Kant and Evolution I
Arthur O. Lovejoy
The Johns Hopkins University
I
IT has come to be one of the generally accepted legends of the history of science that the author of the " Kritik der reinen Vernunft " was also a pioneer of evolutionism. In the anthropological essays of the Koenigsberger, for example-we are assured by the writer of a German treatise on Kant's philosophy of natures[1] — we already find the most essential conceptions of the modern theory of descent indicated, at least in germ—and, indeed, in a way that marks Kant out as a direct precursor of Darwin." The same expositor says:
Throughout these writings the idea of evolution plays everywhere the same rôle as in contemporary science.... The series of organisms is for Kant in a constant flux, in which the seemingly so stable differentiae of genera and species have in reality only a relative and subsidiary significance.
And in a famous passage of the " Kritik der Urteilskraft," says another writer, " the present-day doctrine of descent is clearly expressed in its fundamental features."[2] Haeckel, who is in the main followed by Osborn, goes even farther in his ascription of Darwinian and "monistic " ideas to Kant's earlier works, though he thinks that in later life Kant fell from grace. Haeckel says:[3]
In various works of Kant, especially in those written in his earlier years (between 1755 and 1775) are scattered a number of very important passages which would justify our placing him by the side of Lamarck and Goethe as the principal and most interesting of Darwin's precursors. . . . He maintains the derivation of the various organisms from common primary forms.... and was the first to discover the principle of the "struggle for existence" and the theory of selection. For these reasons we should unconditionally have to assign a place of honor in the history of the theory of development to our mighty Koenigsberg philosopher, were it not that, unfortunately, these remarkable monistic ideas of young Kant were at a subsequent period wholly suppressed by the overwhelming influence of the dualistic, Christian conception of the universe.
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Yet even at the last, though Kant's nature-philosophy became less " monistic," Haeckel finds his biology scarcely less evolutionistic. In the " Kritik of Judgment " Kant, according to Haeckel, still " asserts the necessity of a genealogical conception of the series of organisms, if we at all wish to understand it scientifically." In the supposition of a marked " change of view from Kant's earlier to his later years " with respect to the applicability of the principles of natural causation in the realm of the organic, Osborn concurs with Haeckel. Finally, the writer of the historical article in the volume issued by English biologists in commemoration of the Darwin centenary, declares that Kant may be " best regarded as the culmination of the evolutionist philosophers " of the eighteenth century.[4]
These accounts of Kant's historic position in relation to transformism are interesting but scarcely accurate. Kant wrote for the most part at a time when the conception of organic evolution had been made familiar by two of the most celebrated and most influential men of science of the period, Maupertuis and Buffon. He was himself throughout his life especially interested in two distinct scientific problems, both of which made a consideration of the hypothesis of the mutability of species inevitable, and an acceptance 'of it natural. He accordingly more than once refers to it. But on no occasion does he unequivocally express belief in it; and on several occasions, some of then in his earlier, some in his "critical," period, he vehemently rejects it. The utmost that can be said for him as a biological evolutionist is that, late in life, lie once timidly coquetted with the hypothesis-speaking in a vaguely favorable way of it in the text, and then in a definitely unfavorable way in a footnote; and that at the very end of the century it occurred to him to wonder whether the higher apes may not yet acquire a gait, speech and intellectual powers similar to man's. On the other hand, it is not true that any such change of view as Haeckel and Osborn have described took place in Kant's mind with respect to the possibility of explaining the origin of organisms or the processes of organic life in mechanistic terms. Kant at no time affirmed any such possibility; and he repeatedly gave expression to an emphatic denial of it, in his earlier as well as his later utterances. Upon both this question and the question of descent, so far as any change of emphasis is distinguishable at all in Kant's successive opinions, it is a change in quite the contrary direction to that which Haeckel indicates.
These statements, in view of the wide prevalence of contrary be-
( 540) -liefs, can be properly substantiated only by an examination of all the more important writings of Kant (in their approximate chronological order) which bear upon the topic in question. Such an examination will at the same time show that the misapprehensions of his position which have arisen are by no means unnatural results of taking certain of his expressions apart from their contexts and in disregard of the meanings which he was accustomed to give to certain terms.
