Mollusca of Sandwich Isles 



external appearance when the environment is 

 changed. In the one case the peculiarity is not 

 inherited ; in the other it is inherited. 



The Wallaceian explanation is, of course, that 

 the phenomenon is the result of natural selection. 

 There must, say Wallace and his followers, be 

 some differences in the environment, differences 

 which we poor human beings cannot perceive, 

 that have caused the divergence between the 

 various isolated sections of the species. In the 

 case of some local species this explanation is 

 probably the correct one, but we have no hesita- 

 tion in saying that natural selection is unable 

 to offer a satisfactory explanation in a con- 

 siderable number of instances. Take, for 

 example, the case of the land mollusca of the 

 Sandwich Islands. Mr Gulick worked for fifteen 

 years at them, and states that so far as he is able 

 to ascertain the environment in the fifteen valleys 

 is essentially the same. " To argue," writes 

 Romanes, on p. 17 of vol. iii. of Darwin and 

 after Darwin, " that every one of some twenty 

 contiguous valleys in the area of the same small 

 island must necessarily present such differences 

 of environment that all the shells in each are 

 differently modified thereby, while in no one 

 out of the hundreds of cases of modification in 

 minute respects of form and colour can any 

 human being suggest an adaptive reason therefor 

 to argue thus is merely to affirm an intrinsic- 



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