Edward O. Wilson
Edward O. Wilson; drawing by David Levine

Edward O. Wilson, the Harvard scientist who is one of the world’s foremost authorities on the lives of ants and on the problems of ecology, begins his book on a dark night in the middle of the Brazilian rain forest:

The forest at night is an experience in sensory deprivation most of the time, black and silent as the midnight zone of a cave. Life is out there in expected abundance. The jungle teems, but in a manner mostly beyond the reach of the human senses. Ninety-nine percent of the animals find their way by chemical trails laid over the surface, puffs of odor released into the air or water, and scents diffused out of little hidden glands and into the air downwind. Animals are masters of this chemical channel, where we are idiots. But we are geniuses of the audiovisual channel, equaled in this modality only by a few odd groups (whales, monkeys, birds). So we wait for the dawn, while they wait for the fall of darkness; and because sight and sound are the evolutionary prerequisites of intelligence, we alone have come to reflect on such matters as Amazon nights and sensory modalities.

But is this as it should be? Wilson asks. Only one species is able to reflect on nature, but is it right that this unique species should commandeer the earth’s resources to the detriment of millions of others? There is a moral dilemma here, one that is felt acutely by a biologist whose passion is the diversity of life on earth.

What is the biodiversity of which Professor Wilson writes with such conviction and authority? What is the scope of it? How did it originate? Where is it found? How are humans diminishing it? And why should it matter that humans are diminishing it? Professor Wilson offers answers to all these questions in engaging and nontechnical prose. His account, accompanied by a scattering of line drawings, is carefully organized, systematic, and instructive, and could serve as a college text. But it is much more than a text in its prodigious erudition and its original and fascinating insights into the Lilliputian world of insects, mites, and microbes.

Biodiversity, in the simplest terms, is the sum total of life, comprehending all species of organisms, large and small, terrestrial and aquatic. Notice that the units are species, mutually interbreeding populations which are reproductively isolated from other sets of interbreeding populations. Some scientists would expand the definition of biodiversity to include the genetic information contained in all organisms, on the grounds that the genetic makeup of every individual of a sexually reproducing population is unique. But, with few exceptions, the genes carried by individuals are not unique. Most genes are widely dispersed in populations. Individuals serve only as their transitory bearers. Genetic continuity is maintained in populations, and the distinctions between the populations of a species tend to blur over time as individuals disperse and habitats shift in space. Hence it is most reasonable, as well as practical, to consider species and their component populations as the units of biodiversity, just as they are the units of evolution.

At another level, biodiversity can be divided into two great categories, one encompassing natural species and populations, and the other encompassing the products of man’s efforts to elaborate on natural diversity through artificial selection. Man’s additions to the evolutionary process have provided the foundations for modern agriculture, yielding for example domestic cattle and hybrid corn. Less in the forefront of modern agriculture, but priceless for the wealth of genetic diversity they contain, are thousands of varieties of wheat, rice, potatoes, and other crop plants that are propagated by traditional societies. Such artificially selected varieties make up a highly utilitarian element of biodiversity, one of many stressed by Wilson in his plea for “precaution” in our stewardship of the world’s genetic resources. Nevertheless, and rightly so, Wilson’s primary concern is for natural biodiversity, both for its own sake and because nature is the source of all selected varieties. If nature is preserved, utilitarian strains can in principle be recreated by artificial breeding; the reverse is simply not possible.

The immensity of natural biodiversity is beyond one’s intuitive grasp. Ten thousand species of microbes may teem in a pinch of European soil; 12,000 species of beetles may dwell in the treetops of a single hectare of Panamanian rain forest. This is not the biodiversity one sees on television nature programs, but it is an integral part of life on earth. It is so unexplored that biologists can’t say with certainty whether the total number of species on our planet is 10 million, 30 million, or, not impossibly, even 100 million. Does it matter?