1. The " Universal Natural History and Theory o f the Heavens.—That Kant in his earliest important writing, the " Allgemeine Naturgeschichte and Theorie des Himmels," 1755, gave an outline sketch of cosmic evolution which anticipated the nebular hypothesis of Laplace, is one of the things that every schoolboy knows. Like most such things, it is not exactly true. Kant's cosmological speculations were, as we shall see, in scope and in method and in their most essential principles, extremely dissimilar to the nebular hypothesis. Kant's enterprise was far more ambitious than that of the French astronomer; lie was concerned with the evolution of a universe out of primeval chaos, not merely with the formation of a planetary system out of a whirling nebula. As a detail of his scheme, it is true, he sought also to explain how planets are formed, and how their orbital revolution is to be accounted for; but his version of their origin is such as to justify us in classifying him with a school of cosmogonists of much later date than Laplace, who are strongly opposed to Laplace's hypothesis. Kant's treatise in its entirety will, I think, hardly be found to merit the extravagant eulogies which it has won-at any rate, upon the score of originality or of historic influence and importance. On these two points, at least, we shall find it necessary to agree with a German writer who has recently dealt with the book. Gerland says:[5]
An epoch-making or a foundation-laying piece of work it has not been, either for the eighteenth century or the nineteenth. The assertion of Kuno Fischer and others that Kant became by virtue of it "the founder of modern cosmogony," is a. false and unhistorical exaggeration. It would be justified only if Kant's book had been the first in its field, and if our present cosmogony had developed in direct dependence upon it; but nothing is farther from being the case—in spite of a number of points of coincidence between Kant's conceptions and contemporary ones.
Gerland adds the opinion that Kant's book remained unknown in its own time, "not because of the bankruptcy of the publisher [which for many years interfered materially with its sale], nor through the fault of the people or of the men of science of Kant's day; it remained unknown through its own faults."
Even at the risk of a somewhat lengthy digression from the question of Kant's place in the history of biology—with which this paper is primarily concerned—I think it worth while to try to make clear the
( 541) historic relations of his cosmic evolutionism to that of both his predecessors and his successors. The matter has never, it seems to me, been quite justly set forth. It will at the same time be pertinent to observe the position with respect to organic evolution in which Kant's cosmic evolutionism left him.
The great, outstanding scientific event of the early eighteenth century was the triumph of the Newtonian system of celestial mechanics, based on the principle of gravitation in accordance with the law of inverse squares, over the Cartesian system of vortices, which had dominated seventeenth century physics and astronomy. Now Descartes, a more versatile and ingenious and a bolder mind than Newton, had himself elaborated his physical theories into a comprehensive philosophy of nature and a fairly detailed cosmology and cosmogony. But Newton had inscribed upon the last page of the " Principia " the maxim hypotheses non ftingo; moved both by scientific caution and by religious piety, he had deliberately refrained from putting forward either a general system of the heavens outside of the solar system or a mechanistic explanation of the genesis of the revolutional and rotatory motions and the arrangement of the planets of our system. " All these regular notions," declared the concluding scholium of the great treatise, " do not have their origin from mechanical causes. . . . This most elegant structure of sun and planets and comets could not have arisen apart from the wisdom and the rule of an intelligent and powerful being." And Newton sums up with, as it were, a " let us hear the conclusion of the whole matter," by which he would define the whole duty of explanatory astronomy : Satis est quod gravitas rev era existat, et agat secundum leges a nobis expositas, et ad corporum caelestium et maris nostri motus omnes sufficiat. "It is enough that gravity really exists, and that it acts according to the laws which we have set forth, and that it suffices for all the motions of the heavenly bodies and of our sea."
