We spend a couple of hours here with binoculars, map, and compass, scanning 100-mile visibility, scrutinizing the area below the rim and trying to find a trail we might travel another day. Although we don't know it, we're peering down into the place where a lost hiker is desperately trying to find the same trail and a freshwater spring midway along it. At this point he has been without water for three days. We don't see him stumbling through cholla and nopales cactus and writing farewell notes to loved ones—though he is likely staring up at the mirage of us silhouetted against the sky.
Ironically, this corner of the Chihuahuan Desert is lush at the moment, watered by rains two months ago that are still working their way through soils and roots and cells, so that many plants are blooming and an explosion of butterflies jams the breezes. The cacti are swollen with hoarded water. The Chisos oaks are dropping so many acorns that park rangers have closed trails where black bears are fattening on them. Countless millions of walking-stick insects are coupled in such dense mating congregations in the canopies of mesquites that entire trees appear to be walking through the sky. Everything is haloed in the golds, yellows, and greens of desert grasses, some taller than us, all bowed under heavy seed heads destined to feed and water kangaroo rats.
It is these same tall grasses that have woven closed the trail below and launched the lost hiker on his final wayward odyssey. Tomorrow, on his fourth day without water, he will be located by search-and-rescue personnel who find him alert and oriented, but too weak to stand. They administer oral and IV fluids, but he dies anyway. Like many before him, he succumbs to the peculiar capabilities of Homo sapiens that allowed him to enter Eden but not to survive its vicissitudes.
IN THE FINAL STAGES OF DEHYDRATION the body shrinks, robbing youth from the young as the skin puckers, eyes recede into orbits, the tongue swells and cracks. Brain cells shrivel and muscles seize. The kidneys shut down. Blood volume drops, triggering hypovolemic shock, with its attendant respiratory and cardiac failures. These combined assaults disrupt the chemical and electrical pathways of the body until all systems cascade toward death.
Such is also the path of a dying species. Beyond a critical point, the collective body of a unique kind of mammal or bird or amphibian or tree cannot be salvaged, no matter the first aid rendered. Too few individuals spread too far apart or too genetically weakened are susceptible to even small natural disasters. A passing thunderstorm. An unexpected freeze. Drought. At fewer than 50 members, populations experience increasingly random fluctuations until a kind of fatal arrhythmia takes hold. Eventually, an entire genetic legacy, born in the beginnings of life on Earth, is smote from the future.
Scientists recognize that species continually disappear at a background extinction rate estimated at about one species per million species per year, with new species replacing the lost in a sustainable fashion. Occasional mass extinctions convulse this orderly norm, followed by excruciatingly slow recoveries as new species emerge from the remaining gene pool until the world is once again repopulated by a different catalog of flora and fauna. From what we understand so far, five great extinction events have reshaped Earth in cataclysmic ways in the past 439 million years, each one wiping out between 50 and 95 percent of the life of the day, including the dominant lifeforms, the most recent event killing off the non-avian dinosaurs. Speciations followed, but an analysis published in Nature showed that it takes 10 million years before biological diversity even begins to approach what existed before a die-off.
Today we're living through the sixth great extinction, sometimes known as the Holocene extinction event. We carried its seeds with us 50,000 years ago as we migrated beyond Africa with Stone Age blades, darts, and harpoons, entering pristine Ice Age ecosystems and changing them forever by wiping out at least some of the unique megafauna of the times, including, perhaps, the saber-toothed cats and woolly mammoths. When the ice retreated, we terminated the long and biologically rich epoch sometimes called the Edenic period with assaults from our newest weapons: hoes, scythes, cattle, goats, pigs.
But as harmful as our forebears may have been, nothing compares to what's under way today. Throughout the 20th century the causes of extinction—habitat degradation, overexploitation, agricultural monocultures, human-borne invasive species, human-induced climate change—amplified exponentially, until now in the 21st century the rate is nothing short of explosive. The World Conservation Union's Red List—a database measuring the global status of Earth's 1.5 million scientifically named species—tells a haunting tale of unchecked, unaddressed, and accelerating biocide.
When we hear of extinction, most of us think of the plight of the rhino, tiger, panda, or blue whale. But these sad sagas are only small pieces of the extinction puzzle. The overall numbers are terrifying. Of the 40,168 species that the 10,000 scientists in the World Conservation Union have assessed, 1 in 4 mammals, 1 in 8 birds, 1 in 3 amphibians, 1 in 3 conifers and other gymnosperms are at risk of extinction. The peril faced by other classes of organisms is less thoroughly analyzed, but fully 40 percent of the examined species of planet Earth are in danger, including up to 51 percent of reptiles, 52 percent of insects, and 73 percent of flowering plants.
By the most conservative measure—based on the last century's recorded extinctions—the current rate of extinction is 100 times the background rate. But eminent Harvard biologist Edward O. Wilson and other scientists estimate that the true rate is more like 1,000 to 10,000 times the background rate. The actual annual sum is only an educated guess, because no scientist believes the tally of life ends at the 1.5 million species already discovered; estimates range as high as 100 million species on Earth, with 10 million as the median guess. Bracketed between best- and worst-case scenarios, then, somewhere between 2.7 and 270 species are erased from existence every day. Including today.
