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ESSAY Preserving Biological Diversity global change the worldwide modification of the envi- ronment as a result of human activities has become front-page news. Three broad trends seem responsible for this new-found concern with the environ- ment. Industrial pollution, long a problem at the local level, has become national and international in scope, particularly through its contributions to acid rain. Increasing levels of greenhouse gases in the atmosphere are co- inciding with a gradual warming of global temperatures, raising fears about the effects of future warmings on agriculture, rainfall, and sea levels. And an observed thinning of the ozone layer, including its virtual disappearance over Antarctica in the spring, has sparked concern that continued releases of chlorofluorocarbons could dramatically increase the ultraviolet radiation reaching the earth's surface. However, discussions of global change often overlook another critical trend, according to Edward O. Wilson, professor of science at Harvard University. "There is a fourth horseman in the environmental apocalypse, which needs to be much more closely monitored and acted upon. Unlike the others, it is truly irreversible and hence unpredictable in its consequences. I'm speaking of the extinction of species caused by habitat destruction, especially the destruction of tropical forests." Human beings are now causing a mass extinction that rivals any of the extinction events that have occurred in the earth's 4.5-billion-year history. Over the course of a hundred years little more than a human lifetime as many as half of the species living on the earth could become extinct. The biological diversity of the world is being irrevocably reduced, not through any conscious decision to reduce diversity but because no decision has been made to preserve it. "This is the folly our descendants are least likely to forgive us," Wilson believes. Ethical beliefs inevitably shape a person's attitudes toward the extinction of species. Some people may hold with the Book of Genesis that (~3 gave lo, ~ ~ ~ ~ ~ ~ ~ 1 1 1 . 1 IlUtildllb Q~111~11~1 over all living Inlngs to use as we see fit. Others may believe that we are charged with the stewardship of other species and are responsible Too

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for their welfare. Some people may see humans as a self-contained species, with no intrinsic responsibility toward other species except as they influence human welfare. Others might feel that because humans are a product of evolution, it diminishes humanity to let the other products of evolution be destroyed. "The field biologist is impatient with these niceties of moral reasoning," says Wilson. `'He is like a molecular biologist watching the laboratory burn down." Species are disappearing much too fast to withhold action until an ethical consensus emerges, Wilson says. Given the many known benefits of biological diversity and the unknown consequences of reducing that diversity, simple prudence would dictate that we act to preserve the world's biological heritage. Measures of Diversity C`It is a remarkable fact that no one knows the amount of biological diversity in the world even to the nearest order of magnitude," Wilson points out. 1.4 million species of all types since formal systems of class~cahon were inaugurated in the 1750s. But except for a few well-studied categories such as flowering plants and verte- brates, many more species exist than have been named and described. Wilson estimates that there may be anywhere between 4 and 30 million species on the earth, over half of them insects. Biologists have named and described over Each of these species is an irreplaceable repository of genetic information. The estimated number of genes in various organisms are about 1,000 in bacteria, approximately 10,000 in some fungi, from 50,000 to 100,000 in humans and many other animals, and around 400,000 in many flowering plants. Moreover, the individual members of a species contain different genes and different versions of the same gene, resulting in diversity within as well as between species. "A species is not like a molecule in a cloud of molecules," says Wilson. "It is a unique population of organisms, the terminus of a lineage that split off from the most closely related species thousands or even millions of years ago. It has been hammered and shaped into its present form by mutations and natural selection, during which certain genetic combinations survived and reproduced differentially out of an almost inconceivably large possible total." Relatively few genes have been studied in great detail, and except for a handful of laboratory organisms the nucleotide sequences for any given or- ganism, including humans, are largely unknown. Hence, when a species becomes extinct, the genetic information it contained is lost forever. PRESERVING BlOEOGICAE DIVERSITY 101

