CHAPTER XXIX 
SECONDARY SEXUAL CHARACTERS (continued) 
Theories of the Origin of Secondary Sexual Characters 
WuEN Darwin proposed his theory of natural selection in 
1859 he brought forward also at the same time his theory of 
sexual selection to account for the origin of secondary sexual 
characters. ‘‘This form of selection depends not on a struggle 
for existence in relation to other organic beings or to external 
conditions, but on a struggle between the individuals of one sex, 
generally the males, for the possession of the other.sex. The 
result is not death to the unsuccessful competitor, but few or no 
offspring.”’ Darwin believed that the secondary sexual char- 
acters have arisen in either of two ways: either as a result of a 
contest between the males that has led to the development of such 
structures as the horns of the stag and the spur of the cock; 
or as the result of selection by the females of the most adorned, 
or brilliantly colored, or highly scented male individuals. This 
latter form of selection has brought about the development of 
such characters as the color, the ornaments, the song, and the 
scent glands of the males. 
Of these two forms of sexual selection the first is merely an 
extension of the principle of natural selection applied to the male 
individuals of the same species; while the second form of selec- 
tion depends on the esthetic taste of the females. 
In 1871 Darwin developed his theory of sexual selection much 
more fully in his book on “‘The Descent of Man.” Here he 
appears at times to give the theory precedence over the theory 
of natural selection itself, and attempts even to account for the 
development of color and ornamentation, when it exists in both 
sexes, by assuming that through the selection of the female it 
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