250 THE FEELINGS AND EMOTIONS 
his leg. The one provoked yawns, and in a slow, tired kind of 
way puts himself on the defensive ; but gradually instinct con- 
quers fatigue on him too, and in a few minutes both are tear- 
ing madly about in furious rivalry until want of breath puts 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 
energy urges him to activity.” * 
Coming now to Professor Groos’s interpretation of play, we 
find in it, perhaps for the first time in the literature of the 
subject, adequate stress laid on its biological value. ‘ The 
play of young animals,” he says,f ‘‘ has its origin in the fact 
that certain very important instincts appear at a time when 
the animal does not seriously need them. . . . Its utility con- 
sists in the practice and exercise it affords for some of the 
more important duties of life, inasmuch as selection [in the 
higher animals] tends to weaken the blind force of instinct, 
and aids more and more the development of independent intel- 
ligence as a substitute for it. At the moment when intelli- 
gence is sufficiently evolved to be more useful in the struggle 
for existence than the most perfect instinct, then will selection 
favour those individuals in whom the instincts in question 
appear earlier and in less elaborated forms—in forms that are 
merely for practice and exercise,—that is to say, it will favour 
those animals which play. ... Animals cannot be said to 
play because they are young and frolicsome, but rather they 
have a period of youth in order to play; for only by so doing 
can they supplement the insufficient hereditary endowment with 
individual experience, in view of the coming tasks of life.” 
Some stress is here laid on the fact that important instincts 
appear at a time when the animal does not seriously need them. 
It seems to imply the doctrine of what biologists term “ accele- 
ration ’—which means the development of an organ or mode 
of behaviour at an earlier period in the descendants than that 
at which it appeared in the ancestors. Thus the adult fighting 
or hunting instinct of past generations appears in the young 
* Op. cit., p. 19. t Op. cit., pp. 75, 76. 
