144 THE ORIGIN OF SPECIES 



eral distant and isolated points where now found. Never- 

 theless the simplicity of the view that each s])ecies was 

 first produced within a single region captivates the mind. 

 He who rejects it, rejects the vera causa of ordinary 

 generation with subsequent migration, and calls in the 

 agency of a miracle. It is universally admitted that 

 in most cases the area inhabited by a species is continu- 

 ous; and that when a plant or animal inhabits two points 

 so distant from each other, or with an interval of such a 

 nature, that the space could not have been easily passed 

 over by migration, the fact is given as something re- 

 markable and exceptional. The incapacity of migrating 

 across a wide sea is more clear in the case of terrestrial 

 mammals than perhaps with any other organic beings; 

 and, accordingly, we find no inexplicable instances of the 

 same mammals inhabiting distant points of the world. 

 No geologist feels any difficulty in Great Britain pos- 

 sessing the same quadrupeds with the rest of Europe, 

 for they were no doubt once united. But if the same 

 species can be produced at two separate points, why do 

 we not find a single mammal common to Europe and 

 Australia or South America? The conditions of life are 

 nearly the same, so that a multitude of European animals 

 and plants have become naturalized in America and Aus- 

 tralia; and some of the aboriginal plants are identically 

 the same at these distant points of the northern and 

 southern hemispheres? The answer, as I believe, is, 

 that mammals have not been able to migrate, whereas 

 some plants, from their varied means of dispersal, have 

 migrated across the wide and broken interspaces. The 

 great and striking influence of barriers of all kinds is 

 intelligible only on the view that the great majority of 



