CHAPTER XIII 



SOME TEST CASES BETWEEN THE 

 RIVAL THEORIES 



D. GEOGRAPHICAL DISTRIBUTION 



X HIS group of test cases is placed last, as the author is at 

 present writing a book upon geographical distribution, and many 

 tests that could be given would require such long quotations 

 from that work that they are not suitable to the present one. 



Geographical distribution, properly so called, unlike ecology, 

 is so bound up with the question of the origin of the species with 

 which it deals, that it must be based upon some theory of that 

 origin, and this theory must be able to explain all or most of the 

 well-known facts of distribution without serious difficulty. To 

 take one case only, special creation could not explain the 

 relationship of species in one country, say Britain, to those in 

 another far removed, like New Zealand. It was succeeded by 

 natural selection, which, however, did its great work rather in 

 establishing evolution, and thus opening out a great field for 

 research, than in explaining geographical distribution. Not only 

 did it show that resemblances were mainly due to relationship, 

 but it also seemed to show that wide dispersal, or successful 

 spread, as it now began to be called, must be due to unusually 

 good "adaptation". This latter, however, has never been proved. 

 The struggle for existence was undoubtedly in full operation 

 among individuals, but even there, chance had probably a much 

 greater effect, for the great struggle was amongst the young, and 

 better water supply, better light, better soil, earlier arrival or 

 germination, etc., etc., would have greater effect than any slight 

 advantage that the young plant could carry in itself. 



Natural selection had to explain geographical distribution, and 

 there seemed no other way to explain it than by transferring the 

 hypothesis from individual to species; but as yet we have no 

 evidence in favour of this great assumption. We do not know that 

 species or varieties can come into direct competition with one 

 another as units in a war a Voutraiice, especially as in general 

 they will occupy more or less different areas, and one would 

 hardly expect that species B would follow its defeated rival A 

 into all its habitats, and kill it out there. If this was the way in 



