All of us, especially biologists, share the disappointment over the failure of the National Zoo's giant panda to successfully rear her cubs. What may be overlooked, however, is that there is much more here than just a poignant "animal interest" story. Zoos and their captive-breeding programs have an important role to play in preserving endangered species, but Ling-Ling's case perfectly demonstrates the limitations of such efforts. Here we have a species unexcelled for popular appeal and enjoying maximum publicity; its precarious status in the world (because of the destruction of its habitat) makes captive-breeding programs highly desirable if not imperative; and the world's finest zoos and most competent zoo biologists are making heroic efforts to breed it. Yet success remains elusive.

The moral? We humans have limitless ability to destroy things, but very limited ability to undo the damage. So far, all our horses and men, zoos and zoo keepers have been unable to put the panda puzzle together again. Despite some success stories, the same is true of whooping cranes, California condors and other species. Even while dozens or hundreds of individuals remain alive, a species can already have started a slide to extinction that we may be utterly unable to stop. Many of our favorite animals may already be in this situation.

Instead of counting on our (often illusory) technical know-how for last-minute rescues, we must preserve larger chunks of unaltered real estate where healthy populations of organisms can keep themselves going without our help. We cannot hope to preserve any species indefinitely apart from its habitat.

DARYL P. DOMNING

Washington