Wyoming Attorney General Patrick Crank once argued that Preble's meadow jumping mouse was no more real than the jackalope, that taxidermist's fantasy -- half jackrabbit, half antelope -- that adorns bars and gas stations throughout the West. Populations of meadow jumping mice are scattered over half the continent, from the Carolinas to Alaska. Preble's, a three-inch beast with outsize feet and legs that leaps like a miniature kangaroo along streamsides and over wet grasslands, lives at the southwestern edge of jumping mouse territory, in an isolated patch of habitat between the foothills of southeastern Wyoming and the eastern edge of the Rockies in Colorado.

The fate of this obscure little creature has enormous implications for the new science of conservation genetics, the pace of development of the Rocky Mountain West, and the future integrity of the Endangered Species Act, which has been so vital in protecting iconic species such as the grizzly and the bald eagle. At the heart of the dispute among developers, politicians, scientists, and environmentalists is a simple question: Does Preble's mouse deserve federal protection, either as a unique subspecies or as a small, isolated group within the broader jumping mouse population?

Preble's was first identified as a subspecies in 1954, based on characteristics of coat color and skull size found in a handful of captured mice. In 1998 the mouse was formally listed as threatened under the act, mightily annoying many housing developers and landowners in Colorado and Wyoming, as well as their allies in government.

All parties to the dispute have invoked scientific studies to justify their positions. Opponents of the mouse's listed status cite research by biologist Rob Roy Ramey, who proposed in 2002 to use modern genetic techniques to test whether the listing of Preble's had a scientific basis. Ramey, who had already used genetic data to challenge (unsuccessfully) the protection of California's bighorn sheep, concluded that Preble's shared significant genetic traits with the Bear Lodge jumping mouse, its closest neighbor to the north. Expensive protection efforts, he said, were being wasted on a creature that was common. Embracing Ramey's findings, the State of Wyoming filed a petition with the U.S. Fish and Wildlife Service to have Preble's removed from the threatened list.

However, many scientists who subsequently reviewed Ramey's study saw serious flaws. They suggested that Ramey had misinterpreted his data and that his DNA samples, which came from long-dead skins stored in museums, might have been contaminated or too old to be reliable. James Patton, curator of mammals at the University of California-Berkeley's Museum of Vertebrate Zoology, says, "When you're trying to go after degraded DNA from museum specimens, it requires very careful control." Andrew Martin, an evolutionary biologist at the University of Colorado, agrees: "Ramey's study was hasty, his data suspect, and his interpretation of results biased."

In response to the controversy, the service commissioned a second study, from Tim King, a geneticist with the Biological Resources Division of the U.S. Geological Survey. Unlike Ramey, King used tissue from live mice, sampled many more specimens, and looked at four times as many DNA markers. His conclusion: Preble's is indeed a distinct subspecies, headed down its own evolutionary pathway and therefore deserving of protection. In July 2006 a panel of three independent experts in genetics and evolution unanimously endorsed King's findings. Since then the Fish and Wildlife Service -- a federal institution holding a political hot potato -- has remained silent, while an August deadline for a decision on Wyoming's delisting petition came and went without action.

The Endangered Species Act requires biologists to consider all available scientific data in their listing decisions, including basic information about an animal's distribution, ecology, and physical characteristics. However, genetic studies are so much in vogue that they may be given too much weight and too little critical examination. Sylvia Fallon, a conservation genetics fellow at the Natural Resources Defense Council, has reviewed more than 40 endangered species listing decisions that relied on genetic information over the past 10 years. "About 80 percent of the decisions corresponded with genetic findings," she says, "suggesting that genetics plays a large role in federal agencies' decisions.

"The problem with blind faith in genetics," says Fallon, "is that the type and amount of data you use really have an effect on the results. If you just look at a small portion of the genome, you're likely to see a lot of similarities and miss the differences between populations." While genetic studies hold great potential for conservation research, they are often subject to interpretation, in part because many biologists see diversity in nature as a spectrum, with one subspecies shading into another rather than being sharply demarcated. But this was not the case with Preble's, where the scientific consensus supported King's findings.

Fallon believes that agencies charged with making listing decisions should establish basic guidelines for the use of genetic data, requiring that studies use a variety of markers. But if a genetic study is less than conclusive, she says, biologists should rely more heavily on other types of data, such as ecology and distribution. As the Preble's saga suggests, if genetic studies -- regardless of their quality -- are seen as a magic bullet, they risk being misused in a politicized effort to weaken the legitimacy of the Endangered Species Act. And that would mean forsaking the world of science for the world of the jackalope.

-- Sharon Levy