Genesis of Eden

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Wilson, Edward O 1992 The Diversity of Life,
Penguin Books, London.


Edward 0. Wilson is Frank B. Baird jr, Professor of Sdence and Curator in Entomology, Museum of Compuative Zoology, Harvud University. A native of Alabama, he has been a member of the Harvard faculty since 1956. His field research has taken him to countries all over the world. His many contzibutions to our understanding of the biological world include several books published by Harvard: On Human Nature, which won the Pulitzer Prize, Sociobiology, The Insect Societies and Biophilia. He is co-author (with Bert Holldobler) of the Pulitzer Prize-winning T'he Ants. His many scientific awards include the National Medal of Science, the Tyler Prize for Envirorunental Achievement and the Crafoord Prize of the Royal Swedish Academy of Sciences.

The Diversity of Life was awarded the Sir Peter Kent Conservation Book Prize for the best book published on environmental issues in 1993.


EVERY COUNTRY has three forms of wealth: material, cultural, and biological. The first two we understand well because they are the substance of our everyday lives. The essence of the biodiversity problem is that biological wealth is taken much less seriously. This is a major strategic error, one that will be increasingly regretted as time passes. Diversity is a potential source for immense untapped material wealth in the form of food, medicine, and amenities. The fauna and flora are also part of a country's heritage, the product of millions of years of evolution centered on that time and place and hence as much a reason for national concern as the particularities of language and culture. The biological wealth of the world is passing through a bottleneck destined to last another fifty years or more. The human population has moved past 5.4 billion, is projected to reach 8.5 billion by 2025, and may level off at 10 to 15 billion by midcentury. With such a phenomenal increase in human biomass, with material and energy demands of the developing countries accelerating at an even faster pace, far less room will be left for most of the species of plants and animals in a short period of time. The human juggernaut creates a problem of epic dimensions: how to pass through the bottleneck and reach mid-century with the least possible loss of biodiversity and the least possible cost to humanity. In theory at least, the minimization of extinction rates and the minimization of economic costs are compatible: the more that other forms of life are used and saved, the more productive and secure will our own species be. Future generations will reap the benefit of wise decisions taken on behalf of biological diversity by our generation. What is urgently needed is knowledge and a practical ethic based on a time scale longer than we are accustomed to apply. An ideal ethic is a set of rules invented to address problems so complex or stretching so far into the future as to place their solution beyond ordinary discourse. Environmental problems are innately ethical. They require vision reaching simultaneously into the short and long reaches of time. What is good for individuals and societies at this moment might easily sour ten years hence, and what seems ideal over the next several decades could ruin future generations. To choose what is best for both the near and distant futures is a hard task, often seemingly contradictory and requiring knowledge and ethical codes which for the most part are still unwritten. If it is granted that biodiversity is at high risk, what is to be done? Even now, with the problem only beginning to come into focus, there is little doubt about what needs to be done. The solution will require cooperation among professions long separated by academic and practical tradition. Biology, anthropology, economics, agriculture, government, and law will have to find a common voice. Their conjunction has already given rise to a new discipline, biodiversity studies, defined as the systematic study of the full array of organic diversity and the origin of that diversity, together with the methods by which it can be maintained and used for the benefit of humanity. The enterprise of biodiversity studies is thus both scientific, a branch of pure biology, and applied, a branch of biotechnology and the social sciences. It draws from biology at the level of whole organisms and populations in the same way that biomedical studies draw from biology at the level of the cell and molecule. Where biomedical studies are concerned with the health of the individual person, biodiversity studies are concerned with the health of the living part of the planet and its suitability for the human species. What follows, then, is an agenda on which I believe most of those who have focused on biodiversity might agree. All the enterprises I will list are directed at the same goal: to save and use in perpetuity as much of earth's diversity as possible.

1. Survey the world's fauna and flora.

In approaching diversity, biologists are close to traveling blind. They have only the faintest idea of how many species there are on earth or where most occur; the biology of more than 99 percent remain unknown. Systematists are aware of the urgency of the problem but far from agreed on the best way to solve it. Some have recommended the initiation of a global survey, aimed at the discovery and classification of all species. Others, sensibly noting the shortage of personnel, funds, and time, think the only realistic hope lies in the rapid recognition of the threatened habitats that contain the largest number of endangered endemic species (the hot spots). In order to move systematics into the larger role demanded by the extinction crisis, its practitioners have to agree on an explicit mission with a timetable and cost estimates. The strategy most likely to work is mixed, aiming at a complete inventory of the world's species, but across fifty years and at several levels, or scales in time and space, from hot-spot identification to global survey, audited and readjusted at ten-year intervals. As each decade comes to a close, progress to that point could be assessed and new directions identified. Emphasis from the outset would be placed on the hottest spots known or suspected. Three levels can be envisioned. The first is the RAP approach, from the prototypic Rapid Assessment Program created by Conservation International, a Washington-based group devoted to the preservation of global biodiversity. The purpose is to investigate quickly, within several years, poorly known ecosystems that might be local hot spots, in order to make emergency recommendations for further study and action. The area targeted is limited in extent, such as a single valley or isolated mountain. Because so little is known of classification of the vast majority of organisms and so few specialists are available to conduct further studies, it is nearly impossible to catalog the entire fauna and flora of even a small endangered habitat. Instead a RAP team is formed of experts on what can be called the elite focal group. Organisms, such as flowering plants, reptiles, mammals, birds, fishes, and butterflies, that are well enough known to be inventoried immediately and can thereby serve as proxies for the whole biota around them. The next level of inventory is the BIOTROP approach, from the Neotropical Biological Diversity Program of the University of Kansas and a consortium of other North American universities formed in the late 1980s. Instead of pinpointing brushfires of extinction at selected localities in the RAP manner, BIOTROP explores more systematically across broad areas believed to be major hot spots or at least to contain multiple bot spots. Examples of such regions include the eastern slopes of the Andes and the scattered forests of Guatemala and southern Mexico. Beyond identifying critical localities, the larger goal is to set up research stations across the area that embrace different latitudes and elevations. The work begins with a few focal organisms. It expands to less familiar groups, such as ants, beetles, and fungi, as enough specimens are collected and experts in the groups are recruited to study them. In time, close studies of rainfall, temperature, and other properties of the environment are added to the species inventory. The most important and best equipped of the stations are likely then to evolve into centers of long-term biological research, with leadership roles taken by scientists from the host countries. They can also be used to train scientists from different parts of the world. We now come to the third and highest stage of the biodiversity survey. From inventories at the RAP and BIOTROP levels in different parts of the world, accompanied by monographic studies of one group of organisms after another, the description of the living world will gradually coalesce to create a fine-grained image of global biodiversity. The growth of knowledge wall inevitably accelerate, even given a constant level of effort, by producing its own economies of scale. Costs per species logged into the inventory fall as new methods of collecting and distributing specimens are devised and procedures for accessing information are improved. Costs are not simply additive when non-elite groups of organisms are included, but instead decline on a per-species basis. Botanists, for example, can collect insects living on the plants they study, while identifying these hosts for the entomologists, and entomologists can run the procedure in reverse, gathering plant specimens in company with the insects they collect. Groups such as reptiles, beetles, and spiders can be sampled across entire habitats, then distributed to specialists on each group in turn. As biodiversity surveys proceed at the several levels, the knowledge gathered becomes an ever more powerful magnet for other kinds of science. Field guides and illustrated treatises open doors to the imagination, and networks of technical information draw geologists, geneticists, biochemists, and others into the enterprise. It will be logical to gather much of the activity into biodiversity centers, where data are gathered and new inquiries planned. The prototype is Costa Rica's National Institute of Biodiversity (Instituto Nacional de Biodiversidad), INBio for short, established on the outskirts of the capital city of San Jose in 1989. The aim of INBio is nothing less than to account for all the plants and animals of this small Central American country, over half a million species in number, and to use the information to improve Costa Rica's environment and economy. It is perhaps odd that a developing nation should lead the way in such a concerted scientific enterprise, but others will follow. Detailed distribution maps of plants and many kinds of animals have been drawn up in Great Britain, Sweden, Germany, and other European countries under governmental and private auspices. As I write, plans for a national biodiversity center in the United States have been advanced by the Smithsonian Institution and are under wide discussion. Enabling legislation has been placed before Congress but is not yet passed.

