Hen’s Teeth and Horse’s Toes (8 page)

For each of these contributions—deep time and a concept of repair—Hutton supplied a key empirical observation. For time, Hutton recognized the significance of what geologists call an angular unconformity. Old sedimentary rocks, originally deposited in horizontal sheets, are often uplifted and tilted during the operation of Hutton’s restorative forces. They may then be eroded down, covered again by water, and overlain by a new sequence of horizontal sediments. The contact between these two packages of sedimentary rocks is called an angular unconformity because the tilted older strata meet the horizontal younger strata at an angle. Hutton rejoiced in these unconformities because they yielded direct evidence for his theory of cycles. Each angular unconformity recorded
two
Huttonian worlds placed in sequence one atop the other—an older world in the first package, made in the depths of the sea, uplifted, and eroded down again, and a younger world in the second package, made in a later ocean and now uplifted to our view. John Playfair, Hutton’s greatest interpreter and the most literate man who ever wrote about geology, recorded his awe upon viewing an angular unconformity on a field trip with Hutton:

Hutton’s original figure of an angular unconformity. Note vertical strata below and horizontal above.
DRAWING BY JOHN CLARK APPEARED IN HUTTON’S
1795
TREATISE
.

For a concept of repair, Hutton recognized the igneous nature of two common rocks, basalt and granite. Many geologists at the time argued that basalt and granite were sedimentary rocks, deposited from water; Hutton held (correctly) that they had risen as magma from the depths of the earth and cooled to their present state. Thus, they represented the products of Hutton’s restorative force. This issue became the focus of a great struggle in science, the debate between Neptunists, who advocated water, and Plutonists (like Hutton), who opted for internal fires as the source of granite and basalt. The debate received a good popular press and even spilled onto the pages of
Faust
(Goethe being, among other things, a brilliant geologist) where, from the error of its author, Faust argues for water and Mephistopheles (only appropriately) for fires within the earth. Arcane scientific debates don’t receive this much notice unless the stakes are high—and indeed they were. Basalt and granite occupy vast areas of the earth’s surface. If they, like all other common rocks then recognized, are sedimentary, then all rocks may be products of an original ocean, and the entire history of our earth may be short and directional—a few thousand years of deposition and drying out. But if granite and basalt are igneous, then they record a restorative force of sufficient power to cover much of the earth with its products. History may be cyclical and long. Hutton relied primarily upon field evidence for his Plutonian conclusions. He noted, in particular, that granite and basalt often occur as vertical dikes cutting through horizontal sediments and marking the passageway of magmas from the earth’s interior.

Did Hutton base his general theory upon these observations? Did he triumph, as the usual story goes, because he was an objective modernist who combated ancient traditions of prejudiced speculation by using the “real” scientist’s tool of pure and unfettered observation, and by holding a modern concept of mechanical causality? Hutton’s countryman, the great Scottish geologist Sir Andrew Geikie, gave this common myth its strongest support in his 1905 volume,
The Founders of Geology
. Geikie wrote: “In the whole of Hutton’s doctrine he rigorously guarded himself against the admission of any principle which could not be founded on observation. He made no assumptions. Every step in his deductions was based upon actual fact.” Geikie’s heroic Hutton gathered his facts by the method that provides both the strength and the mystique of geology—fieldwork:

This Hutton matches the idealized image of geology presented to generations of students, but it bears little relation to the original. To be sure, Hutton did not remain perennially in his armchair. He made many excursions and saw many things. His observations no doubt inspired and instructed him; but we can show, also without doubt, that fieldwork was not the source of his theory. For his two key observations, the chronology of the official myth is backward. Hutton saw his first angular unconformity after he had presented his full-blown theory in public. Moreover, by his own admission, he had observed granite in only one uninformative place before publishing his theory. Fieldwork, at best, provided confirmation for a theory developed elsewhere.

When we consult Hutton’s written record, we find—if we may take his own presentation at face value—that he developed his general theory by the accepted route of eighteenth-century system builders: he reasoned from his own version of first principles and then gathered arguments for what he regarded as necessary conclusions. And when we examine Hutton’s concept of first principles, we find that he was not a mechanist committed to empirical test, but a follower of Aristotle’s notion of causality.

Hutton did have a mechanical concept of causality; his earth is a perfect machine, working with no hint of senescence until God chooses to ordain an end. But Hutton followed Aristotle in arguing that events have
both
a mechanical (or efficient) cause and a purpose, or final cause. Of the two, Hutton clearly regarded final causes as more important and more fundamental to his system. When Geikie and others chose to ignore Hutton’s own writing, and to use him as a moral homily for an idealized view of science, they did major disservice to a great, if not a modern, intellect.

The very first paragraph of Hutton’s great work (the original 1788 version), in emphasizing both machines and purposes, advances the Aristotelian argument that any adequate theory of the earth must explain both how and why:

In the fourth paragraph, we learn that the earth’s final cause must be expressed in terms of fitness for its sentient inhabitants, namely us: “This globe of the earth is a habitable world; and on its fitness for this purpose, our sense of wisdom in its formation must depend.”

