Popular Science Monthly/Volume 14/February 1879/Darwin vs Galiani
By Professor EMIL DU BOIS-REYMOND,
OF THE UNIVERSITY OF BERLIN.
IT was a hundred years ago, in the salon of the Grand-Val, after dinner. Here was assembled that fastidious company of wits as well known to us through the letters of Diderot to Mademoiselle Voland as though we, too, had been guests under Holbach's roof. There was Diderot himself, the most German-like of Frenchmen, and Grimm, the most Frenchy of Germans; that peevish Scot, Hoop, and the little Neapolitan abbé, Galiani, in whom playfulness and levity often concealed profound thinking. There, too, were those women whose redoubtable charms are immortalized in Rousseau's "Confessions," as those of Helen in the "Iliad" and "Odyssey."
The fortunate ones of this world had then a good time, especially in France. The trammels of superstition which for seventeen centuries had made slaves of the human race seemed to have been burst asunder. The sun of a cloudless day was illumining and warming the intellectual world; while on the other side of the Atlantic the dawn of popular freedom and human dignity was beginning to appear. Despotism in church and state was tottering before assaults which daily grew bolder; and Cazotte's prophecy had not as yet cast its ominous shadow over this gay and brilliant coterie. Moreover, what was there now that man might not do, after Montgolfier had ascended in the air, and Franklin had subdued the lightning?
The company talked first of the great American citizen; then of the great Frederick, who also was conceded to be somebody; next of Voltaire, with whom Frederick seemed to be fully reconciled. But, with all their worship of Voltaire, and with all their willingness to recognize his services in the cause of enlightenment, there was no getting over the fact that, in truth, he was an incorrigible deist.
"How childish," remarked the host, "is his conception of the universe as a watch from which we may infer the watch-maker! Inasmuch as nothing is certain save the existence of matter, why look for any other causes than the forces of matter? What is there so inconceivable in the idea that an infinity of atoms, acting upon one another from eternity, should assume a definite arrangement, and so form worlds; that when in these worlds light, heat, moisture, and certain elements were present in the right proportions, the phenomenon which we call life should first appear as a germ, and then expand into ever-widening and more varied circles; that in this way the animal mechanism, and, finally, that of man himself, should have come into being?—a well-contrived mechanism, indeed, but not without many an imperfection; endowed with strength and beauty, but also afflicted with many a sad infirmity; capable of enjoying many a pleasure, but also threatened, alas! with still crueler sufferings."
There was general assent, but then were heard coming from a corner the piping tones of Galiani's voice:
"Ladies and gentlemen, for Heaven's sake, no metaphysics to-day! Let us talk of something else. Suppose I tell you of an occurrence I once witnessed on the Marina at Naples. A juggler had set up his booth, around which stood a group of lazzaroni and other folk, myself among them. After performing sundry tricks which have escaped my memory, the fellow offered us a wager that he could every time, with his dice, throw sixes. One or two of the gapers took up the bet. He did, in fact, throw sixes the first time, the second, third, fourth—"
"But, monsignor, this is a farce; either you are joking, or else the dice were cogged."
"Of course they were," Galiani replied. He had, as was his wont, climbed into his arm-chair, on which he squatted with his legs doubled up beneath him; he had his wig poised on his left hand, for the weather was hot, and, with his right, he gesticulated wildly, after the manner of his countrymen. "Of course they were cogged, and that was just the trick. The juggler did not say that he would throw sixes every time with honest dice. Any man in his senses might have known beforehand that the dice were cogged, and the fellows who found this out only after their money was gone were laughed at heartily. But the point of the story is this: If two dice fall on the same side four times in succession, you, not being lazzaroni, hold it to be impossible that the thing should happen by accident. You conclude, with undoubting certitude, that a hidden cause, designed to produce this effect, has been incorporated in the dice, in the shape of a little lead. But, when you see all around you this universe, with its innumerable suns, planets, and moons, which, poised in vacancy, have for thousands of years been rhythmically traveling in their courses, without ever a collision; when you see on this globe dry land, sea and atmosphere, sunshine and rain, so distributed that myriads of plants and of terrestrial, aquatic, and aerial animals swarm in joyous life; when, for all these creatures, you see the alternation of day and night, of winter and summer, beneficently answering, in all respects, to the requirements of activity and rest, cessation and growth; when, in your own body, you see each particle of its ineffably complicated structure performing exactly the functions which the good of the whole organism demands, while in turn it can itself subsist only in the whole; when, in your own members, your eye, your ear, you see the profoundest