To Wilson, it matters as much as life itself. It should matter to the rest of us too, for most of the hidden, unglamorous components of biodiversity are intimately engaged in the biological recycling processes that purge the air, soil, and water of toxins and wastes. The small organisms are immensely important, but their services are ones we take for granted. We would quickly acquire a keen appreciation of their unesteemed roles if they were suddenly to go on strike.


Most contemporary biodiversity is to be found in the tropics. Depending on how many insects there are—estimates run from 2 to 30 million—at least 50 percent, and perhaps 90 percent of all living species occur in tropical forests. Tropical lakes and rivers nurture many more fish than their temperate counterparts, the Amazon alone containing more than 2,000 species. And tropical seas and reefs are vastly richer in fish, molluscs, corals, and almost any other type of marine life than the cool waters of higher latitudes. The disproportionate concentration of the earth’s biological wealth in the tropical belt enormously complicates the challenge of conserving it, because the natural resources of many tropical countries are under intense and mounting pressure as impoverished human populations struggle to improve their lot.

Wilson ranks the task of conserving biodiversity as the greatest challenge of our time. In his estimation, the masterworks of nature deserve at least the same solicitous attention we lavish on the masterworks of man. During World War II, both sides secured their art treasures in deep underground vaults. No human beings were so well sheltered. Artworks are unique and priceless, and represent deep cultural values. It would be a crass person indeed who questioned these values. But the truth is that our cultural origins are far more deeply and pervasively embedded in nature than in art. Yet why are we not equally concerned about nature? Perhaps it is because nature has no appointed custodian. If nature is to survive, we must all become its custodians. If we fail,we must bear responsibility for what Professor Wilson has called the one misdeed of this generation which future generations will never forgive.

How to preserve biodiversity is the central theme of the newly emergent discipline of conservation biology. Species of organisms live in natural assemblages that biologists refer to as ecological communities. The species that compose these communities cannot readily be bought, sold, traded, separated, or transported. They are best preserved in their natural habitats. This is because ecological communities are structured by webs of interdependency; and links between producer and consumer, predator and prey, host and parasite, provide the checks and balances that confer longterm stability. Disrupt these links, and the interlocking mechanism begins to fail. Simplification of the community through loss of diversity is the predictable result.

Ecologists are just now beginning to comprehend the systems of checks and balances that maintain biodiversity. No species is independent of the others with which it lives. Although the functions of some species in any community may potentially be fulfilled by others, we don’t know enough about most communities to make such predictions in confidence. Therefore when Manuel Lujan, the current secretary of the interior, asks, “Do we have to save them all?” the only safe answer is “Yes.”

The same caution, Wilson writes, should lead us to regard with special concern a roster of “keystone” species, the most equal among equals in the panoply of organisms. By definition, keystone species are critical in the functioning of a community. If such a species is removed or incidentally lost, the community will decay to a less diverse state. The principle of keystone species was discovered by the University of Washington biologist Robert Paine, who found that a rich intertidal community of limpets, chitons, snails, barnacles, brachipods, bivalves, and other invertebrates would be quickly monopolized by mussels if the top predator, a starfish, were removed from the system. In the absence of the keystone predator, a highly diverse community collapsed into one of monotonous simplicity.

Ecologists are now finding that the same principle applies to terrestrial communities as well. An example of increasing familiarity to suburban Americans is the exploding whitetailed deer population, an explosion attributable to the absence of wolves and mountain lions, their natural predators. Overbrowsing by legions of deer threatens the survival of numerous endangered plant species, and is drastically altering the patterns of tree regeneration in forests throughout the US. It is unfortunate that the keystone species in this case, wolves and mountain lions, are ones that are persecuted by human beings and that require vast expanses of wilderness in which to maintain themselves.

The persistence of keystone predators and other wide-ranging species is severely jeopardized when human beings enter the picture. As settlers begin to colonize an erstwhile wilderness, the natural habitat is almost invariably converted in a patchwork. Little clearings first appear. Later, these are expanded, while more are created nearby. Soon the landscape is a checkerboard of fields, pastures, and woodlots. Any time you fly over the eastern US, you will see such patterns. Ecologists refer to this process as habitat fragmentation. Formerly continuous populations of plants and animals are broken up into small isolated subunits. Usually fragmentation is accompanied by various sorts of disturbance, including increased pressure on predators, aggravating an already precarious situation. The largest species, such as bear, wolves, and elk, cannot maintain themselves in small habitat patches, and disappear almost immediately. The remnant populations of many other species are too small to survive for long, and these gradually fade out in piecemeal progression.


