Chap. xiii. Islands to those of the Mainland. 



355 



to any other region : and this is what might have been expected ; 

 but it is also plainly related to South America, which, although 

 the next nearest continent, is so enormously remote, that the fact 

 "becomes an anomaly. But this difficulty partially disappears on 

 the view that New Zealand, South America, and the other southern 

 lands have been stocked in part from a nearly intermediate though 

 distant point, namely from the antarctic islands, when they were 

 clothed with vegetation, during a warmer tertiary period, before the 

 commencement of the last Glacial period. The affinity, which 

 though feeble, I am assured by Dr. Hooker is real, between the flora 

 of the south-western corner of Australia and of the Cape of Good 

 Hope, is a far more remarkable case ; but this affinity is confined 

 to the plants, and will, no doubt, some day be explained. 



The same law which has determined the relationship between 

 the inhabitants of islands and the nearest mainland, is sometimes 

 displayed on a small scale, but in a most interesting manner, 

 within the limits of the same archipelago. Thus each separate 

 island of the Galapagos Archipelago is tenanted, and the fact is a 

 marvellous one, by many distinct species : but these species are 

 related to each other in a very much closer manner than to the 

 inhabitants of the American continent, or of any other quarter 

 of the world. This is what might have been expected, for islands 

 situated so near to each other would almost necessarily receive im- 

 migrants from the same original source, and from each other. But 

 how is it that many of the immigrants have been differently 

 modified, though only in a small degree, in islands situated within 

 sight of each other, having the same geological nature, the same 

 height, climate, &c. ? This long appeared to me a great difficulty : 

 but" it arises in chief part from the deeply-seated error of considering 

 the physical conditions of a country as the most important ; whereas 

 it cannot be disputed that the nature of the other species with 

 which each has to compete, is at least as important, and generally 

 a far more important element of success. Now if we look to the 

 species which inhabit the Galapagos Archipelago and are like- 

 wise found in other parts of the world, we find that they differ 

 considerably in the several islands. This difference might indeed 

 have been expected if the islands have been stocked by occasional 

 means of transport— a seed, for instance, of one plant having been 

 brought to one island, and that of another plant to another island, 

 though all proceeding from the same general source. Hence, when 

 in former times an immigrant first settled on one of the islands, 

 or when it subsequently spread from one to another, it would 

 undoubtedly be exposed to different conditions in the different 



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