The Making of Species 



mitted sometimes in one way and sometimes in 

 another is not in most cases known ; but the 

 period of variability seems often to have been 

 the determining cause. When the two sexes 

 have inherited all characters in common, they 

 necessarily resemble each other ; but, as the suc- 

 cessive variations may be differently transmitted, 

 every possible gradation may be found, even 

 within the same genus, from the closest simi- 

 larity to the widest dissimilarity between the 



sexes." 



This statement, although it does not throw any 

 light upon the problem, is somewhat damaging 

 to the theory of sexual selection. If it be 

 admitted that dissimilarity between the sexes 

 is due to the fact that the males have varied in 

 one way and the females in another way, there 

 seems no necessity for invoking the aid of 

 feminine preference. 



Even greater is the difficulty presented by 

 those species in which the males alone are pro- 

 vided with horns or antlers. " When," writes 

 Darwin (Descent of Man, p. 767), "the males 

 are provided with weapons which in the females 

 are absent, there can hardly be a doubt that 

 these serve for fighting with other males ; and 

 that they were acquired through sexual selection, 

 and were transmitted to the male sex alone. 

 It is not probable, at least in most cases, that 

 the females have been prevented from acquiring 



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