which it fulfils in excess some single vital need, only if its other vital needs are fulfilled for it by other parts that have meanwhile undertaken other special activities. One portion of a living aggregate cannot devote itself exclusively to the respiratory function, and cease to get nutriment for itself, unless other portions, that have become exclusively occupied in absorbing nutriment, give it a due supply. That is to say, there must be exchange of services. Organization in an individual creature is made possible only by dependence of each part on all, and of all on each. Now, this is obviously true also of social organization. A member of a primitive society cannot devote himself to an order of activity which satisfies one only of his personal wants, thus ceasing the activities required for satisfying his other personal wants, unless those, for whose benefit he carries on his special activity in excess, supply him with the benefits of their special activities. If he makes weapons instead of continuing a hunter, he must be supplied with the produce of the chase on condition that the hunters are supplied with his weapons. If he becomes a cultivator of the soil, no longer defending himself, then he must be defended by those who have become specialized defenders. That is to say, mutual dependence of parts is essential for the commencement and advance of social organization, as it is for the commencement and advance of individual organization.
Even were there no more to be pointed out, it would be clear enough that we are not here dealing with a figurative resemblance, but with a fundamental parallelism in principles of structure. We have but just begun to explore the analogy, however. The further we inquire, the closer we find it to be. For what, let us ask, is implied by mutual dependence—by exchange of services? There is implied some mode of communication between mutually-dependent parts. Parts that perform functions for one another's benefit must have appliances for conveying to one another the products of their respective functions, or for giving to one another the benefits (when these are not material products) which their respective functions achieve. And obviously, in proportion as the organization becomes high, the appliances for carrying on the intercourse must become involved. This we find to hold in both cases. In the lowest types of individual organisms, the exchange of services between the slightly-differentiated parts is effected in a slow, vague, inefficient way, by an irregular diffusion of the nutrient matters jointly elaborated, and by an irregular propagation of feeble stimuli, causing a rude coordination in the actions of the parts. It is thus, also, with small and simple social aggregates. No definite arrangements for interchanging services exist, but only indefinite ones. Barter of products—food, skins, weapons, or what not—takes place irregularly between individual producers and consumers throughout the whole social body: there is no trading or distributing system, as, in the rudimentary animal, there is no vascular system. So, too, the social organism of low type, like the individual organism
