1899] THE SCOPE OF NATURAL SELECTION 187 



between accommodations which are the direct result of environ- 

 mental influence, just as wood becomes altered in its composition by a 

 sufficient amount of heat, and those other forms of accommodations 

 which are the result of the organismal response to its environment, and 

 I pointed out that only in the former set of conditions was it strictly 

 correct to speak of acquired modifications, and further that this 

 somatic responsiveness was not in the least discordant with the 

 principle of selection — it would, in fact, aid selectional development 

 making the process of evolution more rapid. Now just as the 

 chemical analogy tells against climatic modification, and in favour of 

 use-development or organismal response with elimination of the less 

 responsive, so I hope to show in this concluding portion of the paper 

 that every broad generalisation tells against climatic modification, and 

 in favour of organismal response, and I shall endeavour to show that 

 the somatic response becomes increasingly separated off from the 

 germinal, not through any special isolation of the germinal products, 

 but for precisely similar reasons as other organs have become separated, 

 namely, by increasing specialisation and complexity of structure. 1 In 

 this concluding portion, therefore, of the article, I wish to keep these 

 distinctions constantly in view : — (1) The direct climatic response, an 

 external influence or influences producing internal modifications ; 

 except in so far as these external forces are destructive, I believe this 

 influence to be negligible. (2) The response of the organism whether 

 it lie uni- or multicellular to external conditions and alterations that 

 will ensue through elimination of the less fitted and preservation of 

 the more fitted, internal response to external conditions, and external 

 elimination of the less responsive organisms. (3) The relation, if 

 any, that the somatic response bears to germinal variability. 



In considering the chief differences between plants and animals, 

 we find certain more or less constant conditions which lead to the 

 conclusion that protoplasm is not directly modifiable ; thus a broad 

 general difference is found between these two great divisions of the 

 living world in the fact that vegetable organisms live on simpler foods 

 than animal. The fact that the fungi and certain insectivorous plants 

 form a partial exception to this rule, only increases the strength 

 of the selectionist position, for, from the fact that the vast majority of 

 the various forms of vegetable life do live on simpler foods than 

 animal, we may infer that the difference in the structure of the 

 protoplasm was not easily overcome, while the constancy of the 

 character of the exceptions now that a change has been produced is 

 almost positive proof that if organisms can be directly modified by 

 climatic action it must be to a very slight degree. The same line of 

 argument applies to the other differences observable between plants 

 and animals. On the assumption that this difference of metabolism 



1 Lloyd Morgan, in his "Animal Life and Intelligence," has put forward a theory of 

 reproductive specialisation to which I am greatly indebted. 



