352 GEOGRAPHICAL DISTRIBUTION. Chap. XI. 



is also obvious that the individuals of the same species, 

 though now inhabiting distant and isolated regions, must 

 have proceeded from one spot, where their parents were 

 first produced : for, as explained in the last chapter, it 

 is incredible that individuals identically the same should 

 ever have been produced through natural selection from 

 parents specifically distinct. 



We are thus brought to the question which has been 

 largely discussed by naturalists, namely, whether species 

 have been created at one or more points of the earth's 

 surface. Undoubtedly there are very many cases of 

 extreme difficulty, in understanding how the same spe- 

 cies could possibly have migrated from some one point 

 to the several distant and isolated points, where now 

 found. Nevertheless the simplicity of the view that 

 each species was first produced within a single region 

 captivates the mind. He who rejects it, rejects the 

 vera causa of ordinary generation with subsequent mi- 

 gration, and calls in the agency of a miracle. It is 

 universally admitted, that in most cases the area in- 

 habited by a species is continuous ; and 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 be easily passed over by migration, the 

 fact is given as something remarkable and exceptional. 

 The capacity of migrating across the sea is more dis- 

 tinctly limited in terrestrial mammals, than perhaps in 

 any other organic beings ; and, accordingly, we find no 

 inexplicable cases of the same mammal inhabiting dis- 

 tant points of the world. No geologist will feel any 

 difficulty in such cases as Great Britain having been 

 formerly united to Europe, and consequently possessing 

 the same quadrupeds. But if the same species can 

 be produced at two separate points, why do we not 

 find a single mammal common to Europe and Aus- 

 tralia or South America? The conditions of life are 



