Popular Science Monthly/Volume 82/January 1913/Modern Scientific Thought and its Influence on Philosophy
|MODERN SCIENTIFIC THOUGHT AND ITS INFLUENCE ON PHILOSOPHY|
TO enter upon a discussion of the influence of modern scientific thought upon philosophy is to find one's self beset by temptations to a discursiveness not possible within the given conditions of time and space. Under such pressure, one might be led easily into a consideration of relative values—efficacy of methods, seriousness of limitations, ultimate soundness of criteria, the final significance of present tendencies. As I write, however, these problems seem so turgid with potential misunderstanding as to embarrass rather than facilitate the discussion that, as a student of biology, I had planned. To avoid such embarrassments, attention will be focused on the general theme through an examination into the nature of scientific truth. This procedure not only will put into my hands an instrument whose uses are relatively familiar to me, but will serve, I believe, to illuminate some of the most significant phases of modern philosophic thought.
Poincaré has somewhere made a suggestive comparison between the Gallic and Anglo-Saxon genius. Characteristic of the one is a feeling for form, for symmetry, for logical completeness, for finality; characteristic of the other is a feeling for substance, development, function, change. For the one, truth lies in the result; for the other, in the process. One is represented by a deductive, the other by an inductive type of mind.
I have no desire to raise here a national issue. Whatever the merit of this characterization of these ethnic groups, it will serve my purpose if it give vividness to the statement that the same general differences distinguish certain philosophers and scientific investigators. Wherever one finds a faith in final causes, a hope in the revelation of ultimate truth, there one finds a philosopher who, like the Frenchman of Poincaré, has drawn the essential elements of his inspiration from the philosophy characteristic of ancient Greece. Modern science may have supplied his convenience with the telephone and the electric light, the automobile and the thoroughbred, aniline dyes and serum therapy; but it has done little more. Until he views the truth as nothing final, as existing in the process rather than in the result, as a growing, expanding, changing vision, blooming with youth as long as human life can use it, it can hardly be said that his eyes have felt the touch of the spirit of modern science.
Wherever modern science has affected characteristic changes in the trend of philosophic thought, the result has been achieved by lessening the influence of that ancient legacy which may be conveniently referred to as the doctrine of final causes.
It must not be inferred, however, that the influence of this doctrine has been confined to philosophy alone. It has been felt in every field of human inquiry that presents a speculative aspect, an opportunity to reach by means of the imagination into the unknown. The history of science is one long record of struggle between just those types of mind that Poincaré has sketched. In none of the sciences, however, has the conflict been more prolonged and bitter than in biology. There the fight has been waged about the four great problems of evolution, individual development, vitalism and adaptation. None more than these offer speculative opportunity—abundantly accepted. None more convincingly than these show the inexorable incompatibility of faith in final causes and scientific progress.
I present them, therefore, as my chief aids in developing, if I may, a fruitful conception of the nature of scientific truth. Having reached such a conception, we will proceed to discuss its relation to the philosophic thought of the day.
Faith in final causes is not a necessary product of a particular civilization, of civilization at all. Though it may persist in the midst of sophistication, it is born of inexperience. Under one form or another, it has existed among peoples of all sorts, wherever they have possessed sufficient intelligence to hazard an interpretation of their universe of experience. Of these peoples, the Greeks and Hebrews claim our especial attention, since it is from them that the main streams of our philosophy and science and religion flow.
Compared with the sophistication of Aristotle's theories of life, the cosmology of the Mosaic record is strikingly anthropomorphic and naive. In spite of this naivete, however, there is no question of its astounding control over the history of scientific thought; the more so, since it is to the second and far cruder story of the creation, in fact, in the second chapter of Genesis that the church chiefly pinned its faith in its long struggle with the doctrine of evolution. The struggle has been at times debased with bitterness and violence. One grows heartsick at the sad spectacle of a Galileo swearing away his scientific probity as he groveled in fear of torture before the Inquisition.