The national center of the United States will not have to start from scratch. Many kinds of organisms have been already carefully studied and mapped. Several of the states, including Massachusetts and Minnesota, have undertaken programs to locate endangered species of plants and vertebrate animals within their borders. For fifteen years the Nature Conservancy, one of the premier private American foundations, has conducted a similar effort across all the states. The operation, setting up Natural Heritage Data Centers, has recently been extended to fourteen Latin American and Caribbean countries. Another key element of biodiversity studies at all levels will be microgeography, the mapping of the structure of the ecosystem in sufficiently fine detail to estimate the populations of individual species and the conditions under which they grow and reproduce. A working technology already exists in the form of Geographic Information Systems, a collection of layers of data on topography, vegetation, soils, hydrology, and species distributions that are registered electronically to a common coordinate system. When applied to biodiversity and endangered species, the cartography is called gap analysis. Even though incomplete, gap analysis can reveal the effectiveness of existing parks and reserves. It can be used to help answer the larger questions of conservation practice. Do protected areas in fact embrace the largest possible number of endemic species? Are the surviving habitat fragments large enough to sustain the populations indefinitely? And what is the most cost-effective plan for further land acquisition? The same information can be used to zone large regions. Parcels of land will have to be set aside as inviolate preserves. Others will be identified as the best sites for extractive reserves, for buffer zones used in part-time agriculture and restricted hunting, and for land convertible totally to human use. In the expanded enterprise, landscape design will play a decisive role. Where environments have been mostly humanized, biological diversity can still be sustained at high levels by the ingenious placement of woodlots, hedgerows, watersheds, reservoirs, and artificial ponds and lakes. Master plans will meld not just economic efficiency and beauty but also the preservation of species and races. The layered data can further aid in defining "bioregions," areas such as watersheds and forest tracts that unite common ecosystems but often extend across the borders of municipalities, states, or even countries. A river may make economic or military sense in dividing two political units, but it makes no sense at all in organizing land use management. Bioregionalism has had a long but inconclusive history within the United States. It dates back at least as far as John Muir's successful championing of national parks and the establishment of the national forest system in 1891. Since the 1930s it has received increasing governmental sanctions with variable specific agendas, from the Tennessee Valley Authority, which managed land and created hydroelectric power through a large part of the southeast, to the establishment of the Appalachian National Scenic Trail, federal and state management of the south Florida water system and the Everglades, and the multiple regulatory and promotional activities of the New England River Basins Commission during its tenure from 1967 to 1981. Other examples of bioregionalism abound in the United Sates, but it cannot be said that the movement has coalesced around any single philosophy of land management. Nor has the preservation of biodiversity ranked as more than an auxiliary goal. In fact the great dams built by the Tennessee Valley Authority, while providing cheap electric power to an impoverished part of the nation, inadvertently wiped out a substantial part of the native river fauna. The lower priority given diversity has not been by deliberation but from incomplete knowledge of the faunas and floras of the affected regions. Systematics, having emerged as a prerequisite for effective longterm zoning and bioregionalism, is a labor-intensive enterprise. Scientists who study the classification of particular organisms, such as centipedes and ferns, are often by default the only authorities on the general biology of those organisms. About 4,000 such specialists in the United States and Canada attempt to manage the classification of the many thousand species of animals, plants, and microorganisms living on the continent. To a varying degree they are also responsible for the millions of species occurring elsewhere in the world, since even fewer systematists are active in other countries. Probably a maximum of 1,500 trained professional systematists are competent to deal with tropical organisms, or more than half of the world's biodiversity. A typical case is the shortage of experts on termites, which are premier decomposers of wood, rivals of earthworms as turners of the soil, owners of 10 percent of the animal biomass in the tropics, and among the most destructive of all insect pests. There are exactly three people qualified to deal with termite classification on a worldwide basis. A second revealing case: the oribatid mites, tiny creatures resembling a cross between a spider and a tortoise, are among the most abundant animals of the soil. They are major consumers of humus and fungus spores, and therefore key elements of land ecosystems almost everywhere. In North America only one expert attends to their classification on a full-time basis. With so few people prepared to launch it, a complete survey of earth's vast reserves of biological diversity may seem beyond reach. But compared with what has been dared and achieved in high-energy physics, molecular genetics, and other branches of big science, the magnitude of its challenge is not all that great. The processing of 10 million species is achievable within fifty years, even with the least efficient, old-fashioned methods. If one systematist proceeded at the cautious pace of ten species per year, including field trips for collecting, analysis of specimens in the laboratory, and publication, taking time out for vacations and family, about one million person-years of work would be required. Given forty years of productive life per scientist, the effort would consume 25,000 professional lifetimes. The number of systematists would still represent less than 10 percent of the current population of scientists active in the United States alone, and it falls well short of the number of enlisted men in the standing armed forces of Mongolia, not to mention the trade and retail personnel of Hinds County, Mississippi. The volumes of published work, one page per species, would fill 12 percent of the shelves of the library of Harvard's Museum of Comparative Zoology, one of the larger institutions devoted to systematics. I have based these estimates on what is the least efficient procedure imaginable, in order to establish the plausibility of a total inventory of global biodiversity. Systematic work can be speeded up many times over by new techniques now coming into general use. The Statistical Analysis System (SAS), a set of computer programs already running in several thousand institutions worldwide, records taxonomic identifications and localities of individual specimens and automatically integrates data in catalogs and maps. Other computer-aided techniques compare species automatically across large numbers of traits, applying unbiased measures of similarity, the procedure caged phenetics. Sill others assist in deducing the most likely family trees of species, the method called cladistics. Scanning-electron microscopy has accelerated the illustration of insects and other small organisms. Computer technology will in time include image scanning that can identify species instantly while flagging specimens that belong to new species. Biologists are also close to electronic publication, which will allow retrieval of descriptions and analyses of particular groups of organisms by desktop personal computers. Every other form of biological information on species ecology, physiology, economic uses, status as vectors, parasites, agricultural pests-can be layered in the databases. DNA and RNA sequences and gene maps can be added. GenBank, the genetic-sequence bank, has been chartered to provide a computer database for all known DNA and RNA sequences and related biological information. By 1990 it had accumulated 35 million sequences distributed through 1,200 species of plants, animals, and microorganisms. The rate of data accession is ascending swiftly with the advent of improved sequencing methods.

2. Create biological wealth.

As species inventories expand, they open the way to bioeconomic analysis, the broad assessment of the economic potential of entire ecosystems. Every community of organisms contains species with potential commodity value-timber and wild plant products to be harvested on a sustained basis, seeds and cuttings that can be transplanted to grow crops and ornamentals elsewhere, fungi and microorganisms to be cultured as sources of medicinals, organisms of all kinds offering new scientific knowledge that points to still more practical applications. And the wild habitats have recreational value, which will grow as a larger sector of the public travels and learns to enjoy natural history. The decision to make bioeconomic analysis a routine part of land management policy will protect ecosystems by assigning them future value. It can buy time against the removal of entire communities of organisms ignorantly assumed to lack such value. When local faunas and floras are better known, the decision can be taken on how to use them optimally-whether to protect them, to extract products from them on a sustainable yield basis, or to destroy their habitat for full human occupation. Destruction is anathema to conservationists, but the fact remains that most people, lacking knowledge, regard it as perfectly acceptable. Somehow knowledge and reason must be made to intrude. I am willing to gamble that familiarity will save ecosystems, because bioeconomic and aesthetic values grow as each constituent species is examined in turn-and so will sentiment in favor of preservation. The wise procedure is for law to delay, science to evaluate, and familiarity to preserve. There is an implicit principle of human behavior important to conservation: the better an ecosystem is known, the less likely it will be destroyed. As the Senegalese conservationist Baba Dioum has said, "In the end, we will conserve only what we love, we will love only what we understand, we will understand only what we are taught."

A key enterprise in bioeconomic analysis is what Thomas Eisner has called chemical prospecting, the search among wild species for new medicines and other useful chemical products. The logic of prospecting is supported by everything we have learned about organic evolution. Each species has evolved to become a unique chemical factory, producing substances that allow it to survive in an unforgiving world. A newly discovered species of roundworm might produce an antibiotic of extraordinary power, an unnamed moth a substance that blocks viruses in a manner never guessed by molecular biologists. A symbiotic fungus cultured from the rootlets of a nearly extinct tree might yield a novel mass of growth promoters for plants. An obscure herb could be the source of a sure-fire blackfly repellent-at last. Millions of years of testing by natural selection have made organisms chemists of superhuman skill, champions at defeating most of the kinds of biological problems that undermine human health.

Because chemical prospecting depends so heavily on classification, it is best conducted in tandem with biodiversity surveys. In order to succeed, investigators must also work in laboratories equipped with advanced facilities, which are usually available only in industrialized countries. In 1991 Merck and Company, the world's largest pharmaceutical firm, agreed to pay Costa Rica's National Institute of Biodiversity $1 million to assist in such a screening effort. The institute will collect and identify the organisms, sending chemical samples from the most promising species to the Merck laboratories for medicinal assay. If natural substances are marketed, the company is conunitted to pay the Costa Rican government a share of the royalties, which will then be earmarked for conservation programs. Merck has previously marketed four drugs from soil organisms originating from other countries. One, derived from a fungus, is Mevacor, an effective agent for lowering cholesterol levels. In 1990 Merck sold $735 million worth of this substance alone. It follows that a single success in Costa Rica-a commercial product from, say, any one species among the 12,000 plants and 300,000 insects estimated to live in the country could handsomely repay Merck's entire investment. There are historical reasons why Merck and other research and commercial organizations are increasingly inclined to take on chemical prospecting. The search for naturally occurring drugs and other chemical products has been cyclical through the years. In the 1960s and 1970s pharmaceutical companies phased out the screening of plants on the grounds that it was too complicated and expensive. With only one in 10,000 species yielding a promising substance (by procedures then in use) and millions of dollars needed to bring a product fully on line, the eventual payoff seemed marginal. The companies turned to new technologies in microbiology and synthetic chemistry, hoping to design the magic bullets of the new medical age with chemicals taken from the shelf. To rely on human ingenuity rather than evolved natural chemistry in distant jungles seemed much more "scientific" and direct, and perhaps less expensive. Yet natural products remained a potential shortcut, a Columbus-like journey west, for those willing to acquire the essential skills. Now the pendulum has begun to swing back, again from advances in technology, because high-volume, robot-controlled biological assays allow larger companies to screen up to 50,000 samples a year using only bits of fresh tissue or extract flown to them from any part of

the world. The path from wild organism to commercial production can sometimes be shortened further by taking clues from the lore and traditional medicine of indigenous peoples. It is a remarkable fact that of the 119 known pure pharmaceutical compounds used somewhere in the world, 88 were discovered through leads from traditional medicine. The knowledge of all the world's indigenous cultures, if gathered and catalogued, would constitute a library of Alexandrian proportions. The Chinese, for example, employ materials from about 6,000 of the 30,000 plant species in their country for medicinal purposes. Among them is artemisinin, a terpene derived from the annual wormwood (Artemisia annua), which shows promise as an alternative to quinine in the treatment of malaria. Because the molecular structures of the two substances are entirely different, artemisinin would have been discovered much less quickly if not for its folkloric reputation.