Other species, such as white-tailed deer, thrive in the mosaic of forests and fields and, in the absence of predators, increase until their populations are held in check by starvation. Other animals also increase in response to fragmentation, including raccoons and opossums. But raccoons and opossums relish the eggs and nestlings of songbirds; so where they have increased, bird populations have gone into decline. Fragmentation thus disrupts nature’s system of checks and balances. The consequence is an ecological chain reaction that unleashes a cascade of local extinctions. Local extinctions then spread and merge, just like the expanding patchwork of pioneer fields in a virgin forest, until global extinctions are the result. For this reason, conservation biologists regard fragmentation as perhaps the greatest threat to biodiversity short of complete loss of the natural habitat.

Today, the human species poses new threats to biodiversity by quite literally overwhelming the earth. Already an estimated 20 to 40 percent of the earth’s photosynthetic productivity, including that of the sea as well as the land, is appropriated to human use. (Photosynthesis is the process by which plants use the energy of the sun to manufacture carbohydrates while releasing oxygen as a byproduct.) There is in prospect no technological quick fix that will significantly augment the efficiency of photosynthesis. What clearer warning could there be that the limits to growth lie within another doubling of the earth’s population?

Wilson makes what he calls a conservative prediction of the loss of bio-diversity to be expected by 2020—about 20 percent of all extant species. His projection is based on a relationship ecologists call the species-area curve, a measure of the increase in diversity to be encountered in a series of progressively larger areas. As a rule of thumb, a tenfold larger area can be expected to hold double the number of species. This rule can then be turned around to predict that a 90 percent reduction in area of habitat will result in a halving of the number of species. As we have seen, tropical forests are the habitat of primary concern, because they harbor more than half of the earth’s biodiversity. Already more than half of the original extent of tropical forests has been appropriated to human uses. Less than eight million square kilometers remain in something resembling a natural condition. Estimates of the fraction of this natural territory that will be lost by 2020 range from half to 90 percent. If the projection of 90 percent should prove closer to the mark, a loss of perhaps a quarter of the world’s species can be expected to occur within the next thirty years. This is truly a horrendous prospect.

The primary response of conservationists to such projections has been to call for the creation of more parks and reserves. So far about 4.5 percent of the earth’s land area has been given some level of protection from development. But if ecologists, who may be the most contentious of all scientists, agree on anything, it is that a 4.5 percent remnant of nature will not preserve more than a minor fraction of the world’s biodiversity, particularly when much of the nominally protected area takes the form of officially allocated but unguarded “paper” parks. The International Union for the Conservation of Nature has called for extending protection to 10 percent of the earth’s surface, but in an era of rapidly mounting pressure on natural resources, this goal may be unattainable. And as we have seen, 10 percent of the earth’s natural habitat can be expected to preserve only half its biodiversity.

Behind every force that is driving species to extinction is the silent engine of population growth. Wilson refers to it as a “raging monster.” “The time has come,” he concludes, “for population policy.” That governments will eventually agree with him seems inevitable; the real question is whether a serious population policy will become politically acceptable before the world has gone beyond the point of no return for biodiversity.

A number of countries are already on the threshold of ruin. Close to home, one has only to look at Haiti and El Salvador, where the respective population densities are 230 and 260 per square kilometer, the highest in the western hemisphere. These two countries are beset by such unrelenting strife and misery that to advocate nature conservation in them seems so incongruous as to be morally embarrassing.

