Page:Darwinism by Alfred Wallace 1889.djvu/393

 violent and long-continued gales of wind, we shall not only be better able to account for the floras of some of the remotest oceanic islands, but shall also find in the fact a sufficient explanation of the wide diffusion of many genera, and even species, of arctic and north temperate plants in the southern hemisphere or on the summits of tropical mountains. Nearly fifty of the flowering plants of Tierra-del-Fuego are found also in North America or Europe, but in no intermediate country; while fifty-eight species are common to New Zealand and Northern Europe; thirty-eight to Australia, Northern Europe, and Asia; and no less than seventy-seven common to New Zealand, Australia, and South America. On lofty mountains far removed from each other, identical or closely allied plants often occur. Thus the fine Primula imperialis of a single mountain peak in Java has been found (or a closely allied species) in the Himalayas; and many other plants of the high mountains of Java, Ceylon, and North India are either identical or closely allied forms. So, in Africa, some species, found on the summits of the Cameroons and Fernando Po in West Africa, are closely allied to species in the Abyssinian highlands and in Temperate Europe; while other Abyssinian and Cameroons species have recently been found on the mountains of Madagascar. Some peculiar Australian forms have been found represented on the summit of Kini Balu in Borneo. Again, on the summit of the Organ mountains in Brazil there are species allied to those of the Andes, but not found in the intervening lowlands.

Now all these facts, and numerous others of like character, were supposed by Mr. Darwin to be due to a lowering of temperature during glacial epochs, which allowed these temperate forms to migrate across the intervening tropical lowlands. But any such change within the epoch of existing species is almost inconceivable. In the first place, it would necessitate the extinction of much of the tropical flora (and with it of the insect life), because without such extinction alpine herbaceous plants could certainly never spread over tropical forest {{hws|low|lowlands}