Hutton then explains how he developed his general theory of the earth as a self-restoring machine with a cyclical history of erosion, deposition, consolidation, and uplift. He appeals neither to field observations nor to mechanical causes but bases his argument on a puzzle arising from his own experience as a farmer and centered squarely on the idea of final cause. We may refer to this puzzle as the “paradox of the soil.”

Without soil for agriculture, we could not support ourselves on this planet. Soil is a product of erosion, the destructive phase of the Huttonian cycle:

Now, the paradox. To form the soil so necessary for our lives and, therefore, so essential to the earth’s final cause, nature uses a mechanical process that must destroy the land: “We are, therefore, to consider as inevitable the destruction of our land, so far as effected by those operations which are necessary in the purpose of the globe, considered as a habitable world.” But God would not play such a joke on his favored creatures. He could not employ as a source of life-giving soil a process that must soon obliterate all humanity by washing our land into the sea. A restorative force must exist a priori, so that the earth may display wisdom in its adaptation for human life:

Hutton did not find his restorative force unexpectedly in the field by stumbling upon an angular unconformity or pondering the nature of granite. He deduced the necessity of a restorative force from a threatening paradox in final cause, and then set out to find it. Indeed, he portrays his entire treatise as an earnest search for purpose in physical objects:

When Hutton locates his restoring forces in the earth’s internal fire, he continues the Aristotelian strategy of identifying both how they work and why, in human terms, they operate as they do:

Volcanoes, Hutton tells us, are “not made on purpose to frighten superstitious people into fits of piety and devotion, nor to overwhelm devoted cities with destruction.” They are escape vents for internal fires, “spiracles to the subterranean furnace, in order to prevent the unnecessary elevation of land, and fatal effects of earthquakes.” Some may die in their eruptions, but only so that more may live: “While it may occasionally destroy the habitations of a few, it provides for the security and quiet possession of the many.”

Hutton’s contemporaries certainly understood the central role of final cause in his theory, both as an original motivation and a sustaining theme. Playfair wrote of his treatise: “We see everywhere the utmost attention to discover, and the utmost disposition to admire, the instances of wise and beneficent design manifested in the structure, or economy of the world.” Hutton, he continued, regarded final causes as preeminent:

I am not, of course, suggesting that final cause be readmitted into science as a component for the explanation of physical events. I merely wish to point out that, although theories may be winnowed and preserved empirically, their sources are as many as people and times and traditions and cultures are varied. If we use the past only to create heroes for present purposes, we will never understand the richness of human thought or the plurality of ways of knowing.

Final cause inspired the greatest of all geological theories, but we may use it no longer for physical objects. This creative loss is part of Darwin’s legacy, a welcome and fruitful retreat from the arrogant idea that some divine power made everything on earth to ease and inform our lives. The extent of this loss struck me recently when I read a passage from the work of Edward Blyth, a leading creationist of Darwin’s time. He wrote of the beauty and wisdom “so well exemplified in the adaptation of the ptarmigan to the mountain top, and the mountain top to the habits of the ptarmigan.” And I realized that this little line expressed the full power of what Darwin had wrought—for while we may still speak of the ptarmigan adapting to the mountain, we may no longer regard the mountain as adapted to the ptarmigan. In this loss lies all the joy and terror of our current view of life.

IN HIS MANIFESTO
for a science of paleontology, Georges Cuvier compared our ignorance of geological time with our mastery of astronomical space. He wrote, in 1812, in the preliminary discourse to his great four-volume work on the bones of fossil vertebrates:

Cuvier, an ambitious man, may have held personal hopes, though Darwin (whose earthly remains do lie next to Newton’s in Westminster Abbey) has generally commandeered the proffered title. Still, Cuvier didn’t do badly. His immediate successors, at least in France, usually referred to him as the Aristotle of biology.

The centenary of Darwin’s death (April 1882) has prompted a round of celebrations throughout the world. But 1982 is also the sesquicentenary of Cuvier’s demise (1769–1832), and our erstwhile Aristotle has attracted scant notice. Why has Cuvier, surely the greater giant in his own day, been eclipsed (at least in the public eye) during our own? In power of intellect, and range and breadth of output, Cuvier easily matched Darwin. He virtually founded the modern sciences of paleontology and comparative anatomy and produced some of the first (and most beautiful) geological maps. Moreover, and so unlike Darwin, he was a major public and political figure, a brilliant orator, and a high official in governments ranging from revolution to restoration. Charles Lyell, the great English geologist, visited Cuvier at the height of his influence and described the order and system that yielded such a prodigious output from a single man:

Cuvier has suffered primarily because posterity has deemed incorrect the two cardinal conclusions that motivated his work in biology and geology—his belief in the fixity of species and his catastrophism. Since being wrong is a primary intellectual sin when we judge the past by its approach to current wisdom, dubious motives must be ascribed to Cuvier. How else can one explain why such a brilliant man went so far astray? Cuvier then becomes an object lesson for aspiring scientists. Cuvier must have failed because he allowed prejudice to cloud objective truth. Conventional theology must have dictated both his creationism and the geological catastrophism that supposedly squeezed our earth into the Mosaic chronology. Consider this assessment of Cuvier presented by a leading modern textbook in geology:

