32G SINGLE CENTRES OF CREATION. Chap. XI. 



old home, were to mi^^atc in a body into a new and afterward 

 isolated country, they Avould be little liable to modification ; 

 for n('itli(>r niig-ration nor isolation in themselves can effect any 

 tiling. These principles come into play only by bringin*:^ or- 

 ganisms into new relations with each other, and in a lesser de- 

 gree Avith the surrounding physical conditions. As we have 

 seen in the last chai)tcr that some forms have retained nearly 

 the same character from an enormously remote geological 

 period, so certain s})ecies have migrated over vast spaces, and 

 have not become greatly or at all modified. 



According to these views, it is obvious that the several 

 species of the same genus, though inhabiting the most distant 

 quarters of the world, must originally have proceeded from the 

 same source, as they are descended from the same progenitor. 

 In the case of those species, which have undergone during 

 whole geological periods but little modification, there is not 

 much difficulty in believing that they may have migrated from 

 the same region ; for, during the vast geographical and climatid 

 changes which have supervened since ancient times, almost 

 any amount of migration is possible. But in many other cases, 

 in Avhich we have reason to believe that the species of a genus 

 have been produced within comparatively recent times, there is 

 great difficulty on this head. It is also obvious that the individ- 

 uals of the same species, though now inhabiting distant and 

 isolated regions, must have proceeded from one spot, where 

 their parents were lirst produced: for, as explained in the last 

 chajiler, it is incredible that individuals identically the same 

 should have been produced from parents specifically distinct. 



Single Centres of supposed Creation. — We are thus brought 

 to the question which has been largely discussed by naturalists, 

 namely, whether species have beeia created at one or more 

 points of the earth's surface. Undoubtedly there are many 

 cases of extreme difficulty in understanding how the same species 

 could possibly have migrated from some one point to the several 

 distant and isolated points where noAV found. Nevertheless the 

 simplicity of the view that each species was first produced 

 within a single region captivates the mind. lie Avho rejects it, 

 rejects the vera causa of ordinary generation with subsequent 

 migration, and calls in the agency of a miracle. It is univer- 

 sally admitted that in most cases the area inhabited by a spe- 

 cies is continuous ; 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 be easily passed over 



