In Galápagos, the holocaust of depopulation arrives by the relatively mild route of a bacterium that destroys human egg cells. This scourge first gains a toehold by striking women at the annual international book fair in Frankfurt, but quickly spreads throughout the world, sterilizing all but an isolated remnant of Homo sapiens. Human survival becomes concentrated in a tiny and motley group carried by boat beyond the reach of the bacterium to the isolated Galápagos—the last of the Kanka-bono Indians plus a tourist and adventurer or two. Their survival and curious propagation proceeds through a wacky series of contingencies, yet all future human history now resides with this tiny remnant:
In a matter of less than a century the blood of every human being on earth would be predominantly Kanka-bono, with a little von Kleist and Hiroguchi thrown in. And this astonishing turn of events would be made to happen, in large part, by one of the only two absolute nobodies on the original passenger list for “the Nature Cruise of the Century.” That was Mary Hepburn. The other nobody was her husband, who himself played a crucial role in shaping human destiny by booking, when facing his own extinction, that one cheap little cabin below the waterline.
Contingency has also been an important theme in films, both recent and classic. In Back to the Future (1985) Marty McFly (Michael J. Fox), a teen-ager transported back in time to the high school attended by his parents, must struggle to reconstitute the past as it actually happened, after his accidental intrusion threatens to alter the initial run of the tape (when his mother, in an interesting variation on Oedipus, develops a crush on him). The events that McFly must rectify seem to be tiny occurrences of absolutely no moment, but he knows that nothing could be more important, since failure will result in that ultimate of consequences, his own erasure, because his parents will never meet.
The greatest expression of contingency—my nomination as the holotype* of the genre—comes near the end of Frank Capra’s masterpiece, It’s a Wonderful Life (1946). George Bailey (Jimmy Stewart) has led a life of self-abnegation because his basic decency made him defer personal dreams to offer support for family and town. His precarious building and loan association has been driven to bankruptcy and charged with fraud through the scheming of the town skinflint and robber baron, Mr. Potter (Lionel Barrymore). George, in despair, decides to drown himself, but Clarence Odbody, his guardian angel, intervenes by throwing himself into the water first, knowing that George’s decency will demand another’s rescue in preference to immediate suicide. Clarence then tries to cheer George up by the direct route: “You just don’t know all that you’ve done”; but George replies: “If it hadn’t been for me, everybody’d be a lot better off.… I suppose it would have been better if I’d never been born at all.”
Clarence, in a flash of inspiration, grants George his wish and shows him an alternative version of life in his town of Bedford Falls, replayed in his complete absence. This magnificent ten-minute scene is both a highlight of cinematic history and the finest illustration that I have ever encountered for the basic principle of contingency—a replay of the tape yielding an entirely different but equally sensible outcome; small and apparently insignificant changes, George’s absence among others, lead to cascades of accumulating difference.
Everything in the replay without George makes perfect sense in terms of personalities and economic forces, but this alternative world is bleak and cynical, even cruel, while George, by his own apparently insignificant life, had imbued his surroundings with kindness and attendant success for his beneficiaries. Bedford Falls, his idyllic piece of small-town America, is now filled with bars, pool halls, and gambling joints; it has been renamed Pottersville, because the Bailey Building and Loan failed in George’s absence and his unscrupulous rival took over the property and changed the town’s name. A graveyard now occupies the community of small homes that George had financed at low interest and with endless forgiveness of debts. George’s uncle, in despair at bankruptcy, is in an insane asylum; his mother, hard and cold, runs a poor boarding house; his wife is an aging spinster working in the town library; a hundred men lay dead on a sunken transport, because his brother drowned without George to rescue him, and never grew up to save the ship and win the Medal of Honor.
The wily angel, clinching his case, then pronounces the doctrine of contingency: “Strange, isn’t it? Each man’s life touches so many other lives, and when he isn’t around he leaves an awful hole, doesn’t he? … You see, George, you really had a wonderful life.”
Contingency is both the watchword and lesson of the new interpretation of the Burgess Shale. The fascination and transforming power of the Burgess message—a fantastic explosion of early disparity followed by decimation, perhaps largely by lottery—lies in its affirmation of history as the chief determinant of life’s directions.
Walcott’s earlier and diametrically opposite view located the pattern of life’s history firmly in the other and more conventional style of scientific explanation—direct predictability and subsumption under invariant laws of nature. Moreover, Walcott’s view of invariant law would now be dismissed as more an expression of cultural tradition and personal preference than an accurate expression of nature’s patterns. For as we have seen, Walcott read life’s history as the fulfillment of a divine purpose guaranteed to yield human consciousness after a long history of gradual and stately progress. The Burgess organisms had to be primitive versions of later improvements, and life had to move forward from this restricted and simple beginning.