I devote this essay to defending Cuvier (who ranks, in my judgment, with Darwin and Karl Ernst von Baer as the greatest of nineteenth-century natural historians). But I do not choose to do so in the usual manner of historians—by showing that Cuvier’s beliefs were not rooted in irrational prejudice, but both arose from and advanced beyond the social and scientific context of his own time. Nor (obviously) will I defend Cuvier’s creationism or more than a sliver of his catastrophism. Instead, I want to argue that Cuvier used the very doctrines for which he stands condemned—creationism and catastrophism—as specific and highly fruitful research strategies for establishing the basis of modern geology—the stratigraphic record of fossils and its attendant long chronology for earth history. Some types of truth may require pursuit on the straight and narrow, but the pathways to scientific insight are as winding and complex as the human mind.

Cuvier is often portrayed as an armchair speculator because his conclusions are now regarded as incorrect and error supposedly arises from aversion to hard data. In fact, he was a committed empiricist. He railed against the prevalent tradition in geology for constructing comprehensive “theories of the earth” with minimal attention to actual rocks and fossils. “Naturalists,” he wrote, “seem to have scarcely any idea of the propriety of investigating facts before they construct their systems.” (Cuvier correctly includes Hutton, subject of essay 6, among the system builders, although he confesses more sympathy for his Scottish colleague than for most of his ilk.)

Instead, Cuvier argues, we must seek some empirical criterion for unraveling the earth’s history. But what shall it be? What has changed with sufficient regularity and magnitude to serve as a marker of time? Cuvier recognized that the lithology of rocks would not do, since limestones and shales look pretty much alike whether they occur at the tops or bottoms of stratigraphic sequences. What about the fossils entombed in rocks?

The idea that fossils reflect history is now so commonplace, we tend to regard it as an ancient truth. It was, however, a contentious issue in Cuvier’s day, when debate centered on whether or not species could become extinct—for without extinction, all creatures are coeval and fossils cannot measure time (unless new forms keep accumulating and we can date rocks by first appearances. But a finite earth would seem to preclude continual addition with no subtraction).

Many of Cuvier’s illustrious contemporaries (including Thomas Jefferson who, when not preoccupied with other matters, devoted a paper to the subject) argued strongly that extinction could not occur. Cuvier decided that the a priori (and often explicitly biblical) defenses of nonextinction were worthless and that the issue would have to be decided empirically. But previous studies of fossil vertebrates (his specialty) had been undertaken in the mindless manner of mere collection. Fossils had been gathered primarily as curiosities—but scientists must
ask questions
and collect systematically in their light.

Cuvier then provides a two-page compendium of questions, an empiricist’s
vade mecum
to combat the older speculative tradition.

But this research program for establishing a geological record cannot work unless extinction is a common fact of nature—and ancient creatures are therefore confined to rocks of definite and restricted ages. Cuvier’s great four-volume work (
Recherches sur les ossemens fossiles
, “studies on fossil bones”) is a long demonstration that fossil bones belong to lost worlds of extinct species.

Cuvier used the comparative anatomy of living vertebrates to assign his fossils to extinct species. Since fossils come in bits and pieces, a tooth here or a femur there, some method must be devised to reconstruct a whole from scrappy parts and to ascertain whether that whole still walks among the living. But what principles shall govern the reconstruction of wholes from parts? Can it be done at all? Cuvier recognized that he must study the anatomy of modern organisms—where we have unambiguous wholes—to learn how to interpret fragments of the past. The second paragraph of his essay presents this program for research:

As his cardinal rule for reconstruction, Cuvier devised a principle that he called “correlation of parts.” Animals are exquisitely designed and integrated structures—perfect Newtonian machines of a sort. Each part implies the next, and a whole lies embodied in the implications of any fragment—a grand version of that immortal commentary on Ezekiel’s vision, “the foot bone’s connected to the ankle bone….”

Cuvier presents the law of correlation as if it could be applied by reason alone, using the principles of animal mechanics:

Cuvier’s principle of correlation lies behind the popular myth that paleontologists can see an entire dinosaur in a single neck bone. (I believed this legend as a child and once despaired of entering my chosen profession because I could not imagine how I could ever obtain such arcane and wondrous knowledge.) Cuvier’s principle may well apply in the most general sense: if I find a jaw with weak peglike teeth, I do not expect to find the sharp claws of a carnivore on the accompanying legs. But a single tooth will not tell me how long the legs were, how sharp the claws, or even how many other teeth the jaw held. Animals are bundles of historical accidents, not perfect and predictable machines.

When a paleontologist does look at a single tooth and says, “Aha, a rhinoceros,” he is not calculating through laws of physics, but simply making an empirical association: teeth of this peculiar form (and rhino teeth are distinctive) have never been found in any animal but a rhino. The single tooth implies a horn and a thick hide only because all rhinos share these characters, not because the deductive laws of organic structure declare their necessary connection. Cuvier, in fact, knew perfectly well that he operated by empirical association (and not by logical inference), although he regarded his observational method as an imperfect way station to a future rational morphology: