GEOGRAPHICAL DISTRIBUTION 



the last chapter that some forms have retained nea^ 

 the same character from an enormously remote geological 

 period, so certain species have migrated over vast spaces, 

 and have not become greatly or at all modified. 



According to these views, it is obvious that the sev- 

 eral 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 

 little modification, there is not much difficulty in believ- 

 ing that they have migrated from the same region; for 

 during the vast geographical and climatal changes which 

 have supervened since ancient times, almost any amount 

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

 which 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 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 has been explained, 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 been 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 sev° 



