62 THE THEORY OF NATURAL SELECTION 



pointed out, there are insuperable difficulties in the 

 way of adopting the belief that such a power can have 

 been acquired through the action of natural selection. 

 Many crustaceans, when they have lost a claw or limb, 

 proceed straightway to grow a new one. To account 

 -for this power by natural selection we should have to 

 suppose, firstly, that every stage in the growth of a 

 partly regenerated claw, even its first small rudiment, 

 was useful to the animal ; and, secondly, that there 

 was so much competition between lobsters which had 

 lost their claws, that those which could regenerate 

 them a little better would survive rather than the 

 others. The first of these suppositions as to the utility 

 of a partly regenerated claw is in the highest degree 

 improbable; but against the second there is an 

 entirely fatal argument, since, if the lobsters which 

 regenerated badly were exterminated owing to com- 

 petition with those which had better powers of re- 

 generation, much more would all the injured lobsters 

 be exterminated in competition with those which had 

 escaped injury. 



The theory of sexual selection constitutes an im- 

 portant branch of the Darwinian account of the origin 

 of specific structures. We are here concerned with 

 this hypothesis only in so far as it leads to a criticism 

 of the efficacy of natural selection from another point 

 of view. By the theory of sexual selection Darwin at- 

 tempted to explain the origin of two sorts of characters 

 in particular, one or other of which frequently appears 

 in the male sex only of many of the higher animals. 



