Climate and Animals.— The geographic distribution of animals is doubtless the out come of definite laws — laws that stand in close relation with the past history of the earth through a large portion of geological time. What those laws are forms a subject of great importance in studies of evolution,— a subject, it may be remarked, entirely too great to be adequately treated in the present connection. Naturalists are generally of the opinion that all animals have been produced from those that preceded them by some process of slow trans mutation or development, and that this modifi cation of animal forms took place very slowly, as evidenced by the fact that the historical period of nearly 4,000 years has hardly pro duced any perceptible change in a single species. That marked changes in the climate of the earth have occurred during the remote past there can be no doubt, and that those changes left a marked impress upon the fauna of the globe there can also be no manner of doubt. The great northern ice sheet and the accompanying cold of the glacial period, if it did not cause the extermination of the receding fauna, doubt less led to its migration to more congenial climates.
The part played in the faunal distribution of the globe by the present climate seems to be indirect rather than direct, although there are many facts which seem to point to a direct rela tion. While it is true that the fur-bearing ani mals of the frozen north are generally to be found in Arctic regions, yet they send their representatives far into the temperate latitudes, and indeed into the borders of the regions in habited by the more exclusively tropical species. On the other hand, the tiger, whose home is naturally associated with the hot districts of India and the Indian Archipelago, is equally at home in the elevated regions of the Caucasus and the Himalayas, where his footprints are not infrequently found impressed in fields of snow. Other groups of animals are more limited in their migrations. Some are so closely adapted to an arboreal life that they never stray far beyond the limits of forest vegetation, while others are so tolerant of climatic change that the limit of their possible range is conditioned only by the character and quantity of the food supply and the interposition of impassable physical bar riers.
Climate and The factors neces sary to the development of plant life are light, heat, soil and moisture. The ideal conditions as
regards these essentials do not usually obtain, or, if they do, multitudes of plants seek to take possession of the region,. so that there is a con tinuous struggle for existence in which many more plants fail than succeed.
The climatic factors heat and moisture are combined in several ways in different parts of the globe, and these combinations give widely different vegetation; thus a maximum of heat and a minimum of water give desert conditions where only specially adapted plants can exist. If, on the other hand, a maximum of heat is combined with a maximum of water, the result will be vegetation such as exists only in the rainy tropics. The possible combinations of the two climatic factors are very numerous, as are also those of soil and the effects of animal life and human agencies. Yet the vegetation of the globe is susceptible of a fairly definite classifi cation. Following Humboldt, and adopting such terms as express in a general manner the vegetation characteristic of each zone, we have the following classification: While in a general way these zones stretch around the world in wavy belts, somewhat as do the isotherms, similar belts may be found en circling mountain peaks and chains with in creasing altitude above sea-level. Indeed it is possible to pass successively from tropic to arctic vegetation on a single mountain peak in the tropics.
Abercromby, (Weather' (International Scientific Series); Bacon, 'Cli mate and the Atmosphere,' in the Nineteenth Century (Vol. XLVI I, 94); Bartholomew, 'Meteorology,' Vol. III of his (Atlas' ; Dick son, (Recent Researches on Climate,' in the Geographical Journal (Vol. X, 303); Hann, der Klimatologi0 (3d ed., 3 vols., Stuttgart 1911); Koppen, einer Klas sifikation der Klimate,' in Geogr. Zeitschrift (6 Jahrg. 1901) ; Moore 'Descriptive Meteorol ogy' (New York 1910) ; Waldo, 'Elementary Meteorology' (New York 1896); Woeikof, Klimate der Erde' (Jena 1887); Ward, The Climatic Zones and their Subdivisions,' in Bulletin of the American Geographical So ciety (July 1905); Mill, (Climate and the Effects of Climate,' in the Quarterly Journal of the Royal Meteorological Society (Vol. XXVII, 237), and the publications of the United States Weather Bureau.
Witus L. MOORE, Professor of Meteorology, George Washington University.