Room of One's Own - ecological communities

Stephen Jay Gould

Limited space evokes competition between sects, suds, siblings, and species.

Golgotha, the site of Christ's crucifixion, appears in most paintings as a substantial hill in the countryside, far from the city walls of Jerusalem depicted in a distant background. In fact, if the traditional spot has been correctly identified, Golgotha is a tiny protuberance located just next to the old city limits but now inside the walls built by Suleiman the Magnificent in the early sixteenth century. These walls extended the boundaries of Jerusalem, and the old city now sits as a small "jewel" at the center of a much bigger, modern city. Golgotha is small and low enough to fit within the Church of the Holy Sepulchre, located within Suleiman's city walls. Visitors just have to climb an internal staircase to reach the top of Golgotha, located on the Church's second story. (Several theories compete to explain the derivation of the name, for Golgotha denotes "skull" in Aramaic, while the alternative label of "Calvary" means the same in Latin. Most scholars think that the name designates the shape of the small hill, not the mortal remains of executions.)

As one of the most sacred sites on earth, the Church of the Holy Sepulchre might be expected to exude dignity, serenity, and a spirit of transcendence above merely earthly cares. Yet in maximal, almost perverse, contrast, the church is a site of constant bickering and division. The etymology of "religion" may refer to "tying together," but the actual experience, given the propensities of Homo sapiens, the earth's most various and contradictory species, tends more often to separation and anathematization. The precious space is "shared" (in this case, a euphemism for "wrangled over") by six old Christian groups--Greek Orthodox, Roman Catholic, Armenian, Syrian, Coptic, and Abyssinian. (The various Protestant denominations came upon the scene a few centuries too late and didn't even get a pew.)

Before visiting the church several years ago, I thought of the Latin phrase status quo as a purely general description for leaving well enough alone. But I learned that the phrase can also be a proper noun--capital S, capital Q. In 1852, after centuries of less-controlled bickering, the six groups signed an agreement, called the Status Quo, to regulate every move and every square inch in the building. At this point, I will yield to Baedeker's Guide to Jerusalem (1982 edition), a publication generally known for authoritative and stodgy prose but uncharacteristically pungent in this case:

   No lamp, no picture, nothing whatsoever may be moved without its giving
   rise to a complaint. The rules governing when and where each community may
   celebrate Mass are minutely prescribed as are the times when the lamps may
   be lit and the windows may be opened. Everything must be done in accordance
   with the originally agreed rules, i.e. the "status quo." ... Modifications
   to this are persistently being sought and just as persistently
   rejected--they even cropped up in the negotiations for the Treaty of
   Versailles and in the League of Nations.... Anyone hoping to find harmony
   and quiet contemplation ... is due for a disappointment--the sects are on a
   Cold War footing. Even the background noise can be put down to
   psychological warfare--the sound of the blows of hammers and chisels
   constantly engaged on improvement work mingles with the chanting of Greek
   plainsong, blasts from the Franciscan organ and the continual tinkling of
   Armenian bells.

And lest anyone hope that equality might reign among the six groups, I hasten to point out that the Status Quo assigned 65 percent of the church to the Greek Orthodox, while granting the Abyssinians--the only black African group by ethnicity--just the tomb of Joseph of Arimathea ("a tiny cavity that can only be reached by passing through Coptic territory," to quote Baedecker's one more time). Adding insult to this injury, the poor Abyssinians can't even reside within the church but must live instead in tiny cells built on the roof! (And let me tell you, it was really hot up there the day I visited.)

To move from a ridiculous story about a sublime place to the fully ridiculous all around, I got the idea for this essay from an English newspaper story of July 9, 1997: "Punch-up Between Brewery Rivals Over Future of Historic Hostelry." One of London's most interesting pubs, the Punch Tavern on Fleet Street, bears a name that reflects a former role as the favorite watering hole for staff members of the famous humor magazine. These ghosts of the past could have filed quite a story on the current situation. Bass, a large national brewery, owns two-thirds of the property, including the only toilets. But Samuel Smith, a smaller, regional operation, bought the other third, including the passageway for delivery of beer to the Bass side. The two businesses have coexisted in constant tension and bickering but have now opted for something closer to the Holy Sepulchre solution of strict division. A new wall is now rising within the pub, and the Bass people are building "a new cellar drop so workers can move beer supplies without using Samuel Smith's passageway." We must assume that the Smith folks will construct some new toilets, for we all know that such items rank second only to what comes in the other end as a necessary fixture in these establishments.

