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Opposing all theories of species transformation, including that of Chambers, Hugh Miller appealed to Aristotelian metaphysics: nature is pervaded by design and purpose. But design requires a designer, purpose requires a planning mind. Miller also appealed to the empiricist tradition in the philosophy of science: the proper foundation for science is unbiased observation, not idle speculation. Chambers had appealed to the continuity of nature: the unbroken Great Chain of Being was paralleled in the Fossil Record and in embryonic development. In contrast, Miller maintained that even if there were an unbroken succession of fossils through the Geological Record, there was still no process of species transformation to be observed, but rather only a certain ‘top upon bottom order of things’. And it was precisely this pattern which revealed design, purpose and goal-directedness in the Fossil Record through the occurrence of fossils of a ‘prophetic type’. The characteristics of such ‘prophetic’ fossils announced at an earlier epoch of earth history the later appearance of new forms of life.

Design, purpose, and goal-directedness were also apparent, for Miller, in embryonic development, which preserved the perfect adaptation of species to the place in the household of nature to which they had been assigned by the Creator. Species cannot undergo gradual transformation, as this would disrupt their perfect adaptation to their environment. There consequently must be gaps in nature separating not only species from one another, but also man from beast. The rejection of the concept of ‘perfect adaptation’ was likely the most difficult intellectual hurdle that Darwin faced in developing his theory of evolution. Perfection cannot vary, but wherever Darwin investigated nature with enough concern for detail, he found organisms that form a population to be subject to variation. Organisms were not perfectly adapted, but adequately adapted – adequate for survival. This insight provided Darwin with the key to his theory of natural selection.

4.1 Hugh Miller (1802–1856)

On October 10, 1802, Hugh Miller was born in Cromarty, Scotland. His father, a proud owner of a fishing schooner, drowned when Hugh was only 5-years old.Footnote 1 At school, the boy drew attention neither by his diligence nor by his accomplishments. He preferred to roam in the Scottish landscape, strolling through the fields and hills and along the seaside, thereby experiencing the first self-taught lessons in natural history, which proved so productive in the later years – as his spiritual father, the paleontologist Louis Agassiz, was to profess.Footnote 2 It was not easy for the adolescent to submit to the reality of life; however, in February 1821, he finally decided to become a stonemason, working in the quarries of northern Scotland. The quarry where he found employment was located close to Stromness on the Orkney Islands. The workers there excavated the Old Red Sandstone, deposited at the bottom of an ancient Sea during the Devonian, approximately from 416 to 359 million years ago.Footnote 3 Unaware of the actual time involved, the accredited scientists at the time, nevertheless, believed that these deposits of early age were devoid of any signals of ancient vertebrate life. “Geologists of high character had believed that the Old Red Standstone was defective in organic remains; and it was not till after 10 years, acquaintance with it that Mr. Miller discovered it to be richly fossiliferous.”Footnote 4 Miller unearthed the remains of bizarre creatures, fishes of an as yet unknown structure. These discoveries not only gained Miller the appreciation and support of one of the leading paleontologists and zoologists of his time, Professor Louis Agassiz, but also stimulated him to communicate his insights to a wider public. His book “The Old Red Sandstone” was published in 1841, a text that by no means was restricted to the enumeration of properties characteristic of these strange early fishes, but which really was intended as a polemic against early theories of evolution, in particular against the theory sketched in 1809 by Jean-Baptiste Chevalier de LamarckFootnote 5, renowned invertebrate zoologist and paleontologist at the National Museum of Natural History in Paris.

Given Agassiz’ role as spiritual mentor of Hugh Miller, it is of importance to shed some more light on this person and his background.Footnote 6 Although his work on glaciers that resulted in the concept of an Ice Age was important, as can be judged from Chambers’ public support for it (see the previous chapter), it was not the main research focus of Agassiz. His real love was for fishes, both living and fossil. First, he got involved with research on fishes when he was invited to work on collections from Brazil that had been brought back by Johann Baptist von Spix, who had deposited them in the Natural History Collections in Munich. Having completed this task in 1829, Agassiz embarked on a description of the fish fauna in lake Neuchâtel (Switzerland), quickly expanding his scientific interests to the fossil fishes from the black shales of Glarus (Switzerland), and from the limestones of Monte Bolca (Italy). During these early phases of his career, young Louis Agassiz remained undeterred in his attempts to make the acquaintance of the famous Georges Cuvier from the National Museum of Natural History in Paris. At the zenith of his career, during which he became one of the most influential zoologists, paleontologists, and geologists of the early nineteenth century, Cuvier was not an easily approachable man. But by the end of 1831, Agassiz has established himself in Paris as a student of the great man.Footnote 7

4.2 Georges Cuvier and Louis Agassiz: Experts on Fossil Fishes

Georges Léopold Chrétien Frédéric Dagobert CuvierFootnote 8 had joined the Paris Museum after the French Revolution, when, under Napoleon Bonaparte, he embarked on a stunning career, which took him not only to the position of the leading comparative and functional anatomist of his time, but also to the privileges and power of France’s Secretary of Education. Cuvier is said to have worked at seven desks simultaneously, his investigations spanning the entire series of vertebrate animals from fossil fishes to fossil mammals. Behind his back he came to be nicknamed “the mammoth,” not only because of his increasing gravitas that translated into a massive bodily Gestalt but also because of his many scientific achievements, which included the conclusive proof for the extinction of fossil species such as the mastodon and the mammoth.Footnote 9 Cuvier was a typical representative of the conservative restauration that followed the revolution in Paris. He rejected all ideas of species transformation, as he remained the last surviving proponent of the doctrine of the encapsulation of preformed and preexisting embryos, all created at the beginning of time.Footnote 10 In a celebrated presentation to the National Institute of France in 1796, Cuvier argued that Buffon was dead wrong when he claimed that the present day elephant represents a “degenerated,” that is, transformed mammoth. Instead, Cuvier was the first to show that today there exist two species of elephants, the African and the Asian one, and that the mammoth is a third, separate species that went terminally extinct instead of having been transformed into an elephant. Such an extinct species Cuvier called “une éspèce perdue,”Footnote 11 a “lost species,” that is, one that had irretrievably disappeared from the surface of the earth. Cuvier thus became the first to prove the fact of extinction. If a fossil mollusk shell did not match with that of any living mollusk, it was at that time still possible to claim that the species documented by fossils was still extant. But because its occurrence might be restricted to some small bay along the coast of some remote island, it might have escaped the collecting efforts of past and present explorers. In contrast, nobody could claim that the mammoth known from fossils still existed somewhere, for surely such a large mammal could not have escaped its discovery.

