IN BRAZIL, FARMERS clearing land for planting crops are destroying the habitat of the golden lion tamarin, a South American monkey, driving it to the edge of extinction. In India, poachers ruthlessly hunt the endangered snow leopard for its thick coat because they can earn more in one week from selling the pelt than they can from months of farming. In Southeast Asia, the development of once deserted coastal areas into tourist beaches has significantly eroded the habitat of the Mediterranean monk seal, reducing the number of animals left in the world to just a few hundred.

Scenarios such as these are occurring every day around the world: People's needs clash with the needs of other species. Almost inevitably, when these clashes occur, the nonhuman species is the loser, often reduced so greatly in number that it becomes endangered. Sometimes, it even becomes extinct.

Conflicting rights

The pressures...