science of the mechanician or the optician so far transcended that our friend D'Alembert and the great Euler yonder in St. Petersburg, e tutti quanti, appear as fools; when you see this machine—alongside of which your Le Roy's finest watch is, as it were, some coarse piece of mill-gearing, your Vaucanson's most ingenious automaton a wretched toy—perfecting itself by practice, making its own repairs; when you see it even reproduce its own kind, and male and female most charmingly, mother and child most beautifully adapted to each other; when, in the Jardin du Roi, under a thousand animal forms, from the elephant to the shrew-mouse, M. de Buffon shows you as many types of your own organization, each one adapted in its own way for the enjoyment of life and the pursuit of its prey, for defense against its foes for propagation of its kind, and for care of its young; when you see the bees solving their cell-problem as correctly as the most learned of mathematicians, the spiders bracing their polygons of silken threads, the mole excavating its galleries, the beaver constructing its dams; when, further, in all these instances you see the agreeable combined with the useful, and magnificence, ornament, and grace everywhere lavishly displayed—Flora's children clothed with beauty, the gaudy butterfly flitting about among them, the peacock spreading his tail feathers; finally, when Mr. Needham shows you, under his microscope, how each drop of vinegar or of paste is alive with creatures as numerous as the worlds you have been able to descry through M. de Cassini's telescope—you confidently say that all this is chance. And yet the spectacle presented to us by nature is the same as though some one were every instant, with an infinite number of dice, to make exactly the throw which he announces in advance. I judge differently, ladies and gentlemen. I say that nature's dice are cogged, and there, above, is the greatest of jugglers making sport of us."
What reply was, on the spot, made to the abbé we know not. But of the impression which the apologue of the cogged dice made on the encyclopædists we learn something from a passage in the "Système de la Nature," that work which, in the opinion of the young Goethe and his Strasburg associates, was "senile, cimmerian, cadaverous, the very quintessence of senility, offensive to all correct taste, nay, insipid." And yet it is not to be denied that the "Système de la Nature," in most points, very nearly represents the idea of the universe now held by scientific men.
In that work Holbach vainly squirms to escape from the snare in which he had been caught by the Neapolitan. "The molecules of matter," says he, "may be likened to cogged dice, i. e., they always produce certain effects of a determinate kind. Inasmuch as these molecules are in themselves and by their combinations essentially diverse, we may say that they are cogged in infinitely diversified ways. The brain of Homer or of Virgil was nothing but an aggregate of molecules, or if you please of cogged dice—i. e., things so constituted and so elaborated that they must of necessity produce an Iliad or an Æneid."
To say nothing of the fact that Holbach speaks of mental phenomena being produced by material conditions as of a self-evident proposition, nothing could be more awkward than the mode in which he strives to wrest the weapon from the hand of his opponent. By adopting the comparison of the molecules of matter with cogged dice, he unwittingly admits that in nature, just as in a gambler's den, there is trickery; whereas the problem before him was to explain how material particles not directed toward any definite end should nevertheless cooperate to that end.
Here is the knot, here the enormous difficulty, that racks every understanding that would comprehend the universe. Whoever will not surrender all occurrences into the hand of Epicurus's Chance, whoever admits even the veriest nevertheless presently he finds himself speaking of the use, functions, and purposes of the organs.of the doctrine of teleology, must perforce accept Paley's disparaged natural theology, and this the more inevitably the more clearly and accurately he reasons, the more independently he exercises his judgment. But so weighty and so numerous are the facts which seem to favor teleology; so irresistibly do these facts daily force themselves upon us in common life; so interwoven are final causes with time-honored imaginations of our race instilled into us during childhood, that even minds possessed of considerable powers of abstraction can not in their habitual thoughts refrain from postulating them. A man may, with Lichtenberg, ridicule the teleological explanations offered in earlier times. Be he ever so determined to regard the processes occurring in the animal body simply as effects produced by the mechanical or chemical organs, and so to represent them to others,
The possibility, however remote, of banishing out of nature this apparent adaptation to ends (teleology), and of everywhere setting up blind necessity in the place of final causes, is to be regarded as one of the greatest advances ever made in the world of thought, as a step from which will be dated a new epoch in the treatment of these problems. That he has in some measure diminished that torture of the mind which tries to understand the universe, will be Charles Darwin's highest title to fame so long as there exists a philosophic student of nature.
