Vanishing Before Our Eyes

By Edward O. Wilson

Known as the biosphere to scientists and as the creation to theologians, all of life together consists of a membrane around earth so thin that it cannot be seen edgewise from a satellite yet so prodigiously diverse that only a tiny fraction of species have been discovered and named. The products of billions of years of evolution, organisms occupy virtually every square centimeter of the planet's surfaces and fill nearly every imaginable niche.

Biologists estimate that more than half the species occur in the tropical rain forests. From these natural greenhouses, many world records of biodiversity have been reported--425 kinds of trees in 2.5 acres (1 hectare) of Brazil's Atlantic forest and 1,300 butterfly species from a corner of Peru's Manu National Park, both more than 10 times the number from comparable sites in Europe and North America. At the other extreme, the McMurdo Dry Valleys of Antarctica, with the poorest and coldest soils in the world, still harbor sparse communities of bacteria, fungi and microscopic invertebrate animals.

A few remarkable species, the "extremophiles," have achieved astonishing feats of physiological adaptation at the ends of habitable Earth. In the most frigid polar waters, fish and other animals flourish, their blood kept fluid by biochemical antifreezes. Populations of bacteria live in the spumes of volcanic thermal vents on the ocean floor, multiplying in water above the boiling point. And far beneath Earth's surface, to a depth of 2 miles (3.2 km) or more, dwell the SLIMES (subsurface lithoautotrophic microbial ecosystems), unique assemblages of bacteria and fungi that occupy pores in the interlocking mineral grains of igneous rock and derive their energy from inorganic chemicals. The SLIMES are independent of the world above, so even if all of it were burned to a cinder, they would carry on and, given enough time, probably evolve new life-forms able to re-enter the world of air and sunlight.

Earth's biodiversity (short for biological diversity) is organized into three levels. At the top are the ecosystems, such as rain forests, coral reefs and lakes. Next down are the species that compose the ecosystems: swallowtail butterflies, moray eels, people. At the bottom are the variety of genes making up the heredity of each species. How much biodiversity is there? Biologists have described a total of between 1.5 million and 1.8 million species. Yet this impressive achievement is only a small beginning. Estimates of the true number of living species range, according to the method employed, from 3.6 million to more than 100 million.

Least known are the smallest organisms. By repeated sampling, biologists estimate that as few as 10% of the different kinds of insects, nematode worms and fungi have been discovered. For bacteria and other microorganisms, the number could be well below 1%. Even the largest and most intensively studied organisms are incompletely cataloged. Four species of mammals, for example, have recently been discovered in the remote Annamite Mountains along the Vietnam-Laos border. One of them, the saola or spindlehorn, is a large cowlike animal distinct enough to be classified in a genus of its own. Earth, as far as life is concerned, is still a little-known planet.

Biologists who explore biodiversity see it vanishing before their eyes. To use two of their favorite phrases, they live in a world of wounds and practice a scientific discipline with a deadline. They generally agree that the rate of species extinction is now 100 to 1,000 times as great as it was before the coming of humanity. Throughout most of geological time, individual species and their immediate descendants lived an average of about 1 million years. They disappeared naturally at the rate of about one species per million per year, and newly evolved species replaced them at the same rate, maintaining a rough equilibrium. No longer. Not only has the extinction rate soared, but also the birthrate of new species has declined as the natural environment is destroyed.

The principal cause of both extinction and the slowing of evolution is the degrading and destruction of habitats by human action. While covering only 6% of Earth's land surface, about the same as the 48 contiguous United States, the rain forests are losing an area about half the size of Florida each year. Damage to intact forests, which occurs when they are broken up into isolated patches or partly logged, or when fires are set, threatens biodiversity still more. With other rich environments under similar assault, including coral reefs (two-thirds degraded) and salt marshes and mangrove swamps (half eliminated or radically altered), the extinction rate of species and races is everywhere rising.

Not all doomed species disappear immediately. Most first suffer loss of their ranges and gene pool to dangerously low levels, eventually descending to join what biologists call the "living dead." Throughout the world, 976 tree species, for example, are classified as critically endangered. Two are down to three or four surviving individuals and three others to only one. I have been grimly compiling what I call the Hundred Heartbeat Club of animal species--those consisting of a hundred or fewer individuals, hence that number of heartbeats away from total extinction. The club's more familiar members include the Javan rhinoceros, Philippine eagle, Hawaiian crow, Spix's macaw and Chinese river dolphin. Other endangered species lined up for early admission are the giant panda, Sumatran rhinoceros and mountain gorilla.

