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- Herausgeber: Icon Books
- Kategorie: Lebensstil
- Sprache: Englisch
- Veröffentlichungsjahr: 2022
'An original, wide-ranging and carefully researched book ... contains important lessons for humanity.' Mark Cocker, The Spectator A fascinating insight into climate change biology around the globe, as well as in our own backyards. Hurricane Lizards and Plastic Squid is the first major book by a biologist to focus on the fascinating story of how the natural world is adjusting, adapting, and sometimes measurably evolving in response to climate change. Lyrical and thought-provoking, this book broadens the climate focus from humans to the wider lattice of life. Bestselling nature writer Thor Hanson - author of Buzz (a Radio 4 'Book of the Week') - shows us how Caribbean lizards have grown larger toe pads to grip trees more tightly during frequent hurricanes; and how the 'plasticity' of squid has allowed them to change their body size and breeding habits to cope with altered sea temperatures. Plants and animals have a great deal to teach us about the nature of what comes next, because for many of them, and also for many of us, that world is already here.
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Praise for Hurricane Lizards and Plastic Squid
“A masterful storyteller, Hanson interweaves his own formative experiences into the narrative … The book’s forward-looking approach seems intended to encourage readers’ curiosity about climate change, with the notion that, once suitably informed, they will feel compelled to take action.”
— Science
“Hanson is an affable guide and storyteller, with a knack for analogy, a sense of humor and the natural curiosity of a scientist.”
— Jonathan Balcombe, The New York Times
“Close study of how animals are living with climate change reveals that humans are at the center of more things than we realize … [Hanson makes] glaringly clear that we are not in command of what we have set in motion. The biodiversity and versatility on display in the animal kingdom of which we are part have lots to teach us. To remain at home in the world, we too will need to change.”
— The Atlantic
“[Hanson is] an ideal guide to a topic that might otherwise send readers down a well of despair… . The challenge feels over-whelming, and as a single concerned citizen, much feels out of my hands. Yet Hanson’s words did inspire me to take a cue from the rest of the species on this warming world to do what I can.”
— Science News
“With contagious curiosity, Hanson nimbly avoids pedantic, moralistic admonishments. Nature-lovers will be thrilled to see science so vividly described, and will marvel at the incredible ingenuity of creatures across the globe.”
— Publishers Weekly
“Thor Hanson’s clear-eyed science writing meets its best topic yet in this book. While governments and publics joust over climate change, biologists studying all the ways wild animals are already responding to it are five steps ahead of the game. Hanson takes his readers on a tour of this cutting edge in our rapidly-changing world. Yes, there are looming extinctions. But before you wring your hands in despair, read this book. As it always has, life finds a way.”
— Dan Flores, New York Times–bestselling author of Coyote America
“Hanson writes a hopeful and compelling story exploring various climate adaptations in the animal and plant worlds with a rare combination of engrossing clarity and robust interrogation. He encourages us to lift our own voices and actually assert change. Each enormously engaging essay proves what I’ve known for some time: Thor Hanson is a marvel whose enthusiasm for this planet is utterly contagious.”
— Aimee Nezhukumatathil, New York Times–bestselling author of World of Wonders
“One of our finest writers of literary natural history takes on the most crucial topic of our times—how will life itself respond to a warming world?—and brings back answers both utterly beguiling and strangely reassuring. This is arguably the most significant discussion of the biology of global warming I know, brought to us in the intelligent, wise, and beautiful prose we’ve come to rely upon Thor Hanson to deliver. If you read only one book on climate change this year, let it be this one.”
— Robert Michael Pyle, PhD, author of Wintergreen and Nature Matrix
“Thor Hanson is not just a scientist and writer—he is a gifted raconteur, filled with wonder and love for the wild earth. In HurricaneLizards and Plastic Squid, Hanson brings his unique perspective to this time of ecological crisis. Rather than just a warming planet, we find stories from the infinite and varied tangle of life, with every being—from bacteria to birds—seeking to adapt with ingenuity and resilience. This book bears witness to the individual stories so often lost in climate headlines, and invites us all to live with greater depth and awareness as we seek a hopeful path forward.”
