THE DISTRIBUTION OF LIFE. The distribution of plants and animals is determined by a number of factors, which are more or less interdepend ent. The chief of these are the physical charac teristics, the climate, topography, etc., of the region, with which should be coupled the charac teristics of plant and animal life. Closely re lated to these are the changes in climate, topog raphy, etc., and the adaptability of various species. Other factors are the means of dispersal of forms of life, and the results of the com petitive struggle for existence among them. Under the last should be included the results of man's interference with the adjustment of life conditions which prevailed upon his advent.
The play of the above agencies has resulted in a somewhat complex distribution, some of whose features are not yet easy to explain. In some cases widely separated regions have fauna and flora remarkably similar, like the British Isles and those of Northern Japan. The physical conditions are quite similar, but the areas are separated by almost the semi-circumference of the globe. On the other hand, adjacent regions, with similar physical conditions, often differ widely in fauna and flora, as in the case of Australia and New Zealand. Regions with very different fauna and flora are, in some cases, connected by transition zones, through which the change is made gradually, while in other cases the change is a sudden and violent one. Certain well-marked types occur in scattered localities, in various parts of the earth, without apparent connection one with another.
Although much study has been devoted to the subject, no satisfactory classification of the earth's surface with respect to its life has yet been evolved.
In polar regions, such as the northern parts of North America, Europe, and Asia, the soil is permanently frozen below, thawing only at the surface in summer, thus forming the well-known tundra, whose chief vegetation is reindeer-moss, among which bloom in summer many bright colored flowers. This tundra passes in less cold regions into moors and heaths.
Desert regions are characterized by a scanty growth of yucca, and many species of thorny shrubs; where desert conditions are less intense, various species of Artemisia abound. The great plains of North America, the pampas of Argen tina, and the Siberian steppes, which may be characterized as sub-humid regions, are clothed with grasses, and these pass, by insensible de grees. through prairie regions, of mingled grasses and woods, to forested regions. These differ widely in character in different parts of the earth. In the colder regions coniferous forests prevail; in the more temperate regions conifers: and broad-leaved trees are mingled, while the forests of tropical regions are commonly of the latter class, with dense undergrowth. The great est and densest forests are, as a rule, found in regions of heaviest rainfall. Thus the broader distinctions in• the .character of the vegetation are in great part controlled by temperature and rainfall. See DISTRIBUTION OF PLANTS.
The faunas of the earth are less dependent upon climate than the floras, since animals can migrate somewhat freely, and have, in greater or less degree, the ability to protect themselves from its adverse elements. Still, each climatic zone has a fauna of its own, differing markedly from neighboring ones; the polar from the temperate, and the temperate from the tropic zone. The
musk-ox, polar bear, and Arctic foxes, blue and white, are confined to regions of ice and snow. In temperate regions their nearest relatives are the bison, the black and grizzly bears, and the red fox, who range with the wapiti, antelope, and many species of deer. The tropic• fauna is prob ably less closely related to that of temperate legions. It is characterized by large mammals, the elephant, rhinoceros, hippopotamus, camel, lion, tiger, leopard, many species of marsupials (in Australia), monkeys, etc. The fauna of the desert differs widely from that of well-watered regions in amount, variety, and species, which is due, in great part, of course, to the difference in plant food-supply. In the same latitudes and similar climates there are both close agreements and wide differences. Thus the faunas of Europe and North America do not differ materially, but between Australia, Africa, and South America there are wide, even radical differences. Austra lia, with its marsupial fauna, resembles no other region on earth, and at few points are there re semblances between Africa and South America. The great carnivora of the former continent have few representatives in South America. See DIS TRIBUTION OF ANIMALS.
Of all forms of life, man is the most cosmopoli tan. He is found from the frozen regions to the equator. His ability to protect himself from hostile climatic conditions enables him to sur vive even under those most adverse, but certain conditions seem to be the most favorable to his development. Arctic conditions, where besides a hostile climate the economic conditions are se vere, are not conducive to his development. On the other hand, the languid climate of the tropics, with the ease of living, seems equally unfitted for the development of civilization. It is in temperate climates, which stimulate exer tion, and where effort meets with adequate re ward, that man has reached the highest level.
The races of mankind are commonly classified according to color and other characteristics as fair-complexioned or Caucasian, yellow or Asiat ic, brown or East Indian, red or American Indian. and black or negro. The Caucasians (including all the Indo-European peoples, the Semites and the Hamites, the last-named being dark-skinned) inhabit Europe, a large part of Asia (mainly in the south and southwest), Northern Africa, North America, South America (in parts of which they are outnumbered by the red race), and Australia, and are scattered, in greater or less numbers, over other parts of the earth. The yellow race comprises the Chinese, Japanese, Koreans, Tibetans, and various peoples of Central and Southeastern Asia. The brown peoples are those of the Malay Peninsula, the East India Islands, and Polynesia. The American Indians inhabited the entire continent from Bering Strait to Cape Horn, but in Central and South America they have become much mixed in blood with their Spanish conquerors. The black race, whose home is Africa, have been subjected to forced migrations, under slavery, and many millions of them are now found in the United States, the West India Islands, and Brazil. See MAN, SCIENCE OF.