Mr. Darwin's "Origin of Species" undoubtedly found zoölogy, botany, and paleontology in a state bordering on doctrinaire lethargy. The knowledge of organic forms was daily increasing in an overwhelming proportion. The sole concernment of scientific men was, as far as possible, to classify the superabundant harvest in the existing systematic frame-work; and where this could not be done, to extend the latter and add to it on this side and on that, as need was. Natural history in its narrower sense, i. e., the study of the modes of life and the instincts of animals, was hardly to be found anywhere save in books for children. As for ascertaining the meaning of the facts gathered up by naturalists, as for any theory of organic beings, such things were hardly so much as thought of. The ancient dogmas of the immutability of species—a conception which, however, no one was able to define—of the infertility of hybrids, of successive acts of creation, of the impossibility of spontaneous generation, of the recent origin of the human race—these dogmas precluded all effort in that direction. The earlier attempts, in our own time brought to light again, of Lamarck and others, at solving this problem with the aid of insufficient data, and in part from the point of view of nature-philosophy, had fallen into oblivion, and long since it was the custom to regard it as irresolvable by natural science. Independent thinkers who would not bow down before the infallibility of the school were solemnly admonished of the error of their ways. For there existed a hidden community, composed for the most part of people who were unconnected with the zoölogical school, but to which many also within the school now profess to have belonged, though at the time they showed no symptom of it: this party already entertained secret doubts concerning the inerrancy of the received dogmas. Johannes Müller himself, who in other respects clung to these dogmas with strict orthodoxy, who as a professor inculcated them on his pupils, and who labored with indefatigable industry in building up the orthodox system, betrayed, on the occasion of his discovery of the development of Mollusca in holothurians, heretical tendencies which brought him into no little trouble with the school.
It is a pity that he did not live to witness the catastrophe which only one year after his death overtook this very self-assured school. The disaster was of a kind never before seen in the history of Science—so long preparing and yet so sudden; so quietly planned and yet so mighty in its effect; a scientific event without a parallel, whether we consider the extent and the importance of the system which was overturned, or the reverberations of the downfall to the uttermost limits of human knowledge. Just as, after the overturning of thrones, the neighboring countries are for a long time all commotion and tumult, whereas in the center of the disturbance itself new institutions are beginning to take root, so in consequence of the Darwinian movement the always unsettled border-land between science and philosophy is yet in a state of violent fermentation, as we see nearly every day from the many-hued bubbles of literary effort which come to the-surface. But in the field of calm and earnest science this first turmoil has given way to more quiet contemplation. Already a new generation, which has grown up amid this revolution, is beginning to take the lead with renewed courage. Leaving out of the account a few cross-grained geniuses, whose lamentations we can disregard and pass to the order of the day, it is on all sides admitted that the old ground was untenable, and that in the place of Cuvier's and Agassiz's series of creations must be substituted Mr, Darwin's doctrine of descent.
At the same time the opinion seems to be steadily growing that the evolution of organic nature is to be explained only by the so-called laws of organic structure. The peculiar merit assigned to Darwin is that he has gained the victory for the doctrine of descent. On the other hand, the doctrine of natural selection is regarded, at the best, as an ingenious idea, set forth with much skill, but in point of fact of no value.
This view, in my opinion, calls in question the very best portion of the new advance in science.
Compared, indeed, with the doctrine of the systematic school, as it reigned unquestioned in manuals and lecture-rooms down to the publication of Darwin's work, the doctrine of descent appears in itself to be a great step of progress. None can be more ready to admit this than they who therein see the triumph of their own views, silently entertained; none can more highly esteem than these pre-Darwinian Darwinists the merit of having aided in giving to the doctrine of descent its present commanding position. Still it was not to be expected that these men should feel as much indebted, intellectually, to the doctrine of descent, as others who before were not quite certain whether whales didn't come forth ready made out of nothing; whether each species manufactured at pleasure by the ornithologist or the entomologist was not created in the beginning, and did not enter Noah's ark. If naturalists of this class, though now they accept the doctrine of descent, are nevertheless a little uneasy in their consciences, and wonder at their own audacity, it is, on the other hand, perfectly natural that those older adherents of the doctrine of descent should not rest content with the triumph of their views, but that they should follow even in his further conquests the great leader who by a single blow won the victory for their side. But the end which he points out to us is high above the doctrine of descent, which doctrine, in so far as it attempts to explain the evolution of organic nature solely by its laws of development, is in fact still of little avail to us.
We must remark, in the first place, that what morphologists denominate laws are not laws at all in the sense of theoretical science. These so-called laws are simply rules deduced from a greater or less number of cases, and like grammatical rules only serve to classify and explain, by a process of vicious circle-reasoning, other facts embraced within the same definition. Even Kepler's laws were but rules of this kind, until Newton deduced them from the universal law of gravitation, and so raised them to the dignity of laws. But now that they are firmly based on the principle of gravitation, the whole doctrine of the movements of the heavenly bodies may be inferred from Kepler's laws with the highest attainable degree of certitude; and our longing to know the causes of things is as fully appeased by this explanation as the nature of the human understanding will permit. We know, with that kind of certitude which we denominate absolute, that, like the planets of our own solar system, so those of unseen suns move in ellipses whose radii vectores describe equal areas in equal times, and that the squares of their revolution times are as the cubes of their distances from their suns.
