Origins and history

On the other hand, units that are of a given functional type and therefore occupy equivalent positions in the power hierarchy may raise their power potential by the formation of categoric unions. Any threat to a function or to the conditions of its performance can provoke such a response; groups of elders, the medieval guilds, labor unions, professional associations, councils of churches, retail associations, and associations of manufacturers are examples of categoric units. A social class is at most a loose form of categoric unit.

As with the corporate union, the categoric union may be composed of units of any size or kind. It may appear as a federation of categoric units or as an association of corporate units. So long as it retains its pure categoric form, however, such a unit can do little more than react to circumstances affecting it. Nor can it have more than a transitory existence, since in order to engage in positive action of any kind and to attain some measure of permanence, it must develop at least a core of specialists. Although the categoric unit tends to assume the characteristics of the corporate unit, it remains distinctive as long as its criterion for membership is possession of a given, common characteristic. In any event, the categoric unit is a source of rigidity in a social system, and once formed, its effect is to preserve the position of a functional category in the system.

The concept of dominance has been widely employed for the purpose of delimiting the boundaries of systems. It is argued that centers of settlement, such as cities, exercise dominance over their surrounding areas, in diminishing degrees as the distance from the center increases; the margin of influence marks the boundary of the system. Empirical support for this proposition is provided by the evidence of nonrandom distribution of related functions and by the gradient pattern that appears in the frequencies with which outlying functions are involved with central functions.

Two qualifications of this conclusion are needed; first, dominance is exercised from and not by centers, since it resides in functional units rather than in the places where they are located. Further, the apparent decline of dominance results less from an effect of distance in reducing control over related functions than from the increased difficulty of establishing dominance uniformly over an exponentially widening area.

Isomorphism. A principle of isomorphism has been implied in much that has been said and needs now to be stated. Units subject to the same environmental conditions, or to environmental conditions as mediated through a given key unit, acquire a similar form of organization. They must submit to standard terms of communication and to standard procedures in consequence of which they develop similar internal arrangements within limits imposed by their respective sizes. Each unit, then, tends to become a replica of every other unit and of the parent system in which it is a subsystem.

Since small units cannot acquire the elaborate organizations of which large units are capable, they jointly support specialized functions that complement their meager organizations. For example, whereas a large unit may include among its functionaries accountants, lawyers, engineers, public relations experts, and other specialists, the small unit must purchase comparable services from units specializing in each of the relevant functions. The principle of isomorphism also applies to the size of units, at least as a tendency; that is, all units tend toward a size that enables them to maintain contact with all relevant sectors of the parent system.

Closure and social change

Operation of the several principles mentioned thus far moves a system toward a state of closure. This term must be employed here with circumspection, for it cannot have its usual connotation of independence of environment. Closure can only mean that development has terminated in a more or less complete system that is capable of sustaining a given relationship to environment indefinitely. For closure to be realized, it is required not only that the differentiation of function supportable by the productivity of the key function has attained its maximum but also that the various functions have been gathered into corporate and categoric subsystems; moreover, the performance of the key function should have been reduced to one unit or to a number of units united in a categoric federation. Then a system is highly selective of its membership and capable of exercising some control over factors that threaten change in the system.

Under these circumstances, certain conditions of equilibrium are held to obtain: the functions involved are mutually complementary and collectively provide the conditions essential to the continuation of each; the number of individuals engaged in each function is just sufficient to maintain the relations of the functions to each other and to all other functions; and the various units are arranged in time and space so that the accessibility of one to others bears a direct relation to the frequency of exchanges between them. Needless to say, equilibrium as thus defined is a logical construct; the conditions express an expected outcome if the principles of organization are allowed to operate without any external disturbances.

Origins and effects of change

Every social system is continuously subject to change, for since the environment is always in some state of flux, the equilibrium that can be attained is seldom more than partial. A system founded on nonreplaceable resources is faced with “immanent change”; sooner or later it will either pass into decline or shift perforce to a different resource base. Such, for instance, has been the experience of innumerable mining communities; in a similar manner agricultural communities often alter the soil composition of their lands by the uses they practice, with the ultimate result that the lands will no longer support the systems as they are constituted. Instances of maladaptation, such as the reliance of the Irish on the potato as a food staple in the nineteenth century, can lead to catastrophic consequences.

