. . . And Still We Evolve
A Handbook on the History of Modern Science
[This handbook, which has been prepared by Ian Johnston of Malaspina University-College, Nanaimo, BC (now Vancouver Island University), for Liberal Studies students, is in the public domain and may be used without charge and without permission, released May 2000]
[Table of Contents]
Section Two: The Early Development of Modern Geology
Geology and Religion: The Problem of Historical Science
The major 18th century challenge to orthodox religion and traditional order came not from astronomy or physics, which, as we have seen, generally supported natural theology (except in their extreme materialistic version), but from the growing interest in geology, the study of the earth (1). And the enquiries undertaken by the geologists, which proved so essential to 19th century biology, not least of all to Darwin, were to have revolutionary consequences for religion and society, in many respects consequences far more fundamental than those brought about by the Copernican-Newtonian revolution in physics.
One of the major reasons why geology and biology proved so devastating had to do with the way in which they introduced a new element into the human understanding of the world, the study of phenomena historically, that is, as the unique results of a process of change. As Stephen Jay Gould has remarked, once the astronomers set the stage, the geologists and biologists then set about attending to the plot.
For the most part, constructing a narrative of the earth's origins had not been an issue raised by the great astronomers. They had been primarily concerned with establishing the eternal design of the cosmos and the permanent mathematical laws of motion. How the universe developed from a more primitive state to its present order they were content to ascribe to myth or to religion.
One instructive exception to the above remarks is Descartes. In his theory of vortices he had offered a hypothesis to explain the development of the solar system in naturalistic terms. However, Newton demonstrated that Descartes's idea violated Kepler's laws, and in so doing Newton stressed that the only satisfactory account for the present structure of our solar system was that it had been created by God in its present form:
. . . it is unphilosophical to seek for any Origin of the World [except divine creation], or to pretend that it might arise out of a Chaos by the mere Laws of nature; though being once form'd, it may continue by those Laws for many Ages.
Thus, Newton's physics did not, in itself, promote a historical approach to scientific problems; indeed, it was hostile to such a hypothesis.
It is easy to see why the revolution in our conceptions of space which the astronomers effected should have had less challenging impact than the revolution in our conceptions of time which the geologists and biologists introduced. Placing the sun rather than the earth in the centre of our solar system and insisting on the infinite distances of space were certainly potentially disturbing ("The eternal silences of the infinite frighten me," wrote Pascal in Fragment 206 of the Pensées). However, they did not directly challenge revealed religion or established order in so dramatic and fundamental a way as did a theory which insisted that Biblical accounts of the creation of the world and of human beings were historically impossible.
For the same reasons, one can see why people were less disturbed by the unwelcome realization that they were inhabitants of a minuscule planet somewhere in space than they were by the announcement that human beings had existed for only a minuscule portion of the history the earth (2).
The issue was not simply a matter of the feelings arising from a new orientation to nature. The difference between the apparently eternal stability of Newton's system and the dynamic, changing history of the new understanding of the earth had enormously important implications for one's views of everything which relied upon a natural order to endorse a particular political or religious view. Whether that natural order was a stable, recurring pattern or a constantly unfolding, non-repeatable process, and, if the latter, whether or not the historical process was governed by law, by God, or by chance, had a direct effect upon a wide range of social, philosophical, political, and religious issues.
Historical Critiques and Progress Through Science
Historical arguments in the 17th century were commonly closely linked to proposals for social reform. Hobbes, for example, appealed to an original state of nature (before the development of society) in order to advance his idea of a social contract. Following Hobbes's lead a century later, Rousseau anchored his political arguments on the same historical thinking. While neither Hobbes nor Rousseau made strong claims about the historical existence of such a state of nature, the tactics had obvious implications for those interested in developing a critical understanding of society and nature in terms of process, something powerfully encouraged by the discovery of so many "primitive" societies in the New World of the Americas.
Throughout the 18th century, appealing to historical developments from the Classical World to the Middle Ages, invoking, that is, the notion of a unique historical process, became an increasingly popular and persuasive method to analyze social institutions, particularly with a view to undermining present arbitrary authority by showing its historically based character (as opposed to all official notions about the eternal rightness of the present power arrangements). The most famous example in England was Edward Gibbon's Decline and Fall of the Roman Empire (1776), a devastating historical critique of early Christianity (3).
Linked to the rationality of the new science, such historical arguments often offered a reassuring sense of human progress, the modern idea that the growth of scientific knowledge led to social and political reform and was, in fact, society's best hope for an improved and improving future. For the most part, such optimism in the 18th century was cautious, but it fostered a belief in science as the enterprise most likely to lead to appropriate solutions to social and personal ills. This Enlightenment idea, which gained increasing support during the 19th century in all aspects of human life, was to have enormous implication for Western thought (only in recent years have we begun to entertain widespread doubts about this reassuring scenario).
In the spirit of this hope, during the French Revolution the Marquis de Condorcet, in a book with the revealing title Sketch for a Historical Picture of the Progress of the Human Mind (1795), could look back proudly on the achievement of his century:
[The progress of the sciences has] destroyed prejudices and . . . redirected the human intelligence, which had been obliged to follow the false directions imposed on it by the absurd beliefs that were implanted in each generation in infancy with the terrors of superstition and the fear of tyranny. All errors in politics and morals are based on philosophical errors and these in turn are connected with scientific errors. There is not a religious system nor a supernatural extravagance that is not founded on ignorance of the laws of nature. The inventors, the defenders of these absurdities could not foresee the successive perfection of the human mind.
Ironically, as Condorcet was writing these words, one of France's greatest scientists, Antoine Laurent Lavoisier (1743-1794) was led to the guillotine, after being informed that the Republic "had no need of scientists" (4).
The History of the Earth
For all of Newton's emphasis that, seen in its entirety, the universe was static, in his era a completely different view started to emerge, one that stressed the dynamic, developing, changing nature of both the heavens and the earth. In other words, the rising popularity of historical accounts of society extended itself to natural philosophy (science).
As we have seen, Rene Descartes (1596-1650) proposed as part of his mechanical philosophy the idea that there had been a history of the earth's formation. The Creation did not fix the present state of the earth, a condition which was the result of natural laws governing the development of the original matter over a long time span.
Descartes was very careful to make this suggestions with extreme tact (for he was on risky ground), arguing that it was only a hypothetical suggestion, a demonstration of how God, had He so wished, might have produced the earth and its life very slowly by natural secondary causes, rather than an account of how, Descartes assured his readers, God really did create the world (in six days) (5).