It is very different with the laws of organic structure. If in a Jurassic rock we find a fragment of a rhombic enameled scale, we infer with a very high degree of probability that the fish of whose panoply this scale was a part thousands of years ago had an independently pulsating aorta-peduncle. If on breaking up a shapeless piece of fossil bone we discover a spiral auditory cochlea, we know that the animal of whose skull the fragment was a part was a mammal. It is no small triumph that we dare make such assertions as these. Still, there is not absolute certitude here. Even the most firmly established laws of organic structure possess only a greater or less probability. Absolute characters are in systematics the philosopher's stone. True, in some cases the probability grounded on laws of organic development borders on certitude. That we shall never find a centaur, pegasus, griffin, a configuration like that of an angel or a demon, whether living or fossil, we may affirm with almost the same certainty as that a planet which has never been observed will obey the laws of Kepler. Whether we can with equal certitude affirm that never will a vertebrate be found in which by a transposition of the central nervous system the posterior and the anterior roots of the spinal-cord nerves will have interchanged functions, may perhaps be open to doubt, however improbable such a thing may be. Would the comparative anatomist ever have supposed a priori that such a structure could exist as that of the Pleuronectæ Then, in the Invertebrata the uncertainty of the laws of organic structure is in so much greater as the Invertebrata, with perhaps the exception of the Articulata and the Radiata, are less pronouncedly typical and physiologically less intelligible.
This uncertainty of the laws of organic structure comes from the fact that these laws themselves are purely experimental, containing in themselves no ultimate, logically cogent truth such as we find in physico-mathematical laws. Hence, a departure of nature from these rules implies no contradiction, no impossibility; and if a thing is not impossible, of course it is possible.
Physico-mathematical laws form, as it were, a resting-place on which we may safely step without fearing that it will ever fail under our weight. In the history of development, on the other hand, what has been our experience? Within a short period of time, a very restricted survey of the animal world, a survey guided by chance, made us acquainted with a series of facts that conflict with all our previous knowledge. Discoveries like that of the inverted position of the embryo in certain rodents, of the development in the deer, of alternate generations, of the development of the echinoderms, of the Entoconcha mirabilis, of parthenogenesis, of hectocotyly—all these are calculated to put us on our guard against premature generalization in this field. But in fact such anomalies as these are only counterparts of others with which we have long been familiar, as the marsupials, viviparous fishes, etc., which make no impression on us, because already known to science.
Under such circumstances the application of the biogenetic fundamental law to individual cases is very hazardous, even though we admit the principle in a general sense. The inferences which ontogeny, guided by a few scattered paleontological characters, permits us to draw with regard to phylogeny, will never possess more than a very restricted degree of probability. It will ever be open to the individual understanding to take whatever way it chooses amid the confusion of innumerable and complex possibilities, and, excepting a few indisputable points, which, however, were understood long ago, to conceive a great many different modes of development of the organic world as it exists now. As for certain genealogies of our race drawn up in unfettered presumptuousness rather by an artistic imagination than by a scientifically trained mind, they are of about the same value as the pedigrees of Homeric heroes in the eyes of the historical critic. For my part, if I want to read a work of fiction, I can find something better than a "History of Creation."
But this is not the point which concerns us just now. Granting the scheme of descent from the little mass of protoplasm with which life is supposed to have begun, up to man himself, to be clearly made out (which it is not), the fashioning of organic nature will, after all, be as great a riddle as ever, if laws of structure have alone determined its development.
And this, not because molecular mechanics, which produces modifications of structure, is a sealed book to us, and will for ever remain so. The molecular mechanics of crystallization, of chemical processes, seems, it is true, to be more easily understood than that of cells; still, for the present it is as hidden from us as is the latter, though its unintelligibility is of a different kind. It is the adaptation seen in the development and in the functions of the cell which, even were we acquainted with the descent of all forms, would still leave organic nature a mystery. By laws of structure alone we can not explain adaptation in organic beings. Hence, however complete our doctrine of descent, the ancient riddle which has confronted mankind from the beginning persists with all its original obscurity, unless something else comes to succor us. The sphinx of teleology still threatens unconquered from her crag. What boots it to know the reason why all vertebrates are made up of the self-same homologous parts, if we do not further know what natural cause so transformed these parts as to make them exactly answer to the purposes of each separate species? If, to explain this latter fact, a supernaturalistic intervention is still necessary, then we are yet in about the same old rut. Formerly the question used to be why, in repeated creative acts, Omnipotence always clung to the same models, and at times did only indifferent work? But now we must ask why it should, in advance, have tied its own hands, committing itself to faulty constructions and making it impossible for itself, e. g., to create a vertebrate with six extremities, though in a given case such a plan might be a very serviceable one. Hence we are, on the whole, no better off, and have only altered the form of the problem, without coming nearer to a solution.
