CHAPTER IV 



VARIATION AND HEREDITY: THE SPRINGS 

 AND CHANNELS OF EVOLUTION 



What Organic Evolution Implies Heredity and Variation 

 Why Like Tends to Beget Like Organic Changes 

 Analyzed Darwin's Position in regard to Variations 

 Modern Study of Variations The Mutation Theory 

 Mendelism Causes of Variation. 



WHAT ORGANIC EVOLUTION IMPLIES. Or- 

 ganic evolution is racial change along a 

 definite line. It is for the variety or species, 

 breed or race, what embryonic development 

 is for the individual a mode of becoming. 

 Its continuity is sustained by a succession of 

 generations, whereas in development the con- 

 tinuity is obviously one of personal identity. 

 Evolution implies three things: (a) raw ma- 

 terials in the form of variations, or organic 

 changes of some sort; (6) an arrangement for 

 securing the hereditary entail of some of 

 these; and (c) a directive mechanism for 

 securing consistency and effectiveness of 

 racial change. The importance of (c) will 

 vary with what is provided by (a) and with 

 the degree of persistence allowed by (6). 

 HEREDITY AND VARIATION. - - Heredity is 



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