Blood doesn’t flow through our arteries and veins by gravity or magic or the force of our personalities. It is pushed. What pushes it is an elaborately engineered muscle (or muscular organ) that serves as a pump: the heart. Without the continuing, impelling action of that pump, the rest dies. The heart can survive without a right hand attached to the body in which it beats, or without a left eye, or even without one of the two kidneys; but the kidney or the eyeball or the hand can’t survive without the heart. I am belaboring this obvious biological fact for the sake of analogy. The heartbeat of great natural ecosystems can be seen as a combination of features crucial to preserving the viability of the whole, just as auricles and ventricles and valves and innervation are crucial to maintaining the beat of a heart. Foremost among those ecological features are scale, connectivity, diversity, and certain processes. Put them together, and you have a quality that can go by the word “wildness.”
Wildness is intangible, maybe even ineffable, but not imaginary. It’s a matter of size and function and gloriously unpredictable complexity, as well as a matter of the greenness of the green leaves, the redness of tooth and claw. Religious people might say, It’s like a soul. Network scientists might say, It’s an emergent property.
People sometimes imagine that wildness can survive in small or simplified pieces. It cannot. Is a solitary tiger caged in a zoo an example of wildness? I would say no. The poor animal may be frantic and dangerous, but that’s different from wild. The zoo may be valuable, as some zoos certainly are; it may teach things about animals to people with no other opportunity for such learning, but it can’t easily teach about wildness. Wildness in its fullest sense has got to be big and complex and interactive and uncontrolled by humans. The best zoos can interest people in wildness, can illuminate wildness, can lead people toward wildness, but they can never replace it.
Defining wildness is not an easy task. There are multiple possible answers, but here’s the best I can do: Wildness is a name we give to living nature, on planet Earth, at its most robust, unfettered, undiminished, dynamic, and diverse. I’ve made a few undergirding assumptions. Wildness is biological. The stormy dynamics of Jupiter’s Great Red Spot, the eruption of solar flares, and the inexorable suck of a black hole are all formidable phenomena, robust and intricate in their ways, but different from what we mean when we say “wildness.” They are dynamic but inanimate. Conversely, Times Square at 5 PM may be wild in its way, and more so on New Year’s Eve, and there’s plenty of life—the human sort—but not much biological diversity, even if you count the rodents and roaches in the tunnels underfoot.
Wildness, as I see it, requires living creatures of many different forms entangled in a system of surging and ebbing interactions, marked by fluctuations that depend on the near-infinite unpredictability of individual behavior as well as the finite predictability of biophysical and biochemical laws. Wildness also assumes a certain threshold of bigness. A piranha in a fishbowl, a single baobab tree that stands in a village roundabout, or a tiger behind bars in a zoo are not wildness. At best, those creatures are small samples from (not of) wildness. They are melon balls scooped from juicy pulp, but they aren’t the melon. What’s missing are those four crucial ecosystem features: scale, connectivity, diversity, and processes. Each of them is as essential to this property, wildness, as are the animals we tend to think of as its embodiments.
What I mean by processes is the interactive dynamics of the system, the various activities that turn one form of creature and one form of behavior and one form of matter and one form of energy into the makings of others. Those include photosynthesis, herbivory, pollination, parasitism, competition, predation, seed dispersal, and decomposition, among others. What I mean by connectivity is the linkages and dependencies that such processes build among living creatures and their physical environments. What I mean by scale is the important reality that connectivity and processes—and biological diversity too—all depend on the sheer size of the place where they exist. Big areas of natural landscape can accommodate more kinds of creatures, more connectivity, and more processes than can small areas. This crucial fact was discerned by several observant naturalists over the centuries; delineated in math by a little-known civil engineer, birdwatcher, and amateur ecologist named Frank Preston, in papers published between 1948 and 1962;1 and then further considered, systematized, and enshrined in theoretical ecology by Robert H. MacArthur and Edward O. Wilson, first in another paper, in 1963, and soon afterward in a landmark book, The Theory of Island Biogeography, published in 1967.
That book contains some of the intellectual foundations of the modern conservation movement. Biogeography is the study of what creatures live where. Island biogeography is the study of what creatures live on which islands—and why. But the little MacArthur and Wilson volume was about much more than islands, and it awakened a new awareness among ecologists.
The book was about ecosystems as they exist everywhere on the planet: patches of landscape made into “islands” by the natural arrangement of physical conditions (as in caves and tide pools) and vegetation types (such as gallery forest along a river’s bottomland). Insularized ecosystems of that sort obey principles—losing or gaining biological diversity, preserving or surrendering their wildness—very similar to what happens on real, water-encircled islands in the Galápagos or the Hawaiian chain or elsewhere. But there is also the matter of ecosystem bits made insular by human impacts on landscape. “The same principles apply, and will apply to an accelerating extent in the future,” MacArthur and Wilson wrote, “to formerly continuous natural habitats now being broken up by the encroachment of civilization.”
