On the whole, therefore, we find the Surplus-Energy Theory of play quite inadequate.
II. Another theory therefore becomes necessary if we are to meet these difficulties. Such a theory has recently been developed. It holds that the plays of the animals are of the greatest utility to them in this way: they exercise the young animals in the very activities—though in a playful way—in which they must seriously engage later on in life. A survey of the plays of animals with a view to comparing them in each case with the adult activities of the same species, confirms this theory in a remarkably large number of cases. It shows the young anticipating, in their play, the struggles, enjoyments, co-operations, defeats, emergencies, etc., of their after lives, and by learning to cope with all these situations, so preparing themselves for the serious onset of adult responsibilities. On this theory each play becomes a beautiful case of adaptation to nature. The kitten plays with the ball as the old cat handles the mouse; the little dogs wrestle together, and so learn to fight with teeth and claws; the deer run from one another, and so test their speed and learn to escape their enemies. If we watch young animals at play we see that not a muscle or nerve escapes this preliminary training and exercise; and the instinctive tendencies which control the play direct the activities into just the performances which the animal's later life-habits are going on to require.
On this view play becomes of the utmost utility. It is not a by-product, but an essential part of the animal's equipment. Just as the infancy period has been lengthened in the higher animals in order to give the young time to learn all that they require to meet the harsh conditions of life, so during this infancy period they have in the play-instinct a means of the first importance for making good use of their time. It is beautiful to see the adults playing with their young, adapting their strength to the little ones, repeating the same exercises without ceasing, drilling them with infinite pains to greater hardihood, endurance, and skill.
On this theory it is also easy to see why it is that the plays are different for the different species. The actual life conditions are different, and the habits of the species are correspondingly different. So it is only another argument for the truth of this theory that we find just those games natural to the young which train them in the habits natural to the old.
This view is now being very generally adopted. Many fine illustrations might be cited. A simple case may be seen in so small a thing as the habit of leaping in play; the difference, for example, between the mountain goat and the common fawn. The former, when playing on level ground makes a very ludicrous exhibition by jumping in little up-and-down leaps by which he makes no progress. In contrast with this the fawn, whose adult life is normally in the plains, takes a long graceful spring. The difference becomes clear from the point of view of this theory, when we remember that the goat is to live among the rocks, where the only useful jump is just the up-and-down sort which the little fellow is now practising; while the deer, in his life upon the plains, will always need the running jump.
Finally, on this theory, play becomes a thing for evolution to cultivate for its utility in the progress of animal life, and for that reason we may suppose it has been perfected in the remarkable variety and beauty of form which it shows.
On the psychological side, we find a corresponding state of things. The mind in the young animal or child gets the main education of early life through its play situations. Games have an extraordinary pedagogical influence. The more so because they are the natural and instinctive way of getting an education in practical things. This again is of supreme utility to the individuals.
Both for body and mind we find that play illustrates the principle of Organic Selection explained above. It makes the young animal flexible, plastic, and adaptable; it supplements all his other instincts and imperfect functions; it gives him a new chance to live, and so determines the course of evolution in the direction which the playful animal represents. The quasi-social and gregarious habits of animals probably owe much of their strength to the play-impulse, both through the training of individual animals and through the fixing of these tendencies as instincts in various animal species in the way just mentioned.
In another place below I analyze a child's game and draw some inferences from it. Here it may suffice to say that in their games the young animals acquire the flexibility of mind and muscle upon which much of the social co-operation, as well as the individual effectiveness, of their later life depends. With children, it is not the only agency, of course, though its importance is not less. We have to carry the children further by other means; but the other means should never interfere with this natural schooling. They should aim the rather by supplementing it wisely to direct its operation and to extend its sphere.