ISOLATION 177 



must greatly reduce a character that shows itself at the outset 

 only in one individual, however prepotent. Stability cannot be 

 maintained without isolation. 



However sound a principle may be, it is possible to make too Romanes 

 much of it, to make it a hobby and ride it to death. This ^ Gu lick 

 was done by Romanes whose persistence converted the scientific 

 world to a belief in the importance of isolation. It is with regret 

 that I say anything that may seem depreciatory of a man who 

 showed throughout his life such a devotion to science, so much 

 zeal for truth, such patience in the search for it. It cannot, 

 however, be denied that instead of putting isolation in its proper 

 place as one of the conditions without which species could not 

 have arisen through Natural Selection, he dethroned Natural 

 Selection and made isolation supreme. Natural Selection, he 

 maintained, was only one form of isolation, for all those that 

 weie not selected died off. Mr Gulick also, his supporter, put 

 isolation on an equally high pedestal, having been led to do so 

 by his study of the land molluscs of the Sandwich Islands. Land 

 There are no less than three hundred species in this small area, 

 nearly all of them belonging to the same family. In valleys on Sandwich 

 the same side of the mountain range and having the same vegeta- 

 tion, the molluscs belong nevertheless to different species. These 

 are very remarkable facts, and the conclusion Mr Gulick has 

 come to is that Natural Selection cannot account for them, since 

 we have separation into species where the conditions are similar. 

 These snails, he maintains, have not been modified in each valley 

 to suit their environment, but differences have arisen, without 

 reference to environment, through isolation. So far I think he 

 makes good his point, and Dr Russel Wallace's answer is un- 

 convincing. It consists mainly in an appeal to ignorance. " The 

 conditions," he argues, " in each valley may be different though 

 the difference may be indiscernible to us ; and the fact that the 

 mammals and birds of Ireland are the same as those of Britain, 

 shows that isolation alone, without difference of conditions, leaves 

 species as they were." As to this last point it is well to re- 

 member that recently it has been shown that the Irish stoat has 

 constant markings that differentiate it from the English stoat and 



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