Chapter One

BIODIVERSITY AND OUR LIVES

A Cautionary Tale

Mother Earth is in trouble, at least as a habitat for humanity. Pollution fouls our air and waters, stark evidence of our presence. Ozone holes gape above the poles. Population continues to expand, while fisheries crash. New diseases like AIDS and Ebola ravage the unfortunate, while old ones like tuberculosis reassert themselves, overcoming miracle antibiotics. Clearly, our environment is in need of attention.

So many problems, so many reasons! How do we even begin to deal with our dilemma? Should we turn all our energies to worrying about elevated temperatures, the rise of sea level, and the potential loss of coastal communities? Or do more immediate problems, such as malnutrition, pollution, and the spread of disease, take precedence? The thesis of this book is that, to have any hope of dealing with such a complex combination of threats to our survival, we must study the Earth as an integrated physical and biological system. By understanding what makes that system work, we will understand how it can fail, thereby finding a way to prioritize actions and maintain the Earth's ability to continue to nurture and sustain us.

The central environmental challenge of our time is embodied in the staggering losses, both recent and projected, of biological diversity at all levels, from the smallest organisms to charismatic large animals and towering trees. Largely through the actions of humans, populations of animals and plants are declining and disappearing at unprecedented rates; these losses endanger our way of life and, indeed, our very existence. Biodiversity loss provides immediate evidence of environmental change, and it also threatens the very structural and functional integrity of the Earth's systems, and ultimately the survival of humanity.

Undergirding the dynamic Earth--its atmosphere, its physical and chemical fabric, and its biological essence--is a prototypical complex adaptive system (CAS), one that we call the biosphere . It has, over ecological and evolutionary time, spawned increasing biological diversity, but simultaneously it has evolved patterns of arrangement and interaction of its pieces. The result is an integrated network, with characteristic flows of materials, energy, and information that exhibit regularity in dynamics over long periods of time. Understanding the essential features of the biosphere's internal organization, and what maintains it, is fundamental to developing a rational and effective strategy for preserving the environment with quality sufficient to sustain us, our children, and our children's children.

Human Stewardship of a

Changing Environment:

A Historical Perspective and a

Glance at the Future

The second half of the twentieth century has been characterized by a heightened awareness of environmental change and by the introduction of measures to slow ecological degradation. The institution and implementation of adequate laws and responses has worked best for issues such as local and regional pollution, where the signals are clear, effects are closely related to causes, and the potential for solutions is therefore greatest. The familiar acronym NIMBY ("not in my back yard") expresses the principle that people can best be motivated to take action when the problems and rewards hit closest to home. The nature of the process of addressing local issues makes for tighter feedback loops , a key element in maintaining resiliency in any system.

Increasingly, however, we are being challenged by a new class of problems, including global climate change and biodiversity loss, in which the feedback loops are weaker and less specific. Change is slower, and signals less clear (hence the delay in recognizing them). Cause and effect are more weakly linked, involving diffuse couplings among many elements. The lack of tight correlations makes the incentive for self-regulation weaker and the solutions less obvious. Recovery is delayed and eventually may become impossible because of irreversible shifts that may occur before solutions can be implemented.

A concern for biodiversity is not new. Humans have been fascinated with biological diversity since biblical times, and surely before: ancient texts display clear appreciation for the most basic ecological principles. In the Old Testament version of the Creation, primary producers of energy (plants) enter the picture on day three, within hours of the appearance of dry land and only after the first rainstorm. Phytoplankton , the tiny aquatic plants, are never mentioned explicitly, though in theory they could have come on the scene the day before; there was already plenty of water. The absence of sunlight would have created some difficulties, though only until day four; it did not seem to inhibit the other plants much. The text says simply, "Let the earth put forth grass, herb yielding seed, and fruit-tree bearing fruit after its kind, wherein is the seed thereof, upon the earth." Thus, not only were there plants, but there were lots of different kinds. A good day's work.

Animal life followed two days later; it was bad enough that there was no sunlight for photosynthesis until day four, so it was reasonable not to have the plants contend with herbivory as well. But on day five things really got going: "Let the waters swarm with swarms of living creatures, and let fowl fly above the earth, in the open firmament of heaven." Specifically, this led right away to the creation of "the great sea-monsters, and every living creature that creepeth, wherewith the waters swarmed, after its kind, and every winged fowl after its kind." Just before nightfall, they were given instructions on how to reproduce, and by the next day there was a proliferation of biodiversity, marked by fish, fowl, cattle, and creeping things--all setting the stage for the arrival of the latecomers, humans.