For a preview of the future, consider the situation in Bangladesh. If every human being in the world were squeezed into the continental US, the population density would still not match the 774 people per square kilometer who live there. The largely rural populace of this most crowded country ekes out the barest subsistence on 0.08 hectare of cropland per capita. This is equivalent to an area 93 feet on a side, the size of a moderate suburban backyard. Ten times as much land is required to pasture a single cow. Meat in Bangladesh is therefore a scarce luxury. Yet the population is expected to double by 2020. One can legitimately wonder whether human densities of over 1,000 per square kilometer can be attained in such an economy without bringing about a complete breakdown of social order.

With productive cropland rapidly becoming the most precious commodity on earth, we persist in acting as if the supply were unlimited. Since 1950, an area of farmland equal to that of China and India combined has had to be abandoned. As much damage has been done to the earth’s environment during this brief period than in all of prior human history. The causes are familiar ones: erosion, soil exhaustion, desertification, salinization, urbanization. In many parts of the world, it has long been easier and less costly to keep expanding into virgin lands than to rehabilitate exhausted land. But the remaining virgin lands are mostly unsuitable for agriculture, and constitute the last redoubt of the world’s biodiversity. Here is where the conflict between burgeoning humanity and dwindling nature is most acute.

Already (although it is not admitted in official circles), such countries as Haiti and Bangladesh are permanent charity wards of the international community. Neither has a realistic expectation of being able to achieve self-sufficiency, much less a standard of living that anyone reading these words would consider even marginally acceptable. As the scale of human misery grows, and as resources continue to dwindle, there may come a time when we face a choice between preserving human beings or preserving nature. That is a form of triage none of us wishes to contemplate, yet, through inaction, we are allowing such dire choices to be made by default.

Wilson most ardently constructs his case for saving nature on the basis of utilitarian arguments. He stresses the known and potential benefits mankind would forgo if biodiversity were seriously depleted: the loss of miracle genes, undiscovered drugs, and potential food plants. In the jargon of economics, these losses represent the opportunity costs of biodiversity loss. Such strictly utilitarian arguments, while an understandable expedient in the current emergency, leave me ill at ease.

Suppose we could test each microbe for its chemosynthetic and antibiotic properties, and suppose we could assess the agricultural and medicinal potential of every plant. We would then know what we needed to know about utilitarian possibilities, and could retain the useful species while discarding the rest. Nature as we know it, the endpoint of 3.5 billion years of evolution, would then cease to exist. The utilitarian argument ignores nature, but isn’t nature what we are really talking about? What would the quality of our lives be without nature? What would a children’s coloring book be without tigers, elephants, and giraffes? These seem to me to be the kinds of questions we should really be asking, questions that far transcend the narrow utilitarian viewpoint.

Wilson hints at them in his mention of biophilia—the spontaneous affinity we show toward other creatures such as our pets, and toward natural beauty as it is recreated in our gardens; but the overall impression he leaves is that biodiversity should be most valued for its utilitarian potential. My concern is that the utilitarian argument has only transitory validity. Both the argument that diversity enhances the quality of life and the ethical argument that man has no moral right to permanently destroy nature are eternal and irrefutable. These arguments are based on intuitions of fundamental values; but they are tragically lacking in persuasive force in our materialistic world.

In an effort to conclude on a constructive note, Wilson prescribes a five-point program for biodiversity. (1) Survey the world’s flora and fauna, so that scientists can base their investigations on a complete inventory of species, rather than a small sample. (2) Create wealth out of new biological products, materials, medicines, and foods. (3) Promote sustainable development. (4) Save what remains of bio-diversity. And (5), restore wildlands in areas that have been abused, exhausted, and abandoned.

Of the five goals, all of them important, the fourth is the most crucial, yet Wilson’s approach to it is more hortatory than practical. As an expedient, he advocates seed banks, arboretums, zoological parks, and other forms of conservation outside natural areas, but recognizes these will be inadequate to the task of saving millions of species, many of them still undescribed. Parks and reserves encompassing only 4.5 percent of the earth’s land area are certain to be more effective in conserving biodiversity than technologies applied in managed institutions; but, for the reasons presented above, such reserves are unlikely to offer a long-term solution for more than half the world’s species.

