Apply this proof to society. Society consists of numbers of interrelated and highly specialised functions, the functionaries being individual human animals. Society develops them—they could never have been evolved in solitude. As easily conceive of independent eyes, rolling around and doing business by themselves, as of independent teachers, carpenters, dentists. Society maintains them, as the body does the eye; intricate labours of many others feeding, warming, housing, protecting the teacher, while he teaches. Alone he might hunt, and “support himself” as a separate animal; as if, conceivably, the eye could return to a protoplasmic condition and soak up a living somehow; but as an eye it would cease to exist; and he would cease to exist as a teacher. The teacher, teaching, cannot support himself. His time, his strength, his enormously specialised skill, are spent in teaching, and the society which made him and which needs him, necessarily supports him. Teaching as an activity is not predicable of individuals. It is a power to transmit the social gain in intelligence and knowledge among the social constituents. No solitary individual could have attained this knowledge and experience; and, if he had it, he could _not teach it to himself_. Teaching is a social function; a very elaborate and long-developed social function. The teacher is an extreme instance of the social functionary. Other than as a social functionary he does not exist. This test may be applied far and wide, in every trade, art, science, or business; no human occupation escapes it. Whatever a man can do separately for himself, an ape can imitate. Whatever a man does which is worth falling human is done collectively and for others, it is a social function. He may work alone at his business, but the tools he works with are the fruit of slow social evolution, and the work he does is done for others. He may retire to the forest and think alone, but he thinks on the problems of human life; no personal affairs can occupy the energies of a human brain; and the brain he thinks with is a slow social product too. The evolution of the interdependence of social function is as clear as that of the interdependent physical functions of our separate bodies. As early animal forms have few and simple functions, gradually evolving those more delicate and complicated, so do early societies have few and simple arts or trades, and similarly evolve them. As society progresses the trades flow wider, dividing and subdividing as they go, until we have the exquisitely sublimated special skill of the modern worker; and at each step of the process the organic relation tightens as well as widens; the specialist is less able to “take care of himself,” and the others are less able to do without the specialist. “Every man to his trade” voices our popular recognition of this law, and “Jack-of-all-trades and master of none” shows the true merit of the “all-around-man.”