The Argument for Organic Evolution Before The Origin of Species I
Arthur O. Lovejoy
University of Missouri
I
IN this year of the Darwin centenary it is worth while to raise two questions which have, in the mass of literature elicited by the occasion, received less consideration than they merit. At what date can the evidence in favor of the theory of organic evolution—as distinct from the hypothesis of natural selection—be said to have been fairly complete : in other words, how early were the facts and principles from which the truth of that theory is now ordinarily inferred sufficiently known to all competent men of science, to require the inference, even though it was not, in fact, generally made? And by what English writer was a logically cogent argument for the theory first brought together and put before the public? The interest attaching to these questions is much more than merely historical. The answer to them will afford a sort of object-lesson in the logic of scientific reasoning. Here is a doctrine now accepted by all naturalists : at what point, in the century-long accumulation, through half a dozen separate sciences, of the evidences inclining to that doctrine, ought we to say that the balance of logical probability turned decisively in its favor? The inquiry will also be found, I think, to throw a somewhat instructive light upon the psychology of belief, and to show how far, even in the minds of acute and professedly unprejudiced men of science, the emotion of conviction may lag behind the presentation of proof.
By this time, no doubt—though it has not long been so—every schoolboy knows that Darwin did not invent the theory of evolution. The Darwin centenary itself has served to remind the public of the names and works of at least some of the earlier protagonists of the doctrine : of the elder Darwin, namely, of Lamarck, of Geoffroy St. Hilaire, of the author of the "Vestiges of the Natural History of Creation," and of Herbert Spencer. It is less commonly remembered, but perhaps not universally forgotten, that among English-speaking naturalists, the theory was a commonplace topic of discussion for two or three decades before 1859, and especially after the publication and immense circulation of the successive editions of Robert Chambers's " Vestiges," of which the first appeared in 1844. Geological text-books of same period referred to the "theory of transmutation of species" as
(500) a matter of course, though usually only to reject it as an exploded hypothesis. Thus the "Elements of Geology," of Alonzo Gray and C. B. Adams, 1852, enumerates three theories which have been advanced respecting the origin of animal species: (1) Successive special creations; (2) "transmutation, which supposes that beings of the most simple organization having somehow come into existence, the more complex and the higher orders of animals have originated in them by a gradual increase in the complexity of their structures";[1] (3) gencratio aequivoca of individuals and species. The first is adopted, but the second is discussed at greatest length; on it the authors remark that "those who have adopted the theory of transmutation have generally detached it from Lamarck's theory of appetency, and not attempted to explain how the process of transmutation goes on." The argument for evolution is similarly discussed and "refuted " in " Geological Science," a popular text-book by D. T. Ansted, F.P.S., 1854. To this refutation, indeed, the greatest of English geologists had devoted three chapters of his " Principles of Geology "[2] before 1835.
But though such facts as these are, as I have said, now fairly familiar, the notion still widely prevails, even among biologists, that no serious proof of. evolution either existed or had been published before the appearance of the " Origin of Species "—or at all events, before the late 1850's.[3] Professor Joseph Le Conte, indeed, in his " Evolution and Its Relation to Religious Thought,"[4] made it a reproach against both Lamarck and Chambers that they had unscientifically embraced the hypothesis before the evidence for it was ripe; and considered it fortunate for science that their notions died still-born, under the weight of the great authority of Cuvier and Agassiz. " I know," wrote Le Conte, " that many think with Haeckel that biology was kept back half a century by the baleful influence of Agassiz and Cuvier; but I can not think so. The hypothesis was contrary to the facts of science, as then known and understood. It was conceived in the spirit of baseless speculation, rather than of cautious induction; of skilful elabora-
(501) -tion, rather than of earnest truth-seeking. Its general acceptance would have debauched the true spirit of science.... The ground must first be cleared . . . and an insuperable obstacle to. hearty rational acceptance must first be removed, and an inductive basis laid." This last, Le Conte goes on to argue, was largely the work of Agassiz, opponent of evolutionism though he was. Now, it is, of course, undoniable that the premature adoption of a hypothesis is a sin against the scientific spirit, and that the chance acceptance by some enthusiast of a truth in which, at the time, lie has no sound reason for believing, by no means entitles him to any place of honor in the history of science. But what constitutes prematurity in this particular matter? And was the evolutionary hypothesis " contrary to the facts of science, as known and understood " at any three after 1840 ?
