Applying this law to man, it will be found to be a fact that, whereas the barbarian is most tenacious of custom, the European can adopt new fashions with comparative ease. The obvious inference is, that in proportion as the brain is feeble it is incapable of the effort of origination; therefore, savages are the slaves of routine. Probably a stronger nervous system, or a peculiarity of environment, or both combined, served to excite impatience with their surroundings among the more favored races, from whence came a desire for innovation. And the mental flexibility thus slowly developed has passed by inheritance, and has been strengthened by use, until the tendency to vary, or think independently, has become an irrepressible instinct among some modern nations. Conservatism is the converse of variation, and as it springs from mental inertia it is always a progressively salient characteristic of each group in the descending scale. The Spaniard is less mutable than the Englishman, the Hindoo than the Spaniard, the Hottentot than the Hindoo, and the ape than the Hottentot. Therefore, a power whose existence depends upon the fixity of custom must be inimical to progress, but the authority of a sacred caste is altogether based upon an unreasoning reverence for tradition,--in short, on superstition; and as free inquiry is fatal to a belief in those fables which awed the childhood of the race, it has followed that established priesthoods have been almost uniformly the most conservative of social forces, and that clergymen have seldom failed to slay their variable brethren when opportunity has offered. History teems with such slaughters, some of the most instructive of which are related in the Old Testament, whose code of morals is purely theological.