iveness because it is correlated with another variation of 

 greater vital value" (Geddes and Thomson, Evolution). 



Organic Selection. — "If the variation favored by 

 the environment coincides with an innate variation of simi- 

 lar nature, the effects of both variations are more likely to 

 make themselves felt than either separately. It may 

 happen that a slight innate variation, too insignificant to 

 serve a useful purpose is somehow amplified by an acquired 

 variation of similar nature which adds itself to it and the 

 two variations in combination form a proper basis for na- 

 tural selection." 



Sexual Selection. — To account for the occurrence of 

 marked secondary sex-characters in many males Darwin 

 proposed the supplementary theory of Sexual Selection. 

 "This form of selection depends on a struggle between the 

 individuals of one sex, generally the males, for the possess- 

 sion of the other sex. The result is not death to the un- 

 successful competitor, but few or no offspring." There 

 are two modes of this sexual selection, the fights between 

 rival males and the preference the female shows for "the 

 male whose tout ensemble has most successfully excited her 

 sexual interest." (See also page 52 for Darwin's theory of 

 Pangenesis). 



Criticisms oj the Natural Selection Theory. 



Criticisms of this Theory have been very severe, es- 

 pecially by theologians about 40 years ago. The following 

 are among the most important from a scientific standpoint : 



1. The two types of variations are not clearly differenti- 



ated, and it is believed that fluctuating variations 

 have a limit beyond which they cannot pass by con- 

 tinuous selection. 



2. It is also believed that acquired characters are not heri- 



table. 



3. It is hard to understand how Natural Selection favors 



. organisms with variations too small to be of any 

 advantage. The theory does not explain the origin 

 of useful variations. "It may explain the survival 

 of the fittest but it cannot explain the arrival of the 

 fittest." 



4. It does not explain sterility between most species. 



5. "Many characters useless for the preservation of in- 



dividuals have been developed by one sex of a given 

 species," e.g. the plumage of many male birds. 



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