The prevalent belief that it was is chiefly due to two things. The first is the fact that before 1859 few English naturalists of high. standing accepted, and almost none publicly avowed, the theory of descent, whereas, after the publication of the Origin," such notable names as Huxley, Lyell, Hooker and Asa Gray were speedily numbered among the disciples of the doctrine, and in the ensuing five years it was well upon its way towards its eventual complete triumph. The other source of the supposition that Darwin presented the fits[ adequate grounds for believing in evolution is the express testimony of Huxley, whose paper on the reception of the " Origin of Species "[5] has come to be the principal source of information on its subject. In that article, and in several letters and other writings, Huxley takes credit to himself for his rejection of the transformation-theory until he became acquainted with Darwin's work; and he never expressed. any sentiment far short of contempt for Chambers's "Vestiges." He wrote in 1887
I must have read the "Vestiges" . .. before 1846; but if I did, the book made very little impression on me, and I was not brought into serious contact with the "species" question until after 1850. . . . It seemed to nee then, as now, that " creation," in the ordinary sense of the word, is perfectly conceivable. .. . I had not then, and have not now, the smallest a priori objection to raise to the account of the creation of plants and animals given in " Paradise Lost." ... Far be it from me to say that it is untrue because it is impossible. I confine myself to what must be regarded as a modest and reasonable request—for some particle of evidence that the existing species of animals and plants did originate in that way, as a condition of my belief in a statement which appears to me highly improbable. And, by way of being perfectly fair, I had exactly the same answer to give to the evolutionists of 1851-58. . . . The only person known to me whose knowledge and capacity compelled respect, and who Bras, at the same time, a thorough-going evolutionist, was Mr. Herbert Spencer. . . . But even my friend's rare dialectic skill and copiousness of apt illustration could not, drive me from my agnostic position. I took my stand upon two grounds: Firstly, that at the time the evidence in favor of transmutation was wholly insufficient; secondly, that no suggestion respecting the causes of the
(502) transmutation assumed, which had been made, was in any way adequate to explain the phenomena. Looking back at the state of knowledge at the time, I really do not see that any other conclusion was justifiable. . . . As for the "Vestiges," I confess the book simply irritated me by the prodigious ignorance and thoroughly unscientific habit of mind manifested by the writer. If it had any influence at all, it set me, against evolution. . . . Thus, looking back into the past, it seems to une that my own position of critical expectancy was just and reasonable . . . .. So I took refuge in that tatige Skepsis which Goethe has so well defined; and, reversing the apostolic precept to be all things to all men, I usually defended the tenability of received doctrines, when I had to do with the transmutationists; and stood up for the possibility of transmutation, among the orthodox.
In this matter Huxley is assuredly, a witness whose testimony should not lightly be set aside; for to his attainments as a naturalist he ordinarily joined singular logical acumen and rare openness of mind. Yet I think it possible to show that the passage just quoted gives a thoroughly misleading view of the logical status of the argument for evolution, as it existed in the light of the science of the period; that the attitude which Huxley assumed. from 1850 to 1858 was contrary to all sound ideas of scientific method; and that lie does the reputations of both Spencer and Chambers serious injustice. I shall attempt to establish these conclusions mainly by showing that the arguments and facts chiefly relied upon by Huxley himself and other early champions of transformism were entirely familiar and well authenticated from fifteen to twenty years before 1859, and had virtually all been clearly noted and pertinently used in the published evolutionary reasonings of Chambers or of Spencer. The truth is—as the, evidence to be adduced will make clear—that Huxley's strongly emotional and highly pugnacious nature was held back by certain wholly non-logical influences from accepting an hypothesis for which the evidence was practically as potent for over a decade before lie accepted it as it was at the time of his conversion. These influences did not in Huxley's case, as they did in so many others, proceed from religious tradition or temperamental conservatism. But Huxley had unquestionably been strongly repelled by the " Vestiges.'' The book was written in a somewhat exuberant and rhetorical style; with all its religious heterodoxy, it was characterized b3; a. certain pious and edifying tone, and was given to abrupt transitions from scientific reasoning to mystical sentiment; it contained numerous blunders in matters of biological and geological detail; and its author inclined to believe, on the basis of some rather absurd experimental evidence, in the possibility of spontaneous generation. All these things were offensive to the professional standards of an enthusiastic young naturalist, scrupulous about the rigor of the game, intolerant of vagueness and of any mixture of the romantic imagination with scientific inquiry, a little the victim, perhaps, of the current scientific cant about " Baconian induction," and quite incapable of
