CHAPTER III 



VARIATION 



The assumption of Darwin and Wallace that variations are 

 haphazard in origin and indefinite in direction If these 

 assumptions be not correct Natural Selection ceases to be the 

 fundamental factor in evolution Darwin's views regarding 

 variation underwent modification He eventually recognised 

 the distinction between definite and indefinite variations, and 

 between continuous and discontinuous variations Darwin 

 attached but little importance to either definite or discon- 

 tinuous variations Darwin's views on the causes of variations 

 Criticism of Darwin's views Variations appear to occur 

 along certain definite lines There seems to be a limit to the 

 extent to which fluctuating variations can be accumulated 

 De Vries' experiments Bateson on " discontinuous varia- 

 tion " Views held by De Vries Distinction between con- 

 tinuous and discontinuous variations The work of De Vries 

 Advantages enjoyed by the botanist in experimenting on the 

 making of species Difficulties encountered by the animal 

 breeder Mutations among animals The distinction between 

 germinal and somatic variations The latter, though not 

 transmitted to offspring, are often of considerable value to 

 their possessor in the struggle for existence. 



AS we have already seen, the Darwinian 

 theory, unlike that of Lamarck, does 

 not attempt to explain the origin of 

 variations. It is content with the 

 fact that variations do occur. 



Although Darwin did not try to explain how 

 it is that variation occurs, and was very guarded 



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