But to many of those who devoted themselves with enthusiasm to the propagation of Newton's positive doctrines, the self-denying ordinance with which lie had ended was far from agreeable. That that ordinance should be transgressed by more intrepid and more architectonic minds was inevitable. W e find, therefore, in the early eighteenth century a number of writers who busied themselves with the further elaboration of the Newtonian "natural philosophy," with the application of Newton's laws to problems the master himself had refused to discuss. In these attempts the writers in question were in part merely doing over again upon Newtonian principles what had already been done upon Cartesian principles (now discovered to be erroneous) by Descartes himself. Among the German enthusiasts for the completion of Newton's system and the extension of it into a general cosmology, one of the most zealous and most active was the young Kant. His early preoccupation with these matters was doubtless due to the influence of
( 542) one of his university teachers, Knutzen, professor of logic and metaphysics at Koenigsberg, who was at once an ardent Pietist, an ardent Wolffian, and an ardent Newtonian. All of the earliest three considerable writings[6] of Kant may be said to be chiefly attempts to give new applications to Newton's principles, or to supply his omissions, or to do both at once. Of these three, the treatise with which we are here concerned, the "Allgemeine Naturgeschichte" of 1755, was an endeavor to fill up two of the most obvious gaps (from the cosmical systemmaker's point of view) which the author of the " Principia " had left. It required no great originality and no stroke of genius on Kant's part to recognize these gaps and to devise the general outlines of the hypotheses by which he tried to fill them. The problems, and in one of the two cases at least, the proposed solution even in most of its details, were present in the scientific atmosphere of the period as epidemic infections.
The first of these gaps, and the one less pertinent to our present topic, lay in Newton's failure to suggest even a, conjectural hypothesis concerning the systematic arrangement of the heavenly bodies beyond the boundaries of our system. To three of his disciples at almost the same time[7] —but to the two others at an earlier date than to Kant—it occurred as a " probable," though perhaps not strictly verifiable. supposition that our group of planets with its central sun is only a part of an analogous but larger concentric system of revolving bodies, or of similar groups of bodies, constituting the Milky Way; and that this in turn is but part of a single, universal system, all the members of which are similarly arranged with respect to one another, and revolve about a body at the center of gravitation of the entire universe in accordance with Newton's laws. The hypothesis had, of course, an attractive combination of grandiosity and simplicity; and it was natural enough to inquire whether or not it were true. But it was, I suppose, essentially incapable of any serious testing by any data then in the possession of astronomers. It is apparently only within the past five years that some light has been thrown upon the problem of a possible " systematic ar-rangement" of the fixed stars;[8] and the arrangement which recent re-
( 543) -search seems to disclose is not in the least such as Kant imagined. Kant himself is at pains to notify his readers, in his preface, that his reasonings on the subject do not pretend to "extreme geometrical precision and mathematical infallibility." Yet it can not be denied that in the body of the work Kant presents his hypothesis as if it could be, and had been, established with rather more than a high degree of probability.
If all the worlds and systems of worlds acknowledge the same mode of, origination; if attraction is unlimited and universal, while the repulsion of the elements is likewise everywhere active; if in the infinite both great and small are small alike;—then must not all these worlds have received the same relative constitution and systematic arrangement as that which the bodies of our own solar system exhibit on a small scale? . . . If, again, these are viewed as members in the great chain of Universal Nature, then there is still the same reason to think of them, in turn, as existing in the same reciprocal relations and interconnections—which, in virtue of the primary structural law ruling all nature, make of them a new and greater system, ruled by a body of incomparably mightier attractive force at the center of their systematically ordered positions.
Thus the whole universe will compose a single system held together " by the connecting power of gravity and of centrifugal force." For if it were made up, instead, of a multitude of irregularly scattered systems, of groups of stars not in revolution about a central body, Kant argues that, in order to prevent the reciprocal attractions of these systems from " destroying them" there would be requisite
such an exactly measured disposition of them at distances proportionate to the attractions, that even the slightest displacement of them would bring about the ruin of the universe.... But a world-order that could not maintain itself without a miracle would lack that character of stability which is the distinguishing mark of the designs of God. It is therefore far more consistent with those designs to make the whole creation a single system in which all the worlds and systems of worlds that fill the whole of infinite space stand related to a single center.[9]
It will, I suppose, hardly be maintained, even by Kant's most devout admirers, that in his argumentation in behalf of his " theory of the heavens " he displays a high degree of scientific caution or a very nice sense for the distinction between the considerations that are, and those that are not, admissible in scientific inference.