One last item, ridiculous but personal this time, will serve to establish this theme as a generality. My brother and I shared a small room throughout our childhood. We usually got on reasonably well, but we did have our battles from time to time. One day, following our worst blowup, Peter decided that we would just have to divide the room right down the middle, and each of us promise never to set so much as a toe into the other's territory. He proceeded to gather all his possessions and move them to his side. But I just lay on my bed laughing--as he got progressively angrier at my lighthearted approach to such a serious situation. When he finished all the moving and shoving, he confronted me in a fury: "What are you laughing about?" I didn't say a word, but only lifted my finger and pointed at the room's single door--located on my side. Fortunately, Peter started to laugh too; so we made up and amalgamated all our stuff again.

If people, representing a mere few billion souls within a single species spread throughout the planet, can generate so much strife about divvying a space, what can nature possibly do with millions of species, gazillions of individuals, and nothing with the ability or power to negotiate, or even to understand, a status quo? Much of ecological theory has been devoted to debating concepts that may usually be framed differently, but really represent variants of this fundamental question.

Consider just two examples that generally make the rounds in any basic college course on evolution. In discussing the crucial question of how many species can coexist in a single habitat (obviously an ever more important issue as natural spaces shrink before human onslaught, and many species face imminent extinction), students invariably hear about something called the "competitive exclusion" principle, or the notion that two species cannot occupy the same "niche." This conclusion follows more as a logical consequence of natural selection than an observation from nature. If two species really lived in identical environments, sharing all the same spaces and resources, then one of the two would surely hold some advantage, however slight, over the other, and the relentless force of natural selection, acting on even the tiniest differential over countless generations, should secure total victory for the species with a small edge in the competitive struggle for existence.

But this principle probably says less than its weighty words would seem to imply, for niches do not exist independently of species that inhabit them. Niches are not like houses in a suburban development, built "on spec" and fully decked out with all furnishings and utilities before people come to buy under a strict rule of "one lot for one family." Niches are constructed by organisms as they interact with complex environments--and how could two different species read an environment in exactly the same way for all particulars?

A related principle (and second example) called "limiting similarity" attempts to put this theme into a more reasonable and testable light. If two separate species cannot be identical in appearance and behavior, and cannot read the surrounding environment in exactly the same way, then how close can they get? What are the limits to their similarity? How many species of beetles can live in a tropical tree? How many species of fishes in a temperate pond?

We can at least pose such a question without logical contradiction, and we can test certain ideas about minimal discrepancies in body size, feeding preferences, and so on. Much useful research has been done on this subject, but no general answers have emerged. And none may be possible (at least in such simplistic form as "no more similar than a 10 percent difference in body weight on average"), given the irreducible uniqueness of each species and each group of organisms. Beetle rules (if such there be) will almost surely not work as fish rules, not to mention the vastly more different world of bacteria rules.

But if we cannot generate quantitative laws of nature about numbers of species in a single place, we can at least state some general principles. And the rule behind Jerusalem's Status Quo, whatever its moral dubiety in the ethical systems of Homo sapiens, provides a good beginning: large numbers of species can be crammed into a common territory only if each can commandeer some room of its own and not always stand in relentless competition with a maximally similar form.

Two general strategies may be cited, the second far more interesting than the first, for acquiring the requisite "breathing room"--a little bit of unique space that no other species contests in exactly the same way. In the first strategy--the "Holy Sepulchre solution" if you will--two species perceive the surrounding environment in basically the same manner and therefore must divide the territory to keep out of each other's way. Division may be strictly spatial, as in my fraternal dispute about our single common room. But organisms may also use nature's other prime dimension and construct temporal separations as well. The Status Quo divides the space within the Church of the Holy Sepulchre, but the agreement also decrees when the unitary domain of sound belongs to the masses, instruments, and voices of various competing groups.

To make an ugly analogy, based on cruel social practices now thankfully abandoned, but in force not long ago, I encountered both spatial and temporal modes of segregation when I began my college studies in southwestern Ohio during the late 1950s. The town movie theater placed whites in the orchestra and blacks in the balcony, while the local skating rinks and bowling alleys maintained different "white" and "Negro" nights. (Student and community activism, spurred by the nascent Civil Rights movement, fought and vanquished these cruelties during my watch. I remember my own wholehearted and, in retrospect, pretty inconsequential participation with great pride.)

An instructive evolutionary example of this first strategy can be found in a classical argument about modes of speciation, or the origin of a new species by branching from an ancestral population. Such branching can only occur if a group of organisms can become isolated from the parental population and begin to breed only among themselves in a different environment that might favor the evolution of new features by natural selection. (If members of the separating group continue to interact and breed with individuals of the parental population, then favorable new features will be lost by dilution and diffusion, and the two groups will probably reamalgamate, thus precluding the origin of a new species by branching.)