(503) taking, towards any doctrine or movement, any attitude intermediate between contemptuous hostility and ardent partizanship. Full advantage, moreover, had been taken, by the eminent scientists who were also champions of religious orthodoxy, of the faults of Chambers's book; they contrived very successfully to put about the impression that to be a " Vestigiarian" , was to be " unscientific " and sentimental and absurd. These were the qualities which Huxley would have been peculiarly averse to being ?ed with. Finally, he seems to have been exasperated most of all by â single loose piece of phraseology that now and then recurs in the " Vestiges." Chambers, namely, was prone to speak of " laws " as if they were causes and, more particularly, as if they were secondary causes to which the " Divine Will " delegated its agency and control. To Huxley, from the beginning of his career, this hypostatizing fashion of referring to "laws of nature" was a bête noire; and in 1887 we still find him pursuing the author of the "Vestiges" with ridicule because of his "pseudo-scientific realism."[6] He, therefore,[7] in 1854, almost outdid the Edinburgh Review in the ferocity of his onslaught upon the layman who had ventured to put forward sweeping generalizations upon biological questions while
(504) capable of errors upon particular points which were palpable to every competent specialist.
Yet the layman was, after all, sound in his main thesis; and, what is far more significant, his thesis was based upon sound and sensible arguments, substantially the same arguments that Huxley was destined before long to use in the same cause, though with far superior skill as a debater. It will, I think, appear impossible to acquit the young Huxley of a certain measure of scientific Pharisaism in this episode. He was so shocked by minor breaches of scientific propriety, in the "Vestiges," that he forgot the weightier matters of the law of scientific method. In his irritation at Chambers's incidental slips in zoology, he became blind to the importance and suggestiveness of the general outline of that writer's reasoning. Quite other was Alfred Rassel Wallace's reaction upon the little book. As early as 1845 lie wrote
I have rather a more favorable opinion of the " Vestiges " than you appear to have. I do not consider it a hasty generalization, but rather as an ingenious hypothesis, strongly supported by some striking facts and analogies, but which remains to be proved by more facts and the additional light which more research may throw upon the problem. It furnishes a subject for every observer of nature to attend to; every fact lie observes will make either for or against it.[8]
By 1847 Wallace had become thoroughly convinced of the truth of transformism; and from that time forward his mind was occupied with the problem of explaining the cause and modus operandi of evolution. At this time, he writes:
The great problem of the origin of species was already distinctly formulated in my miHd. . . . I believed the conception of evolution through natural law, so clearly formulated in the " Vestiges," to be, so far as it went, a true one; and I firmly believed a full and careful study of the facts of nature would ultimately lead to the solution of the mystery.
Wallace thus escaped the fatal error in logical procedure into which Huxley fell. For Huxley, in the passage already cited, gives as one of his two reasons for refusing to accept, even provisionally, the evolutionary hypothesis, the fact that "no adequate suggestion respecting the causes of the transmutation assumed" had then been made. But, that no causal explanation of a fact is at hand, is not good reason for denying the fact, if serious evidence of its reality is presented. Wallace properly discriminated the two issues; becoming first convinced that there was an established balance of scientific probability in favor of the fact, he then set himself upon the quest of a hypothesis that would explain it. He verily had his reward; a decade later lie appeared, with Darwin, as joint author of the doctrine of natural. selection.
(505)
It is time to proceed to the proof of the contentions of this paper. In presenting it, I shall first recall to the reader passages—some of them, doubtless, already familiar—from Huxley or other post-Darwinian defenders of the evolution theory, and then exhibit the parallel arguments found in Chambers, Spencer and other pre-Darwinians. Since, in such a case, textual precision is of some importance, it is hardly needful to apologize for copious citation of the ipsissima verba of the authors in question. The arguments for evolution will be taken up in the order of their generality or of their logical interconnection.
