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 geographical 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 reduced 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.

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