We now understand that the majority of life on Earth has never been—and will never be—known to us. In a staggering forecast, Wilson predicts that our present course will lead to the extinction of half of all plant and animal species by the year 2100.
You probably had no idea. Few do. A poll by the American Museum of Natural History finds that 7 in 10 biologists believe that mass extinction poses a colossal threat to human existence, a more serious environmental problem than even its contributor, global warming, and that the dangers of mass extinction are woefully underestimated by most everyone outside of science. In the 200 years since French naturalist Georges Cuvier first floated the concept of extinction, after examining fossil bones and concluding "the existence of a world previous to ours, destroyed by some sort of catastrophe," we have only slowly recognized and attempted to correct our own catastrophic behavior.
Some nations move more slowly than others. In 1992, an international summit produced a treaty called the Convention on Biological Diversity that was subsequently ratified by 190 nations—all except the unlikely coalition of the United States, Iraq, the Vatican, Somalia, Andorra, and Brunei. The European Union later called on the world to arrest the decline of species and ecosystems by 2010. Last year, worried biodiversity experts called for establishing a scientific body akin to the Intergovernmental Panel on Climate Change to provide a united voice on the extinction crisis and urge governments to action.
Yet despite these efforts, the Red List, updated every two years, continues to show metastatic growth. There are a few heartening examples of so-called Lazarus species lost and then found: the Wollemi pine and the mahogany glider in Australia, the Jerdon's courser in India, the takahe in New Zealand, and, maybe, the ivory-billed woodpecker in the United States. But for virtually all others, the Red List is a dry country with little hope of rain, as species ratchet down the listings from secure to vulnerable to endangered to critically endangered to extinct.
All these disappearing species are part of a fragile membrane of organisms wrapped around Earth so thin, writes E.O. Wilson, that it "cannot be seen edgewise from a space shuttle, yet so internally complex that most species composing it remain undiscovered." We owe everything to this membrane of life. Literally everything. The air we breathe. The food we eat. The materials of our homes, clothes, books, computers, medicines. Goods and services that we can't even imagine we'll someday need will come from species we have yet to identify. The proverbial cure for cancer. The genetic fountain of youth. Immortality. Mortality.
The living membrane we so recklessly destroy is existence itself.
BIODIVERSITY IS DEFINED as the sum of an area's genes (the building blocks of inheritance), species (organisms that can interbreed), and ecosystems (amalgamations of species in their geological and chemical landscapes). The richer an area's biodiversity, the tougher its immune system, since biodiversity includes not only the number of species but also the number of individuals within that species, and all the inherent genetic variation—life's only army against the diseases of oblivion.
Yet it's a mistake to think that critical genetic pools exist only in the gaudy show of the coral reefs, or the cacophony of the rainforest. Although a hallmark of the desert is the sparseness of its garden, the orderly progression of plants, the understated camouflage of its animals, this is only an illusion. Turn the desert inside out and upside down and you'll discover its true nature. Escaping drought and heat, life goes underground in a tangled overexuberance of roots and burrows reminiscent of a rainforest canopy, competing for moisture, not light. Animal trails crisscross this subterranean realm in private burrows engineered, inhabited, stolen, shared, and fought over by ants, beetles, wasps, cicadas, tarantulas, spiders, lizards, snakes, mice, squirrels, rats, foxes, tortoises, badgers, and coyotes.
To survive the heat and drought that killed the lost hiker, desert life pioneers ingenious solutions. Coyotes dig and maintain coyote wells in arroyos, probing deep for water. White-winged doves use their bodies as canteens, drinking enough when the opportunity arises to increase their body weight by more than 15 percent. Black-tailed jackrabbits tolerate internal temperatures of 111 degrees. Western box turtles store water in their oversized bladders and urinate on themselves to stay cool. Mesquite grows taproots more than 160 feet deep in search of perennial moisture.
These life-forms and their life strategies compose what we might think of as the "body" of the desert, with some species acting the role of the lungs and others the liver, the blood, the skin. The trend in scientific investigation in recent decades has been toward understanding the interconnectedness of the bodily components, i.e., the effect one species has on the others. The loss of even one species irrevocably changes the desert (or the tundra, rainforest, prairie, coastal estuary, kelp forest, coral reef, and so on) as we know it, just as the loss of each human being changes his or her family forever.
Nowhere is this better proven than in a 12-year study conducted in the Chihuahuan Desert by James H. Brown and Edward Heske of the University of New Mexico. When a kangaroo rat guild composed of three closely related species was removed, shrublands quickly converted to grasslands, which supported fewer annual plants, which in turn supported fewer birds. Even humble players mediate stability. So when you and I hear of this year's extinction of the Yangtze River dolphin, and think, how sad, we're not calculating the deepest cost: that extinctions lead to co-extinctions because most every living thing on Earth supports a few symbionts and hitchhikers, while keystone species influence and support a myriad of plants and animals. Army ants, for example, are known to support 100 known species, from beetles to birds. A European study finds steep declines in honeybee diversity in the last 25 years but also significant attendant declines in plants that depend on bees for pollination—a job estimated to be worth $92 billion worldwide. Meanwhile, beekeepers in 24 American states report that up to 70 percent of their colonies have recently died off, threatening $14 billion in U.S. agriculture. And bees are only a small part of the pollinator crisis.
