But we shall never understand the course of civilization, and the varied phenomena which its history presents, without a consideration of what I may term the internal resistances, or counter forces, which arise in the heart of advancing society, and which can alone explain how a civilization once fairly started should either come of itself to a halt or be destroyed by barbarians. The mental power, which is the motor of social progress, is set free by association, which is,--what, perhaps, it may be more properly called,--an integration. Society in this process becomes more complex; its individuals more dependent upon each other. Occupations and functions are specialized. Instead of wandering, population becomes fixed. Instead of each man attempting to supply all of his wants, the various trades and industries are separated--one man acquires skill in one thing, and another in another thing. So, too, of knowledge, the body of which constantly tends to become vaster than one man can grasp, and is separated into different parts, which different individuals acquire and pursue. So, too, the performance of religious ceremonies tends to pass into the hands of a body of men specially devoted to that purpose, and the preservation of order, the administration of justice, the assignment of public duties and the distribution of awards, the conduct of war, etc., to be made the special functions of an organized government. In short, to use the language in which Herbert Spencer has defined evolution, the development of society is, in relation to its component individuals, the passing from an indefinite, incoherent homogeneity to a definite, coherent heterogeneity. The lower the stage of social development, the more society resembles one of those lowest of animal organisms which are without organs or limbs, and from which a part may be cut and yet live. The higher the stage of social development, the more society resembles those higher organisms in which functions and powers are specialized, and each member is vitally dependent on the others. Now, this process of integration, of the specialization of functions and powers, as it goes on in society, is, by virtue of what is probably one of the deepest laws of human nature, accompanied by a constant liability to inequality. I do not mean that inequality is the necessary result of social growth, but that it is the constant tendency of social growth if unaccompanied by changes in social adjustments, which, in the new conditions that growth produces, will secure equality. I mean, so to speak, that the garment of laws, customs, and political institutions, which each society weaves for itself, is constantly tending to become too tight as the society develops. I mean, so to speak, that man, as he advances, threads a labyrinth, in which, if he keeps straight ahead, he will infallibly lose his way, and through which reason and justice can alone keep him continuously in an ascending path.