— Lyanda Lynn Haupt, author of Rooted and Mozart’s Starling
Praise for Buzz
“Popular science at its most accessible: fun, fascinating and full of engaging pen portraits of the scientists and bee enthusiasts [Hanson] meets in the course of his research.”
— Melissa Harrison, The Guardian
“Since finishing the book I can’t walk past flowers without looking for bees. Buzz is illuminating, inspiring and irresistible: in short, the bee’s knees.”
— Francis Wheen, Mail on Sunday, Books of the Year
“Entertaining, well-informed … The real joy of the book is Hanson’s celebration of the range of lifestyles and extraordinary capabilities that bees possess, other than honey production.”
— Mark Cocker, New Statesman
“Popular science at its intelligent best.”
— The Economist
“Thor Hanson is a gifted story teller and naturalist…. This book really is the buzz about bees, and it’s destined to become a natural history classic.”
— Stephen Buchmann, author of The Reason for Flowers
“[Thor Hanson] is a charmingly enthusiastic bee fanatic and his book is a pleasure to read.”
— Daily Mail
“Surely among the finest nature writers of our time—whatever subject Hanson turns his hand to, the result is spellbinding.”
— Katrina Van Grouw, author of The Unfeathered Bird and Unnatural Selection
Hurricane Lizards and Plastic Squid
How the Natural World is Adapting to Climate Change
Thor Hanson
vFor my brother
Contents
Author’s Note
Introduction
Thinking About It
I am thinking, brother, of a prediction I read …
—William ShakespeareKing Lear (c. 1606)
I pitched my tent in the dark and the pouring rain, hoping I’d scrambled far enough up the slope to be out of the range of flash floods. Crawling inside was like entering a washing machine on spin cycle—wind lashed the wet fabric inches from my up-turned face, rattling the tent poles and spraying me with a fine mist. As the storm raged late into the night, and as my sleeping bag slowly soaked through, I began to second-guess my choice of activities for the spring break holiday.
I could have joined friends on a fishing trip, partaking in the sort of beery camaraderie that is more or less expected of college students during the final term of their final year. Instead, I decided at the last minute to make a stack of sandwiches, throw xiimy camping gear into a backpack, and head out to explore a remote corner of the Southern California desert that would one day become Joshua Tree National Park. It never occurred to me to pack waterproof tarps and rain gear—I was going to the driest place in North America! But while that first night was among the most miserable I’ve ever spent in a tent, its rain produced a wondrous result. Thirsty seeds and perennials sprang to life all around, and as the skies cleared in the days ahead I found myself hiking through that rarest of landscapes—a desert in bloom. My field notes describe a profusion of gold, blue, and purple blossoms, splashed like brushstrokes across the red earth and granite. I recorded over two dozen species in flower, from bright daisies and bluebells to less familiar varieties with names straight out of a Western novel: scorpion-weed, Spanish needle, and jackass clover. The plant that I wrote about most, however, didn’t have flowers at all. It bore decorations of a different kind.
I came across it growing alone in a narrow mountain pass, an old Joshua tree with branches that spread upward like the tines of a rake. Even from a distance, I could see that it shimmered oddly as it swayed in the breeze, and when I got close I knew the reason. Prevailing winds, channeled by rocks and elevation, had festooned the tree with trash. There were plastic bags, food wrappers, strands of baling twine, and no fewer than three helium party balloons in varying stages of deflation. “Happy Birthday,” one still read, shaking feebly at the end of its tangled ribbon. At the time, I compared the litter to fruit—a strange harvest so deep in the wilderness, fifty miles from the nearest sizable town. Decades later, I can still picture that tree and it still strikes me as a potent symbol for our far-reaching impacts on the natural world. But I recognize now that the problem wasn’t so much in what the windy air had deposited; it was in the air itself. xiii
FIGURE I.1. The Joshua tree is the world’s largest variety of yucca and grows exclusively in the Mojave Desert, a region changing rapidly as the climate warms. National Park Service / Robb Hannawacker.