The second undeveloped problem which Newton had left to tempt the ingenuity of his disciples was the problem of cosmogony. In attacking this upon Newtonian principles Kant showed no greater originality; he had many forerunners in the enterprise, in the preceding half century, and the enterprise itself was an obvious one. For the celestial mechanics of Descartes had found one of its earliest and most striking applications in a cosmogony. Descartes's first book, his " Traité du Monde," written in 1633, had been chiefly a treatise on cosmic evolu-
(544) -tion based upon mechanical principles. That book had, it is true, been suppressed by its author, who, upon hearing of the treatment received by Galileo, had preferred to take no chances for the prize-of martyrdom. But he had in Pt. V. of the " Discourse on Method " recapitulated briefly the outline of his scheme of world-evolution; in the "Principia " he had given some of the details of it; and the treatise itself, or a revision of the principal part of it, had been published after his death by his friend Clerselier, in 1664. While refraining, with what might seem sufficiently unimpeachable orthodoxy, from maintaining that the present constitution of the world actually had been evolved, rather than created ready made, Descartes also insisted that it was perfectly conceivable that it should have been evolved. e declared himself ready, if given as a starting point even " a chaos more confused and involved than any poet ever could describe," to deduce, with the aid only of the ordinary laws of the motion of matter, the necessity of the gradual formation out of that primeval chaos of a world having the characters and the contents of the world as man now finds it. He endeavored to show how matter " must needs, in consequence of those laws, have arranged itself in a certain way which made it similar to our heavens; how some of its parts would necessarily become an earth, and some planets and comets, and others a sun and fixed stars. And .. . coming to speak more particularly of the earth," he set forth, "how the mountains, seas, fountains and rivers can naturally have been formed in it, and the metals have conic to exist in the mines, and the plants to grow in the fields, and, in general, how all the bodies which are called mixed or composite could have been generated."
Now, it is certain that Kant had the cosmogony of Descartes in mind in writing the " Universal Natural History," for he refers to it in his preface. Defending himself against the imputation of materialism and irreligion, Kant writes :
I shall not be refused the justice which fair judges have always rendered to Descartes, with respect to his attempt to explain the formation of the world from purely mechanical laws. I therefore cite the remark upon this subject of the authors of the " Universal History": "We can not but think the essay of the philosopher who endeavored to account for the formation of the world in a certain time from rude matter, from the sole continuation of a motion once impressed, and reduced to a. few simple and general laws; or of others who have since attempted the same, with more applause, from the original properties of matter, with which it was endued at the creation, is so far from being criminal or injurious to God, as some have imagined, that it is rather giving a more sublime idea. of his infinite wisdom." [10]
Thus Kant, anticipating vituperation from the orthodox on account of his cosmic evolutionism, pleads not only the Cartesian precedent, but
( 545) also the favorable views already taken of that precedent by writers of recognized respectability.
Moreover, as the passage just cited indicates, Descartes was not the only, though he was the most eminent, predecessor of Kant to set an example of an undertaking similar to that upon which Kant was entering. Hypotheses about the origin of the world or of our planet may be said to have been especially in fashion during the late seventeenth and early eighteenth century. In the words of Cuvier,[11]
The end of the seventeenth century saw the birth of a new science, which took in its infancy the high-sounding name of " Theory of the Earth." Starting from a small number of facts badly observed, connecting them by fantastic suppositions, it professed to go back to the origin of worlds, to, as it were, play with them, and to create their history.
