PLAY AND INSTINCT. 81 



Play is found among adult animals. A creature 

 that once knows the pleasure of play will derive satis- 

 faction from it even when youth is gone. And preserva- 

 tion of the species is advanced by exercise of the mind 

 and body even in later years. I have a dog twelve 

 years old that still shows a disposition to play now and 

 then. We often see grown-up animals playfully roll 

 over and over without any object, and many birds ap- 

 pear to sing from mere sportiveness without relation to 

 courtship. Proof of this is difficult to substantiate, how- 

 ever. We do know that adult cats and dogs play, but 

 in regard to other animals we can only speak of proba- 

 bihties. If the playful character of some of the exam- 

 ples which I cite in the following chapters is not estab- 

 lished beyond a doubt, I am consoled by a statement 

 of Darwin's, made with great emphasis in The Descent 

 of Man: * " Nothing is more common than for animals 

 to take pleasure in practising whatever instinct they 

 follow at other times for some real good. How often 

 do we see birds which fly easily, gliding and sailing 

 through the air obviously for pleasure? The cat plays 

 with the captured mouse and the cormorant with the 

 captured fish. The weaver-bird when confined in a cage 

 amuses itself by neatly weaving blades of grass between 

 the wires of the cage. Birds which habitually fight dur- 

 ing the breeding season are generally ready to fight at 

 all times, and the males of the capercailzie sometimes 

 hold their Balzen at the usual place of assemblage dur- 

 ing the autumn. Hence it is not at all surprising that 

 male birds should continue singing for their own amuse- 

 ment after the season for courtship is over." 



* Descent of Man, vol. ii, p. 60. 