Two months after that hike, I collected my undergraduate diploma and began a career in conservation biology. By chance, my graduation day occurred just as delegates were gathering for the 1992 Earth Summit in Rio de Janeiro, Brazil, where they would introduce and sign the first international treaty on climate change. It wasn’t a new concept—scientists predicted the impact of carbon emissions in the nineteenth century, and the phrase “global warming” had been common in environmental circles for xivyears. But the Earth Summit marked a turning point, the moment when climate change officially transitioned from a scholarly topic to a global public concern. In the years ahead, mounting evidence and calls for action would clash repeatedly with politics, particularly in the United States. There would be climate change protests, campaigns, and debates, not to mention that ultimate sign of collective angst: a string of Hollywood disaster movies. As a scientist, I never doubted the urgency of the issue, but I still struggled alongside everyone else to find a meaningful response. The irony of flying to far-flung field sites in places like Africa and Alaska did not escape me—I wasn’t exactly going to cancel out burning all that jet fuel by carpooling to the airport. But beyond such hazy worries, the climate problem felt remote at first, alarming but intangible, like a diagnosis in want of a symptom.
My reaction was typical. When it comes to climate change, there is a glaring disconnect between what we know is happening and what we seem able or willing to do about it. Longtime climate campaigner George Marshall explored this disparity in his excellent and aptly titled book Don’t Even Think About It. He noted how the human brain is perfectly capable of simultaneously understanding and ignoring abstract threats. When consequences seem distant or gradual, the rational part of our mind simply files them away for future reference and rarely triggers the more instinctive, emotional pathways associated with quick action. (We do better responding to physical threats, such as spear thrusts and charging lions, the sorts of immediate problems that our ancestors evolved with.) Marshall’s book ends with a laundry list of strategies for bridging that mental gap, many of which rely on something else the human brain is known for: storytelling.
When complex ideas are attached to a narrative, they immediately become more relatable. There is a reason why Plato framed so many of his philosophical dialogues around the drama of the xvtrial of Socrates, and why Carl Sagan chose to teach astrophysics from the glowing deck of an imaginary spaceship. Stories engage parts of the brain left untouched by facts alone, releasing chemicals that demonstrably change the way we think, feel, and remember. Learning about climate change is no different, and much of how we understand and act upon it will ultimately boil down to stories—those we tell, and, in another sense, those that it tells to us. My own perspective has shifted dramatically over the course of my career, transformed from detachment to utter fascination by narratives—not necessarily the ones found in headlines or policy debates, but by those playing out in some place more fundamental: the lives of the plants and animals I’ve studied.
Like biologists everywhere, I’ve watched climate change leap from background to forefront in project after project, because while people may have spent the past thirty years struggling to even think about a response, every other species on the planet has simply been getting on with it. Their reactions remind us that the outcome of every future climate scenario, no matter how complex or contentious, relies ultimately on one thing: how individual plants and animals respond to change. If every living thing on Earth got along just as well in any situation, then tweaking the weather wouldn’t matter in the slightest. Conditions for life, however, are anything but universal. Biodiversity stems from specialization—millions of species intimately adapted to the nuances of their own particular niche. Altering those conditions forces a response, and when that alteration comes quickly it can restructure whole ecosystems. The speed of climate change is a large part of what makes it a crisis. But for scientists, farmers, birdwatchers, gardeners, backyard naturalists, and anyone with an interest in nature, it also creates an opportunity. Never before have people been in a position to witness such a radical biological event, and if the early results are any indication, it has a great deal xvito teach us. Because just as the planet is changing faster than anyone expected, so too are the plants and animals that call it home.
This book is an exploration of that emerging world, where species from beetles to barnacles (and even Joshua trees) are meeting the challenge of rapid change head-on—adjusting, adapting, and sometimes measurably evolving, all in real time. Apart from a brief introduction to carbon dioxide, this book does not include detailed explanations about why and how the planet is warming; nor does it address the many controversies that continue to hamper progress on policy. Those are vital topics, but they have been extensively covered in the press and elsewhere. (For an excellent summary, I refer readers to Andrew Dessler’s lucid and evenhanded text, Introduction to Modern Climate Change.) Instead, this book delves into what some are calling a distinct new field of study—climate change biology. Beginning with chapters about how scientists discovered that the climate was changing, and that greenhouse gasses were the culprit, the narrative then follows three questions at the heart of this emerging field: (1) What challenges does climate change create for plants and animals? (2) How do individuals respond? and (3) What can the sum of those responses tell us about the future—theirs as well as our own?
