420 RECAPITULATION. Chap. XIV. 



of any kind, and on outlying islands, Mliat a multitude of 

 forms exist, ■which some experienced naturalists rank as vari- 

 eties, others as geographical races or sub-species, and others 

 as distinct though closely-allied species ! 



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

 or so slowlv, why should we doubt that the variations or in- 

 dividual dill'erences, which are in any way beneficial, would be 

 preserved and accumulated through natural selection, or the 

 survival of tlie fittest ? If man can by patience select varia- 

 tions useful to him, Avhy, under changing and complex condi- 

 tions 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 scrutinizing the whole constitution, structure, and 

 habits of each creature — fiworing the good and rejecting the 

 bad ? I can see no limit to this power, in slowly and beauti- 

 fully adapting each form to the most complex relations of life. 

 The theory of natural selection, even if we looked no further 

 than this, seems to me to be in itself 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 fii-st 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 A\hicli arc 

 acknowledged to have been produced by secondary laws. On 

 this same view we can imderstand how it is that in each region 

 where many sjiecies of a genus have been produced, and where 

 they now ilourish, these same species should present many 

 \ aricties ; for whei'e the manufactory of species has been 

 active, Ave might expect, as a general rule, to find it still iu 

 action ; and this is the case if varieties be incipient species. 

 ^Moreover, the; species of the larger genera, which ailord the 

 greater number of varieties or incipient species, retain to a 

 certain degree the character of varieties ; for they dilfer froiu 

 cacli other by a less amount of dilference than do the species 

 of smaller genera. The closely-allied species also of the larger 

 genera ap])arently have restricted ranges, and in their affinities 

 tliey are clustered in little groups round other species — in both 

 of Avhich respects they resemble varieties. These are strange 