One of the most alarming developments is the rapid decline not just of species but of higher taxa, such as the class Amphibia, the 300-million-year-old group of frogs, salamanders, newts, and toads hardy enough to have preceded and then outlived most dinosaurs. Biologists first noticed die-offs two decades ago, and since have watched as seemingly robust amphibian species vanished in as little as six months. The causes cover the spectrum of human environmental assaults, including rising ultraviolet radiation from a thinning ozone layer, increases in pollutants and pesticides, habitat loss from agriculture and urbanization, invasions of exotic species, the wildlife trade, light pollution, and fungal diseases. Sometimes stressors merge to form an unwholesome synergy; an African frog brought to the West in the 1950s for use in human pregnancy tests likely introduced a fungus deadly to native frogs. Meanwhile, a recent analysis in Nature estimates that in the last 20 years at least 70 species of South American frogs have gone extinct as a result of climate change.
In a 2004 analysis published in Science, author Lian Pin Koh and colleagues predict that an initially modest co-extinction rate will climb alarmingly as host extinctions rise in the near future. Graphed out, the forecast mirrors the rising curve of an infectious disease, with the human species acting all the parts: the pathogen, the vector, the Typhoid Mary who refuses culpability, and, ultimately, one of up to 100 million victims.
IT'S ONE OF SCIENCE'S GREAT IRONIES that many of today's feel-good nature stories come from researchers scrambling to catalog Earth's life-forms before they disappear. Breaking through the daily news of war and politics are the quiet announcements of novel species, including truly startling finds: a new catlike mammal in Borneo, a new phylum of wormlike creature, a new songbird in India, a snake that changes colors. Most astounding are the marine discoveries, including an average of three new species of fish a week since 2000.
The discovery of novel oceanic life-forms comes thanks to the Census of Marine Life, a network of 2,000 researchers in more than 80 nations engaged in a 10-year initiative to assess ocean life and its changes over time. The census is a veritable factory of revelations: life-forms thriving in 765-degree-Fahrenheit thermal vent waters in the Atlantic; species surviving below 2,300 feet of ice off Antarctica; a living shrimp believed extinct for 50 million years; pairs of mated seabirds flying 44,000-mile, figure-eight loops in the 200 days between nesting seasons, only occasionally resting on the waves; a fish school 20 million strong, the size of Manhattan, swimming off New Jersey.
The quest reveals a startling truth about our planet: that life thrives even in "lifeless" conditions, harvesting energy from sources we thought were ours alone—radioactive uranium, hydrogen, hydrogen sulfide, and methane—in places no one ever thought to look before, including between the crystals in rock. Some (archaea, bacteria, fungi) live nearly two miles below the Earth's surface. Some (cyanobacteria) in Antarctica live inside quartz clear enough to allow them to perform photosynthesis while escaping the weather. We call these organisms extremophiles because their worlds are uninhabitable to us, although many dwell in conditions that mimic what we know of the first life on Earth—in the eons before photosynthesizing plants freed oxygen from water to make our atmosphere.
On Hydrate Ridge 50 miles off the coast of Oregon, the mud on the bottom of the sea is more alive than dead. Thousands of feet below the surface, under pressures that would crush you and me, in temperatures that would turn our blood to sludge, worms, crustaceans, snails, bacterial filaments, and other life-forms as yet undescribed thrive in an environment largely devoid of oxygen and toxic with hydrogen sulfide and methane. This is the world of a cold seep, a seafloor ecosystem not discovered until 1984, where hydrocarbon-rich fluids bubble from the bottom to support unique biological communities fundamentally different from our own.
Seep life is driven not by photosynthesis (where plants use sunlight to power the food web) but chemosynthesis, whereby single-celled organisms use methane and hydrogen sulfide to fuel a gas-powered food web. The process also creates underwater reefs of carbonate rocks, something like coral reefs, which shelter otherworldly communities, including tubeworms with minimum life spans of 170 years. Scattered erratically across the bottom, cold seeps and their cousins, the hydrothermal vents, are the ocean's deepest, farthest flung, and perhaps most ancient communities.
Among their more enduring mysteries are exactly how these ecosystems become populated with life. There's evidence that whale falls act as critical steppingstones, or once did. In preindustrialized whaling days, when millions of behemoths were alive at any given time, their carcasses—which may endure and produce gases for up to a century—would have abounded in the deep, providing oases for the drifting larvae of seep organisms.
Most of the extremophile life-forms living at Hydrate Ridge are invisible to the naked eye—though through the dissecting microscope they're mind-bendingly huge: translucent worms with blood cells chasing each other through their vessels; miniature crustaceans like the alien from Alien. The mud from the seep reeks of sulfur. In fact the whole ship, the hardworking, far-sailing research vessel Atlantis, is full of mud that stinks of rotten eggs and flatulence. The goop comes aboard via the submersible Alvin, which cruises 2,500 feet below in a world so remote and so unwelcoming that only three people at a time can get to it in undersea assignments as coveted as space shuttle berths.
