132 Darwin, and after Darwin. 



change. But although, for the reason above stated, 

 they are without relevancy in this respect, they 

 appear to me fatal to the explanation which he gives 

 of specific changes under apogamy where only small 

 sections of species are concerned. For example, can 

 it be rationally maintained that there are more 

 differences of environment between every two of 

 the many contiguous valleys of a small island, 

 such as Mr. Gulick describes, than there are in 

 the incomparably larger area of the whole of 

 Ireland? But, if not, and if natural selection is 

 able to work such " occult " wonders in each succes- 

 sive mile on the Sandwich Islands, why has it so 

 entirely lost this magic power in the case of Ireland 

 or in the " many other cases of isolation " to 

 which Mr. Wallace refers? On his theory there 

 is no coherent answer to be given to this question, 

 while on our theory the answer is given in the 

 very terms of the theory itself. The facts are 

 plainly just what the theory requires that they 

 should be ; and therefore, if they were not as they 

 are, the theory would be deprived of that confirma- 

 tion which it now derives from them. 



Thus, in truth, though in an opposite way, the 

 case of Ireland is, as Mr. Wallace says, "an excel- 

 lent test case," when once the theory of apogamy 

 as a " vera causa " of specific change is understood ; 

 and the effect of applying the test is fully to corro- 

 borate this theory, while at the same time it as 

 fully negatives the other. For the consideration 

 whereby Mr. Wallace seeks to explain the inactivity 

 of natural selection in the case of Ireland is not 

 " coherent." What he says is, "That changes have 