The beauty of this story is not just that it includes a rudimentary understanding of a number of ecological principles (albeit an apparent lack of understanding of others), but also that it exhibits a fascination since the earliest writings with the diversity of the biological world around us. In fact, it recognizes that biodiversity was created before humans were even introduced as a part of that biodiversity. In a variety of ways, the biblical tale also addresses ecological function: plants exist for animals to eat, and animals exist, at least in part, to serve humans. This proposes a view of evolutionary purpose that would not sit comfortably with most evolutionary biologists today, but it does clearly recognize the interconnectedness of nature.

In the Great Deluge in the time of Noah, the importance of preserving biodiversity is made clear by the construction and design of the Ark, the purpose of which was to preserve not only humans but "every living thing of all flesh." The focus clearly was on animals, and in particular on sexual species: "And of every living thing of all flesh, two of every sort shalt thou bring into the ark, to keep them alive with thee; they shall be male and female." But obviously provisions were made for plants and asexual animal species as well, many of which could not have survived the Flood if its geographic dimensions were as great as suggested.

Human fascination with biodiversity, its causes and consequences, continues unabated, even as our own activities create perils no less severe than did the Deluge. Natural historians since Linnaeus, and before, have been fascinated with cataloging biodiversity and arranging it systematically. The search for generative explanations for these patterns culminated in Darwin's evolutionary theories, which provided a dynamic context for understanding not only existing patterns but also the emergence of diversity and its maintenance. Darwin's theoretical structure gave only the outlines of an explanation. Evolutionary theory today still struggles to develop understanding of the origins and maintenance of biodiversity and of the importance of processes such as mutation, recombination , and selection . These continually provide and reinforce new forms of genetic variability, thereby building and sustaining diversity.

Ecological studies, in the meantime, offer a complementary approach to an appreciation of biodiversity, elucidating the interdependence of species and their links to the physical world; more recently, recognition has grown of the manifold ways in which biodiversity, at many levels of organization, is essential to human life and to the maintenance of an environment consistent with human existence. Nevertheless, the connections between the ecological and evolutionary points of view leave fundamental issues unresolved. The biblical view of the Earth as an integrated whole resonates with much current thinking; the suggestion, however, that evolutionary forces have shaped the pieces to serve the whole, or to serve certain chosen components such as humans, is not consistent with what we know about evolution . There is a chasm here, by no means restricted to the biblical rendition, between these two differing perspectives on what has shaped the world's biota , its assemblage of biological organisms. To bridge this chasm, we need to understand how the complex biosphere has emerged from natural selection and other forces operating at small scales. We need to relate the macroscopic to the microscopic , and in particular we must elucidate the fundamental importance of biodiversity for the sustenance of life as we know and enjoy it, and the degree to which the evolutionary process operates to maintain that critical support system.

Disappearing Biodiversity

I have focused on biodiversity loss for two reasons: the seriousness of the problem, and the consequences for our lives and those of our children. According to the Nature Conservancy, which has done so much to preserve our natural heritage, one-third of U.S. plant and animal species are at risk of extinction , and hundreds of species may already have disappeared forever. There is no return from extinction, and the evolutionary history and biological resources embedded in each species are permanently lost when that species is lost. Globally, the dilemma is even worse--we are losing species at rates never before observed. Indeed, the dimensions of the threat go beyond simply loss of species. Maintaining populations of species in a few isolated outposts may nominally preserve those species, but it conceals the consequences of the disappearance of most populations of those species, and of the associated loss of diversity. It is a bit like preserving a few specimens of a species in a zoo: technically, the species still exists, but it is doomed to extinction. That matters not just for the preservation of those species but also for the reduced services those species provide to humans.

According to Ian Turner, an expert on the forests of Singapore, nearly five hundred forest species have already been lost from Singapore. Because Singapore is only six hundred meters from the Malay peninsula, it has virtually no endemics --that is, species found nowhere else. Thus, few of these local extinctions represent global species losses. Nonetheless, the loss of these organisms from Singapore has tremendous implications for the biology of Singapore; for example, nearly one hundred forest bird species have been lost in Singapore, deprived of their natural habitat . And as more Singapores emerge, the threats to worldwide distributions of these species increase. Species extinction is like an epidemic in reverse: loss of local populations contributes to loss of their neighbors, leading to spreading patterns of local and ultimately global extinctions. Thus, species loss is just the tip of the iceberg, reflecting but masking the far greater and perhaps more important loss of diversity within species.

