The cause of the introduction of these varieties of color among the inferior animals of the same species, which have become permanent, is involved in great obscurity; but we have good reason to suppose that differences of climate, situation, food, and habits, are some of the influential agencies in their production, chiefly perhaps the former, which appears to operate to a considerable extent in the various coloring of the human race. Both the plants and animals of hot regions display the deepest colors with which we are acquainted, while lighter shades are characteristic of those that are situated in cold countries. Within the tropics, the birds, beasts, flowers, and even fishes have the respective hues of their feathers, hairs, petals, and scales uniformly very deeply tinctured; while, as we recede from the equator, the color of the animal races progressively becomes of a lighter cast, till, approaching the poles, white is their common livery. The same remark is true very generally of the complexion of mankind. The black, dark-brown, and copper colors prevail in equatorial districts; the lighter olive is distinctive of the nations immediately north of the tropic of Cancer; and still lighter shades become more universal in the higher latitudes. The Abyssinians are much less dark than the Negro races, for though their geographical climate is the same, their physical climate is very different, the high, table-land of the country placing them in a lower temperature. Shut up within the walls of their seraglios, and secluded from the sun, the Asiatic and African women are frequently as white as the Europeans; while, in our own country, exposure to the sun is well-known to produce a deeper complexion, and artificial protection from its influence is adopted to preserve a fair and unfreckled skin. The larvæ of many insects deposited in dark situations are white, and acquire a brownish hue upon being confined under glasses that admit the influence of the solar rays. Facts of this kind indicate the powerful operation of diverse climates in the various coloring of the human skin, and are sufficient to show, that the different complexions of mankind are mere varieties of species, introduced and made permanent by the continued action of local causes.