xx THE PLAY OF ANIMALS. 



and critical investigation of the subject, I intrench 

 myself in the principles denned by H. E. Ziegler, who, 

 as a disciple of Weismann, refers all instincts directly to 

 natural selection. Accordingly, I have not used the La- 

 marckian principle of the transmission of acquired char- 

 acters, which, to say the least, is doubtful, in the inter- 

 pretation of fact. On this definition of instinct as a basis 

 a new biological theory of play is developed, of which the 

 following are the main points : The real problem lies in 

 the play of the young; that once successfully explained, 

 adult play will offer no special difficulties. The play of 

 youth depends on the fact that certain instincts, espe- 

 cially useful in preserving the species, appear before the 

 animal seriously needs them. They are, in contrast with 

 later serious exercise (Ausubung), a preparation (Vor- 

 ubung) and practice (Einubung) for the special instincts. 

 This anticipatory appearance is of the utmost impor- 

 tance, and refers us at once to the operation of natural 

 selection; for, when the inherited instinct may be sup- 

 plemented by individual experience, it need not be so 

 carefully elaborated by selection, which accordingly fa- 

 vours the evolution of individual intelligence as a substi- 

 tute for blind instinct. At the moment when the intelli- 

 gence reaches a point of development where it is more 

 useful than the most perfect instinct, natural selection 

 will favour individuals in whom instinct appears 

 only in an imperfect form, manifesting itself in early 

 youth in activity purely for exercise and practice — that 

 is to say, in animals which play. Indeed, the conclusion 

 seems admissible, in summing up the biological signifi- 

 cance of play, that perhaps the very existence of youth is 

 due in part to the necessity for play; the animal does 

 not play because he is young, he has a period of youth 

 because he must play. Whoever has observed the tre- 