The new view, on the other hand, is rooted in contingency. With so many Burgess possibilities of apparently equivalent anatomical promise—over twenty arthropod designs later decimated to four survivors, perhaps fifteen or more unique anatomies available for recruitment as major branches, or phyla, of life’s tree—our modern pattern of anatomical disparity is thrown into the lap of contingency. The modern order was not guaranteed by basic laws (natural selection, mechanical superiority in anatomical design), or even by lower-level generalities of ecology or evolutionary theory. The modern order is largely a product of contingency. Like Bedford Falls with George Bailey, life had a sensible and resolvable history, generally pleasing to us since we did manage to arise, just a geological minute ago. But, like Pottersville without George Bailey, any replay, altered by an apparently insignificant jot or tittle at the outset, would have yielded an equally sensible and resolvable outcome of entirely different form, but most displeasing to our vanity in the absence of self-conscious life. (Though, needless to say, our nonexistent vanity would scarcely be an issue in any such alternative world.) By providing a maximum set of anatomically proficient possibilities right at the outset, the Burgess Shale becomes our centerpiece for the controlling power of contingency in setting the pattern of life’s history and current composition.
Finally, if you will accept my argument that contingency is not only resolvable and important, but also fascinating in a special sort of way, then the Burgess not only reverses our general ideas about the source of pattern—it also fills us with a new kind of amazement (also a frisson for the improbability of the event) at the fact that humans ever evolved at all. We came this close (put your thumb about a millimeter away from your index finger), thousands and thousands of times, to erasure by the veering of history down another sensible channel. Replay the tape a million times from a Burgess beginning, and I doubt that anything like Homo sapiens would ever evolve again. It is, indeed, a wonderful life.
A final point about predictability versus contingency: Am I really arguing that nothing about life’s history could be predicted, or might follow directly from general laws of nature? Of course not; the question that we face is one of scale, or level of focus. Life exhibits a structure obedient to physical principles. We do not live amidst a chaos of historical circumstance unaffected by anything accessible to the “scientific method” as traditionally conceived. I suspect that the origin of life on earth was virtually inevitable, given the chemical composition of early oceans and atmospheres, and the phys
ical principles of self-organizing systems. Much about the basic form of multicellular organisms must be constrained by rules of construction and good design. The laws of surfaces and volumes, first recognized by Galileo, require that large organisms evolve different shapes from smaller relatives in order to maintain the same relative surface area. Similarly, bilateral symmetry can be expected in mobile organisms built by cellular division. (The Burgess weird wonders are bilaterally symmetrical.)
But these phenomena, rich and extensive though they are, lie too far from the details that interest us about life’s history. Invariant laws of nature impact the general forms and functions of organisms; they set the channels in which organic design must evolve. But the channels are so broad relative to the details that fascinate us! The physical channels do not specify arthropods, annelids, mollusks, and vertebrates, but, at most, bilaterally symmetrical organisms based on repeated parts. The boundaries of the channels retreat even further into the distance when we ask the essential questions about our own origin: Why did mammals evolve among vertebrates? Why did primates take to the trees? Why did the tiny twig that produced Homo sapiens arise and survive in Africa? When we set our focus upon the level of detail that regulates most common questions about the history of life, contingency dominates and the predictability of general form recedes to an irrelevant background.
Charles Darwin recognized this central distinction between laws in the background and contingency in the details in a celebrated exchange of letters with the devout Christian evolutionist Asa Gray. Gray, the Harvard botanist, was inclined to support not only Darwin’s demonstration of evolution but also his principle of natural selection as its mechanism. But Gray was worried about the implications for Christian faith and the meaning of life. He particularly fretted that Darwin’s view left no room for rule by law, and portrayed nature as shaped entirely by blind chance.
Darwin, in his profound reply, acknowledged the existence of general laws that regulate life in a broad sense. These laws, he argued, addressing Gray’s chief concern, might even (for all we know) reflect some higher purpose in the universe. But the natural world is full of details, and these form the primary subject matter of biology. Many of these details are “cruel” when measured, inappropriately, by human moral standards. He wrote to Gray: “I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of Caterpillars, or that a cat should play with mice.” How, then, could the nonmorality of details be reconciled with a universe whose general laws might reflect some higher purpose? Darwin replied that the details lay in a realm of contingency undirected by laws that set the channels. The universe, Darwin replied to Gray, runs by law, “with the details, whether good or bad, left to the working out of what we may call chance.”
And so, ultimately, the question of questions boils down to the placement of the boundary between predictability under invariant law and the multifarious possibilities of historical contingency. Traditionalists like Walcott would place the boundary so low that all major patterns of life’s history fall above the line into the realm of predictability (and, for him, direct manifestation of divine intentions). But I envision a boundary sitting so high that almost every interesting event of life’s history falls into the realm of contingency. I regard the new interpretation of the Burgess Shale as nature’s finest argument for placing the boundary this high.
This means—and we must face the implication squarely—that the origin of Homo sapiens, as a tiny twig on an improbable branch of a contingent limb on a fortunate tree, lies well below the boundary. In Darwin’s scheme, we are a detail, not a purpose or embodiment of the whole—“with the details, whether good or bad, left to the working out of what we may call chance.” Whether the evolutionary origin of self-conscious intelligence in any form lies above or below the boundary, I simply do not know. All we can say is that our planet has never come close a second time.