One of the first attempts to narrate a story about the earth's surface was undertaken by Nicolaus Steno (1648-1686), a Danish natural philosopher and later a bishop. In Prodromus (1699) Steno sought to reconstruct the history of the earth's surface on the basis of present empirical evidence. The task was to find out "in what way the present condition of any thing discloses the past condition of that same thing." The basic assumption here, and a fundamental difference between the historical approach and Newton's method, was that originally the earth had had a very different surface. In Steno's theory, this surface had originally been a smooth pile of sediments. Somehow, over time, disruption had taken place. The major scientific task was to provide a coherent narrative account of what had happened and why.
Steno relied heavily on scripture, but he had also undertaken field work in Italy and recognized the marine origin of fossils. His theory introduced into science a narrative of mechanically caused events (crustal collapse) to account for present phenomena. Thus, Steno's work is traditionally considered to mark the beginning of modern geology (there are, however, other claimants).
In the same period, Thomas Burnet, an Anglican clergyman and private chaplain to William III, produced in four volumes his Sacred Theory of the Earth (1680-1690). Burnet attempted, like Steno, to provide a natural explanation for the historical narrative given about the Creation in the Bible. He assumed the literal truth of the scriptural account and sought to explain the physics of those events. Burnet was confident that reason and scripture could be reconciled, because apparent contradictions, which were not compatible with the nature of God, would be resolved by future discoveries. Thus, he urged readers to be careful about too readily using scripture to deny scientific findings:
'Tis a dangerous thing to engage the authority of scripture in disputes about the natural world, in opposition to reason; lest time, which brings all things to light, should discover that to be evidently false which he had made scripture to assert. . . . We are not to suppose that any truth concerning the natural world can be an enemy to religion; for truth cannot be an enemy to truth, God is not divided against himself.
One of Burnet's central claims was that the present uneven features of the earth's surface were created at the time of Noah's Flood, which took place when the earth cracked open and waters rose from the abyss and subsided leaving the original perfection of the earth's surface forever altered.
Traditionally Burnet's book has been treated (especially by historians of geology) as an example of pseudo-scientific mumbo-jumbo and not considered significant. However, Newton (who corresponded with Burnet on the topic) praised the book, and a recent re-evaluation has called attention to the importance of Burnet's methodology, which refused to rest a scientific argument on miraculous interventions but which stressed the operation of physical laws in the service of a narrative explanation (6).
One of the major problems faced by Burnet and other early theorists about the history of the earth was an acute lack of enough empirical evidence. There were many speculative theories advanced on this topic throughout the 18th century. These drew attention to the issue of a historical approach to scientific questions and prompted more field work. The increasing attention paid to collecting information gradually gave the speculative narratives a firmer empirical basis, so that throughout the 18th century the narrative accounts fundamental to historical science acquired an increasingly firm factual basis.
Such facts seemed more and more to suggest that the earth had gone through different stages of development. So, for example, Benoît de Maillet (1659-1738) in Telliamed, or Conversations between and Indian Philosopher and a French Missionary on the Diminution of the Sea, the Formation of the Earth, the Origin of Man, etc. (1748) proposed that the world had undergone a series of epochs, a history incompatible with the literal scriptural accounts. According to de Maillet, the earth had been formed by natural causes and species of life had evolved over time, with land animals arising originally from creeping marine life.
Similar views were advanced by Georges Leclerc, Comte de Buffon (1707-1788), director of the royal botanical collection in Paris and one of the outstanding scientists of the century. His Histoire Naturelle, published from 1749 onward, used evidence of horizontal strata and marine fossils to infer that the earth had been formed by the slow action of natural causes. Buffon also proposed a theory for the historical origin of the planets as a result of a near collision of the sun and a comet (later called the dynamic encounter hypothesis).
While not totally denying scripture, Buffon nevertheless seriously offended the religious establishment, and in 1753, when the fourth volume of his work appeared, he disassociated himself from his own views, affirming (in an echo of Galileo) that he held to the literal Mosaic account and would give up his theory of the formation of the planets, which had been only "a purely philosophical supposition" (i.e., a thought experiment). These statements were probably ironic, since Buffon's later efforts continued his former work.
Buffon's emphasis on the essential similarity between the work of the historian and that of the natural scientist illustrates just how firmly entrenched the narrative approach to science had become within a century of the first triumph of Newton's ahistorical method:
Just as in Civil History, one consults titles, searches for medals, and deciphers ancient inscriptions in order to determine the epochs of human revolutions and to establish the dates of human or civil events, so in the same way in Natural History, it is necessary to dig into the archives of the world, drawing ancient monuments from the entrails of the earth, collecting their debris, and gathering together in one body of proofs all the clues of physical changes which can enable us to regain the different ages of Nature. (1779)
In Buffon's narrative view of nature, constant changes were an inherent part:
It is not possible to doubt . . . that there have occurred an infinity of revolutions, of upheavals, of particularly changes, and of alterations on the surface of the earth, as much by the natural movement of the waters of the sea as by the action of rains, of frosts, of running waters, of winds, of subterranean fires, of earthquakes, of floods, etc. (1749)
To support this notion, Buffon proposed that the earth was 75,000 years old (and perhaps much older, even millions of years) and that this history was characterized by distinct epochs (he described seven). In each of these epochs the earth had had a significantly different form. In tracing the narrative of these epochal changes, Buffon placed great stress on the importance of fossils (7).
This idea of narrative changes in the history of the earth is such a common notion for us nowadays that it is sometimes difficult fully to appreciate just how significant a change the new historical attitude was and how challenging many people found it. For if the earth was not a permanent entity but something with a unique history of change, what authority had those theories which defended particular social, religious, and political structures by an appeal to eternal verities manifested in the unchanging structure of the natural world or which insisted upon the eternal truth of biblical accounts? Newtonian physics had seemed to guarantee permanence, but the new historical science was offering a very different vision.
One can get a sense of the impact of this new idea by considering the different meanings of the world revolution. In Newtonian astronomy revolution meant an eternally recurring regular motion (like a planetary orbit), an unvaryingly repetitive pattern set at the creation and continuing indefinitely. In natural history, by contrast, revolution was increasingly being used to refer to a series of unique, irreversible, catastrophic, and still operating changes in a constant process of transformation. Thus, in the new scientific accounts there was less and less firm a basis for maintaining a faith in the permanent rightness in any present state of things (scientific or otherwise). The political implications of this new sense of time were not insignificant (8).
The Nebular Hypothesis
By the end of the 18th century and early in the 19th, a detailed historical approach was taken to Newton's astronomy itself. The nebular hypothesis, derived from the independent work of the Marquis de Laplace (1749-1827), the French mathematician, who was, as we have mentioned in Section One, very enthusiastic about denying any place for God in scientific explanations, of Immanuel Kant (1724-1804), and of William Herschel (1738-1822), the discoverer of the planet Uranus (in 1781) (9).
