We tend to become beguiled by such warm and integrative feelings (for science rightly seeks unity and generality of explanation). But does integration by reduction of all scales to the rates and mechanisms of the smallest really work for evolution—and do we crave this style of unification as the goal of all science? I think not, and I also regard our best general reason for skepticism as conclusive for this particular subject—however rarely appreciated, though staring us in the face.
These shortest-term studies are elegant and important, but they cannot represent the general mode for building patterns in the history of life. The reason for their large-scale impotence strikes most people as deeply paradoxical, even quite funny—but the argument truly cannot be gainsaid. Evolutionary rates as measured for guppies and lizards are vastly too rapid to represent the general modes of change that build life’s history through geological ages.
But how can I say such a thing? Isn’t this statement ridiculous a priori? How could these tiny, minuscule changes—a little less leg, a minimally larger size—represent too much of anything? Doesn’t the very beauty of these studies lie in their minimalism? We have always been taught that evolution is wondrously slow and cumulative—a grain-by-grain process, a penny a day toward the domain of Bill Gates. Doesn’t each of these studies document a grain? Haven’t my colleagues and I found the “atom” of evolutionary incrementation?
I believe that these studies have discerned something important, but they have discovered no general atom. These measured changes over years and decades are too fast by several orders of magnitude to build the history of life by simple cumulation. Reznick’s guppy rates range from 3,700 to 45,000 darwins (a standard metric for evolution, expressed as change in units of standard deviation—a measure of variation around the mean value of a trait in a population—per million years). By contrast, rates for major trends in the fossil record generally range from 0.1 to 1.0 darwin. Reznick himself states that “the estimated rates [for guppies] are … four to seven orders of magnitude greater than those observed in the fossil record” (that is, ten thousand to ten million times faster).
Moreover and with complete generality—thus constituting the “paradox of the visibly irrelevant” in my title—we may say that any change measurable at all over the few years of an ordinary scientific study must be occurring far too rapidly to represent ordinary rates of evolution in the fossil record. The culprit of this paradox, as so often, can be identified as the vastness of time (a concept that we can appreciate “in our heads” but seem quite unable to place into the guts of our intuition). The key principle, however ironic, requires such a visceral understanding of earthly time: if a case of evolution proceeds with sufficient speed to be discerned by our instruments in just a few years—that is, if the change becomes substantial enough to stand out as a genuine and directional effect above the random fluctuations of nature’s stable variation and our inevitable errors of measurement—then we have witnessed something far too substantial to serve as an atom of steady incrementation in a paleontological trend. Thus, to restate the paradox: if we can measure it at all (in a few years), it is too powerful to be the stuff of life’s history.
If large-scale evolution proceeded by stacking Trinidad guppy rates end to end, then any evolutionary trend would be completed in a geological moment, not over the many million years actually observed. “Our face from fish to man,” to cite the title of a famous old account of evolution for popular audiences, would run its course within a single geological formation, not over more than 400 million years, as our fossil record demonstrates.
Evolutionary theory must figure out how to slow down these measured rates of the moment, not how to stack them up! In fact, most lineages are stable (nonchanging) nearly all the time in the fossil record. When lineages do change, their alteration usually occurs “momentarily” in a geological sense (that is, confined to a single bedding plane) and usually leads to the origin of a new species by branching. Evolutionary rates during these moments may match the observed speed of Trinidadian guppies and Bahamian lizards—for most bedding planes represent several thousand years. But during most of a typical species’s lifetime, no change accumulates, and we need to understand why. The sources of stasis have become as important for evolutionary theory as the causes of change.
