单项选择题

Origin of Vegetable and Animal Life in America When the new world was first discovered, it was found to be, like the old, full of plants and animals, and a great many tribes and nations of men lived there. Yet the plants and animals, if not the men, were all essentially different from those known in the old world. This was unexpected; it was thought to be quite remarkable. Then a question arose, what is the origin of these plants and animals and men How could they come to a continent that is cut off apparently from all intercourse (交流) and connection with the rest of the world For the American continent is entirely separated from the old. The nearest approach to it is at Behring’’sStraits (白令海峡), on the north-west, where it is divided from the Asiatic continent by a channel about forty miles wide. Means of Communication with the Old World Some animals and perhaps some plants, and most certainly men, may be supposed to have been transported across such a channel of water as this of Behring’’s Straits, either by boats made by the savages living on the coasts, or possibly by means of ice at some time when the whole channel was entirely frozen over. There is also at some distance south of Behring’’s Straits a remarkable chain of islands, called the Aleutian Islands (阿留申群岛), which extend in a regular and continuous line from the American to the Asiatic shore. These islands are volcanic. They contain now numerous volcanoes, some active and some dead. They bear no trees, but they produce a great variety of animals. They look, upon the map, like a row of stepping stones, placed on purpose to enable men and animals from the old world to make their way to the new. These islands are nearly all inhabited, and the natives navigate (航海) the seas around them in boats made of a frame-work of wood or bone, covered externally with seal skins. It is perhaps possible to imagine also that a company of men might have been forced accidentally to sea in some large canoe from the coast of Africa, or on the other side from some of the islands of the Pacific, and landed upon the American shores. It is true that it would be exceedingly improbable that any such combination of circumstances would occur as could lead to such a result. The canoe or boat must have been very large, the stock of provisions very great. The wind must not have been violent enough to engulf (吞没) the boat and must still have blown very long and very steadily to have carried a company of men so far before they all perished of hunger and thirst. All this would have been very improbable. Still it would be difficult to show that it could not occur. From the hundreds and perhaps thousands of boats full of savages that have been blown off to sea from the coasts of Africa, or from the South Sea Islands, it would be impossible to prove positively that there could never have been one that by any chance could have reached the American shores. There is still another mode by which we can imagine the animal and vegetable life of America to have been communicated to it from other regions, and that is, by supposing that there was in former ages some direct connection between the two continents by a tract of land which has since become submerged (淹没的). It is well known now that the crust of the earth is not in a stable condition. It is subject to changes and movements of various kinds, which are now going forward all the time, and have probably always been going forward. In some places the land is slowly rising; in others it is slowly subsiding (下沉). There are many places in the world where towns and cities which formerly stood high and dry on the land are now under water. The land has slowly subsided, so that the sea at the present time flows over it, and people passing in boats now look down and see the old foundations, and fragments of the fallen walls and columns, at the bottom. The Plants and Animals of America Generally New These and various other similar theories were devised in former times in endeavors to contrive some way of bringing plants and animals from other countries to America. But they have been generally considered unsatisfactory, since when people examined the plants and animals living here, they were found to be, as it seemed, essentially different from those found in other countries, so different that they could ever be descended from the same stock (祖先，血统), at least by ordinary generation. The fauna (动物群) and the flora (植物) were both found to be in general essentially dissimilar. The flora is its system of plants. By the fauna of a country is meant the system of animals that inhabit it. With a moderate number of exceptions such as these, however, the plants and animals found in America proved on examination to be entirely new. So, since both the fauna and the flora of America were so essentially different from those of the old world, it seemed to be wholly useless to attempt to design means by which the forefather (祖先) of the present races in America could have sailed across the ocean, or could have migrated by means of countries and territories which once existed but are now submerged. It is possible that man swam across Behring’’s Straits to the new world.