CHAPTER III 



HERITABLE DIFFERENCES 



1. THE MUTATION IDEA 



VARIETY is not only the "spice of life" but it is also 

 the central necessity in the origin of new kinds of ani- 

 mals and plants. If there was no variation from gen- 

 eration to generation then nothing new would appear 

 which nature could in any way seize upon in order to 

 escape from conservative monotony and as a result 

 there would be no possible evolution in any direction. 

 This deplorable state of affairs we know is contrary to 

 fact. 



There are at least three ways, according to Baur, 

 by which an organism can become different from its 

 relatives, viz. 1, modification; , combination; 3, 

 mutation. Which of these three ways has been followed 

 in any specific instance can only be determined with 

 certainty by the test of subsequent breeding, for there 

 is nothing in the appearance of an animal or plant to 

 indicate by which of these three paths it has gained 

 any distinctive variation. 



By modifications we understand those widespread 

 differences which are the result of nurture rather than 

 nature. They are simply environmental effects upon 

 the somatoplasm and consequently are, in all probabil- 



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