But it has not been through such violence alone that the influence of the Hebrew tradition has been felt. More subtly did it discourage the great anatomist, Vesalius, who, in the flower of his young manhood, filled with the spirit of the pioneer, linked his fortunes to the throne of Charles and Philip. It is significant that, while he idly fretted out his life on Spanish soil, Suarez, the Spanish Jesuit, was born, destined to create the doctrine of special creation in its modern form by reaffirming in detail the Mosaic account of the creation—even the episode of the rib. The fact carries a suggestion of the reason why the productive years of that great progressive in biological science were limited to five, and ended with his thirtieth anniversary.
It was against this anachronistic doctrine of special creation, crystallized out of the civilization of the seventeenth century, that Darwin launched his great argument in the shape of the "Origin of Species." But, in doing so, he found in his opponents Hebrew tradition mixed with Greek. Evolution was not a conception hostile to the mind of Aristotle, though what we now recognize as phenomena of evolution did not especially engage his attention. The two rather ambiguous passages in which he arranges living creation in a series of closely intergrading types might be interpreted in terms of evolution without doing essential violence to his general conception of life. The origin of species of organic beings was not with him an issue. He was unaffected by the Mosaic record. Historical problems were to him of less moment than essential relations of structure and function. His especial interest in the ultimate analysis of truth was not, however, incompatible with an admission of the transformation of organic types. Indeed, under the influence of Aristotelian philosophy, St. Augustine himself sought to interpret the Mosaic cosmology with its conception of an external Creator, in naturalistic terms that should harmonize with the Greek conception of forces and potentialities inherent in the universe itself. It is this mixed derivation that complicates to some extent attempts to trace to their origins the ideas of the modern world.
There was no fundamental incompatibility then, between Greek tradition and the doctrine of descent with modification. As an evolutionist, Aristotle was at least as modern as Charles Bonnet. Were he alive to-day, I should confidently look for him in the foremost ranks of biological thinkers. His biological contributions, however, have been largely obscured by his versatility of interest in final causes. This interest I am disposed to believe was a product of his time, of the age into which he was born, of his education, his companionships, rather than a fundamental tendency of his mind. However it may be interpreted, there is no doubt that his ideas on transformism in organic nature were definitely limited thereby. If he was an evolutionist, he was also a teleologist. Adaptation in nature spelled for him design. Organic types might change, but in accordance with a perfecting principle that should lead finally to the crowning glory of the evolutionary series, the human species. Perfecting principles are not unknown—witness Lamarck and Nägeli—in the speculative biology of the last century. In the hands of no one, however, have they proved to be instruments by means of which discoveries are made. Their influence has been conspicuously negative.
It was essentially Aristotle's teleology that Darwin, as late as 1859, overmastered with the doctrine of natural selection. It was Aristotle's evolutionary series, ending with man, that, fashioned into the semblance of a pine tree by Lamarck, was finally displaced by Darwin's conception of a genealogical tree without a central axial trunk flowering at the tip in man, but branching polychotomously in all directions from a common center. This modern conception harmonizes with the fact that there is no evidence that man has been fashioned, whether by special act of an external creator as in the old Hebrew account, or by the less direct process of evolution under the guidance of a final principle inherent in nature, as in the Aristotelian tradition, to be the lord and highest product of organic creation.
The Hebrew tradition embodies too naïve a conception of final causes for the philosophic as for the scientific minds of to-day, although it still lingers in various forms of religious doctrines that typically compose themselves, as President Jordan has somewhere aptly remarked, out of the debris of our grandfathers' science. Aristotelian evolution still lingers, though negative and barren on the fertile soil of modern experience, in the minds of those who admit with Aristotle the evolution of the physical man, but view, with him, the mind as a thing apart. It is characteristic of a faith in final causes that it permits distinctions of this sort. To the average biologist, however, to admit the validity of the distinction would be to question the validity of organic evolution itself. For the evolution of the body is neither more nor less certain than the evolution of consciousness. Both, for the student of objective science, rest upon evidence of the same order.
It was to be expected that Aristotle, a pioneer in science, would overestimate the simplicity of his problem of creating order where order had not reigned before, that he would seek for final causes with a suggestion of the simple confidence of the woodsman who traces smoke to fire or hunts his quarry to its lair. He was, scientifically, of necessity unsophisticated.
It is on other grounds that we must seek an interpretation of the persistence of this phase of his influence in contemporary thought; a phase which I suspect he would now agree was the portion of his legacy least worthy of our regard. There is something foreign to the spirit of Aristotle, something savoring of a sophistication born of conflict he could not have known, in the following passionate challenge of a modern defender of the faith in final causes:
"Let not science contrive its own destruction by venturing to lay profane hands, vain for explanation, on that sacred human nature which is its very spring and authorizing source." Modern developments in philosophy itself indicate that the challenger need have no fear. Whatever the inevitable expansion of human knowledge may accomplish for human nature will not be by means of violent or profane hands. Conceptions of human nature, like all other conceptions of the human mind, adapt themselves quietly, impersonally, without anguish, to successive discoveries of truth.
Passing now to the problem of development, one is struck by the modern aspect of Aristotle's contribution.
Have you ever seen an egg grow? Have you perhaps followed the frog's egg, as it splits up into a group of segments; seen a cleavage furrow spread across it, new furrows succeeding each other with every half hour; observed the segments rhythmically swell and flatten with each cleavage; felt the mystery of this marvelous plastic process of development? Here is life; here is activity. And the juxtaposition of these phrases is not accidental.
Aristotle knew nothing of the cleavage of the frog's egg. He had no knowledge of the segments thus formed—which are now called cells. He did not know that the egg, is a cell also, comparable with the cells that make up, as fundamental structural units, the various organs and tissues of the body; that the egg like these other cells, possesses a characteristic body called the nucleus, which, as in all nuclei, contains a substance (chromatin) now generally understood to be most intimately concerned with the phenomena of differentiation and heredity. He was ignorant, also, of the nature of the male sex element, vastly smaller than the egg and differing from it remarkably in form, being adapted to a life of great activity. Otherwise, he would have known that the sperm, like the egg, is, in spite of its size and form, a cell, furnished with a nucleus and chromatic substance. And had he lived as late as 1875, he might have known that the essential facts of fertilization consist not only in the stimulation, the activation of the egg by the single sperm which penetrates its substance, but in the fusion of the egg and sperm nuclei and the mixture of the chromatin thus derived from the two sexes.
Nothing of this Aristotle knew. But he had observed the development of the chick. Without the microscope he had failed to note the early stages one sees so readily in the frog. But he had seen the embryo gradually appear on the upper side of the inert yolk, and he had seen the heart begin to beat on the third day of incubation. It all impressed him to an extent that led to a treatise on generation.
To account for what he saw, he conceived the egg—the female contribution—to be essentially passive, containing elements that could be wakened into life by the active principle of the male. This he conceived to be a sort of enzyme, a ferment, which acted upon the female germinal substance like rennet upon milk. From this simple beginning he believed the development to progress, organ following organ; and since the spermatic fluid, the active principle, was itself unorganized, he rejected the possibility that parts should preexist.
Crude as all this is, it was an approximation to the truth, based on the facts as Aristotle had observed them. To this extent, his theory of development has a modern look. On a second glance, however, one discovers signs of the same eagerness for final explanations that we have already observed in our discussion of the problem of evolution. How, from so simple a beginning, was the remarkable complexity of the adult structure to be differentiated? And how was the fact to be explained that chick eggs, when they develop, always produce chicks, turtle eggs turtles; that animals reproduce after their kind? These were problems that at once engaged his attention, and were answered with characteristic promptness and confidence. Though the germ may be substantially simple, it is subject to two transcendental potentialities that constrain its development with reference to species and form.