It is necessary first of all, however, to remind the reader of the general outlines of the situation in the science of the time. It was a situation essentially different from that in which Lamarck had carried on the propaganda of transformism. The difference was due to two changes that had taken place in the intervening period. First, the science of geology had gone through a brilliant development, and had fought and won its battle against religious orthodoxy; and in England, though not all geologists were consistent uniformitarians, all geology had been profoundly influenced by the principles and the methods of Hutton and Lyell. Second, the two allied subsidiary sciences of paleontology and stratigraphic geology had been created, through the work of Cuvier and of William Smith. One result was that the recognized age of the planet had been vastly extended ; enough time was thus granted for the evolutionary process. A still more significant result was that the Mosaic cosmogony bad been entirely abandoned by even the most orthodox of men of science. The doctrine of creation which such men defended against the hypothesis of development no longer bore any close resemblance to the narratives of Genesis; it was no longer a question of a single, original creation of all things, but of a large number of repeated acts of " special creation," separated from one another by wide intervals of time, and confined to the production of organisms. Meanwhile, it was assumed, in the organic realm things were going on in an orderly and normal manner, in accordance with natural laws of geologic change; even the Cuvierian " catastrophes " were " natural " phenomena. The effect, in short, of the triumph of geology had been, curiously enough, to increase the resort to supernatural agency in the current accounts of the genesis of the existing order of nature. In place of one great, obscure miracle at the origination of the universe, the revised version of the doctrine of creation assumed a large number of petty and definite miracles; it supposed, in Chambers's words, " an immediate exertion of the creative power, at one time to produce zoophytes, at another time to add a few marine mollusks, another to bring in one or two crustacea, —again to produce crustaceous fishes, again perfect fishes, and so on to the end.'[9] Creationism, to conform to the accepted principles and accumulated knowledge of geological science, had been
(506) compelled, like the Ptolemaic astronomy before it, to interpolate some very singular epicycles in its hypothesis. And while all these miraculous interpositions were taking place in order to keep the organic kingdom in a going condition, the Creator was not for a moment allowed by the orthodox geologists to interfere in a similar manner in their own particular domain of the inorganic processes. Their attitude was like that of the French authorities who, a century earlier, suppressed the " miraculous cures " of the Jansenist abbé at the church of St. Médard in Paris, and, in a famous lampoon, were represented as posting the following proclamation on the church doors:
De par le roi, défense à Dieu
De faire miracle en cc lieu.[10]
So, in the ruling science of 1830-60, the only officially licensed place (outside of Palestine) in which miracles might be performed by the Creator was the domain of organic phenomena. Here, as a measure of compensation, the number of miracles scientifically sanctioned had been materially increased.[11]
It was a further consequence of these changes in the scientific situation that the men who, in the name of orthodoxy but under the mantle of science, attacked the pioneers of evolutionism, themselves taught doctrines no less completely at variance with the usual—and with any natural-interpretation of Scripture. Accommodations and. forced interpretations had, indeed, been devised in abundance, to "harmon-ize" the new science with theology; but if these could be invented to justify geology, others could as well be, as they since have been, invented to justify evolutionary biology. Any consistent scriptural believer could make out as good a case of heresy against Cuvier, Owen, Sedgwick, Agassiz, or Hugh Miller, as against the author of the "Vestiges"' or Herbert Spencer. These writers, therefore, occupied a position of a strange and rather damaging incongruity, as Chambers did not fail to point out:
Strange to say, those who every day give views of physical cosmogony altogether discrepant in appearance with that of Moses, apply hard names to my book for suggesting an organic cosmogony in the same way liable to inconsiderate odium.... The views which I gave of this history of organization stand exactly upon the same ground upon which the geological doctrines stood, fifty years ago. . . . If the men newly emerged from the odium which was thrown upon Newton's theory of the planetary motions, had rushed forward to turn that odium upon the patrons of the dawning science of geology, they would have been prefiguring the conduct of several of my critics, hardly escaped from
(507) the rude hands of the narrow-minded, yet eager to join the rabble against a new and equally unfriended stranger, as if that were the best way of purchasing immunity for themselves. The public must soon see that if a literal interpretation of scripture is an insufficient argument against the true geognostic history of our earth, so also must it be against all associated phenomena, supposing they are presented on good evidence.[12]
