Throughout history, many species of animals have been threatened with extinction When Europeans first arrived in North America, more than 60 million buffalo (水牛) lived on the continent. Yet hunting the buffalo was so popular during the 19th century that by 1900 the animal's population had fallen to about 400 before the government stepped in to protect the species. In some countries today. the elephant faces a similar challenge, as illegal hunters kill the animals for the ivory in their tusks.
Yet not all animals with commercial value face this threat(威胁).The cow, for example, is a valuable source of food, but no one worries that the cow will soon be extinct. Why does the commercial value of ivory threaten the elephant. while the commercial value of beef protects the cow?
The reason is that elephants are a common resource. While cows are private goods Elephants wander freely without any owners. The hunter has a strong motivation to kill as many elephants as he can find. Because illegal hunters are numerous, each has only a slight motivation to preserve the elephant population. By contrast, cattle live on farms that are privately owned. Each farmer makes great effort to maintain the cattle population on his farm because he harvests the benefit of these efforts
Governments have tried to solve the elephant's problem in two ways. Some countries, such as Kenya and Uganda, have made it illegal to kill elephants and sell their ivory. Yet these laws have been hard to put into effect, and elephant populations have continued to dwindle. By contrast, other countries, such as Malawi and Namibia, have made elephants private goods and allowed people to kill elephants, but only those on their own property.
With private ownership and the profit motive now on its side, the African elephant might someday be as safe from extinction as the cow. The ancient Greek philosopher Aristotle pointed out the problem with common resources: "What is common to many is taken least care of, for all men have greater regard for what is their own than for what they possess in common with others."