Origins and history

The term “ecology,” which has its root in the Greek word oikos (household or living place), came into use in the latter part of the nineteenth century in the works of zoologists and botanists to describe the study of the ways in which organisms live in their environments. Soon two branches of ecology were distinguished: autecology, the study of the individual organism’s interaction with environment, and synecology, the study of the correlations between the organisms engaged with a given unit of environment. The latter study has prevailed, however, and has become the principal connotation of ecology, since it became evident in numerous field studies that organisms, whether plant or animal, establish viable relationships with environment, not independently but collectively, through the mechanism of a system of relationships. Bioecologists were thus led to employ a set of concepts and techniques of investigation that imparted a markedly sociological coloration to their work.

Origins and history

The ecological approach was introduced as human ecology into the field of sociology at a critical period in the development of the latter discipline. In the 1920s the reformistic phase of sociology was drawing to a close, and the subject was gaining acceptance as a respected discipline in the curricula of American universities. That the transition would have been effected so quickly without the aid of a theoretical framework lending itself to empirical research seems doubtful. Ecology opportunely provided the necessary theory. A period of vigorous research followed that was to prove instrumental in launching sociology on its career as a social science.

Sociologists made free use of analogy as they borrowed heavily from the concepts of plant and animal ecology. The Darwinian notion of animate nature as a web of life became at once a general orienting concept and a basic postulate; it directed attention to the necessary interdependence among men as well as among lower forms of life. A second concept, the balance of nature, denoting a tendency toward stabilization of the relative numbers of diverse organisms within the web of life and of their several claims on the environment, provided human ecology with its characteristic equilibrium position. The more or less balanced web of relationships, when viewed in a specific local area, presented the aspect of community, a concept with obvious appeal for students of human social life.

According to plant and animal ecologists, the community, or ecosystem, is a population comprising a set of species whose reactions to the habitat and coactions between each other constitute an integrated system having some degree of unit character. Coactions involve members behaving both with reference to their similarities in an mtraspecific relationship known as commensalism and with reference to their differences in what is called symbiosis, an interspecific relationship. The community develops from simple to more complex forms through a sequence of stages described as succession. Each stage in the sequence is marked by an invasion of a new species or association of species, the series culminating in a climax stage in which a dominant species appears. The dominant species is related to the environment in such a way that it is able to control and maintain the community indefinitely. The community, then, tends to approximate a self-maintaining, or “closed,” system.

Community and environment

The application of the concepts from plant and animal ecology to the human community carried with it the implication that the community was essentially a natural phenomenon, which meant that it had developed independently of plan or deliberation. From this it was a short, though uncritical, step to the interpretation of human ecology as a study of the biotic or subsocial aspect of human social organization (Park 1936), a view that was elaborated at some length by Quinn (1950). Not only did the subsocial characterization convey an excessively narrow concept of social organization, but it posed an operational problem for which there was no workable solution.

A somewhat different definition of human ecology, which ignored any reference to the cognitive level of events, was enunciated by McKenzie ([1924] 1925, pp. 63–64), whose formulation of the subject as a study of the spatial and temporal relations of human beings, affected by the selective, distributive, and accommodative forces of the environment, was widely accepted as authoritative. Although McKenzie’s definition inspired a large amount of fruitful research effort, it had the unfortunate effect of concentrating attention almost exclusively on spatial distributions and correlations. In consequence, many promising implications of ecological assumptions were neglected.

Hawley, in attempting to restore a conceptual continuity with plant and animal ecologies, advanced the view of human ecology as the study of the form and development of the human community (1950, p. 68). Community, in this connection, is construed as a territorially localized system of relationships among functionally differentiated parts; human ecology, then, is concerned with the general problem of organization conceived as an attribute of a population—a point of view that has been shown to be consistent with a long-standing sociological tradition (Schnore 1958). Although the emphasis is centered on the functional system that develops in a population, it is not intended to exclude concern with spatial and temporal aspects; rather, these aspects are regarded as useful dimensions for the measurement of organization.

A further step in making the orientation of human ecology explicit within the larger context of general ecological theory was made by Duncan (1959, pp. 683–684), who described four principal variables of human ecology—population, organization, environment, and technology—that constitute an ecosystem. In other words, while any one of the four may be treated as a dependent variable for certain purposes, it is also reciprocally connected with each of the other variables. The virtue of this perspective lies in the range of problems it opens to the student of human ecology. Yet it seems unlikely tin various eco-logical studies, although hat that advantage can be fully enjoyed without a clear notion of how organization is constituted.

