The Encyclopedia Americana (1920)/Immigrations, Animal and Vegetal
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Immigrations, Animal and Vegetal
|Edition of 1920. See also Introduced species on Wikipedia, and the disclaimer.|
IMMIGRATIONS, Animal and Vegetal, into America began in early geological times. At the dawn of the Age of Mammals, when the great Mesozoic reptiles were disappearing, and the Tertiary Era introduced the dominance of mammalian and other types of animal life, that became more and more modernized as time, advanced, the circumpolar regions of the Northern Hemisphere seem to have been a continuous mass of land. The climate was mild, and animals and plants had free space in which to wander right around the northern world. The origins of the strange primitive creatures then prevalent are unknown; but their scanty fossil remains show their substantial identity in Europe, Asia and America. Before long — as geological time is reckoned — changes in the restless crust of the earth caused separation of North America from both Asia on the west and Europe on the east, and fossils of the Middle Eocene show that local types speedily developed in every Continent. This independent and divergent adaptive modification continued until the Eocene had merged into the Oligocene, as shown by rocks of the White River formation in eastern Wyoming. Land connection had been restored by a lifting of the Bering Sea region, and an isthmus thus formed between Alaska and Siberia. By this bridge came new forms from Asia, while American migrants wandered into the Old World; but the interchange was very limited, bringing to us only certain small forerunners of the sabre-toothed “cats,” of the mustelines of some early creodonts (as Hyænodon), and of primitive rodents. At this time were introduced also the anthracotheres, short-legged, somewhat swine-like, hoofed animals, which have no near relatives in the modern world, but had been previously well represented in Europe. There came also the earliest of the horses (Eohippus), the first opossums and a few others. The Oligocene was followed by the Miocene, a period of mild climate and wide-spread volcanic activity, in which land connection with Siberia, long interrupted, appears to have been restored, and when the first small forms of proboscidians entered this continent, on which subsequently they developed so extensively. “The place of origin and ancestry of these animals,” says Prof. W. B. Scott, “were long exasperating puzzles. Appearing suddenly in the Miocene of Europe and North America, in which regions nothing was known that could, with any plausibility be regarded as ancestral to them, they might as well have dropped from the moon for all that could be told respecting their history. The exploration of Eocene and Oligocene beds of Egypt has dispelled the mystery, and shown that Africa was the original home of the group.” Pliocene time witnessed important introductions from both Asia and South America, where an independent fauna was developing. The most striking novelty, probably, were the bears — a distinctly Old World family. Among the notable importations in the next, or Pleistocene, period, were the antelopes and the bisons. These instances of animal invasion in the distant past are only a few of the list that might be compiled were palæontologists as certain of the foreign origin of some groups as they are of others. More important to us than this, however, is consideration of the invasions of animals and plants within historic times. Horses, cattle, sheep, dogs, cats and poultry, were brought in by the conquerors of tropic America, and by the colonists of its northern coasts, and these aids to agriculture, hunting and housekeeping were too quickly followed by invading foreigners of a harmful character. In the same way grain-plants, forage-plants, garden vegetables, fruits and ornamental trees, shrubs and flowers, came into the country from all parts of the world. Some, unsuited to the conditions, died out; or, like tea and indigo, proved unprofitable and have been neglected. With the ships that brought these beneficent additions to our fauna and flora came many unwelcome visitors — true invaders in the modern sense of the word. Weeds innumerable began with the first settlements. Most of them were accidental importations, in seed, or in the discharged ballast of ships, or were attached to trees, shrubs and plants imported. Some were garden-flowers, controllable and harmless at home, but here flourishing inordinately and spreading into fields and highways; others, weeds and grasses pestiferous everywhere; others the molds, smuts and similar bacteric or fungoid diseases afflicting grains and fruits. It was long before the government took any precautions against such evils.
Simultaneously, and in a similarly careless way, various animals gained entrance and became pests, among them innumerable injurious insects. One of the most noticeable of the early invaders of this kind was the Hessian fly. The famous gypsy moth began here with escapes from an entomologist's collection near Boston in 1869. Among higher animals the house-mouse and black rat came across the Atlantic in early days, the brown rat previous to the Revolution, and these have become troublesome and even dangerous everywhere. (See Rat). Later, unwise persons imported the European house sparrow (“English” sparrow), about 1851. A few years later the skylark, European goldfinch and some other birds were introduced, but fortunately have not become naturalized. Starlings were set free in New York city in 1890, bred abundantly and threaten to become a costly nuisance. Rabbits are common in domestication, but by good fortune have not colonized wild, as has happened so disastrously in Australia. Lapp reindeer have been colonized in Alaska to the great advantage of the Eskimos there.
A few years ago the United States government, warned by naturalists, began to realize the danger in further invasions of this kind, and laws were passed requiring inspection of every plant and animal brought into the country, to make sure that some new and harmful insect or disease did not come with them; and prohibitions were made against the importations of foreign animals, especially certain dreaded ones, as the mungoos. These precautions are in the hands of the Department of Agriculture, and have been highly beneficial in their purpose and effect.
It was formerly believed that human invasions had taken place in prehistoric times on a large scale. Some of the theories, as of arrival of peoples from Egypt, or India, or Polynesia, or Japan, were highly fanciful; but more reasonable was the belief that this continent was populated by the invasion, thousands of years ago, of immigrants from Asia by way of Siberia and Alaska. It is not to be denied that something of the sort may have taken place in the very remote past on an extended scale, but there is no direct evidence of it, either then or more recently.
Bibliography.— Osborn, ‘Age of Mammals’ (New York 1910); Scott, ‘History of Land Mammals in the Western Hemisphere’ (New York 1913); and histories of the economic development of the United States.