In reading this book I hope you will come to agree with me that climate change deserves our curiosity as well as our concern. It’s hard to solve a problem if we aren’t even interested in it. Fortunately, this is a crisis that happens to be deeply and profoundly fascinating, affecting the biology of the world around us in ways worth thinking about every day. I am writing these words, for instance, on a fine spring afternoon, with my office door flung wide open to the buzzing of insects in the orchard and the trill of warblers newly arrived from points south. Rising global temperatures touch every aspect of this scene, from the pace of pollination and migration to the fact that my door is open and that I’m xviicomfortable wearing a short-sleeved shirt. Understanding biological responses to climate change can help us find our place within it, and it’s my hope that the stories in this book will inspire as well as inform. Simply put, if bush crickets, bumblebees, and butterflies can learn to modify their behaviors, then it stands to reason that we can too. Plants and animals have a great deal to tell us about the nature of what comes next, because for many of them, and also for many of us, that world is already here. xviii
PART ONE
The Culprits(Change and Carbon)
If you want to make enemies, try to change something.
—Woodrow WilsonAddress at the Salesmanship Congress (1916)
As a prospective graduate student, I spent months looking for the right doctoral program—touring various university campuses, writing emails, talking on the phone, and meeting with potential advisors. I knew I’d found the right match when I interviewed with a professor who didn’t bother showing me his lab or office until after we’d spent a day together out in the woods. “Let’s go for a walk,” he said, “and see if we have anything to talk about.” It was a lesson in the importance of fundamentals, making sure that the basics are covered before getting too far into a complex endeavor. With that in mind, the first chapters of this book focus on essentials that often get glossed over: how scientists started thinking about change and carbon dioxide in the first place …2
3
CHAPTER ONE
Nothing Stays the Same
All change in habits of life and of thought is irksome.
—Thorstein VeblenThe Theory of the Leisure Class (1899)
I heard them before I saw them, screeching and croaking from somewhere overhead like a pair of deranged roosters. The noise went on and on, and it struck me as preposterous that any sane person would want to keep one of these birds inside their house. Yet demand for the pet trade had helped transform the great green macaw from a commonplace species into an endangered species. I’d spent three years studying their main food source in what was once prime habitat, but to actually spot a macaw required two days of backcountry travel by bus, river launch, and finally, a motorized canoe. So when two birds suddenly launched themselves from a treetop and soared out over the river, I felt the thrill of a moment long anticipated, and I also knew immediately what made pet fanciers so willing to overlook all that racket and clamor. Even from a distance, the macaws’ brilliant green plumage shone in the sunlight, rippling with accents of crimson, chestnut, and bronze, and framed by wide blue wings, as if every color 4within view, from sky to river to rainforest, had been distilled and brought to life in feathers.
I watched with satisfaction as the birds crossed from the Nicaraguan to the Costa Rican side of the river and disappeared over a row of low hills. It seemed fitting to close out my research in Central America by glimpsing evidence of the avian resettlement it was designed to encourage. Though I hadn’t studied macaws directly, my work showed that almendro trees—whose almond-like nuts the birds rely upon—could persist and reproduce in patches of forest indefinitely, connected to one another over long distances by the busy pollination efforts of bees. That finding helped justify a new law protecting almendros throughout the lowlands of eastern Costa Rica, where cattle ranching and fruit production had left the rainforest divided by pastures, roads, and cropland. People hoped that if the right kind of trees remained, the macaws might return, repopulating old haunts from their stronghold to the north, in the large Nicaraguan nature reserve that I’d traveled so far to visit. As it turned out, that process was already well under way. In the years ahead, hundreds of birds would set off on the same flight I’d witnessed, crossing the San Juan River and heading south to once again make great green macaws a regular sight (and sound) in parts of Costa Rica. It was briefly held up as a conservation success story—the returning birds not only found food in almendros, they also nested and raised chicks in hollows within the trees’ massive trunks. But scientists soon realized that the fate of the macaws and their favorite tree was an even better example of something entirely different, and far more consequential.
