Chap. XII.] SINGLE CENTRES OP CREATION. 137 



and striking influence of barriers of all kinds, is intelli- 

 gible only on the view that the great majority of species 

 have been produced on one side, and have not been able 

 to migrate to the opposite side. Some few families, 

 many sub-families, very many genera, and a still greater 

 number of sections of genera, are confined to a single 

 region; and it has been observed by several naturalists 

 that the most natural genera, or those genera in which 

 the species are most closely related to each other, are 

 generally confined to the same country, or if they have 

 a wide range that their range is continuous. What a 

 strange anomaly it would be, if a directly opposite rule 

 were to prevail, when we go down one step lower in the 

 series, namely, to the individuals of the same species, 

 and these had not been, at least at first, confined to some 

 one region! 



Hence it seems to me, as it has to many other natu- 

 ralists, that the view of each species having been pro- 

 duced in one area alone, and having subsequently mi- 

 grated from that area as far as its powers of migration 

 and subsistence under past and present conditions per- 

 mitted, is the most probable. Undoubtedly many cases 

 occur, in which we cannot explain how the same species 

 could have passed from one point to the other. But 

 the geographical and climatal changes which have cer- 

 tainly occurred within recent geological times, must 

 have rendered discontinuous the formerly continuous 

 range of many species. So that we are reduced to con- 

 sider whether the exceptions to continuity of range are 

 so numerous and of so grave a nature, that we ought to 

 give up the belief, rendered probable by general con- 

 siderations, that each species has been produced within 

 one arer and has migrated thence as far as it could, 



