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The Diversity of Life.

No one is better qualified than E. O. Wilson to write an overview of the diversity of life--and the problems it faces as we enter the 21st century. Equally at home in ecology and evolutionary biology, Wilson's track record as an innovator is impressive. Among other contributions, he was the cofounder (with ecologist Robert H. MacArthur) of the theory of "island biogeography," establishing a direct relationship between the size of a habitable area and the number of species occupying it. And, of course, he was the principal codifier (if not the chief conceptual architect) of sociobiology, an ambitious application of contemporary neo-Darwinian evolutionary theory to the biology of social systems.

Most recently Wilson has brought this eclectic biological perspective to bear on the immediate threat of extinction of a vast proportion of the world's living creatures--the so-called biodiversity crisis. In The Diversity of Life he presents for a general readership an overview of the scope and nature of life's diversity, the threats it faces, and the policies that he advocates to stem the tide of what promises to be the next great wave of mass extinction. When writing The Miner's Canary, in which I examined the relationship between the mass extinctions of the geological past and the present-day biodiversity crisis, I relied heavily on Wilson's published data and arguments. This welcome new book extends the debate over biodiversity beyond the confines of academic science into the arena of public policy.

Skeptics, who abound, pose two challenging questions: What is the evidence that mass extinction is really going on right now? And even if we are in the throes of a manmade biodiversity cataclysm, so what? University of Maryland economist Julian Simon, for example, has mocked attempts to measure the rate of disappearance of modern species and has discounted the threat that such disappearances pose to our own continued well-being. The "so what" position usually cites the recovery that life has--so far--always made after struggling through a mass extinction. After all, according to University of Chicago paleobiologist D. M. Raup, perhaps as many as 96 percent of all species on earth disappeared 245 million years ago in the worst extinction episode to strike so far--yet here we are. The skeptics' punch line: Evolution will take care of everything, so let's get on with the unbridled exploitation of natural resources that destroys habitats wholesale.

Wilson's book is potentially pivotal in an increasingly public dialogue. We turn to Wilson to get the numbers, the hard facts that support the assertion that we are at the very brink of biodiversity Armageddon. And Wilson delivers.

The science of biodiversity

Wilson's game plan is sound. After a somewhat lyrical opening and a few summary chapters on the reality of past and present extinctions, he tackles the science of biological diversity with seven chapters on the genesis, maintenance, and degradation of living systems--in other words, evolutionary biology and ecology. He follows up with five concluding chapters on "The Human Impact." Though the chapters on biological theory are less engagingly written than those sections that simply describe aspects of nature in exquisite detail, the science in this book should prove to be both intelligible and interesting to nonspecialists. Wilson strives throughout the book to base his conclusions on firm scientific principles and evidence. A reader could skip the chapters on the evolution and ecology of diversity but would then miss the underpinnings of Wilson's thesis: Biology has shown without a shadow of a doubt that the biodiversity crisis is very real indeed.

In general, Wilson's version of ecological and evolutionary biology serves his purpose very well. Were it not for the fact that Wilson himself insists on using science to legitimize his conclusions, I would not pause here to criticize his science (in this review, that is; I have many differences with Wilson on purely scientific matters). But there are a few problems of a scientific nature that affect his more general discourse.

For instance, Wilson presents a hierarchy of biological systems that defines organisms as parts of species, and species as parts of ecosystems. But species are not parts of ecosystems; parts of species are parts of ecosystems. Whether talking about evolution or extinction, throughout his text Wilson persistently says "species," but either means, or illustrates his point with, those parts of species that biologists call "populations."

This mistake is actually common in ecological parlance. And though it sounds like quibbling, consider the pragmatic effects that confounding population biology with species biology has in conservation praxis. We constantly read in the popular press of newly designated endangered species. The marbled murrelet (a marine bird) is one of the most recent species to be listed as endangered--in California, Oregon, and Washington. I have yet to see any mention in the newspapers of the huge populations of this species thriving in Alaska.

Wilson knows, and even in places makes clear, that there is a real distinction between the extinction of a part of a species and an entire species. Yet many of his examples, like those in the newspapers, tend to blur this distinction--and I blame this lapse as much on faulty biology as on rhetorical convenience.

The point is important because we biologists have to be credible as we approach the skeptics. I was nonplussed to learn, years after Rachel Carson alerted us all to the dangers that pesticides posed for ospreys and peregrine falcons, that both happen to be worldwide species, neither of which was in imminent danger of extinction in its entirety. Skeptics like to seize on such examples to question the very validity of the crisis we face.