In these straits we find in the doctrine of natural selection a measurably acceptable solution. Associated with the laws of structure, it would forthwith enable us to understand why organized beings are so wonderfully adapted to one another and to the world around them; why in themselves they are adapted to these ends, at the same time, however, exhibiting many an inadaptation; why they always stand in groups made up of the self-same parts, as though Nature had not been able to invent something new, while nevertheless each one of these parts is cleverly so transformed as to answer a special purpose in each species. Sexual selection, then, comes in to perfect the weapons, offensive and defensive, of the wooing male animal, and furnishes the answer to the question how animated nature happens to lavish plumage adornment on birds; whereas Maupertuis's theorem of the smallest action precludes any superfluity in inanimate nature. Even the glowing hue of Alpine flowers is accounted for by the attraction which brighter-colored individuals exercise upon the insects scarce in those heights, and necessary for fertilization. And mimicry, a fact brought to light by Mr. Alfred Russel Wallace, to whom we owe an important share in the discovery of the grand principle of natural selection, still further multiplies the conditions under which new forms come into existence and become fixed. Finally, this principle extends into the field of psychology and throws light even upon the origin of our ethical aspirations. In short, in lieu of final causes we would have in organic nature a most complex but blindly acting mechanism; and the cosmic problem would be reduced to the two enigmas: "What are matter and force?" and, "How can these think?"
The objections to this doctrine of natural selection are essentially three in number:
The first group of its opponents simply question the facts on which the theory is based, namely, the tendency to variation, the transmissibility of varieties, the fecundity of hybrids, the mutability of species; above all, Darwin's very ingenious explanation of the dying out of intermediate forms. These opponents, however, urge but little beyond the arguments on which the doctrine of the old systematic school rested, and which have been shown by Darwin to be untenable. Still, there is one objection which possesses undoubted weight. I myself early called attention to it in my lectures, in which I believe I was the first public expositor of the new doctrine in Germany. The objection was not printed till much later, so far as I know, and then by Prof. A. W. Volkmann. It is this, that the minute variations in which new species are supposed to have their rise can not be of any material advantage to the individual in which they appear. Still, in my opinion, this objection applies only in certain cases, and perhaps only provisionally. In the case of electrical organs, for instance, it still seems to be unanswerable, for we can not assign any possible use for the so-called pseudo-electrical organs. But, as concerns wings, we see in the example of the flying opossum, the flying lemur, and of the flying frog, discovered by Wallace, how difficult it is to say of a rudimentary organ whether it is or is not of advantage to an animal. In short, the question is not whether this or that definite structure, but whether any adapted structure whatever, can be explained in the way pointed out by Mr. Darwin. In many cases of adaptation by mimicry, and of sexual selection, this is admitted by the great majority of naturalists; and this, as we shall see, is for the present enough.
The second group of opponents do not question the general correctness of the principle or the validity of natural selection in certain cases. But they object that the principle does not explain all structures. To suppose that it must, implies a misapprehension. It never was pretended that natural selection could, by itself alone, account for the fashioning of organic nature; laws of organic structure have always been supposed to act simultaneously with it. Mr. Darwin himself has dwelt on this aspect of the problem, but, as was natural, it has no paramount place in his treatise, despite its importance. If I mistake not, in the innumerable essays which have been written on the Darwinian theory, sufficient stress has not been laid on the fact that the laws of organic structure must account for whatever in organisms is either not adapted or is even dysteleological; while, on the other hand, natural and sexual selection has to account for most of what is adapted or what is present for ornament's sake only, and which is therefore unexplainable by the simple laws of structure. So truly is this the correct view of the case, that in fact the structure of organisms seems everywhere to be a compromise between the requirements of the laws of structure and the effects of natural selection, as we see—to employ an illustration familiar to the physiologist—in the crossing of the air-passage by the digestive passage in lung-breathing vertebrates, an arrangement full of peril to life. On a previous occasion I showed that, in accounting for this state of things, the Darwinian theory coincides, in its results, with the optimism of Leibnitz. Still I am very far from overlooking the difficulties which still remain on this point. One of the most serious of these, in my opinion, is the power of regeneration, as it is called by physiologists, and the nearly allied vis medicatrix naturæ, whether as seen in the healing of wounds, in the circumscription and compensation of internal morbid processes, or—at the outermost end of the series—in the reproduction of a complete fresh-water polyp out of each of the two halves into which one such polyp has been divided. This power could not have been acquired through natural selection; and here it seems inevitable for us to recognize laws of structure working toward an end. But have we not a like phenomenon in the restoration of mutilated crystals, a fact observed by Jordan, Lavalle, Pasteur, Sénarmont, Scharff, and others? So, too, the power which organisms possess of perfecting themselves by practice appears to me not to have yet been sufficiently studied with reference to natural selection.