In this account, which became popular in England in the 1830's, the solar system originated through the action of natural law upon a condensing and rotating gaseous nebula of gravitating matter. As the contraction continued, according to this hypothesis, rings of matter formed at regular intervals, and then each ring condensed into a planet.
The development of this theory, which completed the mechanistic view of the cosmos by extending it back to primordial time, provided evolutionary biologists in the early 19th century with support from the most prestigious discipline of all (10).
Historical Science, Politics, and Scripture
The problems initiated by the historical approach arose, in large part, because orthodox Judaeo-Christian religion is a historically based faith which rests upon a belief in God's actions in history, so that the Biblical accounts of the creation of the world and of the life in it and of the relationship between the Creator and his creations are absolutely central to what it means to be a devout Christian. In addition, Christian religion was anchored upon a single codified text (a historical narrative) which had the status of the revealed word of God. While symbolic or allegorical interpretations of the Bible had long been an important part of Christian theology, the literal truth of the many parts of the story, especially of Genesis, was for many crucial to the faith.
Challenges to the literal authority of the scriptures were not new to the 18th century. A particularly strong attack on conventional interpretation of scripture had been launched by Hobbes (1651), and another followed soon after on the Continent in Tractatus Theologico-Politicus (1670) by Spinoza. The way in which these two writers were widely despised and vilified as atheists in the 18th century is a clear indication of the general hostility to any radical tampering with the narrative established by the revealed word in the Bible.
One does not have to probe very deeply to appreciate the political implications of any serious challenge to traditional interpretations of scripture. Sorting out the appropriate relationship between historical investigations of the earth's development and orthodox interpretation of scripture was obviously much more than simply a doctrinal dispute. It involved, and was clearly seen to involve, significant social and political implications for both conservatives and those demanding reform.
The first immediate challenge posed by the development of a historical interest in the development of the earth was twofold: (a) Did geological investigation confirm or contradict Genesis (especially the time frame of creation and the flood)? (b) Did the events in Genesis occur as a result of natural laws and, if not, what evidence was there for a divine purpose?
In response to these questions a number of different theoretical positions were adopted by 18th century geologists. At one extreme, advocates of naturalism or materialism held that eternal natural laws rule and have always ruled all nature, without divine design or final causes, and with only a material causation. Not surprisingly, such a position tended to be linked with radical and revolutionary politics.
At the other (non-scientific) extreme, the supernaturalists, especially those concerned about unwelcome social consequences latent in natural history, abolished all faith in rational and material connections between events, since the only adequate cause of all events in the world was the work of God, who, in His freedom, might produce order or depart from it, as His Divine Will chose. Reason must therefore adapt itself to revelation, not the other way around. According to some who held this view, the fossil record was unreliable since it was the work of Satan and intended to deceive human beings about revealed truth.
Intermediate between these two extremes were the deists, who held, as we have seen in Section One, that God created matter and laws according to a plan fixed at the time of creation and that the design of nature was the only sure evidence human beings had of God's activity (since there were no more divine interventions). This position corresponded with Charles Darwin's original stance in his work. The semi-deists were closer to religious orthodoxy. They permitted God occasional "unnatural" interventions, usually catastrophic.
In England, with some exceptions, the main arguments did not generally involve scriptural literalists or even very conservative Anglicans (who, for all the influence they exerted over scientific patronage, were not strongly represented in scientific circles, except in the universities) (11). The main disputes took place between moderate Anglicans and deists. The former maintained that the evidence of geology could be compatible with an interpretation of the Bible, and some devout Christian geologists maintained that geology, like Newton's astronomy, provided evidence for Christian belief. In the words of Richard Kirwan, president of the Royal Academy of Dublin, in 1799:
Recent experience has shown that the obscurity in which the philosophical knowledge of this [original] state has hitherto been involved, has proved too favorable to the structure of various systems of atheism or infidelity, as these have been in their turn to turbulence and immorality, not to endeavor to dispel it by all the lights which modern geological researches have struck out. Thus it will be found that geology naturally ripens . . . into religion, as this does into morality.
The main challenge to this position came from deists like James Hutton (1726-1797) and Charles Lyell (1797-1875), who believed in a deity but not in divine intervention or in the revelations of scripture.
We know less about the relationship between geology and religion on the Continent. It appears that outside Britain, geologists did not concern themselves so much about religion, perhaps because the advanced state of historical biblical scholarship in Germany had already convinced many that there was no great need to take the bible literally (in 1835 D. F. Strauss's Life of Jesus Critically Examined proposed that the Gospels were second-century mythological writings; the book was translated into English by George Eliot in 1846).
Moreover, in Germany there was a growing tendency by the end of the 18th century to base Christian belief less on concepts of God or on evidence of God's handiwork in the natural world than on the personal experience of faith. As S. T. Coleridge, one of the first importers of German thought into England, later put it,
Evidences of Christianity! I am weary of the word. Make a man feel the want of it, rouse him, if you can, to the self-knowledge of his need of it; and you may safely trust it to its own Evidence. (12).
In France, where in the 18th century there was a strong reform trend which attacked the abuses of the church, the scientific evidence against revealed religion was often welcomed as ammunition in an on-going struggle against old authority (especially by the deistic philosophers). However, once the monarchy was restored in France (after the defeat of Napoleon), some eminent French scientists, notably Georges Cuvier, linked their scientific narratives of the earth to attempts to preserve some authority for the scriptural account.
Fossils are the evidence in rocks of earlier animal and plant life. They may consist of actual remains (bones, teeth) or be casts or impressions of the hard parts. At times the bone or shell can be replaced by something harder, like silica. Other fossils remains can include tracks or molds of tracks and trails.
For a long time the origin of fossils was a very disputed matter. Some people thought they grew from seed (sperm) deposited on rock. Others saw in fossils evidence of Noah's flood. On the other hand, Leonardo da Vinci concluded that fossils now on high inland mountains could not have reached their present location during the Deluge (Noah's Flood).
Steno's work with fossils encouraged further studies of this key subject. Martin Lister (1638-1712) wrote the first book devoted to fossils based on their organic nature and proposed a geologic map. Buffon relied extensively upon fossil evidence. This growing interest in fossils was prompted by, among other things, an accelerating accumulation of fossil evidence throughout the 18th century, the result of field work, explorations, and the rapidly increasing rate of construction projects, particularly rock quarries (for building materials) and canals.
William Smith (1769-1839), a civil engineer who worked on the construction of canals in England, kept an extensive record of the fossils he observed in his tireless inquiries. Smith produced the first coloured geological map (1815) and in Stratigraphic System of Organized Fossils (1817) proposed the sedimentary rock units could be classified according to the fossil remains they contained and that, with the aid of the fossil record, geologists could assign relative ages to rocks. The identification and classification of fossils at that time provided the only sure means of comparing the ages of different rocks (other than the Law of Superposition, mentioned below).
For some scriptural geologists, fossils were convincing evidence of the truth of the Biblical account of the flood. One such inquirer was delighted to find fossils with Hebrew characters on them. Only when he discovered one containing his own name did he realize that his students had been playing a practical joke on him. However, the growing evidence for the different ages of sedimentary rocks (rocks formed in water by the deposit of small particles) and therefore of the fossils they contained gradually convinced most geologists that one single universal deluge was not a satisfactory explanation for the empirical evidence.
The accumulating facts brought out, too, certain difficulties in the narrative sequence of fossils. A particularly vexing problem for geologists and biologists was the apparently erratic nature of the fossil record. This appeared to contain confusing evidence about the varieties and frequency of fossils in successive layers of rock. A good deal of this evidence seemed to point to a discontinuous and progressive history of the earth and the life in it, with more frequent and more complex organisms in the younger strata (i.e., the strata closest to the surface of the earth).
Darwin himself relied upon the fossil record to back up his notion of descent with variation. However, since he was well aware that the inconsistent facts in the fossil record were a weak point in his theory of a constant rate of change, he appealed to the future: continued research would yield further evidence for his ideas by filling in the gaps in the fossil record (13).
James Hutton and Uniformitarianism
James Hutton (1726-1797), a Scotsman who is generally acknowledged (at least in British science) as the founder of the modern study of geology, in his work adopted a deistic position and a firm faith in the argument from design. He sought to find evidence of a wise and benevolent deity in the order of nature by research into the earth's crust, "to acknowledge an order, not unworthy of Divine wisdom, in a subject which, in another view, has appeared as the work of chance, of an absolute disorder and confusion" (1788).
Thus, Hutton, like Boyle before him, linked his work, which, unlike many of the theories of his contemporaries on the Continent, he conducted with a strong empirical emphasis (continuing the tradition recommended by Bacon), to an investigation which he hoped would reveal final causes. In discovering the laws of the earth's crust, he would be demonstrating "the purpose of a habitable world . . . a world peculiarly adapted to the purposes of man."
Hutton's fundamental assumption, which has remained the most important working principle of historical geology and biology every since, is the principle of uniformitarianism (often referred to, by a direct translation of the French term for the idea, as the actualistic principle). This notion was not original to Hutton. Leonardo da Vinci had anticipated it three hundred years earlier, and it had been explicitly formulated by French physician Georges Fushsel (1722-1773), as follows: "the manner in which nature at the present time is still acting and producing things must be assumed as the rule in our explanation."
In other words, the uniformitarian principle committed the scientist to explaining the past events of the earth's history in terms of processes still at work (without miraculously powerful events unknown today). This assumption is, in effect, making the same initial claim about time that Newton made about space. Just as the physical laws of motion are the same everywhere in the universe, so they have been the same throughout the history of the universe.
Uniformitarianism, as it later developed, involved at least three important assumptions about the continuity of physical processes of the present and the past: (a) that they were the same in kind and proceeded in the same way, (b) that they were the same in intensity, and (c) that they occurred at the same rate (14).
Hutton was aware that uniformitarianism committed him to a theory of very gradual changes, something which would dramatically conflict with the time spans given in Biblical accounts and, further, that it ruled out the operation of any sudden Divine interventions into the history of the earth.
On the basis of this principle and his observations, Hutton developed a picture of the earth as undergoing an endless mechanical steady-state cycle: oceans became land, land sunk down to lie under the ocean. The system was always undergoing change, but the change was cyclical and repetitive. There was a creative and omnipotent God, who had set this process in motion in accordance with natural laws and who did not intervene.
If we believe that there is almighty power and supreme wisdom employed for sustaining that beautiful system of plants and animals . . . we must certainly conclude that the earth, on which this system of living things depends, has been constructed on principles adequate to the end proposed, and procure it a perfection which it is our business to explore. Therefore, a proper [theory] should lead us to see that wise construction by which this earth is made to answer the purpose of its intention, and to preserve itself from every accident by which the design of this living world might be frustrated. For, as this world is a material machine, we must see how this machine is so contrived as either to have parts to move without wearing or decay, or to have those parts which are wasting and decaying again repaired.
Hutton's most lasting and best known symbol of this eternal process is the rock cycle: rocks are weathered and broken down to form sediments which are then buried in water. As they get buried (by more material being deposited on top), they are subjected to pressure and heat, so that the rocks melt or undergo transformations of some kind. Then by uplift they become mountains, subject to erosion and a new start to the endless cycle.
This same process, Hutton wrote, "is also manifest in the animal and vegetable kingdoms," and, in his most disputatious (although frequently misunderstood) claim, he concluded
If the succession of worlds is established in the system of nature, it is in vain to look for anything higher in the origin of the earth. The result, therefore, of our present enquiry is, that we find no vestige of beginning,--no prospect of an end.
Hutton's notion of an endlessly repetitive cycle, in contrast to the ideas of Buffon, bore an obvious similarity to the regularity of Newton's cosmology. In a sense, Hutton's theory drew much of the revolutionary threat out of historical geology, at least to the extent of denying its uniquely irreversible character. To Buffon's idea of constant change, Hutton added the notion of constant repair and renewal, so that the narrative of the earth's crust was more reassuringly cyclical and permanent.
It is not, therefore, perhaps surprising that his theory (which appeared just before the outbreak of the French Revolution) should have been given such an honoured place in British science in the early 19th century, at a time when the establishment was trying with all the means at its disposal to counter Continental notions of historical process and change as progressive, the favoured ideology of radicals in Paris, Edinburgh, and London (15).
The Neptunist-Plutonist/Vulcanist Controversy
At the end of the 18th century the dominant school of geology was at Freiburg (in present day Germany) where Abraham Werner (1750-1817) was the inspector of mines and professor of mining and mineralogy at the Mining Academy. Many of Werner's students came from Great Britain and were early members of the Geological Society of London (founded in 1807 as a society committed to no particular theory but rather to cooperative fact gathering on the Baconian model) (16).
In his Short Classification and Description of Rocks (1787) and in his immensely popular lectures, Werner insisted that geologists should classify rocks according to the age of their formation (i.e., arrange them in chronological order) rather than according to mineral types (the traditional method). In other words, Werner placed at the centre of geological inquiry a reconstruction of historical processes. This is an important example of how an apparently minor change in a system of classification can have significant effects on how people understand the processes which produced the material being classified.