Other applications

While sociologists were at work defining human ecology for their purposes and pursuing many of its research leads, the concept spread into various other fields of inquiry. Human geographers wondered if the term “human ecology” was not a more apt characterization of their discipline; but their historic preoccupation with the landscape and their general addiction to a macroscopic treatment of occupance led them to discard this notion. Archeologists, in their efforts to reconstruct population distributions, have made use of ecological concepts and techniques, but without attempting to give formal statement to the approach.

Studies of human evolution by anthropologists involved questions of the man-environment relationship, which, in turn, led them to describe their work as human ecology; indeed, social or cultural anthropologists have long engaged in various ecological studies, although not until recently have they so defined their activity. One definition by an anthropologist is that of Steward (1955), for whom human ecology is the study of the adaptation of specific items of culture to particular environments. This conception, which reduces ecology to something akin to a research technique, is shared by a number of Steward’s contemporaries.

The language of human ecology has also made its appearance in economics, psychology, epidemiology, and other fields. In some instances, the term is used merely as a label for an environmental emphasis; in others, it is put forward in an effort to broaden the purview of a discipline.

But in spite of the widespread diffusion of ecological concepts, responsibility for systematic development of human ecology has been left to sociologists, who have drawn heavily on related fields for both theoretical and technical aid. The writings on real estate, finance, public administration, demography, planning, history, and other areas of inquiry, in addition to the literature of the fields previously mentioned, have at one time or another been exploited in the interest of human ecology. The reason for that catholicity of taste is not hard to find; human ecology is concerned with sociological problems in their fullest breadth. It overlaps, therefore, all the spheres of learning that concern the social life of man.

Distinctive features of human ecology

As human ecology has moved toward a major concern with the general problem of social organization and thus closer to the central concern of sociology, it has retained certain distinctive features. Foremost among these is the importance attributed to environment.

The broad, positional hypothesis is that organization arises from the interaction of population and environment. Environment, however, defined as whatever is external to and potentially or actually influential on a phenomenon under investigation, has no fixed content and must be defined anew for each different object of investigation. Environment is seen both as presenting the problem of life and as providing the means for its resolution; to adopt this position is to place the problem in a time-space context.

A second distinguishing characteristic is the emphasis on population as the point of reference; organization, it is contended, is exclusively the property of a population taken as a whole and not of an assemblage of individuals. Obvious as this position may be, it has profound methodological and theoretical implications for the manner in which the ecological problem is put, the variables employed, and the data to be observed. The concreteness of population, however, in contrast with the seemingly ephemeral nature of organization, tends to beguile the student to a view of population as the independent variable in all things pertaining to organization. It is obviously more convenient to proceed from the more accessible to the less accessible by asking how a population makes a unitary response to its environment; yet that is merely a common-sense way of approaching the problem, and investigation soon makes it apparent that population is for many purposes better regarded as the dependent variable, delimited and regulated by organization.

A third characteristic is the treatment of organization as a more or less complete and self-sustaining whole. The interaction of population and environment is seen as culminating in a system of relationships between differentiated parts which gives the population unit character and enables it to maintain its identity. As the property of a population, organization lends itself most readily to a morphological, or structural, analysis. The parts are the units—individuals or clusters of individuals—that perform functions and the relationships by which these units are linked. Differing configurations of unit functions and relationships are expected to occur with differences in relationship to environment and at different stages in development.

A morphological concern does not exclude the problem of development. Presumably, any given form of organization had an earlier form and is capable of having a later form. Every organization has a history, perhaps a natural history, the knowledge of which may shed light on the nature of organizations by indicating, for example, at what points they are vulnerable to change and how change spreads through them.

Related to the conception of organization is a fourth distinctive, although by no means unique, attribute of human ecology: the central position given to an equilibrium assumption. Morphological change is assumed to be a movement toward an equilibrium state, whether through a succession-like sequence of stages or through a process of continuous modification. Unlike the equilibrium notion in some of its other applications, such as in functionalist theory, the ecological usage of the term harbors no teleological overtones; on the contrary, this usage merely implies that as an organization attains completeness, it acquires the capacity for controlling change and for retaining its form through time, although the interval need not be specified. To put it differently, to the extent that an organization possesses unit character, an approximation to equilibrium obtains.

There is a further implication that a stable relationship with environment is contingent on relative stability in the relationships between the parts of an organization. A population always remains open to environment, but the formation of organizations canalizes environmental influences and makes for increasing selectivity of response.

The term “community” has commonly been used to denote the unit of organization for ecological purposes. Operationally defined as that population which carries on its daily life through a given system of relationships, the community is regarded as the smallest microcosm in which all the parameters of society are to be found. For reasons that were largely fortuitous, human ecologists at first focused their attention on the city and its tributary area as the prototype of community; later, in an effort to encompass the antecedents of cities, they broadened their consideration to include all forms of nucleated settlement. The term “community,” however, has the disadvantage of referring to the organization of a more or less localized settlement unit that does not always approximate a self-maintaining whole. For example, in an extensively urbanized society, local settlement units are usually components of more inclusive systems; in that event, the entire system must be treated as the object of study. But the difference between a simple, compact organization and a large, diffuse one is primarily a difference in scale; accordingly, the principles of organization should be the same in each. Since the designation of both simple and complex systems as communities threatens confusion, a more neutral term, such as “social system,” is to be preferred.

Principles of ecological organization

Inasmuch as principles of organization hinge on what is meant by population, it is imperative that the concept be developed more fully.

A human population is an aggregate of individuals who possess the following characteristics. As a living organism, every individual must have access to environment, for that is the only possible source of sustenance. Moreover, the interdependence of individuals is necessary; this condition, which obtains for all forms of life, holds true to an exceptional degree in the case of man, because of the naked state in which he comes into the world and his long period of postnatal maturation. Interdependence is the irreducible connotation of sociality.

The human being also possesses an inherent tendency to preserve and expand his life to the maximum permitted by prevailing circumstances; this is a general motive of which all other motives are special cases. In its most elementary sense, expansion of life refers to the multiplication of man-years through either the leaving of progeny or the extension of longevity; but it also includes all that is involved in the realization of that objective. Another important characteristic is the indeterminacy of the human being’s capacity to adapt; there is no known restriction on the kind or extent of refinement of activity in which he can engage. Finally, the human individual, again like other organisms, is time-bound; the recurring needs for food and rest fix the fundamental rhythm of life and regulate the allocation of time to all other activities. Accordingly, the time available for movement is limited and, in consequence, the space over which activities can be distributed is correspondingly limited.

These several attributes of individuals not only define the kind of population with which human ecology deals, but they also constitute a cardinal set of assumptions from which principles of ecological organization may be deduced. The following are some of the more salient of these principles of organization.

Principle of interdependence

Interdependence develops between units on each of two axes: the symbiotic (on the basis of their complementary differences) and the commensal (on the basis of their supplementary similarities). That is, units that combine in a symbiotic union may also enter into other combinations of a commensal character; the effect of each type of union is to raise the power of action above what it would be were the units to remain apart.

The effect, however, is not the same in each case. The symbiotic union enhances the efficiency of production or creative effort; the commensal union, since its parts are homogeneous, can only react and is suited, therefore, only to protective or conservative actions. Although commensalism is an elemental form of union, it is applicable to a wide array of situations. The point of importance at present is that a population tends to be knit together through an interwoven set of symbiotic and commensal relationships.

It should be evident that interdependence has temporal and spatial implications for the units involved. Relations of functional complementation and supplementation require mutual accessibility among units; since this is contingent on the time available for movement, the distance separating related units is always subject to some limitation. In general, for every set of related units, there should be, other things being equal, an appropriate pattern of distribution in the temporal and spatial dimensions.

Principle of the key function

A second principle may be described as the principle of the key function. That is, in every system of relationships among diverse functions, the connection of the system to its environment is mediated primarily by one or a relatively small number of functions, the latter being known as the key function or functions. To the extent that the principle of the key function does not obtain, the system will be tenuous and incoherent; in the extreme case, in which no system exists, every function has the same relationship to environment. Given a functional system, then, there are always some functions or functional units directly involved with environment and others that secure access to the environment indirectly, through the agency of the key function.

The notion of key function invokes the question of how to define the notion of environment, which can refer to many different kinds of things. For present purposes, these things may be classified in two broad categories: the natural and the social. Although every organized aggregate must contend with both, the relative importance of each may vary over a wide range. In some instances, because of the inaccessibility of the settlement, activities of necessity center on the exploitation of the local natural environment, while influences from the social field are relatively infrequent or of no great consequence. In this event, the key function is the activity that extracts the principal sustenance supply from local resources. But where the product from local resources, or a substantial part of it, is exchanged for other sustenance materials, whether through trade or other distributive mechanisms, the key function is determined by the comparative importance of production and of trade as sources of sustenance.

