280 RECAPITULATION. [Chap. XV. 



select variations useful to him, why, under changing 

 and complex conditions of life, should not variations 

 useful to nature's living products often arise, and be 

 preserved or selected ? What limit can be put to this 

 power, acting during long ages and rigidly scrutinising 

 the whole constitution, structure, and habits of each 

 creature, — favouring the good and rejecting the bad ? I 

 can see no limit to this power, in slowly and beautifully 

 adapting each form to the most complex relations of life. 

 The theory of natural selection, even if we look no farther 

 than this, seems to be in the highest degree probable. 

 I have already recapitulated, as fairly as I could, the 

 opposed dithculties and objections : now let us turn to 

 the special facts and arguments in favour of the theory. 



On the view that species are only strongly marked 

 and permanent varieties, and that each species first 

 existed as a variety, we can see why it is that no line 

 of demarcation can be drawn between species, commonly 

 supposed to have been produced by special acts of crea- 

 tion, and varieties which are acknowledged to have been 

 pr« kduced by secondary laws. On this same view we can 

 understand how it is that in a region where many species 

 of a genus have been produced, and where they now 

 flourish, these same species should present many varieties; 

 for where the manufactory of species has been active, we 

 might expect, as a general rule, to find it still in action ; 

 and this is the case if varieties be incipient species 

 Moreover, the species of the larger genera, which afford 

 the greater number of varieties or incipient species, 

 retain to a certain degree the character of varieties ; for 

 they differ from each other by a less amount of difference 

 than do the species of smaller genera. The closely allied 



