When one asks how much an ecosystem has been changed by human influence, the inevitable next question must be: "changed in relation to what?" There is no simple answer to this. Before we can analyse the ways people alter their environments, we must first consider how those environments change in the absence of human activity. This investigation of the workings of woods, rivers and grassland lead to the birth of ecology as a scientific endeavour. In particular, as a biological science, ecology from the outset has had to define what we mean by an ecological "community.

The first generation of academic ecologists, led by Frederic Clements, defined the communities they studied, literally as superorganisms which experienced birth, growth, maturity, and sometimes death, much as individual plants and animals did. Under this model, the central dynamic of community change could be expressed in the concept of "succession." Depending on its region, a biotic community might begin as a pond, which was then gradually transformed by its own internal dynamics into a marsh, a meadow, a transient forest of pioneer trees, and finally to a forest of dominant trees. This last stage was assumed to be stable, and was known as the "climax," a more or less permanent community, which would reproduce itself indefinitely if left undisturbed. Its equilibrium state defined the mature forest "organism," so that all members of the community could be interpreted as functioning to maintain the stability of the whole. Here was an apparently objective point of reference: any actual community could be compared with the theoretical climax, and differences between them could then usually be attributed to "disturbance." Often the source of disturbance was human, implying that humanity was somehow outside of the ideal climax community.

This functionalist emphasis on equilibrium and climax had important consequences, for it tended to remove ecological communities from history. If all ecological change was either self-equilibrating (moving toward climax), or nonexistent (remaining in the static condition of climax), then history was more or less absent except in the very long time frame of climatic change or Darwinian evolution. The result was a paradox. Ecologists trying to define climax and succession for intensively settled regions were faced with an environment massively altered by human beings, yet their research program demanded that they determine what that environment would have been like without a human presence. By peeling away the corrupting influences of human settlement they could discover the original ideal community of the climax. In the process, historical change was defined as an aberration rather than the norm.

In time, the analogy that involved comparing biotic communities to organisms came to be criticised for being both too monolithic and too teleological. The model forced one to assume that any given community was gradually working either to become or to remain a climax, with the result that the dynamics of nonclimax communities were too easily ignored. For this reason, ecology by the mid- twentieth century had abandoned the organism metaphor in favor of a less teleological "ecosystem." Now individual species could simply be described in terms of their associations with other species along a continuous range of environments; there was no longer any need to resort to functional analysis in describing such associations. Actual relationships rather than mystical super- organisms could become the focus of study, although an infusion of theory from cybernetics encouraged ecologists to continue their interest in the self-regulating, equilibrating characteristics of plant and animal populations.

With the imperatives of the climax concept no longer so strong, ecologists were prepared to become, at least in part, scientific natural historians of the countryside for which change was less the result of "disturbance" than of the ordinary processes whereby wildlife communities maintained and transformed themselves. Ecologists began to express a stronger interest in the effects of human beings on their environment. What investigators had earlier seen as an inconvenient block to the discovery of ideal climax communities, could become an object of research in its own right. But accepting the effects of human beings was only part of this shift toward a more historical ecology. Just as ecosystems have been changed by the historical activities of human beings, so too have they had their own less-recorded history: forests have been transformed by disease, drought, and fire, species have become extinct, and landscapes have been drastically altered by climatic change without any human intervention at all. The period of human postglacial occupation of the northern hemisphere, even in the so-called North American wilderness, has seen environmental changes on an enormous scale, many of them wholly apart from human influence. There has been no timeless wilderness in a state of perfect change-lessness, no climax forest in permanent stasis.

But admitting that ecosystems have histories of their own still leaves us with the problem of how to view the people who inhabit them. Are human beings inside or outside their systems? In trying to answer this question, appeal is too often made to the myth of a golden age, as Thoreau sometimes seemed inclined to do. If the nature of Thoreau's community environment in Concord in the 1850s was a nature which many Americans now romanticise as the idyllic was as "maimed" and "imperfect" as he said, what are we to make of the wholeness and perfection which he thought preceded it? It is tempting to believe that when the Europeans arrived in the New World they confronted Virgin Land, the Forest Primeval, a wilderness which had existed for eons uninfluenced by human hands. Nothing could be further from the truth. The land was less virgin than it was widowed. Indians had lived on the continent for thousands of years, and had to a significant extent modified its environment to their purposes. The destruction of Indian communities in fact brought some of the most important ecological changes which followed the Europeans' arrival in America. The choice is not between two landscapes, one with and one without a human influence; it is between two human ways of living, two ways of a species Homo sapiens belonging to an ecosystem.

The riddle of the ecological view of nature requires exploring why these different ways of living had such different effects on New England ecosystems. A group of ecological anthropologists has tried to argue that,for many non-Western societies, like those of the New England Indians, various ritual practices have served to stabilise people's relationships with their ecosystems. In effect, culture in this anthropological model becomes a homeostatic, self-regulating system much like the larger ecosystem itself. Thus have come the now famous analyses designed to show that the slaughter of pigs in New Guinea, the keeping of sacred cows in India, and any number of other ritual activities, all function to keep human populations in balance with their ecosystems. Such a view would describe precolonial New England, not as a virgin landscape of natural harmony, but as a landscape whose essential characteristics were kept in equilibrium by the cultural practices of its human community.

Unfortunately, this functional approach to culture has the same penchant for teleology as does the organism model of ecological climax. Saying that a community's rituals and social institutions "function" unconsciously to stabilize its ecological relationships can lead all too quickly into a static and ahistorical view of both cultural agency and ecological change. If we assume a priori that cultures are systems which tend toward ecological stability, we may overlook the evidence from many cultures, even preindustrial ones, that human groups often have significant unstable interactions with their environments. When we say, for instance, that the New England Indians burned forests to clear land for agriculture and to improve hunting, we describe only what they themselves thought the purpose of burning to be. But to go further than this, and assert its unconscious "function" in stabilising Indian relationships with the ecosystem, is to deny the evidence from places like Boston and Narragansett Bay that the practice could sometimes go so far as to remove the forest altogether, with deleterious effects for trees and Indians alike.

All human groups consciously change their environments. To some extent one might even argue that this, in combination with language, is the crucial trait distinguishing people from other animals. The best measure of a culture's ecological stability may well be how successfully its environmental changes maintain its ability to reproduce itself. But if we avoid assumptions about environmental equilibrium, the instability of human relations with the environment can be used to explain both cultural and ecological transformations.

An ecological history begins by assuming a dynamic and changing relationship between environment and culture, one that is as apt to produce contradictions as continuities. Moreover, it assumes that the interactions of the two are dialectical. Environment may initially shape the range of choices available to a people at a given moment, but then culture reshapes environment in responding to those choices. The reshaped environment presents a new set of possibilities for cultural reproduction, thus setting up a new cycle of mutual determination. Changes in the way people create and re-create their livelihood must be analysed in terms of changes not only in their social relations but in their ecological ones as well.