In view of this situation, the arguments for evolution, in 1844 or 1859, were primarily significant, not as direct evidences in favor of one hypothesis, but as touchstones for deciding between the claims of twothe only two-rival hypotheses : that of the ready-made production of species, with their known characteristics and relations, by repeated special acts of creation; and that of their production through the gradual modification, in the course of natural descent, of earlier and. simpler forms. Huxley, it is true, refused to face the alternative, and cried, " a plague o' both your houses !" Nothing can be said, however, in justification of such a position on the part of a man of science. Hypotheses non lingo has never been a sound or serviceable maxim; it had certainly not been by following it that the sciences of astronomy and geology had developed.[13] Now, if other hypotheses, beyond the two in question, were conceivable in 1844, certainly no others were seriously advanced. The first concern of a biologist of the period should, then, have been to compare the two hypotheses of the origin of species, in the light of the then known principles and facts, hereafter to be enumerated. This comparison, if made honestly, by a logically competent mind, must necessarily have led, at almost any time after 1840, to the conclusion to which Spencer tells us that he found himself forced somewhere about 1850. By this time, he says:
The belief in organic evolution had taken deep root [in my mind] and drawn to itself a large amount of evidence-evidence not derived from. numerous special instances, but derived from the general aspects of organic nature and from the necessity of accepting the hypothesis of evolution when the hypothesis of special creation had been rejected. The special creation belief had dropped' out of my mind many years before, and I could not remain in a suspended state; acceptance of the only possible alternative was imperative.[14]
After these preliminaries, tine reader is prepared for viewing the ,arguments for evolutionism, now to be recalled in a more detailed manner, in their proper historical and logical perspective.
1. Argument from the General Presumption of Science against " Supernatural " ,Explanations o f Phenomena.— In his " Belfast Address," 1874, Tyndall pointed out that the main argument for evolu-
( 508) -tion lay in the superior congruency of the hypothesis—as contrasted with the special creation doctrine—with the methodological presuppositions of modern science and with the general view of nature which in most of the other provinces of science had already been accepted.
The basis of the doctrine of evolution consists, not in an experimental demonstration—for the subject is hardly accessible to this mode of proof—but in its general harmony with scientific thought. From contrast, moreover, it derives enormous relative strength. On the one side we have a theory which converts the Power whose garment is seen in the visible universe into an artificer, fashioned after the human model, and acting by broken effects, as man is seen to act. On the other side, we have the conception that all we see around us and feel within us—the phenomena of physical nature as well as those of the human mind—have their unsearchable roots in a cosmical life, .. . an infinitesimal span of which is offered to the investigation of man. Among thinking people, in my opinion, this last conception has a higher ethical value than that of a personal artificer.
Reviewing the past triumphs of the scientific method over supernaturalism, he concludes
We claim, and we shall wrest, from theology the entire domain of cosmological theory. All schemes and systems which thus infringe upon the domain of science must, in so far as they do this, submit to its control.... Acting otherwise proved always disastrous in the past, and it is simply fatuous to-day.
Similarly Romanes put in the fore-front of the arguments for evolution
The fact that it is in full accordance with what is known as the principle of continuity—by which is meant the uniformity of nature, in virtue of which the many and varied processes going on in nature —are due to the same kind of method, i. e., the method of natural causation. . . . The explanations of . . . phenomena which are at first given are nearly always of the supernatural kind. ... Now, in our own day there are very few of these strongholds of the miraculous left. . . No one ever thinks of resorting to supernaturalism, except in the comparatively few cases where science has not yet been able to explore the most obscure regions of causation.... We are now in possession of so many of these historical analogies, that all minds with any instincts of science in their composition have grown to distrust on merely antecedent grounds, any explanation which embodies a miraculous element. . . . Now, it must be obvious to any mind which has adopted this attitude of thought, that the scientific theory of natural descent is recommended by an overwhelming weight of antecedent presumption.
This "overwhelming weight of antecedent presumption" against special creation, and in favor of evolution, was pointed out by Chambers with entire clearness; his arguments present in part an almost verbal parallel to the passages I have quoted from Tyndall and Romanes. In the already established results of geology and astronomy, lie writes in the " Vestiges'':
We have seen powerful evidence that the construction of the globe and its associates was the result, not of any immediate or personal exertion on the part of the Deity, but of natural laws which are expressions of his will. What is to hinder our supposing that the organic creation is also the result of natural
(509) laws, which are in like manner the expression of his will? ... The fact of the cosmical arrangements being an effect of natural law, is a powerful argument for the organic arrangements being so likewise; for how can we suppose that the august Being who brought all these countless worlds into form by the simple establishment of a natural principle flowing from his mind, was to interfere personally whenever a new shell-fish or reptile was to be introduced in one of these worlds? Surely this idea is too ridiculous to be for a moment entertained. This would certainly be to take a very mean view of the Creative Power—in short to anthropomorphize it.