Through his functional anatomical studies, Cuvier hardened the doctrine of the functional correlation of parts, which rendered an atomistic conception of organisms as an aggregate of originally separate parts impossible, and which further emphasized the perfect adaptation of species to their specific environment. To him, such a perfectly adapted organism was a complex machine that could not be changed part by part without its function being compromised. Such a complex clockwork would either have to remain the same, or to be redesigned from ground up and transformed all at once, which evidently was impossible. For Cuvier, the Law of the Functional Correlation of Parts was the most important law that governs the animated world, a law of such high rank and universal generality that even the almighty Creator would submit Himself to its reign. The reason is that Cuvier thought that this law would impart on the living world a necessity on par with that expressed by mathematical lawsFootnote 12: “In one word, the form of a tooth indicates the form of the jaw joint, the latter implies the structure of the palate, which in turn presupposes the structure of the claw, in the same way as the mathematical equation of a curve implies all is properties.”Footnote 13 It was on the basis of this law that Cuvier believed that he could reconstruct the whole organic machinery of an animal known only from an incompletely preserved fossil. “The most insignificant facet on a bone, the most weakly expressed apophysis, determine the class, the order, the genus and the species to which this bone belongs. This is true to the degree that if we only have the well-preserved extremity of a limb bone available… we can identify it with as much certainty as if we had the whole animal at our disposal.”Footnote 14 There was no room for gradual, piece-meal change of organic forms in Cuvier’s world, no room for accidental “mistakes” in the coming together of parts that would form an embryo. Species, such as the mammoth, may go extinct, but they do not change. It was Lamarck, overseeing the collections of invertebrate animals other than insects, who along with Etienne Geoffry Saint-Hilaire supported Cuvier’s appointment at the Paris Museum.Footnote 15 Having demonstrated the extinction of fossil mammal species, Cuvier expected his senior colleague, Lamarck, to develop equally conclusive proof for the extinction of fossil mollusk and cephalopod species. But Lamarck drew quite different conclusions from his studies of fossil invertebrates. According to him, the successive appearance of different species in the Fossil Record would not document the extinction of species and their miraculous replacement with new ones, but instead the transformation of older species into different, new ones. This was enough to turn Cuvier from a supporter into an enemy. Cuvier did not even refrain from expressing his complete disagreement by ridiculing Lamarck’s ideas in the eulogy he held at the latter’s funeral in 1829.Footnote 16

In contrast, Cuvier was so impressed by Agassiz’ work on fossil fishes that he left his own notes on the subject to the young adept.Footnote 17 After Cuvier’s death in 1832, Agassiz returned to Neuchâtel, where he became a professor in natural history at the Lyceum. Throughout his life, Agassiz held up and defended Cuvier’s ideas and theories about the earth and its inhabitants. And just as Cuvier remained, till the end of his life, a staunch opponent to early theories of transformationism such as Lamarck’s, so did Louis Agassiz oppose Darwin’s theory of evolution till the end of his life. In one of his reviews of Darwin’s work dating from 1874, Agassiz concluded that “however broken the geological record may be, there is a complete sequence [of fossil species] in many parts of it”, and yet – in spite of this – “there is no evidence of a direct descent of later from earlier species in the geological succession of animals.”Footnote 18 This echoes the theme of Hugh Miller’s book The Old Red Sandstone from 1841, which was designed to highlight the putative flaws that are incurred when species transformation is inferred from the Fossil Record. Miller was concerned that authors might draw illegitimate conclusions from the sequence of fossils that marks out earth history. But why should it be illegitimate to conclude from a graded series of superimposed fossils to a theory of species transformation? Agassiz’ and Miller’s arguments here reflect a strict adherence to a now defunct empiricist philosophy that was dominant at their time, one that admitted sensory experience alone and nothing else as the sole basis of secure, scientific knowledge. True enough, a graded series of superimposed fossil forms may be suggestive of species transformation. But since species transformation itself was not a process observable in the Fossil Record, corresponding theories could in Agassiz’ and Miller’s views not claim a sound scientific basis. Indeed, and before too long, Miller should find his concerns in that regard fully justified: Chambers’ “Vestiges of Natural Creation” was published in 1844. Miller, who had by that time become the frontman of the Creationist campFootnote 19, set out to deal transformationism another and hopefully definitive blow with the description of yet another fossil from the Old Red Sandstone, a fish he identified as belonging to the genus Asterolepis. Because of the author’s health problems, the book entitled “Foot-Prints of the Creator or, the Asterolepis from Stromness,” appeared somewhat delayed in 1849. The title Chambers had chosen, “Vestiges,” derived from the Latin term vestigium, meaning a “trace” or a “mark”, such as a “foot-mark.”Footnote 20 Miller set out to retrace the footprints of the Creator in a different light than Chambers had shone on them.

Miller’s interpretation of fossils becomes a lot more intelligible when viewed in the light of an early but crucial experience he had during his career as a stonemason, an experience that was recounted by Agassiz in his introduction to a later edition of Miller’s book on Asterolepis.Footnote 21 The first blasting Miller witnessed in the quarry exposed two dead birds, hidden in a deep fissure of the quarry walls. Obviously, the birds had sought shelter during a recent storm that had devastated the Orkney Islands off the coast of northern Scotland. This incidence led the self-taught paleontologist to the erroneous conclusion that fossils, remains of once living organisms found in the succession of layers of rocks that form the earth’s crust, need not to have lived and strived where they are found today. And indeed, there are circumstances where fossils are found in so-called fissure fillings. A fissure may have developed in ancient bedrock, to be filled during a later geological epoch with sediment carrying fossils. The age of the fossils will then not correspond to that of the bedrock, but to that of the fissure-filling sediment. But Miller’s conclusions were more radical: the incidence indicated to him that the mere stratigraphical succession, i.e. the successional occurrence of fossils through geological time, was not in and of itself enough to determine ancestor–descendant relationships. While the latter claim is correct in the light of modern paleontology, the former claim is not. Birds caught in a fissure between rocks is not the same thing as fossils embedded in sedimentary deposits, irrespective of whether these are filling ancient fissures, or – as is normally the case – superimposed one on top of the other. As early as 1666, the Danish scientists, Niels Stensen, working in Florence and generally known as “Steno,” had raised and answered the question how it could be possible for one solid body, such as a fossil shark tooth, to be fully encased in another solid body, such as a chunk of rock? The answer: the shark must have lived, died, and decomposed (or shed its tooth as a function of tooth replacement) before the sedimentary rock that encloses it had formed. The tooth must have sunk into the sediment, and become fully enclosed in it before the sediment compacted to form solid stone.Footnote 22

