So that humanity, in its twofold nature, is dependent for its development upon two distinct species of stimulants, objective and subjective. Material causations, or those forces which minister to the requirements of man's material nature but upon which his intellectual progress is dependent, are configurations of surface, soil, climate, and food. Those physical conditions which, when favorable, give to their possessors wealth and leisure, are the inevitable precursors of culture. Immaterial causations are those forces which act more directly upon man's immaterial nature, as association, religion, wealth, leisure, and government. Continuing the analysis, let us first examine physical stimulants. Admitting readily two of M. Taine's primordial humanity-moving forces, 'le milieu' or environment, and his 'le moment' or inherited impulse, we will pass over the third force 'la race';--for inherent differences in race, in the present stage of science, are purely hypothetical; it remains yet to be proved that one nation is primarily inherently inferior or superior to another nation. That man once created is moulded and modified by his environment, there can be no doubt. Even a cursory survey of the globe presents some indications favorable and unfavorable to the unfolding of the different forms of organic being. Great continents, for instance, appear to be congenial to the development of animal life; islands and lesser continents to the growth of exuberant vegetation. Thus, in the eastern hemisphere, which is a compact oval, essentially continental, with vast areas far removed from the influence of the ocean, flourish the elephant, the hippopotamus, the rhinoceros, the courageous lion, the fierce tiger, the largest and lordliest of animal kind, while in the more oceanic western hemisphere inferior types prevail. Cold and dryness characterize the one; heat and humidity the other; in one are the greatest deserts, in the other the greatest lakes and rivers. Warm oceanic currents bathe the frosty shores of the northern extremities of the continents and render them habitable; the moisture-laden equatorial atmosphere clothes the adjacent islands and firm land in emerald verdure. Upon the same parallel of latitude are the great Sahara Desert of Africa, and the wilderness of luxuriant billowy foliage of the American Isthmus. In warm, moist climates, such species of animal life attain the fullest development as are dependent upon the aqueous and herbous agencies. In tropical America are seen the largest reptiles, the most gorgeous insects,--there the inhabitants of warm marshes and sluggish waters assume gigantic proportions, while only upon the broad inland prairies or upon elevated mountain ranges, away from the influences of warm waters and humid atmospheres, are found the buffalo, bear, and elk. The very complexion and temperament of man are affected by these vegetative and umbrageous elements.