Looking back, I see now that the phrase “climate change” did not make a single appearance in the many proposals, reports, and peer-reviewed papers associated with my almendro research. At the time, it didn’t seem relevant to such a specific and local biological study. But I did receive one suggestive hint along the way, 5 delivered in an offhand comment from another scientist working out of the same field station. Her data showed how almendro trees responded to hot weather by increasing their rate of respiration, the process plants use to get oxygen to their cells. In a sense, the trees were panting. This and other signs of stress didn’t bode well in a warming world, and when climate modelers later began making predictions about Central America, it was clear that almendros were in a tight spot. “The trees you studied will be gone by the end of the century,” one expert told me, explaining how the species’ survival depended on shifting its range upward in elevation to find the temperatures it preferred. Suddenly, the most important result of my work was something I’d published almost as an afterthought—the fact that large fruit bats could disperse almendro seeds in leaps of a half mile (eight hundred meters) or more. Would that be far enough and fast enough to beat the heat? Would the bats be moving in the right direction? Could almendros even establish themselves in higher forests already crowded with trees? And what did all this mean for the macaws, who were expected to simply fly north to cooler climes, unconstrained by the slow pace of seed dispersal? Instead of a tidy relationship between parrots and trees, the macaw-almendro story has become yet another case study in uncertainty, symbolic of a planet in flux.
As a biologist, perhaps I shouldn’t have been surprised by the sudden plight of almendro trees. After all, change lies at the heart of evolution, and evolution is the heart of biology. The very word evolve comes from a Latin verb meaning “to unroll,” and every organism is a product of that constant motion. Species wheel into existence, adapting and often giving rise to new things along the way, before eventually winking out as the world moves on around them. Even if almendros fail to reach the foothills and disappear altogether, that would be perfectly normal; extinction is the fate of all species. I knew this, but still found it head-spinning to think 6 that my giant study trees—some measuring ten feet (three meters) in diameter—might soon be gone. It was more than sentimentality or simple surprise. Resistance to change is considered a hallmark of the human psyche. Experts link it to our instinctive sense of comfort and safety in the familiar, combined with a need for social cohesion and consistency. The result is a common sentiment neatly captured in the words of cartoon everyman Homer Simpson: “No new crap!”
FIGURE 1.1. The great green macaw is the largest parrot in Central America, where its relationship with almendro trees is now uncertain. P. W. M. Trap, Onze Vogels in Huis en Tuin (1869). Biodiversity Heritage Library.
I certainly wasn’t the first person unsettled by the idea of a changing environment. For most of human history, people preferred 7to dismiss the notion entirely and regard the natural world as something immutable. Certainly, there were seasons and the occasional drought or flood, but the land and the seas and the creatures within them were fixed. Greek philosopher Parmenides went so far as to prove that change was impossible. Nothing comes from nothing, he argued, nor can anything come from what already exists, because, “what is … is.”
Aristotle found some wiggle room in that argument by suggesting that objects might change form so long as their underlying essence persisted. An acorn could grow into an oak tree, for example, or bronze could be melted and cast to form a statue. This accounted for the obvious processes of change encountered in daily life, without challenging the idea of nature as something absolute. Aristotle also proposed organizing the natural world into a strict hierarchy, with what he perceived as simpler forms like plants near the bottom and more sophisticated things like animals (and Greek philosophers) on top.
Later scholars embraced and embellished this notion, finding rungs on the ladder for any newly discovered species, as well as things like precious metals, planets, stars, and even various types of angels. The paradigm held for nearly two thousand years, and it was echoed in the taxonomic ranking system developed by that great cataloger, Carl Linnaeus, who noted in 1737 that all true species “have been assigned by Nature fixed limits, beyond which they cannot go,” and that their number “is now and always will be exactly the same.” Even as Linnaeus wrote those words, however, new ideas were already shaking the foundations of the old worldview. Fittingly, the evidence that change was not only common, but in fact a prime mover in nature, came from stone, a substance that had always been placed at the very bottom of Aristotle’s hierarchy. 8
FIGURE 1.2. This sixteenth-century illustration depicts the natural world as an immutable “Great Chain of Being,” ascending from rock and soil to plants, animals, and humanity. Images of heaven and hell (and their inhabitants) frame the scene above and below. Diego Valadés, Rhetorica Christiana (1579). Getty Research Institute.
