328 THE ORIGIN OF SPECIES 



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 Australia; 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 species have been produced on 

 one side, and have not been able to migrate to the opposite side. 

 Some few families, many sub-famihes, very many genera, a still 

 greater number of sections of genera, are confined to a single re- 

 gion; 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 con- 

 tinuous. 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 naturalists, 

 that the view of each species having been produced in one area 

 alone, and having subsequently migrated from that area as far 

 as its powers of migration and subsistence under past and present 

 conditions permitted, 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 geograph- 

 ical and climatical changes which have certainly occurred within 

 recent geological times, must have rendered discontinuous the 

 formerly continuous range of many species. So that we are re- 

 duced to consider 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 considerations, that 

 each species has been produced within one area, and has migrated 

 thence as far as it could. It would be hopelessly tedious to discuss 

 all the exceptional cases of the same species, now living at distant 

 and separated points, nor do I for a moment pretend that any 

 explanation could be offered of many instances. But, after some 

 preliminary remarks, I will discuss a few of the most striking 