Weather permitting, the sub dives each morning carrying two researchers who spend the day in near-fetal positions, staring out portholes the size of grapefruit and breathing recirculated air infused with the smell of dirty socks. While the researchers work their task lists, the pilot manipulates Alvin's robotic arms, biopsying holes in the ocean bottom and collecting mud from around the seeps. Seven hours from launch, tired and dehydrated, all three aquanauts return to the surface looking a decade older.
Lisa Levin of the Scripps Institution of Oceanography is one of the foremost experts on these strange chemical worlds, and is chief scientist for one of the two research teams sharing the cruise. Her group is composed of 12 marine biologists and biogeochemists collaborating on a study of seep ecology and evolution. Petite, in jeans and Converse sneakers, Levin leans forward in pursuit of perpetual questions, then leans back to issue commands. Most of the time she just moves—fast and quiet, mud-spattered, clipboards in hand. She doesn't say much, maybe the result of working the deepwater for 27 years, making more than 70 dives into a quiet world no humans have words for.
She loves the bottom. It's possible to read mud, she says. I picture her peering out Alvin's porthole and tracking the infinitesimal movements of clams and sea stars.
We're sitting in Atlantis' library, a room familiar from many a Robert Ballard National Geographic documentary. It's six days into a three-week cruise, and her team is holding a heated powwow on mud allocation. Levin's job is peacemaker, and she tries hard to satisfy a grumpy biogeochemist who spends many hours alone in a radioisotope lab in a shipping container on a weather deck and wants more tube cores and fewer bio boxes to come up from the bottom. The other principal investigators seem willing to compromise, but to no avail.
Typical of my position on this cruise, I sit in a no man's land—in this case beside the accordion wall separating the library from the mess deck. Willingly or not, I can also monitor the conversation on the other side from a bunch of off-duty seamen swearing colorfully about their right to smoke cigarettes. They have lately been curtailed by smoke-sensitive scientists.
Levin's group is studying bristleworms, in particular why so many from the family Dorvilleidae inhabit these seeps (17 species so far, including 10 in one genus). Dorvilleid worms appear to be the underwater equivalent of the Galápagos finches that proved seminal in Charles Darwin's thinking on evolution. All 14 species of finches currently inhabiting the Galápagos radiated from a handful of ancestors blown to sea from South America, making landfall on the largely birdless islands, there to evolve into new species more like blackbirds, wrens, grosbeaks, woodpeckers, and mockingbirds than finches.
Having likewise arrived at the "islands" of underwater seeps and whale falls, the dorvilleid worms build ephemeral communities lasting as long as fuel is available. Like Darwin's finches, these worms are rapid responders, filling empty niches in no time at all, evolutionarily speaking, with fully functioning communities. They are also living examples of the kind of speciations that follow on the heels of mass extinctions.
Listening to the simultaneous griping and negotiating in the library and mess deck, it occurs to me that our floating community of 51 souls aboard Atlantis illustrates the divergent human impulses between competition and cooperation that will, in the near future, seal the fate of all Earth's species—counted, uncounted, ancient, and newborn.
WITHIN DAYS OF BOARDING ATLANTIS I'm learning to sort worms. Until today, the seas have been calm enough that staring at tiny living creatures magnified 12 or 50 times in petri dishes full of deoxygenated water has been a hypnotic, through-the-rabbit-hole exercise: foraminiferans like frosted Christmas-tree ornaments, spaghetti worms like exploded dissections gone bad, snails wearing circa-1960 bathing caps with bobbing bacterial filaments, all amid a snow-globe blizzard of gold, mica, and dragonfly-iridescent flakes. We work with paper-thin forceps and glass pipettes, yet these creatures are so delicate that many disintegrate when touched.
The seas have kicked up today, and some of the researchers normally glued to stools along the microscope bar have retired to ride out the bad weather in their bunks. Through my looking glass, the mud world in the petri dish reels from mini-tsunamis, worms flailing, snails spinning in shells, amphipods sprinting on swimmerets, bacterial filaments tying themselves into knots. It's a stomach-churning chaos presumably unknown in their deepwater home.
The truth is, I'm beginning to have qualms. I feel sorry for the worms, some of which, I keep remembering, might be more than 170 years old. My doubts crystallize when Ken Halanych, a marine biologist from Auburn University, tells me I have to dissect the worms out of the tubes they've built, and not just collect the ones floating free. This is all part of the sorting business, of course, seeing who lives where, correlating it with gas measurements of the mud layers they inhabit, quantifying the ecosystem, and searching for new species. Halanych is my friend at the dissecting scope, one of the only scientists, in fact, who seems enthusiastic about the hours I spend there and willing to teach me. But I can't do it.
Even though all these worms brought up from the bottom are destined to die anyway, to sacrifice themselves for science, as the grad students weakly joke, I still can't bring myself to yank them from their glovelike tubes. So I leave the dissecting scope and return to my mindless tasks of labeling Nalgene sample bottles, dubbing the Alvin's dive tapes, assembling tube cores for collecting mud.
