Eight Little Piggies (5 page)

These are the natural time scales of evolution and geology on our planet. But what can such vastness possibly mean for our legitimately parochial interest in ourselves, our ethnic groups, our nations, our cultural traditions, our blood lines? Of what conceivable significance to us is the prospect of recovery from mass extinction 10 million years down the road if our entire species, not to mention our personal lineage, has so little prospect of surviving that long?

Capacity for recovery at geological scales has no bearing whatever upon the meaning of extinction today. We are not protecting Mount Graham Red Squirrels because we fear for global stability in a distant future not likely to include us. We are trying to preserve populations and environments because the comfort and decency of our present lives, and those of fellow species that share our planet, depend upon such stability. Mass extinctions may not threaten distant futures, but they are decidedly unpleasant for species caught in the throes of their power. At the appropriate scale of our lives, we are just a species in the midst of such a moment. And to say that we should let the squirrels go (at our immediate scale) because all species eventually die (at geological scales) makes about as much sense as arguing that we shouldn’t treat an easily curable childhood infection because all humans are ultimately and inevitably mortal. I love geological time—a wondrous and expansive notion that sets the foundation of my chosen profession—but such vastness is not the proper scale of my personal life.

The same issue of scale underlies the main contribution that my profession of paleontology might make to our larger search for an environmental ethic. This decade, a prelude to the millennium, is widely and correctly viewed as a turning point that will lead either to environmental perdition or stabilization. We have fouled local nests before and driven regional faunas to extinction, but we were never able to unleash planetary effects before this century’s concern with nuclear fallout, ozone holes, and putative global warming. In this context, we are searching for proper themes and language to express our environmental worries.

I don’t know that paleontology has a great deal to offer, but I would advance one geological insight to combat a well-meaning, but seriously flawed (and all too common), position and to focus attention on the right issue at the proper scale. Two linked arguments are often promoted as a basis for an environmental ethic:

1. We live on a fragile planet now subject to permanent derailment and disruption by human intervention;

2. Humans must learn to act as stewards for this threatened world.

Such views, however well intentioned, are rooted in the old sin of pride and exaggerated self-importance. We are one among millions of species, stewards of nothing. By what argument could we, arising just a geological microsecond ago, become responsible for the affairs of a world 4.5 billion years old, teeming with life that has been evolving and diversifying for at least three-quarters of this immense span. Nature does not exist for us, had no idea we were coming, and doesn’t give a damn about us. Omar Khayyam was right in all but his crimped view of the earth as battered, when he made his brilliant comparison of our world to an eastern hotel:

This assertion of ultimate impotence could be countered if we, despite our late arrival, now held power over the planet’s future. But we don’t, despite popular misperception of our might. We are virtually powerless over the earth at our planet’s own geological timescale. All the megatonnage in all our nuclear arsenals yields but one ten-thousandth the power of the 10 km asteroid that might have triggered the Cretaceous mass extinction. Yet the earth survived that larger shock and, in wiping out dinosaurs, paved a road for the evolution of large mammals, including humans. We fear global warming, yet even the most radical model yields an earth far cooler than many happy and prosperous times of a prehuman past. We can surely destroy ourselves, and take many other species with us, but we can barely dent bacterial diversity and will surely not remove many million species of insects and mites. On geological scales, our planet will take good care of itself and let time clear the impact of any human malfeasance.

People who do not appreciate the fundamental principle of appropriate scales often misread such an argument as a claim that we may therefore cease to worry about environmental deterioration, just as Copeland argued falsely that we need not fret about extinction. But I raise the same counterargument. We cannot threaten at geological scales, but such vastness has no impact upon us. We have a legitimately parochial interest in our own lives, the happiness and prosperity of our children, the suffering of our fellows. The planet will recover from nuclear holocaust, but we will be killed and maimed by billions, and our cultures will perish. The earth will prosper if polar icecaps melt under a global greenhouse, but most of our major cities, built at sea level as ports and harbors, will founder, and changing agricultural patterns will uproot our populations.

