CHAP. X.] SEXUAL SELECTION. 303 



Under the head of &quot; sexual selection &quot; Mr. Darwin includes, 

 however, two very distinct processes. One of these Has been 



* l . . made to in- 



consists in the action of superior strength or activity, ciude two 



1 . . . distinct 



by which one male succeeds in obtaining possession things. 

 of mates and in keeping away rivals. This is, undoubtedly, 

 a vera causa, but may be more conveniently reckoned as one 

 mode of &quot;natural selection&quot; than as a branch of &quot;sexual 

 selection.&quot; The second process consists in alleged preference 

 or choice, exercised freely by the female in favour of parti 

 cular males on account of some attractiveness or beauty of 

 form, colour, odour, or voice, which such males may possess. 

 It is this second form of &quot; sexual selection &quot; (and which alone 

 deserves the name) that is important for the truth of Mr. 

 Darwin s views, but the validity of which has to be proved. 



Now, to prove the existence of such a power of choice Mr. 

 Darwin brings forward a multitude of details respecting the 

 sexual phenomena of animals of various classes ; but it is the 

 class of birds which is mainly relied on to afford evidence in 

 support of the exercise of this power of choice by female 

 animals. It is contended, however, that not only is the 

 evidence defective even with respect to birds, but that much 

 of his own evidence is in direct opposition to his views ; while 

 the unquestionable fact, that male sexual characters (horns, 

 mane, wattles, &c. &c.) are developed in many cases where 

 sexual selection has certainly not acted, renders it probable, 

 a priori, that the unknown cause which has operated in these 

 numerous cases has operated in those instances also which 

 seem to favour the hypothesis Mr. Darwin supports. Still he 

 contends that the greater part of the beauty and melody of 

 the organic world is due exclusively to this selective process, 

 by which, through countless generations, the tail of the 

 peacock, the throat of the humming-bird, the song of the 

 nightingale, and the chirp of the grasshopper have been 

 developed through the females, age after age, selecting for 

 their mates, males possessing in a more and more perfect 

 degree characters which must thus have been continually and 

 constantly preferred. 