4.3 Miller’s Attack on Transformationism

Miller opened his defense of creationism by attacking the transformationist idea endorsed by Chambers that humans could have emerged from the animal kingdom by gradual progressive evolution through a series of intermediate stages. Such an outlook would imply that the distinction of humans from animals was no longer a principal, an essential one, but only a matter of degree. There would be no essential property left that distinguished man from beast. This, according to Miller and many of his contemporaries, would undermine the whole codex of morale and ethics founded on a belief in Christian values, which in his view provided the foundation of human society. In making this point, Miller sided with eminent authorities of his time, such as the Reverend Adam Sedgwick, Woodwardian Professor of Geology at Cambridge University, who in his review forcefully rejected Chambers’ “Vestiges” on the grounds that the new cosmology negated all distinctions between the realm of physical objects and that of moral values.Footnote 23 Miller could not agree more: “It is the fact that man must believingly coöperate with God in the work of preparation for the final dynasty, or exist throughout its never-ending cycles as a lost and degraded creature, that alone renders the development hypothesis formidable.”Footnote 24 The destruction of the argument of human descent from the animal kingdom necessarily had to start with a clear refutation of the thesis of the continuity of progressive development, believed by transformationists to bridge the gap between animals and humans. Here again, Sedgwick showed the way. The problem is, once again, one of change.

Ancient Greek atomists thought that the changing objects of nature were formed by the coming together of eternal, unchanging, and indestructible atoms of different kinds in different combinations at different times. But for these atoms to come together, and separate again, required them to move through space. And for that to be possible, the atomists claimed the existence of “empty space” through which the atoms could move. In contrast, Aristotle thought that nature abhors empty space. According to him, the vacuum does not exist. From the rejection of “empty space” followed the famous “Principle of Continuity”: everything is connected in an unbroken series or chain of forms or events. There are no gaps in nature, neither in terms of empty space, nor in terms of interrupted processes. Darwin himself would reach the same conclusion in his “Origin” of 1859: “Natura non facit saltum” – nature does not make jumps.Footnote 25 According to Darwin, both the animated and inanimate realms of nature are subject to gradual, instead of saltational change. Just as earthquakes build mountains in a long series of small steps, and erosion would gradually flatten out mountains over time, species would gradually transform in small steps over long periods of time. Nature forms an unbroken continuum without gaps or empty space. The natural flow of events was thought to be governed by uniform and universal laws of nature. A gap, or empty space, in nature would disrupt the governance of natural processes by uniform laws of nature. A geometrical line, a spatial distance, the flow of time, a spatially extended body can all logically be subdivided into an infinite number of segments or parts. The same is true for a continuous process of change: the continuity of any process can be subdivided into infinitesimally small segments, the explanation of any one of which through natural causes would stretch nobody’s imagination. Darwin’s experience, mentioned in the preceding chapter, of the earthquake of Valdivia, provides a classic example: The earthquake had elevated the land, but to such a minor degree that only the local population, acquainted with every detail of the natural environment, would recognize it: “I could discover no evidence of this fact, except in the united testimony of the inhabitants, that one little rocky shoal, now exposed, was formerly covered with water.”Footnote 26 A minimal uplift of the coastline was the effect, and its cause was a single earthquake of natural dimensions. This observation should not evoke much surprise or skepticism. But it could also be adduced to explain a second observation made by Darwin of fossil seashells “found at a height of 1,300 feet” above current sea level.Footnote 27 “A bad earthquake at once destroys our oldest associations: the earth, the very emblem of solidity, has moved beneath our feet like a thin crust over a fluid.”Footnote 28 A succession of such events stretching through deep time could change the face of the earth dramatically. One simply has to allow nature enough time to complete its works: the successive accumulation of small effects of a natural magnitude, each caused by natural causes such as an earthquake, could dramatically reshape the landscape if allowed to play out over a long enough period of time. Enormous was the power of argumentation based on the principle of continuity, and although not yet pronounced with the sophistication and power of persuasion commanded by Darwin at the time of his writing, Miller correctly identified the force of Chambers’ arguments that were built on the continuity of the Great Chain of Being and on the underlying lawfulness linking each level of organization in a gradual and progressive process of change that runs parallel to the lawful development of the physical universe.

Indeed, only a slow, gradual, and stepwise process of transformation would be amenable to an explanation that links natural causes to equally natural effects which each could be viewed as quite plausible in a chain of natural events governed by universal laws of nature. The tale of a human being with six fingers and toes might evoke some surprise and interest, the tale of a human being with six arms and six legs would evoke an incredulous stare. Buffon would not countenance deMaillet’s idea that humans arouse from mermaids and their male counterparts, but he found it plausible to think that the donkey might have originated from the horse through a process of degeneration. Maupertuis speculated that the accumulation of minor heritable changes could lead to the origin of new species, and so did Darwin, a century later. Any criticism of theories of species transformation had to target the thesis of continuity in nature. The documentation of major discontinuities would leave gaps in the chain of natural events governed by secondary causes, and open the door to the intervention of the First Cause, to the possibility of a spontaneous Act of Creation. Miller was a skilled polemic, and early on in his book he pointed to the fact that the transition from life to death was by no means a gradual one. Death, like birth or pregnancy, does not come in degrees. One cannot be dead and alive at one and the same time, just as one cannot be pregnant and not pregnant at one and the same time. Claims to the contrary would run up against the law of noncontradiction. Consequently, a continuity of such transitions that would create fuzzy boundaries could not be reconciled with logic and rational argumentation, no more than other transitions such as, for example, from a dead rock to a living coral, or from a morally indifferent animal to a rationally thinking and morally sensitive human being. However, rhetoric may be good enough a weapon to try and win a battle, but is generally insufficient to win the war. Miller consequently set out to defeat the transformationists using their own weapons on the battlefield of natural sciences.