In his " Explanations,"[15] 1846, he puts the considerations urged by Romanes far more tellingly than Romanes put them forty years later. Chambers wrote:
The whole question stands thus: For the theory of universal order that is, order as presiding both in the origin and administration of the world—we have the testimony of a vast number of facts in nature, and this one in addition—that whatever is reft from the domain of ignorance and made undoubted matter of science, forms a new support to the same doctrine. The opposite view, once predominant, has been shrinking for ages into lesser space, and now maintains a footing only in a few departments of nature which happen to be less liable than others to a clear investigation. The chief of these, if not the only one, is the origin of the organic kingdoms. So long as that remains obscure the supernatural will have a certain hold upon enlightened persons.. . . One after another the phenomena of Hature, like so many revolted principalities, have fallen under the dominion of order and law; but here is one little province still faithful to the Boeotian government; and as it is nearly the last, no wonder it is so vigorously defended. As in tlne political world, however, men do not trust in the endurance of a dynasty which is reduced to a single city or nook of its dominions, so we may expect a speedy extinction to a doctrine which has been driven from every portion of nature but one or two limited fields.
Huxley, it is true, seems in his pre-Darwinian period to have disapproved of this type of argument; creation being "perfectly conceivable . . . the so-called a priori arguments against the possibility of creative acts " appeared to him " to be devoid of reasonable foundation." This, of course, was a perverse misapprehension of the issue. It was not a question of conceivability, but of the relative probability of the only two available hypotheses. And the first criterion of probability in such a case must be the agreement of any proposed hypothesis with the general type of hypothetical explanations which the whole previous experience of men of science has found to be capable of fruitful application, and of the sort of verification which comes through fruitful application. By such a criterion, no hesitation between the two hypotheses was admissible. " Special acts of creative volition '' had never been found by science to be a very causa at all; the hypothesis was vague, sterile, impossible of verification, contrary to all the principles of method by the use of which the past successes of science had been achieved ; "gradual development through natural descent" was, as a
(510) working theory, definite, suggestive of precisely formulable problems to which inductive tests could be applied, harmonious with the initial assumptions through which several other disciplines had already been converted from mere masses of information into sciences. Huxley later saw this clearly enough, and expressed it forcibly, though he never seems to have confessed the unreasonableness of his earlier position. The publication of Lyell's "Principles of Geology" in 1830, wrote Huxley [16] in 1887, "constituted an epoch in the modern history of the doctrine of evolution, by raising in the mind of every intelligent reader this question: If natural causation is competent to account for the not-living part of our globe, why should it not also account for the living part ?" If every intelligent reader had this question in his mind after 1830, it is a little singular that Huxley himself, and almost every other naturalist of the period, saw no importance whatever in the reasonings of Chambers, Spencer, Baden Powell, and a few others, who were the only writers of the time to press the question home.
2. The Argument from Uniformitarianism inGeology.—Huxley, indeed, from the time of his conversion to Darwin's views, always set great store by the argument from the presumptions of scientific method; but usually in a more specialized and less philosophical form of it. Geology was, in England, the dominant and the most brilliantly successful science of the first half of the century; and Lyell had made it a working principle of geological reasoning that past phenomena, not directly open to experiment, were, so far as possible, always to be referred to the operation of " causes " similar to those now at work. Whether the uniformitarian doctrine was not, as some contemporary geologists hold, a good deal overstrained by Lyell, it does not lie within the purpose of this paper to ask; at all events, the doctrine was accepted by Huxley and most of the men of science of that time. And in uniformitarianism evolutionism seemed to Huxley—after 1858—to be directly implied. We find him writing Lyell in June, 1859:
I by no means believe that the transmutation hypothesis is proven, or anything dike it. But I view it as a powerful instrument of research. Follow it out, and it will dead us somewhere; while the other notion is, like all the other modifications of " final causation," a barren virgin. . . . I would very strongly urge upon you that it is the logical development of uniformitarianism.