Estimating extinctions

Using a combination of solid biological theory, data, and analysis, Wilson builds a powerful case to answer in the affirmative the skeptics' first question: Is the crisis real? He takes great pains to show his reader just how daunting is the task of taking inventory of the world's biological riches. He calculates that scientists have described approximately 1.4 million species--a mere fraction of what is really there.

But how do we know how many species we haven't found yet? We must estimate. Over the past decade, a number of clever sampling experiments have helped scientists zero in on the actual number of species in nature. But Wilson admits that we really can't do much better than to say that there are at least 10 million and perhaps as many as 100 million species in the modern world. Our monumental ignorance stems not from scientific incompetence but simply from a shortage of scientific personnel--biological systematists--qualified to inventory a richness that is disappearing before its elements can be numbered.

What we can say is that the number is shrinking. There are the famous examples of individual species--passenger pigeons, dodos--that have disappeared in historical times. But there are also what Wilson calls the "Centinelan" extinctions, in which destruction of habitat (generally for agricultural purposes) literally obliterates hundreds of obscure and unheralded species that happen to be restricted to very limited areas.

Herein lies one of the very great difficulties of the conservation movement. We know that many species, especially tropical ones, have limited geographic distributions. We can measure the rate of destruction of tropical rain forest and obtain a reliable estimate of how many species are likely to be going extinct each year. According to Wilson, the figure is 27,000 a year--or 3 an hour. But will the skeptics buy this argument?

Wilson's careful biological exegesis is convincing. He explains that we know that we are losing species, even if we don't know their names and numbers, precisely because we know so much about how ecosystems are constructed and how species are distributed in nature. The modeling is credible because the general biology is basically sound.

The skeptic will then turn to question two: So what? We seem, as a species, so removed from nature in our everyday concerns that the mass extinction of remote species might not matter very much to us. Why should we care about biodiversity?

Wilson comes down hard on the side of the potential utilitarian uses of biodiversity. The famous cancer-fighting properties of Madagascar's rosy periwinkle can be imagined to extend to many as-yet-undiscovered fruits of the biotic wilderness. He cites other reasons as well, including esthetics and, in his final chapter, a vague if heartfelt expression that humans really are still a part of nature--as evidenced, for example, by primordial fears (of heights, of snakes). His utilitarian argument may convince some skeptics; the rest of his reasons will appeal only to those who already agree.

A snappier retort is needed--and Wilson supplies it himself, though he seems to waffle a bit. We need to show the skeptics that biotic extinction threatens our very existence. In an astonishing passage, Wilson writes: "So important are insects and other land-dwelling arthropods that if all were to disappear, humanity probably could not last more than a few months." His argument hinges on the interdependence of plant and insect life. Though Wilson later is less definitive in his assessment, he has laid the basis for a rational and eminently pragmatic retort to the "so what" stance: Our own survival depends upon stemming the next tide of mass extinction.

Indeed, Wilson covers all the bases. I waited a very long time for him to get to what is patently the real point: establishing unbridled human population growth as the underlying cause of habitat destruction. But it is there, in a scant but powerful two paragraphs. He also presents a well-reasoned five-point agenda for action and enriches his discussion with many concrete examples. In sum, he advocates: (1) surveying the world's fauna and flora to find out what's there before much of it disappears; (2) creating biological wealth--in other words, mining the economic riches of the biological world; (3) promoting sustainable development, in which local human populations are supported without further environmental degradation--which necessitates sharply curbing human population growth; (4) saving what remains, using conservation techniques well discussed in the book; and (5) restoring wildlands, which Wilson concedes will be difficult to achieve, given the stiff resistance to such measures coming from many in political power, since it requires "the strong hand of protective law."

Wilson's book is crammed with facts, statistics, hard-reasoned conclusions--and revealing glimpses of the natural world. I can cheerfully report that, having read it, I feel better armed to meet the skeptics.

Niles Eldredge is a curator in the Department of Invertebrates, The American Museum of Natural History. He is author of The Miner's Canary: Unraveling the Mysteries of Extinction (Prentice-Hall, 1991) and editor of Systematics, Ecology and the Biodiversity Crisis (Columbia University Press, 1992).
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Author:Niles Eldredge
Publication:Issues in Science and Technology
Article Type:Book Review
Date:Dec 22, 1992
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