Alfred Russel Wallace

“ Sumatra, Borneo, and Malacca have, as we have seen, a great similarity as regards their species of mammals and birds, while Java, though it differs from them in so curious a manner, has no greater degree of speciality, since its species, when not Malayan, are almost all North Indian or Siamese.
There is, however, one consideration which may help us over this difficulty. It seems highly probable that in the equatorial regions species have changed less rapidly than in the north temperate zone, on account of the equality and stability of the equatorial climate. ”

“ The distance from Borneo to the southern extremity of the Malay Peninsula is about 350 miles, and it is nearly as far from Sumatra and Java, while it is more than 600 miles from the Siamese Peninsula, opposite to which its long northern coast extends. There is, I believe, nowhere else upon the globe, an island so far from a continent, yet separated from it by so shallow a sea. ”

“ We have here, still more pronounced than in the case of Borneo, the remarkable fact of the true land birds presenting a larger amount of speciality than the land mammals; for while more than four-fifths of the birds are peculiar, only a little more than half the mammals are so, and if we exclude the bats only two-thirds.
The general character of the fauna of this group of islands is evidently the result of their physical conditions and geological history. ”

“ It is, at the same time, too distinct and indisputable to be ignored; and a change of climate which should drive a portion of the Himalayan fauna southward, leaving a few species in Java and Borneo from which they could not return owing to the subsequent isolation of those islands by subsidence, seems to be a cause exactly adapted to produce the kind and amount of affinity between these distant countries that actually exists. ”

“ The proportion here shown of less than one-fourth peculiar species of mammalia and fully one-fourth peculiar species of land-birds, teaches us that the possession of the power of flight affects but little the distribution of land-animals, and gives us confidence in the results we may arrive at in those cases where we have, from whatever cause, to depend on a knowledge of the birds alone. ”

“ Its mammalia (ninety species) are nearly as numerous as those of Borneo, but are apparently less peculiar, none of the genera and only five or six of the species being confined to the island. In land-birds it is decidedly less rich, having only 300 species, of which about forty-five are peculiar, and only one or two belong to peculiar genera; so that here again the amount of speciality is considerably less than in Borneo. ”

“ This will be more evident if we consider that Borneo is as large as the Indo-Chinese Peninsula, or as the Indian Peninsula south of Bombay, and if either of these countries were separated from the continent by the submergence of the whole area north of them as far as the Himalayas, they would be found to contain quite as many peculiar genera and species as Borneo actually does now. ”

“ We have seen, in Chapter X., how important an agent in producing extinction and modification of species must have been the repeated changes from cold to warm, and from warm to cold conditions, with the migrations and crowding together that must have been their necessary consequence. ”

“ Everett, as being either representative species of, or closely allied to birds inhabiting other islands or countries. The majority of these are, as might be expected, allied to species inhabiting the surrounding countries, especially Sumatra, the Malay Peninsula, or Java, a smaller number having their representative forms in the Philippine Islands or Celebes. But there is another group of eight species whose nearest allies are found in such remote lands as Ceylon, North India, Burma, or China. ”

“ This one simple series of elevations and subsidences, combined with the changes of climate already referred to, and such local elevations and depressions as must undoubtedly have occurred, appears sufficient to have brought about the curious, and at first sight puzzling, relations, of the faunas of Java and the Philippines, as compared with those of the larger islands. ”

“ The insects and land-shells of Borneo and of the surrounding countries are too imperfectly known to enable us to arrive at any accurate results with regard to their distribution. They agree, however, with the birds and mammals in their general approximation to Malayan forms, but the number of peculiar species is perhaps larger. ”

“ Mammalia.—Nearly a hundred and forty species of mammalia have been discovered in Borneo, and of these more than three-fourths are identical with those of the surrounding countries, and more than one half with those of the continent. ”