SPECIES become extinct for various reasons. Consider three main causes. Humans are indirectly responsible for two of them and directly responsible for the other.
Destruction of habitat contributes much to a species' decline. The Atlas of Endangered Species labels this "the most significant threat" but also "the most difficult to prevent." The world's booming population growth forces humans to encroach more and more on land that was formerly home to wildlife. A striking example of this comes from the world's rain forests.
'Within 40 years there will be no rain forests left' is the dire estimate that focuses attention on what many regard as a regrettable loss of valuable resources. In fact, nearly a quarter of all medicines known to the Western world have come from tropical rain forest plants. Although rain forests cover only an estimated 7 percent of the planet's land surface, they are home to four fifths of the world's terrestrial vegetation.
Logging operations and shifting patterns of agriculture rob the West African rain forests of their rich heritage of trees. Loss of timber on the Indian subcontinent has changed even the weather, reducing the rainfall in some areas but causing floods elsewhere.
As man fells trees to clear the ground for agriculture, the plants, animals, birds, reptiles, and insects die off. Harvard professor Edward Wilson estimates that the loss of forest amounts to 1 percent a year, and this dooms thousands of species to eventual extinction. It is feared that many species will vanish before they are even assigned a scientific name.
The situation is similar in the world's wetlands, another threatened habitat. Developers drain these areas so that they can build houses, or farmers convert them into arable land they can cultivate. In the last 100 years, as much as 90 percent of Europe's dry grassland has been taken over for agriculture. The loss of pasture in Britain over the last 20 years has prompted a 64-percent decline in the number of song thrushes.
Although Time magazine calls the island of Madagascar "a geological Noah's ark," its abundant variety of wildlife is in danger. When the population rises and international indebtedness grows, pressure on the island's inhabitants to turn forests into rice paddies increases. Because three quarters of the golden bamboo lemur's habitat has disappeared in the last 20 years, only 400 of these animals remain.
Man's radical change of land use certainly undermines regional wildlife. For another example, consider the Polynesians, who arrived in Hawaii 1,600 years ago. As a result of their activity, 35 species of birds became extinct.
Early settlers who came to Australia and New Zealand imported domestic cats, some of which became wild. According to New Scientist magazine, these feral cats now prey on 64 species of native Australian mammals. Together with imported European red foxes, they attack remnant populations of threatened species.
Hunting is no new phenomenon. The Bible account in Genesis describes the rebel Nimrod, a hunter who lived more than 4,000 years ago. Although there is no mention of his wiping out a whole species, he was nevertheless a formidable exponent of the hunt.—Genesis 10:9.
Through the centuries hunters have exterminated lions from Greece and Mesopotamia, hippopotamuses from Nubia, elephants from North Africa, bears and beavers from Britain, and wild oxen from Eastern Europe. "During the 1870s and 1880s, hunters killed a quarter of a million elephants in East Africa alone," reports the BBC listings magazine, Radio Times. "For half a century, Africa rang to the rapid fire of people of fame, fortune and rank, blasting away at elephants, rhinos, giraffes, big cats and whatever else caught their aim. . . . What seems quite shocking today was entirely acceptable behaviour then."
Return to the situation of the majestic tiger. Censuses in the 1980's indicated that conservation efforts had met with success. "Nonetheless, things were not as they seemed," notes the 1995 Britannica Book of the Year. "More careful counts revealed that previous censuses had been inflated by officials who either were in connivance with poachers or were merely eager to impress their superiors. . . . The underground trade in tiger parts flourished as the dwindling supplies pushed prices ever higher." Thus, in 1995, estimates of a Siberian tiger's value ranged from $9,400 to $24,000—no, not just for its prized skin but also for its bones, eyes, whiskers, teeth, internal organs, and sexual organs, all prized in traditional Oriental medicine.
Trade in elephant ivory, rhino horn, tiger skins, and other animal parts is now a multibillion-dollar black-market business, second only to drug smuggling, notes Time. And it is not limited to large mammals. In 1994 traditional Chinese medicine consumed a staggering 20 million sea horses, causing catches to fall by a reported 60 percent in two years in some areas of Southeast Asia.
It is not difficult to identify who is to blame when a species is hunted out of existence. Then, what about collectors? An endangered macaw, the golden conure, fetches a black-market trader in Brazil a reported $500. But when he sells it abroad, he gains more than three and a half times that sum.
Wars and their by-products, growing crowds of refugees, together with a spiraling birthrate, increased pollution, and even tourism, threaten endangered species. Sightseers in powerboats injure the dolphins they flock to see, and underwater noise from the boats can interfere with the dolphins' delicate echo-location system.