevails with their own species, but differs from every other. " Every species," says Hudson most truly, " or group of species has its own inherited form or style of performance; and however rude and irregular this may be, as in the case of the pretended stampedes and fights of wild cattle, that is the form in which the feeling will always be expressed." Such a fact, depending as it does on the phenomena of hereditary transmission, evidently can not be explained by simple overflow of energy in an individual. Spencer has attempted to make use of the theory of imitation to point out the how and why of play activity. But we have seen that the most elementary and important plays can not be referred to it. It thus becomes necessary to call in the aid of some other conception of the subject. The solution of the problem is near at hand. Instead of pressing the idea of imitation exclusively, it is necessary to include that of instinct in general. Spencer himself has approached the right understanding of the problem. When he asks, What acts are chiefly imitated?—he reaches the conclusion, chiefly such actions as " in the life of this particular creature play the most important rôle."
And proceeding to give some examples of this, he
(13) points out that these important activities are instincts, in particular destructive and robbing instincts. Thus it is only necessary for him to modify his theory of imitation to stand directly in the presence of the right conception of play which lies so near his own. What form would the theory of play take in this case? Something like this: The activity of all living beings is in the highest degree influenced by hereditary instincts—that is, the way an animal of a particular species controls his members and uses his voice, the way he moves about in his natural element, supplies himself with food, fights with other animals, or avoids them—his manner of doing all these things is governed fundamentally by inherited instincts. When, now, there is on the one hand little demand for the serious activity of such instincts, and, on the other hand, the reintegration of nerve energy so far surpasses its expenditure that the organism requires some discharge of the accumulated supply of force — and both conditions are likely to be the case in youth —then such instincts find expression even without serious occasion. The kitten treats a scrap of paper as its prey, the young bear wrestles with his brother, the dog which after long confinement is set free hunts aimlessly about, etc. But such actions are exactly what we mean by the word play. 
Paul Souriau seems to occupy a position similar to this in an interesting article where he advances the following idea: There are various grounds for the pleas-
(14) -ure that animals almost universally take in movement. One of them is found in the fact that the animal is obliged to have a great capacity for movement in all the tasks of its life, for obtaining food, fleeing from its enemies, etc., and accordingly is endowed by nature with a correspondingly great feeling of the necessity for movement. When there is no occasion to give free play to this feeling, of necessity the confined impulses seek to break through all restrictions, even without serious motive, and so play arises. "Hence the movements of captive animals, of the lion who walks up and down his cage, of the canary bird that hops from perch to perch." So the necessity for movement controls even an inactive existence. For Souriau, too, there are inherited instincts that lead to play when superfluous nervous energy is present and the occasion for serious activity wanting.
Such a conception as this, which does not need the principle of imitation, seems to me to be much nearer the truth. If we glance backward from this point of our inquiry we perceive that the essential points of the whole question have shifted considerably. At first the idea of the overflow of energy stood predominantly in the very centre of our mental horizon. But soon it appeared that for a full estimate of play it was necessary to consider something else. Now that we have found this something else to be instinct, the principle of surplus energy begins to lose some of its original importance. For it is now apparent that the real essence of
(15) play, the source from which it springs, is to be sought in instinct. It is an essential fact that the instincts are constantly lurking in ambush ready to spring out on the first occasion. A condition of surplus energy still appears as the conditio sine qua non, that permits the force of the instincts to be so augmented that finally, when a real occasion for their use is wanting, they form their own motive, and so permit indulgence in merely sportive acts. Here I reach the limits of a merely physiological explanation of play. But before going a step further in the criticism of the overflow-of-energy theory by seeking to find a standpoint which includes the biological significance of play, I may here consider another theory which at first appears to be diametrically opposed to that of surplus energy. I mean the conception which obtains, especially in Germany, that play is for recreation. Steinthal has recently shown very beautifully how recreation may be considered from its intrinsic significance to mean making one's self over— that is, creating anew, restoring lost powers, both physical and mental. Such restoration can be had partially by means of sleep and nourishment. But in recreative play strength is needed to win strength. This idea is advanced by many. Guts Muths entitles his collection of games, Games for the Exercise and Recreation of Body and Mind. 