Later, I overhear Victoria Orphan, a serene geobiologist from the California Institute of Technology and chief scientist of the other team aboard Atlantis, confess her own squeamishness about worm dissections. Maybe because of this, her chosen work is with the methane-eating bacteria and archaea that fuel the gas-powered food web at the seep. She observes these single-celled creatures through chemistry alone, death throes mercifully invisible.
Orphan's study addresses a pressing issue in the biodiversity crisis. In past warming eras, vast undersea deposits of methane ice may have melted, burping gas into the atmosphere and accelerating global warming. Some scientists theorize that a methane burp precipitated or at least contributed to the Permian-Triassic extinction event approximately 251 million years ago, killing 90 percent of all marine life, and 50 to 70 percent of all terrestrial life.
The fact that little methane seeping from the seafloor today ends up a greenhouse gas is because it's consumed on the bottom by the microorganisms around cold seeps, at least in part. In other words, Orphan's single-celled bacteria and archaea keep our world livable to some extent, and maybe to a critical extent in the years ahead—a reminder of the power of the meek, including the unknown power of the undiscovered meek, all 10 to 100 million species of them.
For a while, I switch to Orphan's lab—younger, noisier, more crowded, and less reverent. The students on her team name their tube cores for rappers and discuss the quantity of bling in their mud. They are powerfully, almost alarmingly, focused on their work, barely breaking to take note of schools of dolphins on our bow, humpback whales, soaring albatross—which they refer to, wistfully or dismissively, as charismatic megafauna.
I wonder if anywhere along their educational route they are encouraged to consider science's own footprint. The cold seeps we're visiting are frequented by teams from all over the world. Every submersible drops its ballast before ascending to the surface, and popular dive sites are slowly but surely being paved with metal brick weights. When I mention this, I'm told the metal will rust away in the seawater. When I point out that the seeps are anoxic environments, nearly devoid of rust-inducing oxygen, they blink. Like Mount Everest, Hydrate Ridge is littered with the refuse of exploration.
A week later, at Eel River Seeps off California, Alvin brings up big slabs of rock punctured with deep, perfectly round holes. The two returned scientists tell me of scores of holes as far as they could see down there. Everyone is excited by the doughnut rocks. There's speculation about bubbling methane "chimneys." Yet somehow the holes look familiar to me. They remind me of the tube cores I spend nights reassembling for the next day's dive. I walk to my station and return with a tube core and plug it into a doughnut hole. It's a perfect fit—with this hole, and that hole, and the next one. It fills all the holes I see and test as impeccably as a cookie cutter.
Only Anand Patel, a grad student on Levin's team, seems interested in this; the other scientists studiously avoid it. Since tube cores can sample soft sediments, not hard rock, Patel and I speculate the process of biopsying might prompt a reaction that turns the mud to stone, like scar tissue. He's interested in the chemistry of it. I'm interested in the possibility that all the scientists who love mud so much may be hastening its demise here.
But who knows? Maybe science's footprint will prove useful eventually. With the whale falls largely gone, perhaps a new life-form will evolve to feed on iron ballast.
BEFORE I ABANDON SORTING, I discover two worms I'm told are interesting, code for: They might be new species. One is secreted away in formaldehyde in its own vial. The other I'm told to transfer to my sort dish for Brigitte Ebbe, from the Zoologisches Forschungsinstitut in Bonn, Germany, to look at. Strangely, horrifyingly, I lose it. Clamped between the tips of my forceps, it's invisible to the naked eye, and somewhere along the four-inch pathway between examination dish and sort dish it disappears.
I realize this is why no one is enthusiastic about me sorting. I don't tell Brigitte—though someone else probably does. She's a member of a declining species herself, a taxonomist. At a glance, she can tell one identical-looking dorvilleid worm from another, a skill that's being supplanted by costly and time-consuming DNA analysis.
A few days later, in the same fashion, Brigitte loses what she knows to be a new species. Just like that.
THE LAST DAYS of the lost hiker in Big Bend's high desert mark the apex of a transient butterfly explosion. Countless millions waft across the desert like bouncing confetti. Southern dogfaces, fatal metalmarks, great purple hairstreaks, American snouts, common buckeyes. Splashes of yellow, orange, blue, purple, and metallic silver flutter by, each with characteristic flight styles: hopping, skipping, low to the ground, erratic as lightning, speedy as bullets.
Scattered among them are the strong, slow fliers with black-veined orange wings. These monarch butterflies are powering across 2,000 miles of North America en route to volcanic mountains in eastern Michoacán, Mexico. None have made this journey before, and each is at least three generations removed from an ancestor who made the reverse northward migration. Nevertheless, as many as 3 billion are homing there now with a surety the lost hiker must envy.
Crossing prairies, mountains, deserts, rivers, wetlands, and woodlands, the monarchs connect these places to each other—changing the locations they visit, being changed by them. Such transfluent energy is good for all parties involved, and satisfies a deep need of wild places. Because the truth is, wildernesses get lonely. Parks and reserves need social contact with others of their kind just as bees and kangaroo rats and people do. They may survive alone, but they do not thrive. Even preserves such as Yellowstone National Park continue to lose biodiversity despite their large size and protected status.
