THE EXTINCTION of species is nothing new; neither is the role of humans in hastening the process. A new report from the United Nations Environment Program notes that the prehistoric colonization of the area around the Pacific and Indian oceans by humans, and by animals like rats, dogs, rabbits or pigs who live near humans, may have led to the extinction of as many as one-fourth of the world's bird species.
That fact helps lend some perspective to recent findings that the rate of extinction of species is speeding up. Yet no one knows exactly how many species of plants and animals inhabit the Earth; by one estimate, only about 13 percent, or some 1.75 million of a total of about 13 or 14 million, have been scientifically described. Of those species we do know about, some 112 bird and mammal species have become extinct since 1810, nearly three times the rate of extinction recorded between 1600 and 1810.
As human beings become more numerous, there is less room for the forests, wetlands and other ecosystems to remain sufficiently undisturbed to support the vast array of life they are capable of supporting. Does it matter?
Scientists say it does. A wide diversity of life forms keeps the planet healthier -- and provides resources to keep humans healthier, too. Pharmaceutical companies are acutely aware that vanishing rain forests take with them countless undiscovered weapons in the fight against diseases old and new. Often the weapon stems not just from one species, but from the complex interaction of different organisms.
A case in point: During its caterpillar stage, a moth found in Mexico and northern South America feeds exclusively on trees and vines of a particular genus, Omphalea. When the caterpillar population exceeds a certain level in any area, it defoliates the plants. That spurs the trees and vines to produce protective chemical toxins, which cause the moth to migrate elsewhere -- leaving behind a toxic plant compound which has shown promising results against the AIDS virus in laboratories.
We humans have so fully populated the Earth that we are now a tempting target for viruses and other microscopic enemies. The U.N. report on Earth's dwindling biodiversity -- and on ways to stem the losses -- brings welcome attention to the fact that the land and seas around us contain an arsenal of useful tools that, once lost, can never be replaced.