We must squarely face an unpleasant historical fact. The conservation movement was born, in large part, as an elitest attempt by wealthy social leaders to preserve wilderness as a domain for patrician leisure and contemplation (against the image, so to speak, of poor immigrants traipsing in hordes through the woods with their Sunday picnic baskets). We have never entirely shaken this legacy of environmentalism as something opposed to immediate human needs, particularly of the impoverished and unfortunate. But the Third World expands and contains most of the pristine habitat that we yearn to preserve. Environmental movements cannot prevail until they convince people that clean air and water, solar power, recycling, and reforestation are best solutions (as they are) for human needs at human scales—and not for impossibly distant planetary futures.

I have a decidedly unradical suggestion to make about an appropriate environmental ethic—one rooted, with this entire essay, in the issue of appropriate human scale vs. the majesty, but irrelevance, of geological time. I have never been much attracted to the Kantian categorical imperative in searching for an ethic—to moral laws that are absolute and unconditional, and do not involve any ulterior motive or end. The world is too complex and sloppy for such uncompromising attitudes (and God help us if we embrace the wrong principle and then fight wars, kill, and maim in our absolute certainty). I prefer the messier “hypothetical imperatives” that invoke desire, negotiation, and reciprocity. Of these “lesser,” but altogether wiser and deeper principles, one has stood out for its independent derivation, with different words but to the same effect, in culture after culture. I imagine that our various societies grope towards this principle because structural stability (and basic decency necessary for any tolerable life) demand such a maxim. Christians call this principle the “golden rule” Plato, Hillel, and Confucius knew the same maxim by other names. I cannot think of a better principle based on enlightened self-interest. If we all treated others as we wish to be treated ourselves, then decency and stability would have to prevail.

I suggest that we execute such a pact with our planet. She holds all the cards, and has immense power over us—so such a compact, which we desperately need but she does not at her own timescale, would be a blessing for us and an indulgence for her. We had better sign the papers while she is still willing to make a deal. If we treat her nicely, she will keep us going for a while. If we scratch her, she will bleed, kick us out, bandage up, and go about her business at her own scale. Poor Richard told us that “necessity never made a good bargain,” but the earth is kinder than human agents in the “art of the deal.” She will uphold her end; we must now go and do likewise.

DARWIN MARVELED
at the abundance of giant Galápagos tortoises when he visited the islands in September, 1835, but he also noted a marked decline based on ease of human exploitation for food. (Ships would often take tortoises away by the hundreds, stacking them live in the hold to provide months of fresh meat “on the hoof.” The tortoises were essentially defenseless. As a single barrier to capture, Darwin notes that ships usually sent out hunting parties in pairs, and two men could not lift the largest animals.) Darwin wrote in the
Voyage of the Beagle:

The species, though not threatened as a whole, is much depleted today, and several distinctive forms, once limited to single islands, have disappeared. I saw the saddest story of this legacy—Lonesome George, last survivor of the saddle-backed race from Pinta Island. No mate has been found for George, though the island has been scoured. He has been moved, for safe-keeping (and in apparently vain hope for salvation of his kind), to a research station on Santa Cruz Island, where I saw him several years ago. He is well fed and surely pampered, and he may live for another century or more; but his lineage, at least as a pure pedigree, is already extinct.

Every George must have his Martha. The last passenger pigeon, also a mateless vestige of a doomed race, died in the Cincinnati Zoo on September 1, 1914. Martha’s body was taken to the Cincinnati Ice Company, suspended in a tank of water, frozen into a three-hundred-pound block of ice, and sent for extrication and stuffing to the Smithsonian Institution, where she resides today.