Because the lives of people and the reputations of shamans have depended on it for generations, much of the traditional pharmacopoeia is reliable. Extraction procedures and dosage have been tested by trial and error countless times. But this preliterate knowledge, lie so many of the plant and animal species to which it pertains, is disappearing rapidly as tribes move from their homelands onto farms and into cities and villages. When they take up new trades, their languages fall into disuse and the old ways are forgotten. During the 1980s, all but 500 of the 10,000 Penans of Borneo abandoned their centuries-old semi-nomadic life in the forests and settled in villages. Today their memories are fading quickly. Eugene Linden notes, "Villagers know that their elders used to watch for the appearance of a certain butterfly, which always seemed to herald the arrival of a herd of boar and the promise of good hunting. These days, most of the Penans cannot remember which butterfly to look for." On the other side of the world, 90 of Brazil's 270 Indian tribes have vanished since 1900, and two thirds of those remaining contain populations of less than a thousand. Many have lost their lands and are forgetting their cultures. Small farms around the world are giving way to the monocultures of agrotechnology. The raised garden squares of the Incas have all but vanished; the densely variegated gardens of Mesoamerica and West Africa are threatened. The revitalization of local farming is another aim of biodiversity studies. The goal is to make the practice more economically practical, while conserving the genetic reserves that will contribute to crops of the future. Species and strains of high economic efficiency, from perennial corn to amaranth and iguanas, can be fed through research centers into the local regions best suited to use them. A successful prototype of such enterprises is the Tropical Agricultural Research and Training Center (CATIE) at Turrialba, Costa Rica. Created by the Organization of American States in 1942, CATIE maintains large samples of plant species, including disease-resistant strains of cacao and other tropical crops. Its staff members experiment with propagation methods for crops and timber, design wildland preservation programs, search for new crop species and varieties, and train students in the new methods of agriculture and conservation. Institutions of the future can be profitably built to include not only these activities but also chemical prospecting and molecular techniques of gene transfer from wild to domestic species.

3. Promote sustainable development.

The rural poor of the Third World are locked onto a downward spiral of poverty and the destruction of diversity. To break free they need work that provides the basic food, housing, and health care taken for granted by a great majority of people in the industrialized countries. Without it, lacking access to markets, hammered by exploding populations, they turn increasingly to the last of the wild biological resources. They hunt out the animals within walking distance, cut forests that cannot be regrown, put their herds on any land from which they cannot be driven by force. They use domestic crops if suited to their environment, for too many years, because they know no alternative. Their governments, lacking an adequate tax base and saddled with huge foreign debts, collaborate in the devastation of the environment. Using an accountant's trick, they record the sale of forests and other irreplaceable natural resources as national income without computing the permanent environmental losses as expense. The poor are denied an adequate education. They cannot all move into the cities; in most countries, and especially those in the tropics, industrialization will be too slow to absorb more than a small fraction into the labor force. Their striving billions will, for the next century at least, have to be accommodated in rural areas. So the issue comes down to this: how can people in developing countries achieve a decent living from the land without destroying it? The proving ground of sustainable development will be the tropical rain forests. If the forests can be saved in a manner that improves local economies, the biodiversity crisis will be dramatically eased. Within that 'if " are folded technical and social difficulties of the most vexing kind. But many paths to the goal have been suggested, and some have successfully tested. One of the most encouraging advances to date is the demonstration, cited in the last chapter, that the extraction of non-timber products from Peruvian rain forests can yield similar levels of income as logging and farming, even with the limited outlets available in existing local markets. The practice has been regularized by the rubber tappers of Brazil without a bit of theory or cost-benefit analysis. The tappers, or seringueiros as they are locally called, are the descendants of immigrants from northeastern Brazil who colonized portions of the Amazon during the late nineteenth century and found a steady living in latex harvesting. Half a million strong, they draw their principal income today not only from rubber but also from Brazil nuts, palm hearts, tonka beans, and other wild products. Each family owns a house in the midst of harvesting pathways shaped like clover leaves. In addition to harvesting natural products, rubber tappers also hunt, fish, and practice small-scale agriculture in forest clearings.

Because they depend on biological diversity, the tappers are devoted to the preservation of the forests as stable and productive ecosystems. They are in fact full members of the ecosystems. In 1987 the Brazilian government authorized the establishment of seringueiro extractive reserves on state land, with thirty-year renewable leases and a prohibition on the clear-cutting of timber. Extractive reserves represent a major conceptual advance, but they are not enough to save more than a small portion of the rain forests. In 1980 rubber-tapper households occupied 2.7 percent of the area of the North Region of Brazilian Amazonia, including the states of Amazonas and Acre, while farms and ranches occupied 24 percent. Only a small fraction of the flood of new immigrants now pouring into the region can become extractivists. The rest will seek income wherever they find it, primarily by advancing the agricultural frontier. The key to the future of Amazonia and other forested tropical regions is whether employment made available to them saves or destroys the environment. 'The real challenge," John Browder writes, 'is not where to designate extractive reserves, but rather, how to integrate sustainable extraction and other natural forest management practices into the production strategies of those existing rural properties, small farms and large ranches alike, that are responsible for most of the devastation being visited upon Amazonian rainforests. Fundamentally, the problem is not where to sequester forests, but how to turn people into better forest managers." It is possible to harvest timber from the Amazonian wilderness and other great remaining rain forests extensively and profitably with little loss of biodiversity. The method of choice, first suggested by Gary Hartshom in 1979 and extended by other foresters, is strip logging. While lowland forested basins are not rugged in terrain, most are moderately rotting with well-defined slopes and dense systems of drainage streams. Strip logging imitates the natural fall of trees that create linear gaps through the forest, with the artificial gaps being aligned along the contours. The technique is described by Carl Jordan:

In this scheme, a strip is harvested on the contour of a slope, parallel to the stream. Along the upper edge of the strip is a road used for hauling out the logs. After harvesting, the area is left for a few years until saplings begin to grow in the cut areas. Then the loggers clear-cut another strip, this time above the road. The advantages of this system are that the nutrients from the freshly cut second strip wash downslope into the rapidly regenerating first strip, where the trees can quickly use the nutrients, and that seeds from the mature forest above the cut area will roll down into the recently cut strip. In contrast, in clear-cutting there are no saplings with well-developed roots capable of retaining nutrients in the system, nor is there a source of seed for regeneration of the forest.

So far so good, but how can governments and local peoples be persuaded to adopt such innovations as extractive reserves and strip logging? The shift to sustainable development will depend as much on education and social change as on science. Around the world modest projects are being advanced with one common result: if procedures tailored to the special case are used, economic development and conservation can both be served. People can be persuaded; they understand their own long-term interest and they can adapt. Here are three successful programs from Latin America.

By Panama law, the Kuna Indians hold sovereign rights over the San Blas Islands and 300,000 hectares of adjacent mainland forest. The Kuna maintain 'spirit sanctuaries," areas of primary forest in which only certain kinds of trees may be cut and no farming is allowed. Local communities depend on the sea for most of their protein, on the forests for wood, game, and medicine, and on limited patches of cleared land for domestic crops. When a spur of the Pan-American Highway was brought to the edge of their land, the Kuna established a forest reserve and guarded it with their own people. Well aware of the outside world, welcoming to visitors, the tribes have nevertheless chosen to discourage immigration and to preserve their own culture within the bountiful natural environment that has sustained them for centuries.