And here Aristotle lapses out of the company of objective scientists. To say that an egg reaches a certain form because it possesses the potentiality to reach that form, is like defining a word in terms of itself. It is hardly the type of interpretation to commend itself to modern investigators. Yet it has been the refuge of many minds throughout the ages, and in a more refined and subtle form is used to-day by the distinguished author of "The Science and Philosophy of the Organism," to mask the hopelessness in his retreat from the firing line of experimental biology.
It is the ugly function of final explanations, causes, elements, principles, in biology, to call a halt. Trust them and, like the genii of old, they whisk one swiftly out of the current of scientific thought. One ceases to ask questions that are amenable to objective tests. And science itself stagnates until such questions germinate again in the minds of men.
From Aristotle to Caspar Friedrich Wolff extend two thousand years barren of inspiration. Harvey, the famous author of the "Exercitation on the Motion of the Heart and Blood in Animals"; Malpighi, his great Italian contemporary; and the indefatigable Dutchman, Swammerdam, had each made serviceable observations on the development of mammals, birds and insects, but had contributed no new ideas. By the middle of the eighteenth century, there had still been no advance upon Aristotle, but there had developed a sharp contrast between two theories of development. On the one hand, Wolff supported the Aristotelian theory—now dubbed, since Harvey, epigenesis. On the other, Charles Bonnet, Albrecht von Haller and others elaborated its direct opposite in their theory of preformation.
Again, in Wolff's restatement of it, epigenesis takes on a modern aspect. The parts follow each other in development, and each part is primarily an effect of another preceding part and thereupon becomes the cause of another part that succeeds it. This is essentially the modern doctrine that one stage of development is conditioned by the stage preceding it as it conditions the stage that follows. It is crowded with suggestions; that bear no fruit, however, for lack of knowledge, in Wolff's imagination. Just as Aristotle endowed the simple germ with controlling potentialities that had no objective existence, Wolff achieved the same differentiation of the homogeneous germ by means of a vis essentialis, that sent him sailing also through the airy altitudes of final causation.
Contrary to the belief of Wolff, Bonnet and Haller found it impossible, on philosophical grounds, to conceive the beginning of the parts of an individual. For them, the germ contained the whole preformed in every part. While Bonnet insisted that man's body was not made like a watch, of added parts, but existed from the beginning as a whole, Haller was emphasizing the absurdity of believing that such a complicated apparatus as the eye could be formed as the epigenesis of the day demanded, out of crude materials by mechanical forces. Malebranche brought forward the clever device of infinite divisibility to overcome the patent objection that ordinarily the parts, whether present or not in the germ, could not at first be seen. And Bonnet admitted the obvious qualification that the parts need not exist in just the same form in the germ as they possessed in the adult. For him they belonged in the germ to a sort of invisible meshwork.
To this theory of development which sought to substitute for Aristotelian entelechies and Wolffian essential forces the conception that differentiation merely consisted in the expansion, with a push here and a pull there, of a structurally preexisting whole, numerous objections arose both in logic and in objective fact. If an individual were preformed in the germ, all the offspring of that individual must be preformed in it also. Which meant that, encased in the body of Mother Eve, one within the other, were all the germs of all the individuals of possible future generations—a sufficiently grotesque result. Wolff himself contributed one of the most telling facts against it when he described the formation of the tubular gut of the chick by the folding up of a flat layer of tissue on the yolk. Obviously in this case the gut did not exist as such in the germ.
It is unnecessary to multiply objections to this interesting bit of metaphysic. Both the epigenetic and the preformationist theories of the eighteenth century are dead and buried under the relentless logic of events. Essential forces and preformed miniatures, alike in their finality, were unable long to withhold the attention of naturalists from the more potent suggestions of a rapidly growing body of new observations.
With the discoveries that organisms are built up of morphologically equivalent protoplasmic units, or cells; that both egg and sperm are cells, also; that the nucleus, especially the chromatic substance, is the part of the cell chiefly if not wholly concerned with the inheritance of the individual and specific characters and their distribution in the developing organism; more than all, with the discovery of the essential nature of fertilization, new theories were devised to interpret the still puzzling problem of individual and specific differentiation. These, like their prototypes of the previous century, fall into two contrasting classes.