In the self-same paper in which we saw Huxley justifying his refusal for some twelve years to adopt the doctrine of transformation, even as a working hypothesis, there is also to be found the following passage
I have recently read afresh the first edition of the " Principles of Geology "; and when I consider that for nearly thirty years this remarkable book had been in everybody's hands, and that it brings home to every reader of ordinary intelligence a great principle and—a great fact—he principle that the past must be
(511) explained by the present unless good cause can be shown to the contrary; and the fact that, so far as our knowledge of the past history of life on our globe goes, no such cause can be shown—I can not but believe that Lyell was, for others, as for myself, the chief agent in smoothing the road for Darwin. For consistent uniformitarianism postulates evolution as much in the organic as the inorganic world. The origin of a new species by other than ordinary agencies would be a vastly greater "catastrophe" than any of those which Lyell successfully eliminated from sober geological speculation.[17]
But however much Lyell may have "smoothed the road," Huxley, and most of the biologists of those thirty years, declined to go in thereat. It remained for an anonymous amateur, whom they there. upon with one accord fell to abusing, to point out the practicability of that highway. In the " Vestiges " and the "Explanations" Chambers urged the presumption from geological uniformitarianism with an effective use of concrete examples.[18]
If there is anything more than another impressed on our minds by the course of geological history, it is that the same laws and conditions of nature now apparent to us have existed throughout the whole time. Admitting that we do not now see any such fact as the production of new species, we at least know that, while such facts were occurring upon earth, there were associated phenomena of a perfectly ordinary character. For example, when the earth received its first fishes, sandstone and limestone were forming in the manner exemplified a few years ago in the ingenious experiments of Sir James Hall. ... It was about the time of the first mammals that the forest of the Dirt Bed was sinking in natural ruin amidst the sea. sludges, as the forests of the Plantagenets have been doing for several centuries upon the coast of England. In short, all the common operations of the physical world were going on in their usual simplicity, obeying the laws which we now see governing them; while the supposed extraordinary causes were in requisition for the development of the animal and vegetable kingdoms. There surely hence arises a strong presumption against any such causes.
It is a curious circumstance, however, that the argument from uniformitarianism cut both ways. As Wallace says:
One of the greatest, or perhaps we may say the greatest, of all the difficulties in the way of accepting the theory of natural selection as a complete explanation of the origin of species, has been the remarkable difference between varieties and species with respect to fertility when crossed.[19]
This difference, as Darwin said in the " Origin," seemed, on the face of it, "to make a broad and clear distinction between varieties and species." And the apparent existence of such a radical distinction between the varieties produced under domestication and true physiological species was an objection, not only against natural selection, but also against evolution itself; for it meant that we do not see now, nor within the limits of human observation, organisms actually getting
( 512) transformed, through the accumulation of variations, into new species . differing from their progenitors by the final test of specificity of character. In the 1850's such a radical distinction seemed to hold; even by the sixth edition of the " Origin," dated 1872, Darwin was able to point to only four somewhat debatable instances, in plants, of the infertility of varieties when intercrossed. If this difficulty appeared to Huxley and other zoologists an insuperable objection to evolutionism before 1858, it was not, in Huxley's opinion, removed after that date. Yet he no longer found the difficulty insuperable; it was purely a negative argument, e silentio, and he had faith to believe that by further investigation it would be removed. In his Edinburgh lectures of 1862, "he warned his audience of the one missing link in the chain of evidence—the fact that selective breeding has not yet produced species sterile to one another. But it is to be accepted as a working hypothesis, like other scientific generalizations, `subject to the production of proof that physiological species may be produced by selective breeding.' " In the same year Huxley wrote Darwin:
I have told my students that I entertain no doubt whatever that twenty years' experiments on pigeons, conducted by a skilled physiologist, instead of by a mere breeder, would give us physiological species sterile inter se from a common stock, . . . and I have told them that when these experiments have been performed I shall consider your views to have a complete physical basis.[20]
It is certainly interesting thus to observe that, as Huxley, before his conversion, saw no potency in arguments which afterwards seemed to him conclusive, so also he was able, in his second phase, to pass over by an act of faith one of the most serious of the pre-Darwinian objections to evolutionism. This provisional disregard of the " missing link" in an argument otherwise impressively well concatenated was, under the circumstances, far from unreasonable. But it would have been equally reasonable in 1846 or in 1851.