Should we care? Surely respect for those who co-inhabit the planet with us, and for their right to exist, is a natural outgrowth of all of our religious and ethical teachings. But we also know that change is part and parcel of the dynamic history of the planet. Species go extinct, and others replace them. That is the way it has always been. The dinosaurs are no more, and there is not much that we would have been able to do about their predicament even if we had been there. What is different now, however, is the magnitude of the problem, the fact that we may have something to do with present and impending extinctions, and the reality that we ourselves are possibly among the endangered species. Our turn for extinction will also come, but we should avoid speeding its arrival. Our own existence is not independent of that of biodiversity: we rely on a wide range of services that other species provide, and their demise hastens our own.

In her recent book Nature's Services , the Stanford ecologist Gretchen Daily has assembled critical essays by some of the leading experts on our dependence on natural systems. Her book provides the best summary available of what humanity is given by nature. At one level, these services are obvious. We cannot eat plastic, and hence we depend on plants and animals for our very nourishment, as well as for materials for building shelter and powering our machines. Less appreciated, perhaps, is the degree to which we depend on natural products for medicines. Two-fifths of all prescription drugs in the United States contain active ingredients originally derived from nature, and these products represent only a small portion of what could be discovered. Antibiotics, anti-cancer drugs, birth control pills, and a whole range of products derive from natural plants, which still hold many secrets for dealing with human disease and frailty. As we destroy these natural storehouses, we bury forever their potential to provide remedies to ameliorate the human condition. Just as we will never hear any of the symphonies or concerti Mozart would have composed had he not met an untimely death, so too will we never know what treasures lie in those species prematurely eradicated. What pain not to hear the gems that Wolfgang surely would have produced; how much greater the ache to see human suffering that might have been prevented had the secrets locked up in extinct species not been lost.

Less obvious than the direct services that ecological systems provide humans in the way of food, fuel, fiber, and pharmaceuticals are the indirect services we receive through the maintenance of natural ecosystems . Freshwater ecosystems dilute, detoxify, and sequester poisons that could otherwise cause untold damage to human and other animal populations. As Sandra Postel and Stephen Carpenter argue in Nature's Services , waterborne diseases are the major source of mortality among the poor of the world, primarily because those peoples lack access to safe drinking water. Concern for the quality and quantity of water is paramount on any list of environmental problems that society must address. Just maintaining water supplies is not sufficient; the natural communities that live in freshwater must also be sustained to keep water supplies pure. Aquatic biodiversity is essential to human health.

Soil loss and degradation represent a global threat not far behind water on the list of endangered natural resources. The activities of humans have led to huge soil losses in the last half-century, with consequent leakages of water and nutrients, leading to the potential for declining agricultural productivity and increasing desertification. In Indonesia, about one-fifth of the country has been lost to erosion; the effects have been particularly devastating on the island of Java, which in the late 1980s was losing the capacity to satisfy the needs for rice of more than 10 percent of its population every year. As with water, maintenance of soil as a resource also requires safeguarding its quality by preserving the natural communities of organisms in the soil.

Natural systems help secure the very conditions that permit our survival, moderating weather, stabilizing soil, coastlines, and climate; influencing our atmosphere; and in general making it possible for humans to exist and persist. They do not maintain those conditions in order to preserve the world for Homo sapiens ; rather, Homo sapiens exists because those conditions permit it to do so. The subtlety of this distinction should not disguise the importance of the lesson. That is, we cannot count on the biosphere to maintain the biota and environment to our specifications; the world is constantly in transition, more so today than ever before in recorded history. Biodiversity is being lost at alarming rates, and with it the services that sustain the human population. Should we care? We had better care if we care about our own survival.