Until now, conservation efforts have rarely addressed this reality. The protected lands we've made so far, 102,102 sites covering 7 million square miles of earth and water, total less than 4 percent of the planet's surface. Many if not most of these isolated fragments are surrounded by hostile neighbors: farms, used-car lots, urban sprawl, clearcuts.
Segregated wildlands experience the same challenges as the dwindling members of an endangered species. Spread too far apart or too genetically weakened, they're cut off from the vital contact that renews and refreshes them, and likewise suffer debilitating arrhythmias in their demographics. Initial species losses are followed by overcrowding, then by population crashes, and insularization, with its attendant biodiversity decline.
The picture is complicated by mysterious realities: that many species will not populate a small wilderness even though it's big enough for their needs. Others will not cross the openings that fragment wilderness, particularly roads, which prove impermeable barriers to many from beetles to bears, either because they refuse to cross or because they die trying. Fragmentation also produces a dreaded edge effect by breaching the protective skin of wilderness, disrupting microclimates, allowing pathogens, alien species, and human development inside, then sealing the edges through the scarification of weed growth.
Ten thousand feet up in Mexico's Sierra Chincua, in dense forests of oyamel firs, arriving monarchs seek protection under heavy evergreen boughs. For millennia, these high-altitude forests transformed monarchs into winter survivors, able to weather five months of deep freeze beneath the insulating canopy. Thanks to the seasonal sanctuary, monarchs can complete the other phase of their lives, and in doing so cinch vast areas of North America from Canada to Mexico, literally connecting the landscape one milkweed bush at a time—helping milkweed to thrive and making monarchs one of the most abundant butterflies on Earth. Species connected to the milkweed economy also prosper, including aphid-farming ants, honeybees, orioles, and moths. Although monarchs do not appear on the Red List, conservation biologists consider their migration an endangered biological phenomenon—a recognition that biodiversity also embraces large temporal and geographical scales: the migration of wildebeest in the Serengeti, caribou in Canada and Alaska, saiga in Outer Mongolia, the synchronous flowering cycles of bamboo in Asia (some at 120-year intervals), the 17- and 13-year cicada emergences in North America, and the annual travels of 1 billion individual songbirds of 120 species between Canada and the tropics.
These are nature's big shows, and they're important to biodiversity. If one phase of a biological phenomenon is disrupted, the consequences are likely to ripple farther and wider than a local species extinction. The gutting of Mexico's oyamel forests by logging, slash-and-burn agriculture, charcoal manufacture, and mismanaged ecotourism do not endanger monarchs overall, because nonmigratory populations inhabit the tropics. Yet the squandering of the forests is a threat to the milkweed trading route, and thereby to the body of North America.
The fragmentation of the Sierra Chincua woodlands is already disrupting the microclimates the migrating butterflies need to survive. At the present rate of deforestation, there'll come a winter night not far in the future when a surge of cold air sinking down from Canada will overwhelm the threadbare forests, scattered too thinly to blanket the butterflies. The only monarchs that know the way north, trapped at 10,000 feet in lonely fragments of wilderness, will die. Just like that.
TWO WEEKS AFTER LEAVING BIG BEND, along Interstate 10 in Arizona, I happen to see a flock of big birds lumbering on the reluctant elevator of an early morning thermal—white birds with black flight feathers, afloat with outstretched necks and trailing legs, flapping with a characteristic flick on the upbeat, yodeling. They're whooping cranes, 30 adults and juveniles rearranging themselves into a lopsided V and heading west.
It's a remarkable sight since it represents about 6 percent of the total world population of whoopers. It's also a confusing sight, since at this time of year they should be well east of here en route from Canada to the Texas Gulf Coast...though one of the things I've learned from decades of working with animals in the wild is their ability, with the flip of a wing, to rewrite expectation. But, most of all, it's a poignant sight, these 30 whoopers, the descendants of a breeding population of only 16 birds in 1941. "Because it is a wild, wary, wilderness bird," wrote John K. Terres, longtime editor of Audubon magazine, "it could not stand the intrusion of mankind."
Their decline is an extinction textbook. They suffered the conversion of prairies and wetlands to farms. They were hunted for meat. By 1922, the last known breeding pair in Saskatchewan died, leaving only one winter population in Texas whose summer nesting grounds remained an intractable mystery for most of the 20th century. In 1954, the colony was finally tracked to remote Wood Buffalo National Park in Canada's Northwest Territories, about as far as they could get from human beings without leaving planet Earth.
Since then, the cranes have been rehabilitated in every way we know, as well as in ways we've made up as we went along, forging techniques now considered the blueprint for endangered species recovery. Yet whoopers today number about 500 birds: 350 in the wild, the rest in captivity. They're only marginally less vulnerable than they were in 1941. A bird flu, an oil spill, a hurricane. Seventeen died in the tornadoes that struck Florida in February, highlighting how tenuously this tribe survives.
