But the shadow has fallen again. This time the problem is neither as concentrated nor as easily tackled as that of pesticides or pollution. This time the problem is the disappearance of nature itself.
Biodiversity loss is now lining up to be the greatest man-made crisis the world has ever known. Biologists call it the Sixth Great Extinction, or the Holocene extinction event, after our current geologic time period. (The five previous extinction events all came before the evolution of Homo sapiens, apparently triggered by a cataclysmic event or combination of events, such as a fall in sea level, an asteroid impact, volcanic activity.) Mass extinctions are different in kind from what specialists term “background” extinctions, the rare but regular loss of between one to ten species per decade. Two hundred and fifty million years ago, the most catastrophic, “the Great Dying” of the Permian age, wiped out over 90 percent of all species in the oceans and70 percent on land. It took tens of millions of years for life to recover.
The current extinction rates are alarming enough. Preeminent biologist E. O. Wilson believes we stand to lose half of all species by the end of this century. Of the 45,000 species evaluated in the 2008 Red List, issued by the International Union for Conservation of Nature, 17,000, or nearly forty percent, may vanish. Conservative estimates suggest that the extinction rate in the modern era has reached a hundred to a thousand times normal.
Climate change further exacerbates biodiversity loss, and each of these crises magnifies and intensifies the effects of the other. As the planet warms and dries in some areas, species are pushed out of niches they currently occupy. Some of them, including the emperor penguin in Antarctica and the polar bear in the Arctic, have nowhere to go. Worldwide, as water temperatures rise and ponds dry, exposing amphibians and their eggs to ultraviolet radiation and disease, a third of those species are threatened with extinction. As people burn forests for agriculture and grazing, as they replace native vegetation with mono-culture crops that discourage cloud formation, they alter the dynamic relationship between the earth’s surface and the atmosphere, initiating further drying and warming, and further species loss.
Why do species matter? Why worry if some go missing? Part of the answer lies in the relationships coming to light between creatures like the canyon coyotes and the chaparral birds. After the nineteenth century’s great age of biological collecting, when collectors filled museums to bursting with stuffed birds and pinned beetles, the twentieth and twenty-first centuries have proved to be an age of connecting. Biologists have begun to understand that nature is a chain of dominoes: If you pull one piece out, the whole thing falls down. Lose the animals, lose the ecosystems. Lose the ecosystems, game over.
This was the essential insight of conservation biology, a new scientific field launched with the determination to identify threats to ecosystems and to design the methods to deal with them. E. O. Wilson has called it “a discipline with a deadline.” The Society for Conservation Biology, founded in 1985, became one of the fastest-growing scientific organizations of its time, bringing together diverse specialties from ecology and population genetics to sustainable agriculture and forestry, revolutionizing the once sleepy field of natural history.
The tremendous variety of species held in wilderness areas, particularly the tropics, is our bank and lifeline, our agricultural and medical insurance policy. Three-quarters of the world’s food supply comes from twelve plant species, but those species are dependent on thousands of others: pollinators (insects, bats, birds), soil microbes, nitrogen-fixing bacteria, and fungi. The tropical rain forests contain a pool of genetic diversity for important food crops, a source for vital new strains that can be hybridized to fight pests and diseases. Botanists are combing the planet for wild ancestors of soybeans, tomatoes, hard wheat, and grapes, believed to contain valuable genes for drought tolerance and other characteristics, but much diversity has already been lost. Genetic engineering alone cannot replace what hundreds of millions of years of evolution have given us. Wild replacements for pineapples, pomegranates, olives, coffee, and other crops lie in biodiversity-rich areas that must be saved.