The " Theoria Telluris Sacra," 1681, 1689, and the " Archwologim Philosophien," 1692, of Thomas Burnet, and the " New Theory of the Earth," 1696, of William Whiston—successor to Newton's professorship at Cambridge, effective popularizer of the Newtonian doctrines, and the supposed original of Goldsmith's " Dr. Primrose "—were based upon an incongruous mixture of scientific and scriptural considerations ; but they at least made cosmogony a topic of general interest. As much, if little more, can be said of Woodward's " Essay toward a Natural History of the Earth and Terrestrial Bodies," 1695. But in 1734 there was published at Leipsic a treatise which resembled Laplace's theory much more nearly than did Kant's. The "Principia rerum naturalium " of Swedenborg—already celebrated as a geologist and metallurgist, not yet celebrated as a mystic and religious reformer—enunciated the following theses :[12]
That the sun is the center of a vortex; that it rotates upon its axis; that the solar matter concentrated itself into a belt or zone or ring at the equator, or rather at the ecliptic; that by the attenuation of the ring it became disrupted; that upon the disruption, parts of the matter collected into globes; .. . that the globes of solar matter were projected into space; ... that in proportion as the igneous matter thus projected receded from the sun it gradually experienced refrigeration and consequent condensation; that hence followed the formation of the elements of ether, air, aqueous vapor, etc., until the planets finally reached their present orbit; that during this period the earth experienced in a succession of geological changes which originated all the varieties in the mineral kingdom, and laid, as it were, the basis of the vegetable and afterwards of the animal kingdoms.
The idea of planetary evolution was thus anything but a novelty in 1755. What is more, the decade immediately preceding the completion of Kant's "Allgemeine Naturgeschichte" may be said to have been especially distinguished by the prominence with which, during it, questions of cosmogony were brought to the attention of the learned world.
( 546) The work from which Kant quoted a justification of Descartes's enterprise—and, by implication, of his own—the " Universal History " (1736-65) appeared in an (incomplete) German translation in 1744. This huge historical compilation, one of the great publishing enterprises of the time, contained an introduction of (in the German edition) over one hundred pages devoted to the subject of cosmogony, giving the theories of the Greek philosophers, of Descartes, Burnet, Whiston and other moderns, and a new hypothesis of the author's own. In 1749 the first volume of a still more celebrated, and scarcely less voluminous, publication—Buffon's " Histoire Naturelle "—saw the light. This volume was chiefly devoted to a " history and theory of the earth," with a chapter on the formation of planets which contained ideas more closely related than those of Kant to the nebular hypothesis. Buffon remarked upon the peculiar uniformities of the solar system which seemed to call for a mechanical explanation, but which gravitation alone did not account for, viz., the revolution of all the planets in the same direction, approximately in the same plane, and in nearly circular orbits. Buffon's own explanation of these phenomena in his " Théorie de la Terre " of 1749 is given in the following passages :
This uniformity of position and direction in the movement of the planets necessarily presupposes some common factor in their original movement of impulsion, and makes us suspect that it has been communicated to them by one and the same cause. . . . This impulsive force was certainly imparted to the stars in general by the hand of God when he set the universe in motion. But since, in physical science, we ought to abstain so far as possible from having recourse to causes outside of nature, it seems to me that in the solar system we can account for this impelling force in a sufficiently probable manner and in accordance with the principles of mechanics.... May it not with some probability be imagined that a comet falling upon the surface of the sun may have separated from that body certain parts, to which it has communicated a movement of impulsion in a common direction? . . . The planets would thus have formerly belonged to the sun, and would have been detached from it by an impelling force, common to all alike, which they still retain.[13]
Buffon was the only one [14] of his precursors (of the post-Newtonian period) known to Laplace. He made this passage of the "Histoire Naturelle" the starting point of his own earliest exposition of his nebular hypothesis, in the concluding chapter of the " Système du Monde." The hypothesis of Buffon, he remarked, accounted for most of the non-gravitational peculiarities of planetary motion that require to be accounted for; but since there remained certain other such phenomena which Buffon's supposition could not explain, a new hypothesis must be devised.
Finally, in the same year, 1749, a generation after its famous
(547) author's death, the "Protogaea" of Leibniz was published. In this Leibniz contended, on grounds now familiar enough, that the earth must have originally been in a fluid and intensely heated state; that through the cooling of the surface a solid crust was formed and the viscous fiery substance of the globe concentrated in the interior; that the present earth-structure is due to the successive action in the past of fire (fusion) and water (sedimentation) ; and that the existence of fossils testifies to the extinction of once flourishing species of animals, in consequence of modifications of the earth's surface due to one or the other of these agencies.