But what can we do about the problem? Aldo Leopold, in his elegant plea for rationality in dealing with biodiversity loss, said, "To keep every cog and wheel is the first precaution of intelligent tinkering." But the global ecosystem is not a machine just out of warranty; rather, it has been out of warranty since Eve met the serpent in the Garden of Eden. It has survived because of functional redundancies--that is, the existence of multiple species that fill similar ecological roles. This form of diversity, a level up from diversity within species, provides the biosphere with the potential for alternative ways to maintain its functioning even in the face of changes. This stability is termed homeostasis , meaning the maintenance of state. Why the Earth enjoys those redundancies is a problem worthy of deep examination, and one that admits no easy solution. At this point, we should simply rejoice that it does benefit from them, and recognize the potential consequences of their loss. To understand the generation, maintenance, and importance of structure, of heterogeneity, and of redundancy of function is foundational to the theory of all complex adaptive systems, from individual organisms to whole economies. Hence, the incentive is strong for exploring biodiversity within the context of the analysis of such systems; indeed, this orientation provides the central theme for the rest of this book.

Dissecting Biodiversity

To say that not every cog or wheel or rivet is essential does not imply that none are. Paul and Anne Ehrlich, eloquent campaigners for common sense in preserving our environment, have provided a potent and oft-cited metaphor that emphasizes this point:

Ecosystems, like well-made airplanes, tend to have redundant subsystems and other "design" features that permit them to continue functioning after absorbing a certain amount of abuse. A dozen rivets, or a dozen species, might never be missed. On the other hand, a thirteenth rivet popped from a wing flap, or the extinction of a key species involved in the cycling of nitrogen, could lead to a serious accident.

The point is that the cumulative effects of species loss may be devastating even if the loss of individual species is not. This does not imply that every rivet is equally important, or that every species is equally valuable. Critically placed rivets may play pivotal roles in any machine, just as critical species may play pivotal roles in the functioning of ecosystems. One of the most dramatic examples is the California sea otter, the lovable creature that is the delight of tourists up and down the West Coast of the United States. The otter disappeared over much of its historical range during the nineteenth century, owing to excessive hunting for its pelts. Protected as a marine mammal, the otter has made a dramatic comeback, and a population of several thousand exists once again in California, Oregon, and parts of Washington. With the sea otter present, the coastal ecosystem is very different than it was without it. The sea otter feeds heavily on shellfish, especially sea urchins; when otters are around, the number of urchins is much lower. The chain of consequences does not stop there. The urchin feeds on the large kelp that grace the coastal waters; with fewer urchins feeding on them, kelp populations expand, buffering the shores from wave activity and increasing the supply of nutrients available to fish populations. The resurgent otter thus has had both ecological and economic consequences: in coastal fisheries once largely dedicated to shellfish, finfish populations now predominate. It is no surprise that shellfishermen are not big fans of the cuddly otter.

The California sea otter is perhaps the most impressive example of a keystone species , a term introduced into the ecological literature by my friend and colleague Robert Paine, one of the leading ecologists of our time. Paine has spent the last thirty-five years studying the spectacular rocky intertidal communities of the Washington coast, documenting the mechanisms that sustain the high diversity characteristic of the outer coast. The most famous and far-reaching of his discoveries was that the multicolored sea star, Pisaster ochraceous , plays a role in the intertidal similar to that played by the otter elsewhere; indeed, Paine's work predated studies of the otter's role, and his insights led James Estes and John Palmisano to evaluate the otter in the same light. Pisaster feeds preferentially on the large mussel, Mytilus californianus , which is the bully of the intertidal in that it can outcompete all other species that, like the mussel, attach to the rock surface. In areas of the intertidal where the starfish cannot survive, for example, in the upper zones where the lack of protection from the hot sun would lead to baked starfish, the mussel completely dominates the rock surface, eliminating all other species from that resource except in areas where it cannot survive owing to desiccation or wave damage. In the presence of the starfish, however, the picture is very different: the mussel is reduced to manageable population densities, leaving plenty of room for other species to find temporary safe haven. The starfish is the original and prototypical keystone species.

Since Paine's original and seminal work, the notion of keystone species has remained attractive and led to deeper understanding of the dynamics and functioning of a wide variety of ecological communities. But the situation is not usually that simple. More generally, one finds groups of species that perform critical tasks but whose roles in maintaining the integrity of the ecosystem are to some degree interchangeable. These groups may involve species high in the food chain--the starfish and the otter are considered top predators in their systems, feeding at the apex of the pyramid of energy flow, what ecologists call the trophic pyramid . But more generally, such groups involve those less charismatic species that form the foundation of the networks of energy transfer. These may be plants, which convert the sun's energy into biomass through photosynthesis , or microbial organisms, which transform nutrients into forms that are usable by higher organisms.

