72 THB POUR SBGREGATIVB PRINCIPLES. 



17. Theories Compared. 



It will be observed that in the above-quoted statements recognition 

 is given to the following facts, to which attention was called in the 

 papers reproduced in the Appendix of the present volume. 



(i) That there may be divergent varieties that are not produced 

 by exposure to different environments. 



(2) That these varieties are often local. 



(3) That when isolated the peculiar character of the variety is not 

 swamped by crossing. 



(4) That these varieties may be so accumulated as to produce di- 

 vergent species, whose differences are not due to differences in the 

 environment. 



(5) That the differences found in allied varieties and species are 

 often differences that are not necessary for the survival of the different 

 groups. 



This series of important facts that have been either overlooked or 

 assumed to be impossible by a leading school of evolutionists are, I 

 believe, fully recognized by the expounders of the mutation theory, 

 though it seems to me that a fuller explanation may be given than any 

 they have offered. It seems to me that both the Darwinian theory and 

 the mutation theory are lacking in that they have not given sufficient 

 attention to the influence of isolation, first in protecting divergent 

 types, whether great or small, second in cutting off all community of 

 action in the different forms of reflexive selection, and third in open- 

 ing the way for diversity of environal selection, through diversity in 

 the methods of dealing with the environment. They have also failed 

 of recognizing that this controlling influence, arising from methods of 

 using the environment, and leading to increasing divergence in suc- 

 ceeding generations, may find its starting point in the individual pe- 

 culiarities of the founders of the colony, whether these peculiarities 

 be inherited aptitudes or acquired habitudes. The Darwinian theory 

 is deficient in that it has no explanation of the divergent evolution of 

 two isolated groups of the same species exposed to the same environ- 

 ment. The mutation theory recognizes that the individuals starting 

 one colony may happen to be of a different mutation from those form- 

 ing the other colony, and that, therefore, the colonies may be different 

 from the first generation ; but it fails to give any explanation of why 

 they should become increasingly divergent in the generations that 

 follow. In opposition to the Darwinian theory, it denies that any 

 permanent effect can be produced by the selection of individual 

 variations, and, therefore, if two pairs of individuals belonging to the 