Galápagos tortoises were vulnerable and restricted in geography; their extreme reduction and partial extinction merits no special surprise. But how could the superabundant and widespread passenger pigeon crash and die within a century? By some estimates, they were once the most common bird in America. They migrated in huge flocks over most of eastern and central North America. Pioneer ornithologist Alexander Wilson estimated one such aggregation as containing more than 2 billion birds. One colony in Wisconsin spread out over 750 square miles. The famous testimony of Audubon himself, made in Ohio just one hundred years before Martha’s death, not only identifies human rapacity as the cause of eventual decline, but also depicts the fabulous abundance:

In 1805, passenger pigeons sold for a penny a piece in markets of New York City. By 1870, birds were reproducing only in the Great Lakes region. Hunters used the newly invented telegraph to inform others about the location of dwindling populations. Perhaps the last large wild flock, some 250,000 birds, was sighted in 1896. A gaggle of hunters, alerted by telegraph, converged upon them; fewer than 10,000 birds flew away. The last wild passenger pigeon was killed in Ohio in 1900. The few zoo colonies dwindled, as keepers could never induce the birds to breed regularly. By 1914, only Martha remained.

These sad, oft-told tales are canonical stories of the extinction saga: defenseless populations composed of individuals that are easy to find and profitable to kill. Restricted compass on an island is the surest path to destruction—the dodo or tortoise model. But even a large, continental spread will not save a vulnerable population—the passenger pigeon model.

One environment, however, has been seen as a refuge for at least most kinds of organisms—the open ocean. Here, or so the argument goes, geographic: ranges are usually large enough, and ecological tolerances sufficiently broad, to prevent rapacious humanity (or any other agent of extinction) from getting every last one. Populations may be beaten way back, but a few survivors will always find a refugium.

This claim is as old as modern biology itself. In the first great document of evolutionary theory, published in 1809, Lamarck tried to deny extinction altogether. (In his theory of creative response to perceived needs, and inheritance of characters thus acquired, organisms should evolve fast enough to overcome any environmental danger.) But Lamarck did allow an exception for conspicuous species on land. Even “Lamarckian” response cannot be quick or extensive enough to overcome the most powerful and efficient agency of environmental disturbance—human depredation. Lamarck wrote: “If there really are lost species, it can doubtless only be among the large animals which live on the dry parts of the earth; where man exercises absolute sway, and has compassed the destruction of all the individuals of some species which he has not wished to preserve or domesticate.” But small inconspicuous oceanic species should be immune from our influence: “Animals living in the waters, especially the sea waters,…are protected from the destruction of their species by man. Their multiplication is so rapid and their means of evading pursuit or traps are so great, that there is no likelihood of his being able to destroy the entire species of any of these animals.”

We would downplay Lamarck’s optimism about the oceans today. Conspicuous species of large organisms with small populations are vulnerable—and several fish and marine mammals, including Steller’s sea cow, have succumbed. But Lamarck’s distinction and prognostication has held. The ledgers of death in historic times do not include marine invertebrates.

Extinction has certainly received its fair share of attention in our newspapers and TV specials. We are so used to tales of destruction, so inured or even numbed, that we expect almost any species, anywhere in the world, to be the next victim. We have engraved the notion of fragility upon our souls.

But step back from all these accounts of death and think for a moment: Have you ever heard about the extinction of a marine invertebrate species, even among widely exploited lobsters, scallops, or conchs. We may drive a local population of marine invertebrates to death, but never an entire species. In
The Panda’s Thumb
, a previous volume in this series published in 1980, I told the sad story of
Cenobita diogenes
, a large Bermudian hermit crab, now apparently doomed because the only shell large enough to hold its body, the whelk
Cittarium pica
, was eaten to destruction on Bermuda. (The crabs now eke out a tenuous existence within fossil
Cittarium
shells eroded from Bermudian hillsides.) I was deluged with suggestions for salvation. One man offered to design a plastic
Cittarium
and to ship them by the thousands for distribution on Bermudian beaches. I was touched by his ingenuity and generosity, but a much simpler and more effective solution exists.
Cittarium pica
is extinct on Bermuda, but not elsewhere. This species is eaten with gusto on most West Indian islands, and piles of empty shells are stacked on beaches and roadsides. Any enterprising savior of
Cenobita
could easily fill a boat and bring the real McCoy back to Bermuda.