If it were true, as Chambers had claimed that the succession of fossils through time would parallel the unfolding of complexity through the process of embryonic development, or the ascent to increasing complexity as reflected by natural classifications that place mushrooms at the bottom, humans at the top, then one would have to predict that early fossils would resemble the embryos of higher organisms, i.e., of organisms of greater complexity that appear later in the Fossil Record. Even Louis Agassiz had claimed that the class of fishes was still in an embryonic stage of differentiation during the early phases of its occurrence in the Fossil Record (i.e., in the Devonian).Footnote 29 Quarrying the Old Red Sandstone of Devonian age, Miller had dug up a strange creature that was named Asterolepis, at that time one of the earliest known fossil fishes, but it was neither small, nor of simple structure. It was a large animal with a highly complex anatomy, which, in some of its features such as the structure of its teeth, Miller believed to “foreshadow” the age of reptiles, animals that Miller erroneously believed to share a similar tooth structure as his newly found fossil. Using the current time scale and modern knowledge of the Fossil record, Astereolepis lived about 390 million years before the present, whereas the earliest uncontested reptiles appeared around 315 million years before the present. It is crucial at this point to recognize the implications of Miller’s claim that the tooth structure seen in this archaic fish, Asterolepis, would foreshadow the later ascent of reptiles. This could only mean that the much later appearance of reptiles was already announced by the earliest fossils of vertebrate animals and that the eventual appearance of reptiles on the surface of the earth therefore had already been planned and preordained – something that could certainly not be explained with reference to unconscious and “blind” laws of nature.

Again it was Louis Agassiz who had first introduced the concept of “prophetic types,”Footnote 30 which during early phases of earth history would foreshadow what was to follow in what he thought represented the unfolding of the Plan of Creation through geological time.Footnote 31 Thus, marine reptiles or ichthyosaurs, widespread during the Mesozoic, were thought to represent a type of organization announcing the later appearance of dolphins, a group of mammals; flying reptiles of the order Pterosauria would prophesize the later appearance of birds. No genealogical relationship was implied in the notion of “prophetic types”, however, only a correspondence of type of construction and of mode of living, that is, a correspondence of the functional and ecological role these types would play at different geological times in the household of nature. The concept of “prophetic types” could make sense only if one was willing to agree that foresight and goal-directedness underlie the succession of fossils through time, in other words, that there existed a blueprint of Creation. Any claim that the structure of early fossils would hint at later forms of life must presuppose the existence of a rational and conscious agent who had thought through, planned, and executed the Creation of organismic diversity and its successive manifestation in the course of geological time. Only conscious planning could impart a direction and goal, such as progress, on an unfolding process, culminating in the appearance of humans. If Asterolepis could be shown, as Miller (erroneously) believed, to share certain similarities in tooth structure with reptiles, it could be regarded as a “prophetic type,” and as such would lend support to the belief in a goal-directedness of nature. Yet, on that account, what in the Fossil Record may appear like a progression from one “type” of organization (fishes) to another (reptiles) through time does not correspond to any real process of change. Like the oak tree that preexists in the acorn, the “prophetic type” preexists in an atemporal, ideal world, a world beyond matter, space, and time. The “type” is rooted in Divine thought; Divine thought is revealed by the succession of fossils. The “prophetic type’s” appearance on the surface of earth is only its becoming instantiated, that is, its becoming revealed in an instance or an example located in space and time – in this case in the form of Asterolepis from Stromness. It announced the arrival of the reptiles in a later geological epoch. But that did not imply that reptiles evolved from fishes through intermediary amphibians. It only meant that the type of construction of a reptile, just only hinted at in the teeth of Asterolepis, would be fully revealed through examples at a later epoch of earth history. Ancient reptile species, such as the species of non-avian dinosaurs so popular today, did go extinct. They are irretrievably lost in deep time. The “type” of construction of a reptile cannot go extinct: it existed before the reptiles appeared in the Fossil Record, and it would persist even if all reptiles had vanished from the surface of the earth. The “type” of a reptile, again, does not exist in nature, only its exemplars do. For Agassiz and Miller, the “type” of a reptile was grounded in Divine thought. Although the succession of fossils might suggest to the naïve observer a progression that results from change through time, nothing really changes in Miller’s view. The world may appear as a dynamic one to the human observer, but it is really only one of dynamic permanence.

“Vestiges of the Natural History of Creation” proclaimed a progressive development of organisms on the basis of natural laws (i.e., secondary causes) rather than through Special Creation (i.e., as a direct effect of a First Cause). The reason for Chambers was that a Creator wrapped up in time and space would cast an anthropocentric view of the Deity. In order to support his claim for a progressive process of change in nature, he had to link the living organisms in an unbroken chain of increasing complexity. One example, mentioned in the previous chapter, was Chambers’ use of the red blood color as a character that links annelid worms with vertebrates, relating the two groups in a series of ancestors and descendants. But that was not the most important character he turned to. The main feature on which Chambers based his evolutionary conclusions was the progressive development of the brain through the vertebrate series.Footnote 32 In Chambers’ view, brain size steadily and continuously increased from fish through reptiles and birds to mammals and humans. In his critique of Chambers, Miller agreed that there was an increase in complexity of the brain as could be shown by calculating and tabulating relative brain size of vertebrate animals. In fishes, the brain was calculated by Miller to be about twice the volume of the spinal cord; in reptiles and birds, the ratio had increased to 2.5:1–3.5:1; mammals showed a ratio of 4:1; however, humans displayed a ratio of 23:1. Viewing these figures, as they obtained on Miller’s account, who could argue persuasively for a continuity of transition between animals and humans? The Plan of Creation was progressive, but not continuous: on Miller’s account, there was a jump, a discontinuity in brain size between mammals and humans. In the very same sense, there was for Miller a striking discontinuity between even the highest mammals and humans, as it is only the latter that are endowed with the powers of rational thinking, language, and morality. Both the vegetative soul that regulated growth, as well as the animal soul that regulated movement and sensibility, may well be inherent in matter. In contrast, humans become endowed with a rational soul through divine intervention. This is what creates the gap between humans and animals that was appealed to by Adam Sedgwick and, in his tow, by Hugh Miller.

