In no part of the world, and at no period of time, do we find the behavior of men left to unchartered freedom. Everywhere human life is in a measure organized and directed by customs, laws, beliefs, ideals, which shape its ends and guide its activities. As this guidance of life by rule is universal in human society, so upon the whole it is peculiar to humanity. There is no reason to think that any animal except man can enunciate or apply general rules of conduct. Nevertheless, there is not wanting something that we can call an organization of life in the animal world. How much of intelligence underlies the social life of the higher animals is indeed extremely hard to determine. In the aid which they often render to one another, in their combined hunting, in their play, in the use of warning cries, and the employment of "sentinels," which is so frequent among birds and mammals, it would appear at first sight that a considerable measure of _mutual understanding_ is implied, that we find at least an analogue to human custom, to the assignment of functions, the division of labor, which mutual reliance renders possible. How far the analogy may be pressed, and whether terms like "custom" and "mutual understanding," drawn from human experience, are rightly applicable to animal societies, are questions on which we shall touch presently. Let us observe first that as we descend the animal scale the sphere of _intelligent activity_ is gradually narrowed down, and yet behavior is still regulated. The lowest organisms have their definite methods of action under given conditions. The amoeba shrinks into itself at a touch, withdraws the pseudopodium that is roughly handled, or makes its way round the small object which will serve it as food. Given the conditions, it acts in the way best suited to avoid danger or to secure nourishment. We are a long way from the intelligent regulation of conduct by a general principle, but we still find action adapted to the requirements of organic life. When we come to human society we find the basis for a social organization of life already laid in the animal nature of man. Like others of the higher animals, man is a gregarious beast. His interests lie in his relations to his fellows, in his love for wife and children, in his companionship, possibly in his rivalry and striving with his fellow-men. His loves and hates, his joys and sorrows, his pride, his wrath, his gentleness, his boldness, his timidity--all these permanent qualities, which run through humanity and vary only in degree, belong to his inherited structure. Broadly speaking, they are of the nature of instincts, but instincts which have become highly plastic in their mode of operation and which need the stimulus of experience to call them forth and give them definite shape.