The major problem facing any historical reconstruction of the processes involved in the earth's surface were obvious enough to anyone who had undertaken geological observations. Some of the major questions were the following: (a) How is it that the greater part of the land is made up of material formed in the sea? (b) How did the uniform strata come to be broken and intersected by fissures and intrusions of various kinds? (c) How did rocks formed under the sea come to make up some of the highest portions of the earth's crust? (d) Where did rock come from?
In his response to these and other basic questions about the history of the earth, Werner championed what has come to be called the Neptunist theory of the earth. This concept holds, in brief, that the earth was originally a great body of water containing suspended matter. The earth's core was formed by sedimentation and was exposed when the waters retreated to form continents. Noah's flood overwhelmed the continents and added new rock layers. Subsequent volcanic activity disrupted the continents and added more sediment. Later floods added more layers. Thus, all rock formations, according the Neptunist theory, were deposited by water (with a minor exception, volcanic rocks).
Werner based his theory on very wide observations which led him to the generalization that there was a basic similarity in all formations as one moved from the mountains to the lowlands, with clearly demarcated transitions from granite (the oldest and highest rocks), to loose or cemented aggregates, marked by an increasing frequency of fossils and a decrease in metals. On the basis of this theory of rock formation, Werner constructed a classification system.
In contrast to this Neptunist hypothesis was the idea that rocks were formed in fire, a theory which came to be called the Plutonist (or Vulcanist) theory of the earth. Originally proposed by Abbé Anton Moro (1687-1750) on the basis of a study of volcanic islands, this alternative to Werner's ideas was taken up by James Hutton. In response to the Neptunist theory of the Wernerians, Hutton advocated a view that the surface of the earth was subject to two basic processes: rocks were worn away by weathering and erosion, and then they were re-formed and uplifted by heat and pressure.
A key question in the dispute between the Neptunists and the Plutonists was the origin of basalt, a common dark fine-grained rock. Werner denied any volcanic origin for basalt, and Neptunists claimed to have observed fossils in basalt, a sure sign of a rock's origin as a sedimentary deposit. Hutton, together with his close associate, friend, and popularizer, John Playfair, asserted that basalt never contained fossils, that it was always insoluble, hard, and crystalline, and that masses of basalt often cut across other rocks, all of which pointed to its origin from magma, or molten rock under the earth's crust (magma which reaches the surface is called lava). If the disputants had had access to areas of active volcanic activity, the argument would have been resolved quickly, since basaltic lava is easily observed in such places (e.g., Iceland).
The most significant difference between the disputants here was not their evidence but their initial assumptions. Werner and his followers were committed to a historical understanding of the earth and to the notion of gradual processes of transformation and to a qualified uniformitarianism. They were not, however, prepared to accept the full principle of uniformitarianism, and their theory depended upon certain causes (for the sudden movement of the oceans) which no longer operated. For Neptunists, the present might be the key to the past, but that did not mean for them, as it did for Hutton, that present causes must account for all past processes.
For some of the Plutonists, on the other hand, Werner and his followers were simply trying too hard to accommodate historical geology to the writings of Moses and were, by compromising uniformitarian principles, merely speculating about a model which did not work in practice and abandoning the idea of natural laws governing all physical processes.
The controversy came to an end gradually in the 19th century, and the verdict of history has come down on the side of Hutton and the Plutonists (at least insofar as the origin of rocks is concerned) (17).
Catastrophism and Uniformitarianism
Early in the development of modern geology it became generally agreed that stratified rocks (i.e., rocks made up of particles in horizontal layers), because they frequently contained remains of aquatic life, had been formed as deposits in water. This theory gave rise to the corollary (proposed by Steno in the 17th century) that each stratum of such rocks was younger than the ones beneath it (later this notion came to be called the Law of Superposition).
Initially, the presence of such stratified rocks (called sedimentary rocks) prompted certain scriptural geologists to claim that all stratified rock had been created at the time of the flood described by Moses in Genesis 7. This idea received a death blow from the work of Georges Cuvier (1769-1832), the most important and influential figure in French science in the early 19th century. His study of the different layers of the Paris Basin led him to propose a series of sudden inundations and retreats of the sea.
Cuvier's study of the composition and fossil record of the different strata convinced him that
the breaking to pieces and overturning of the strata [show] plainly enough that [earlier revolutions] were sudden and violent like the last; and the heaps of debris and rounded pebbles which are found in various places among the solid strata demonstrate the vast force of the motions excited in the mass of waters by these overturnings.
For Cuvier the only satisfactory explanation for such evidence was a series of huge catastrophes (hence his theories came to be called catastrophism). Present processes produced effects too small and slow, and volcanic action, although violent, was too local. The evidence required the action of some extremely unusual and overwhelming force: "The thread of operations is here broken; the march of Nature is changed; and none of the agents which she now employs would have been sufficient for the production her ancient works." Cuvier could suggest no physical cause for such repeated catastrophes, but his work effectively demonstrated that the geological record could not be explained by reference to simply one major flood.
Cuvier's work was translated and published in England in 1813, where the catastrophic theory became very popular, not least of all because part of his theory gave strong support to the notion that the last such catastrophic flood could be dated at roughly the same time as the flood described in Genesis. To make this point more persuasively, Cuvier had included in this theory a survey of mythological accounts of a great flood from many cultures and had traced them back to an approximate common date.
The scriptural geologist William Buckland (1784-1856) drew on Cuvier's theory, which he supported with the discovery in 1821 of the Kirkdale Caves in Yorkshire, which contained the bones of many extinct animals which had apparently died in a sudden flood, to confirm the truth of the Biblical account: "had we never heard of such an event [Noah's Flood] from scripture . . . Geology of itself must have called in the assistance of some such catastrophe to explain the phenomenon" (18).
This version of catastrophism was particularly helpful in resolving the growing problem of the age of the earth. A literal interpretation of scripture strongly suggested that Creation had taken place somewhere between about 4032 BC and 3946 BC, that is, about six thousand years earlier. Cuvier's theory dated the last great flood at approximately that time. Hence, invoking the notion that the Mosaic account described the last of several Creations, the earlier ones having involved different lands and alternative forms of life, geologists could reconcile their time requirements with scripture.
Catastrophism, of course, violated the principle of strict uniformitarianism, since it appealed to occasional unknown catastrophic processes. This meant that the history of the earth was, in part, a record of unique events rather than constant evidence for the operation of the same physical processes in a dynamic but steady-state system. Hence catastrophism aroused the opposition of the followers of Hutton. Prominent among them was John Fleming (1785-1857), who insisted that Buckland's evidence indicated only localized flooding and not a universal deluge. Moreover, he argued, catastrophism contradicted rather than confirmed Genesis.
