Hen’s Teeth and Horse’s Toes

by Stephen Jay Gould

  Hutton’s theory rests, in part, on his choice of metaphors for the earth. With friendship for James Watt and with reverence for Isaac Newton, Hutton chose to see the world as a perfect machine that, once wound, would run forever (or until God changed the rules) without wearing out or breaking down. “This world,” Hutton proclaimed,

  is an active scene or a material machine moving in all its parts. We must see how this machine is so contrived, as either to have those parts to move without wearing or decay, or to have those parts, which are wasting and decaying, again repaired.

  Hutton therefore contrived a four-stage, cyclical theory of earth history. In the first stage, the only one we can observe directly, the land is worn away by erosion and eventually (stage two) deposited as strata in the depths of the ocean. There (stage three), the strata are compacted and consolidated by heat (both from the interior fires of the earth and from the weight of overlying sediments), and then (stage four), as a result of the same internal heat, fractured and uplifted to form new continents. Land and sea have changed places and the cycle starts again: erosion, deposition, consolidation, and uplift—forever and ever. Thus, in the most famous words ever written by a geologist, Hutton ends his 1788 treatise by explicitly comparing his world machine with the endless cycling of planets about the sun:

  Having, in the natural history of this earth, seen a succession of worlds, we may from this conclude that there is a system in nature; in like manner as, from seeing revolutions of the planets, it is concluded, that there is a system by which they are intended to continue those revolutions…. The result, therefore, of our present enquiry is, that we find no vestige of a beginning,—no prospect of an end.

  Although Hutton had predecessors for each individual claim, the revolutionary content of his comprehensive system has two primary sources. First, he burst the boundaries of time, thereby establishing geology’s most distinctive and transforming contribution to human thought—“deep time,” as John McPhee (Basin and Range, 1981) puts it. In his next most famous statement, Hutton wrote: “Time, which measures everything in our idea, and is often deficient to our schemes, is to nature endless and as nothing.”

  One of the major barriers to an acceptance of deep time had been the absence of any recognized restoring force in the operations of nature. Geologists before Hutton generally lacked a “concept of repair.” They knew that erosion constantly wore down the land, and cultural traditions supported the idea of history as a continual decline from the original perfection of Eden. They did not recognize that the earth’s internal heat could fracture and raise vast areas of the continents into mountains and high plains; (they regarded mountain ranges as part of the earth’s original structure and volcanoes as mere pimples on the globe’s degrading surface). Without such a concept of repair, the earth must be very young. After all, it would not take long to erode all continents beneath the sea, and mountains still tower above us. As his second great contribution, Hutton demonstrated that igneous forces within the earth supplied a restorative power that uplifted continents, prevented the land’s destruction, permitted a theory of endless cycling, and established the possibility of deep time.

  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.

  What clearer evidence could we have had of the different formation of these rocks, and of the long interval which separated their formation, had we actually seen them emerging from the bosom of the deep?…The mind seemed to grow giddy by looking so far into the abyss of time.

  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:

  He went far afield in search of facts, and to test his interpretation of them. He made journeys into different parts of Scotland…. He extended his excursions likewise into England and Wales. For about thirty years, he had never ceased to study the natural history of the globe, constantly seeking to recognize the proofs of ancient terrestrial revolutions, and to learn by what causes they had been produced.

  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:

  When we trace the parts of which this terrestrial system is composed, and when we view the general connection of those several parts, the whole presents a machine of a peculiar construction by which it is adapted to a certain end. We perceive a fabric, erected in wisdom, to obtain a purpose worthy of the power that is apparent in the production of it.

  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:

  A solid body of land could not have answered the purpose of a habitable world; for a soil is necessary to the growth of plants; and a soil is nothing but the materials collected from the destruction of the solid land…. The heights of our land are thus leveled with the shores; our fertile plains are formed from the ruins of mountains.

  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:

  If no such reproductive power, or reforming operation, after due enquiry, is to be found in the constitution of this world, we should have reason to conclude, that the system of this earth has either been intentionally made imperfect, or has not been the work of infinite power and wisdom.

  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:

  This is the view in which we are now to examine the globe; to see if there be, in the constitution of this world, a reproductive operation, by which a ruined constitution may be again repaired, and a duration or stability thus procured to the machine, considered as a world sustaining plants and animals…. Here is an important question…a question which, perhaps, it is in the power of man’s sagacity to resolve; and a question which, if satisfactorily resolved, might add some lustre to science and the human intellect.

  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:

  The end of nature in placing an internal fire or power of heat, and a force of irresistible expansion, in the body of this earth, is to consolidate the sediment collected at the bottom of the sea, and to form thereof a mass of permanent land above the level of the ocean, for the purpose of maintaining plants and animals.

  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:

  They were the parts…which he contemplated with greatest delight; and he would have been less flattered, by being told of the ingenuity and originality of his theory, than of the addition which it had made to our knowledge of final causes.

  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.

  7 | The Stinkstones of Oeningen

  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:

  Genius and science have burst the limits of space, and…have unveiled the mechanism of the universe. Would it not also be glorious for man to burst the limits of time…. Astronomers, no doubt, have advanced more rapidly than naturalists; and the present period, with respect to the theory of the earth, bears some resemblance to that
in which some philosophers thought that the heavens were formed of polished stone, and that the moon was no larger than the Peloponnesus; but, after Anaxagoras, we have had our Copernicuses, and our Keplers, who pointed out the way to Newton; and why should not natural history also have one day its Newton? [I have followed the famous Jameson translation of 1817, which is as canonical for Cuvier’s Discours préliminaire as its namesake King James’s is for Moses—hence some pleasant archaisms throughout, although I have checked the original in all cases for accuracy.]

  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: