Flying north over Luzon on a rare clear day three years ago I was reminded of Aldo Leopold's remarkable commentary on being a biologist. Leopold, the father of modern wildlife management, once said that a biologist is cursed with the ability to see a landscape not only for what it is but also for what it once was. Luzon, the largest island in the Philippines, is a patchwork that, from 30,000 feet, tells a sad story of destruction. Urban centers reach out into rice fields, the hand of humanity dominating the landscape. Nearly all of Luzon's native lowland forest is gone, and with it the remarkably diverse community of organisms it once supported.

Hundreds, perhaps thousands, of species have been lost, even before most were formally "discovered" by scientists. The riches these species could have provided -- for medicine, for ecosystem "services" such as cleaning the water or air, for the simple value of their existence -- are gone and can never be recovered.

I've returned to the Philippines several times since that first trip in 2005 and, as my experience has grown, my perspective of these remarkable islands has been refined. I now see the Philippines as a microcosm of the larger world, a crystal ball of sorts, that shows us one possible future for our planet.

A complex set of factors -- including colonial history, cultural patterns, religion, Cold War politics, corruption and globalization -- have combined to create today's Philippines, with its growing economic strength and festering weaknesses. Among the weaknesses is the environmental path on which this nation is traveling.

Slightly larger than Arizona, the Philippines is about the 70th largest country in the world. But it is home to 91 million people, ranking it 12th in population and near the top in population density. The population is growing rapidly, too, which puts enormous pressure on other species in this global hot spot of biodiversity.

The environmental statistics are ghastly. In addition to the nearly complete destruction of lowland habitats, only 5 percent of the original Philippine forest remains. The vast majority of uncatalogued Philippine species are disappearing faster than scientists can discover them.

Every year Larry Heany of Chicago's Field Museum of Natural History and his Filipino colleagues encounter mystifying new species of small mammals. Rafe Brown of the University of Kansas and Arvin Diesmos of the Philippine Natural History Museum regularly uncover amazing new amphibian species. Yet with so many habitats gone or going, it is almost certain that countless other species are lost before they can be found.

Many Americans might ask, "So what? How does it hurt me if a frog goes extinct on a mountainside in a remote island of some far-off tropical country?"

The reality is that the extinction of any individual species poses little risk to humanity.

Few species provide distinct and identifiable help to the human race such as the Rosy Periwinkle -- the plant from Madagascar that is the origin of the leukemia drug Vincristine. But some do.

The odds are tiny of discovering another Pacific Yew -- the North American plant that gave rise to the breast cancer drug Taxol. But some will be.

Still fewer species will provide a critical gene that could protect crops from novel diseases capable of initiating a global food crisis. Although some might.

The truth is that we could destroy much of the world's biodiversity and human populations would, in empirical terms, suffer only minimally. Only a few thousand or million of us would die -- a drop in the big bucket of humanity.

Even more important to many of us, few who would die would be North Americans. The statistical and demographic odds are pretty straightforward.

But the ethics of killing off innumerable species and destroying the habitats that sustain them are more complex and disturbing.

Whether you view the Earth as a gift from God, a mystical druidic place or simply as ours to use regardless of its origin, there is no rational reason to damage it to the point that we hand down a comparatively lifeless orb to our children. And there is no rational reason to believe that alone among Earth's creatures, we have the right to destroy all the others.

The loss of biodiversity also is directly relevant to us as a measure of habitat destruction. On a local scale in the Philippines, and in many other places on Earth, landslides caused by rain falling on steep, denuded hillsides wipe out entire villages, killing thousands of people at a time. On a global scale, habitat loss is a major cause of climate change. As forests are stripped from the landscape, so too is the Earth's ability to absorb carbon dioxide from the air, leaving it to drift in the atmosphere and trap heat from the Sun.

At the National Aviary our mission is to inspire a respect for nature through an appreciation of birds. Crucial to this mission is an understanding of the associations between wildlife and the natural systems that sustain them. To this end we are building a conservation and field research department to examine and mitigate the impact of human populations on the environment.

We work in the Philippines because it is one of the most biodiverse places in the world and because lessons from the Philippines can help answer questions about the future of our own nation and the rest of the planet.

One of the world's most endangered birds is the Philippine Eagle. This magnificent animal is among the largest of eagles and historically has lived almost exclusively in lowland Philippine forest. It faces a variety of threats from humans, all of which are made worse because of the Philippines' incredible population density.

This past February, and again in April, I returned to Manila and to the Philippine island of Leyte to attend workshops aimed at developing strategies aimed at saving the few remaining Philippine Eagles. The bird is what we in conservation call an "umbrella" species, one whose preservation helps protect multiple other species. It also is a "flagship" species, charismatic and emotive, a rallying call and symbol of the need to conserve its habitat and those of other species.

The springtime workshops generated a broad consensus about how to protect Philippine Eagles, including the need to breed them in captivity. But such measures are Band-aids. They might help us to preserve this remarkable bird while doing little to stanch the hemorrhaging of species after species. Largely undiscussed were the fundamental causes of biodiversity loss -- the number of humans that live on the land and the way they consume its resources. Addressing root causes is difficult anywhere, but especially in a country as poor and overwhelmed by humanity as is the Philippines.

Twenty years ago U.S. environmentalists predicted a future of gloom and doom, which most people think has not yet come to pass. But the future they described is arriving in the Philippines.

In North America, our population density is much lower and the environmental damage we have caused -- at least to our homeland -- is not yet so advanced. But we are getting there.

The American writer Edward Abbey once said, "Growth for growth's sake is the ideology of the cancer cell." His words still ring true.

So the question is, do we want a future of unmitigated growth in population and consumption? A landscape stripped of life and color that can no longer support us or our children?

The choice is ours, reflected at the individual level in the daily decisions we make about the resources we consume and at the governmental level by the wide-reaching decisions of our elected officials.