CHAPTER VI. 
ANALYSIS OF THE FOUR PRINCIPLES OF SEGREGATION, WITH 
ILLUSTRATIONS. 
I. Cuter DIvIsIONS OF THE FOUR PRINCIPLES. 
1. Six Conditions on which the Racial Evolution of a Cross-Fertilizing 
Group must rest. 
Before we proceed further with the analysis of the principles pro- 
ducing segregation, we shall enumerate certain vital conditions which 
must be constantly present in order that there should be any divergent 
evolution in allogamic (7. e., cross-fertilizing) organisms. Besides 
individual assimilation and growth there must be, first, the power of 
reproduction; second, survival (that is, the number and adaptations 
of individuals produced by members of the group must be sufficient to 
meet the losses through death in the struggle for life), for otherwise 
the group will be exterminated; third, variation (that is, tentative 
diversity in individual innate characters and aptitudes); fourth, 
heredity (that is, the reproduction of fundamental racial characters), 
and, therefore, the continuance of types; fifth, free crossing between 
the males and females of the different variations of any one group; 
sixth, segregate intergeneration (that is, the breeding of like with 
like), setting limits to the sphere of free crossing, and so controlling 
variation and heredity.* 

* It will be observed that I regard heredity as one of the fundamental powers 
on which the evolution of organisms depends. If there were no heredity a,proto- 
zoa might, in one generation, produce the highest as well as the lowest types of 
organic life; an elephant might be the father of a mouse, and a cabbage might be 
the mother of arational child. The importance of variation in the process of 
evolution can not be overstated; but there can be no variation except as there is 
a type from which the variation departs, and heredity is the maintenance with 
more or less exactness of the ancestral type. This being so, it seems impossible 
to accept Prof. H. S. William’s theory that “Variation, and not heredity, is the 
fundamental characteristic of the phenomena of organisms.’”’ (See article on 
“Variation versus Heredity ,’’ American Naturalist for1898, p.831.) In this case, 
as in many others, the propositions that we may rightly make concerning a prin- 
ciple depend on our definition of the principle. If heredity is defined as absence 
of the power to vary, Prof. Williams’s contention may be justified. If, onthe other 
hand, we define it as the power to maintain a type in the midst of variation, we 
must regard it as one of the fundamental characteristics of the organic world. 
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