30 GEOGRAPHICAL DISTRIBUTION 



regions in a greater degree than proportionally to 

 the difference of climates on each side. Thus great 

 chains of mountains, spaces of sea between islands 

 and continents, even great rivers and deserts. In 

 fact the amount (of) difference in the organisms 

 bears a certain, but not invariable relation to the 

 amount of physical difficulties to transit 1 . 



There are some curious exceptions, namely, 

 similarity of fauna of mountains of Europe and N. 

 America and Lapland. Other cases just (the) reverse, 

 mountains of eastern S. America, Altai (?), S. India 

 (?) 2 : mountain summits of islands often eminently 

 peculiar. Fauna generally of some islands, even 

 when close, very dissimilar, in others very similar. 

 [I am here led to observe one or more centres of 

 creation 3 .] 



The simple geologist can explain many of the 

 foregoing cases of distribution. Subsidence of a 

 continent in which free means of dispersal, would 

 drive the lowland plants up to the mountains, 

 now converted into islands, and the semi-alpine 

 plants would take place of alpine, and alpine be 

 destroyed, if mountains originally were not of great 

 height. So we may see, during gradual changes 4 of 

 climate on a continent, the propagation of species 

 would vary and adapt themselves to small changes 



1 Note in the original, "Would it be more striking if we took animals, 

 take Rhinoceros, and study their habitats ?" 



2 Note by Mr A. R. Wallace. "The want of similarity referred to, is, 

 between the mountains of Brazil and Guiana and those of the Andes. Also 

 those of the Indian peninsula as compared with the Himalayas. In both 

 cases there is continuous intervening land. 



"The islands referred to were, no doubt, the Galapagos for dissimilarity 

 from S. America ; our own Islands as compared with Europe, and perhaps 

 Java, for similarity with continental Asia." 



3 The arguments against multiple centres of creation are given in the 

 Origin, Ed. i. p. 352, vi. p. 499. 



4 In the Orii/in, Ed. i. p. 366, vi. p. 516, the author does not give his 

 views on the distribution of alpine plants as original but refers to Edward 

 Forbes' work (GeoJog. Survey Memoirs, 1846). In his autobiography, 

 Darwin refers to this. " I was forestalled" he says, "in only one important 

 point, which my vanity has always made me regret." (Life and Letters, i. 

 p. 88.) 