Leaving these antecedent considerations in favor of evolutionism drawn from the general principles of scientific method, I turn to the more specific facts which—when illumined by those principles—provide the now usual and familiar arguments for the theory. All the more essential of these facts were known before 1844; and attention was duly called to their bearings by the neglected prophets of evolutionism during the fifteen years preceding the publication of the " Origin of Species." In speaking of these "facts," it is well to explain what is meant, in this connection, by the expression. The theory of evolution does not rest immediately upon an induction of individual phenomena; and the evidence for it did not increase by a slow arithmetical progression, through the accumulation of observations of individual phenomena. It is a generalization established inferentially, by
(513) virtue of the fact that it unifies and explains a number of lesser generalizations, themselves for the most part established by direct induction,_ in several special sciences. When, in these separate sciences, the subsidiary generalizations underlying the theory of the transformation of species were well established, and generally accepted by specialists, the evidence for evolution must be said to have been logically complete. This does not mean that more facts were not subsequently added; it does mean that the argument was adequate without them, and that no one who found the original evidence unconvincing had any logical ground for being convinced by any of the considerations adduced in the " Origin of Species " or in Huxley's earlier evolutionary writings.
3. Argument from the Homologies in Vertebrates.—This argument was, by 1844, already so old and even hackneyed a one, that it may, in a consideration of the status of the evolutionary argument at that special period, be passed over very briefly. The facts upon which the argument rests had been in the possession of zoologists ever since Button and Daubenton had laid the foundations of the science of comparative anatomy (1749). These facts chiefly had, before the end of the eighteenth century, made evolutionists of Diderot,[21] of Kant, and (but for perfunctory reservations in favor of religious orthodoxy) of Buffon himself. It can, therefore, scarcely be necessary to cite evidence to show that the argument was familiar a quarter of a century after the whole conception of homologous organs had been clearly elaborated by E. Geoffroy St. Hilaire.[22] Nor, for the purposes of the present paper, is it necessary to estimate the precise logical weight of this argument when it stands alone. At the time with which this inquiry is concerned, it did not stand alone, but had been complemented by a number of considerations more recently brought to light by scientific discovery.
4. Argument from the Variability of Existing Species.—Not less old than the last-mentioned was the argument from the fact that existing—and, especially, domesticated—species have a marked tendency to variation, exhibit an extensive diversity of form, and are capable of transmitting variations to their descendants. It was mainly this group of facts that had caused Maupertuis[23] to embrace the evolutionary hypothesis before 1751. The same argument, with that from the homologies, is set down by Erasmus Darwin in the "Zoonomia," 1794, as among the principal reasons for believing in the transformation of species. We are led to such a belief, wrote the grandfather of the author of the " Origin,"
When we think of the great changes introduced into various animals by artificial or accidental cultivation, as iii horses, ... or in dogs, ... or in the
(514) changes of form in cattle, Add to these the differences we daily see produced in smaller animals by our domestication of them, as rabbits or pidgeons, or from the differences of climate or even of seasons.... Add to these the various changes produced in the forms of mankind by their early nodes of exertion, or the diseases occasioned by their habits of life, both of which become hereditary, and that through many generations.[24]
The
argument had often been repeated in the nineteenth century; and in the period
under consideration we find. Spencer observing that
The supporters of the Development Hypothesis . . . can show that the degrees of
difference so produced [through structural changes under altered conditions] are
often, as in dogs, greater than those on which distinctions of species are in
other cases founded. They can show that it is a matter of dispute whether some
of these modified forms are
varieties or separate. species.[25]
This argument, it is true, if taken by itself, suffered from two serious limitations. One has already been adverted to, in another connection : the absence of evidence that variation can produce varieties sterile inter se, as species are sterile. But we have already seen that this difficulty, upon the testimony of Huxley himself, was not removed in 1.859. The other limitation of the argument was that, before the promulgation of the hypothesis of natural selection, it was commonly associated with a belief in the inheritance of acquired characters. But this association was not logically necessary; and in any case, the wholesale denial of such inheritance is a doctrine of neo-Darwinism unknown to the pre-Darwinian period and to Darwin himself; and was in that period, therefore, not a ground of difficulty.
In a subsequent instalment of this inquiry it will remain to consider, somewhat more minutely, four more of the principal general arguments for evolutionism, three of these being, in 1844, of a much less venerable age than the two last mentioned.
