This degeneration of the poor white is no mystery. Their poverty of blood and weakness of mind were not engendered by the insalubrity of climate, nor even by the sterility of the soil alone. Deny to any race, class, or community free social condition, freedom of thought, the expansion of the mind, the liberty of political and religious ideas, and it is sure to degenerate, and in time to perish. The doctrine of Adam Smith and the theory of Malthus as to the fatal necessity of starvation, are in some measure correct, but they are mistaken in the view that human fecundity tends to get the start of the means of subsistence, for on the contrary it keeps pace with it. We find that the fishes in the lakes, and the wolves in the forests, increase in exact ratio to the amount of food furnished. Nature regulates the fecundity of animals and human beings when society neglects it. X. The influences of climate, of food, of temperature, of domesticity upon the variation of species is well known. These mediate and external causes act with more vigor when the immediate and internal causes favor the effect. "All the mechanism of the formation of varieties," says Flourens, "turns upon these two internal causes--the tendency of the species to vary, and the transmission of the acquired variations." Cultivated plants and domesticated animals, when deprived of the modifying influence of man, return to the state of nature, and undergo new modifications, alterations, degenerations, even so far as to disguise and conceal the primitive type. A few generations suffice to restore a variety to the primitive stock without retaining any of the organic elements which would debase it. The more the influence of civilized man makes itself felt, the more the superior species overpower, absorb, or modify the inferior species. The more rude the people and the less polished their societies, the more powerful and rapid will be the influences of climate. Civilized men are continually exercising their talents to conform their conditions to the necessities of the time and place, and by their ingenuity remedy the defects, and by the resisting powers of a cultivated and occupied mind resist many of the morbid influences of climate. But plants and animals succumb at once if not protected by man. XI. During the more than two centuries of occupation of these southern lands there appear sufficient data to form, perhaps, some definite ideas of the success or failure of colonization, and the vague and doubtful process of acclimation. These evidences, thus far, are decidedly in favor of the black man. For he has multiplied with astonishing rapidity, and preserved his physical forces, and during this long and brutalizing term of his servitude he has not exhibited the ferocity of his master, save when hunted down like the beasts of prey, as in Hayti; neither has he sunk so low in the scale of true humanity as those who have held him in bondage.