The po'ouli, a small honeycreeper found only on the island of Maui, went extinct on November 28, 2004 when the last bird died. Many of the surviving native Hawaiian forest birds are slipping towards extinction. (Photo credit unknown)

Despite the incredible importance of biological diversity, a grim scientific consensus is emerging: we are in the throes of an extinction crisis. Extinction is the irrevocable disappearance of a species everywhere on planet Earth. Unlike 'extirpation', which refers to a species disappearing from a particular jurisdiction (such as one state or country), extinction cannot be undone. Extinction is the killing off of all individuals, forever extinguishing the life of an entire species.

Currently there is little doubt left in the minds of professional biologists that Earth is faced with a mounting loss of species that equals or exceeds any mass extinction in the geological record. Human activities have brought the Earth to the brink of this crisis.

Dr. Paul R. Ehrlich is Bing Professor of Population Studies and president of the Center for Conservation Biology at Stanford University. (Photo courtesy Stanford)

As of 2000, a total of 539 species out of roughly 200,000 in the United States have been recorded by NatureServe as extinct or missing. Of these, 100 meet the stricter criteria of presumed extinct, with the remaining 439 falling into the possibly extinct category.

Dr. Edward Osborne Wilson is the Pellegrino University Professor Emeritus and honorary curator in entomology at Harvard University, where he has studied and worked for the past 54 years. (Photo courtesy Harvard University)

In the United States, there have been more extinctions of birds than of any other group of vertebrates - 2.3 percent of our endemic bird species are gone forever. The most current NatureServe data shows 30 bird pecies in all that are either presumed extinct or missing and possibly extinct. The majority of these birds (23 species) were native only to Hawaii.

Four species native to the continental United States are presumed extinct: the passenger pigeon, Carolina parakeet, the great Auk, and Labrador duck. Furthermore, in the past 100 years the United States has lost 2.2 percent of its endemic amphibians, 1.2 percent of the freshwater fishes, 1.1 percent of the plant species, and a staggering 8.6 percent of the freshwater mussels forever.

Worldwide, the situation is even worse. Because of the incredible density of species in tropical regions that are facing rapid deforestation, we may be losing species at a rate of 30,000 per year, or an overwhelming three per hour. Many biologists predict that coming decades will see the loss of large numbers of species.

One quarter of all mammals, including lions, tigers, rhinos, and most primates, could be declared extinct by the end of this century, along with one in eight bird species, and thousands of plant species. Habitat destruction is widely recognized as the primary cause of species loss.

Dr. Peter Raven is director of the Missouri Botanical Garden and adjunct professor at the University of Missouri, St. Louis University, and Washington University. (Photo courtesy St. Louis Earth Day)

Pollution, overexploitation, and global warming are also responsible for sending numerous species toward extinction. The future of humanity is inextricably tied to the fate of the natural world. In perpetuating this, the Earth's sixth mass extinction, we may ultimately compromise our own ability to survive. We need to steer this nation and lead the world towards a more sustainable path.

David Wilcove is professor of ecology and evolutionary biology and public affairs at Princeton University. (Photo courtesy Princeton)

In both its scope and its irreversibility, extinction is the most frightening, most conclusive word in our language. When a species has been declared extinct, not only have all its individuals died, but the possibility of any such individuals ever existing again has been foreclosed. The variety of life with which we share the earth is sadly in rapid decline. Life is rounded in biological diversity, and the fate of this diversity, which created and sustains us, is now in our hands.

Fortunately, we have the wherewithal and the tools we need to address this crisis. The most important of them is the Endangered Species Act. It is the alarm system our nation crafted to warn us when species are facing extinction. It is the measure by which we halt species' decline and give species a fighting chance at recovery. Viewing our looming extinction crisis as a crisis for humans as well as wildlife, the importance of the Endangered Species Act takes on even greater significance. In the face of this crisis, we must strengthen the Act and broaden its protections, not weaken them.

Thank you for considering our concerns and recommendations.
Sincerely,

• E.O. Wilson, Ph.D., University Research Professor, Emeritus
  Harvard University Cambridge, MA 02138
  
  
• Paul R. Ehrlich, Ph.D., Bing Professor of Population Studies
  President, Center for Conservation Biology Stanford University Stanford, CA 94305-5020
  
  
• Stuart Pimm, Ph.D., Doris Duke Professor of Conservation Ecology
  Duke University Durham, NC 27708
  
  
• Peter H. Raven, Ph.D., Director Missouri Botanical Garden
  St. Louis, MO 63166-0299 and Adjunct Professor, University of Missouri, St. Louis University, and Washington University.
  
  
• Gordon H. Orians, Professor Emeritus
  University of Washington Seattle, WA 98195-1800
  
  
• Jared Diamond, Ph.D., Professor of Geography
  University of California, Los Angeles Los Angeles, CA 90095-1524
  
  
• Harold A. Mooney, Paul S. Achilles Professor of Environmental Biology Stanford University
  Stanford, CA 94305-5020 and Chair, Millennium Ecosystem Assessment
  
  
• Daniel Simberloff, Gore Hunger Professor of Environmental Science
  University of Tennessee Knoxville, TN 37996 USA
  
  
• David S. Wilcove, Professor of Ecology and Evolutionary Biology and Public Affairs
  Princeton University Princeton, NJ 08544
  
  
• James T. Carlton, Director and Professor of Marine Science
  Williams College-Mystic Seaport Mystic, CT 06355"