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 esthetic 
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 
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 alate 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. Butit 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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