DARWIN, AND THE ORIGIN OF SPECIES 1 87 



eration would be so slight as to be unrecognizable except by actual 

 trial. 



A living thing is a being which responds to the stimulus of 

 one event in such a way as to adjust its actions to other events 

 of which the stimulus is the sign, and as all that have not thus 

 responded have been exterminated in the struggle for existence, the 

 adjustment of the survivors is no more than might have been 

 expected. 



Natural selection seems to me a strictly scientific explanation 

 of the fitness of living things, and they who assert that it is inade- 

 quate because it fails to show why beneficial response should ever 

 follow a stimulus, and thus furnish fitness to be selected, must 

 remember that all science is inadequate to exactly the same degree ; 

 for in no case does science tell us why natural phenomena do 

 occur in order, although it does tell what order we may reasonably 

 expect. 



If we find in nature no reason why extended things should 

 have weight, except that the fact is so, need we wonder if we 

 fail to discover any ultimate or final reason why sensitive things 

 should respond, for does not every scientific explanation rest 

 upon something which is granted even if unexplained? 



" It passeth with many, I know not how, that mechanical 

 principles give a clear solution of the phenomena. . . . But, 

 things rightly considered, perhaps it will be found not to solve 

 any phenomena at all." 



They who challenge the sufficiency of natural selection, because 

 it does not show why there should be any fitness to select, must 

 find all science equally inadequate; although the common verdict 

 of mankind is that scientific knowledge is very adequate and suf- 

 ficient for all the practical needs of living beings; even if it does 

 fail to show us in nature any efficient cause for any phenomenon 

 at all. 



The task which faced Darwin when the " Origin of Species " 

 was written, was to convince those who deny that species are 

 mutable. At the present day, when all naturalists admit this, 

 many question the adequacy of natural selection as an explanation 

 of the origin of species. Now the way of presenting the argu- 

 ment, and the choice of words, which are best adapted for con- 



