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. 
