Human cooperation — division of labor — based on integrated family-households and on separated households, villages, tribes, nations, races, etc., wherein man’s natural biological attractions and repulsions for and against one another are transformed into a mutually recognized system of spatial (geographical) allocation (of physical approximation and integration or of separation and segregation, and of direct or of indirect contact, exchange and trade), leads to improved standards of living, a growing population, further extensification and intensification of the division of labor, and increasing diversity and differentiation. [6]
As a result of this development and an ever more rapid increase of goods and desires which can be acquired and satisfied only indirectly, professional traders, merchants, and trading centers will emerge. Merchants and cities function as the mediators of the indirect exchanges between territorially separated households and communal associations and thus become the sociological and geographical locus and focus of intertribal or interracial association.
It will be within the class of merchants in which racially, ethnically, or tribally mixed marriages are relatively most common; and since most people, of both reference groups, typically disapprove of such alliances, it will be the wealthier members of the merchant class who can afford such extravagances. However, even the members of the wealthiest merchant families will be highly circumspect in such endeavors. In order not to endanger their own position as a merchant, great care must be taken that every mixed marriage is to be a marriage between “equals.” [7]
Accordingly, it will be in the big cities as the centers of international trade and commerce, where mixed couples and their offspring typically reside, where members of different ethnicities, tribes, races, even if they do not intermarry, still come into regular direct personal contact with each other (in fact, that they do so is required by the fact that their respective tribesmen back home do not have to deal directly with more or less distasteful strangers), and where the most elaborate and highly developed system of physical and functional integration and segregation will arise. [8] It will also be in the big cities where, as the subjective reflection of this complex system of spatio-functional allocation, citizens will develop the most highly refined forms of personal and professional conduct, etiquette, and style. It is the city that breeds civilization and civilized life.