In general, however, change has an external origin, a proposition that follows by definition from an equilibrium position. Some influences emanate from the physical or biotic environment, such as variations in the growing season or invasion by parasites. To the extent that episodic occurrences of that order fail to modify one or more functions comprised in the system, their effects are transitory; the system returns to its original form. But where a function, particularly a key function, is substantially modified, the system must be reconstituted. The disappearance of a game supply, the silting of an estuary, or the eruption of a volcano may render a key function inoperative in its usual location. The population must relocate and work out a new system of activities. Unless there is an increase of productivity, new ways of acting will merely displace old ways, and the change will not be cumulative.

Cumulative change

Cumulative change, or growth of the system, presupposes an increase in the productivity of a key function. Only in this way is it possible to multiply specialization, to employ a greater variety of techniques, and to support a larger population. The probability of the occurrence of disturbances having that effect rises with the number of points of contact with a social environment; location, therefore, is an important factor. A site on a traveled route is more exposed to external influences than one situated at a distance from an avenue of movement; a site at a conflux of routes is much more vulnerable to disturbances from without. Any location that fosters frequent meetings of people from diverse backgrounds is a gateway for the infusion of alien experiences and techniques into the social system centered there. Whether change is released through a deposit of numerous small additions to the culture or through a simple, dramatic innovation is immaterial.

The process of cumulative change may be generalized as a principle of expansion. Expansion is a twofold process involving, on the one hand, the growth of a center of activity from which dominance is exercised and, on the other hand, an enlargement of the scope of the center’s influence. The process entails the absorption and redistribution of the functions formerly carried on in outlying areas, a centralization of mediating and control functions, an increase in the number and variety of territorially extended relationships, a growth of population to man a more elaborate set of activities, and an accumulation of culture together with a leveling of cultural differences over the expanding domain. After the revival of trade in Europe, from the tenth century onward, the favorably situated village with its narrow vicinage grew into a market town that served as a center of an enlarged territorial organization. That gave way, in turn, to the emergent city capable of exercising an integrating influence over an area of regional scope. Most recently, the metropolis has superseded the city and has brought under its dominion a vast interregional territory. Although the process is as old as recorded history, it has not advanced in a simple linear progression. It has moved and then stalled in one place, only to surge ahead in another; it has faltered and even on occasion has seemed to turn back upon itself, but it has always resumed its course with renewed vigor.

The limits to expansion are sometimes fixed by the facility of movement between center and periphery—by the maximum distance over which the exercise of dominance is feasible. More often than not, however, the limits are drawn at the points of juncture with the expanding domains of social systems in neighboring regions. As a system encounters its limits, however they are fixed, it loses capacity to absorb further change, and equilibrium tendencies begin to assert themselves once more.

In many instances, however, the first symptoms of change are experienced at the periphery of a system. Since the effects of dominance grow more uneven with increased distance from a center, boundaries are apt to be permeable at many points. Yet, in the degree to which a system is integrated, events at the boundary are transmitted directly to the key unit, from which they are communicated to ancillary units; it is always at the boundary that one system begins its absorption of another. Expansion may be resumed at any moment and in any of the systems that hem in one another. An innovation, even though it might present itself to all systems about the same time, gains admission to one or another by virtue of a more favorable location for its use, a more appropriate organization for its acceptance, or some other local advantage. The renewed expansion encroaches upon the territories of adjoining systems, sometimes reducing them to mere components of a single, greatly enlarged system.

Under conditions of closure, environmental effects, and particularly cultural innovations, would be expected to enter a system through the key function, for the obvious reason that it has the most direct connection with environment. And, presumably, change would spread through the system by affecting units successively in the order in which they are removed from direct relation with a key function. But in a system centered on a convergence of routes, many units may have direct, although not equal, access to the outside world. Change may therefore enter the system at many points, at least until its structure is fully developed with the parts systematically arrayed relative to a key unit. An expanding system, in other words, is an open system, and it remains so until the limits to expansion are reached.