For comparison with the hypotheses of his precursors and successors, Kant's own scheme of cosmogony must now be indicated in its more essential features. He assumes for a starting point a "state of nature which is the very simplest that could follow upon nonentity," namely, a chaos in which all the matter in the universe was scattered throughout infinite space. It somehow "filled" the whole of that space, and yet its component particles were infinitely more diffused than now; Kant expressly declares that space was onde "full," and is now " empty," except for the actual celestial bodies. ' The original particles were not all alike; they differed in "specific density, and force of attraction." Consequently, when the universe is once permitted to begin active business, " the scattered elements of the denser sort, by virtue of their attraction, gather together out of the space surrounding them all the matter of less specific gravity; these elements in turn, with the material which has united with them, collect in points where the particles of a yet denser kind are found"; and so on.
If we follow in imagination this process by which nature fashions itself into form throughout the whole extent of chaos, we easily perceive that the sole result of this process would consist finally in the agglomeration of divers masses which, when their formation was complete, would be forever at rest and unmoved.
Fortunately, nature has other forces at her command; besides gravitation, there is also operative a force of repulsion, which shows itself especially when matter is decomposed into fine particles." By this force the elements, " as they fall towards the attracting body are deflected by one another and have their perpendicular fall converted into a movement of revolution." Having indicated the two general working principles of his cosmical mechanics, Kant now judiciously leaves the problem of the genesis of a universe, and turns somewhat abruptly to the simpler problem of the formation of our solar system, from the solution of which " we shall be able by analogy to infer a similar mode of origination in the case of the larger world-systems."
The lesser process, as Kant conceives it, may be said to fall into four stages : (1) The formation o f the nucleus o f a sun. There is formed at the point of maximum attraction of a given region of space, " a body which, so to say, grows from an infinitely small germ, at first
( 548) slowly (through chemical attraction), then more rapidly (through the so-called Newtonian attraction), and always in proportion as its mass increases, draws the surrounding parts more and more strongly to unite with itself." This central body is not strictly to be called a sun at the outset, for it is not yet " in. a flaming state "; this it only gradually becomes as, in the course of the subsequent processes of readjustment, "the lighter and more volatile portions of the primitive matter," f ailing to maintain a movement of periodic revolution, drop into the center of attraction. (2) The formation of a whirl of unaggregated particles moving round this central body in circular but separate and intersecting orbits.
When the mass of the central body has grown to such a point that the velocity with which it draws particles to itself from great distances is, by the weak degrees of repulsion with which the particles impede one another, deflected into lateral motions which, by virtue of centrifugal force, encompass the central body in an orbit-then there are produced great whirls of particles, each of which, by reason of the composition of the gravitational force and the force making for deflection sideways, describes a curved line. These orbits all intersect one another . . . and are in conflict with one another.
(3) The transformation of this disordered whirl of particles into a ring or disc of particles moving in free, parallel, circular orbits round the central body. The conflicting movements of the preceding stage come eventually to such an adjustment that they interfere with one another as little as possible. This happens in two ways:
First, by the particles limiting each others' movements till they all advance in one direction; second, by their limiting their vertical movements towards the center of attraction till, all moving horizontally in parallel circles round the sun as their center, they no longer intersect one another's paths, and, by the equalization of the centrifugal and centripetal forces, they maintain themselves constantly in free circular orbits. In this state, when all the particles are moving in one direction and in parallel circles, the conflict and collision of the elementary bodies is annulled, and all things are then in the condition of least reciprocal interference.