Few readers are thought to have made it through all 1,548 pages of James Hutton’s 1795 opus, Theory of the Earth, not to 9 mention its 2,193-page companion, Principles of Knowledge. But even the Scotsman’s daunting wordiness couldn’t obscure the power of his central geological theme—that the bedrock of continents and islands was formed from constant erosion and sedimentation, cemented and then uplifted by the heat of the Earth. Instead of a static landscape, he proposed an ongoing “succession of worlds,” continually unfolding over huge spans of time. It was a radical thought, but one supported by ample evidence then coming to light in the mine shafts proliferating across Great Britain. Demand for coal and metals to feed the Industrial Revolution had inadvertently opened a window into deep time, exposing layers of bedrock with ancient stories to tell. Some contained marine fossils, bolstering Hutton’s notion that rocks—even those found high up on hills and mountains—had formed from ocean sediments. Other stones held the remnants of strange plants or unfamiliar animals, suggesting that life, as well as landscapes, had looked quite different in the distant past. This raised an obvious and troubling question: Where had those species gone?
Extinction was a purely hypothetical concept until French naturalist Georges Cuvier started thinking about elephants. Shortly after Hutton upended the idea of permanence in geology, Cuvier took aim at its biological counterpart. His meticulous examination of fossil elephant teeth showed that various mastodons and woolly mammoths were distinctly different—not only from one another, but from all living elephant varieties. He called them lost species, and because elephants are enormous and impossible to overlook, it was hard for doubters to argue that mammoths and mastodons were still out there somewhere, waiting to be noticed. (Interestingly, mastodon enthusiast and third US president Thomas Jefferson suggested just that, instructing members of the 1804 Lewis and Clark Expedition to scour the American West for animals that “may be deemed rare or extinct.”) Cuvier spent the 10 rest of his career driving the point home, describing extinct forms of everything from turtles and sloths to pterodactyls. But one of his most lasting contributions was the observation that species didn’t just wink out one by one. Sometimes whole communities disappeared from the fossil record all at once, replaced by a vastly different group of organisms in shallower, younger layers of rock. He famously held this up as a challenge to Hutton’s ideas about gradual geological change, arguing that ancient landscapes (and all their inhabitants) had instead been repeatedly destroyed by a series of floods or other catastrophes. As a general theory, known as catastrophism, it was eventually debunked. Aside from the occasional earthquake or volcano, most processes in geology do indeed play out slowly, just as Hutton had suggested. But Cuvier’s fossils showed that extinction events could at least occasionally be abrupt and widespread—the first indication that the natural world was capable of rapid change. It was an idea that the greatest naturalist of the next generation would always struggle to reconcile.
Hutton’s and Cuvier’s theories challenged religious norms as well as scientific dogma, and decades of contention followed. Many scholars countered with biblical arguments—if rocks contained traces of marine life, then they must have formed during the Flood, and any unfamiliar fossils were simply creatures that hadn’t made it onto the ark. Others accepted the concept of ancient worlds, but offered different theories about rock formation, fossil origins, and what caused the transition from one era to the next. Such debates fascinated the young Charles Darwin, who devoted much of his early career to geology. He called himself a “zealous disciple” of the Hutton viewpoint, as popularized and expanded upon by the great nineteenth-century geologist (and Darwin’s good friend) Charles Lyell. Darwin collected thousands of fossils and rock specimens during his voyage on the Beagle—often at the expense of zoological pursuits—and looked forward 11to visiting the Galápagos Islands not for their finches, but because “They abound with active Volcanoes.” He later drew on fossil evidence to support his thinking about species formation, and so did Alfred Russel Wallace. Joint publication of their papers on evolution by natural selection in 1858 (and Darwin’s The Originof Species the following year) did for biology what Hutton had done for geology—embracing change as fundamental, and giving it a convincing mechanism. But both men considered the pace of that change to be slow and incremental, neatly complementary to the emerging consensus on gradual geological forces like erosion and sedimentation. More than a century would pass before 12biologists began to grasp how quickly things could happen—in the environment, in evolution, and in the critical ways those forces interact. Once again, the first insights came not from studying modern creatures, but from an understanding of stone, fossils, and vast spans of time.
FIGURE 1.3. In Exhuming the First American Mastodon, artist and naturalist Charles Willson Peale immortalized his own 1801 excavation of a creature originally dubbed the American incognitum. Sketches of the fossil eventually reached Georges Cuvier in Paris, who confirmed it as a mastodon, one of the first species definitively established as extinct. Maryland Historical Society.