Schaller says that to the cultivated consciousness play presents itself somewhat as follows: An occupation not directed to flip satisfaction of simply natural requirements or to the discharge of the practical busi-
(16) -ness of life, but securing rather the end of recreation. Lazarus directs us, when we need restoration, to flee from empty idleness to active recreation in play. The Jesuit Julius Caesar Bulengerus begins his book on the games of the ancients with these words: " Neque homines neque bruta in perpetua corporis et animi contentione esse possunt non magis quam fides in cithara aut nervus in arcu. Ideo ludo egent. Ludunt inter se catuli equulei, leunculi, ludunt in aquis pisces, ludunt homines labore fracti, et aliquid remittunt, ut animos reficiant." But the most attractive exposition of the theory of recreation is given in an old legend quoted by Guts Muths. John the Evangelist was once playing with a partridge, which he stroked with his hand. A man came along, in appearance a sportsman, and beheld the evangelist with astonishment because he took pleasure in a little creature which was of no account. " Art thou, then, really the evangelist whom everybody reads and whose fame has brought me here? How does such vanity comport with thy reputation? " " Good friend," replied the gentle John, "what is that I see in your hand?" " A bow," answered the stranger. "And why do you not have it always strung and ready for use? " " That would not do. If I kept it strung it would grow lax, and be good for nothing." "Then," said John, " do not wonder at what you see me do."
Here, then, there seems to be an irreconcilable conflict. The Schiller-Spencer theory allows the accumulated surplus of energy to expend itself in play; the rec-
(17) -reation theory, on the contrary, finds in the very acts restoration of the powers that are approaching exhaustion. There they are wastefully cast off; here, thriftily stored away. Is it not remarkable that the same object can present itself to the observer in ways so contrary? A closer examination, however, shows that in this case the contradiction is only apparent. In fact, the two ideas can in many cases be so developed that they appear as different aspects of the same conception mutually explanatory of each other. When, for example, a student goes to have a game of ninepins in the evening, he thus tones up his relaxed mental powers at the same time that he finds a means of relieving his accumulated motive impulses, repressed during his work at the desk. So it is the same act that on the one hand disposes of his superfluous energy, and on the other, restores his lost powers. This is true in all cases when play can be considered as recreation. The recreation theory is thus, so far as it has any value at all, not contradictory, but rather supplementary to the Schiller-Spencer idea of play. An exhaustive criticism of the recreation theory, in so far as it claims to explain play, I do not consider necessary in a book treating of the play of animals. For it must be evident to any one, on reflection, that this idea, which may be very effective in a limited sphere, could not be justifiably expanded for application to the whole field of play. It occupies too much the standpoint of the adult who seeks recreation in a " little game " after the burden and heat of the day. That play can furnish recreation is not questioned, only that the necessity for recreation originates play. That the young dog romps with his fellows because he feels the need of recreation no one will seriously affirm. Evidently the advocates of the recreation theory, as a rule, know very little about the
(18) play of animals, and probably they have no conception of the extent of the subject. But the child whose whole mental life, as J. Schaller rightly remarks, partakes predominantly of the character of play, must bear witness to the fact that while play may satisfy in many cases the need for recreation, it most certainly does not originate in it. I have been obliged to give special attention to the recreation theory, because it seemed to contradict the doctrine of surplus energy. It has now been shown that this is not the case. In seeking to go a step further in my criticism of the Spencerian theory, I find no support in the recreation idea, but must attempt to go on independently. Let us present clearly to our minds the position of our inquiry. Setting out with the overflow-of-energy idea, we found that Spencer's connection of this principle with that of imitation was not applicable to all play. Thus the expectation of explaining it all by means of surplus energy alone was found to be untenable. We then went on to include the idea of instinct. The overflow of accumulated vigour no longer appeared as the source of play, but yet as its conditio sine qua non. As now I proceed in the following pages to throw doubt also upon this formulation of the Schiller-Spencerian principle, I wish to avoid misunderstanding by making it clear at the outset that I do not underestimate the worth of that idea. It only seems to me that, even considering it as a mere conditio sine qua non of play, there is still a large territory to be accounted for outside of its limits. However, the overflow of energy is sufficiently important, and must be considered still the most favourable though not the necessary condition of play.
