The Extinction Crisis

The Crisis

The most important—and gloomy—scientific discovery of the twentieth century was the extinction crisis. During the 1970s, field biologists grew more and more worried by population drops in thousands of species and by the loss of ecosystems of all kinds around the world. Tropical rainforests were falling to saw and torch. Wetlands were being drained for agriculture. Coral reefs were dying from god knows what. Ocean fish stocks were crashing. Elephants, rhinos, gorillas, tigers, polar bears, and other "charismatic megafauna" were being slaughtered. Frogs were vanishing. Even leviathan—the great whales—were being hunted down in their last redoubts of the Antarctic and Arctic seas, and their end was in sight. These staggering losses were in oceans and on the highest peaks; they were in deserts and in rivers, in tropical rainforests and Arctic tundra alike.

A few biologists—including geneticist Michael Soulé (who later founded the Society for Conservation Biology) and Harvard's famed E. O. Wilson—put these worrisome anecdotes and bits of data together. They knew, through paleontological research by others, that in the 570 million years or so of the evolution of modern animal phyla there had been five great extinction events. The last happened 65 million years ago, at the end of the Cretaceous when dinosaurs became extinct. Wilson and company calculated that the current rate of extinction is one thousand to ten thousand times the background rate of extinction in the fossil record. That discovery hit with all the subtlety of an asteroid striking Earth: right now, today, life faces the sixth great extinction event in earth history. The cause is just as unsettling and unprecedented: eating, manufacturing, traveling, warring, consuming, and breeding by six billion human beings. For the first time in the history of life on Earth, one species is killing countless others. For the first time, one species, Homo sapiens—that's us—is waging a war against nature.

The crisis we face is biological meltdown. Wilson warns that the proportion of species driven to extinction "might easily reach 20 percent by 2022 and rise as high as 50 percent or more thereafter." Soulé has said that soon the only large mammals left will be those we consciously choose to protect; that "[the twentieth] century will see the end of significant evolution of large plants and terrestrial vertebrates in the tropics." He writes, "The end of speciation for most large animals rivals the extinction crisis in significance for the future of living nature. As [Bruce Wilcox and I] said in 1980, 'Death is one thing, an end to birth is something else.'"

I wish Soulé and Wilson could be brushed away as crackpots hanging off a far edge of science, but not only are they among the most lionized biologists of our time, their dismal views are commonplace in the scientific community. In 1998, the American Museum of Natural History commissioned the Louis Harris poll to survey the nation's leading biologists. "Nearly seven out of 10 of the biologists polled said they believed a 'mass extinction' was underway, and an equal number predicted that up to one-fifth of all living species could disappear within 30 years."

However, few members of the public are aware of the crisis. "Sixty percent of the laymen polled professed little or no familiarity with the concept of biological diversity, and barely half ranked species loss as a 'major threat.'" A Newsweek Earth Day poll in 2000 found that a mere 5 percent of Americans thought that endangered or vanished species was the most important environmental problem. Even among members of nature conservation groups, most seem unaware of the magnitude of species loss, and few conservation organizations are forthright in putting the extinction crisis at the top of their agendas and sounding the alarm about the dead-end road down which humanity is hurtling. The crisis is made worse by this ignorance.

Considering the biological catastrophe we are in, it is gut-wrenching to find that only a small percentage of people are aware of the crisis and our responsibility for it. There may be several reasons for this head burying. First, scientists and conservationists have not done the best job of publicizing and explaining the extinction crisis, nor has the media given it due heed. Second, the money and research time given to the problems facing nature are so small that we do not even know how many species there are. That alone makes accurate analysis difficult. Third, anticonservationists have fogged the issue so well that the public and mainstream media have been turned away from the core issues regarding extinction. Fourth, extinction events happen in time and territorial scales that are hard to comprehend. After all, humans have evolved to react to short-term and close-range stimuli. Fifth and closely related, much of the devastation is slow and incremental. Many of us are blind to that which is not sudden. Sixth, the mere thought that we are causing a mass extinction is so soul shattering that most people who hear of it refuse to even consider it. Finally, the values we place on nature make it easy for us to exploit it for our personal economic gain.

The Diversity of Life

Before we can understand the extinction of species, we must know what species are and what their significance is. And before we can understand the extinction crisis, we must know something about biological diversity, or biodiversity.