Paleontologists recognize six previous mass-extinction events during the past half-billion years (the number was until recently believed to be five, but now another, from early Cambrian times, has been added). The last and most famous, which occurred 65 million years ago and was caused by a giant meteorite strike off the present-day coast of Yucatan, ended the age of dinosaurs. These catastrophes followed a typical sequence. First, a large part of biodiversity was destroyed. There was a bloom of a small number of "disaster species," such as medleys of fungi and ferns, that survived and reproduced rapidly to fill the habitable spaces emptied of other life. As more time passed, a few "Lazarus species" reappeared in localities from which they had been wiped out, having been able to spread from isolated pockets difficult to detect. Then, very slowly, across 2 million to 5 million or more years, life as a whole evolved again to its full, original variety.

Researchers of biodiversity agree that we are in the midst of the seventh mass extinction. Even if the current rate of habitat destruction were to continue in forests and coral reefs alone, half the species of plants and animals would be gone by the end of the 21st century. Our descendants would inherit a biologically impoverished and homogenized world. Not only would there be many fewer life forms, but also faunas and floras would look much the same over large parts of the world, with disaster species such as fire ants and house mice widely spread. Humanity would then have to wait millions of years for natural evolution to replace what was lost in a single century.

In the long term, I am convinced, the quenching of life's exuberance will be more consequential to humanity than all of present-day global warming, ozone depletion and pollution combined. Why? For practical reasons, if nothing else. Humanity's food supply comes from a dangerously narrow sliver of biodiversity. Throughout history, people have cultivated or gathered 7,000 plant species for food. Today only 20 species provide 90% of the world's food and three--maize, wheat and rice--supply more than half. Tens of thousands of species of the world's still surviving flora can be bred or provide genes to increase production in deserts, saline flats and other marginal habitats.

Natural pharmaceuticals offered by biodiversity are also underutilized. Only a few hundred wild species have served to stock our antibiotics, anticancer agents, pain killers and blood thinners. The biochemistry of the vast majority--millions--of other species is an unfathomed reservoir of new and potentially more effective substances. The reason is to be found in the principles of evolutionary biology. Caught in an endless arms race, these species have devised myriad ways to combat microbes and cancer-causing runaway cells. We have scarcely begun to consult them for the experience stored in their genes.

If the future enhancement of agriculture and medicine is not thought enough to merit conservation, then consider survival. The biosphere gives us renewed soils, energy, clean water and the very air we breathe, all free of charge. The more species that compose wild communities, the more stable and resilient becomes the planet as a whole.

Then consider ethics. More and more leaders of science and religion now pose this question: Who are we to destroy or even diminish biodiversity and thus the creation? Look more closely at nature, they say; every species is a masterpiece, exquisitely adapted to the particular environment in which it has survived for thousands to millions of years. It is part of the world--part of Eden if you prefer--in which our own species arose.

The profligacy of the 20th century has led humanity into a bottleneck of overpopulation and shrinking natural resources. Through this bottleneck humanity and the rest of life must now pass. By the end of the new century, if we are both lucky and wise, we will exit in better shape than we entered, with the population peaked around 8 billion or less and a gradual decline begun. People everywhere will have acquired a decent quality of life, with the expectation of more improvement to come. One of the defining goals of the century must also be to settle humanity down before we wreck the planet. To that end it is important to accept the challenge and responsibility of global conservation--and to do so right now, before it is too late. We will be judged by the amount of biodiversity we carry through the bottleneck with us.

There are reasons to be warily optimistic that biodiversity may be salvageable. Whether it happens in time depends fundamentally on the shift to a new ethic, which sees humanity as part of the biosphere and its faithful steward, not just the resident master and economic maximizer. That change of heart has begun in most countries among a few farsighted leaders and a growing part of the general public, albeit very slowly.

Success also depends on attention to sustainable management of the environment, including protection of biodiversity. Conservation experts now give top priority to "hot spots," pockets of wild nature that contain high concentrations of endangered species, which give hope that a great deal can be accomplished in a short span of time. From the coastal sage of California to the rain forests of West Africa, the hottest of the terrestrial hot spots occupy only 1.4% of the world's land surface yet are the exclusive home of more than a third of the terrestrial plant and vertebrate species. Similarly, from the streams of Appalachia to the Philippine coral reefs, aquatic hot spots occupy a tiny fraction of the shallow water surface. This much of the world can be set aside quickly without crippling economic or social consequences. More difficult but equally important are the preservation and long-term nondestructive use of the remaining fragments of the old-growth forests, including the tropical wildernesses of Asia, Central Africa and Latin America.

None of this will be easy, but no great goal ever was. Surely nothing can be more important than to secure the future of the rest of life and thereby to safeguard our own.

Wilson is University Research Professor at Harvard. His most recent book is Consilience: The Unity of Knowledge