In Miller’s view, continuity of progressive transformation was further denied by the fact that the earliest representatives of any particular group need not also be the most simple in structural terms. Asterolepis was the perfect example, representing one of the earliest fossil fish then known, which, nevertheless, was characterized by a relative brain size estimated by Miller – erroneously, but befitting a “prophetic type” – to be comparable to that of reptiles. And finally, Miller marshaled the old argument of retrogressive development, again following in the footsteps of SedgwickFootnote 33: progress was not the only attribute of organismic diversity reflected by the Fossil Record, embryonic development, and classification – there were also incidences of rudimentation. For example, snakes have too many characters in common with lizards to classify them as anything else but reptiles. Yet, as Agassiz was to show in great detail in his Essay on Classification, published a little less than a decade later in 1857, this implied that snakes must have lost limbs, which are generally present in the group of which they form a part (i.e., reptiles). Snakes were to be characterized not by the absence of limbs but by the loss of limbs through retrogressive embryonic development. Borrowing in a roundabout and indirect way from the theories of the great French anatomists Etienne Geoffroy Saint-Hilaire and Etienne Serres, who had developed the “loi de compensation,” the law of compensationFootnote 34, Miller pointed out that snakes compensated for the loss of limbs by an increase in the number of vertebral elements during their embryonic development.Footnote 35

4.4 Miller’s Concept of “Proper Science”

Like many of his contemporaries, Miller considered the significance of the Fossil Record an important issue in the creation debate. At the same time, however, there existed for Miller a constant threat that science could be corrupted by the social and political agendas of scientists.Footnote 36 To oppose such tendencies, Miller proposed definitions for scientific subdisciplines, which would serve the purpose to concentrate research efforts to the objects and goals of those particular fields of interest. Remember that Chambers’ “Vestiges” was perceived as an account of natural history that drew from a great variety of special sciences such as astronomy, geology, and biology. Its author was consequently castigated for trying to break down the conceptual and instrumental barriers that separated the various subdisciplines, which professional scientists were engaged in. “Vestiges” simply came across as eccentric writing compared to the standard scientific practice of the day.Footnote 37 In support of such professionalization through the compartmentalization of science, Miller defined the task of comparative anatomists to determine with accuracy the level of complexity at which organisms had to be classified in the Great Chain of Being. The task of the paleontologist was to document the temporal succession of organisms in the Fossil Record, and nothing more. Like the science of the anatomist, paleontology was – on Miller’s definition – concerned not with causal explanation but with order in nature. The great British empiricist philosophers such as David Hume (1711–1776) and John Stuart Mill (1806–1873) had argued that all sound scientific knowledge ultimately derives from sensory, in particular perceptional (observational) experience. Accordingly, an empirical approach to the Fossil Record consisted in the documentation of the stratigraphic succession of fossil species, based on observation that must be free of all theory and preconception. This is what the paleontologist was called upon to do according to Miller’s definition of this field of research. To stretch theory construction beyond such a documentation of the occurrence of fossils in successive layers of rock would be nothing but idle speculation. The result of paleontological research has to be a catalogue of the spatial and temporal distribution of extinct species, and not theories about their possible transformation that remain without observational support. The Fossil Record shows beyond any doubt, however, that not all levels of organization known today existed from the beginning: there were times when fishes cruised the oceans, but no amphibians or reptiles populated the continents. And again: amphibians and reptiles existed long before mammals, and mammals existed long before the appearance of humans. And yet, for Miller, this was not an effect of species transformation at all. Instead, and as indicated by the existence of “prophetic types,” what seemed to be a newcomer in earth history is merely the coming into actual existence through exemplification of a “type” of animal construction that has neither past nor any future but just is in the form of a template, of a blueprint of Creation that is not tied to time and space.

Miller maintained that the simple fact of temporal succession of the appearance of fossils was, in itself, far from a valid or even significant proof for genealogical relationships. The nature of fossils had, indeed, remained controversial over a long period of time. As already mentioned, it was Steno who, in a dissertation dating back to 1669, pointed out that sedimentation, the natural settlement of suspended matter at the bottom of water bodies, was the obvious process by which hard tissues of once living animals such as shark teeth could become enclosed in successive layers of sedimentary rocks. This insight paved the way to the understanding that underlying strata of an undisturbed sequence of deposits must be geologically older than overlying strata. Folding and thrusting of the earth’s crust might alter the original sequence of strata, a job for geologists to find out, but the basic “Law of Superposition” must still hold, since it is subsumed by the Law of Gravity: the geologically younger deposits, and the fossils they contain, lie on top of underlying deposits in the sequence of the stratigraphical column that date from an earlier time, just as long as the sequence of layers has not been altered by some geological (tectonic) events. But the superposition of strata and the fossils they contain does not also and always imply that earlier fossils are ancestors of later forms of life. This is because the Fossil Record will remain incomplete to a certain degree. Recognizing a fossil as the earliest known representative of its group does not, at the same time, imply that this fossil is also the most primitive member of its group, ancestral to all the later representatives of the same group. An even earlier, and more primitive representative of the same group may have existed, but may simply not have been found (yet). Asterolepis, one of the earliest fossil fish known to Miller, shows a highly complex anatomy. But that, in itself, did not necessarily refute Chambers’ “Law of Development,” for it could always be argued that still earlier, more primitive fishes had existed, but had not yet been found. This, indeed, proved later to be the case.

For Miller, such an appeal to the incompleteness of the Fossil Record was a leap of faith, not knowledge backed up by observation. In the absence of evidence, any claim could be made in hypothetical support of any theory anybody wants to be true. Miller countered forcefullyFootnote 38 that “The possible fossil can have no more standing in this controversy than the “possible angel.” What he meant by this was that the Fossil Record had to be taken for what it is, and not for what it could be. Unbiased, simple, and straightforward observation, he contended, would reveal patterns of similarity among fossils, but nowhere was a process of descent with modification to be seen. Miller introduced a farmer into this hypothetical discourseFootnote 39, “a plain, observant, elderly man,” who – as a consequence of these virtues – simply cannot follow the expositions his companion, an enlightened philosopher who wants him to accept the theory of species transformation. The philosopher is convinced that the temporal succession of fossils in itself provides sufficient evidence for the development of life on earth: “Look here… life, both vegetable and animal, first began,” he explained as he pointed to the farmer’s own “deep ditch” – and from its beginning species continuously transformed to reach ever higher levels of complexity. The farmer, however, characterized by Miller as being less inclined toward speculation, maintained that he could not see anything else but a “certain top-upon-bottom order of things.” Unbiased, simple, and straightforward observation is what Miller wanted his science to be based on, and such a science did not, in his view, support the hypothesis of species transformation.