In many such instances, no distinction is necessary because the producer is also the trader—two functions combined in one functionary. But even before the two functions appear as separate specialties, the requisites of trade or distribution begin to regulate the uses of local resources. As the reliance on exchange advances, the social environment actually displaces the natural environment as the critical set of influences. A population is never emancipated from its dependence on physical and animate matters, but the importance of locale declines with increasing involvement in a network of intersystem relations; the natural environment is extended and diffused, and contacts with it are mediated through a variety of social mechanisms. Hence, the functions that link the local system to the social environment come to occupy the key position.

Principle of differentiation

The extent of functional differentiation varies with the productivity of the key function or functions; this is the principle of differentiation. A corollary is that the size of population supportable by the system varies with the productivity of the key function. For given the simplifying assumption that each unit is fully occupied, the number of people is determined by the number of functions to be performed.

In a hunting and gathering community, for instance, productivity is usually low, even though the physical environment is richly endowed; hence, there is little time or opportunity available for the cultivation of more than a few specialized functions. Nor is it possible to support enough people to staff even a moderate extent of specialization. By contrast, where the key function is devoted to stable agriculture, the range of possibilities is much greater, while in an industrial system productivity is so great that there are no known upper limits on either the number of specializations or the size of the population that can be supported.

The productivity of the key function, then, constitutes the principal limiting condition on the extent to which a system can be elaborated, on the size of population that can be sustained in the system, and on the area or space the system can occupy.

A question of some importance has to do with the relative number of units engaged in each of several interrelated functions. That question remains unanswered at present. It may be suggested, however, that the number of units engaged in any given function is inversely proportional to the productivity of the function and directly proportional to the number of units that utilize the product of the function.

It follows, of course, that functional differentiation involves a differentiation of environmental requirements. As the materials and conditions used by diversely specialized units differ, so also will their needs for location in space and time. In general, units performing key functions have the highest priority of claim on location. Other units tend to distribute themselves about the key function units, their distances away corresponding to the number of degrees of removal separating their functions from direct relation with the key functions. The temporal spacing may be expected to reveal a similar pattern. Special location requirements, however, as for type of soil or other resource, may obscure the tendency to a symmetrical arrangement of functions by degree of indirectness of relationship with key functions.

An important implication of the principles of the key function and of differentiation is that of transitivity in the relation among functional units. Relations with environment are necessarily transitive for some units. By the same token, relations among many units are transitive. The advance of specialization increases transitive relations more than proportionally and lengthens the transitive sequences. Thus, it is possible for functional units widely removed from one another so far as direct encounters are concerned to be inextricably linked through their respective linkages with one or more units performing intervening functions. All functions, regardless of kind, are subject to the environmental nexus. They differ only in the immediacy with which influences reach them. Those which operate at or near the ends of chains of relationships may appear to have large degrees of independence of environment. The appearance is illusory, however. It is due, rather, to the time required for effects to reach them and, in complex systems, to their having positions in two or more relational sequences which expose them to countervailing influences.

Principle of dominance

Given the principles stated above, it is a simple inferential step to a principle of dominance. According to this principle, functional units having direct relations with environment, and thus performing the key function, determine or regulate the conditions essential to the functions of units having indirect relations with environment. Dominance, in other words, is an attribute of function.

But while the power inherent in a system is unevenly distributed, it is not confined to the key function unit. Power is held in varying degrees by all other units, in measures that vary inversely with the number of steps of removal from direct relation with the unit performing the key function. A single power gradient running through all the units involved in a system assumes a very simple situation, of course, one in which a single unit occupies a key function position. Before introducing complications into this overly simplified conception, it is opportune to note some further implications of the dominance principle.

Where the progress of differentiation has distinguished a relatively large number of units, they tend to form clusters or complex units. A corollary to the dominance principle sheds light on how that comes about: the greater the extent to which variously specialized units are subject to the environmental conditions mediated by some one unit, the greater their tendency to coalesce in a corporate body. The interdependence among such units is manifestly close, and their requirements for mutual accessibility are correspondingly acute. A hierarchic pattern emerges in which the number of strata corresponds to the number of degrees that the parts are removed from direct relations with the key function; thus, symbiotic subsystems appear as components of a parent system. The nuclear family, although its origins are obscure, fits this principle. But instances with more proximate origins are found in the combinations of specialists to form producing enterprises, welfare agencies, governing bodies, etc., and again in the combinations of producing enterprises, retail establishments, or governments to constitute larger, more complex units. There is no restriction of scale or complexity in the formation of symbiotic or corporate units.