564 EELATIONS OF TlIK INHABITANTS OF Chap. XII. 



the fact is a iiiarvcllous ono, by distinct species; but these 

 species arc related in a very much closer manner to each other 

 than to the inhabitants of any other quarter of the world. Tliis 

 is what mii^ht have been expected, for islands situated so near 

 each other would almost necessarily receive immi<Ti"ants from 

 the same orig'inal source, and from each other. But how is it 

 that many of the immif^rants 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, etc. ? This long appeared to me a great diffi- 

 culty: but it ai-ises 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 Avhich 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 Avliich inhabit the 

 Galapagos Archipelago and are likewise found in other parts 

 of the world, Ave find that they differ considerably in the sev- 

 eral islands. This difference might indeed have been expected 

 if the islands have been stocked by occasional means of trans- 

 port — 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 or- 

 ganisms : a plant, for instance, would find the ground best 

 fitted for it occujiied by somewhat different species in the dif- 

 ferent islands, and would be exposed to the attacks of some- 

 what dillerent enemies. If, then, it varied, natural selection 

 would probably ffivor 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 degrcx; in some analogous cases, 

 is, that each new species, after being formed in any one island, 

 did not quickly spread to the other islands. But the islands, 

 though in siglit of each other, are se])arated by deep arms of 

 the sea, in most cases wider than the Britisli Channel, and 

 there is no reason to suppose that they have at any former 



