32 Comparative Conccpiions 



impulse — was looked upon as a by-product, an unjustified 

 remainder, not due to selection at all, and subserving no 

 utility in the economy of the genetic processes of evolution. 

 Now, thanks to the illuminating works of Groos,^ develop- 

 ing the scattered hints of others, we discover the psycho- 

 logical and sociological utilities of play, which supplement 

 its biological utihty in the practice theory ; and the whole 

 is an important contribution, not only to the body of evidence 

 for Darwinism, but also to the psychophysical interpreta- 

 tion of evolution. Play and art are now no longer luxuries 

 for the rich ; they are necessities as well for the poor — to 

 speak in terms not entirely figurative. 



Indeed, in this conception of correlated variation many of 

 the mysteries of evolution are pooled. The position taken 

 above, and elaborated in the later chapter, to the effect 

 that the conditions which are ' nomic ' to a genetic move- 

 ment are to be carefully distinguished from the forces 

 intrinsic to the movement, avails to indicate the capital 

 importance of the fact of variation in mind and body 

 together. Natural selection is in itself a negative prin- 

 ciple, a ' nomic ' or directive condition ; heredity is a 

 principle of conservation in so far as it is specifically and 

 only heredity ; and the remaining foundation stone of the 

 entire evolution structure, variation, remains the point of 

 direct and emphatic importance. In it the intrinsic vital 

 processes must exhibit themselves. It is by variation that 

 the materials of selection arise, it is the character of varia- 

 tion that must decide the question of determination — the 

 issue between vitalism and the opposed views. Here, in 

 the opinion of the writer, much of the great biological 

 work of the future is to be done. Witness, indeed, the 



1 The Play of Animals, and T/ie Play of Man. 