As a third argument against the theory of natural selection—one which is supposed to negative all its claims to consideration—its opponents always urge in the last place that in no single instance has any one ever actually observed adaptive transformation of an organ by inheritance and selection of the fittest forms. What transformations have been thus effected in the past no man can tell, it is objected; and inasmuch as, even in the future, observations and experiments on this subject seem to be impracticable on many accounts, it is claimed that the doctrine of natural selection is not only an unproved hypothesis now, but that it is fated for ever to remain so. Taking their stand upon this ground, and contrasting themselves with the believers in Darwinism, its opponents boast not a little that they are upholding the standard of strict method, which requires us to accept as demonstrated only what is proved by experiment or by mathematical reasoning.
But this again is a mistake. If it is conceded that any one adapted structure can be explained by natural selection, and if therefore this theory is admitted to be legitimately deduced from legitimate premises, then, in order to suppose the operation of natural selection, wherever it is needed to explain phenomena, it is not necessary for us to actually demonstrate such operation in the individual instance. It might be an exceedingly difficult thing to distinguish, in the performance of a complex machine, the part played by certain forces, as gravity and inertia, everywhere operating according to known laws. Nevertheless, no one would doubt that gravity and inertia do coöperate in the machine, nor should we for a moment hesitate to ascribe to the one or the other of these two forces whatever subordinate effects are only explainable by each respectively. And so in the present case. Natural selection is not, like the supposititious laws of organic structure, an empirical rule which may to-morrow, perhaps, prove nugatory. Neither, indeed, is it, like mathematico-physical laws, an infallible leading principle governing material events. But, as being a proposition deduced by a chain of valid inferences from universally admitted facts, and at the same time a proposition necessary in se, natural selection stands midway between a rule and a law, though it comes nearer to the latter. Hence, of the two evolution principles of organic nature, laws of structure and natural selection, the latter is in theory the surer, whatever may be its shortcomings in practice.
Undoubtedly it were much to be desired that we could in the individual instance demonstrate the working of natural selection, and follow the process step by step. But this we can not reasonably expect to do. Between the work of natural selection for one generation and the result after 100,000 generations, there subsists about the same ratio as between differential and integral. How seldom it is that we are able to understand this latter ratio, even though we subject it to calculation! But do we for that reason question the correctness of our integration? The corresponding problem, in the present instance, would be to investigate and ascertain the evolution of a species through an endless line of generations and under diverse external conditions, while at the same time, as has been already stated, unintelligible laws of structure, working either not adaptively or only accidentally so, enter the problem as undetermined constants, or even as undetermined functions. Though this can not be done, it does not follow that we must misapprehend the ratio between the differential and the integral found for us by nature, as though by a calculating-machine.
Thus, then, so far as the validity of the principle in general is concerned, it may be for us a matter of indifference whether or not in the individual instance we can discern and demonstrate the operation of natural selection. As things stand, it must be operative, and the only question is, whether its influence, as regards quantity, is comparable to that of the laws of structure, or whether other more powerful influences obliterate its effects, so that the adaptation prevailing throughout nature would be attributable solely to the action of these laws. In view of this question, the following appears to me to be the proper attitude of the investigator of nature:
That natural selection can perform what we must ascribe to it in order to explain thereby the adaptation of organic nature, is no more demonstrated than is the contrary proposition. The aim of the theoretical investigator of nature is to understand nature. If this aim is not to be an absurdity, the man of science must presuppose the intelligibility of nature. Final causes in nature are incompatible with nature's intelligibility. Hence, if there is any way of banishing teleology from nature, the man of science is bound to take it. Such a way is found in the theory of natural selection; and hence we must follow in it. Be it that, in holding this theory, we experience the sensations of a man who as his only hope of rescue from drowning clambers on a plank which can only just keep him above the water: when the choice lies between a plank and drowning, the plank has a decided advantage.
Galiani's apologue does not now puzzle us as once it puzzled the encyclopædists. We should have known how to reply to it, for Mr. Darwin has enabled us to see why it is that nature generally, though not always, throws doubles, and that, too, without cogged dice. And, as in our opinion systematics did not attain its true significance and its full value till now, when it no longer deludes itself with its artificial frame-work of classification, so even in physiology we continue to make use of teleology as an aid in discovery, but with the understanding that the teleology of organs being apparent only, there will also be much that is unteleological, or even antiteleological.
