DARWIN 



tuating element, as perhaps we see in certain poly- 

 morphic species, or would ultimately become fixed, 

 owing to the nature of the organism and the nature 

 of the conditions. "^^ 



As a corollary to natural selection, Darwin added 

 the element of choice which he calls Sexual Selection. 

 "This form of selection depends, not on a struggle for 

 existence in relation to other organic beings or to ex- 

 ternal conditions, but on a struggle between the indi- 

 viduals of one sex, generally the males, for the pos- 

 session of the other sex. The result is not death to the 

 unsuccessful competitor, but few or no offspring. Sex- 

 ual Selection is, therefore, less rigorous than natural 

 selection. Generally, the most vigorous males, those 

 which are best fitted for their places in nature, will 

 leave most progeny. ... I can see no good reason to 

 doubt that female birds, by selecting, during thou- 

 sands of generations, the most melodious or beauti- 

 ful males, according to their standard of beauty, 

 might produce a marked effect."^* 



Of late years the doctrine of selection has been 

 somewhat modified by de Vries under the name of the 

 Theory of Mutations, Darwin insisted that evolution 

 required that variation must proceed by minute 

 changes, and he maintained this view in spite of the 

 warning of Huxley who wrote : "First, you have load- 

 ed yourself with an unnecessary difficulty in adopt- 

 ing Natura non facit sal turn so unreservedly. . . . 



^3 Origin of Species, vol. I, p. 98. 

 ''■■^Ibid., vol. I, pp. 108 and 109. 



C 213 3 



