CHAPTER VII 



VARIATION AND HEREDITY 



Variation. --When we see twins that resemble 

 each other closely, or two unrelated individuals 

 that have many features in common, our attention 

 is at once attracted, and the fact that the phenomenon 

 excites our interest attests its comparative rarity; 

 in other words, we are accustomed to the fact that 

 individuals do not resemble one another, and the 

 occasional exception is therefore conspicuous. If 

 we apply exact measurements or other criteria to 

 any sort of plant or animal, or to a structural parl , 

 and compare with similar measurements on other 

 individuals, we find that the same thing holds true, 

 that variation is a universal phenomenon, and 

 duplication almost non-existent. 



The analysis of this fact of universal variation 

 resolves itself into a comparison of structures, - 

 the components, so to speak, that go to make up 

 the individual. Thus, if we wished to compare the 

 individual seeds in a handful of beans, we should 

 describe their size, shape, color, texture, etc. These 

 components are technically called " characters." 

 It is obvious that a complex individual may be 

 resolved into a large number of such characters, 

 displaying all sorts of variations when compared 



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