On the other hand, a man is not to be censured who, under the influence of such impressions as we have described, finds it impossible to believe that all nature, the human brain included, was created by the forces of matter out of a chaotic nebulous sphere. What, at the utmost, seems possible when applied to a minute mass of protoplasm, will appear rather hard to believe even to the most uncompromising monist, when he looks at a human blossom, beaming with grace and genius; and yet the difference between such mass of protoplasm and a human being is a difference simply of degree; in fact, the human being was once a mass of protoplasm. In matters of this kind, personal bias, determined by natural constitution, education, and accidental influences, will ever play a great part: Teleology and Vitalism—both in one shape or another as old as mankind—will last as long as the race itself. Hence, let every man take his own course; only, the partisans of Final Causes must not imagine, as they are wont to do, that they offer a better solution of the problem, or any solution at all that is worthy of that name, when they invoke the aid of supernatural conceptions of any sort.
This was well understood by Leibnitz. True, he did indeed suppose that he had discovered a dualistic theory of the universe, but the part he there assigns to final causes proves the correctness of the remark just made. Leibnitz utterly rejected teleology in the material world. Here, for him, reigns mechanical causality, and nothing else. Matter is, according to him, created by God, but at the same time it is so invested once for all with motive force that there is no need of setting the clock of the universe to make it go right. The sum of matter, like the sum of motive force, remains ever the same. Whatsoever has occurred or ever shall occur in the material world is ideally determinable mathematically. In a word, the material world is a mechanism, only infinitely more ingenious than any mechanism contrived by man, and composed of an infinity of parts inclosed one in the other.
Alongside of this machine of the corporeal world, Leibnitz supposed a spirit world—the world of his monads—whose ideas, from their creation down, keep pace with the changes of the corporeal world and answer to them; but between them and the corporeal world no reciprocal action of cause and effect is possible. On this theory, when we suppose we are working for ends, or that we have sensations produced by external causes, such ideas are preëstablished phantasms of our soul-monad, which is ever presenting to itself exactly the course of things that is passing outside at the same instant, and that seemingly, but not in reality, works through or upon the monad. Once only, miracles apart, has anything been done in the universe for an end, according to Leibnitz, and that was when God created the universe as perfect as he could. How Leibnitz supposed it possible to reconcile his theory with freedom of will, is a question which does not concern us here.
Thus, there was no doubt in Leibnitz's mind that material particles may, in virtue of the forces imparted to them, constitute an apparently teleological universe. Nay, all difference between his and our theory of the material universe vanishes if God created the world infinite ages ago. But even if God created the universe at the finite time—t, the course of events necessitated by Leibnitz's theory corresponds perfectly with what it would be in our theory, onward from the instant—t. For, inasmuch as Leibnitz looks on the condition of the universe at each instant as a function of time, God could, according to him, create the world in the instant—t only in that condition in which it was at that time, according to our view.
Take away from Leibnitz's theory of the universe the illusory appendage of the monadology, of preëstablished harmony, and of optimism, and the only solid nucleus that remains is his mechanical conception of the material world, and his perception of the impossibility of explaining on supernatural grounds a material fact, or, conversely, of explaining on mechanical grounds a spiritual fact. His having, over and over again, clearly and sharply expressed this perception—indeed, it was this perception that forced him to resort to the hopeless idea of preëstablished harmony—may well be esteemed to be Leibnitz's special service to metaphysics, though he himself, and his followers, hitherto make that claim rather for those more brilliant speculations. Certain it is that matter, as we have to do with matter in physico-mathematical studies, is not all, not the substance of things. But what there is over and above matter is hidden from us; and when we strive to set up before our mind's eye objectively a spiritual substance, we simply deny the properties of matter as reported to us by our senses, and hence the product of our phantasy proves incapable of causal action and reaction with matter.
How profoundly in error, then, are they who, often in a tone of scientific pharisaism, lament our blindness in trying to account for the universe without final causes which so easily and so beautifully solve all problems, even those of ethics! These people simply show that at bottom they are ignorant of what knowledge means. For us there is no other knowledge save mechanical knowledge, however beggarly a substitute that may be for true knowledge, and consequently there is only one truly scientific form of thought, the physico-mathematical one. Hence there can be no more mischievous illusion than that whereby we are led to believe that we explain the teleology of organic nature by calling to our aid an immaterial intelligence, conceived in our own likeness, and working for ends. It is of no consequence what form we give to this anthropomorphism; whether with the "Timæus" of Plato we postulate as an emanation of Deity in living beings moving ideas, with which never any definite conception has been connected in anybody's mind; whether with other philosophers we suppose an unconscious soul which constructs bodies after the types of their various kinds ever present to itself, which sees through all the enigmas of physics and chemistry, and which is thus far more intelligent than the conscious soul; or, finally, whether with Leibnitz we suppose God to have once for all in the beginning ordered the universe with a view to ends. It is, I repeat, of no consequence under which of these forms one attempts the impossible. So soon as one quits the region of mechanical necessity, he enters the boundless cloud-land of speculation. But it is all to no purpose; for, if the teleological character of nature weaves a crown of thorns for monism, at the same time her occasional antiteleology is anything but a bed of roses for dualism. The appeal to the advantages presented by dualism for the explication of ethical problems is of no avail with one who knows the true state of the case. Must we over again be reminded of the obscurity which Leibnitz vainly labored to remove in his "Theodicy"?
