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. Qr- 



definite ling*. 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 

 s. whereas in development, the mrt- 



ti|j||jjt.y i flbvio^fijy pne^of personal identify. 

 Evolution implies three things: (a) raw ma- 

 terials in the form, of variations T or organic 

 changes of pom^prt.! (6) an arrangement for 



gntm'1 nf grirnP W 



tfegse: and (c) a directive mechanism for 



Securing _mn*\*t<*nf*y anf] ^ff^fi\rAnPgg of 



raciaL^ciiajige. The importance of (c) will 

 vary with what is provided by (a) and with 

 the degree of persistence allowed by (&). 

 HEREDITY AND VARIATION. Heredity is 

 112 