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Diversity in the Tropics By far the richest known collections of species in the world occur in tropical rain forests. Though such forests cover only about one-fourteenth of the worlcl's lane! surface, they contain over half of the worId's species. More accurately known as closed moist tropical forests, these forests typically contain three or more canopies of vegetation. The top canopy, formed by evergreen broadleaf trees, is very thick, so that little direct light reaches the forest floor. This absence of direct light reduces the amount of undergrowth, so that humans can walk through such forests with relative ease. The diversity of living things within these forests is legendary among bi- ologists. ``Every tropical biologist has a favorite example to offer," Wilson says. "From a single leguminous tree in Peru, I recovered 43 species of ants belonging to 26 genera. That's approximately the same as the entire ant population of the British Isles or Canada." In ten plots totaling 25 acres in Borneo, one tropical biologist identified about 700 species of trees, more than the number of native tree species occurring in all of North America. A square kilometer of forest in Central or South America may contain several hundred species of birds and many thousands of species of butterflies, beetles, and other insects. This increclible biodiversity is colliding head-on with a harsh reality of modern history: these areas are under some of the most intense development pressures of any ecosystems in the world. Most tropical forests occur in developing countries with rapidly growing populations. Already, 40 percent of the land that once supported tropical forests no longer does so because of human activities. And as population and economic pressures continue to grow, so will the pressures on the remaining tropical forests. By the most conservative estimates, about 1 percent of the existing tropical forest is being clearer] or permanently disrupted each year an area about the size of West Virginia. Other estimates are much higher, though in the politically charged atmosphere surrounding (reforestation such numbers are inevitably controversial. '`The important point is that the rates are very very high, however you look at them,' says Wilson. Most of these areas are being permanently cleared to make way for agri- culture. But one of the tragedies of tropical deforestation is that these lands are not particularly well suited to agriculture. The existence of lush tropical forests can give the impression of an abundant fertility. ``But the existing +~: ~] (~ ~ _ ~ ~ ~ ~L ~ .: _1_ r~ ~ 1 ~ Ll~J~l~1 lUlO~ ~ IlOt tIl~ rears Peruse environments easily regenerated that most people imagine," says Wilson. ``They're quite the contrary. They are what you could call wet deserts." Most tropical forests exist on what are known as tropical red and yellow earths, which are acidic and poor in nutrients. When the trees are cut down 102 SHAPING THE FUTURE

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and burnt, they release their nutrients into the soil, and for two or three years these nutrients can support crops. But after that the nutrients are used up or washer] away, and agricultural yields decline precipitously without extensive use of fertilizers. Once the forests are chopped down, it will take centuries for comparable ecosystems (minus the exterminated species) to regenerate fully. In some cases where damage is severe and the soil is particularly poor, the forests may never regenerate naturally. Tropical forests are therefore not necessarily a renewable resource, like forests in temperate areas. In many respects they are a non- renewable resource, like oil or minerals. If current rates of deforestation continue, the tropical rain forests will be virtually gone by the beginning of the twenty-seconl(l century. However, some areas are disappearing much faster than the average and will be gone within a decade or two. The rate of deforestation is also increasing, leading many tropical biologists to place the disappearance of the rain forests well within the twenty-first century. The amount of extinction that this destruction of habitat will cause cJepencis on the number of species living in these ecosystems now (a number that is not yet known with certainty) and on how much of the forests can be preserver!. Studies of island biogeography indicate that, as a general rule, when the area of a particular habitat is reduced by 90 percent, the number of species living in that habitat drops by half. In the tropics, however, this general rule may underestimate the true loss of species. Many tropical species occur in small geographical areas, so a relatively small loss of habitat can spell their ex- tinction. Such habitat destruction can also reduce the genetic diversity within a species, leaving it more vulnerable to future disruptions. Without conservation efforts on a massive scale, existing tropical forests will eventually be reduced to much less than 10 percent of their current area. It is therefore likely that more than half of the species now living in these areas will be lost. Linking Development and Conservation In the industrial world, development anal conservation are often seen as competitors in a zero-sum game: when development wins, conservation loses. But that equation does not necessarily hole! in the developing world. There, the biological wealth contained in natural environments can be a valuable source of increased human prosperity. `'Wild species in the rain forests and other natural habitats are among the most important human resources," says Wilson, ``and so far the least utilized." Food production is the prime example. At present, people rely on only 15 to PRESERVING BlOEOGICAL DIVERSITY 103

