2o8 Darwin^ and after Darwin, 



distribution is not to be regarded as a crucial test 

 between the rival theories of creation and evolution 

 in all cases indiscriminately, I must next remark that 

 it is undoubtedly one of the strongest lines of evidence 

 which we possess. When vi^e once remember that, 

 according to the general theory of evolution itself, the 

 present geographical distribution of plants and animals 

 is "the visible outcome or residual product of the 

 whole past history of the earth," and, therefore, that of 

 the conditions determining the characters of life in- 

 habiting this and that particular area continuity or 

 discontinuity with other areas is but one, — when we 

 remember this, we find that no further reservation has 

 to be made: all the facts of geographical distribution 

 speak with one consent in favour of the naturalistic 

 theory. 



The first of these facts which I shall adduce is, that 

 although the geographical range of any given species 

 is, as a rule, continuous, such is far from being 

 always the case. Very many species have more or 

 less discontinuous ranges — the mountain-hare, for 

 instance, extending from the Arctic regions over the 

 greater portion of Europe to the Ural Mountains and 

 the Caucasus, and yet over all this enormous tract 

 appearing only in isolated or discontinuous patches, 

 where there happen to be either mountain ranges or 

 climates cold enough to suit its nature. Now, in all 

 such cases of discontinuity in the range of a species 

 the theory of evolution has a simple explanation to 

 offer — namely, either that some representatives of the 

 species have at some former period been able to 

 migrate from one region to the other, or else that at 



