F2 THE FOUR SEGREGATIVE 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. 
(1) 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 
