280 / RECAPITULATION. [Chap. XV. 



I 

 select vai-iafions 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, act ig during long ages and rigidly scrutinising 

 the whole constitution, structure, and habits of each 

 creature, — fa\'ouriilg the good and rejecting the bad? I 

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

 adapting eacii form to the most complex relations of life. 

 The theory oi natural selection, even if we look no far- 

 ther than thi.^, seems to be in the highest degree prob- 

 able. I have already recapitulated, as fairly as I could, 

 the opposed dafficulties and objections: now let us turn 

 to the special ^'acts and arguments in favour of the theory. 



On the y,iew 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 t') have been produced by special acts of crea- 

 tion, and Tarieties which are acknowledged to have been 

 produced by secondary laws. On this same view we can 

 unde^cstand how it is that in a region where many species 

 of a geinus have been produced, and where they now 

 flourish, these same species should present many varie- 

 ties; for where the manufactory of species has been ac- 

 tive, we might expect, as a general rule, to find it still in 

 action; and this is the case if varieties be incipient spe- 

 cies. Moreover, the species of the larger genera, which 

 afford the greater number of varieties or incipient spe- 

 cies, retain to a certain degree the character of varieties; 

 for they differ from each other by a less amount of differ- 

 ence than do the species of smaller genera. The closely 