Both of these classes of theories recognize that individual differentiation can not be interpreted without regard to race development. The germ from which the individual springs has history behind it, is composed, indeed, of two fragments of two preexisting individuals, the parents, who, in turn, sprang similarly from a previous generation. It is at once apparent that all modern theories of development must reckon with these facts; which means that, however simple we may conceive a given germ to be, the probabilities are overwhelmingly opposed to the conception that it is homogeneous; and they are equally in favor of the conception that it possesses from the start, in view of its relation to a preexisting parent, some degree of differentiation.
In perfect accord with these requirements, modern epigenesis and modern preformation nevertheless exhibit characteristic differences. On the one hand, is the preformationist theory of determinants devised especially to explain the persistence, through many generations, of very trifling characters, such, for instance, as a small pit on a human ear, recognized as a family trait, or a spot on one surface of a butterfly's wing, or a lock of white hair on a particular area of an otherwise dark-haired head. Such characters appear to come and go without effecting in any way the other characters of the organism. This independent variability is interpreted on the assumption of fundamental living units in the chromatin of the germ nucleus that represent and determine all the various characters of every individual. The germ chromatin is accordingly conceived to contain the determinants of all the heritable characters; and these are further conceived to be so associated, that in the course of development the determinants are parceled and reparceled by the repeated divisions of the nuclear chromatin, an element in the cleavage process that, we have seen, is so striking a phenomenon in development. Differentiation thus depends not upon the literal expansion of a preexisting whole, but upon the distribution of the preformed determinants in the germ that have been inherited from preexisting individuals. And this distribution takes place, by nuclear division, in such a way that the right determinant always finds itself ultimately in the right place, that is, in the same relative position that that sort of determinant occupied in the parent.
The germ, then, is not only the abiding place of an enormous and complex assemblage of determinants, but these determinants are living morphological units. Not only that. They struggle for existence, according to the conception, just as organisms do. The basis of this struggle lies in inequalities in the food distribution in the germ, whereby some determinants will obtain less nourishment and weaken correspondingly, while others will obtain more nourishment and correspondingly strengthen. As the determinants in the germ, so the organs, the characters which they determine, vary.
By means of this ingenious application of the theory of natural selection to the vital units of which living substance is composed, the determinant hypothesis obtains a theory of variation which at once distinguishes it from the preformation theory of Bonnet. It goes still farther. Even the biophors vary—those ultimate vital units of which the determinants are the first aggregates.
With this liberal provision for variation, the determinant hypothesis would appear to have approached very close to modern conceptions of epigenesis. Certain fundamental differences, however, still persist. Whatever the provision for variation in the germ, differentiation proceeds, according to the determinant hypothesis, by the segregation of determinants already present in the germ; and these determinants are vital morphological units. According to the most advanced epigenetic theory, differentiation proceeds from a relatively simple germinal organization, not by the segregation of hypothetical vital units, but by means of progressive changes of a physico-chemical nature.
Just here appears the characteristic of the determinant hypothesis most significant for us. While the great inventor of the determinants finds it fundamentally necessary to assume a structure for living substance that is based upon ultimate vital units that have individuality, grow and reproduce, various investigators are discovering no such necessity in the facts. What is necessary is a hypothesis that will work. One of the strongest objections to the determinant hypothesis is, that, paradoxically enough, the chief researches it has stimulated are those which have been guided by the assumption that it would not work. One need not fail to appreciate its logical completeness, its symmetry, and the skill with which it has been defended, and yet one need not be blind to the fact that it has not been a stimulating guide for its friends. It has been conservative rather than progressive. Founded on a definite morphological conception of the ultimate constitution of living substance, it has not adapted itself plastically to the rapidly changing conditions in biological science. The considerable amendment it has received in the last eighteen years has only made it so cumbersome and complex that it is now little more than a mere formulation of the facts it attempts to explain.