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20 species of plants for the great majority of their food supplies, and just three species wheat, maize (corn) and rice supply more than half. Yet there are at least 75~000 plants that are edible, Wilson observes, and many of them have qualities superior to those of the crops now in use. Even if a wild plant is not grown as a crop, its qualities can be introduced ; ~ [A ; ~ 1 ~1 . 1 . 1 1 1 - . lilt ~IlL~l~;~UlAAv crops Inrougn Iraultlona1 reefing programs. Furthermore, using genetic engineering it should soon be possible to transfer valuable traits, such as disease or pest resistance. between Hint that An not n~tilroll`7 ;- terbreed. Wild species are also a vast and larg`P,]V l]nt.nnnP~ rP~~r`7~ir.Af-n=~`r ~h~' ~ ~ ~ A,, I: ~ _ 1 ~ 1_ _ _ , 1 ---7 -~ ~ '' It's ~--TV L,A1C4L ~ll~L 11aLul "fly 111 1 1 . . V J A ~ - ' ~ ~^ ~ ~^ ~ . A ~ ~ '' ~11~1 lll~;~;ULll;~l~v' 1loers, petroleum substitutes, and other products. For instance, one in ten plants contains anticancer compounds of some degree of effec- tlveness. The rosy periwinkle of Madagascar provides two alkaloids, notes Wilson, vinblastine and vincristine, that can largely cure Hodgkin's disease and acute childhood lymphocytic leukemia. Now the basis of a $100 million a year industry, the rosy periwinkle is one of six related species on Madagascar. Tithe other five have largely been unstudied," Wilson notes, '`and one is at the moment on the verge of extinction due to the destruction of natural habitats." Plants are not the only wild species of potential value. Insects can act as crop pollinators, control agents for weeds, and parasites and predators of other , ~ new me dicinals, foods, and procedures of soil restoration. Proposals for how wild species can promote human welfare C`fill volumes," says Wilson. . insect pests. Bacteria, yeast, and other microorganisms can yield Approaches to Conservation C`You can't stop a Mexican peasant from shooting the last imperial wood- pecker to feed his family, which in fact happened 15 years ago," says Wilson. C`But in less desperate cases you can persuade people and governments, at least to some extent. that it is to their short-term and long-term benefit to preserve biodiversity. In the short term, they can get longer and richer yields from existing resources. In the l`^,n~ term- thPv~rp Bovine one of th-;' m~;~1 treasures. " V 7 - -~ ~ ~ ~ ' ^~ ~ ~' ~AA~11 11~1~1~1 A number of methods have been developed that can ~imlllt~nPollclv filrthPr 1 1 ~ ~ Am -- ~~- ~4 V-A^~ ~ - BRA t ~_~J-V1) 1 ~1 L11~1 economic development and preserve biological diversity, Wilson notes. New methods of strip lumbering can yield income from tropical forests while pre- servina forest tracts. PronPr a~rio.liltilr~l m~n~PmPnt non m.~nec`~rm th~ ~' V _ 1 ~=--- --- _~ we ,,,,~,,_,~,,,~,^~ BAA ~11~1 V I_ Lll~ llU trlents in tropical soils, so that farmers do not have to keep moving to be able to work fertile ground. Land that has already been cleared needs to be enriched or restored to take the pressure off undeveloped land. And crops especially stilted in id iropies, such as fast-growing trees that can be mowed to yield fiber and wood pulp, should find much wider use. ~ ~ I ~ { ~T A r ~ A t~A~ ~ ~ ~A,, ~ ~{_ ~. 1 . 104 SHAPING THE FUTURE

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Governments and international development organizations need to make biodiversity a major consideration when planning and supporting development projects, Wilson observes. Encouraging steps in this direction have been taken; for instance, the U.S. Congress has mandated that programs funded by the Agency for International Development include an assessment of en- vironmental impact. But much more needs to be done. More innovative measures have also been proposed. Some people have advocated that the international debts of developing countries be partially forgiven if they undertake conservation projects. A similar approach is to buy the debt of developing countries at a substantial discount and use that credit to purchase land for preservation. "There are a lot of techniques that have been developed," says Wilson, '`and it is not going to take an enormous amount of money in terms of foreign aid compared with what we have been contributing, for example, in military aid to many of these countries." The Role of Biologists Biological research will be an important complement to policy measures in preserving biological diversity. First of all, research in systematics and ecology is needed to get a better idea of the dimensions of biodiversity and the magnitude of the threat facing it. `'There's clearly a need for a strong new effort in systematic biogeography to find out where the species are located, which areas are in need of protection, and where the species exist that might be put to immediate use in the economic sphere," says Wilson. "We're going to have to rebuild our museums and other institutes devoted to biodiversity studies to concentrate a lot more fieldwork out there in the real world." Wilson is in favor of a biotic survey of every species plants animal, and microorganism that exists on the earth, "a project comparable to mapping the human genome." Such a survey could help answer a number of vital questions in evolutionary biology. For instance, what accounts for the number of species on the earth? Is it due to something about the nature of the planet or to something about evolution? Why do hot spots of biological diversity exist? Can the diversity of natural systems be increased through human in- tervention? The restoration of damaged ecosystems is another area in which biologists can make a major contribution. What are the best methods to promote the regeneration of a natural ecosystem? How can ecosystems be maintained in such a way as to promote diversity? These areas of biological research need to undergo substantial growth in the near future, Wilson contends. Biology is not the only science that needs to become more involved in preserving biodiversity. Economics has traditionally had difficulty assigning PRESERVING BlOLOGICAE DIVERSITY 105

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value to biological diversity and other environmental assets because these entities exist outside the narrowly definecl market economy. Psychology and sociology have never made serious efforts to study the relation of mental and social health to the vitality of the natural environment. In general, Wilson asserts, the social sciences need to become much more integrated into the realities of the natural environment and the uses of biodiversity. Stuclies of biodiversity are unusual in science, because there is a strict time limit on when they can be done. Biologists and other scientists are in a race with time, and the competition is running ever faster as population pressures increase. "The study of biodiversity has unexpectedly gained a new urgency," Wilson says. `'It has become as important to humanity now as medicine or molecular biology." 106 SHAPING THE FUTURE