Dr. Michael Zasloff of the National Institutes of Health, commenting on his remarkable and beautiful discovery of the magainins in the skin of the African clawed frog, is quoted in The Post {July 30} as saying, "My political statement is going to be that you never know the ways of research. Let science be free. . . . We are not so smart as to know if what we do today is going to be important tomorrow."

Zasloff is right on target. But his work, a classic example of scientific method -- observation, wonder, conjecture, experimenting and testing -- has another lesson too: let nature be conserved. We are not so smart as to know whether we may not need tomorrow what we casually think of destroying today.

Human knowledge, like practically everything else in this complex world of ours, advances by a process that pits variety and proliferation against selection and elimination. People are always having ideas and making suggestions, and other people are always challenging and rejecting them; the ones that survive criticism and work out in practice are added to the stock of tested wisdom.

An obvious question is: Where do the proliferation and variety come from? In the case of ideas the answers aren't always helpful -- genius? serendipity? creativity? In fact it's rarer than we might think for something genuinely new to crop up, because we have inherited the products of some thousands of years of human imagination; a lot of scholarship consists of rereading and reinterpreting the work of our forebears.

Even in the humanities much of the new comes directly or indirectly from nature -- a feeling produced by an experience, an unexpected conjunction of events. But in science nature remains one of the great and apparently inexhaustible sources of novelty. One reason for this is that nature has had millions of years, not just thousands, to try out combinations of things. Most of them have been selected out, eliminated by adversity -- inhospitable conditions, scarcity of resources, competition. Those that remain offer miracles of adaptation, like the ability of the clawed frog to heal itself in the soup of bacteria it inhabits.

Sometimes the new is threatening. Nature has recently come up with the AIDS virus, for example. Very likely, out there somewhere is (or was) a natural substance that would help to counteract it. It isn't, as people sometimes piously think, that nature cunningly provides remedies, but rather that almost anything -- whether disease or remedy -- that can come into being and survive, through the endless recombinations of matter in the energy-rich biosphere, probably has provided remedies or will do so.

Nature, then, is the storehouse of the possible. We don't know what's in the storehouse, or whether it's of any use to us, until we look. Zasloff reminds us that there are still some pretty incredible things in there. But while he's recovering something medically invaluable from his frogs, other frogs, and plants and insects and birds and fish and other species by the thousands are being wiped out by unwise development, in Amazonia, in Africa and for that matter closer to home.

Everyone knows about the snail darter, the tiny fish for which environmentalists went to bat against the Tennessee Valley Authority. But not everyone appreciates that it's not the sanctity of a species as such, or even of life as such, that makes the strongest argument for this kind of conservation. At a much deeper level it's the irreversible loss of as yet unexplored natural structures. And no natural structure is ever, perhaps, fully explored. No extinction that could have been avoided is excusable.

It would be ironic -- but we'd never know -- if the very organism we'd needed for the cure of AIDS had been ploughed under by the bulldozers of some multinational conglomerate. Of course there are other approaches to medical research than the extraction of naturally occurring substances. But our imaginations aren't so fecund that we can afford to waste any source of variety, and we've learned that nature is not, in fact, an inexhaustible source.

It should not be the struggle it is for environmentalists to defend, case by case, the dwindling biological resources of the earth. Everyone, including the executives of governments and corporations, ought to be aware of how precarious these resources -- not just of living things but of the knowledge they promise -- have become. No one can be sure that he or she may not have cause, sooner or later, to be grateful to Zasloff and his magainins or the future discoveries his successors will make if we conserve their raw materials.

Let science be free, indeed: let it be taught, let it be funded. And as far as humanly possible (which may not mean economically profitable, and sooner or later we'll have to wake up to that), let the world it studies be kept intact for it against exploitation and depredation.

The writer is a professor of philosophy at The George Washington University.