At first sight, this objection seems rather trivial, or else simply wrong. Trivial, because the process of descent with modification is supposed to have taken place in the past, and therefore has to be inferred from the patterns of greater or lesser similarity observed among the fossils distributed over time and space. Wrong, because Miller was appealing to the possibility of theory-free observation, something that modern philosophers of science have found to be impossible. The philosophy of science that started out with David Hume’s claim that all knowledge comes from unbiased observation is called empiricism, and Miller insisted that paleontology, the study of fossils, has to be founded on empiricism as has to be the case for any other respectable science. The issue of empiricism will necessitate a more detailed discussion, as does the significance of “observation” in the construction of scientific theories. At this juncture, it may suffice to point out that Miller insisted on “raw” observation that yields brute sense-data, which, to his knowledge, and to the date of the publication of his book, had never revealed any process of transformation from one fossil (or living) species to another. All that was recognized at that time was a constancy of form of species, and a succession of different species through time. Was there a way to bring the issue of species transformation into closer focus, to seek a way to confirm or disconfirm species transformation through observation? In empirical support of his views, Miller quoted the mummies brought back to Paris by Etienne Geoffroy Saint-Hilaire, who had accompanied Napoleon Bonaparte on his unsuccessful campaign to incorporate Egypt into the French empire.Footnote 40 Thousands of years old, these mummies indicated no essential change of human anatomy compared to Miller’s compatriots. The absence of anatomical change had likewise been demonstrated by Georges Cuvier in his study of Hibiscus skeletons that had been retrieved from Egyptian tombsFootnote 41 and brought back to Paris by Geoffroy. It is ironic that Geoffroy Saint-Hilaire was instrumental in the appointment of Cuvier at the Paris Natural History Museum, when later in their life, they would be divided about issues of comparative anatomy, animal classification, and the potential for species transformation. Cuvier took the evidence at face value: species do not change over time, and if different species are observed at different time horizons, this cannot be due to species transformation. This was also the point of view endorsed by Agassiz and Miller. The reason for Cuvier to take this stance was, of course, his “Law of the Functional Correlation of Parts.” With a carnivore dentition goes a carnivore’s intestinal system; with an herbivore dentition goes an herbivore’s intestinal system. There can be nothing in between. Organisms are complex machines that cannot change in any partial or gradual, stepwise manner. Cuvier had so much confidence in the functional correlation of parts that he proceeded to a public demonstration of the predictive power of what he believed to be a natural law. A fossil from the quarries of Montmartre had only been partially freed from the surrounding sediment, yet enough for Cuvier to recognize it as the skeleton of a marsupial mammal. Cuvier proceeded to enact a public presentation of the further preparation of the fossil that was to expose the pelvic girdle. Once completed, the procedure confirmed Cuvier’s previous prediction that the pelvis would include a marsupial bone.Footnote 42 Geoffroy Saint-Hilaire, on the other hand, reached the conclusion that species could change, within limits, in adaptation to the physical conditions of their life. However, he reached this conclusion not through the study of the Egyptian mummies he had brought back to Paris, but through the study of fossil crocodiles.Footnote 43 This, of course, allowed a much longer stretch of time for transformation to play out. Living crocodiles are characterized by a unique specialization in their skull, which is a secondary palate. What this means is that the internal nostrils (choanae) are displaced backwards to a posterior position in the palate, similar in some loose sense to their (independently evolved) position in mammals. The internal nares thus come to lie behind a skin flap that can close off the buccal cavity from the air passage, such that the animals can breathe with their head partially submerged in water – the typical stalking position of crocodiles. What Geoffroy found in fossil crocodiles was a more anterior position of the internal nostrils, a position that more closely corresponds to the primitive reptile condition. What is furthermore the case is that the developing embryos of living crocodiles show a progressive shift of the internal nares from a primitive anterior position, corresponding to the condition observed in fossil crocodiles, to a posterior position. The embryonic development thus again revealed a parallelism with the Fossil Record. Geoffroy naturally concluded that crocodiles had changed through time as a consequence of species transformation.

4.5 Karl Ernst von Baer and the Importance of Embryology

In contrast, constancy of structure and discontinuity between structural types, this was the message that Cuvier, Agassiz, and Miller took to the public in their argument against transformationism. Chambers had likewise realized that there were gaps to be bridged, or to be explained away, in order to preserve the absolute continuity of the Great Chain of Being. To a reader of his “Vestiges,” he may appear to have done so by a sleight of hand. Charles Babbage, an English mathematician he referred to, had been working on the construction of a calculating machine. The project was to build a machine that would be programmable so that it would switch, suddenly and apparently discontinuously, from one calculating operation to another without special external input, but solely on the basis of the program that was entered beforehand. The operations would have to appear to be discontinuous if the machine was observed from the uninformed perspective of an outsider, but in fact they would be in perfect accordance with the natural course of events as determined from preordained laws. In a similar vein, Chambers maintained that the secondary causes that govern the natural course of events would do so in a uniform and continuous manner, even though a human observer might perceive discontinuity. Etienne Geoffroy Saint Hilaire, who had come to accept the idea that species could have the potential for change within the limits set by their general structural type, had provided an interesting example where continuity of cause could result in discontinuity of anatomical structure.Footnote 44 Reptiles and birds appear to a certain degree to represent a similar structural plan, one that was later recognized as the sauropsidan body plan. Yet, in adaptation to flight, the bird lung had achieved a structural complexity that far exceeded the complexity exhibited by any reptile lung. As far as the anatomy of the lung is concerned, there appeared to be a striking discontinuity between a reptile and a bird. However, if one inspected the lung in an embryonic lizard, and in an embryonic bird, a striking similarity of structure would be revealed. There could be no question also that the continuity of the process of embryonic development in both lizard and bird was governed by a continuity of the underlying causal chain. Geoffroy’s conclusion was that a very minor change in the early embryonic development of a bird could lead to a vastly different anatomy of the lung in the adult, but such a discontinuity in the adult structure of a lizard and a bird lung did not necessarily imply a discontinuity of the underlying causal chain that governs the embryonic development of lizards and birds.