(To illustrate how poorly we grasp this central point about time’s immensity, the reporter for Science magazine called me when my Cerion article, coauthored with Glenn Goodfriend, appeared. He wanted to write an accompanying news story about the exception I had found to my own theory of punctuated equilibrium—an insensibly gradual change over ten to twenty thousand years. I told him that, although exceptions abound, this case does not He among them, but actually represents a strong confirmation of punctuated equilibrium! We found all twenty thousand years’ worth of snails on a single mudflat—that is, on what would become a single bedding plane in the geological record. Our entire transition occurred in a geological moment and represented a punctuation, not a gradual sequence of fossils. We were able to “dissect” the punctuation in this unusual case—hence the value of our publication—because we could determine ages for the individual shells. The reporter, to his credit, completely revised his originally intended theme and published an excellent account.)
In conclusion, I suspect that most cases like the Trinidadian guppies and Bahamian lizards represent transient and momentary blips and fillips that “flesh out” the rich history of lineages in stasis, not the atoms of substantial and steadily accumulated evolutionary trends. Stasis is a dynamic phenomenon. Small local populations and parts of lineages make short and temporary forays of transient adaptation, but these tiny units almost always die out or get reintegrated into the general pool of the species. (Losos himself regards the new island populations of lizards as evolutionarily transient in exactly this sense—for such tiny and temporary colonies are almost always extirpated by hurricanes in the long run. How; then, can such populations represent atoms of a major evolutionary trend? The news report in Science magazine ends by stating: “But whether the lizards continue to evolve depends largely on the winds of fate, says Losos. These islets are periodically swept by hurricanes that could whisk away every trace of anolian evolution.”)
But transient blips and fillips are no less important than major trends in the total “scheme of things.” Both represent evolution operating at a standard and appropriate measure for a particular scale and time—Trinidadian blips for the smallest and most local moment, faces from fish to human for the largest and most global frame. One scale doesn’t translate into another. No single scale can be deemed more important than any other; and none operates as a basic model for all the others. Each scale embodies something precious and unique to teach us; none can be labeled superior or primary. (Guppies and lizards, in their exposition of momentary detail, give us insight, unobtainable at broader scales, into the actual mechanics of adaptation, natural selection, and genetic change.)
The common metaphor of the science of fractals—Mandelbrot’s familiar argument that the coast of Maine has no absolute length, but depends upon the scale of measurement—epitomizes this principle well (see chapter 23). When we study guppies in a pond in Trinidad, we are operating at a scale equivalent to measuring the coastline by wrapping our string around every boulder on every headland of Acadia National Park. When we trace the increase in size of the human brain from Lucy (about four million years ago) to Lincoln, we are measuring the coastline as depicted on my page of Maine in Hammond’s Atlas. Both scales are exactly right for their appropriate problems. You would be a fool to spend all summer measuring the details in one cove in Acadia, if you just wanted to know the distance from Portland to Machiasport for your weekend auto trip.
I find a particular intellectual beauty in such fractal models—for they invoke hierarchies of inclusion (the single cove embedded within Acadia, embedded within Maine) to deny hierarchies of worth, importance, merit, or meaning. You may ignore Maine while studying t
he sand grain, and be properly oblivious of the grain while perusing the map of Maine on the single page of your atlas. But you can love and learn from both scales at the same time. Evolution does not he patent in a clear pond on Trinidad any more than the universe (pace Mr. Blake) lies revealed in a grain of sand. But how poor would be our understanding—how bland and restricted our sight—if we could not learn to appreciate the rococo details that fill our immediate field of vision, while forming, at another scale, only some irrelevant and invisible jigglings in the majesty of geological time.
23
Room of One’s
Own
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 town 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 means “skull” in Aramaic, while the alternative label of calvary has the same definition 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 curmudgeonly 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 had encountered the Latin phrase status quo only as a general description for leaving well enough alone. But I learned that the phrase can also be used as a proper noun—capital S, capital Q. In 1852, after centuries of more serious 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 persistendy 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 Baedeker’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 now rises 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 coexisted 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 lived in truly 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 seem to imply, for niches do not exist independently of the species that inhabit them. Niches are not comparable to 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 r
ule 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 be? 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 will almost surely not work as fish rules, not to mention the vastly more different world of rules for bacteria.
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.
The Lying Stones of Marrakech Page 40