Most of Central America, unlike the land of the Kuna, is plagued by soil erosion and nutrient loss owing to the excessive cultivation of maize and other crops, leading to the cutting of forests on ever steeper slopes, all driven in turn by overpopulation. As production declines, farmers invade the remaining natural areas in search of more arable land. The process is especially acute in the Guinope region of Honduras. In 1981 two private foundations, one intemational and one Honduran, commenced a pilot program in some of the Guinope villages under govemment auspices to raise productivity and restore the land. They introduced drainage ditches, contour furrows, grassy barriers, and intercropping with nitrogen-restoring legumes. The field labor and implementation costs were provided entirely by the farmers. Within several years, yields tripled and emigration nearly ceased. The new agricultural methods began to spread to surrounding areas. When a highway, the Carretera Marginal de la Selva, was cut into Peru's Palcazd Valley, 85 percent of the land was still clothed by rain forest. Like most of the eastern tropical slopes of the Andes, the valley is biologically rich, containing for example more than a thousand species of trees. The region also supported about 3,000 Amuesha Indians and an equal number of settlers who had established small landholdings over the previous fifty years. Once opened to outside commerce, the typical fate of a western Amazonian valley is to be clear-cut by new immigrants and logging companies, then used for cattle ranches and small farms. The thin, acidic soil soon loses most of its free phosphates and other nutrients, launching the next phase: erosion, poverty, partial abandonment. For this valley, however, an alternative plan was proposed by the U.S. Agency for International Development and approved by the Peruvian government. It is to extract timber by strip cutting, regulated to allow perpetual regeneration of the forest through thirty to forty-year rotations. The plan permits limited permanent conversion of the most arable land to agriculture and livestock production. But it also calls for the establishment of a watershed reserve in the adjacent San Matias mountain range and the designation of the neighboring Yanachaga range as the Yanachaga-Chemmin National Park. With luck, the Paicazij will support a healthy human population and a slice of Peru's biodiversity into the next century. Wildlands and biological diversity are legally the properties of nations, but they are ethically part of the global commons. The loss of species anywhere diminishes wealth everywhere. Today the poorest countries are rapidly decapitalizing their natural resources and unintentionally wiping out much of their biodiversity in a scramble to meet foreign debts and raise the standard of living. By perceived necessity they follow environmentally destructive policies that yield the largest short-term profits. The rich debt-holding nations aggravate the practice by encouraging a free market in poor countries while providing subsidies to farmers at home. Consider the infamous 'hamburger connection' between the United States and Central America. By 1983, in response to the excellent U.S. market for beef, Costa Rican landowners had accelerated the creation of new pastures until only 17 percent of the country's original forest cover was left. For a time it was the world's leading exporter of beef to the United States.

Strip logging allows a sustainable timber yield from forests, including the relatively fragile rain forests. A corridor is cleared along the contours of the land, narrow enough to allow natural regeneration within a few years. Another corridor is then cut above the first, and so on, through a cycle lasting many decades.

When northern tastes changed somewhat and the market fell, Costa Rica was left with a denuded landscape and widespread soil erosion. It had also lost part of its biological diversity. Developing countries competing in an international free market have a strong incentive to transfer capital into single-money crops such as bananas, sugar cane, and cotton. To that end governments often subsidize the clearing of wildlands and the overuse of pesticides and fertilizers. The rush to maximize export income also concentrates ever more acreage in the hands of a relatively few, politically favored landowners. Small farmers are then forced to seek new land of marginal productivity, including natural habitats. Faced with ruin, they have no choice but to press into nutrient-poor tropical forests, steep hillside watersheds, coastal wetlands, and other final refuges of terrestrial diversity. This journey to the precipice is hastened by the agricultural support systems of the richest nations. At the present time subsidies to developed-world farmers total $300 billion a year, six times the official foreign aid to Third World countries. When European Community countries recently underwrote a large program of feedlot cattle raising, they created a huge artificial market for cassava. Landowners in Thailand responded by clearing more tropical forest to grow cassava, and in the process displaced large numbers of subsistence farmers into the deep forest and up the eroding hillsides. When the United States tightened import quotas of cane sugar to aid domestic growers, U.S. imports from the Caribbean countries dropped 73 percent in ten years, forcing many of the rural poor out of jobs in the plantations and into marginal habitats for subsistence farming. Japan's extravagant subsidy to its own rice farmers, intended to continue an ancient agricultural tradition (the Japanese written character for rice means "root of life"), has a depressing effect on the rice-growing populations of tropical Asia. Once again, the impact on natural environments is increased. The richest countries set the rules for international trade. They provide the bulk of loans and direct aid and control technology transfer to the poor nations. It is their responsibility to use this power wisely, in a manner that both strengthens these trading partners and protects the global environment. They themselves will suffer if the wildlands and biological diversity are not entered into the calculus of trade agreements and international aid. The raging monster upon the land is population growth. In its presence, sustainability is but a fragile theoretical construct. To say, as many do, that the difficulties of nations are not due to people but to poor ideology or land-use management is sophistic. If Bangladesh had 10 million inhabitants instead of 115 million, its impoverished people could live on prosperous farms away from the dangerous flood-plains midst a natural and stable upland environment. It is also sophistic to point to the Netherlands and Japan, as many commentators incredibly still do, as models of densely populated but prosperous societies. Both are highly specialized industrial nations dependent on massive imports of natural resources from the rest of the world. If all nations held the same number of people per square kilometer, they would converge in quality of life to Bangladesh rather than to the Netherlands and Japan, and their irreplaceable natural resources would soon join the seven wonders of the world as scattered vestiges of an ancient history. Every nation has an economic policy and a foreign policy. The time has come to speak more openly of a population policy. By this I mean not just the capping of growth when the population hits the wall, as in China and India, but a policy based on a rational solution of this problem: what, in the judgment of its informed citizenry, is the optimal population, taken for each country in turn, placed against the backdrop of global demography? The answer will follow from an assessment of the society's self-image, its natural resources, its geography, and the specialized long-term role it can most effectively play in the international community. It can be implemented by encouragement or relaxation of birth control and the regulation of immigration, aimed at a target density and age distribution of the national population. The goal of an optimal population will require addressing, for the first time, the full range of processes that lock together the economy and the environment, the national interest and the global commons, the welfare of the present generation with that of future generations. The matter should be aired not only in think tanks but in public debate. If humanity then chooses to breed itself and the rest of life into impoverishment, at least it will have done so with open eyes.

4. Save what remains.

Biodiversity can be saved by a mixture of programs, but not all the programs proposed can work. Consider one often raised in discussions by futurists. Suppose that we lost the race to save the environment, that all natural ecosystems were allowed to vanish. Could new species be created in the laboratory, after genetic engineers have learned how to assemble life from raw organic compounds? It is doubtful. There is no assurance that organisms can be generated artificially, at least not any as complex as flowers or butterflies or amoebae for that matter. Even this godlike power would solve only half the problem, and the easy one at that. The technicians would be working in ignorance of the history of the extinct life they presumed to simulate. No knowledge exists of the endless mutations and episodes of natural selection that inserted billions of nucleotides into the now-vanished genomes, nor can it be deduced in more than tiny fragments. The neospecies would be creations of the human mind-plastic, neither historical nor adaptive, and unfit for existence apart from man. Ecosystems built from them, like zoos and botanical gardens, would require intensive care. But this is not the time for science-fiction dreams.

On then to the next technical remedy that springs up in scientific conferences and corridor arguments. Can extinct species be resurrected from the DNA still preserved in museum specimens and fossils? Again the answer is no. Fractions of genetic codes have been sequenced from a 2400-year-old Egyptian mummy and magnolia leaves preserved as rock fossils 18 million years ago, but they constitute only the smallest portion of the genetic codes. Even that part is hopelessly scrambled. To clone these organisms or a mammoth or a dodo or any other extinct organism would be, as the molecular biologist Russell Higuchi recently said, like taking a large encyclopedia in an unknown language previously ripped into shreds and trying to reassemble it without the use of your hands.