The heated controversy between these two historical explanations acted as a great spur to geological field work, an activity which culminated early in the 19th century in the work of Charles Lyell, whose Principles of Geology first appeared in 1830. Lyell brought the book out in separate volumes and in many different editions, eleven during his own life time (the last one appeared in 1872). Lyell's book reasserted very strongly the principle of strict uniformitarianism, for Lyell insisted that, given sufficient time, present-day forces operating at present rates could have produced all observable geological phenomena.
Lyell further emphasized in his famous definition of geology its essentially historical character, announcing at once a significant difference between his work and Hutton's:
Geology is the science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature; it enquires into the causes of these changes, and the influence which they have exerted in modifying the surface and external structure of the planet.
Lyell was an important, complex, controversial, and influential scientist (and lawyer) writing about crucial theories at a time when the politics of science was in England marked by particularly fierce disputes. As one of the best known and most articulate spokesmen for the conservative establishment, he devoted his energies to fighting Continental theories of progression, especially the materialistic evolutionary science of Lamarck, "the Orang Outang" concept, which he, along with many of the contemporaries, detested (see Section Three below). His geology, therefore, one writer has recently observed, "was a singular reaction to the threat of bestialization" (19).
Central to Lyell's efforts was an attempt to interpret the fossil record in a non-progressive manner (i.e., to show that it did not demonstrate a history of significantly different epochs in the earth's history). Unlike Hutton, Lyell was committed to a historical view of geology and thus accepted the historical uniqueness of events, at least locally, but he maintained that considered as a totality, the dynamic processes of the earth had a timeless invariability. Thus, life on earth had overall remained always roughly the same.
To resolve the apparent contradiction presented between this theory and the fossil record (which seemed to indicate an uneven and progressive development, with more frequent and more complex organisms in younger strata), Lyell proposed a complex statistical distribution of fossils which, in his view, enabled him to argue for a generally steady-state view of living populations, in spite of the apparent evidence to the contrary.
This increase in existing species, and gradual disappearance of the extinct, as we trace the series of formations from the older to the newer, is strictly analogous . . . to the fluctuation of a population such as might be recorded at successive periods, from the time when the oldest of the individuals now living was born to the present moment. (20)
This effort to prevent the progressive reformers from using fossil history for their politically unacceptable materialistic theories of change may have satisfied Lyell, but his denial of progressive developments in the history of the earth and life in it bewildered many of his conservative colleagues, simply because for them the evidence was so overwhelmingly clear. They appreciated the anti-reform implications but were unwilling to outlaw the progression so obviously indicated by the fossil record, especially with recourse to a theory which, many felt, was not Christian (21).
However, Lyell's emphatic restatement of uniformitarian principles exerted a considerable influence on catastrophism, which gradually modified its stance on scripture, while still maintaining the belief in a series of sudden abnormal processes in the formation of the earth's crust. The debate, however, continued throughout the 1830's, often at the meetings of the Geological Society with the young Charles Darwin (1809-1882) in attendance. Darwin was a firm adherent to Lyell's uniformitarian views; he had read the first volume of Lyell's Principles while on his Beagle voyage (1831-1835).
Nevertheless, by mid-century, on the eve of the publication of The Origin of Species (1859) the modified catastrophist view generally was the more favoured of the two theories, not least of all because catastrophism had adapted itself to theories of progression over geological time. True to the original spirit of Hutton, Lyell and the strict uniformitarians held to the notion of an unchanging, repetitive steady-state process: "we can see neither the beginning nor the end of that vast series of phenomena which it is our business as geologists to investigate" (22). Not only was this out of touch with the progressive spirit of the time, but, more importantly, and quite apart from the problem of fossils, the non-progressive view of the earth had difficulty answering the growing body of evidence about the earth's heat loss, which suggested that the earth's temperature must, over geological time, be changing and that, therefore, the earth could not remain in the same state indefinitely, certainly not long enough to fit the time frame demanded by strict uniformitarianism.
The conflict between the uniformitarians and the catastrophists had an important religious dimension. Strict uniformitarianism, as practiced by Lyell and Darwin, emphasized that of paramount concern were the permanent laws of nature always at work. God never intervened with an inexplicable event in the process. The Catastrophists' insistence that the history of the earth could only be understood by such interventions meant that the catastrophists were able to use their science to support a faith in a living God, an immanent Presence, for sudden, otherwise inexplicable events in the history of the earth provided evidence for the continuing action of a God not bound by natural laws.
Darwinian evolution, from one perspective, turned out to be a workable compromise between catstrophism and uniformitarianism. It proposed essentially a historical development (e.g., the world was not undergoing a constantly repeated, stable process, and thus each stage of the story was unique, as the fossil record suggested), and yet the forces at work in the process were, as Darwin insisted, uniformitarian.
What remained constant, in this view, was not the state of the world or of the species in it, but the processes by which irreversible changes took place. Whether or not such changes represented a progress (i.e., the movement towards higher or better life forms) was a matter of dispute. Although Darwin was, on this point, ambiguous, his theory was widely interpreted as a "progressive" view: evolution led to higher life forms (23).
Seen in this light, we can interpret Darwinian evolution as, for Lyell, in part, what Gould calls a "fallback" position. It enabled him to continue to maintain uniformitarianism in a modified form (uniformity of rate) and yet to take account of the growing evidence for changes in the history of the earth. Lyell himself admitted that, on the basis of the facts, there was little to determine a clear choice between uniformitarian evolution and catastrophism, but the different implications for his work in geology were clear enough (24).
To say this is not to claim that uniformitarians won the day and drove catastrophism from the field. The issue is still alive in the continuing debates about the rates of change and time spans in the history of the development of species (25).
Postscript: Continental Drift and Plate Tectonics
One of the most dramatic theories of modern geology, the idea that the earth's continents were once joined and have gradually drifted apart, first made its appearance in 1858, in a paper published by an American scriptural geologist, Antonio Snider-Pelligrini. His major evidence was the remarkable fit between the coastlines on either side of the Atlantic. In Snider's hypothesis (which was not a particularly scientific argument), America had once been the island of Atlantis, broken off from the single mass of dry land by volcanic action and by Noah's Flood. The shift had occurred in a single violent movement.
The modern arguments about continental drift began later, with papers published by F. B. Taylor in 1910 and by Alfred Wegener in 1915. These versions of the theory arose, in part, as a way of explaining the odd distribution of ancient climates (e.g., fossils of warm-climate plants in coal deposits near the poles) (26).