Going on now to the arguments that ground my own opinion, it can very easily be shown that the facts do not point to the universal or essential value of the Schiller-Spencerian principle. Certainly in innumerable cases the superfluity of unemployed energy gives an impulse to play, but in many others one is impressed with the fact that instinct is a power in itself which does not need special accumulated stores of energy to bring it into activity. Some examples will snake this clear. Notice a kitten when a piece of paper blows past. Will not any observer confirm the statement that just as an old cat must be tired to death or else already filled to satiety if it does not try to seize a mouse running near it, so will the kitten, too, spring after the moving object, even if it has been exercising for hours and its superfluous energies are entirely disposed of? Or observe the play of young dogs when two of them have raced about the garden until they are obliged to stop from sheer fatigue, and they lie on the ground panting, with tongues hanging out. Now one of them gets up, glances at his companion, and the irresistible power of his innate longing for the fray seizes him again. He approaches the other, sniffs lazily about him, and, though he is evidently only half inclined to obey the powerful impulse, attempts to seize his leg. The one provoked yawns, and in a slow, tired kind of way puts himself on the defensive; but gradually instinct conquers fatigue in him too, and in a few minutes both are tearing madly about in furious rivalry until the want of breath pasta an end to the game. And so it goes on with endless repetition, until we get the impression that the dog waits only long enough to collect the needed strength, not till superfluous vigour urges him to activity. I have often noticed that a young dog whom I have taken for
(20) a long walk, and who at last, evidently tired out, trotted behind me in a spiritless manner very different from his usual behaviour, as soon as he was in the garden and spied a piece of wood, sprang after it with great bounds and began playing with it. Just so we see children out walking who are so tired with their constant running about that they can only be kept from tears by coaxing, yet quickly set their tired little legs in motion again and deny their fatigue if an opportunity offers for play. Of children and young animals it is true that, except when they are eating, they play all day, till at night, tired out with play, they sink to sleep. Even sick children play, but only to the extent that their strength admits of it, and not as it exists overabundantly. Similar observations may be made with regard to the playing adult in many cases. A student who has worked all day with a mental strain, so that he can hardly collect his thoughts for any serious effort, sits down in the evening to the mock battle of a card table and takes his part in the game with spirit for its complicated problems. "If any one will analyze the mental operations belonging to a single game of cards, the chains of reasoning which each player carries on for himself and attributes to the others, in order to plan for circumventing them, he will be much surprised at the variety and inexhaustible richness of mental activity displayed." Can we speak in such cases of a superfluity of mental energy that originated from the fact of longer rest than usual?
A soldier or a banker who is engaged day by day in an exciting struggle with the caprices of fortune hurries to the gaming table, and for half the night, wavering between hope and fear, strives to produce the same sen-
(21) -sations. Must it not be admitted that he does not play for recreation nor for the relief of stored-up energy? It is the simple force of the demon instinct that urges and even compels to activity not only if and so long as the vessel overflows (to use a figure of speech), but even when there is but a last drop left in it. The theory of overflowing energy requires that first and necessarily there shall be abounding vigour; from it the impulse must originate. Superabundant life compels itself to act, says Spencer. The instincts would in that case be only the bed prepared for the self-originated stream to flow in. I maintain, on the other hand, that though this often appears true, it does not always prove to be so.
