with its acquirement of greater mass its parts multiply and simultaneously differentiate. It is thus with a society. At first the unlikenesses among its groups of units are inconspicuous in number and degree; but, as it becomes more populous, divisions and subdivisions become more numerous and more decided. Further, in the social organism as in the individual organism, differentiations cease only with that completion of the type which marks maturity and precedes decay.
Though in inorganic aggregates also, as in the entire solar system and in each of its members, structural differentiations accompany the integrations, yet these are so relatively slow, and so relatively simple, that they may be disregarded. The multiplication of contrasted parts in bodies politic and in living bodies is so great that it substantially constitutes another common character which marks them off from inorganic bodies.
This community will be more fully appreciated on observing that progressive differentiation of structures is accompanied by progressive differentiation of functions.
The multiplying divisions, primary, secondary, and tertiary, which arise in a developing animal, do not assume their major and minor unlikenesses to no purpose. Along with diversities in their shapes and compositions there go diversities in the actions they perform: they grow into unlike organs having unlike duties. Assuming the entire function of absorbing nutriment at the same time that it takes on its structural characters, the alimentary system becomes gradually marked off into contrasted portions, each of which has a special function forming part of the general function. A limb, instrumental to locomotion or prehension, acquires divisions and subdivisions which perform their leading and their subsidiary shares in this office. So is it with the parts into which a society divides. A dominant class arising does not simply become unlike the rest, but assumes control over the rest; and when this class separates into the more and the less dominant, these, again, begin to discharge distinct parts of the entire control. With the classes whose actions are controlled it is the same. The various groups into which they fall have various occupations, each of such groups also, within itself, acquiring minor contrasts of parts along with minor contrasts of duties.
And here we see more clearly how the two classes of things we are comparing distinguish themselves from things of other classes; for such differences of structure as slowly arise in inorganic aggregates are not accompanied by what we can fairly call differences of function.
Why in a body politic and in a living body these unlike actions of unlike parts are properly regarded by us as functions, while we cannot so regard the unlike actions of unlike parts in an inorganic body, we shall perceive on turning to the next and most distinctive common trait.