Wegener posited the existence of a single protocontinent called Pangaea. The breaking up of Pangaea and the subsequent drifting apart of the various pieces had resulted in the present shape of the earth's continents. Other reconstructions of the earth theorized that there had been two original continents, Gondwanaland (which included Africa, South America, India, Australia, and Antarctica) and Laurasia (made up of the continental masses in the northern hemisphere).
In the 20th century, the theory of continental drift has been incorporated into a more comprehensive theory called plate tectonics. This posits that on the surface of the earth there are number of large, thin, relatively brittle plates, which move, under pressure from the molten rock of the earth's interior, over the upper mantle. These plates interact with each other to produce a number of major geological features (mountains, marine trenches, inland volcanoes, earthquakes, and so on). The continents ride on these plates and thus move with them (27).
Notes to Section Two
(1) The term geology appears to have been first introduced in 1779 by H. B. de Saussure (1740-1799) of Geneva, the founder of modern mountaineering. [Back to text]
(2) One way to appreciate dramatic impact of a historical understanding is to consider the following analogy about the history of the earth. According to our present understanding, if we were to compress the history of the earth into a single year, then single-celled organisms would appear early in April, the first vertebrates towards the end of May, and the first land plants about the middle of July. Early in August the seas would be filled with fish, and in early September the first insects would turn up. October would mark the flourishing of the dinosaurs and the emergence of the first animals with the ability to fly and of simple mammals. Sometime around noon on December 31 would appear a stooped creature of human-like proportions. At about 11 p.m., Neanderthal humans would emerge, at 11:30 p.m. Neolithic human beings. Between approximately 11:56 p.m. and 11:59 p.m. the story of the Egyptians, Babylonians, Greeks, and Romans would take place. Columbus would discover America at approximately 11:59:40; the American War of Independence would occur at 11:59:53 p.m. [Back to text]
(3) Gibbon's book was for many decades a source of considerable chagrin to the Anglican establishment, for this extremely scholarly, authoritative, and popular history of the early Church was the work of an anti-Christian. It was embarrassing to have the most reliable history of the early church so hostile to Christian doctrine. [Back to text]
(4) This famous blow against French science does not accurately reflect the developments promoted by the French Revolution and Napoleon. Early in the 19th century, the French government reformed entirely the structure of the scientific establishment, including education, appointments, and promotions. The changes really stressed merit and made French science early in the 19th century the leader in Europe and very much the envy of many reform-minded English researchers and teachers, several of whom went to France for their education. For more details on this issue see Guerlac, Chapter 31, "Some Aspects of Science During the French Revolution." [Back to text]
(5) There is no reason to suppose that Descartes was being deliberately ironical on this important point, and the hypothetical nature of his historical speculations created certain problems for his readers. The key passage is worth quoting in full: "I do not doubt that the world was created in the beginning with all the perfection which it now possesses: so that the Sun, the Earth, the Moon, and the Stars existed in it, and so that the Earth did not only contain the seeds of plants but was covered by actual plants: and that Adam and Eve were not born as children but created as adults. The Christian faith teaches us this, and natural reason convinces us that this is true; because, taking into account the omnipotence of God, we must believe that everything He created was perfect in every way. But, nevertheless, just as for an understanding of the nature of plants or men it is better by far to consider how they can gradually grow from seeds than how they were created by God in the very beginning of the world; so, if we can devise some principles which are very simple and easy to know and by which we can demonstrate that the stars and the Earth, and indeed everything which we perceive in this visible world, could have sprung forth as if from certain seeds (even though we know that things did not happen that way); we shall in that way explain their nature much better than if we were merely to describe them as they are now. . . ." (Principles of Philosophy, 1644). The historical scientific proposal here, even if hypothetical, was influential. See Sloan 298 ff. [Back to text]
(6) Stephen Jay Gould's Time's Arrow Time's Cycle offers an interesting and sympathetic reassessment of Burnet's and Steno's work, with a helpful comparison between the two early theories. Gould provides not only an analysis of Burnet's arguments but also a selection of comments from later historians of geology ridiculing Burnet's book. Thus, Gould's analysis is a useful reminder of the dangers of some snap judgments in historical science. [Back to text]
(7) For a useful and brief discussion of Buffon's ideas in the context of his religious beliefs, see Scientific Progress and Religious Dissent 55-60. [Back to text]
(8) For a further analysis of this point, together with a discussion of the influence of the political revolutions in America and France, see Cohen, Section IV (p. 195 ff), "Changing Concepts of Revolution in the Eighteenth Century." [Back to text]
(9) Kant is, of course, most justly famous as the philosopher who delivered science from the skepticism of Hume, but it is worth mentioning that Kant was also a very competent physicist who "anticipated Laplace in formulating a nebular hypothesis to explain the origin of the solar system . . . , was the first to point out that tidal friction must have a slow retarding effect on the Earth's rotation, and that by its reaction it has forced the Moon to present always the same face to the Earth . . . [and who] showed that the different linear velocities of successive zones on the Earth as it rotates explain the 'trade' winds, and other similar steady currents of air. He wrote also on the Causes of Earthquakes, on the Different Races of Men, on Volcanoes in the Moon, and on Physical Geography" (Dampier 195). For a very thorough and generally hostile study of Kant's contributions to astronomy, see Stanley L. Jacki's introduction to his translation of Kant's Universal History of Nature and Theory of Heaven. [Back to text]
(10) For a detailed account of this story see Simon Schaffer, "The Nebular Hypothesis and the Science of Progress," in Moore. For an introduction to Laplace's scientific work see Robert Fox, "Laplacian Physics," in Olby and others, 278-294. [Back to text]
(11) Those who hold unswervingly to the literal truth of the Biblical narrative are nowadays often called fundamentalists. This is hardly the right term to apply to the 18th or 19th century. "[Fundamentalism] seems to have been first used in 1920 to describe certain American Christians opposed to the removal of supernatural elements of Christianity as advocated by certain 'progressive' thinkers at the time. . . . Since that day, however, the word Fundamentalist has acquired a pejorative meaning, relating to the position of extreme ultra-conservatism that had been discredited in the nineteenth century if not before." (Crisis of Evolution 125). [Back to text]
(12) The important shaping influence in this transformation of Christian faith from arguments about evidence for natural order and design (as described in Genesis) to questions of inner conviction and feeling was primarily the work of Friedrich Schleiermacher (1768-1834), whose major work on theology was published in 1821. Schleiermacher's influence throughout the 19th century was very significant. [Back to text]