It is not necessarily true that the impulse results from the overreadiness and straining of the nervous system for discharge. Notice the kitten that lies there lazily, perhaps even softly dozing, till a ball rolls toward it. Here the impulse comes from an external excitement that wakes the hunting instinct. If the kitten has a particular need for motor discharge she will play of
(22) course. But when this need is not present, as is the case in our example, she still leaps after the ball; and only when disabled through utter fatigue would the cat fail to obey the impulse. The physiological conditions that lead a young animal to play at hunting need not be any other than those which enable an adult animal to pursue its natural prey.
If, therefore, these facts lead us to expect to find the chief problems of play in our conception of instinct, they also force upon us a consideration of the great biological significance of play. For even if I should not succeed in convincing the reader that superabundance of nerve energy is not even a conditio sine qua non, but rather only a particularly favourable condition for play, I have still every right to maintain that the Schiller-Spencer theory is unsatisfactory; for while it attempts, it is true, to make clear the physiological conditions of play, this theory has nothing to say about its great biological significance. According to it, play would be only an accidental accompaniment of organic development. For the advance toward perfection, due to the struggle for existence, brings it about that the more highly developed animals have less to do than their powers are competent for. Opposed to this view is the very general conviction among those who study animals that the play of young animals especially has a clearly defined biological end—namely, the preparation of the animal for its particular life activities. I have heard this explanation of play given in similar terms by foresters and by zoölogical specialists. Thus Paul Souriau says, in the article already referred to: " The necessity for movement is especially great in youth, because the young animal must try all the movements that he has to make later, and also exercise his muscles and joints to de-
(23) -velop them. We know that all animals have a tendency to make use of a certain amount of energy, determined not by the accidental needs of the individual, but by the needs of the species in general." But if this is the case, play itself is not merely a result of the accidental needs of the individual, but rather an effect of natural selection, which works for anything that is serviceable for the preservation of the species. The observation of the different kinds of play is sufficient to establish this. Most plays of young animals—and it is this that must always present the essential problem in a theory of play —act for the preservation of the individual, all for the preservation of the species. At the same time the natural—that is, the self-originated—plays of human beings are to be considered as practice that is useful not only to the individual, but also to the race. " Pro patria eat, dum ludere videmur " is the motto that Guts Muths has placed in the front of his book.
Can a phenomenon that is of so great, so incalculable value possibly be simply a convenient method of dissipating superfluous accumulations of energy? In all this there seems nothing to hinder the assumption that the instincts operative in play, like so many phenomena of heredity, first appear when the animal really needs them. Where, then, would be the play of the young? It would not be provoked either by overflowing nervous energy or by the need for recreation. Yet the early appearance of this instinct is of inestimable importance. Without it the adult animal would be but poorly equipped for the tasks of his life. He would have far less than the requisite amount of practice in running and leaping, in springing on his prey, in seizing and strangling the victim, in fleeing from his enemies, in fighting his opponents, etc. The muscular system would
(24) not be sufficiently developed and trained for all these tasks. Moreover, much would be wanting in the structure of his skeleton, much that must be supplied by functional adaptation during the life of each individual, even in the period of growth. The thought presents itself here that it must be the iron hand of natural selection that brings into bold relief without too compelling insistence and apparently without serious motive—namely, by means of play—what will later be so necessary. There need not be any particular superfluity of energy; so long as only a small remnant of unemployed force is present the animal will follow the law that heredity has stamped upon him.
Thus we see that the explanation of play by means of the overflow-of-energy theory proves to be unsatisfactory. A condition of superabundant nervous force is always, I must again emphatically reiterate, a favourable one for play, but it is not its motive cause, nor, as I believe, a necessary condition of its existence. Instinct alone is the real foundation of it. Foundation, I say, because all play is not purely instinctive activity. On the contrary, the higher we ascend in the scale of existence the richer and finer become the psychological phenomena that supplement the mere natural impulse, ennobling it, elevating it, and tending to conceal it under added details.
But the fundamental idea from which we must proceed is instinct. My first task must be the examination of instinct; and after a longer, but I hope not altogether uninteresting, exposition, I shall return to the points made above and give them more adequate treatment.