Appendix to Chapter V. 441 



the several ranges 1 ." Lastly, if instead of considering the 

 case of alpine floras, we take the much larger case of the 

 Old and New World as a whole, we meet with much larger 

 proofs of the same general facts. For, " during the slowly 

 decreasing warmth of the Pliocene period, as soon as the 

 species in common, which inhabited the New and Old 

 Worlds, migrated south of the Polar Circle, they will have 

 been completely cut off from each other. This separation, 

 as far as the more temperate productions are concerned, 

 must have taken place long ages ago. As the plants and 

 animals migrated southward, they will have become mingled 

 in one great region with the native American productions, 

 and would have had to compete with them; and, in the 

 other great region, with those of the Old World. Conse- 

 quently we have here everything favourable for much modifi- 

 cation, for far more modification than with the Alpine 

 productions left isolated, within a much more recent period, 

 on the several mountain ranges and on the arctic lands of 

 Europe and N. America. Hence it has come, that when 

 we compare the now living productions of the temperate 

 regions of the New and Old Worldsj we find very few iden- 

 tical species ; but we find in every class many forms, which 

 some naturalists rank as geographical races, and others as 

 distinct species; and a host of tlosely allied or representative 

 forms which are ranked by all naturalists as specifically 

 distinct 8 /' 



In view then of all the above considerations and 

 especially those quoted from Darwin it appears to me that 

 far from raising any difficulty against the theory of evolution, 

 the facts adduced by Mr. Carruthers make in favour of it. 

 For when once these facts are taken in connection with the 

 others above mentioned, they serve to complete the cor- 

 respondence between degrees of modification with degrees 



1 Origin of Species, p. 332. 

 * Ibid. pp. 333-4. 