I SPOT THE WHOOPERS en route to Arizona's Chiricahua Mountains, one of the 40 ranges collectively known as the Sky Islands—a landscape currently at the forefront of endangered species efforts. The Sky Islands are located at the convergence of four great ecoregions: the lower-elevation Sonoran Desert and the higher elevation Chihuahuan Desert, as well as the temperate Rocky Mountains and the subtropical Sierra Madre Occidental, which together funnel life from north and south, introducing pop-up biodiversity through changes in altitude. Some 4,000 plants and half the breeding birds in North America reside here.
The Chiricahuas are a Sky Island range 20 miles wide, 40 miles long, and rising nearly 10,000 feet. Composed of striking pink rock, they're the eroded remains of volcanic ash and pumice that erupted 27 million years ago, since cut by wind and water into whimsical feats of balance the Apaches called the Land of Standing-Up Rocks. The range is dissected by deep drainages that harbor unlikely kaleidoscope forests of sycamore, oak, juniper, pine, cypress, and madrone, alongside yuccas, agaves, chollas, ferns, mushrooms, grasses, and mosses.
It's a botanical mash-up, part mountain, part desert, part grassland. I can hardly take it in, moving fast, on foot, in pursuit of Kim Vacariu, who sets the pace down a trail that crosses and recrosses the flood-tumbled rocks of the South Fork of Cave Creek. He hikes lightly in what amounts to his back yard, telling me stories of the Chiricahua Apache, who, in their last year of existence here, down to only 39 men, women, and children, eluded one-quarter of the U.S. Army by running full speed at night across the desert floors linking the Chiricahuas to other Sky Island refuges.
Vacariu is the western director of the Wildlands Project, the conservation group spearheading the drive to rewild North America—to reconnect remaining wildernesses (parks, refuges, national forests, and local land trust holdings) through corridors, on a continentwide scale. The idea came into being 15 years ago, a hybridization between activism and science, when Earth First founder Dave Foreman teamed with Michael Soulé, professor emeritus at the University of California-Santa Cruz and one of the founding fathers of conservation biology.
Rewilding is bigger, broader, and bolder than humans have thought before. Many conservation biologists believe it's our best hope for arresting the sixth great extinction. E.O. Wilson calls it "mainstream conservation writ large for future generations." Because more of what we've done until now—protecting pretty landscapes, attempts at sustainable development, community-based conservation, and ecosystem management—will not preserve biodiversity through the critical next century. By then, half of all species will be lost, by Wilson's calculation. To save Earth's living membrane, we must put nature's shattered pieces back together. Only megapreserves modeled on a deep scientific understanding of continentwide ecosystem needs hold that promise. "What I have been preparing to say is this," wrote Thoreau more than 150 years ago, "in wildness is the preservation of the world." This, science finally understands.
The Wildlands Project calls for reconnecting wild North America in four broad megalinkages: along the Rocky Mountain spine of the continent from Alaska to Mexico; across the Arctic/boreal from Alaska to Labrador; along the Atlantic via the Appalachians; and along the Pacific via the Sierra Nevada into the Baja Peninsula. Within each megalinkage, core protected areas would be connected by mosaics of public and private lands providing safe passage for wildlife to travel freely. Broad, vegetated overpasses would link wilderness areas split by roads. Private landowners would be enticed to either donate land or adopt policies of good stewardship along critical pathways.
It's a radical vision, one the Wildlands Project expects will take 100 years or more to complete, and one that has won the project a special enmity from those who view environmentalists with suspicion. Yet the core brainchild of the Wildlands Project—that true conservation must happen on an ecosystemwide scale—is now widely accepted. Many conservation organizations are already collaborating on the project, including international players such as Naturalia in Mexico, national heavyweights like Defenders of Wildlife, and regional experts from the Southern Rockies Ecosystem Project to the Grand Canyon Wildlands Council. And Vacariu reports that ranchers are coming round, one town meeting at a time, and that there is interest, if not yet support, from the insurance industry and others who "face the reality of car-wildlife collisions daily."
At its heart, rewilding is based on living with the monster under the bed, since the big scary animals that frightened us in childhood, and still do, are the fierce guardians of biodiversity. Without wolves, wolverines, grizzlies, black bears, mountain lions, and jaguars, wild populations shift toward the herbivores, who proceed to eat plants into extinction, taking birds, bees, reptiles, amphibians, and rodents with them. A tenet of ecology states that the world is green because carnivores eat herbivores. Yet the big carnivores continue to die out because we fear and hunt them and because they need more room than we preserve and connect. Male wolverines, for instance, can possess home ranges of 600 square miles. Translated, the entire state of Rhode Island would have room for only two.
Vacariu leads me to a bend in Cave Creek where clusters of maple trees shed red leaves into the eddies, a place as ephemerally beautiful as a haiku. The scars of flash floods surround us, yet tranquility abides. The first campaign out of the Wildlands Project's starting gate is the Spine of the Continent, along the mountains from Alaska to Mexico, today fractured by roads, logging, oil and gas development, grazing, ski resorts, motorized backcountry recreation, and sprawl.
The spine already contains dozens of core wildlands, including wilderness areas, national parks, national monuments, wildlife refuges, and private holdings. On the map, these scattered fragments look like debris falls from meteorite strikes. Some are already partially buffered by surrounding protected areas such as national forests. But all need interconnecting linkages across public and private lands—farms, ranches, suburbia—to facilitate the travels of big carnivores and the net of biodiversity they tow behind them.
