Origin of Species Variorum

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 inhabitants 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 likewise 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 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 favour 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