(13) The problem, however, has not gone away. Inconsistencies in the fossil record are still a problem in evolutionary biology. For the record of the first 3000 million years, nothing more complicated than bacteria and slime appears. Then suddenly there seems to have been an "explosion" of life. Moreover, since that time, according to David Raupp, curator of the Field Museum in Chicago, "instead of finding the gradual unfolding of life, what geologists of Darwin's time and geologists of the present day actually find is a highly uneven or jerky record; that is, species appear in the sequence very suddenly, show little or no change during their existence in the record, then abruptly go out of the record." The arguments about what this erratic record means, especially in relation to Darwin's theory, is the source of one of the liveliest, best known, and most interesting contemporary arguments in biology, especially in the exchanges between Stephen Jay Gould and Richard Dawkins. [Back to text]
(14) Uniformitarianism became in the work of Charles Lyell a frequently ambiguous term; Lyell used the multiple meanings to good rhetorical effect to bolster his arguments for a non-progressive geology. On this point, see Gould, Chapter Four. [Back to text]
(15) For a critical reassessment of Hutton which stresses that his importance has been overestimated see Rachel Laudan, "The History of Geology, 1780-1840" in Olby and others, pages 314-325. Sorting out Hutton's contribution to geology creates difficulties for a number of reasons: (a) Hutton's style is very prolix and difficult (many people heard of his work through the interpretative summary produced by his friend John Playfair), (b) the British tradition may have seriously overvalued and misinterpreted his work for nationalistic-political reasons, and (c) there is evidence to suggest that Hutton was not as empirical as the tradition maintains. Stephen Jay Gould's recent analysis of Hutton's work maintains that Hutton, far from conducting himself in an appropriately Baconian way "presents his theory as the a priori solution to a problem in final causation, not as an induction from field evidence" and with a disregard for the historical basis of geological inquiry (Gould 76). In Gould's view Hutton's work was mythologized by Charles Lyell, "one of the most flagrant mischaracterizations ever perpetuated by the heroic tradition in the history of science." [Back to text]
(16) This society was one of the more conservative of the learned societies at the time. Its rules tacitly prohibited divisive arguments over cosmological theories and discussions of origins. Charles Darwin found the atmosphere here far more congenial than at the stormier meetings of the Zoological Society. Darwin had been a member of the Wernerian Society while a young student at Edinburgh. [Back to text]
(17) For a more detailed study of this controversy, with illustrations to clarify each theory, see Binn, Chapter 2. [Back to text]
(18) Cuvier's work was attractive to those who wished to stem the radical implications of much of the new historical science. For Cuvier, as Cohen points out (p. 276), emphasized that the sort of revolutions which Buffon had talked about as causing changes to the earth's crust were, in fact, violent catastrophic events which not only altered the topography but which exterminated whole species. There was nothing particularly orderly or progressive (or welcome) about such events. Cuvier's work in biological taxonomy also was a major inspiration to English conservatives working in biology (see Section Three below). Buckland's orthodoxy ("Geology is the efficient auxiliary and handmaid of religion") was an important influence in getting the suspect science of geology into Oxford's classic-dominated clerical curriculum. [Back to text]
(19) Desmond 328. Desmond, for whom social and political context is all important in understanding the history of science, stresses the points that Lyell's book was written at the height of the agitation over reform in England (1831-2) and that Lyell had visited France and had witnessed the fighting in Paris during the July Revolution in 1830. Moreover, his family on his father's Scottish estate had been harassed by roving gangs of reformers (see pages 328-9). [Back to text]
(20) For a useful analysis of Lyell's attempts to deal with the difficult problem of the fossil record in his uniformitarian theory see Gould, p. 150 ff. [Back to text]
(21) Lyell himself, with a good deal of reluctance, finally gave up this part of his argument. The tenth edition of his most famous book (published in 1866, that is, seven years after the publication of The Origin of Species) and his On the Geological Evidences of the Antiquity of Man (1862) declared this change of mind: progress in life's history is "an indispensable hypothesis . . . [which] will never be overthrown." Gould has an insightful analysis of this change of mind (which has been, in Gould's persuasive view, too easily ascribed to the influence of Darwin, Lyell's close friend. See Gould 168 ff. [Back to text]
(22) Identifying both Hutton and Lyell as uniformitarians should not obscure some important differences between their two theories. One important point is that in Hutton's theory the different stages of the cycle operated sequentially and globally; whereas, in Lyell's view the processes were constant and local. Thus, for Hutton the earth as a whole went through distinctively different stages. For Lyell any particular locality might go through such sequences, but the earth as a totality remained basically the same. See Gould 150 ff. [Back to text]
(23) For a more detailed account of the Catastrophism-Uniformitarianism debate see Chapter 3 of Binn. [Back to text]
(24) Lyell, in fact, not only finally accepted evolution; he also reconciled himself to its progressive character, something not strictly necessary. Gould (p. 170) makes an important point in this matter: "No logical necessity can extract an implication of progress from the fact of evolution. Darwin himself had maintained a very ambiguous attitude toward the idea of progress, accepting it provisionally as a feature of parts of the fossil record, but denying that the theory of natural selection . . . required organic advance. Nonetheless, many evolutionists have always viewed the concepts of progress and transmutation as necessarily connected, and Lyell, for whatever reason, certainly adopted this view. Therefore, for him, a decision to embrace evolution also entailed progress as a fact." Thomas Huxley warned Darwin that linking his theory to uniformitarian principles would create problem: "You have loaded yourself with an unnecessary difficulty," Huxley wrote on the day The Origin of Species was published. And, in fact, the problems created by the fact that Darwin's uniformitarianism demanded huge expanses of time for natural selection to work raised major objections to his theory from physicists, who claimed that the earth's temperature could not have sustained life for such a long period. [Back to text]
(25) In various modified ways, catastrophism has made something of a comeback in recent years (especially in the theory that the extinction of the dinosaurs was brought about by a single violent catastrophe, a collision between the earth and a huge comet). For a brief discussion of some of the recent theories about mechanisms of evolutionary change (hopeful monsters, embryonic change, chromosomal jumps, punctuated equilibria, and so on), see Hitching, Chapter Six. And for a very spirited and thorough defense of Darwinism against such challenges see Dawkins. [Back to text]
(26) The credit for first suggesting that the continents have moved has prompted a long argument. Francis Bacon pointed out the interesting conformity to the shapes of Africa and South America, as did Alexander von Humboldt almost two hundred years later. But neither proposed that the two continents had once been together. For a discussion of Wegener's thesis in context, see Cohen, Chapter 29. [Back to text]
(27) This very incomplete account is intended to serve as only the briefest mention of a complex subject. For a fuller description of the principles of plate tectonics see Spencer or any relatively recent textbook introduction to Physical Geology. [Back to text]
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