The history of life on earth has been punctuated by mass extinctions, the sudden disappearance of a large variety of plants and animals, possibly as the result of impacts by giant meteors or comets. In one of the most dramatic die- offs, 65 million years ago, more than half of all species on earth, including the dinosaurs, vanished. While experts debate the cause of these catastrophes and the probability and timing of the next one, scientists at the recent National Forum on BioDiversity warned that another sort of mass extinction is now taking place.
The current problem has been brought on not by celestial visitors but, as biologists agreed during the four-day meeting in Washington, by man. They attribute the developing ecological disaster to the systematic destruction of the world's tropical rain forests, particularly those in Latin America and Southeast Asia. Deforestation at the hands of loggers, farmers, ranchers and mining concerns, says Norman Myers, an environmental consultant based in Oxford, England, may result in the eradication of 1 million species by the end of the century. Harvard Professor of Science Edward O. Wilson concurs. "The extinctions ongoing worldwide," he says, "promise to be at least as great as the mass extinction that occurred at the end of the age of dinosaurs."
Perhaps most troubling to the scientists is the fact that plants and animals are disappearing faster than they can be found and described. Naturalists have cataloged 1.6 million species, a small fraction of the estimated 4 million to 30 million that remain undiscovered. While most of these unknown species are insects, even a creature as garrulous and brightly colored as a parakeet of the genus Pyrrhura (its species name has not yet been assigned) eluded researchers until it was first sighted in Ecuador in 1980. "No one knows the diversity in the world, not even to the nearest order of magnitude," says Wilson. "We don't know for sure how many species there are, where they can be found or how fast they're disappearing. It's like having astronomy without knowing where the stars are."
Tropical rain forests blanket about 7% of the planet and support nearly 50% of earth's known species. A single hectare (2.5 acres) of this lush arboreal growth may include more than 100 species of tree, each with its own interdependent colonies of plants and animals. But in the past several hundred years, the area of the globe covered by rain forest has decreased by some 44%. According to one U.N. study, 23,000 sq. mi. of rain forests are cut down every year -- an area about the size of West Virginia. One World Resources Institute staffer calculated that developers leveled 350 sq. mi. of rain forest while the biodiversity conference met.