Chapter XIII—Island Peoples
Physical relationship between islands and peninsulas.
The characteristics which mark peninsulas, namely, ample contact with the sea, small area as compared with that of the continents, peripheral location, more or less complete isolation, combined, however, with the function of bridge or passway to yet remoter lands, are all accentuated in islands. A list of the chief peninsulas of the world, as compared with the greatest islands, shows a far larger scale of areas for the former, even if the latter be made to include the vast ice-capped land-mass of Greenland (2,170,000 square kilometers or 846,000 square miles). New Guinea, the largest habitable island, has only one-fourth the area of Arabia, the largest of the peninsulas.[803] Therefore, both the advantages and disadvantages incident to a restricted area may be expected to appear in an intensified degree in islands.
Peninsulas are morphologically transition forms between mainland and islands; by slight geological changes one is converted into the other. Great Britain was a peninsula at the end of the Tertiary period, before subsidence and the erosion of Dover Channel combined to sever it from the continent. It bears to-day in its flora and fauna the evidence of its former broad connection with the mainland.[804] In Pliocene times, Sicily and Sardinia were united by a land bridge with the Tunisian projection of North Africa; and they too, in their animal and plant life, reveal the old connection with the southern continent.[805] Sometimes man himself for his own purposes converts a peninsula into an island. Often he constructs a canal, like that at Kiel or Corinth, to remove an isthmian obstruction to navigation; but occasionally he transforms his peninsula into an island for the sake of greater protection. William of Rubruquis tells us that in 1253 he found the neck of the Crimea cut through by a ditch from sea to sea by the native Comanians, who had taken refuge in the peninsula from the Tartar invaders, and in this way had sought to make their asylum more secure.[806]
The reverse process in nature is quite as common. The Shangtung Peninsula rises like a mountainous island from the sea-like level of alluvial plains about it, suggesting that remote time when the plains were not yet deposited and an arm of the Yellow Sea covered the space between Shangtung and the highlands of Shansi.[807] The deposition of silt, aided often by slight local elevation of the coast, is constantly tying continental islands to the mainland. The Echinades Archipelago off the southwest coast of ancient Acarnania, opposite the mouth of the Achelous River, Strabo tells us, was formerly farther from shore than in his time, and was gradually being cemented to the mainland by Achelous silt. Some islets had already been absorbed in the advancing shoreline, and the same fate awaited others.[808] Farther up this western coast of Greece, the island of Leukas has been converted into a peninsula by a sickle-shaped sandbar extending across the narrow channel.[809] Nature is working in its leisurely way to attach Sakhalin to the Siberian coast. The strong marine current which sets southward from the Okhotsk Sea through the Strait of Tartary carries silt from the mouth of the heavy laden Amur River, and deposits it in the "narrows" of the strait between Capes Luzarev and Pogobi, building up sandbars that come dangerously near the surface in mid channel.[810] Here the water is so shallow that occasionally after long prevailing winds, the ground is left exposed and the island natives can walk over to Asia.[811] The close proximity of Sakhalin to the mainland and the ice bridge covering the strait in winter rob the island of much of its insular character and caused it to pass as a peninsula until 1852. Yet that five-mile wide stretch of sea on its western coast determined its selection as the great penal station of the Russian Empire. The fact that peninsular India accords in so many points of flora, fauna and even primitive ethnic stock with Madagascar and South Africa, indicates its former island nature, which has been geographically cloaked by its union with the continent of Asia.
Character of insular flora and fauna.
Islands, because of their relatively limited area and their clearly defined boundaries, are excellent fields for the study of floral, faunal, and ethnic distribution. Small area and isolation cause in them poverty of animal and plant forms and fewer species than are found in an equal continental area. This is the curse of restricted space which we have met before. The large island group of New Zealand, with its highly diversified relief and long zonal stretch, has only a moderate list of flowering plants, in comparison with the numerous species that adorn equal areas in South Africa and southwestern Australia.[812] Ascension possessed originally less than six flowering plants. The four islands of the Greater Antilles form together a considerable area and have all possible advantages of climate and soil; but there are probably no continental areas equally big and equally favored by nature which are so poor in all the more highly organized groups of animals.[813] Islands tend to lop off the best branches. Darwin found not a single indubitable case of terrestrial mammals native to islands situated more than three hundred miles from the mainland.[814] The impoverishment extends therefore to quality as well as quantity, to man as well as to brute. In the island continent of Australia, the native mammalia, excepting some bats, a few rodents, and a wild dog, all belong to the primitive marsupial sub-class; its human life, at the time of the discovery, was restricted to one retarded negroid race, showing in every part of the island a monotonous, early Stone Age development. The sparsely scattered oceanic islands of the Atlantic, owing to excessive isolation, were all, except the near-lying Canaries, uninhabited at the time of their discovery; and the Canary Islanders showed great retardation as compared with their parent stock of northern Africa. [See map page 105.]