SO MANUAL OF ZOOLOGY. 



of many species of 'animals to secure a preponderance of off- 

 spring from the strongest males. The peculiarities which 

 enable certain males to succeed in these contests will, cceteris 

 paribus, be transmitted to tneir male offspring, and in this way 

 Variations may be perpetuated, initiated, or intensified. 



b. In the preceding cases, the females are believed to be 

 perfectly passive, and the selection is a "natural'' one, the 

 final result depending solely upon the natural advantages 

 which certain males possess' over others in actual combat. 

 It is alleged, however, that there are other cases in which the 

 selection is truly " sexual," since its- result is determined by 

 spontaneous preference, and not by brute force alone. -It is 

 asserted, namely, 'that among certain species of animals, the 

 females exercise a free choice as to the particular male with 

 which they will pair; the males being passive agents in the 

 matter, except in so far as each uses, or may use, his utmost 

 exertions to secure that the choice of the female may fall upon 

 him. The circumstances supposed to influence, and ultimately 

 determine, the choice of the female, are of course, in the main, 

 the personal attractions of some particular male, the female 

 being captivated by some " beauty of form, colour, odour, or 

 voice," which such a male may possess. 



If it be admitted that the females of some of the lower 

 animals have the power of expressing and exercising a pref- 

 erence in the manner above indicated, then it is easy to 

 understand how variations might be transmitted or intensi- 

 fied in this way. The male who is most attractive to the 

 female will, other things being equal, have the best chance 

 of propagating his species, and is likely to leave the largest 

 number of descendants. His male offspring will inherit the 

 peculiarities by which their sire was rendered pre-eminently 

 attractive in the eyes of their mother, and thus a well-marked 

 breed might be produced, by the preservation or intensifica- 

 tion of characters of this nature. Mr Darwin is disposed to 

 believe that colour and song in most, if not in all animals, are 

 thus to be ascribed to the action of sexual selection, through 

 numerous successive generations ; but other competent author- 

 ities are unable to concur in this view. 



15. DISTRIBUTION. 



Under this head come all the facts which are concerned 

 with the external or objective relations of animals that is to 

 say, their relations to the external conditions in which they are 

 placed. 