The student of nature in the present day can only assume the attitude of resignation toward the ultimate principles of things. I have in another place shown how the palpable errors of such thinkers as Leibnitz can be explained by the times in which they live. Between Leibnitz and ourselves there is an enormous chasm dug by scientific research, reënforced by observation and experiment, by calculation and induction.
Above all, qualitative research, so called, has on the scientific mind an educating influence, like that of life on character. Being corrected at every step by nature, and constantly reminded of the uncertainty of his judgments and the fallaciousness of his apparently most firm conclusions; being sooner or later infallibly punished for every over-hasty opinion, for every act of blind trust in appearances: such is the discipline which accustoms the experimental scientist to be chary about rapid and brilliant conquests; to attack the truth which he fain would discover by gradual approaches; to test it as impartially as though his aim were to prove the contrary; and finally, when he is arrived at a number of perhaps mutually contradictory facts held together by a tissue of still obscure relations, and the whole looking toward sundry possibilities whereof experience alone can decide which is stronger, resignedly to keep that state of things present to his mind as the best it is conceded him to know.
Surely it appears as though mathematical research, too, which proceeds inductively to a greater extent than is commonly supposed, might have a like educating effect. It, too, possesses what is lacking to metaphysical speculation, the sure means of determining whether its judgments are correct or not. But the mathematician draws this determination from himself, and hence his occupation is less adapted than experiment for weakening one's trust in speculation. Hence it is that mankind could for two thousand years busy itself about problems in mathematics, without ever curbing their propensity to speculation; hence, again, Descartes and Leibnitz, two of the greatest mathematicians of the seventeenth century, were also the boldest metaphysicians of the same period.
Hardly two centuries have elapsed since chemists, physicists, and physiologists went to work steadily and systematically, and already we see the fruits of their teaching, as transmitted from generation to generation. In this school the human mind has lost the habit of childish reverence and juvenile enthusiasm, grown up to the discretion of manhood, and learned to comport itself modestly in presence of insoluble enigmas. A new phase of its history is observable, partly in the decay of speculativism, and partly in the style of philosophizing now adopted by the best minds.
The practice acquired by the man of science in the small warfare of the laboratory fits him to deal with the great mystery of the universe. The striving which we observe in Leibnitz, toward constructing by hook or by crook a universe wherein preconceptions inherited from the childhood of the race are blended with the insight of an already well-matured physico-mathematical mind, is a thing so foreign to the man of science that he could no more think of adopting that point of view than of adopting the mythological cosmogony of the Hellenes or of the Brahmans. The complacent assurance with which Leibnitz looks on his scheme as demonstrated, reminds him of similar illusions in the beginning of his own scientific development, for in the domain of mind, too, the biogenetic principle holds good. Knowing well how immovably fixed are the bounds set to man's understanding, he has no longing to transcend them. He sees that his field of research lies between the problems, "What are matter and force?" on the one hand, and "How do matter and force think?" on the other; outside of this field he knows only that he knows nothing, can know nothing, and will know nothing. Standing without vertigo on this mountain-summit of Pyrrhonism, he scorns to people the vacuity round about him with the images of his own phantasy and surveys unappalled the unpitying drift of nature without gods. He is not disheartened at the thought that he stands face to face with eternal enigmas. He does not, like an Empedocles, cast himself into the physical abyss whose secrets he is unable to fathom; nor, like a Faust, into the ethical abyss, although no unworthy trammels restrain him from yielding to its temptations. For he contemns not reason and science, though it be denied him to recognize the first cause of things. Like Lessing, he holds the higher good to consist not in the possession but in the pursuit of truth; and therefore does he find solace and exaltation in labor which increases the store of human knowledge; which by healthy effort enhances the powers and the capacities of our race, extends our dominion over nature, ennobles our being by enriching our mind, and beautifies it by multiplying our joys.
From the disheartening conclusion, "Ignoramibus" the student of nature recovers as he pronounces the stirring countersign given by the dying Septimius Severus to his legionaries—