422 ON THE ORIGIN OF SPECIES 



think sufficiently distinct to be worthy of record in 

 systematic works. No one can draw any clear dis- 

 tinction between individual differences and slight 

 varieties ; or between more plainly marked varieties 

 and sub-species, and species. Let it be observed how 

 naturalists differ in the rank which they assign to 

 the many representative forms in Europe and North 

 America. 



If then we have under nature variability and a 

 powerful agent always ready to act and select, why 

 should we doubt that variations in any way useful to 

 beings, under their excessively complex relations of 

 life, would be preserved, accumulated, and inherited ? 

 Why, if man can by patience select variations most 

 useful to himself, should nature fail in selecting varia- 

 tions useful, under changing conditions of life, to 

 her living products? 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 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 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, com- 

 monly supposed to have been produced by special acts 

 of creation, and varieties which are acknowledged to 

 have been produced by secondary laws. On this same 

 view we can understand how it is that in each region 

 where many species of a genu9 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 