It seems that we humans are adapted to classifying things. Even the act of collecting baseball cards or porcelain figurines comes from this fancy. From our earliest times, we have named, numbered, and classified life forms. Genesis recounts the old Middle Eastern myth where Yahweh brought all the animals before Adam to be named. Not only are we driven to classify things, but we seem to be pretty good at it. We also seem to be consistent at it. Ornithologist Jared Diamond has shown how the classification of bird species by traditional New Guineans is almost exactly that of modern ornithology. Michael Soulé writes that "the taxonomies of aboriginal societies are virtually always the same in structure as those of modern, scientific cultures (both are hierarchical and consist of nested sets of exclusive categories); moreover, aboriginal taxonomies typically recognize the same entities as species as do modern taxonomists."

Modern scientific classification of life is called taxonomy (or systematics) and is based on binomial nomenclature developed by Swedish naturalist Carl von Linné (Linnaeus in Latin) about 250 years ago. From the beginning, the goal of taxonomy has been to complete Adam's task and name every creature—a goal we are still far from finishing. In 1990, Soulé wrote that "over 1.4 million species have been described and classified" and that this naming task had been believed to be "about half finished." However, he pointed out, after entomologist Terry Erwin published his research on tropical arthropods in the 1980s, it became clear that there were many more species—perhaps by an order of magnitude or more—than scientists had previously believed.11 Estimates today from the best biologists range upward to 30 million species, and some think 100 million could be closer to the truth.

Linnaeus gave each organism a double Latin name—popularly known today as a scientific name. For example, the wildcat of the Old World is Felis silvestris. The scientific name is italicized, and the first name (the genus) is capitalized, while the second name (the species) is not capitalized. The wildcat is the only cat calledsilvestris (of the forest), but other closely related cats are also part of the Felis genus. However, the North American bobcat (colloquially called a wildcat) is in a different genus, Lynx, that includes the Canadian lynx, the Eurasian lynx, and the Iberian lynx. All cats, whether they are Felis, Lynx, or other genera (plural of genus) are in the family Felidae.

This classification system is based on relationships. In Linnaeus's time (before Charles Darwin and evolutionary theory), these relationships were calculated on gross similarities and anatomy. After Darwin, relationships began to be redefined by evolution, essentially as a family tree. Anatomy (or structural similarity) was still the most significant clue to evolutionary relationships. More recently, classification has become much more accurate as genetic analysis allows researchers to clearly show evolutionary relationships, including how closely related species are to one another and how long ago they split off from a common ancestor. This genetic analysis has not only fine-tuned older classifications, it has also rearranged some relationships. This is not evidence that taxonomists do not know what they are doing, but that they—like other scientists—are constantly improving the description of the world around us.

All life is sorted into five kingdoms (although this is not universally accepted). Each kingdom is divided into phyla (singular: phylum). The wildcat is a member of the phylum Craniata, animals whose brains lie in a cranium (skull). Each phylum is divided into classes. The wildcat is in the class Mammalia, cranium-possessing animals that have fur, are homothermic (warm-blooded, or internally heat-regulated), and with the females bearing mammary glands that produce milk for the young. Within Mammalia, the wildcat is in the order Carnivora, which includes cats, dogs, bears, raccoons, and weasels—flesh eaters. Cats, including the wildcat, make up the family Felidae—-the Cat Family. Among cats, the wildcat and its evolutionary siblings are in the genus Felis. As we have already seen, the wildcat is the species Felis silvestris. Each of these divisions is called a taxon (plural is taxa; remember, the science of classifying creatures is taxonomy).

Within genera are species. Species are the basic divisions of life. Members of a species can breed among themselves and produce viable and fertile offspring. Within species, however, there are often subspecies (or races). The subspecies of a species can interbreed, but they usually breed among themselves because of geographical isolation or behavioral differences. Subspecies often look different in coloration, pattern, size, and the like. Within subspecies (or species that are not divided into subspecies) are populations. According to Gretchen Daily and Paul Ehrlich, "[P]opulations are geographic entities within species that may be defined either ecologically or genetically." These are the basic breeding groups.

