Art and Science 



with the greater number of our more promi- 

 nent biologists on the other, involves the very 

 existence of evolution as a workable theory. 

 For it is plain that what Nature can be sup- 

 posed able to do by way of choice must 

 depend on the supply of the variations from 

 which she is supposed to choose. She cannot 

 take what is not offered to her ; and so again 

 she cannot be supposed able to accumulate 

 unless what is gained in one direction in one 

 generation, or series of generations, is little 

 likely to be lost in those that presently suc- 

 ceed. Now variations ascribed mainly to use 

 and disuse can be supposed capable of being 

 accumulated, for use and disuse are fairly 

 constant for long periods among the indi- 

 viduals of the same species, and often over 

 large areas ; moreover, conditions of existence 

 involving changes of habit, and thus of organi- 

 sation, come for the most part gradually ; so 

 that time is given during which the organism 

 can endeavour to adapt itself in the requisite 

 respects, instead of being shocked out of exist- 

 ence by too sudden change. Variations, on 

 the other hand, that are ascribed to mere 



241 Q 