Time will not permit us to explore thoroughly the mass of evidence on which this criticism has been based. While differentiation according to the determinant hypothesis assumes qualitative divisions of the chromatin in the nucleus, numerous investigations have shown that at least five divisions of the egg in some animals may occur before there is any recognizable difference between the cells thus formed. Each of the first sixteen is competent to develop the entire adult structure. The only way to account for such a result in terms of morphological determinants is to assume that a complete outfit passes to each cell with each division of the nucleus, obviously a serious burden for the determinant hypothesis to bear. Further, among these phenomena of development which are conveniently investigated under the head of regeneration, similar difficulties have so constantly recurred, requiring similar assumptions of reserve determinants, that the theory has long since ceased to interest investigators in this field. It follows, rather than leads, investigation. Finally, in the field of heredity, just that characteristic of Mendelian inheritance—namely, the segregation of parental characters in second generation hybrids—which at first seemed to give the strongest support to the conception of a germ plasm composed of morphological determinants, has now been resolved far more satisfactorily, because more simply and workably, in terms of chemical substances.
These cases lay emphasis upon the distinction between morphological and physiological conceptions that defines the essential difference between modern preformation and modern epigenesis. Instead of a congeries of morphological determinants, the epigenesist finds in the germ a problem in physical and chemical relations. He is interested in the dynamic aspects of development, in the energy transformations. He does not seek to construct a scheme of the ultimate organization of living substance, but he does seek to control its operations, to predict its behavior.
In this new form, the problem of differentiation presents many interesting aspects and is being encouragingly developed. By way of illustration, recent investigations indicate that color differentiation is based essentially on a well-known chemical process, the oxidation, namely, of a chromo-gen or color base in the presence of an oxidizing enzyme or oxidase. Tyrosin, for instance, a colorless chemical compound and a product of the decomposition of tissue proteids, can be oxidized, in the presence of the enzyme tyrosinase, through a series of colors: pink, red, deep brown to black, the color depending, other things equal, on the concentration of the enzyme and the duration of its activity. Tyrosinase has been isolated from many organisms, and has been definitely connected with pigment formation in many cases. We are dealing here with known substances, not hypothetical vital units; with chemical processes that can be followed in the laboratory test tube. That an organism may develop a color characteristic of its parents, in the light of these facts which are representative of a considerable number, it is only necessary that in the course of its development tyrosinase be formed under conditions that make a reaction with the tyrosin in the tissues possible. Local production of tyrosinase would lead to local coloration, to spotting or characteristic marking. The amount of tyrosinase—that is, its concentration—in connection with local conditions that might favor or inhibit the reaction in varying degrees, would determine the characteristic shade of color.
It is impossible in the brief time at my disposal to consider the various complications of this type of problem. The difficulties are very great in the way of investigations which as yet have hardly begun. Enough may have been said, however, to indicate the direction of some of the most recent and most promising work. If color characters are dependent upon chemical reactions, other characters probably are also. In fact, recent work upon the old problem of the heritability of acquired characters has brought to light interesting chemical possibilities in inheritance, and lifted the incubus of presumption laid by Weismann upon the whole subject in the shape of the determinant hypothesis almost twenty years ago.
Modern epigenesis recognizes an organized germ, more or less differentiated, but vastly simple in comparison with the preformed germ. That color may be produced at a given stage in the development of an organism, it is not necessary that the tyrosinase, upon which the formation of the color may depend, should be present as such in the fertilized ovum. It is only necessary that the conditions for its ultimate production be present—relatively simple conditions, that bring about a series of reactions of the type known in physiological chemistry as autocatalyses, in which one phase in the reaction determines the succeeding phase. Not only is this sort of conception more simple than the determinant hypothesis, but it is stimulating. It is workable. It leads to results that are sympathetic with the most advanced scientific work of the day. It is not a final explanation. It is an implement of research.
