20C THE ORIGIN OF SPECIES 



chief part from the deeply-seated error of considering the 

 physical conditions of a country us the most important; 

 "whereas it cannot be disputed that the nature of the 

 other species with wliicb 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 likewise found in 

 other parts of the world, we find that they differ con- 

 siderably 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 islands, for it would have 

 to compete with a different set of organisms; a plant, for 

 instance, would find the ground best fitted for it occupied 

 by somewhat different species in the different islands, and 

 would be exposed to the attacks of somewhat different 

 enemies. If then it varied, natural selection would 

 probably favor different varieties in the different islands. 

 Some species, however, might spread and yet retain the 

 same character throughout the group, just as we see 

 some species spreading widely throughout a continent 

 and remaining the same. 



The really surprising fact in this case of the Galapagos 

 Archipelago, and in a lesser degree in some analogous! 

 cases, is that each new species, after being formed in any* 

 one island, did not spread quickly to the other islands. 