For anyone who feels cosmically discouraged at the prospect of being a detail in the realm of contingency, I cite for solace a wonderful poem by Robert Frost, dedicated explicitly to this concern: Design. Frost, on a morning walk, finds an odd conjunction of three white objects with different geometries. This peculiar but fitting combination, he argues, must record some form of intent; it cannot be accidental. But if intent be truly manifest, then what can we make of our universe—for the scene is evil by any standard of human morality. We must take heart in Darwin’s proper solution. We are observing a contingent detail, and may yet hope for purpose, or at least neutrality, from the universe in general.
I found a dimpled spider, fat and white,
On a white heal-all, holding up a moth
Like a white piece of rigid satin cloth—
Assorted characters of death and blight
Mixed ready to begin the morning right,
Like the ingredients of a witches’ broth—
A snow-drop spider, a flower like a froth,
And dead wings carried like a paper kite.
What had that flower to do with being white,
The wayside blue and innocent heal-all?
What brought the kindred spider to that height,
Then steered the white moth thither in the night?
What but design of darkness to appall?—
If design govern in a thing so small.
Homo sapiens, I fear, is a “thing so small” in a vast universe, a wildly improbable evolutionary event well within the realm of contingency. Make of such a conclusion what you will. Some find the prospect depressing; I have always regarded it as exhilarating, and a source of both freedom and consequent moral responsibility.
CHAPTER V
Possible Worlds: The Power of “Just History”
A STORY OF ALTERNATIVES
In the last chapter I gave the general, abstract brief for contingency. But the case for “just history” cannot rest on mere plausibility or force of argument. I must be able to convince you—by actual example—that honorable, reasonable, and fascinatingly different alternatives could have produced a substantially divergent history of life not graced by human intelligence.
The problem, of course, with describing alternatives is that they didn’t happen—and we cannot know the details of their plausible occurrence. I feel certain, for example, that no Burgess paleontologist could have surveyed the twenty-five possibilities of arthropod design, rejected the most common (and anatomically sleek) Marrella, put aside the beautifully complex Leanchoilia or the sturdy, workaday Sidneyia, and admitted the ecologically specialized Aysheaia and the rare Sanctacaris to the company of the elect. But even if we could envision a modern arthropod world built by descendants of Marrella, Leanchoilia, and Sidneyia, how could we specify the forms that their descendants would take? After all, we cannot even make predictions when we know the line of descent: we cannot see the mayfly in Aysheaia, or the black widow spider in Sanctacaris. How can we specify the world that different decimations would have produced?
I believe that the best response to this dilemma is to adopt a more modest approach. Instead of seeking an illustration based on unknowable descendants of groups that did not in fact survive, let us consider a plausible alternative world different only in the diversity of two groups that graced the Burgess and survive today—for here we need conjecture only about the reasons for relative abundance. Take two groups of modern oceans—one bursting with diversity, the other nearly gone. Would we have known, at the Burgess beginning of both, which was destined for domination and which for peripheral status in the nooks and crannies of an unforgiving world? Can we make a plausible case for a replay with opposite outcome? (Again, as for so much of this book, I owe this example to the suggestion and previous probing of Simon Conway Morris.)
Consider the current distribution of two phyla sharing the most common invertebrate body plan—the flexible, elongate, bilateral symmetry of “worms.” Polychaetes, the major marine c
omponent of the phylum Annelida (including earthworms on land), represent one of life’s great success stories. The best modern epitome, Sybil P. Parker’s McGraw-Hill Synopsis and Classification of Living Organisms (1982), devotes forty pages to a breathless summary of their eighty-seven families, one thousand genera, and some eight thousand species. Polychaetes range in size from less than one millimeter to more than three meters; they live nearly everywhere, most on the sea floor, but some in brackish or fresh water, and a few in moist earth. Their life styles also span the range of the thinkable: most are free-living and carnivorous or scavenging, but others dwell commensally with sponges, mollusks, or echinoderms, and some are parasites.
By contrast, consider the priapulids, burrowing worms with bodies divided roughly into three parts—a rear end with one or two appendages, a middle trunk, and a retractable front end, or proboscis. Both the form of the proboscis and its power of erection from the trunk inevitably reminded early male zoologists of something else to which they were, no doubt, firmly and fondly attached—hence the burden of nomenclature for these creatures as Priapulus, or the “little penis.”
The armature of the priapulid proboscis might give some cause for alarm in unwarranted analogy. In most species the lower portion sports twenty-five rows of little teeth, or scalids, surmounted by a collar, or buccal ring. The upper end contains several inscribed pentagons of teeth surrounding the mouth. Most priapulids are active carnivores, capturing and swallowing their prey whole, although one species may feed on detritus.
Wonderful Life: The Burgess Shale and the Nature of History Page 30