With his contemplations on how a reptile lung could have transformed into a bird lung, Geoffroy invoked a model of embryonic development that was fundamentally different from the one advocated by Chambers in some parts of his “Vestiges.” To see embryonic development as running parallel to the Great Chain of Being is to claim that organisms of higher complexity recapitulate, during their development, the adult anatomy of ancestral forms, which stand on a lower rung of the ladder of life. At some point of its development, the frog tadpole resembles a fish. Geoffroy’s claim was quite different. What he said was that embryos of reptiles and birds look closely similar at early stages of their development, but then become increasingly dissimilar as development proceeds. Historians of biology call the first model one of recapitulation, the second model one of differentiation.Footnote 45 On the first model, the embryo recapitulates during its development the Great Chain of Being up to the placement of its own species on the ladder of life. On the second model, embryos that resemble each other during early phases of their development become increasingly more different from one another as they grow and differentiate.Footnote 46 This second model of diverging development was championed by the eminent developmental biologist Karl Ernst von Baer, who in his monumental monograph of 1828 challenged the idea that embryonic development runs parallel to the Great Chain of Being. In fact, Chambers alluded to both models of embryonic development in his “Vestiges.” To go from a goose to a platypus to a rodent is a march along the Great Chain of Being. To find the embryos of fishes, reptiles, birds, and mammals to be in an “identical condition”Footnote 47 during early stages of development but to progressively diverge from one another during subsequent stages is a von Baerian model of differentiation, which Chambers picked up from William Carpenter, who was a friend of DarwinFootnote 48 and among the earliest authors to defend von Baer’s views in England.Footnote 49 That the two models of embryonic development, recapitulation vs. von Baerian differentiation, are quite different is best brought out in graphical representation. Illustrating “recapitulation” would be a sketch of a ladder, an unbroken chain of ascending forms of organization. To illustrate “differentiation” one would have to sketch a branching diagram, a tree-like structure with gaps between the tips of its terminal branches, as was indeed done by Chambers.Footnote 50 It may seem puzzling that Chambers juxtaposed two distinctly different, even contradictory models of embryonic development in his “Vestiges,” as this could be predicted to invite criticism. But James A. SecordFootnote 51 thinks that there might have been advantages from a strategic point of view, as von Baer’s work remained rather poorly known in Britain.

Von Baer’s was an ingenious idea: apparent discontinuity of adult form did not mean discontinuity of developmental process. In fact, how to bring what appears to be discontinuity of form together with continuity of developmental processes is currently a very active field of research in evolutionary developmental biology. But Miller had, of course, another ax to grind. Assume Geoffroy was right, and assume that minor changes in early embryonic development could indeed result in drastic changes of adult anatomy, how then would it be possible that the developmental process would be programmed such that the changed adult form was perfectly adapted to a changed locale in the household of nature? How, in other words, was it possible that the developmental process in birds was programmed such as to result in an adult lung structure that would be perfectly adapted to the demands of active flight? The concept of “perfect adaptation” so invoked obviously implies some foresight, planning, and design, as William Paley had pointed out in his “Natural Theology” of 1802. How is this notion of design to be understood? In Paley’s case, as well as in Miller’s, quite literally: engineers design structures, such as bridges, or clockworks, according to a blueprint, for a certain purpose, and hence toward a certain goal.

4.6 Intelligent Design and the Four Aristotelian Causes

The search for design, purpose, and goal-directedness in nature goes back to Ancient Greek philosophy. Natural processes in general are understood as events, or chains of events; events, in turn, link a cause with an effect. Science seeks to unravel the causes that underlie natural processes, and – classically – to capture those in the form of natural laws. In contrast to modern science, the Ancient Greek philosopher Aristotle had distinguished four causes, which can perhaps best be explained by invoking a carpenter who sets out to build a cabinet. The wood and the nails the carpenter would need are called the material cause, as they provide the material with which to build the cabinet. The force with which the carpenter’s arm would drive the saw and the hammer is called the efficient cause, as it provoked an effect on the wood being cut and nailed together. However, in order to build a cabinet, the carpenter would be well advised to plan his actions ahead of time, for example by drawing up a blueprint of how the finished cabinet should look like. Aristotle called this blueprint, the plan according to which to build the cabinet, the formal cause. Finally, the cabinet will only be useful if its construction is planned with reference to the future intended use of this piece of furniture; this intended use of the cabinet, the purpose for which the cabinet is being built, that is, the goal of the whole project Aristotle called its final cause. It is easily understood how the concept of perfect adaptation accommodates an Aristotelian conception of causality that implies purpose, goal-directedness, and hence design. Almost all naturalists before Darwin viewed organisms as perfectly adapted to their environment. They seemed to be made to perfectly fit into a particular place in the household of nature, into a particular niche of their environment. And the process of individual development (i.e., the process of ontogeny that comprises both embryonic and postembryonic development) of an organism appeared to replicate and maintain the perfect adaptation of its species through generations: ontogeny looked as if it were goal-directed for a certain purpose, which is the maintenance of perfect adaptation of the developing organism, according to a certain plan, which is the body-plan or type of the species to which the developing organism belongs. Such purposefulness and goal-directedness of natural processes was, according to Hugh Miller, imparted on those by the First Cause. According to Chambers, such natural processes were governed by secondary causes, in particular by his Law of Development. There was no need for a supra-natural agent to direct the natural course of events; that direction was, according to Chambers, inherent in nature, naturalized as a consequence of secondary causes enacted by the First Cause. But direction there still was governed by design and directed toward a goal – even for Chambers.

Formal and final causes are inextricably linked to the notion of intelligent design that results in perfect adaptation. Intelligent design in turn is inextricably linked to a rational entity capable of foresight and planning. For Chambers, the world was composed of two perfectly designed clockworks, constructed and wound up by the Creator, or First Cause, but left on their own to unwind according to plan. The Creator does not reside in nature. He cannot reside in nature if nature is subject to change through time, as argued by Chambers. In Chambers’ system, the formal and final causes were naturalized in the workings of secondary causes. Miller rejected such a naturalization of creative forces. He found such naturalization unsupported by “raw” observation that is free of idle speculation, and he found it objectionable on moral grounds. Steeped in the evangelical traditionFootnote 52, he wanted the Creator more intimately involved with His Creation. His “was the voice of Old Dissent,”Footnote 53 which would not allow to insert secondary causes between God and Nature.