Consider the next possibility raised with regularity: why not just forget the problem and let natural evolution replace the species that are disappearing? It can be done if our descendants are willing to wait several million years. Following the five great extinction episodes of geological history, full recovery of biodiversity required between 10 and 100 million years. Even if Homo sapiens lasts that long, the recovery would require returning a large part of the land to its natural state. By appropriating or otherwise disturbing 90 percent of the land surface, humanity has already closed most of the theaters of natural evolution. And even if we did that much and waited that long, the new biota would be very different from the one we destroyed. Then why not scoop up tissue samples of all living species and freeze them in liquid nitrogen? They could be cloned later to produce whole organisms. The method works for some microorganisms, including viruses, bacteria, and yeasts, as well as the spores of fungi. The American Type Culture Collection, located at Rockville, Maryland, contains over 50,000 species suspended in the deep sleep of absolute biochemical inactivity, ready for warming and reactivation as needed. The cultures are used in research, primarily in molecular biology and medicine. It is possible that many larger organisms could be similarly preserved in nitrogen sleep, at least as fertilized eggs, to be reared later into mature individuals. Even scraps of undifferentiated tissue might be stimulated into normal growth and development. It has been done for organisms as complex as carrots and frogs. So let us suppose for argument that all kinds of plants and animals are salvageable by such means, that biologists will perfect the techniques of total inactivation and total recovery. The cryotorium in which they would rest, the new Noah's ark, must house tens of millions of species. The preservation of the content of even one endangered habitat (say a mountain-ridge forest in Ecuador) would be an immense operation enveloping thousands of species, most of which are still unknown to science. Even if completed at the species level, only a small fraction of the genetic variability of each species could be practicably included. Unless the samples numbered into the millions, great arrays of naturally occurring genetic strains would be lost. And when the time comes to return the species to the wild, the physical base of the ecosystem, including its soil, its unique nutrient mix, and its patterns of precipitation, will have been altered so as to make restoration doubtful. Cryopreservation is at best a last-ditch operation that might rescue a few select species and strains certain to die otherwise. It is far from the best way to save ecosystems and could easily fail. The need to put an entire community of organisms in liquid nitrogen would be tragic. Its enactment would be, in a particularly piercing sense of the word, obscene. I have spoken so far of the maintenance of species and genetic stocks away from their natural habitats. Not all such methods are fantastic or repugnant. One that works for many plants is the maintenance of seed banks: seeds are dried and kept in repositories over long periods. The banks are kept in cool temperatures (about -20'C is typical) but not in the suspended animation of liquid nitrogen. Botanists have proved the technique effective for preserving most strains of crop species. About a hundred countries maintain seed banks and are adding to them steadily by exchanges and new collecting expeditions. Their efforts are aided by the 'Green Board," the International Board for Plant Genetic Resources (IBPGR), an autonomous scientific organization located in Rome that composes part of the network of the International Agricultural Research Centers. In 1990 over 2 million sets of seeds were on deposit, representing more than 90 percent of the known local geographic varieties-landraces, as they are called-of many of the basic food crops. Especially well represented are wheat, maize, oats, potatoes, rice, and millet. An effort has begun to include the wild relatives of existing crop species, such as the richly promising perennial maize of Mexico. The method can be extended to wild, noncrop floras of the world. But there are serious problems with seed banks. Up to 20 percent of plant species, some 50,000 in all, possess 'recalcitrant" seeds that cannot be stored by conventional means. Even if seed storage were perfected for all kinds of plants, an unlikely prospect for the immediate future, the task of collecting and maintaining many thousands of endangered species and races would be stupendous. All the efforts of the existing seed banks to date have been barely enough to cover a hundred species, and even those are in many cases poorly recorded and of uncertain survival ability. Another difficulty: if reliance were placed entirely on seed banks, and the species then disappeared in the wild, the bank survivors would be stripped of their insect pollinators, root fungi, and other symbiotic partners, which cannot be put in cold storage. Most of the symbionts would go extinct, preventing the salvaged plant species from being replanted in the wild. Other ex situ methods rely more realistically on captive populations that grow and reproduce. There are about 1,300 botanical gardens and arboretums in the world, many harboring plant species that are endangered or extinct in the wild. As of June 1991, twenty such institutions in the United States that subscribe to the registry of the National Collection of Endangered Plants contained seeds, plants, and cuttings of 372 species native to the United States. Some of the gardens in North America and Europe are more global in their reach. Harvard's Amold Arboretum, for one, is famous for its collection of Asiatic trees and shrubs. England's magnificent Kew Gardens is engaged in a bold attempt to preserve and cultivate the last remnants of the nearly vanished tree flora of St. Helena. Animals are vastly more difficult than plants and microorganisms to maintain ex situ. Zoos and other animal facilities have attempted the task in heroic fashion. By the late 1980s, those around the world whose stocks are known had gathered breeding populations of 540,000 individuals belonging to more than 3,000 species of mammals, birds, reptiles, and amphibians. The collections include roughly 13 percent of the known land-dwelling species of vertebrate animals. The better-financed zoos, including those in London, Frankfurt, Chicago, New York, San Diego, and Washington, D.C., conduct basic and veterinarian research with results that are applied to both captive and wild populations. The rosters of ')93 zoos in Europe and North America are tracked by the International Species Inventory System (ISIS), which uses the data to coordinate preservation and crossbreeding. The ISIS zoos and research institutions aim not only to save endangered animals but to reintroduce species into their native habitats when land is made available. They have been successful with three species, the Arabian oryx, the black-footed ferret, and the golden horn tamarin. Attempts are underway or planned for at least four other species, the California condor, the Bah starling, the Guam rail, and the Przewalski horse, the ancestor of all domestic horses. The ISIS facilities are trying to get ready if the giant panda, the Sumatran rhinoceros, and the Siberian tiger, now on the brink, should go extinct in the wild. The best efforts by zoos, zooparks, aquariums, and research facilities, however, slow the tide of extinction by a barely perceptible amount. Even the groups of animals most favored by the public cannot be completely served. Conservation biologists estimate that as many as 2,000 species of mammals, birds, and reptiles can only be salvaged if they are bred in captivity, a task beyond reach with the means at hand. William Conway, director of the comprehensive zoo maintained by the New York Zoological Society, believes that existing facilities worldwide can sustain viable populations of no more than 900 species. At best these survivors would contain only a small fraction of their species' original genes. And far worse: no provision at all has been made for the many thousands of species of insects and other invertebrates that are equally at risk. The dreams of scientists come to this: ex situ conservation is not enough and will never be enough. Some of the methods are invaluable as safety nets for the fraction of endangered species that biology best understands and the lay public is willing to support. But even if countries everywhere chose to finance greatly enlarged cryobiological vaults, seed banks, botanical gardens, and zoos, the facilities could not be assembled quickly enough to save a majority of species close to extinction from habitat destruction alone. Biologists are hampered by lack of knowledge of more than 90 percent of the species of fungi, insects, and smaller organisms on earth. They have no way to ensure a reasonable sampling of genetic variation even in the species rescued. They have only the faintest idea of how to reassemble ecosystems from salvaged species, if indeed such a feat is possible. Not least, the entire process would be enormously expensive. All these considerations converge to the same conclusion: ex situ methods will save a few species otherwise beyond hope, but the light and the way for the world's biodiversity is the preservation of natural ecosystems. If that is accepted, we must face two realities squarely. The first is that the habitats are disappearing at an accelerating rate and with them a quarter of the world's biodiversity. The second is that the habitats cannot be saved unless the effort is of immediate economic advantage to the poor people who live in and around them. Eventually idealism and high purpose may prevail around the world. Eventually an economically secure populace will treasure their native biodiversity for its own sake. But at this moment they are not secure and they, and we, have run out of time.

