Wonderful Life: The Burgess Shale and the Nature of History (45 page)

And he added:

Walcott’s explanation may sound forced and
ad hoc
. It was surely born of frustration, rather than the pleasure of discovery. Yet the nonexistent Lipalian was not a fool’s rationalization, as usually presented in our textbooks, but a credible synthesis of geological evidence in the context of a vexatious dilemma. If Walcott deserves any brickbats, direct them at his failure to consider any alternative to his favored way of thinking about the artifact theory—and at his false assumption, imposed by the old bias of gradualism, that equated evolution itself with a long sequence of ancestral continuity for any complex creature. For even if the Lipalian hypothesis made sense in the light of existing geological information, it rested, as Walcott knew only too well, upon the most treacherous kind of argument that a scientist can ever use—negative evidence. Walcott admitted: “I fully realize that the conclusions above outlined are based primarily on the absence of a marine fauna in Algonkian rocks” (1910, p. 6).

And, as so often happens in the face of negative evidence, the earth eventually responded, offering to later geologists abundant late Precambrian marine sediments—still with no fossils of complex invertebrates. The Lipalian interval ended up on the trash heap of history.

Scientists have a favorite term for describing a phenomenon like Walcott’s allegiance to the Burgess shoehorn—overdetermined. The modern concept of maximal disparity and later decimation (perhaps by lottery) never had the ghost of a chance with Walcott because so many elements of his life and soul conspired to guarantee the opposite view of the shoehorn. Any one of these elements would have been enough in itself; together, they overwhelmed any alternative, and overdetermined Walcott’s interpretation of his greatest discovery.

To begin, as we have seen, Walcott’s persona as an archtraditionalist in thought and practice did not lead him to favor unconventional interpretations in any area of life. His general attitude to life’s history and evolution implied stately unfolding along predictable pathways defined by the ladder of progress and cone of increasing diversity; this pattern also held moral meaning, as a display of God’s intention to imbue life with consciousness after a long history of upward striving. Walcott’s specific approach to the key problem that had focused his entire career—the riddle of the Cambrian explosion—favored a small set of stable and well-separated groups during Burgess times, so that a long history of Precambrian life might be affirmed, and the artifact theory of the Cambrian explosion supported. Finally, if Walcott had been at all inclined to abandon his ideological commitment to the shoehorn, in the light of contradictory data from the Burgess Shale, his administrative burdens would not have allowed him time to study the Burgess fossils with anything like the requisite care and attention.

I have labored through the details of Walcott’s interpretation and its sources because I know no finer illustration of the most important message taught by the history of science: the subtle and inevitable hold that theory exerts upon data and observation. Reality does not speak to us objectively, and no scientist can be free from constraints of psyche and society. The greatest impediment to scientific innovation is usually a conceptual lock, not a factual lack.

The transition from Walcott to Whittington is a premier example of this theme. The new view—as important an innovation as paleontology has ever contributed to our understanding of life and its history—was in no way closed to Walcott. Whittington and colleagues studied Walcott’s specimens, using techniques and tools fully available in Walcott’s time, in making their radical revision. They did not succeed as self-conscious revolutionaries, touting a new view in
a priori
assault. They began with Walcott’s basic interpretation, but forged ahead on both sides of the great dialectic between theory and data—because they took the time to converse adequately with the Burgess fossils, and because they were willing to listen.

The transition from Walcott to Whittington marks a milestone that could hardly be exceeded in importance. The new view of the Burgess Shale is no more nor less than the triumph of history itself as a favored principle for reading the evolution of life.

Our language is full of phrases that embody the worst and most restrictive stereotype about science. We exhort our frustrated friends to be “scientific”—meaning unemotional and analytic—in approaching a vexatious problem. We talk about the “scientific method,” and instruct schoolchildren in this supposedly monolithic and maximally effective path to natural knowledge, as if a single formula could unlock all the multifarious secrets of empirical reality.

Beyond a platitudinous appeal to open-mindedness, the “scientific method” involves a set of concepts and procedures tailored to the image of a man in a white coat twirling dials in a laboratory—experiment, quantification, repetition, prediction, and restriction of complexity to a few variables that can be controlled and manipulated. These procedures are powerful, but they do not encompass all of nature’s variety. How should scientists operate when they must try to explain the results of history, those inordinately complex events that can occur but once in detailed glory? Many large domains of nature—cosmology, geology, and evolution among them—must be studied with the tools of history. The appropriate methods focus on narrative, not experiment as usually conceived.

The stereotype of the “scientific method” has no place for irreducible history. Nature’s laws are defined by their invariance in space and time. The techniques of controlled experiment, and reduction of natural complexity to a minimal set of general causes, presuppose that all times can be treated alike and adequately simulated in a laboratory. Cambrian quartz is like modern quartz—tetrahedra of silicon and oxygen bound together at all corners. Determine the properties of modern quartz under controlled conditions in a laboratory, and you can interpret the beach sands of the Cambrian Potsdam Sandstone.