These two scientists foresaw, back in 1967, that human activities like logging and plowing and roadbuilding would increasingly leave ecosystems fragmented into insular pieces, surrounded by the oceanic slosh of what we call civilization. That is, surrounded by people and all the accoutrements we require, all the transformations of landscape we commit, replacing biological diversity and connectivity and ecological processes with cities and highways and great universities and operas and libraries and suburbs and driveways and livestock and crops and parking lots and malls and golf courses.
MacArthur and Wilson analyzed the effects to be expected on such ecological “islands” amid such oceans of human impact, as well as on literal islands amid oceans of salt water. Foremost of those effects, they recognized, was a decrease in biological diversity related to the size of the island and its distance from the nearest mainland. This was proven by empirical studies of island faunas, made logical by the work of Preston, and now explained by MacArthur and Wilson as a matter of how animals and plants colonize new islands or go extinct on old ones.
The smaller the island, the fewer species it will contain; the more distant from the nearest mainland, the fewer species will succeed in colonizing it. Diversity is limited because small islands can support only small populations of animals and plants, and small populations face greater jeopardy of extinction. Colonization is limited because distance presents difficulties—animals or plants will be less likely to immigrate successfully to an island very far from the mainland that serves as source. MacArthur and Wilson represented these inverse relations with a simple figure showing two trend lines crossing each other at the center of a coordinate graph: an immigration line sloping downward as the island gets more remote and an extinction line sloping upward as the island gets smaller. Where the lines crossed was a point of balance, an equilibrium representing the expected diversity of that island over time. MacArthur and Wilson called this an “equilibrium model” of island biotas.
The Theory of Island Biogeography, published by Princeton University Press in a drab mustardy cover, was not much noticed when it first appeared, but it became one of the guiding theoretical works in ecology and conservation—and eventually in the discipline that came to be known as conservation biology. Why? Because it did not speak just about islands. It foretold the fate of ecosystems on mainlands, those “formerly continuous natural habitats now being broken up by the encroachment of civilization.” It projected the consequences of habitat fragmentation. It warned of the inexorable truth that, as we humans increasingly occupy Earth’s surface and arrogate vast areas to our purposes (leaving only smallish fragments of natural landscapes, some of which we call parks or refuges), those fragments will lose biological diversity. And they will lose it in proportion to their smallness and their distance from larger, richer landscapes.
This is why I place scale and connectivity among the four crucial elements of wildness. Diversity, the third, is a blessing dependent largely on those two. Likewise, the fourth, the full presence of ecological processes such as predation, herbivory, competition, and pollination, exists only where scale and connectivity allow diverse creatures to interact.
Now, more than half a century later, we live in the future that MacArthur and Wilson foretold. MacArthur did not survive to see it (he died of renal cancer in 1972), but Wilson (until he died on December 26, 2021) did see it, and resisted it eloquently, in books such as Biophilia and The Diversity of Life. Those intervening decades of human population growth, consumption, habitat loss, species loss, and ecological fragmentation are what turned Wilson into the world’s preeminent voice on the conservation of biological diversity. For instance, when obscure and unrecognized species of beetles or soil microbes or plants disappear from a local habitat transformed by human development, such as a forested ridge known as Centinela in the Andean foothills of Ecuador, Wilson wrote, those species “enter oblivion like the dead of Gray’s Elegy, leaving at most a name, a fading echo in a far corner of the world, their genius unused.”2
The Theory of Island Biogeography probably influenced my life more than any other book I’ve ever read, with the exceptions of Absalom, Absalom! and On the Origin of Species. It guided me toward ideas and drew me to places and issues involving wildness, something I had grown up (in the forests and creek beds of southern Ohio) loving but not much understanding. It leveraged my transition, while I was in my early thirties, from a natural-history essayist who had once been a novelist, with almost no formal science education, into a science journalist and nonfiction author. It led me to faraway forests where I could hear the heartbeat of wildness thumping like blood in my ears: the central Amazon, the Congo Basin, the Okefenokee Swamp, the highlands of New Guinea.
It drew me to other places too, where the heartbeat has grown faint and unsteady, its continuation imperiled by incremental losses of diversity, connectivity, processes, and scale—wondrous but saddening places such as Madagascar, where most of the forest cover has been lost, people struggle to grow food for their families, and so many unique species of lemurs and reptiles and plants, among other groups, stand jeopardized with extinction. It helped me understand that a great forest, a true forest, cannot exist without, for instance, insects. That a living creek, of the sort I knew in Ohio, cannot be truly alive without salamanders and frogs and newts. That a black-water swamp—not just the gentle and circumscribed Okefenokee, but big, punishing swamps like the ones in the Republic of the Congo and Gabon—will quite properly contain crocodiles or alligators, maybe lungfish or cottonmouths, plus mosquito larvae and mud turtles and leeches. If the swamp doesn’t contain those creatures, something is wrong. The vigor of its heartbeat is diminished.