In short, Lamarck was right, and his distinction of sea and land has much to teach us about the general phenomenon of species death. By our records and reckoning, no marine invertebrate species has become extinct during historic times. (Geological extinctions, of course, occur at characteristic rates over millions of years—thus illustrating the immensity of difference between our time and earth time). Geerat Vermeij, a leading expert on oceanic life and its vulnerability, wrote in 1986 that “marine invertebrates are relatively immune from extinction.” So Lamarck was right—that is, until 1991.

The first issue of the
Biological Bulletin
for 1991, the technical journal published by the Marine Biological Laboratory at Woods Hole, contains the following article by James T. Carlton and four other authors (including my good friend Gary Vermeij who must now eat his words or be happy that he wrote the disclaimer “
relatively
immune from extinction”): “The first historical extinction of a marine invertebrate in an ocean basin: The demise of the eelgrass limpet
Lottia alveus
” (see the bibliography).

Limpets are snails with an unusual mode of growth. Snail shells are cones that expand slowly and wind around an axis during growth, producing the conventional corkscrew of increasing width. But the limpet cone expands so rapidly that the shell never winds around its axis for more than a fraction of a whorl. Thus, a limpet shell looks like a Chinese hat of the old caricatures. The large open end clamps tightly down upon a rock, or a food source, and this power of adhesion has made the limpet a symbol of tenacity and stubbornness in many languages and cultures. In England, for example, limpets are (according to the
OED
), “officials alleged to be superfluous but clinging to their offices.”

Lottia alveus
, the eelgrass limpet of the western Atlantic, once lived in fair abundance from Labrador to Long Island Sound. Although this geographic range might have been broad enough to win the usual marine immunity from extinction, two peculiar features placed the eelgrass limpet into a rare category of vulnerability. First, as its name implies, the eelgrass limpet lived and fed only on a single species of plant,
Zostera marina
. (
Zostera
, a fascinating biological oddity in its own right, is one of the few marine genera of angiosperms, or ordinary flowering plants. Most people assume that all marine plants are algae, but a few “advanced” flowering land plants have managed to invade the oceans, usually forming beds of “sea grass” in shallow waters.)

A specimen of
Lottia alveus
, first species of marine invertebrate organisms to become extinct in historical times. Left: side view. Right: top view.

Lottia alveus
had a long and narrow shell, just wide enough to fit snugly over a
Zostera
blade. The limpet fed exclusively on epithelial cells of the sea grass. The fate of
Lottia
therefore depended upon the health of
Zostera
. Moreover,
Lottia
had an unusually narrow range of physiological tolerance, particularly for changes of salinity. This limpet could not survive any marked departure from normal oceanic salinity of some thirty-three parts per thousand, whereas
Zostera
spans a much broader range and can live in brackish waters of much reduced salinity.

Both
Zostera
and
Lottia
originated in the Pacific Ocean and invaded the North Atlantic in late Tertiary times (just before the ice ages), as many other species did, through the Bering Strait and along the Arctic Ocean. Populations of
Lottia
remain in both the eastern and western Pacific, so the entire genus is not lost. (Taxonomists are still debating the status of
Lottia
. Some regard the three populations—eastern Pacific, western Pacific, and extinct Atlantic—as fully separate species, others as subspecies of a single, coherent group. In either case, the Atlantic populations were distinct in form and color, and clearly represent some degree of genetic differentiation.)

Atlantic specimens of
Lottia
were reported as abundant by all collectors from first extensive descriptions of the mid-nineteenth century through the 1920s. The last living specimens were reported in 1933. The five authors have searched diligently for
Lottia alveus
throughout its former range from the early 1970s through 1990. They also looked in fourteen major museum collections for specimens gathered during the past fifty years—and found none that could be verified. They even searched through several herbarium collections of
Zostera
, hoping that dried limpet shells might be found on the pressed sheets. (Museums often preserve reference collections of plants by flattening them onto sheets of paper then bound into books.) Again, no
Lottia
could be found. This diligence certainly wins our assent to their preliminary conclusion that
Lottia alveus
is truly extinct in the Atlantic.