The Theory of Sexual Selection. 385 



selection is both large in amount and massive in 

 weight. 



Our consideration of this evidence will bring us to 

 the second division of our subject, as previously marked 

 out for discussion namely, granting that an aesthetic 

 sense occurs in certain large divisions of the animal 

 kingdom, what is the proof that such a sense is a 

 cause of the beauty which is presented by the animals 

 in question? 



Before proceeding to state this proof, however, it 

 is desirable to observe that under the theory of sexual 

 selection Darwin has included two essentially different 

 classes of facts. For besides the large class of facts 

 to which I have thus far been alluding, i. e. the cases 

 where two sexes of the same species differ from one 

 another in respect of ornamentation, there is another 

 class of facts equally important, namely, the cases 

 where the two sexes of the same species differ from 

 one another in respect of size, strength, and the 

 possession of natural weapons, such as spurs, horns, 

 &c. In most of these cases it is the males which 

 are thus superiorly endowed ; and it is a matter of 

 observation that in all cases where they are so en- 

 dowed they use their superior strength and natural 

 weapons for fighting together, in order to secure 

 possession of the females. Hence results what Mr. 

 Darwin has called the Law of Battle between males 

 of the same species ; and this law of battle he includes 

 under his theory of sexual selection. But it is evident 

 that the principle which is operative in the law of 

 battle differs from the principle which is concerned in 

 the form of sexual selection that has to do with 

 embellishment, and consequent charm. The law of 



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