If the advance of Man towards greater heterogeneity is traceable to the production of many effects by one cause, still more clearly may the advance of Society towards greater heterogeneity be so explained.  Consider the growth of an industrial organisation.  When, as must occasionally happen, some individual of a tribe displays unusual aptitude for making an article of general use—­a weapon, for instance—­which was before made by each man for himself, there arises a tendency towards the differentiation of that individual into a maker of such weapon.  His companions—­warriors and hunters all of them,—­severally feel the importance of having the best weapons that can be made; and are therefore certain to offer strong inducements to this skilled individual to make weapons for them.  He, on the other hand, having not only an unusual faculty, but an unusual liking, for making such weapons (the talent and the desire for any occupation being commonly associated), is predisposed to fulfil these commissions on the offer of an adequate reward:  especially as his love of distinction is also gratified.  This first specialisation of function, once commenced, tends ever to become more decided.  On the side of the weapon-maker continued practice gives increased skill—­increased superiority to his products:  on the side of his clients, cessation of practice entails decreased skill.  Thus the influences that determine this division of labour grow stronger in both ways; and the incipient heterogeneity is, on the average of cases, likely to become permanent for that generation, if no longer.

Observe now, however, that this process not only differentiates the social mass into two parts, the one monopolising, or almost monopolising, the performance of a certain function, and the other having lost the habit, and in some measure the power, of performing that function; but it tends to imitate other differentiations.  The advance we have described implies the introduction of barter,—­the maker of weapons has, on each occasion, to be paid in such other articles as he agrees to take in exchange.  But he will not habitually take in exchange one kind of article, but many kinds.  He does not want mats only, or skins, or fishing gear, but he wants all these; and on each occasion will bargain for the particular things he most needs.  What follows?  If among the members of the tribe there exist any slight differences of skill in the manufacture of these various things, as there are almost sure to do, the weapon-maker will take from each one the thing which that one excels in making:  he will exchange for mats with him whose mats are superior, and will bargain for the fishing gear of whoever has the best.  But he who has bartered away his mats or his fishing gear, must make other mats or fishing gear for himself; and in so doing must, in some degree, further develop his aptitude.  Thus it results that the small specialities of faculty possessed by various members of the tribe,