Internal social movements also may be thus interpreted. Localities naturallyfitted for producing particular commodities -- that is, localities in whichsuch commodities are got at the least cost of energy -- that is, localitiesin which the desires for these commodities meet with the least resistance;become localities devoted to the obtainment of these commodities. Where soiland climate render wheat a profitable crop, or a crop from which the greatestamount of life-sustaining power is gained by a given quantity of effort,the growth of wheat becomes a dominant industry. Where wheat cannot be economicallyproduced, oats, or rye, or maize, or potatoes, or rice, is the agriculturalstaple. Along sea-shores men support themselves with least effort by catchingfish, and hence fishing becomes the occupation. And in places which are richin coal or metallic ores, the population, finding that labour expended inraising these materials brings a larger return of food and clothing thanwhen otherwise expended, becomes a population of miners. This last instanceintroduces us to the phenomena of exchange, which equally illustrate thegeneral law. For the practice of barter begins as soon as it facilitatesthe fulfilment of men's desires, by diminishing the exertion needed to reachthe objects of those desires. When instead of growing his own corn, weavinghis own cloth, sewing his own shoes, each man began to confine himself tofarming, or weaving, or shoemaking; it was because each found it more laboriousto make everything he wanted, than to make a great quantity of one thingand barter the surplus for other things. Moreover, in deciding what commodityto produce, each citizen was, as he is at the present day, guided in thesame manner. In choosing those forms of activity which their special circumstancesand special faculties dictate, the social units severally move towards theobjects of their desires in the directions which present to them the fewestobstacles. The process of transfer which commerce presupposes, supplies anotherseries of examples. So long as the forces to be overcome in procuring anynecessary of life in the district where it is consumed, are less than theforces to be overcome in procuring it from an adjacent district, exchangedoes not take place. But when the adjacent district produces it with an economythat is not outbalanced by cost of transit -- when the distance is so smalland the route so easy that the labour of conveyance plus the labour of productionis less than the labour of production in the consuming district, transfercommences. Movement in the direction of least resistance is also seen inthe establishment of the channels along which intercourse takes place. Atthe outset, when goods are carried on the backs of men and horses, the pathschosen are those which combine shortness with levelness and freedom fromobstacles -- those which are achieved with the smallest exertion. And inthe subsequent formation of each highway, the course taken is that whichdeviates horizontally from a straight line so far only as is needful to avoidvertical deviations entailing greater labour in draught. The smallest totalof obstructive forces determines the route, even in seemingly exceptionalcases; as where a detour is made to avoid the opposition of a landowner.
All subsequent improvements, ending in macadamized roads, canals, and railways,which reduce the antagonism of friction and gravity to a minimum, exemplifythe same truth. After there comes to be a choice of roads between one pointand another, we still see that the road chosen is that along which the costof transit is the least: cost being the measure of resistance. When therearises a marked localization of industries, the relative growths of the populationsdevoted to them may be interpreted on the same principle. The influx of peopleto each industrial centre is determined by the payment for labour -- thatis, by the quantity of commodities which a given amount of effort will obtain.
To say that artisans flock to places where, in consequence of facilitiesfor production, an extra proportion of produce can be given in the shapeof wages, is to say that they flock to places where there are the smallestobstacles to the Support of themselves and families; and so growth of thesocial organism takes place where the resistance is least.
Nor is the law less clearly to be traced in those functional changes dailygoing on. The flow of capital into businesses yielding the largest returns,the buying in the cheapest market and selling in the dearest, the introductionof more economical modes of manufacture, the development of better agenciesfor distribution, exhibit movements taking place in directions where theyare met by the smallest totals of opposing forces. For if we analyze eachof these changes -- if instead of interest on capital we read surplus ofproducts which remains after maintenance of labourers -- if we thus interpretlarge interest or large surplus to imply labour expended with the greatestresults -- and if labour expended with the greatest results means muscularaction so directed as to evade obstacles as far as possible; we see thatall these commercial phenomena imply complicated motions set up along linesof least resistance.