The rescue of biological diversity can only be achieved by a skillful blend of science, capital investment, and government: science to blaze the path by research and development; capital investment to create sustainable markets; and government to promote the marriage of economic growth and conservation. The primary tactic in conservation must be to locate the world's hot spots and to protect the entire environment they contain. Whole ecosystems are the targets of choice because even the most charismatic species are but the representatives of thousands of lesser-known species that five with them and are also threatened. The most inclusive federal legislation in the United States is the Endangered Species Act of 1973, which throws a protective shield around species of "fish, wildlife, and plants" that are "endangered and threatened" by human activities; as amended in 1978, the act also includes subspecies. A bold and creative advance, the legislation is nevertheless destined to be an arena of rising litigation. As any natural environment is reduced in area, the number of species that can live in it indefinitely is also reduced. In other words, some species are doomed to extinction even if all of the remaining habitat were to be preserved from that time on. One of the principles of ecology, as I have stressed, is that the number of species eventually declines by an amount roughly equal to the sixth to third root of the area already lost. Because the great majority of species of microorganisms, fungi, and insects are not well known, it follows that they have been slipping unnoticed through the cracks in the Endangered Species Act. Conflicts between developers and conservationists over birds, mammals' and fishes are already commonplace. As ecosystems are better explored, less-conspicuous endangered species will come to fight and the number of clashes will grow. There is a way out of the dilemma, other than abandoning legal protection of America's fauna and flora altogether. As biodiversity surveys are improved, the hot spots will come more sharply into focus. Well-documented examples already include the embattled coral reef of the Florida Keys and the rain forests of Hawaii and Puerto Rico. As other local habitats are pinpointed, they can be assigned the highest priority for conservation. This means, in most cases, that they will be set aside as inviolate reserves. Warm spots, areas less threatened or containing fewer species not found elsewhere, can be zoned for partial development, with core preserves centered on endemic species and races and buffer strips around the preserves kept partly wdd. Agricultural landscapes and harvested forest tracts can be better designed to harbor rare species and races. All these actions together, wisely administered, will be effective. But the Endangered Species Act or an equivalent is also needed to serve as a safety net for threatened forms of life in all environments, whether harbored in reserves or not. Finally, in those rare cases where the costs are perceived as intolerable by the electorate, a compromise can be sought by means of population management. This means transplantation of the species to suitable habitats nearby, or restoring its environment in places where it was previously extinguished outside the zone of conflict, or-when all else fails exile to botanical gardens, zoos, or other ex situ preserves. The area-species relation governing biodiversity shows that maintenance of existing parks and reserves will not be enough to save an the species living within them. Only 4.3 percent of the earth's land surface is currently under legal protection, divided among national parks, scientific stations, and other classes of reserves. These fragments represent recently shrunken habitat islands, whose faunas and floras will continue to dwindle until a new, often lower equilibrium is reached. Over 90 percent of the remaining land surface, including most of the surviving high-diversity habitats, has been altered. If the disturbance continues until most of the natural outside reserves are swept away, a majority of the world's terrestrial species will be either extinguished or put at extreme risk. And more: even the existing reserves are in harm's way. Poachers and illegal miners invade them, timber thieves work their margins, developers find ways to convert them in part. During recent civil wars in Ethiopia, Sudan, Angola, Uganda, and other African countries, many of the national parks were left to ruin. So we should try to expand reserves from 4.3 percent to 10 percent of the land surface, to include as many of the undisturbed habitats as possible with priority given to the world's hot spots. One of the more promising means to attain this goal is by debt-for-nature swaps. As currently practiced, conservation organizations such as Conservation International, the Nature Conservancy, and the World Wildlife Fund (U.S.) raise funds to purchase a portion of a country's commercial debt at a discount, or else they persuade creditor banks to donate some of it. This first step is easier than it sounds because so many developing countries are close to default. The debts are then exchanged in local currency or bonds set at favorable rates. The enlarged equity is used to promote conservation, especially by the purchase of land, environmental education, and the improvement of land management. By early 1992 a total of twenty such agreements totalling $110 million had been arranged in nine countries, including Bolivia, Costa Rica, Dominican Republic, Ecuador, Mexico, Madagascar, Zambia, the Philippines, and Poland. In February 1991, to take one example, Conservation International was authorized to buy $4 million in debt from Mexico's creditors. After discounting on secondary markets, the actual cost is expected to be as little as $1.8 million. The conservation organization has agreed to forgive the full amount in return for the expenditure of $2.6 million by the Mexican government on a broad range of conservation projects. The most important initiative will be to preserve the Lacandan tract in the extreme south of Mexico, the largest rain forest in North America. The debt of Third World countries has been reduced so far by only one part in 10,000 through debt-for-nature swaps. Nor are the arrangements without risk for the receiving country, notably in the crowding out of domestic expenditures and a sparking of local inflation. But these temporary effects are offset by the immense gain, dollar for dollar, in the stabilization of the environment. More potent still are unencumbered contributions from wealthier nations channeled and carefully targeted through international assistance organizations. The most important enterprise of this kind is the Global Environment Facility (GEF), established in 1990 by the World Bank, the United Nations Environmental Program, and the United Nations Development Program. At this writing, $450 million has been committed to set up national parks, promote sustainable forestry, and establish conservation trust funds in developing countries. Under consideration or already approved are proposals from Bhutan, Indonesia, Papua New Guinea, the Philippines, Vietnam, and the Central African Republic. Two principal difficulties have appeared within the GEF agenda. One is the limited absorptive power of the recipient nations. With limited trained personnel and expert knowledge, national leaders find it difficult to select the best projects and initiate them effectively. Of much greater significance, the brief terms of funding leave little prospect for the proper management and protection of reserves when the money runs out. Fearing loss of employment, the brightest professionals are likely to look to other activities to ensure their futures. The solution to both problems may he in the establishment of national trust funds, producing income that can be fed into the conservation programs gradually and over a period of many years. One such fund has recently been established for Bhutan with the help of the World Wildlife Fund. We come then to the design of the reserves themselves. As land is set aside, the primary goal is to place the reserves in the regions of highest diversity and to make them as large as possible. Another goal is to design their shape and sparing for retaining efficiency. In approaching that secondary end, a debate has arisen in conservation circles on the so-called SLOSS problem: whether to invest allotted land into a Single Large reserve Or into Several Small reserves. A single large reserve, to put the matter as simply as possible, possesses larger populations of each species, but they all fit into one basket. A single catastrophic fire or flood could extinguish a large part of the diversity of the region. Breaking the reserve into several pieces reduces that problem, but it also diminishes the size of the constituent populations and hence threatens each with extinction. All might easily decline in the face of widespread stress, such as drought or unseasonable cold. Some biologists have suggested a compromise solution to the SLOSS problem, which is to create small reserves connected by corridors of natural habitat. For example, several forest patches (say 10 kilometers square each) might be joined by strips of forest 100 meters across. Then if a species vanishes from one of the patches, it can be replaced by colonists immigrating along the forest corridor from another patch. The disadvantage that critics of the compromise have been quick to identify is that disease, predators, and exotic competitors can also use corridors to move through the network. Since populations in the patches are small and vulnerable, all might fall like a row of dominoes. I doubt that any general principle of population dynamics exists that can resolve the SLOSS controversy, at least not in the clean manner suggested by its simple geometric imagery. Instead each ecosystem must be studied in turn to decide the best design, which will depend on the species the system contains and the year-by-year fluctuation of its physical environment. For the time being, conservation biologists will agree on the cardinal rule: to save the most biodiversity, make the reserves as large as possible.

5. Restore the wildlands.

The grim signature of our time has been the reduction of natural habitats until a substantial portion of the kinds of plants and animals, certainly more than 10 percent, have already vanished or else are consigned to early extinction. The toll of generic races has never been estimated, but it is almost certainly much higher than that of species. Yet there is sill time to save many of the "living dead"-those so close to the brink that they will disappear soon even if merely left alone. The rescue can be accomplished if natural habitats are not only preserved but enlarged, sliding the numbers of survivable species back up the logarithmic curve that connects quantity of biodiversity to amount of area. Here is the means to end the great extinction spasm. The next century will, I believe, be the era of restoration in ecology. In haphazard manner, largely through the abandonment of small farms, the area of coniferous and hardwood forests in the eastern United States has increased during the past hundred years. Deliberate efforts to enlarge wild areas are also underway. In 1935 a pioneering effort resulted in the planting of 24 hectares of tall-grass prairie at the University of Wisconsin Arboretum. The arboretum has also served as the headquarters of the Center for Restoration Ecology, devoted to research and the collation of information from projects in other parts of the country. Elsewhere in the United States, small restoration projects by the hundreds have been initiated, all devoted to the increase in area of natural habitats and the return of degraded ecosystems to full health. They range broadly in ecosystem types, from the ironwood groves of Santa Catalina Island to the Tobosa grassland of Arizona, the oakland understory of California's Santa Monica Mountains, the magnificent open mountain woodlands of Colorado, and last savanna remnants of Minois. They include fragments of salt and freshwater wetlands from California to Florida and Massachusetts. In Costa Rica an audacious effort by the American ecologist Daniel Janzen and local conservation leaders has led to the establishment of Guanacaste National Park, a 50,000-hectare reserve in the northwestern corner of the country. The park will be created-literally created-by the regrowth of dry tropical forest planted on cattle ranches. The Guanacaste dream was born of recognition that in Central America dry forest is even more threatened than rain forest, down to only 2 percent of its original cover. The plan is to use existing patches of the original forest to seed a steadily growing area of ranchland. The conversion will be made easier by the low density of the human population in the area. The regenerating woodland will provide a protected watershed, an income from tourism expected to reach $1 million or more annually, and a net increase in employment of the area's residents. Most important in the long run, it will save a significant part of Costa Rica's natural heritage. I have spoken of the salvage and regeneration of existing ecosystems. There will come a time when even more is possible with the aid of scientific knowledge. The return to biology's Eden might also include the creation of synthetic faunas and floras, assemblages of species carefully selected from different parts of the world and introduced into impoverished habitats. The idea struck home for me one late afternoon as I sat at the edge of the artificial lake near the center of the University of Miami campus, surrounded by the densely urbanized community of Coral Gables. At least six species of fishes swarmed in the clear brackish water within 2 meters of shore, some as solitary foragers, others in schools. Most were exotics. Their unusual diversity and beauty reminded me of a newly created coral reef. As the sun set and the water darkened, a large predator fish, probably a gar, broke the surface in the middle of the lake. A small alligator glided out from reeds across the way and cruised into open water. Well beyond the far shore, a flock of parrots returned noisily to their palm-top evening roost. They belonged to one of more than twenty exotic species that breed or occur in the Miami area, all originating from individuals that escaped or were deliberately released from captivity. Thus has the parrot family, the Psittacidae, returned to Florida with a vengeance, only decades after the extermination of the Carolina parakeet, last of the endemic North American species. With flashing wings they salute the vanished native. It is dangerous, I must quickly add, to think too freely of introducing exotics anywhere. They might or might not take to the new environment-between 10 and 50 percent of bird species have succeeded, depending on the part of the world and the number of attempts made to introduce them. Exotics might become economic pests or force out native species. A few, like rabbits, goats, pigs, and the notorious Nile perch are capable not only of extinguishing individual species but of degrading entire habitats. Ecology is still too primitive a science to predict the outcome of the synthesis of predesigned biotas. No responsible person will risk dumping destroyers into the midst of already diminished communities. Nor should we delude ourselves into thinking that synthetic biotas increase global diversity. They only increase local diversity by expanding the ranges and population sizes of selected species. Yet the search for the safe rules of biotic synthesis is an enterprise of high intellectual daring. If the effort is successful, regions already stripped of their native biotas can be restored to places of diversity and environmental stability. A wilderness of sorts can be reborn in the wasteland. Species already extinct in the wild, those now maintained in zoos and gardens, deserve high priority. Transplanted into impoverished or synthetic biotas, they can endure as orphan species in foster ecosystems. Even though their original home has been closed to them, they will regain security and independence. They will repay us by attaining one criterion of wilderness-that we are allowed to lay down the burden of their care and visit them as equal partners, on our own time. A few species will be prosthetic. As keystone elements, such as a tree able to grow rapidly and shelter many other plant and animal species, they will play a disproportionate role in holding the new communities together. Finally, the question of central interest is how much of the world's biodiversity we can expect to carry with us out of the bottleneck fifty or a hundred years hence. Let me venture a guess. If the biodiversity crisis remains largely ignored and natural habitats continue to decline, we will lose at least one quarter of the earth's species. If we respond with the knowledge and technology already possessed, we may hold the loss to 10 percent. At first glance the difference may seem bearable. It is not; it amounts to millions of species. I feel no hesitance in urging the strong hand of protective law and international protocols in the preservation of biological wealth, as opposed to tax incentives and marketable pollution permits. In democratic societies people may think that their government is bound by an ecological version of the Hippocratic oath, to take no action that knowingly endangers biodiversity. But that is not enough. The commitment must be much deeper-to let no species knowingly die, to take all reasonable action to protect every species and race in perpetuity. The government's moral responsibility in the conservation of biodiversity is similar to that in public health and military defense. The preservation of species across generations is beyond the capacity of individuals or even powerful private institutions. Insofar as biodiversity is deemed an irreplaceable public resource, its protection should be bound into the legal canon.