Subtract predators from a great forest, and you diminish it. Subtract amphibians, you diminish it. Reduce its area by 50 percent and cut the rest into fragments with roads, you diminish it. Eliminate the bees and moths and bats, along with their service as pollinators, and you diminish it horribly. Take away scale and connectivity and diversity and the vital processes, bit by bit, and the heartbeat of the wild grows weaker. Eventually it stops. You may still have a stand of trees, but that’s a woodlot, not a forest. Your forest is dead. You may have standing water and a few cattails, but your swamp is no longer a swamp. It’s a sump.
About fifty years ago I began to gravitate, as a reader, toward nonfiction. I started to read books for which an English major had never made time: Rousseau and Thoreau, Herodotus and Mary Kingsley. I read Peter Gay’s history of the Enlightenment and Edmund Wilson’s To the Finland Station. I read a couple of books about Darwin. I did my best to read Descartes and Berkeley and Locke. I read Loren Eiseley and J. Henri Fabre and Annie Dillard. I read African Genesis, by Robert Ardrey, and The Tree Where Man Was Born, by Peter Matthiessen. Also, somehow, I got hold of a book titled Serengeti Shall Not Die, by the German zoologist Bernhard Grzimek.3
I knew nothing about Grzimek and couldn’t even pronounce his name. This was a paperback I had picked up somewhere, out of random curiosity, because it involved big, wild animals on a big, wild landscape, and I had recently moved to Montana. I was unaware at the time that Grzimek’s book was the companion to a 1959 documentary of the same title. Grzimek and his son Michael made the film while doing fieldwork on animal migrations in the Serengeti. During the production, Michael died in the crash of a small plane he was piloting. This was back at a time when Tanzania, within which Serengeti National Park lies, was still a colonized country called Tanganyika. The book became an international bestseller, though it never caught my blindered attention until years later.
Its title derived, in part, from Grzimek’s response to the death of his son. Michael had died, but the wild place they had shared and loved, with its animals and processes and magnificent scale, must not die. (The English word “shall” can denote either a prediction or a vow, but the original German title, Serengeti darf nicht sterben, was clear: “Serengeti Shall Not Be Allowed to Die.”) It was a grieving father’s promise.
I can’t find my old copy of the book, but I can’t imagine discarding it, so it’s probably still with me, somewhere in this book-jammed house. In its pages resides a prophecy. In coming decades and centuries, Grzimek wrote, people would no longer travel to view marvels of engineering, but they would “leave the dusty towns in order to behold the last places on earth” where great creatures live, relatively undisturbed, amid great landscapes:
Countries which have preserved such places will be envied by other nations and visited by streams of tourists. There is a difference between wild animals living a natural life and famous buildings. Palaces can be rebuilt if they are destroyed in wartime, but once the wild animals of the Serengeti are exterminated no power on earth can bring them back.
The “wild animals living a natural life” carry extra significance when you know that Grzimek worked as a zoo director in Frankfurt as well as a field zoologist in Africa. The “famous buildings” and palaces “destroyed in wartime” likewise resonate with his experience rebuilding the Frankfurt Zoological Garden from ruins after Germany’s defeat in World War II, which just twenty of the zoo’s animals had survived.
I remember Grzimek’s Serengeti because it was probably the first book on conservation I ever read, roughly a dozen years before I read The Theory of Island Biogeography. It was not theoretical. Though it had its origin in a laborious census effort—Grzimek and Michael had set out to count the populations of large mammals in Ngorongo Crater, at the edge of the Serengeti ecosystem, during which effort Michael died—the book compelled by description and emotion, not by systematized data, math, and logic. Although my son has died an untimely death, Grzimek was saying, and we will all eventually meet our ends, we cannot let the wildness of the Serengeti die. We shall not allow it, he vowed.
He was right: We cannot let this and other such great landscapes vanish from the planet simply because we feel comfortably distant from wildness, and because its protection is a task for others. We need to think about the things we are doing—and we are all doing some things, with every meal we eat, every mile we travel, every product we consume, every house we build, every child we conceive (but note: it’s not sheer population increase that matters, it’s population increase multiplied by per capita consumption, which varies enormously between high-income and low-income countries)—to diminish those features of wildness: the scale and connectivity of natural landscapes, the biological diversity within them, the processes by which those living creatures and their environment interact. It’s late, but it’s not too late. So long as we humans recognize that reality, respect it, and take pains to preserve those elements through fervent and wise efforts, the heart will keep beating.