Around a hundred years ago, residents on a number of Pacific islands decided to decorate their gardens with giant land snails imported from Africa. Though pleasing to the eye, the introduced species quickly multiplied out of control and began to attack crops and even native snail species. By the mid-1950s, it had become so ubiquitous a pest that something had to be done. Then someone had a nifty idea: why not fight snails with snails? The rosy wolfsnail, known to be a voracious predator, was brought in from the United States with the expectation that it would gobble up its larger African cousins.

Envisioned as a "model case of biological control," the exercise actually triggered an extinction avalanche. The rosy wolfsnail liked the taste of snail meat well enough but understandably preferred easier prey. It left the big African snail alone and proceeded to eat its way through the smaller, more vulnerable native snails. On Hawaii, the rosy wolfsnail was renamed the "cannibal snail," and, along with shell collectors, rats and deforestation, it has helped to wipe out 50 to 75 percent of the 800 or so ground-dwelling Hawaiian snail species.

On the island of Moorea in French Polynesia, the rosy wolfsnail came close to extirpating all seven species of native tree snails. In a last-ditch effort to save them, a couple of biologists collected living specimens and sent them off to universities and zoological parks in the United States and England. Most of the species reproduced successfully in captivity, and three did so well that they were reintroduced to the island, albeit artificially protected behind toxic moats and electric fences.

But one species, Partulina tugida, failed completely. The last living specimen, nicknamed "Turgie" by its keepers at London Zoo, died in 1996, just ten years after the last of its relatives died out in the wild. The little snail's caretakers put up a memorial that outlined the dates of the species' existence: 1.5 Million Years B.C. to January 1996."

If the permanent extinction of an obscure snail like Turgie leaves you feeling cold and unmoved, perhaps you ought to see whether Edward O. Wilson can change your mind. In his new book, The Future of Life, Wilson shares his wonder and appreciation of the natural world at the same time that he warns of its rapidly accelerating demise. A renowned biologist and passionate conservationist, he pulls no punches as he predicts that an unprecedented ecological crisis is lurking just around the corner.

According to Wilson, mankind "is in a final struggle with the rest of life. If it presses on, it will win a Cadmean victory, in which first the biosphere loses, then humanity." As homo sapiens, we must, in order to avoid this catastrophe, not only take immediate remedial action, but we may also need to reappraise some of our most resilient and self-serving notions about what it means to be human.

Wilson obviously isn't just talking about the disappearance of the odd snake or snail. He means to sound the alarm about an extinction tsunami that may be doing its dirty work more than a hundred times faster than the normal background rate. By the end of the present century, up to half of all plant and animal species may have gone the way of New Zealand's eleven moa species, the American chestnut and poor old Turgie.

As human pressure on the environment increases, a multitude of known species are slipping down the list from threatened to endangered, to what is chillingly known as the "living dead," when a species has been whittled down to its last survivor. Some, like Australia's northern gastric breeding frog, are discovered just months before they go extinct. This unique amphibian, which incubates its eggs in its stomach and gives birth through its mouth, first came to light in January 1984. By the following spring it was gone. The manmade pattern of extinction has been so thoroughly documented that it has earned its own acronym, HIPPO (for habitat destruction, invasive species, pollution, population [human] and overharvesting).

Extinction caused by man is not news. In a chapter titled 'The Planetary Killer,' Wilson deconstructs the myth of the noble savage living in harmony with nature. He builds instead a persuasive circumstantial case to show that homo sapiens has been annihilating native fauna ever since the Aborigines found their way to Australia. The same thing happened in Madagascar, in Polynesia, and the New World.

What is different now is that currently the human population exceeds six billion and we are still counting. The pace at which we are extinguishing other species has picked up so much momentum that it rivals the destruction caused by more cosmic cataclysms, like that of an asteroid slamming into the Earth. At first, Wilson explains, "it was mostly large land-dwelling animals that were afflicted, now fishes, amphibians, insects, and plants, are, for the first time, vanishing in large numbers. The dawnless night of extinction is also descending upon rivers, lakes, estuaries, coral reefs, and even the open sea."

As Wilson sees it, human pressure on the biosphere comes from two sides at once. On the one hand, we have the fortunate few in the industrialized countries, who indulge in lavishly wasteful consumption. Then there are the overwhelming majority, who are struggling to achieve more than mere survival. Of these, more than a billion are desperately poor and lack even the most rudimentary requirements, like clean water, adequate nutrition or basic sanitation. As the world population approaches its peak (somewhere around 9 or 10 billion) later this century, all of us, rich and poor, North and South, will be struggling to pass through this "bottleneck."

More people, all needing and wanting more stuff! This sounds like a job for an economist. Or would that be an environmentalist? Many of the world's richest biodiversity "hotspots" are located in precisely those areas where human needs are most acute. Is this really Man against Nature in a fight to the death?

Wilson doesn't think it has to be so grim. Surprisingly optimistic in outlook, he believes that it ought to be possible to provide Earth's growing human population with a decent existence at the same time that we conserve the majority of its nonhuman genetic and ecological heritage. We just have to change the way we do business. Most "people first" economists tend to neglect the $33 trillion in free ecological services that nature so generously provides. The author claims that by replacing traditional economic measures like GNP with measures like the Genuine Progress Indicator (GPI), which includes the environmental costs of economic activity, the environmental viewpoint ought soon to be recognized as the "real world point of view." The main thing is to take a long-term perspective and make sure that all the facts are included as we devise a new 'global ecological economics.'

There are many sound economic reasons to preserve any number of individual species, but Wilson isn't satisfied with shining some light on our own long-term self-interest. He wants to accomplish much more than this and categorically refuses to allow the Earth's ancient, varied genetic heritage to be assessed by teams of gimlet-eyed bookkeepers. Instead he issues this stern warning: "To evaluate individual species solely by their known practical value at the present time is business accounting in the service of barbarism."

The Future of Life then, is as much a moral tract as it is a scientific treatise. Building on some of his previous work, Wilson attempts to construct a new sort of ethical theory from the facts of evolutionary biology. This can be humbling: it is hard to preen when we learn that the recent pattern of human population growth "was more bacterial than primate," or that human short sightedness may be a "hardwired part of our Paleolithic heritage."

As Wilson sees it, the evolutionary story is "a fact-based history" which confirms our kinship with the rest of life. Much of what he says about our innate "biophilia," (love of other forms of life) makes sense. Does anyone really want to argue when he asserts that it isn't "so difficult to love nonhuman life, if gifted with knowledge about it?"

There are times when Wilson's prose drifts toward poetry or wanders surprisingly close to mysticism. The claim that "the biosphere as a whole began to think when humanity was born" surely ought to cock an eyebrow or two. When he encroaches on territory normally defended by philosophers, politicians and theologians, Wilson likely ruffles more than a few feathers.

Yet by calling for a new "global land ethic" based on the idea of stewardship, Wilson does not mean to stir up controversy. He merely asks us to see ourselves as integral parts of the biosphere rather than its divinely appointed owners and consumers. The practical solutions that he outlines in his final chapter wouldn't cost all that much and might even allow a large majority of our Earthly fellow-travelers to pass through the bottleneck with us. Although Wilson's ideas deserve our most urgent attention and rigorously informed debate, the current zeitgeist is vigilantly preoccupied with more trivial pursuits. ò