The Environmental Ethic

THE SIXTH GREAT extinction spasm of geological time is upon us, grace of mankind. Earth has at last acquired a force that can break the crucible of biodiversity. I sensed it with special poignancy that stormy night at Fazenda Dimona, when lightning flashes revealed the rain forest cut open like a cat's eye for laboratory investigation. An undisturbed forest rarely discloses its internal anatomy with such clarity. Its edge is shielded by thick secondary growth or else, along the river bank, the canopy spills down to ground level. The night time vision was a dying artifact, a last glimpse of savage beauty. A few days later I got ready to leave Fazenda Dimona: gathered my muddied clothes in a bundle, gave my imitation Swiss army knife to the cook as a farewell gift, watched an over-flight of Amazonian green parrots one more time, labelled and stored my specimen vials in reinforced boxes, and packed my field notebook next to a dog-eared copy of Ed McBain's police novel Ice, which, because I had neglected to bring any other reading matter, was now burned into my memory. Grinding gears announced the approach of the truck sent to take me and two of the forest workers back to Manaus. In bright sunlight we watched it cross the pastureland, a terrain strewn with fire-blackened stumps and logs, the battlefield my forest had finally lost. On the ride back I tried not to look at the bare fields. Then, abandoning my tourist Portuguese, I turned inward and daydreamed. Four splendid lines of Virgil came to mind, the only ones I ever memorized, where the Sibyl warns Aeneas of the Underworld:

The way downward is easy from Avernus.
Black Dis's door stands open night and day.
But to retrace your steps to heaven's air,
There is the trouble, there is the toil ...

For the green pre-human earth is the mystery we were chosen to solve, a guide to the birthplace of our spirit, but it is slipping away. The way back seems harder every year. If there is danger in the human trajectory, it is not so much in the survival of our own species as in the fulfilment of the ultimate irony of organic evolution: that in the instant of achieving self-understanding through the mind of man, life has doomed its most beautiful creations. And thus humanity closes the door to its past.

The creation of that diversity came slow and hard: 3 billion years of evolution to start the profusion of animals that occupy the seas, another 350 million years to assemble the rain forests in which half or more of the species on earth now live. There was a succession of dynasties. Some species split into two or several daughter species, and their daughters split yet again to create swarms of descendants that deployed as plant feeders, carnivores, free swimmers, gliders, sprinters, and burrowers, in countless motley combinations. These ensembles then gave way by partial or total extinction to newer dynasties, and so on to form a gentle upward swell that carried biodiversity to a peak-just before the arrival of humans. Life had stalled on plateaus along the way, and on five occasions it suffered extinction spasms that took 10 million years to repair. But the thrust was upward. Today the diversity of life is greater than it was a 100 million years ago-and far greater than 500 million years before that.

Most dynasties contained a few species that expanded disproportionately to create satrapies of lesser rank. Each species and its. descendants, a sliver of the whole, lived an average of hundreds of thousands to millions of years. Longevity varied according to taxonomic group. Echinoderm lineages, for example, persisted longer than those of flowering plants, and both endured longer than those of mammals.

Ninety-nine percent of all the species that ever lived are now extinct. The modem fauna and flora are composed of survivors that somehow managed to dodge and weave through all the radiations and extinctions of geological history. Many contemporary world-dominant groups, such as rats, ranid frogs, nymphalid butterflies, and plants of the aster family Compositae, attained their status not long before the Age of Man. Young or old, all living species are direct descendants of the organisms that lived 3.8 billion years ago. They are living genetic libraries, composed of nucleotide sequences, the equivalent of words and sentences, which record evolutionary events all across that immense span of time. Organisms more complex than bacteria-protists, fungi, plants, animals-contain between I and 10 billion nucleotide letters, more than enough in pure information to compose an equivalent of the Encyclopaedia Britannica. Each species is the product of mutations and recombinations too complex to be grasped by unaided intuition. It was sculpted and burnished by an astronomical number of events in natural selection, which killed off or otherwise blocked from reproduction the vast majority of its member organisms before they completed their life-spans. Viewed from the perspective of evolutionary time, all other species are our distant kin because we share a remote ancestry. We still use a common vocabulary, the nucleic-acid code, even though it has been sorted into radically different hereditary languages. Such is the ultimate and cryptic truth of every kind of organism, large and small, every bug and weed. The flower in the crannied wall-it is a miracle. If not in the way Tennyson, the Victorian romantic, bespoke the portent of full knowledge (by which "I should know what God and man is"), then certainly a consequence of all we understand from modern biology. Every kind of organism has reached this moment in time by threading one needle after another, throwing up brilliant artifices to survive and reproduce against nearly impossible odds. Organisms are all the more remarkable in combination. Pull out the flower from its crannied retreat, shake the soil from the roots into the cupped hand, magnify it for close examination. The black earth is alive with a riot of algae, fungi, nematodes, mites, springtails, enchytraeid worms, thousands of species of bacteria. The handful may be only a tiny fragment of one ecosystem, but because of the genetic codes of its residents it holds more order than can be found on the surfaces of all the planets combined. It is a sample of the living force that runs the earth and will continue to do so with or without us. We may think that the world has been completely explored. Almost all the mountains and rivers, it is true, have been named, the coast and geodetic surveys completed, the ocean floor mapped to the deepest trenches, the atmosphere transected and chemically analyzed. The planet is now continuously monitored from space by satellites; and, not least, Antarctica, the last virgin continent, has become a research station and expensive tourist stop. The biosphere, however, remains obscure. Even though some 1.4 million species of organisms have been discovered (in the minimal sense of having specimens collected and formal scientific names attached), the total number alive on earth is somewhere between 10 and 100 million. No one can say with confidence which of these figures is the closer. Of the species given scientific names, fewer than 10 percent have been studied at a level deeper than gross anatomy. The revolution in molecular biology and medicine was achieved with a still smaller fraction, including colon bacteria, corn, fruit flies, Norway rats, rhesus monkeys, and human beings, altogether comprising no more than a hundred species. Enchanted by the continuous emergence of new technologies and supported by generous funding for medical research, biologists have probed deeply along a narrow sector of the front. Now it is time to expand laterally, to get on with the great Linnean enterprise and finish mapping the biosphere. The most compelling reason for the broadening of goals is that, unlike the rest of science, the study of biodiversity has a time limit. Species are disappearing at an accelerating rate through human action, primarily habitat destruction but also pollution and the introduction of exotic species into residual natural environments. I have said that a fifth or more of the species of plants and animals could vanish or be doomed to early extinction by the year 2020 unless better efforts are made to save them. This estimate comes from the known quantitative relation between the area of habitats and the diversity that habitats can sustain. These area-biodiversity curves are supported by the general but not universal principle that when certain groups of organisms are studied closely, such as snails and fishes and flowering plants, extinction is determined to be widespread. And the corollary: among plant and animal remains in archaeological deposits, we usually find extinct species and races. As the last forests are felled in forest strongholds like the Philippines and Ecuador, the decline of species will accelerate even more. In the world as a whole, extinction rates are already hundreds or thousands of times higher than before the coming of man. They cannot be balanced by new evolution in any period of time that has meaning for the human race. Why should we care? What difference does it make if some species are extinguished, if even half of all the species on earth disappear? Let me count the ways. New sources of scientific information will be lost. Vast potential biological wealth will be destroyed. Still undeveloped medicines, crops, pharmaceuticals, timber, fibers, pulp, soil-restoring vegetation, petroleum substitutes, and other products and amenities will never come to light. It is fashionable in some quarters to wave aside the small and obscure, the bugs and weeds, forgetting that an obscure moth from Latin America saved Australia's pastureland from overgrowth by cactus, that the rosy periwinkle provided the cure for Hodgkin's disease and childhood lymphocytic leukaemia, that the bark of the Pacific yew offers hope for victims of ovarian and breast cancer, that a chemical from the saliva of leeches dissolves blood clots during surgery, and so on down a roster already grown long and illustrious despite the limited research addressed to it. In amnesiac revery it is also easy to overlook the services that ecosystems provide humanity. They enrich the soil and create the very air we breathe. Without these amenities, the remaining tenure of the human race would be nasty and brief. The life-sustaining matrix is built of green plants with legions of microorganisms and mostly small, obscure animals-in other words, weeds and bugs. Such organisms support the world with efficiency because they are so diverse, allowing them to divide labor and swarm over every square meter of the earth's surface. They run the world precisely as we would wish it to be run, because humanity evolved within living communities and our bodily functions are finely adjusted to the idiosyncratic environment already created. Mother Earth, lately called Gala, is no more than the commonality of organisms and the physical environment they maintain with each passing moment, an environment that will destabilize and turn lethal if the organisms are disturbed too much. A near infinity of other mother planets can be envisioned, each with its own fauna and flora, all producing physical environments uncongenial to human life. To disregard the diversity of life is to risk catapulting ourselves into an alien environment. We will have become like the pilot whales that inexplicably beach themselves on New England shores. Humanity coevolved with the rest of life on this particular planet; other worlds are not in our genes. Because scientists have yet to put names on most kinds of organisms, and because they entertain only a vague idea of how ecosystems work, it is reckless to suppose that biodiversity can be diminished indefinitely without threatening humanity itself. Field studies show that as biodiversity is reduced, so is the quality of the services provided by ecosystems. Records of stressed ecosystems also demonstrate that the descent can be unpredictably abrupt. As extinction spreads, some of the lost forms prove to be keystone species, whose disappearance brings down other species and triggers a ripple effect through the demographies of the survivors. The loss of a keystone species is like a drill accidentally striking a powerline. It causes lights to go out all over. These services are important to human welfare. But they cannot form the whole foundation of an enduring environmental ethic. If a price can be put on something, that something can be devalued, sold, and discarded. It is also possible for some to dream that people will go on living comfortably in a biologically impoverished world. They suppose that a prosthetic environment is within the power of technology, that human life can still flourish in a completely humanized world, where medicines would all be synthesized from chemicals off the shelf, food grown from a few dozen domestic crop species, the atmosphere and climate regulated by computer-driven fusion energy, and the earth made over until it becomes a literal spaceship rather than a metaphorical one, with people reading displays and touching buttons on the bridge. Such is the terminus of the philosophy of exemptionalism: do not weep for the past, humanity is a new order of life, let species die if they block progress, scientific and technological genius will find another way. Look up and see the stars awaiting us. But consider: human advance is determined not by reason alone but by emotions peculiar to our species, aided and tempered by reason. What makes us people and not computers is emotion. We have little grasp of our true nature, of what it is to be human and therefore where our descendants might someday wish we had directed Spaceship Earth. Our troubles, as Vercors said in You Shall Know Them, arise from the fact that we do not know what we are and cannot agree on what we want to be. The primary cause of this intellectual failure is ignorance of our origins. We did not arrive on this planet as aliens. Humanity is part of nature, a species that evolved among other species. The more closely we identify ourselves with the rest of life, the more quickly we will be able to discover the sources of human sensibility and acquire the knowledge on which an enduring ethic, a sense of preferred direction, can be built. The human heritage does not go back only for the conventionally recognized 8,000 years or so of recorded history, but for at least 2 million years, to the appearance of the first "true" human beings, the earliest species composing the genus Homo. Across thousands of generations, the emergence of culture must have been profoundly influenced by simultaneous events in genetic evolution, especially those occurring in the anatomy and physiology of the brain. Conversely, genetic evolution must have been guided forcefully by the kinds of selection rising within culture.