The conventional theory for speciation--called allopatric, and meaning "living in another place"--holds that a population can only gain the potential to form a new species by becoming geographically isolated from the ancestral group, for only strict spatial separation can guarantee the necessary cutoff from contact with members of the parental population. Much research into the process of speciation has focused on the modes of attaining such geographic isolation--new islands rising in the sea, continents splitting, rivers changing their courses, and so on.

A contrasting idea--called sympatric, or "living in the same place"--holds that new groups may speciate while continuing to inhabit the same geographic domain as the parental population. The defense of sympatric speciation faces a classic conundrum, and most research on the subject has been dedicated to finding solutions: if isolation from members of the parental population is so crucial to the formation of a new species, how can a new species arise within the geographic range of the parents?

This old issue in evolutionary theory remains far from resolution, but we should note, in the context of this essay, that proposed mechanisms usually follow the Holy Sepulchre principle of graining the new group a room of its own within the spatial boundaries of the parental realm--and that such "internal isolation" may be achieved by either the spatial or the temporal route. The best-documented cases of the spatial strategy invoke a process that goes by the technical name of "host specificity," or the restriction of a population to a highly specific site within a general area. For example, to cite an actual (although still controversial) case, flies of the genus Rhagoletis tend to inhabit only one species of tree as an exclusive site for breeding and feeding. Suppose that some individuals within a species that lives on apple trees experience a mutation that leads them to favor hawthorns. A new population, tied exclusively to hawthorns, may soon arise and may evolve into a separate species. The hawthorn flies live within the same geographic region as the apple flies, but members of the two groups never interbreed because each recognizes only a portion of the total area as a permissible home--just as the six sects of the Holy Sepulchre never transgress into one another's territory.

The same principle may work temporally as well. Suppose that two closely related species of frogs live and reproduce in and around the same pond, but one species uses the day-lengthening cues of spring to initiate breeding, while the other waits for the day-shortening signals of fall. The two populations share the same space and may even (metaphorically) wave and wink at each other throughout the year, but they can never interbreed and can therefore remain separate as species.

In the second, and philosophically far more interesting, strategy for securing a requisite room of one's own, species may share the same region, but avoid the need for a natural equivalent of the Status Quo, because they do not perceive each other at all, and therefore cannot interfere or compete--blessedly benign ignorance rather than artfully negotiated separation. This fascinating form of imperception, which can also be achieved by either spatial or temporal routes, raises one of the most illuminating issues of intellectual life and nature's construction: the theme of scaling, or strikingly different ways of viewing the world--with no single way either universally "normal" or "better" than any other--from disparate vantage points of an observer's size or life span.

To begin with a personal story, I share my Harvard office with about a hundred thousand trilobites, all fossils at least 250 million years old, and now housed in cabinets lining the perimeter of my space. For the most part, we coexist in perfect harmony. They care little for my eyeblink of a forty-year career, and I view them with love and respect to be sure, but also as impassive, immobile pieces of rock. They cause me no trouble because I just move the appropriate drawers to an adjacent room when a visiting paleontologist needs to study a genus or two. But one week, about ten years ago, two British visitors wanted to look at all Ordovician trilobites, an endeavor that required exploratory access to all drawers. I had no choice but to abandon my office for several days--a situation made worse by the stereotypical politeness of my visitors, as they apologized almost hourly: "Oh, I do hope we're not disturbing you too much." I wanted to reply: "You bloody well are, but there's nothing I can do about it," but I just shut up instead. I relaxed when I finally figured out the larger context. My visitors, of course, had been purposely sent by the trilobites to teach me the lesson of scaling: we will let you borrow this office for a millimoment of our existence; this situation troubles us not at all, but we do need to remind you about the room's true ownership once every decade or so, just to keep you honest.

Species can also share an environment without conflict when each experiences life on such a different temporal scale that no competitive interaction ever occurs. A bacterial life cycle of half an hour will pass beneath my notice and understanding; unless the population grows big enough to poison or crowd out something of importance to me. But how can a fruit fly ever experience me as a growing, changing organism if I manifest such stability throughout its full life cycle of two weeks or so? The pre-Darwinian Scottish evolutionist Robert Chambers devoted a striking metaphor to this point when he wondered if the adult mayfly, during its single day of earthly life, might mistake the active metamorphosis of a tadpole into a frog for proof of the immutability of species, since no visible change would occur during the mayfly's entire lifetime. (And so, Chambers argued by extension, we might miss the truth of evolution if the process unrolled so slowly that we could never notice any changes during the entire history of potential human observation.) Chambers wrote in 1844:

   Suppose that an ephemeron [a mayfly], hovering over a pool for its one
   April day of life, were capable of observing the fry of the frog in the
   waters below. In its aged afternoon, having seen no change upon them for
   such a long time, it would be little qualified to conceive that the
   external branchiae [gills] of these creatures were to decay, and be
   replaced by internal lungs, that feet were to be developed, the tail
   erased, and the animal then to become a denizen of the land.