The role of microbes in the nitrogen cycle provides a case in point. Nitrogen is plentiful in the atmosphere; indeed, gaseous nitrogen makes up about 80 percent of the atmosphere. But nitrogen in that form cannot be used by higher organisms, though it is essential to their survival. Bacteria and cyanobacteria fix nitrogen; that is, they convert it into other compounds such as ammonium and ammonia, which can be oxidized for energy or assimilated by some organisms. Because nitrogen fixation is essential for the maintenance of ecosystems, a keystone group comprises the species that perform this role; they are essential in a way even more basic than are the keystone predators to the structure and functioning of the systems in which they exist. Groups of species of microbes similarly mediate the other critical stages in the nitrogen cycle: nitrification , which oxidizes ammonia to produce nitrates that plants can easily assimilate, and denitrification , which reconverts nitrate into nitrogen gases. Thus, the concept of a keystone group, or a functional group , is a natural extension of Paine's ideas. To understand the structure of an ecological community is to understand what the keystone functional groups are, and how they relate to one another.

The problem of identifying functional groups, however, is not so easy. What are the crucial structural components in ecosystems, and how much functional redundancy exists within them? If one species of nitrogen fixers were to disappear, would the loss be noticed? How many rivet species could be spared? A functional group is like a bigger version of a species. Within a functional group, there is also diversity, defined largely by the number of different species that make it up; within a species, there is diversity, defined largely by the number of different genetic types that make it up. When a species loses diversity, it is more susceptible to population crashes, and possible extinction, because it does not have the flexibility to respond to changing environmental conditions. It is the diversity or heterogeneity within a population, its genetic variability, that is the raw material for evolutionary change. The same may be said of a functional group, but the players are different. When a functional group loses diversity, it is more susceptible to collapse because it does not have the genetic diversity that provides the flexibility to respond to changing environmental conditions. Were the functional group that fixes nitrogen to collapse, so too would life as we know it; any major perturbation of the nitrogen cycle, in fact, would initiate catastrophic changes. Yet we know little about how to evaluate the diversity within the group of nitrogen fixers, or about what maintains it. Is there excess buffering capacity, maintained either by our good luck or somehow by natural selection? Or has this functional group evolved to the edge of disaster, where any major perturbation would have immediate consequences? The pity is that we do not yet know how to answer this question; it is a classic challenge in the theory of self-organizing systems.

Complex Adaptive Systems

Self-organizing systems have been the fascination of scientists from a diversity of disciplines because the concept of self-organization provides a unifying principle that allows us to provide order to an otherwise overwhelming array of diverse phenomena and structures. By self-organization I mean simply that not all the details, or "instructions," are specified in the development of a complex system. The specifics are in the often simple rules that govern how the system changes in response to past and present conditions, rather than in some goal-seeking behavior. The distinctions between these may seem subtle, and formal definitions are elusive and often debated. In general, however, self-organization characterizes the development of complex adaptive systems, in which multiple outcomes typically are possible depending on accidents of history.

Complex adaptive systems include a wide variety of examples that are familiar to us all. The nervous system of a young child learning to cope with her environment is an example of a complex adaptive system, since she builds on her experiences and changes her behavior according to some scheme of local rewards. Patterns of behavior and conceptual frameworks, termed schemata , emerge and help to facilitate future learning experiences, but the immediate modifications of behavior come from local feedback . Indeed, not just the nervous system but an entire developing organism is a complex adaptive system, taking form from an initially featureless fertilized egg, without benefit of a blueprint.

To varying degrees, corporations, whole economies, ecosystems, and the biosphere represent other examples of complex adaptive systems. The essential features of a CAS are

• Diversity and individuality of components : This feature also implies that there are mechanisms, such as mutation or genetic recombination, that continually refresh diversity.

• Localized interactions among the components : In natural systems, these interactions include processes such as competition for food, predation, and sexual reproduction.

• An autonomous process (such as natural selection) that uses the outcomes of those local interactions to select a subset of those components for replication or enhancement .

I explore each of these features in greater detail in this book, but it should already be clear that the biota of the Earth fit this description to a tee. Indeed, natural selection, by feeding on and enhancing the diversity and individuality of the organisms that inhabit the globe, is the prototypical "autonomous process."

By viewing the Earth as a complex adaptive system, we are not just giving it a fancy new name. Identifying it with other systems that have the same organizing principles enables us to import knowledge that has been learned from research into those systems. And by treating all complex adaptive systems as a family of related entities, we can abstract essential features and explore through simplified models the properties that all such systems have. This is a very powerful technique, no different in philosophy from the use of models within a single discipline.

