270 THE PRINCIPLES OP [Part II. 



degree, either "by expending too much of their vital 

 powers, or by exposing them to any great danger. The 

 development, however, of certain structures — of the horns, 

 for instance, in certain stags — has been carried to a won- 

 derful extreme ; and in some instances to an extreme 

 which, as far as the general conditions of life are con- 

 cerned, must be slightly injurious to the male. From this 

 fact we learn that the advantages which favored males 

 have derived from conquering other males in battle or 

 courtship, and thus leaving a numerous progeny, have 

 been in the long-run greater than those derived from 

 rather more perfect adaptation to the external conditions 

 of life. We shall further see, and this could never have 

 been anticipated, that the power to charm the female has 

 been in some few instances more important than the 

 power to conquer other males in battle. 



LAWS OF INHERITANCE. 



In order to understand how sexual selection has acted, 

 and in the course of ages has produced conspicuous re- 

 sults with many animals of many classes, it is necessary 

 to bear in mind the laws of inheritance, as far as they are 

 known. Two distinct elements are included under the 

 term "inheritance," namely, the transmission and the 

 development of characters ; but as these generally go to- 

 gether, the distinction is often overlooked. We see this 

 distinction in those characters which are transmitted 

 through the early years of life, but are developed only at 

 maturity or during old age. We see the same distinction 

 more clearly with secondary sexual characters, for these 

 are transmitted through both sexes, though developed in 

 one alone. That they are present in both sexes, is mani- 

 fest when two species, having strongly-marked sexual 

 characters, are crossed, for each transmits the characters 