Burgess’ hypothesis of city growth

A hypothesis of city growth, stated by E. W. Burgess ([1925] 1961, pp. 37–44), pertains to a special case of the more general principle. According to that proposal, city growth takes the form of expansion from a zone centered on a highly accessible location. Growth involves increasing density of occupance of the central zone and, at the same time, a redistribution of activities or land uses scattered around the center to conform to a gradient pattern of variation of intensity of land use according to distances from the center. Redistribution results from increasing pressure at the center and a consequent encroachment by high-intensity uses into the spaces occupied by lower-intensity uses in a succession-like manner. Alternating periods of redistribution and stabilization of distribution, and those of growth and partial equilibrium, create a wavelike effect more or less visible in a set of concentric zones. By venturing to describe, in rather specific terms, the content of the zones and by thus reifying a set of statistical constructs, Burgess diverted attention from a growth process and caused it to be fixed on a specious distribution pattern. His argument, therefore, seemed to acquire a historical limitation that it need not have had.

The miscarriage of the import of the Burgess hypothesis is evident in criticisms that have opposed the preindustrial city to the industrial city as a qualitatively different phenomenon. Whereas Burgess suggested that the social-economic status of residents is higher in each successive concentric zone, critics have shown that in the preindustrial city the social-economic gradient runs in the opposite direction. Useful as that finding may be, it misses the essential point. That is, the significant gradient is one of dominance; units tend to distribute themselves over space in a way that reflects their relationships to the dominant unit. In this respect, both industrial and preindustrial cities are similar. The qualitative difference lies in the kinds of units that exercise dominance. In the preindus-trial city, all functions are carried in familial or household units, and power is unevenly distributed among them. But in the industrial society, the household unit has been relegated to a minor position; specialized functions are performed by extra-familial units, and the separation of functions from the household has involved a spatial separation as well.

Furthermore, the notion of a monocentered system is applicable only to the simplest instances. All others include a constellation of settlement nuclei, that is to say, subsidiary service centers within cities, and villages, towns, or cities within hinterlands. Each serves as a locus of influence over a localized area, varying in scope with the types of functions centered in the nucleus. Thus, as Christaller observed, the constellation of nuclei forms a hierarchy by size and number of places and by order of functions performed (1933). Small places provide low-order, or ubiquitous, functions, whereas each larger place performs, in addition to low-order functions, higher-order functions for broader domains. At the apogee of the hierarchy is the metropolis, in which the integrating and coordinating functions for the entire system are domiciled. Thus, dominance is exercised downward and outward through nested sets of subsidiary centers

The least satisfactory aspect of the theory of change concerns its temporal incidence. The idea of succession, borrowed initially from bioecology, lingers in the dictionary of human ecology. Change as cyclical in form, consisting in movements between equilibrium stages, is clearly the most intelligible conception. Nevertheless, apart from the difficulty in empirically identifying an equilibrium stage, there are unsolved conceptual problems of the spacing of stages, and of the factors governing the intervals between stages. Thus far, succession has been applied only in retrospect. Its utility will remain uncertain until it can be projected into prediction. Quite possibly, that may have to wait for more extensive work on social system taxonomy.

The limits of human ecology

Human ecology has progressed since its inception from an effort to apply the concepts of plant and animal ecology to human collective life, through an extended period of preoccupation with spatial configurations, to an increasing concern with the form and development of territorially based social systems. In the last phase, human ecologists have sought to clarify the assumptions of ecology and to draw out their implications for organization. Although the results of that work are far from complete, it seems clear that they indicate the direction in which human ecology will continue to develop.

As with most approaches in social science, human ecology has limited objectives. It seeks knowl-ledge about the structure of a social system and the manner in which the structure develops. Hence, it is not prepared to provide explanations for all of the manifold interactions, frictions, and collisions that occur within the bounds of a social system. The findings of human ecology, however, define the context in which all such phenomena take place, and which is therefore pertinent to their full understanding.

Human ecology is not qualified to deal with the normative order in a social system. Yet consistent with its position is the expectation that a normative order corresponds to and reflects the functional order. The two are different abstractions from the same reality.