What are some of the characteristic aspects of complex adaptive systems? Most fundamental is the heterogeneity of the components, which provides the variability on which selection can act. Typically, through nonlinear interactions among those components, they become organized hierarchically into structural arrangements that determine and are reinforced by the flows and interactions among the parts. These four aspects--heterogeneity, nonlinearity, hierarchical organization, and flows--are key elements of complex adaptive systems.

In his stimulating book Hidden Order , John Holland discusses these properties, and their implications for how we study nature. Because heterogeneity, or diversity, is the most basic feature, it is the unifying theme for this book. How should we measure and understand the importance of ecological diversity, specifically biodiversity? How is it distributed? What maintains it? What are the consequences of losing it? To address these questions, we need to organize the vast mass of data into categories, as Carl Linnaeus did for species, trying to lay bare the intrinsic hierarchical organization through the perspective of our own filters. Through this process, called aggregation , we classify distinct elements into categories, suppressing differences among them in order to emphasize their commonalities and to make clear their differences from elements in other categories. The biological species is such a unit, a collection of distinct entities whose similarities of form and function encourage us to treat them as variations on the same theme. In the same way, a functional group can be viewed as such a category for the functioning of an ecosystem. Different species within a functional group have different properties, but they also fill similar roles within an ecosystem. For purposes of understanding an ecosystem, we may group them together in the same way that biologists group distinct organisms into a population, or distinct populations into a species. These functional groups, aggregates of individual agents, Holland calls meta-agents .

The other key aspects of complex adaptive systems, in Holland's lexicon, are also well illustrated in ecosystems. Nonlinearity refers to the fact that effect and cause are disproportionate, so that small changes in critical variables, such as the numbers of nitrogen fixers, can lead to disproportionate, perhaps irreversible, changes in system properties. Changes in environmental conditions or exploitation patterns can trigger qualitative and largely irreversible changes, such as desertification, in ecosystems. Not surprisingly, ecosystems show the same diversity of patterns and behaviors, and the same dependence on historical accidents, as is seen in other complex adaptive systems. Brian Arthur has emphasized the importance of similar accidents in economic systems, a phenomenon that economists refer to as path dependency . The market success of introduced products, and indeed of political and economic philosophies, depends on their being introduced at just the right time, and under just the right circumstances. Path dependency implies, among other things, that the time and circumstances for particular ideas may never come, except perhaps in one of the infinity of parallel fictional universes in which all possible realizations of the world's evolution are played out.

There is no unique way to describe an ecosystem, any more than there is a unique way to describe an economy or a nation. Meta-agents are aggregates of agents and of smaller meta-agents, and themselves may be bundled into even larger mega-meta-agents. Any system is a mess of overlapping hierarchies of aggregations, limited in any particular description only for the convenience of the observer. For any such simplification of a system's overwhelming complexity, however, there will be flows among meta-agents, as well as flows within. In ecosystems, flow (Holland's final basic property of complex adaptive systems) refers to the flow of nutrients, the flow of water, the flow of toxicants, the flow of energy, the flow of individuals, and the flow of information.

It may well be that natural systems are not so very fragile; they are, after all, complex adaptive systems that will probably change and become new systems in the face of environmental stresses. What is fragile, however, is the maintenance of the services on which humans depend. There is no reason to expect systems to be robust in protecting those services--recall that they permit our survival but do not exist by virtue of permitting it, and so we need to ask how fragile nature's services are, not just how fragile nature is. These questions are perhaps the fundamental ones in the ecological sciences today, and they will occupy our attention for the remainder of this book.

To manage the Earth's systems and ensure our survival, we have to harness the natural forces that organize the biosphere rather than fruitlessly try to resist them. The biosphere is a complex adaptive system whose essential structure has emerged in large part from adaptive changes that were mediated at local levels rather than at the level of the whole system. Humanity's program must therefore be to understand those changes, the forces that have shaped them, and their consequences at the larger level, and then to put that knowledge to work in determining where the pressure points are for effecting changes that will preserve critical ecosystem services. This also provides my agenda for this book. In the following chapters, I develop the notion of the biosphere as a complex adaptive system and explore its emergent nature, returning in the final chapter to the lessons that may be learned for managing our environment.