Subspecies and populations are where evolution happens. When genetically isolated for a long period of time, some subspecies and populations evolve into separate species. We must remember that evolution is a process over time. What we see today is a freeze-frame. The process of speciation may be at several stages for the variety of creatures we look at—anywhere from initial sorting into subspecies because of more or less isolated populations to clear division into separate species. Things are not at a standstill. Because of evolution, species are always changing (though some change very slowly).

All the populations or subspecies of a species are important because they usually carry a greater diversity of genes than does only one population or subspecies. If conditions change, a population or subspecies unable to adapt to the new conditions will become extinct. However, another subspecies or population within a species may have the characteristics that allow it to adapt to the new conditions thereby allowing it to survive and further evolve while the rest of the species dies out. Daily and Ehrlich write, "If, for example, there is rapid climate change, a widespread species with many populations is more likely to include individuals that are genetically suited to new conditions than a species with just a single local population."

For those who argue that species do not exist, that they are just arbitrary categories scientists have dreamed up, and that therefore we should not be concerned with the extinction of a "species," Niles Eldredge of the American Museum of Natural History responds, "When we compare lists of plants and animals drawn up by local peoples with those of professional biologists, it confirms our notion that species are real entities in the natural world, not just figments of Western-world classificatory imaginations."

Biodiversity is scientific shorthand for biological diversity. Reed Noss and Allen Cooperrider propose this definition: "Biodiversity is the variety of life and its processes. It includes the variety of living organisms, the genetic differences among them, the communities and ecosystems in which they occur, and the ecological and evolutionary processes that keep them functioning, yet ever changing and adapting. They consider four levels of diversity: (1) genetic, (2) population/species, (3) community/ecosystem, and (4) landscape. Within each of these levels are "compositional, structural, and functional components of a nested hierarchy." This is beginning to sound pretty complex. And it is. "Because nature is infinitely complex," according to Noss and Cooperrider, and as is well known to anyone who spends time outside watching, listening, and thinking.

Composition includes the genetic constitution of populations, the identity and relative abundances of species in a natural community, and the kinds of habitats and communities distributed across the landscape. Structure includes the sequence of pools and riffles in a stream, down logs and snags in a forest, the dispersion and vertical layering of plants, and the horizontal patchiness of vegetation at many spatial scales. Function includes the climatic, geological, hydrological, ecological, and evolutionary processes that generate and maintain biodiversity in ever-changing patterns over time.

Key to the diversity of life is the total number of species. Stuart Pimm and his University of Tennessee colleagues write, "Any absolute estimate of extinction rate requires that we know how many species there are. In fact, we do not." Furthermore, "the problems of estimating their numbers are formidable." As we have seen, some 1.4 million species have been scientifically named and described, but Pimm and his colleagues calculate that the total number of species is between 10 million and 100 million. Tropical insects, deep-sea creatures, bacteria, algae, and fungi are the main groups that could boost the total number of species well above 10 million.

However, we have a close idea of how many species exist for several taxa. Michael Soulé notes that for vertebrate animals, we have certainly identified more than half of all living species, "although ichthyologists are naming some 250 small species of fish each year, most of them small, freshwater species." For "vascular plants, vertebrates except fishes, [and] butterflies," we have probably named and described around 90 percent of the living species.

Five Great Extinctions

To understand the world today, we must first understand yesterday—in the case of extinction, deep yesterdays. Through careful study of geologic layers and the fossils in them, and armed with sophisticated dating tools, geologists and paleontologists have mapped out a remarkably detailed and precise past. We know, for example, that half a billion years ago—or, 570-some million years ago, to pin it down—a phenomenal blossoming in the diversity of life happened. During this Cambrian "explosion," most of the major phyla of animals appeared for the first time, and fungi and plants show in the fossil record soon thereafter.

During the two hundred years in which there has been a serious study of geology, the theories of uniformitarianism and catastrophism have slugged it out. Uniformitarianism argues that geological change takes place steadily and slowly; catastrophism argues that much dramatic change comes suddenly. Similarly, in evolutionary theory, some argue that most change comes slowly, and others argue that most change comes suddenly, pointing to episodes in the long, unimaginable time of the fossil record that represent catastrophic change when many species become extinct and afterward many new species arise. Of course, both catastrophism and uniformitarianism play a role: widespread extinction and the evolution of many new species associated with rare catastrophes, and "regular" or "background" extinction and evolution in between.