CHAPTER VI. 



ANALYSIS OF THE FOUR PRINCIPLES OF SEGREGATION, WITH 



ILLUSTRATIONS. 



I. Chief Divisions of the Four Principles. 



1. Six Conditions on which the Racial Evolution of a Cross-Fertilizing 



Croup must test. 



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 allogamie (/. c, 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 hereditv.* 



* 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 a rational child. The importance of variation in t he 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 for 1898, 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, on the 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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