A few years ago, Mills attended a meeting of a Western Governors' Association advisory group. There, he began to believe that the contemporary approach to conservation was too narrow. The governors wanted to know how to deal with climate change's coming impacts on their states' ecosystems. The group -- mostly policy people, along with a handful of scientists -- immediately converged on a standard tenet: Do whatever you can to facilitate species' movement northward and up in elevation. "It was astonishing to me," Mills said, "how quickly the conversation went that way." So he raised his hand and made a suggestion: "Let's talk some about adaptation."

Helping ensure that species can move if they need to -- by opening or protecting migration corridors, say -- is a basic, vital principle of conservation thinking in the age of global warming (and a big cause for Soulé, Mills' former advisor). Many species -- the pika, the rufous hummingbird, the sachem skipper butterfly -- have already reacted to climate change by shifting their ranges, and they are only the first responders.

It's not that Mills thinks the approach is wrong. As a respected conservation biologist who recently spent a year in Bhutan on a Guggenheim fellowship, helping train local scientists to monitor and protect their country's crucial populations of tigers and other endangered mammals, Mills understands as well as anyone the growing importance of migration routes. But he believes certain species may have other options.

Some animals and plants may not need to move at all: Changes to their habitat, while significant, could turn out to lie within the range of conditions they can already tolerate. "That's the part we know very little about," Mills said. "We just don't know very much at all about how much animals will be able to locally adapt," either through individual behavior or the process of evolution. A growing number of scientists are now studying this, drawing on evolutionary theory and genetics to answer questions about ecology and conservation.

The notion that some species may adapt perfectly well to their new living conditions -- changing what they eat, or where they nest, or when they turn white -- isn't an excuse to stop worrying about global warming, or an invitation to just sit back and watch what happens. It simply expands the range of policy options we need to consider. If local adaptation is possible through evolution, we need to think about ways to facilitate it -- such as ensuring large-enough gene pools for natural selection to act upon.

But this concept also points to more "extreme" policy options. "I'm not going to be that person," said Mills, "but a person could start talking about 'directed evolution.' Should we be taking hares from Colorado that turned white two weeks later and moving them up to Montana because they will be able to change their phenotype" -- their physical appearance --"in a way that tracks climate change? That very quickly becomes a discussion of, should we be playing God to try to direct evolution? It's an extreme -- and possible -- policy discussion."

Scientists have begun using the term "evolutionary rescue" to describe situations in which species can save themselves from oblivion by adapting to altered environments. In a study published in the journal Science last summer, Andrew Gonzalez and Graham Bell, biologists at Montreal's McGill University, set out to learn whether baker's yeast could evolve to live in saltier conditions. They found that over a relatively short period of time, the yeast evolved ways to deal with a major change to its environment. (The yeast's success in a saltier world depended on whether its population was connected to other populations, enabling genes to migrate, and how quickly salinity increased. Populations that experienced a slow rise in salinity, and had time to build up useful genetic mutations, were far better able to survive a sudden salt increase later.)

You can't exactly extrapolate from single-celled fungi to mammals. As Gonzalez put it, "There's no way we can use yeast to predict how the polar bear will fare." But it's a step toward understanding how evolution and ecology interact.

It's not easy to predict which species will successfully adapt to climate change. "If a species experiences lots of variability in temperature throughout the year, you'd predict it has a high tolerance to changes in temperature," said Chris Funk, a biologist at Colorado State University who is researching that hypothesis in insects. Bugs that live in the world's temperate mountains, such as the Rockies, could fare better than their counterparts in tropical mountains -- in Ecuador, for example -- because they've already evolved to tolerate greater fluctuations.

"The question right now," said Funk's colleague Amy Angert, a CSU biologist who studies plants, "is, do people need to be aiding dispersal" -- physically moving or transplanting plants and animals? "Or will species be able to change quickly enough, through evolutionary adaptation, in a way that will help offset that need? They don't need to rely solely on movement if they can run in place."

In his race to understand the hidden biology of the snowshoe hare, Mills is leaving no lodgepole log unturned. His collaborators include Paulo Alves, a Portuguese scientist who helped sequence the rabbit genome; Steve Running, the climate scientist, who is creating highly localized models that can predict the amount of snow for any day of the year at any specific spot in Mills' study area; and Jeff Good, a geneticist who recently joined the faculty at Missoula.

In the basement of a building not far from Mills' office, dozens of Siberian hamsters scurry about in plastic cages. The cute little dwarf hamsters, roughly the size of gerbils, are native to southern Russia and Kazakhstan. Like snowshoe hares, they change from dark to light and back again with the seasons. Good is breeding them, exposing them to various amounts of light, and studying things like their metabolic rate and how much heat they can retain -- all in an effort to decipher the genes and genetic pathways involved in seasonal coat-color change.

Crucial to unlocking the mystery of the morphing fur is one fairly basic question: Are hares genetically programmed to change at a certain pace?

One potential clue may lie in the Pacific Northwest. There, some groups of snowshoe hares stay brown all year. "Just about every coat-color-changing species you can name has some part of their range where they don't change," said Mills. This indicates genetic variation -- a version of a gene or group of genes that makes coats change color, and another version that keeps them the same year-round. It may be possible, then, for populations of hares to evolve different coat-color reactions.

"If they have potential to evolve," said Mills, "you've gotta think about facilitating the process of evolution." That means ensuring that there are lots of hares in each population, that they can mingle with hares from other populations, and that they aren't affected by "stressors" like diseases or clear-cuts.

The presence of genetic variation also gives researchers convenient tools to study the mechanisms of color change. With his Siberian hamsters, Good is hoping to find a gene that might control the transformation's onset. They could then look for a version of that gene in hares. If hares in Montana and Washington had different forms of the gene, it could prove that the color shift is genetic.

Even in places where most hares change color, some individuals remain brown all year round. So Mills and his colleagues are also asking, are there differences in gene expression, or hormone production, among the hares? It's a lot of steps, a lot of research, and a lot of "ifs."