Masterpieces of Science 



only by the light of analogy. The modifica- 

 tions acquired through sexual selection are often 

 so strongly pronounced that the two sexes 

 have frequently been ranked as distinct species, 

 or even as distinct genera. Such strongly marked 

 differences must be in some manner highly 

 important; and we know that they have been 

 acquired in some instances at the cost not only 

 of inconvenience, but of exposure to actual 

 danger. 



The belief in the power of sexual selection rests 

 chiefly on the following considerations: The 

 characters which we have the best reasons for 

 supposing to have been thus acquired are con- 

 fined to one sex; and this alone renders it prob- 

 able that in most cases they are connected 

 with the act of reproduction. These characters 

 in innumerable instances are fully developed 

 only at maturity; and often during only a part 

 of the year, which is always the breeding season. 

 The males (passing over a few exceptional 

 cases) are the more active in courtship; they 

 are the best armed, and are rendered the most 

 attractive in various ways. It is to be especially 

 observed that the males display their attractions 

 with elaborate care in the presence of the fe- 

 males; and that they rarely or never display 

 them excepting during the season of love. It 

 is incredible that all this should be purposeless. 

 Lastly, we have distinct evidence with some 

 quadrupeds and birds that the individuals of 

 one sex are capable of feeling a strong antipathy 

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