34 



Mutability and Individual Variation. 



The breeder employs both, according as opportunity 

 offers. Darwin asserts over and over again that their 

 method consists in the accumulation of successive slight 

 variations.^ But as to whether these small changes are 

 variations or mutations he gives no decision. Natural 

 selection, he says, like artificial, chooses these ''slight 

 variations,''^ but to which category these severally be- 

 long is left uncertain. Moreover it was Darwin's belief 

 that Natural Selection was not the sole factor, for at the 



Fig. 7. Fragaria alpina, Monthly Strawberry with- 

 out runners. (Fraisier des quatre saisons sans 

 coulants, Fraisier de Gaillon). 



conclusion of the introduction to his Origin he says, '7 



am convinced that natural selection has been the most 



important, but not the exclusive means of modification.'"^ 



In almost all works on Darwin's theory we find the 



.story of how he arrived at his theory of selection by 



reading Malthus's Essay on Population."* Already well 



^ Origin, loc. cit., pp. 3, 63, 64, etc. 



' Ibid. 



^ See also Origin, p. 72. 



* See Life and Letters, I, pp. 83, 84. 



