360 THE ORIGIN OF SPECIES 



of the sea separating islands from each other, or from the nearest 

 continent, and the degree of affinity of their mammahan inhabit- 

 ants. Mr. Windsor Earl has made some striking observations on 

 this head, since greatly extended by Mr. Wallace's admirable 

 researches, in regard to the great Malay Archipelago, which is 

 traversed near Celebes by a space of deep ocean, and this separates 

 two widely distinct mammalian faunas. On either side, the is- 

 lands stand on a moderately shallow submarine bank, and these 

 islands are inhabited by the same or by closely allied quadrupeds. 

 I have not as yet had time to follow up this subject in all quarters 

 of the world; but as far as I have gone, the relation holds good. 

 For instance, Britain is separated by a shallow channel from 

 Europe, and the mammals are the same on both sides; and so 

 it is with all the islands near the shores of Australia. The West 

 Indian Islands, on the other hand, stand on a deeply submerged 

 bank, nearly one thousand fathoms in depth, and here we find 

 American forms, but the species and even the genera are quite 

 distinct. As the amount of modification which animals of all 

 kinds undergo partly depends on the lapse of time, and as the 

 islands which are separated from each other, or from the main- 

 land, by shallow channels, are more likely to have been con- 

 tinuously united within a recent period than the islands separated 

 by deeper channels, we can understand how it is that a relation 

 exists between the depth of the sea separating two mammalian 

 faunas, and the degree of their affinity, a relation which is quite 

 inexplicable on the theory of independent acts of creation. 



The foregoing statements in regard to the inhabitants of 

 oceanic islands, namely, the fewness of the species, with a large 

 proportion consisting of endemic forms — the members of certain 

 groups, but not those of other groups in the same class, having 

 been modified — the absence of certain whole orders, as of batra- 

 chians and of terrestrial mammals, notwithstanding the presence 

 of aerial bats, the singular proportions of certain orders of plants, 

 herbaceous forms having been developed into trees, etc., seem 

 to me to accord better with the belief in the efficiency of occa- 

 sional means of transport, carried on during a long course of time, 

 than with the belief in the former connection of all oceanic 

 islands with the nearest continent; for on this latter view it is 

 probable that the various classes would have immigrated more 

 uniformly, and from the species having entered in a body, their 

 mutual relations would not have been much disturbed, and, con- 

 sequently, they would either have not been modified, or all the 

 species in a more equable manner. 