Only in the last moment of human history has the delusion arisen that people can flourish apart from the rest of the living world. Preliterate societies were in intimate contact with a bewildering array of life forms. Their minds could only partly adapt to that challenge. But they struggled to understand the most relevant parts, aware that the right responses gave life and fulfilment, the wrong ones sickness, hunger, and death. The imprint of that effort cannot have been erased in a few generations of urban existence. I suggest that it is to be found among the particularities of human nature, among which are these:

People acquire phobias, abrupt and intractable aversions, to the objects and circumstances that threaten humanity in natural environments: heights, closed spaces, open spaces, running water, wolves, spiders, snakes. They rarely form phobias to the recently invented contrivances that are far more dangerous, such as guns, knives, automobiles, and electric sockets.

People are both repelled and fascinated by snakes, even when they have never seen one in nature. In most cultures the serpent is the dominant wild animal of mythical and religious symbolism. Manhattanites dream of them with the same frequency as Zulus. This response appears to be Darwinian in origin. Poisonous snakes have been an important cause of mortality almost everywhere, from Finland to Tasmania, Canada to Patagonia; an untutored alertness in their presence saves lives. We note a kindred response in many primates, including Old World monkeys and chimpanzees: the animals pull back, alert others, watch closely, and follow each potentially dangerous snake until it moves away. For human beings, in a larger metaphorical sense, the mythic, transformed serpent has come to possess both constructive and destructive powers: Ashtoreth of the Canaanites, the demons Fu-Hsi and Nu-kua of the Han Chinese, Mudamma and Manasa of Hindu India, the triple-headed giant Nehebkau of the ancient Egyptians, the serpent of Genesis conferring knowledge and death, and, among the Aztecs, Cihuacoatl, goddess of childbirth and mother of the human race, the rain god Tlaloc, and Quetzalcoatl, the plumed serpent with a human head who reigned as lord of the morning and evening star. Ophidian power spills over into modem life: two serpents entwine the caduceus, first the winged staff of Mercury as messenger of the gods, then the safe-conduct pass of ambassadors and heralds, and today the universal emblem of the medical profession. The favored living place of most peoples is a prominence near water from which parkland can be viewed. On such heights are found the abodes of the powerful and rich, tombs of the great, temples, parliaments, and monuments commemorating tribal glory. The location is today an aesthetic choice and, by the implied freedom to settle there, a symbol of status. In ancient, more practical times the topography provided a place to retreat and a sweeping prospect from which to spot the distant approach of storms and enemy forces. Every animal species selects a habitat in which its members gain a favorable mix of security and food. For most of deep history, human beings lived in tropical and subtropical savanna in East Africa, open country sprinkled with streams and lakes, trees and copses. In similar topography modern peoples choose their residences and design their parks and gardens, if given a free choice. They simulate neither dense jungles, toward which gibbons are drawn, nor dry grasslands, preferred by hamadryas baboons. In their gardens they plant trees that resemble the acacias, sterculias, and other native trees of the African savannas. The ideal tree crown sought is consistently wider than tall, with spreading lowermost branches close enough to the ground to touch and climb, clothed with compound or needle-shaped leaves. Given the means and sufficient leisure, a large portion of the populace backpacks, hunts, fishes, birdwatches, and gardens. In the United States and Canada more people visit zoos and aquariums than attend all professional athletic events combined. They crowd the national parks to view natural landscapes, looking from the tops of prominences out across rugged terrain for a glimpse of tumbling water and animals living free. They travel long distances to stroll along the seashore, for reasons they can't put into words. These are examples of what I have called biophilia, the connections that human beings subconsciously seek with the rest of life. To biophilia can be added the idea of wilderness, all the land and communities of plants and animals still unsullied by human occupation. Into wilderness people travel in search of new life and wonder, and from wilderness they return to the parts of the earth that have been humanized and made physically secure. Wildemess settles peace on the soul because it needs no help; it is beyond human contrivance.

Wilderness is a metaphor of unlimited opportunity, rising from the tribal memory of a time when humanity spread across the world, valley to valley, island to island, godstruck, finn in the belief that virgin land went on forever past the horizon.

I cite these common preferences of mind not as proof of an innate human nature but rather to suggest that we think more carefully and turn philosophy to the central questions of human origins in the wild environment. We do not understand ourselves yet and descend farther from heaven's air if we forget how much the natural world means to us. Signals abound that the ' loss of life's diversity endangers not just the body but the spirit. If that much is true, the changes occurring now will visit harm on all generations to come.

The ethical imperative should therefore be, first of all, prudence. We should judge every scrap of biodiversity as priceless while we learn to use it and come to understand what it means to humanity. We should not knowingly allow any species or race to go extinct. And let us go beyond mere salvage to begin the restoration of natural environments, in order to enlarge wild populations and stanch the haemorrhaging of biological wealth. There can be no purpose more enspiriting than to begin the age of restoration, reweaving the wondrous diversity of life that still surrounds us.

The evidence of swift environmental change calls for an ethic uncoupled from other systems of belief. Those committed by religion to believe that life was put on earth in one divine stroke will recognize that we are destroying the Creation, and those who perceive biodiversity to be the product of blind evolution will agree. Across the other great philosophical divide, it does not matter whether species have independent rights or, conversely, that moral reasoning is uniquely a human concern. Defenders of both premises seem destined to gravitate toward the same position on conservation. The stewardship of environment is a domain on the near side of metaphysics where all reflective persons can surely find common ground. For what, in the final analysis, is morality but the command of conscience seasoned by a rational examination of consequences? And what is a fundamental precept but one that serves all generations? An enduring environmental ethic will aim to preserve not only the health and freedom of our species, but access to the world in which the human spirit was born.