Human beings, so far as we have yet been able to learn, are the only creatures who habitually pass judgment upon their own actions, or who think of them as right or wrong. When these thoughts about our actions or the actions of others get themselves formulated and expressed they react back upon and control us. That is one reason we hang mottoes on the wall. That is why one sees on the desk of a busy man the legend "Do it now!" The brutes do not know these devices. They do not need them perhaps. They have no aim in life. They do not work.
What distinguishes the action of men from animals may best be expressed in the word "conduct." Conduct as it is ordinarily used is applied to actions which may be regarded as right or wrong, moral or immoral. As such it is hardly a descriptive term since there does not seem to be any distinctive mark about the actions which men have at different times and places called moral or immoral. I have used it here to distinguish the sort of behavior which may be regarded as distinctively and exclusively human, namely, that which is self-conscious and personal. In this sense blushing may be regarded as a form of conduct, quite as much as the manufacture of tools, trade and barter, conversation or prayer.
No doubt all these activities have their beginnings in, and are founded upon, forms of behavior of which we may find the rudiments in the lower animals. But there is in all distinctively human activities a conventional, one might almost say a contractual, element which is absent in action of other animals. Human actions are more often than not controlled by a sense or understanding of what they look like or appear to be to others. This sense and understanding gets itself embodied in some custom or ceremonial observance. In this form it is transmitted from generation to generation, becomes an object of sentimental respect, gets itself embodied in definite formulas, is an object not only of respect and reverence but of reflection and speculation as well. As such it constitutes the mores, or moral customs, of a group and is no longer to be regarded as an individual possession.
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.