Wilson also advocates “debt-for-nature swaps,” by which debts of the poorer countries would be purchased or forgiven “in exchange for local conservation projects, especially the purchase of land.” But the record of such bargains so far is not encouraging. He also mentions in passing “ecotourism,” by which people would travel to observe flora and fauna; but such tourism offers only a weak argument for preserving the large tracts needed to sustain intact ecosystems.

What is needed is a concerted effort on the part of the developed countries to conserve the world’s remaining wildlands, whether these lands are formally incorporated in parks or not. Biodiversity must be considered a global commons, even though species, ecosystems, and populations reside within national boundaries. Some positive steps in this direction are already being taken. In launching its Global Environment Facility, the World Bank has initiated a program to aid developing countries in the strengthening of institutions engaged in protecting the environment. More than a score of conservation organizations are devoting their full energies to preserving biodiversity in the tropics.

But why should citizens of the industrialized countries pay to preserve resources that are legally the domain of other countries? An obscure tenet of economics provides a rationale. Certain things have what is known as an “existence value.” They are not marketable commodities, but people value them anyway, and are willing to pay to know that they exist. For example, many American citizens have demonstrated their willingness to pay taxes to support museums, even though the same citizens may never visit a museum. Museums are a cultural value. They are good things to have, even if the benefit accrues to someone else, or to society at large. The argument applies equally well to nature. Some people are willing to pay taxes to have national parks, even though they never visit them. The argument can be extended to the biological treasures of other countries in the spirit of a new internationalism.

Two of my colleagues at Duke University, Randy Kramer and Priya Shyamsundar, recently tried to determine the existence value of a park in Madagascar, an impoverished land of extraordinary and unique biodiversity. When they asked villagers living near the boundary of the park what the park meant to them, the reactions were mostly hostile. The villagers said they got no benefits from the park. Its regulations prohibited hunting, timber extraction, fuel-wood gathering, or clearing farm plots. To the villagers, the existence value of the park was decidedly negative. The park’s potential benefits, such as a better water supply, a lowered incidence of water-borne diseases, or future revenues from ecotourism, were discounted by the villagers as abstract and remote. Miles away in the capital city, people were more neutral, or even mildly positive, but in one of the world’s poorest countries, good will does not translate into action.

The power to take action resides in the developed countries of North America, Europe, and the Far East. To many citizens of these countries, the parks in Madagascar have a high existence value. We see this in the millions of dollars conservation organizations have raised to protect the lemurs, chameleons, and plowshare tortoises that live there. Most of the people who contribute to these organizations have no intention of ever traveling to Madagascar to see its remarkable flora and fauna. The gratification of the donors derives merely from the thought that Madagascar’s strange evolutionary relics are being rescued from imminent doom. Here we see a new economics at work, one that offers the best foreseeable hope for salvaging the world’s bio-diversity. If biodiversity is going to survive, the developed countries are going to have to pay for it, because the poor nations of the tropics lack both the will and the means.

In principle it might seem a simple matter to transfer benefits from countries that value biodiversity to those that harbor it. In practice, administering the transfers so that the people who most threaten biodiversity are the ones who will most gain from protecting it will be extremely difficult. Unfortunately no one knows how to construct such a system, much less how to carry it out for the benefit of the citizens of the poorer countries.

I find in this an apt analogy to our own domestic situation. As a student in the 1950s, I well remember taking part in impassioned debates on severe problems of American inner cities—how to cure them of the debilitating social diseases of drugs, poverty, ignorance, and apathy. But despite the Democratic Great Society, a Republican program for the working poor, and other social experiments, these problems have only grown worse. For all the sophistication of our economists and sociologists, we have still not hit upon effective ways to help the poor urban population. My greatest fear is that effective responses to the challenge of international conservation will prove equally elusive. But when it comes to protecting biodiversity, we don’t have thirty years in which to conduct failed experiments. Thirty years from now will be too late to save nature in much of the developing world. We need new and imaginative solutions, and we need them right away.

This Issue

November 5, 1992