But suppose you want to know why dinosaurs died, or why mollusks flourished while
Wiwaxia
perished? The laboratory is not irrelevant, and may yield important insights by analogy. (We might, for example, learn something interesting about the Cretaceous extinction by testing the physiological tolerances of modern organisms, or even of dinosaur “models,” under environmental changes proposed in various theories for this great dying.) But the restricted techniques of the “scientific method” cannot get to the heart of this singular event involving creatures long dead on an earth with climates and continental positions markedly different from today’s. The resolution of history must be rooted in the reconstruction of past events themselves—in their own terms—based on narrative evidence of their own unique phenomena. No law guaranteed the demise of
Wiwaxia
, but some complex set of events conspired to assure this result—and we may be able to recover the causes if, by good fortune, sufficient evidence lies recorded in our spotty geological record. (We did not, until ten years ago, for example, know that the Cretaceous extinction corresponded in time with the probable impact of one or several extraterrestrial bodies upon the earth—though the evidence, in chemical signatures, had always existed in rocks of the right age.)

Historical explanations are distinct from conventional experimental results in many ways. The issue of verification by repetition does not arise because we are trying to account for uniqueness of detail that cannot, both by laws of probability and time’s arrow of irreversibility, occur together again. We do not attempt to interpret the complex events of narrative by reducing them to simple consequences of natural law; historical events do not, of course, violate any general principles of matter and motion, but their occurrence lies in a realm of contingent detail. (The law of gravity tells us how an apple falls, but not why that apple fell at that moment, and why Newton happened to be sitting there, ripe for inspiration.) And the issue of prediction, a central ingredient in the stereotype, does not enter into a historical narrative. We can explain an event after it occurs, but contingency precludes its repetition, even from an identical starting point. (Custer was doomed after a thousand events conspired to isolate his troops, but start again in 1850 and he might never see Montana, much less Sitting Bull and Crazy Horse.)

These differences place historical, or narrative, explanations in an unfavorable light when judged by restrictive stereotypes of the “scientific method.” The sciences of historical complexity have therefore been demoted in status and generally occupy a position of low esteem among professionals. In fact, the status ordering of the sciences has become so familiar a theme that the ranking from adamantine physics at the pinnacle down to such squishy and subjective subjects as psychology and sociology at the bottom has become stereotypical in itself. These distinctions have entered our language and our metaphors—the “hard” versus the “soft” sciences, the “rigorously experimental” versus the “merely descriptive.” Several years ago, Harvard University, in an uncharacteristic act of educational innovation, broke conceptual ground by organizing the sciences according to procedural style rather than conventional discipline within the core curriculum. We did not make the usual twofold division into physical versus biological, but recognized the two styles just discussed—the experimental-predictive and the historical. We designated each category by a letter rather than a name. Guess which division became Science A, and which Science B? My course on the history of earth and life is called Science B-16.

Perhaps the saddest aspect of this linear ranking lies in the acceptance of inferiority by bottom dwellers, and their persistent attempt to ape inappropriate methods that may work higher up on the ladder. When the order itself should be vigorously challenged, and plurality with equality asserted in pride, too many historical scientists act like the prison trusty who, ever mindful of his tenuous advantages, outdoes the warden himself in zeal for preserving the status quo of power and subordination.

Thus, historical scientists often import an oversimplified caricature of “hard” science, or simply bow to pronouncements of professions with higher status. Many geologists accepted Lord Kelvin’s last and most restrictive dates for a young earth, though the data of fossils and strata spoke clearly for more time. (Kelvin’s date bore the prestige of mathematical formulae and the weight of physics, though the discovery of radioactivity soon invalidated Kelvin’s premise that heat now rising from the earth’s interior records the cooling of our planet from an initially molten state not long past.) Even more geologists rejected continental drift, despite an impressive catalogue of data on previous connections among continents, because physicists had proclaimed the lateral motion of continents impossible. Charles Spearman misused the statistical technique of factor analysis to designate intelligence as a single, measurable, physical thing in the head, and then rejoiced for psychology because “this Cinderella among the sciences has made a bold bid for the level of triumphant physics itself” (quoted in Gould, 1981, p. 263).

But historical science is not worse, more restricted, or less capable of achieving firm conclusions because experiment, prediction, and subsumption under invariant laws of nature do not represent its usual working methods. The sciences of history use a different mode of explanation, rooted in the comparative and observational richness of our data. We cannot see a past event directly, but science is usually based on inference, not unvarnished observation (you don’t see electrons, gravity, or black holes either).

A PLEA FOR THE HIGH STATUS OF NATURAL HISTORY

In no other way but this false ordering by status among the sciences can I understand the curious phenomenon that led me to write this book in the first place
—
namely, that the Burgess revision has been so little noticed by the public in general and also by scientists in other disciplines. Yes, I understand that science writers don’t consult the
Philosophical Transactions of the Royal Society, London,
and that hundred-page anatomical monographs can seem rather daunting to those unschooled in the jargon. But we cannot charge Whittington and colleagues with hiding the good news. They have also published in the general journals that science writers do read
—
principally
Science
and
Nature.
They have written half a dozen prominent “review articles” for scientific colleagues. They have also composed a good deal for general audiences, including articles for
Scientific American
and
Natural History,
and a popular guide for Parks Canada. They know the implications of their work, and they have tried to get the message across; others have also aided (I have written four essays on the Burgess Shale for
Natural History).
Why has the story not taken hold, or been regarded as momentous?