362 ON THE ORIGIN OF SPECIES 



namely, that Madeira and the adjoining islet of Porto 

 Santo possess many distinct but representative land- 

 shells, some of which live in crevices of stone ; and 

 although large quantities of stone are annually trans- 

 ported from Porto Santo to Madeira, yet this latter 

 island has not become colonised by the Porto Santo 

 species : nevertheless both islands have been colonised 

 by some European land-shells, which no doubt had 

 some advantage over the indigenous species. From 

 these considerations I think we need not greatly 

 marvel at the endemic and representative species, 

 which inhabit the several islands of the Galapagos 

 Archipelago, not having universally spread from 

 island to island. In many other instances, as in the 

 several districts of the same continent, pre-occupation 

 has probably played an important part in checking the 

 commingling of species under the same conditions of 

 life. Thus, the south-east and south-west corners of 

 Australia have nearly the same physical conditions, 

 and are united by continuous land, yet they are in- 

 habited by a vast number of distinct mammals, birds, 

 and plants. 



The principle which determines the general char- 

 acter of the fauna and flora of oceanic islands, namely, 

 that the inhabitants, when not identically the same, 

 yet are plainly related to the inhabitants of that region 

 whence colonists could most readily have been derived, 

 — the colonists having been subsequently modified and 

 better fitted to their new homes, — is of the widest 

 application throughout nature. We see this on every 

 mountain, in every lake and marsh. For Alpine 

 species, excepting in so far as the same forms, chiefly 

 of plants, have spread widely throughout the world 

 during the recent Glacial epoch, are related to those of 

 the surrounding lowlands ; — thus we have in South 

 America, Alpine humming-birds, Alpine rodents, 

 Alpine plants, etc., all of strictly American forms, 

 and it is obvious that a mountain, as it became slowly 

 upheaved, would naturally be colonised from the 

 surrounding: lowlands. So it is with the inhabitants of 



