Secondary Sexual Characters 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 esthetic development in man, do we not seem to catch a 
glimpse 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 ofa 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 power 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 
Cunnincoam, J. T. Sexual Dimorphism in the Animal Kingdom. A 
Theory of the Evolution of Secondary Sexual Characters. 1goo. 
DALLE TorRE and Friese. Die Hermaphroditen und Gynandromorphen 
Hymenopteran. Innsbruck. 1899. 
Hann, H. Anatomischer und Physiologische Folgeerscheeinungen der 
Kastration. Sitz. Gesell. f. harp u. Phynol. XVIII. 1902-1903. 
Hecar, A. Korrelationen der Keimdriisen und Geschlechtsbestimmung. 
1893. 
Rattooe Wi L. Influence of the Primary Reproductive Organs on the 
Secondary Sexual Characters. Journ. Exp. Zool. I. 1904. 
Lamerrr, A. L’Evolution des ornements sexuels. Bull. PAcad. Roy. 
de Belgique. 1904. 
Maver, A.G. On the Mating Instinct in Moths. Annal. and Mag. Nat. 
History, V. 1900. 
Ovupemanns, J. Tx. Falter aus Castrirten Raupen. Zool. Jahrbiicher. 
Abt. Syst. XII. 1899. 
