Secondary Sexual Chaj^acters 447 



very argument that secondary sexual characters have arisen by 

 sexual selection implies an injurious process that involves a serious 

 loss to the species of the less ornamented individuals, and therefore 

 a lack of adaptation. Thus in the effort to show the purposeful- 

 ness of the secondary sexual characters, the injury caused to the 

 species has been overlooked. 



If it be granted that neither natural selection nor sexual 

 selection can explain the origin of the secondary sexual char- 

 acters, there opens a wide field for future thought and study. 

 If variations can occur that ultimately culminate in the gorgeous 

 tail of the peacock, the wonderful colors of the humming birds, 

 the splendid antlers of the stags, and the musical, mathematical, 

 and aesthetic development in man, do we not seem to catch a 

 ghmpse of a power of progressive development in organisms that, 

 given a suitable environment, may produce extraordinary re- 

 sults? It is improbable that these highly complex structures 

 have been the result of a single variation, and therefore, if the 

 result of several or many successive variations, these must have 

 gone on building up in the same direction. The powTr of 

 advancing in one direction, unguided by selection, is one of the 

 least appreciated biological phenomena, and yet may be one of 

 profound significance. 



LITERATURE, CHAPTERS XXVIII AND XXIX 



Cunningham, J. T. Sexual Dimorphism in the Animal Kingdom. A 



Theory of the Evolution of Secondary Sexual Characters. 1900. 

 Dalle Torre and Friese. Die Hermaphroditen und Gynandromorphen 



Hymenopteran. Innsbruck. 1899. 

 Hahn, H. Anatomischer und Physiologische Folgeerscheeinungen der 



Kastration. Sitz. Gesell. f. harp u. Phynol. XVIII. 1902 -1903. 

 Hegar, a. Korrelationen der Keimdriisen und Geschlechtsbestimmung. 



1893. 

 Kellogg, V. L. Influence of the Primary Reproductive Organs on the 



Secondary Sexual Characters. Journ. Exp. Zool. I. 1904. 

 Lameere, a. L'Evolution des ornements sexuels. Bull. I'Acad. Roy. 



de Belgique. 1904. 

 Mayer, A. G. On the Mating Instinct in Moths. Annal. and Mag. Nat. 



History, V. 1900. 

 Oudemanns, J. Th. Falter aus Castrirten Raupen. Zool. Jahrbiicher. 



Abt. Syst. XII. 1899. 