The problem of vitalism need be very briefly examined. Vitalism, if it means anything in biology, interprets life in terms of forces or agencies or processes that are not found in inorganic nature. According to this definition, Aristotle was a vitalist when he conceived the development of the germ to be guided by the entelechies that determined specific and individual form in organisms. Wolff was a vitalist when he accounted for the differentiation of a homogeneous germ by the aid of a vis essentialis. Vital forces have long since lost their grip. They began to weaken when Wöhler, in 1828, produced in the laboratory the compound urea, till then supposed to be formed only in the bodies of organisms. They broke into full retreat under the fire of calorimetric researches of the last century which demonstrated that oxidation was oxidation, whether it took place within or without the body, and that vital heat was as surely due to chemical reaction as the heat generated by the reaction between sulphuric acid and zinc.
So Wolff's vitalism is dead. The Aristotelian vitalism, however, has a representative at the present day in the neo-vitalism of Driesch. The Aristotelian entelechy has been revamped and applied to the unexplained residuum that has escaped Driesch's experimental analysis. It is interesting that Driesch was a metaphysician first, an experimental biologist second; and that after about fifteen years of unusual activity in this second rôle, he returned to his first love. In these fifteen years he developed what he has called three proofs of vitalism. But he has not succeeded in persuading many biologists to accept his criteria of demonstration. It is difficult to take seriously his conception of entelechy, a non-substantial, non-energetic principle which yet is competent to control the developmental energies of the organism. It is but another final cause, an ultimate term in the analysis of the activities of organisms. And it has weakened Driesch's interest in biological research just as the formulation of final explanations has led to stagnation wherever we have met them along the line of biological inquiry.
In contrast with Driesch, there is a large and eager group of experimental biologists who unite in deprecating his interest in entelechies and, undaunted by its enormous complexity, in investigating the organic mechanism in the hope of reducing more of it than he was able, to terms of physics and chemistry. How far they may go is not, from the standpoint of modern biology, a pertinent question. How they may keep moving is more to the point. To this end the Drieschian entelechy offers not the slightest suggestion of encouragement.
Three of the four problems to which attention was invited at the beginning of this paper have now been considered. If I have succeeded in presenting intelligibly the actual development of modern ideas, it has been shown that science has progressed, with respect to these problems, by abandoning a faith in final causes for a faith in the hypothesis that works, by draining off every stagnant suspicion of ultimateness in explanation, in the light of the conviction—the product of experience—that the ideas that serve us change with our knowledge of objective fact. I shall now attempt to show that this statement applies with equal force to the development of modern conceptions of adaptation in nature.
The problem of adaptation possesses a peculiar fascination for the imaginations of men. It inheres in every mechanism that meets a human end. Watches, beehives, steamships, reciprocating engines, footballs, blackboards, fountain pens and yellow paper—all are obviously fashioned toward ends. Why not that all-inclusive mechanism, the universe itself, and all that in it is?
When Darwin came upon the field in 1859, the widespread opposition which evolution theories had already experienced lay intrenched behind an affirmative answer to this question. These were the works, first of all, that Darwin stormed with his "Origin of Species." The struggle did not center about the problem of species, though one may well gather a contrary impression from the familiar abbreviation of the title of that epoch-making book. It is in the sub-title—"the preservation of favored races in the struggle for life"—that one discovers his real objective—a mechanical theory of adaptation in organic nature. It was just because the supporters of organic evolution had lacked such a theory that they had failed to impress, not only the thinking public; but most of their biological brethren. Darwin was not reviled as an atheist because he believed in evolution; nor for that reason did he revolutionize the whole course of modern thought, it was because his; doctrine of natural selection menaced the traditional Hebraic conception of the creation that he was anathematized by the standpatters of his generation. It was because he raised such a powerful presumption against all doctrines of design in organic nature that he was able effectively to substitute for doctrines of fixity and finality the fruitful conception of change, lie did destroy the doctrine of fixity of species. He did establish the doctrine of evolution in its place. But he did so by eliminating teleological theories from the list of useful hypotheses in science.
