Nature of Variation 



in the expressions he used concerning it, he 

 assumed that variations are indefinite in variety 

 and occur indiscriminately in all directions, as 

 the following quotations from the Origin of 

 Species will show : " But the number and diver- 

 sity of inheritable deviations of structure . . . 

 are endless" (page 14, ed. 1902). " The varia- 

 tions are supposed to be extremely slight, but of 

 the most diversified nature." " I have hitherto 

 sometimes spoken as if the variations so common 

 and multiform with organic beings under domes- 

 tication, and in a lesser degree to those under 

 nature, were due to chance. This, of course, is 

 a wholly incorrect expression, but it serves to 

 acknowledge plainly our ignorance of the cause 

 of each particular variation " (page 164). 



Wallace is far less guarded in his expressions. 

 On page 82 of his Darwinism he speaks of " the 

 constant and large amount of variation of every 

 part in all directions . . . which must afford an 

 ample supply of favourable variations whenever 

 required." 



The double assumption that variations are for 

 all practical purposes haphazard in origin and 

 indefinite in direction is necessary if natural 

 selection is to be the main factor in evolution. 

 For if variations be not haphazard, if they are 

 definite, if there be a directive force behind them, 

 like fate behind the classical gods, then selection 

 is not the fundamental cause of evolution. It 



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