Chap. XXI. AND CONCLUDING EEMAKKS. 399 



racters, when equally transmitted to both sexes can be 

 distinguished from ordinary specific characters only by 

 the light of analogy. The modifications 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 im- 

 portant ; 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 

 chieflv on the followins: considerations. The characters 

 which we have the best reason for supposing to have 

 been thus acquired are confined to one sex ; and this 

 alone renders it probable that they are in some way 

 connected with the act of reproduction. These charac- 

 ters 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 (pass- 

 ing over a few exceptional cases) are the most active in 

 courtship ; they are the best armed, and are rendered 

 the most attractive in various ways. It is to be espe- 

 cially observed that the males display their attractions 

 with elaborate care in the presence of the females ; 

 and that they rarely or never display them excepting 

 during the season of love. It is incredible that all this 

 display should be purposeless. Lastly we have distinct 

 evidence with some quadrupeds and birds that the indi- 

 viduals of the one sex are capable of feeling a strong 

 antipathy or preference for certain individuals of the 

 opposite sex. 



Bearing these facts in mind, and not forgetting the 

 marked results of man's unconscious selection, it seems 

 to me almost certain that if the individuals of one sex 

 w^ere during a long series of generations to prefer pair- 



