Page - 433 - in The Origin of Species

INHABITANTS OF OCEANIC ISLANDS 433 mals were not created for oceanic islands; for man has unin- tentionally stocked them far more fully and perfectly than did nature. Although in oceanic islands the species are few in number, the proportion of endemic kinds (i.e. those found nowhere else in the world) is often extremely large. If we compare, for instance, the number of endemic land-shells in Madeira, or of endemic birds in the Galapagos Archipelago, with the number found on any continent, and then compare the area of the island with that of the continent, we shall see that this is true. This fact might have been theoretically expected, for, as already explained, species occasionally arriving after long intervals of time in the new and isolated district, and having to compete with new associates, would be eminently liable to modification, and would often produce groups of modified descendants. But it by no means follows that, be- cause in an island nearly all the species of one class are peculiar, those of another class, or of another section of the same class, are peculiar ; and this difference seems to depend partly on the species which are not modified having immi- grated in a body, so that their mutual relations have not been much disturbed ; and partly on the frequent arrival of unmodified immigrants from the mother-country, with which the insular forms have intercrossed. It should be borne in mind that the offspring of such crosses would certainly gain in vigour ; so that even an occasional cross would produce more effect than might have been anticipated. I will give a few illustrations of the foregoing remarks : in the Galapagos Islands there arc 26 land-birds; of these 21 for perhaps 23) are peculiar, whereas of the 11 marine birds only 2 are peculiar ; and it is obvious that marine birds could arrive at these islands much more easily and frequently than land- birds. Bermuda, on the other hand, which lies at about the same distance from North America as the Galapagos Islands do from South America, and which has a very peculiar soil, does not possess a single endemic land-bird : and wo know from Mr. J. M. Jones' admirable account of Bermuda, that very many North American birds occasionally or even fre- quently visit this island. Almost every year, as I am In- formed by Mr. E. V. Harcourt. many European and .Xfrican