Looked at from this perspective, it is easily understood that one, if not the major, obstacle that Darwin had to overcome in his thinking was the notion of “perfect adaptation.”Footnote 54 Darwin struggled to free his mind from the concept of “perfect adaptation” to make room for the variation of organisms that would in turn offer natural selection the opportunity to shape new, and different, forms of life. Darwin noted that animal breeding could result in imperfection, such as in hairless dogs that have imperfect teethFootnote 55, he found hybridization to result in imperfect reproductive organsFootnote 56, and perhaps most notoriously, he found “numerous gradations” to link the “perfect and complex eye to one very imperfect.”Footnote 57 A developmental stage of cirripedes, which are barnacle crustaceans, Darwin described as having “six pairs of beautifully constructed natatory legs, a pair of magnificent compound eyes, and extremely complex antennae; but they have a closed and imperfect mouth, and cannot feed.”Footnote 58 Taking the concepts of design and perfect adaptation to communities of co-existing species results in further complications. Consider the coexistence of carnivores, such as lions, and herbivores, such as antelopes. Lions would presumably be perfectly adapted to hunt and capture antelopes; antelopes would presumably be perfectly adapted to escape lions. Something in this system has to give to keep either species from going extinct, lions as a consequence of starvation (because the perfect antelopes would always escape them), antelopes as a consequence of predation (because the perfect lions would always catch them). So how is it that lions and antelopes can coexist, as a result of a certain balance between predator and prey? There seem to be only two options: a perfectly balanced, preordained and preestablished harmony between predator and prey, enacted by the First Cause, or competition. While our old friend from previous chapters Charles Bonnet – among others – opted for the first solutionFootnote 59, Darwin opted for the latter explanation.

Most important for Darwin, though, was what he came to call the “Great Law of Variation.” Again, Darwin had no viable theory of inheritance available as an explanation for variation when he published his Origin in 1859. His “Law” therefore is what philosophers of science call an “empirical generalization,” a generalization based on repeated observation. And indeed, wherever Darwin looked with enough concern for detail, he found that in all plant and animal populations no one individual organism looks exactly the same as any other one. This was true of the beetles he collected while still a student, of the birds he collected on the Galapagos Islands during his voyage on the Beagle, of the barnacles he studied back at home, and of the orchids he liked to grow. Variation spoils the concept of perfect adaptation: perfection cannot vary. There can only be one way to be perfect, and this perfection would be embodied in the specific “type” that is exemplified by each species – in its blueprint. Species, it turns out however, are variable, and hence cannot be perfectly adapted; instead, they are adequately adapted for survival, adequate enough for continued participation in the processes of reproduction, variation, and natural selection. If there were a blueprint specifying the “type” of a species, this blueprint would have to be blurred.

Through his many contacts with plant and animal breeders, Darwin assured himself that the variations he recorded in nature were heritable. Indeed, by selecting from the variants for further breeding, plant and animal breeders mimicked under artificial conditions the process of selection that Darwin eventually proposed also to operate in nature under natural conditions. In 1868, Darwin published his “Variation of Plants and Animals under Domestication,” a book in which he finally came up with his theory of inheritance he called “Pangenesis.” Darwin invoked heritable particles that he called “gemmules” or “gemmulae,” which in his theory performed in much the same way as Buffon had claimed for his “organic molecules.” Circulating through the parental body, the gemmulae would be imprinted by this organism’s characteristics, including characters that the parental organism had acquired during its lifetime (here, Darwin fell victim to the same error that had previously marred Maupertius’ understanding of inheritance, as well as Lamarck’s theory of evolution). Eventually, the imprinted gemmules would be carried through the blood stream to the reproductive organ for storage. Upon conception, both parental organisms, male and female, would contribute gemmules to the formation of the embryo. This is, again, an atomistic conception of embryogenesis, where parts come together to form a new organismic whole. Since the embryo was formed from minuscule particles, and since these particles could be variously recombined in the formation of offspring, the newly formed organism could vary in ever so slight degrees in every one of its parts and particles. Such fundamental variation of organisms that collectively form an interbreeding population is the raw material on which, according to Darwin, natural selection operates. Those variants that have even only a slight edge over others in their adaptation to their natural environment would see this to manifest itself through a relatively greater reproductive success, even if only slightly so. This is not a “nature red in tooth and claw,” as Alfred Tennyson poetically put it. It is variable organisms competing for relative reproductive success, which would see slightly better adapted traits to be more frequently reproduced than less well-adapted traits. Species transform in the course of an extended process of variation and natural selection, interconnected by innumerable transitional forms that together form a continuous, unbroken chain of generations.

This was a theory of species transformation, indeed a theory of the origin of new species, which was far more radical than Chambers’. It was a theory that severed the ties to Aristotelian metaphysics, one that rejected the call for formal and final causes. As we shall see, it was an altogether different approach to science in general, and to biology in particular, than that marshaled by either Chambers or Miller. Indeed, at the end of the day, Darwin would not only have offered a viable theory of evolution but would also have redefined what science is, not necessarily for physics and astronomy but certainly for historical biology. It was a science free of design and purpose, a science where certainty was replaced by probability. But even if the theory of variation and the consequent theory of natural selection were one of numbers and of statistics, respectively, for Darwin these theories were still Laws of Nature.

How did Darwin arrive at this solution? Clearly, the debate between Chambers and Miller – one that Darwin closely studied – had brought a great number of issues to the forefront, some of greater, some of lesser generality. The most important perhaps is the question: what is “respectable science”? How is science to be organized, departmentalized, or synthesized? What role does observation play in science, and how far can theory construction be allowed to transcend observation? What is, quite generally speaking, the proper mode of scientific reasoning? What are secondary causes (i.e., universal laws of nature), how are they discovered, and what are they supposed to explain: unobservable causal relations or merely observed regularity? All of these questions, relevant to science in general, have implications for the more specialized issues that Chambers and Miller were debating. Is there order in nature that can be discovered, or is order in nature merely the reflection of an ordering human mind? And if there is, indeed, order in nature, what does it mean: is it anchored in a blueprint of creation, or is it evidence for evolutionary relationships? What does it mean to have an orderly succession of fossils through the layers of rock that encode earth history? What does it mean that embryos of broadly related groups of organisms, such as the vertebrates, are similar during early stages of development, but become progressively more dissimilar as they grow and differentiate? These are the questions we now must turn to.