One day each year our forebears praised Nature, from whom all blessings and most profits flow. Appropriately, they feasted. But had the pilgrims stuck strictly to native fare, their fish, meat and fowl would have been accompanied primarily by pecans, cranberries, Jerusalem artichokes and sunflower seeds.

In 17th-century America, indigenous vegetables were scarce, and today most of what we eat comes from seeds immigrants first brought from Mexico (corn), Peru via Great Britain (potatoes and tomatoes), Portugal (onions), Cyprus (caulifower), the Netherlands (carrots), France (peas), Germany (cabbage), Italy (broccoli and zucchini) and dozens of other countries. Even autumn's icon, the pumpkin, was probably imported from Latin America.

Last Thanksgiving, Congress acknowledged how much the quality of life in the United States depends on the preservation of flora and fauna everywhere. Under the new International Environment Protection Act, it established a federal task force on biological diversity and gave the departments of State, Interior, Agriculture and other agencies one year to propose ways the United States could help preserve the world's "genetic capital" -- the genes and germplasm needed to make sure that life remains various and new and that evolution is not derailed.

Congress is concerned mainly about losses of plant and animal species in developing countries, the world's great genetic reserves. In our land of plenty, competition between little snail darters and big water projects makes the newspapers, and the consequences of choosing one or the other are clear and well-researched. But in tropical countries, home to more than 40 percent of the planet's 10 million species, no more than a tiny fraction of life forms has even been identified, much less scrutinized for potential contributions to medicine, agriculture, industry and energy production. Indeed, as little is known today about the genetic wealth of vast stretches of Latin America and Africa as the Pilgrims knew about the Great Plains.

Unfortunately, critical losses have already occurred. For example, more than 40 percent of the world's tropical moist forests have been converted or destroyed. In such countries as Madagascar and Costa Rica, most of the remaining forests will be gone in 20 years if current rates of loss continue.

Amid these losses, hope resides in the great unknown. Five years ago, a perennial species of highly disease-resistant wild corn was discovered on a remote Mexican hillside. Zea dip a relative of our sweet corn, has the potential to transform world agriculture. Yet, a bulldozer or a few hungry goats could have ended its tenure on Earth. Similarly, in Madagascar, an inconspicuous little plant, the rosy periwinkle, was found to contain alkaloids that are now used against leukemia and other cancers.

Around the world, efforts to save species and ecosystems -- our common heritage -- will have to center on protecting these faraway lands. Experts have yet to decide how much and which land should be managed for conservation, but they agree that there is simply no substitute for conserving species in their own habitats. Recognizing this, governments and such private groups as the World Wildlife Fund and the International Union for Conservation of Nature and Natural Resources have already helped establish a worldwide network of more than 2,600 major parks and other protected areas. But far more is needed.

For the federal task force to meet the challenge, it must call for both increased support for conservation and management schemes and far more training and technical assistance in conservation. It's important to designate new parks and wildlife refuges; but it's also important to manage them well and meet the worldwide shortage of personnel trained to do the job.

Ironically, some of the world's biologically richest countries number among the economically poorest. In Madagascar, where the rosy periwinkle was discovered, GNP per capita averages $320 (compared with $13,160 in the United States). Indonesia is under the brunt of staggering population pressures, though it has valiantly designated nearly 15 percent of its land to national parks or wildlife reserves.

Clearly, all countries that invest in the preservation of biological diversity stand to gain -- witness today's menu. And if, as Harvard biologist E. O. Wilson says, biological impoverishment is the "one folly our descendants are least likely to forgive us," no doubt we will be thanked on future feast days for preserving life's wealth of biological possibilities.