The Theory of Sexual Selection. 387 



take into consideration the following facts. Namely. 

 {a) secondary sexual characters of the embellishing 

 kind are, as a rule, developed only at maturity; and 

 most frequently during only a part of the year, which 

 is invariably the breeding season : [b) they are always 

 more or less seriously affected by emasculation: [c] 

 they are always, and only, displayed in perfection 

 during the act of courtship : [d) then, however, they are 

 displayed with the most elaborate pains ; yet always, 

 and only, before the females: [e] they appear, at all 

 events in many cases, to have the effect of charming 

 the females into a performance of the sexual act ; 

 while it is certain that in many cases, both among 

 quadrupeds and birds, individuals of the one sex are 

 capable of feeling a strong antipathy against, or a strong 

 preference for, certain individuals of the opposite sex. 

 Such are the main lines of evidence in favour of the 

 theory of sexual selection. And although it is enough 

 that some of them should be merely stated as above 

 in order that their immense significance should be- 

 come apparent, in the case of others a bare statement 

 is not sufficient for this purpose. More especially is 

 this the case as regards the enormous profusion, variety, 

 and elaboration of sexually- embellishing characters 

 which occur in birds and mammals — not to mention 

 several divisions of Arthropoda ; together with the 

 extraordinary amount of trouble which, in a no less 

 extraordinary number of different ways, is taken by 

 the male animals to display their embellishments 

 before the females. And even in many cases where 

 to our eyes there is no particular embellishment to 

 display, the process of courtship consists in such an 

 elaborate performance of dancings, struttings, and 



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