456 RECAPITULATION. 



enced naturalists rank as varieties, others as geographical 

 races or sub-species, and others as distinct though closely 

 aWied species ! 



If, then, animals and plants do vary, let it be ever so 

 slightly or slowly, why should not variations or individual 

 differences, which are in any way beneficial, be preserved 

 and accumulated through natural selection, or the survival 

 of the fittest ? If man can by patience select variations 

 useful to him, why, under changing and complex conditions 

 of life, should not variations useful to nature's living prod- 

 ucts often arise, and be preserved or selected ? What limit 

 can be put to this power, acting during long ages and rigidly 

 scrutinizing the whole constitution, structure, and habits of 

 each creature, favoring 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 further 

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

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

 difficulties and objections : now let us turn to the special 

 facts and arguments in favor 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 creation, and varieties - 

 which are acknowledged to have been produced by second- 

 ary 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 ame 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 varie- 

 ties 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 species also of a larger genera apparently 

 have restricted ranges, and in their ailnities they are 

 clustered in little groups round other species — in both 

 respects resembling varieties. These are strange relations 

 on the view that each species was independently created^ 

 but are intelligible if each existed first as a variety. 