The Wildlands Project has also identified the five most critically endangered wildlife linkages along the spine, each associated with a keystone species. Grizzlies in the lower 48, already pinched at Crowsnest Pass on Highway 3 between Alberta and British Columbia, will be entirely cut off from the bigger gene pool to the north if a larger road is built. Greater sage grouse, Canada lynx, black bears, and jaguars face their own lethal obstacles farther south.
But by far the most endangered wildlife linkage is the borderlands between the United States and Mexico. The Sky Islands straddle this boundary, and some of North America's most threatened wildlife—jaguars, bison, Sonoran pronghorn, Mexican wolves—cross, or need to cross, here in the course of their life travels. Unfortunately for wildlife, Mexican workers cross here too. Of late, Vacariu says, these immigrants have been traveling up the Chiricahuas. Men, women, and children, running at night, one-gallon water jugs in hand.
The problem for wildlife is not so much the intrusions of illegal Mexican workers but the 700-mile border fence proposed to keep them out. From an ecological perspective, it will sever the spine at the lumbar, paralyzing the lower continent.
HERE, IN A NUTSHELL, is all that's wrong with our treatment of nature. Amid all the moral, practical, and legal issues with the border fence, the biological catastrophe has barely been noted. As if extinction is not contagious and we won't catch it.
Vacariu and I drive to Douglas, Arizona, just south of the Chiricahuas. There's already an older border fence here, a hodgepodge of Marine Corps steel landing ramps, concertina wire, and steel beams, all scrappily patched and welded, burrowed under in places, then reinforced with dirt piles that look like cat scratchings. Here and there doors are cut through. Elsewhere, stark white crosses stand as markers of someone's death. Every quarter mile or so, we encounter a lone Border Patrol officer napping in his SUV.
We drive the American side along a dirt road. The fence has been upgraded with motion detectors and floodlighting fit for a gulag. Lights are as much an abrasive to biodiversity as a road or a fence, blinding amphibians, disorienting birds, and disrupting the hunting behaviors of carnivores from snakes to coyotes. We motor to the end of the wall, to the Chiricahuas' eastern Sky Island neighbor, the Peloncillo Range. To the east, the border is marked only by a barbed-wire livestock fence.
Because we can, we step across into Mexico, into a desert stretching as far as the eye can see. It looks grazed but otherwise untouched, though the fence line is littered with empty water bottles: the fill-up station before a trip north into the dry land where travelers don't ask for sustenance.
Jaguars also cross here, Vacariu says, including a recent sighting of what some think might be a female, raising the possibility of the first jaguar births north of the border in decades. But the new fence calls for a far more imposing set of parallel walls surrounding a fully paved two-lane highway. If built, it will end the tentative, hopeful forays of jaguars and much else northward into these parts. Concerned, the Wildlands Project and Defenders of Wildlife organized workshops between government agencies and conservation organizations, hoping to put ecological concerns on the security agenda.
When we step back through the fence to the U.S. side, a weary-looking young man approaches on foot from a dusty track in the Peloncillos. In Spanish, he asks if this is the United States. Yes. Where exactly? We point at Douglas just down the road. He brightens, taps the Kellogg's logo on his vintage 1950s shirt, and says he's headed back to work. I tell him there are sleeping Border Patrol agents on his route. He's not worried.
I have no doubt that not even the Great Wall of Arizona will stop him. Invariably, the youngest, fittest, and most ambitious men and women of Mexico will find a way around. All the new fence will really arrest is the flow of nature's immigrants.
IF, AS SOME INDIGENOUS people believe, the jaguar was sent to the world to test the will and integrity of human beings, then surely we need to reassess. Border fences have terrible consequences. One between India and Pakistan forces starving bears and leopards, which can no longer traverse their feeding territories, to attack villagers.
The truth is, wilderness is more dangerous to us caged than free—and has far more value to us wild than consumed. Wilson suggests the time has come to rename the "environmentalist" view the "real-world" view, and to replace the gross national product with the more comprehensive genuine progress indicator, estimating the true environmental costs of farming, fishing, grazing, mining, smelting, driving, flying, building, paving, computing, medicating, and so on. Until then, it's like keeping a ledger recording income but not expenses. Like us, Earth has a finite budget.
Past sunset in Big Bend's Chisos Mountains we sit around camp in near darkness, alert to the fact that we'll be sleeping in the home of hungry mountain lions and bears—recently returned to the United States from across the Rio Grande. Suddenly the hush is cracked by an eerie sight. A flock of 50 ravens flies overhead, literally wingtip to wingtip in rare unravenlike silence except for their feathers zippering the quiet. They circle above us—a squadron of black ghosts—before sliding from view over the precipice of the south rim.
We speculate, in darkness, on this strange encounter. Are the ravens evading peregrine falcons, as some birds do, in tight, soundless flights? Are they preparing for night travel? It's a mystery we don't want to solve. Not really. Through awe, nature corrodes human hubris. May we evolve to feed on that ballast.