Since organisms span such a wide range of size, from the invisible bacterium to the giant blue whale (or to the fungus that underlies a good part of Michigan--see my essay of July 1992), the spatial strategy of coexistence by imperception achieves special prominence in nature. This concept can best be illustrated by an example that has become something of a cliche (by repetition for its appropriateness) in intellectual life during the past decade.

To illustrate his concept of "fractals," mathematical curves that repeat an identical configuration at successively larger or smaller scales ad infinitum, mathematician Benoit Mandelbrot asked a disarmingly simple question with a wonderfully subtle nonanswer: how long is the coastline of Maine? The inquiry sounds simple but cannot be resolved without ambiguity, for solutions depend upon the scale of inquiry, and no scale can claim a preferred status. (In this respect, the question recalls the classic anecdote, also told about folks "down East" in Maine, of a woman who asks her neighbor, "How's your husband?"--and receives the answer, "Compared to what?")

If I'm holding an atlas with a page devoted to the full state of Maine, then I may measure a coastline at the level of resolution permitted by my source. But if I use a map showing every headland in Acadia National Park, then the equally correct coast line becomes much longer. And if I try to measure the distance around every boulder in every cove of Acadia, then the length becomes ever greater (and increasingly less meaningful as tides roll and boulders move). Maine has no single correct coastline; any proper answer depends upon the scale of inquiry.

Similarly for organisms. Humans rank among the largest animals on earth, and we view our space as one might see all of Maine on a single page. A tiny organism that lives in a world entirely circumscribed by a single boulder in a cove will therefore be completely invisible at our scale. But neither of us sees "the world" any better or any more clearly. The atlas defines my appropriate world, while the boulder defines the space of the diatom or rotifer (while the rotifer then builds the complete universe of any bacterium dwelling within).

We need no Status Quo to share a common space with a baterium, for we dwell in different worlds of a common territory--that is, unless we interfere or devise a way to intrude: the bacterium by generating a population large enough to incite our notice or cause us harm; Homo sapiens by inventing a microscope to penetrate the world of the invisible headland on a one-page map of the earth.

Frankly, given our aesthetic propensities, it is often best that we do not perceive these smaller worlds within our domain. About 40 percent of humans house eyebrow mites, living beneath our notice at the base of hair follicles above our eyes. By ordinary human standards, and magnified to human size, these mites are outstandingly ugly and fearsome. I would just as soon let them go their way in peace, so long as they continue the favor of their utter imperceptibility. And do we really want to know the details of ferocious battles between our antibodies and bacterial invaders--a process already distasteful enough to us in the macroscopic consequence of pus? (Don't get me wrong. As a dedicated scientist, I do assert the cardinal principle that we always want to know intellectually, in order to understand the world better and to protect ourselves. I am just not sure that we should always crave visceral perception of phenomena that don't operate at our scale in any case.)

Finally, this theme of mutually invisible life at widely differing scales has an important implication for the "culture wars" that supposedly now envelop our universities and our intellectual discourse in general (but that have, in my opinion, been grossly oversimplified and exaggerated for their perceived newsworthiness). One side of this false dichotomy features the postmodern relativists who argue that all culturally bound modes of perception must be equally valid, and that no factual truth therefore exists. The other side includes the benighted, old-fashioned realists who insist that flies really have two wings, and that Shakespeare really did mean what he thought he was saying. The principle of scaling provides a resolution for the false parts of this silly dichotomy. Facts are indeed facts and cannot be denied by any rational being. (Facts are often not at all easy to determine or specify--but this is a different matter for another time.) Facts, however, may also be highly scale dependent--and the perceptions of one world may have no validity or expression in the domain of another. The one-page map of Maine cannot recognize the separate boulders of Acadia, but both are equally valid representations of a factual coastline.

Why should we privilege one scale over another, especially when a fractal world can express the same form at every scale? To an eyebrow mite, is my hair follicle any less of a universe than our entire earth to the Lord of Hosts (who might be a local god as tiny as a mite to the great god of the whole universe--who then means absolutely nothing to the mite on my eyebrow)? And yet, each denizen of each scale may perceive an appropriate universe with impeccable, but local, factual accuracy.

We don't have to love or even know about all creatures of other scales (although we have ever so much to learn by stretching our minds to encompass, however dimly and through our own dark glasses, their equally valid universes). But it is good and pleasant for brethren to dwell together in unity--each with some room of one's own.

Stephen Jay Gould teaches biology, geology, and the history of science at Harvard University. He is also Frederick P. Rose Honorary Curator in Invertebrates at the American Museum of Natural History.

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