Ii8 Evolution and Adaptation 



dependently of the change of climate itself, would seriously 

 affect the others. ... In such cases, slight modifications, 

 which in any way favored the individuals of any species, by 

 better adapting them to their altered conditions, would tend 

 to be preserved ; and natural selection would have free scope 

 for the work of improvement." 



The first half of the first of these two quotations seems so 

 plausible, that without further thought we may be tempted 

 to give a ready assent to the second, yet the whole issue is 

 contained in this statement. In the abstract, it undoubtedly 

 appears true that any slightly useful modification might tend 

 to be preserved. Whether it will, in reality, be preserved 

 must depend on many things that should be taken into 

 account. This question will come up later for further con- 

 sideration ; but it should be pointed out here, that, even 

 assuming that one or more individuals happen to possess a 

 favorable variation, it by no means follows that natural 

 selection would have free scope for the work of improvement, 

 because the question of the inheritance of this variation, 

 and of its accumulation and building up through successive 

 generations, must be determined before we can be expected 

 to give assent to this argument, that appears so attractive 

 when stated in an abstract and vague way. 



Darwin again makes the statement that under the term 

 variation it must never be forgotten that mere individual 

 differences are meant. " As a man can produce a great 

 result with his domestic animals and plants by adding up in 

 any given direction individual differences, so could natural 

 selection, but far more easily from having incomparably 

 longer time for action." Too much emphasis cannot be laid 

 on the fact that Darwin believed that selection takes place 

 amongst the small individual differences that we find in 

 animals and plants. Some of his followers, as we shall see, 

 are apt to put into the background this fundamental con- 

 ception of Darwin's view. His constant comparison between 