The solution of the problem of adaptation is being sought with diminishing faith in teleological formularies. These are going the way of the other final explanations that have failed to fulfill in modern science the one prime requisite—active leadership. Since Darwin's time the attention of biologists has been shifting from those secondary adaptations which provide the material for natural selection, to the direct or primary adaptive responses of the organism to given conditions. The phenomena of immunity, especially to bacterial poisons that are so conspicuous in modern medicine, are adaptations of this type. It is still too early to state with any certainty the exact nature of the processes involved in such cases. That they are physico-chemical processes of great complexity seems to be clear. In this respect they ally themselves with the well-known equilibrium reactions in chemistry, and the form changes that certain crystals undergo in response to changes in temperature. Here, in the inorganic world, are relatively simple analogues, at least, of the physiological processes that are associated with adaptation in organisms. It is significant of the present attitude toward problems of adaptation, that suggestions for their solution are being thus eagerly sought among the facts of physics and chemistry.
Scientific truth, then, is not concerned with final solutions. Nothing perhaps has been more conspicuously characteristic of it, in this discussion, than its incompleteness, than its plasticity, than its capacity for indefinite expansion, than its stimulating power. To my mind, this last is its crowning glory. We dwell in a world of hypotheses, and we estimate them according as they are more or less workable. To those hypotheses that approximate most closely to the demands of wide ranges of fact, we give the name of laws. It is obvious, however, that such laws nave varying degrees of certainty. Scientific truth is never absolutely certain, but there are always ways of determining what it may do.
For one who seeks a basis of criticism for a contribution to science, three obvious tests may be applied. (1) It may contribute new facts; (2) it may contribute a formulation of old facts; (3) it may contribute a new idea that, in the presence of facts, may lead to a new point of departure for explorations into the unknown.
If one were to apply these tests to what seem to me to be the two most significant developments in the philosophic thought of to-day, they might be said to fall, very roughly speaking, under the second and third categories. In the former might be placed the synthetic philosophy of Spencer, an avowedly scientific philosophy, whose essential problem was to formulate the known facts of science in term of principles of evolution. This stupendous project, remarkable alike for the powers of its author and the wide range of his interests, ended in a system of philosophy, into which just enough metaphysics succeeded in creeping to justify the criticism that, in spite of all good intentions, he had not been able completely to disentangle himself from the habits of thought to which his critics were happily accustomed.
In the third category may be placed that interesting application of the scientific method to problems of conduct which is known as pragmatism.
Pragmatism distinguishes itself at once from the synthetic philosophy in that it is non-systematic. Instead of an interest in a formulated body of knowledge it appears to possess an insatiable desire to determine practical choices. Given a problem of conduct, the solution unknown; what shall be the line of action? Here one perceives a strictly scientific situation that emphasizes the practical value of the hypothesis. The problem is to find a satisfactory path into a new region. And the answer that pragmatism gives is, trust to luck and your past experience. The truth, says James, is the hypothesis that will work. The truth, says Dewey, if I rightly apprehend him, is the hypothesis that you can work with. There is a suggestion of permanency, of stability, of future significance in the latter phrase that makes it, to my mind, more felicitous. But I do not care to dwell upon that point. What comes closer to my purpose is to point out that here is no faith in final causes, here is no suspicion even of that innocuous phantom, the unknowable. Here is no. distinction between science and philosophy—if indeed pragmatists are philosophers, in spite of the fact that, in one form or other, they fill several of the chairs of philosophy now in our universities. Here is a faith that facts will tell their tale—will inevitably condition the movement of ideas, that one's imagination content is derivable from one's effective experience. Here is a philosophy that is working a transformation on the thought of the day. How? By abandoning the search for lofty peaks of final causation, from which to triangulate the universe according to logical necessity; by emphasizing ideas that shall not only square with the facts as we find them, but shall create others.
Such I conceive to be the most significant effects of modern scientific thought upon philosophy. They are characteristic tendencies of the present day. How one may evaluate them, however, is a problem which, for the purposes of this discussion, I have already promised to avoid.