In 1971, two newly minted paleontologists introduced the phrase “punctuated equilibrium” at the annual meeting of the Geological Society of America. Friends and collaborators since graduate school, Niles Eldredge and Stephen Jay Gould presented their idea as a novel answer to a question that had long plagued the field of paleontology: Where were the missing links? If evolution was indeed a slow and steady process, then shouldn’t the fossil record be filled with gradual transitions from one form to the next? Instead, fossil species tended to appear abruptly and then persist, more or less unchanged, through layers of rock representing thousands or even millions of years. Darwin had been well aware of this problem, calling it “the most obvious and gravest objection which can be urged against my theory.” He devoted a full chapter in TheOrigin of Species to an explanation that people had relied upon ever since: “the extreme imperfection of the geological record.” Because rocks form only under the right conditions, and only a tiny fraction of rocks contain fossils, the vast majority of species (and the transitions from one to another) have gone unrecorded. In Darwin’s memorable description, “I look at the natural geological record, as a history of the world imperfectly kept … only here and there a short chapter has been preserved; and of each page, only here and there a few lines.” Eldredge and Gould didn’t dispute the limits of the geological record, but they suggested something else that would make transitional fossils rare: rapid evolution. If new species arose in quick bursts of change instead of slowly emerging over eons, then there simply wouldn’t be time—from a geological perspective—for their transformations to leave a trace. 13
Punctuated equilibrium managed to challenge evolutionary thinking without actually challenging evolution—natural selection and all the other basic Darwinian principles still applied. Only the tempo was different. A process that involved bursts of rapid activity (punctuations) followed by long periods of stability (equilibria) could explain the fossil records of everything from trilobites to horses, and supporters began applying it broadly. Critics accused Eldredge and Gould of overstating or misinterpreting their case, exaggerating what might be only a minor trend of fits and starts in an otherwise gradual system. That debate continues, but regardless of whether the pattern is common or rare, or exactly what causes it, punctuated equilibrium introduced an important idea: that the rate of evolutionary change is variable, and that—at least some of the time—it moves in rapid bursts.
Over the course of two centuries, scientific and popular perceptions of nature went from something fixed and inviolate, to something that changes slowly in tiny steps, to something capable of swift and abrupt transformations. Biologists saw their role expand accordingly. Instead of simply cataloging species, they began decoding their histories and relationships, and began looking for measurable signs of evolution in action. How did plants and animals respond to their environment, and to one another? What made some species resilient enough to persist for millions of years, while others (like almendro trees) seemed vulnerable to the slightest perturbation? What conditions led to pulses of activity—in the evolution of species as well as the rate of extinction? All of these questions played out against another growing realization. In study after study, in ecosystems around the globe, one species kept emerging as the dominant and overarching agent of change.
Traditional views of nature did not include a significant role for the impacts of human behavior. Farming, hunting, logging, 14and other activities may have exacted a toll, but these costs were seen as local and temporary. When the Roman emperor Trajan’s victory over Dacia was commemorated on a column, for example, the bas-relief carvings showed a wooded kingdom being denuded and stripped of wildlife to supply the conquering army. But it was implicit that this rich landscape would soon recover—why else would Dacia have been worth conquering? In the words of an old Chinese saying, “As long as green hills remain, there will always be firewood.” It wasn’t until well into the nineteenth century that people began to realize those proverbial hills were less than inexhaustible. Industrialization, urbanization, and population growth all brought environmental consequences that people could experience firsthand, from air and water pollution to shortages of game, arable land, and yes, firewood. Overhunting had settled the extinction question once and for all, eliminating common species like the passenger pigeon and great auk, as well as high-profile exotics like the dodo. When German naturalist and explorer Alexander von Humboldt warned in 1819 that cutting forests would create “calamities for future generations,” most people were still skeptical. But by the end of the century, governments around the world had begun setting aside parks, forest reserves, and wildlife refuges as a matter of course, and a growing network of citizen groups were lobbying to protect the environment. It was another of Von Humboldt’s insights, however, that hinted at our current predicament, when he suggested that “vast amounts of gas and steam” given off by centers of industry were altering the climate.