Further, "in accordance with the laws of centrifugal motion, all these revolutions must intersect the center of attraction with the plane of their orbits "; and for bodies moving in a common direction round a common axis, there is only one such plane. Therefore, the revolving particles gather about " that circle which passes through the rotation of the axis in the center of the common attraction," and the system assumes (though there are as yet no planets) that discoid form characteristic of our present planetary system. (4) The gradual formation, within this ring, of planets, through the attractions subsisting between the separate particles composing it. Kant has hitherto treated attraction chiefly as operative between the central mass and the particles; between particle and particle the relation has been one of repulsion. But at this point, " the attraction of the elementary bodies for one another begins to produce its effect, and thereby gives the start to new
( 549) formations which are the seeds of the future planets. For the particles, .as they move round the sun in parallel circles and at not too great a difference of distance from the sun are, by the equality of their parallel motion, almost at rest with respect to one another, and thus the attraction of those particles which are of a higher specific attraction immediately produces an important effect, namely, the collection of those nearest one another so as to form a body which, in proportion to the growth of its mass, extends its attraction farther and draws elements from a wide region to unite with it in its further formation."
It must be left to mathematicians and astronomers to assess the precise merits of these speculations in comparison with those of Kant's predecessors and successors in the same undertaking. But as to the historic affinities of Kant's hypothesis the facts seem so clear that even a layman may pronounce upon them. The Kantian scheme is as different from Laplace's as any post-Newtonian cosmogony could well be. For it does not start with a gaseous, rotating, heated nebula; it does not explain the direction of revolution and rotation of the planets as derived from the rotation of a mass formerly cohering with that now constituting the sun; it does not regard the planets as having ever formed part of any such mass. It is well-known that the rings of Saturn suggested the most characteristic feature of Laplace's theory. Kant has a chapter explaining these rings much as Laplace does; but lie expressly insists that " the ring which surrounds Saturn was not acquired in the general way, nor has been produced by the universal laws of formation which have ruled the whole system of the planets." On the other hand, it is not quite exact to identify (as does Hastie[15] ) Kant's system of planetary evolution with the meteoritic hypothesis of Lockyer and G. H. Darwin. So far as I understand these matters, Kant's cosmogony most nearly resembles an extremely recent doctrine upon the subject—the planetesimal hypothesis of Chamberlin and Salisbury. In the words of those authors :
Under the typical form of that hypothesis it is assumed that the parent nebula of the solar system is formed of innumerable small bodies, planetesimals, revolving about a central gaseous mass much as the planets do to-day. The evolution of the system consisted in the aggregation of these innumerable small bodies into much fewer large ones.... The hypothesis, therefore, postulates no fundamental change in the system of dynamics after the nebula was once formed, but only an assemblage of the scattered material. The state of dispersion of the material at the outset, as now, was maintained by orbital revolution, or, more closely speaking, by the centrifugal acceleration arising from revolution.[16]
( 550)
There are, of course, very material differences between the contemporary and the Kantian form of the hypothesis; notably, our contemporary geologists ascribe "the gathering of the planetesimals to the nuclei, to form the planets, essentially to conjunctions in the course of their orbital motions, not," as does Kant, "to simple gravitation, except as gravitation was the fundamental cause of the orbital motions." But in the two cardinal points Kant's is a planetesimal theory: (1) it conceives the planets to have grown by gradual accretions from very small nuclei, not to have been condensed from large masses "abandoned" or thrown off by a rotating, gaseous sphere; (2) it also conceives these nuclei to have been in regular orbital revolution about a central body before the formation of planets as such. The first trait distinguishes both the planetesimal and the meteoritic hypotheses from the general type of theory to which the conjectures of Swedenborg, Buffon and Laplace alike belong; the second is the specific mark differentiating the planetesimal hypothesis in turn from the meteoritic. " If," in the words of Chamberlin and Salisbury, " the meteorites could be supposed to come together so as to revolve in harmonious orbits about a common center, on a planetary basis, the assemblage might be perpetuated, but this takes the case out of the typical meteoritic class, and carries it over to the planetesimal." It is precisely this that we find exemplified in the third stage of the Kantian cosmogony.
Whether, in view of the state of knowledge in his time, Kant had any good reasons for preferring his theory to those of the other type which Swedenborg and Buffon had already put forward, I shall not venture to discuss. In any case, the features of Kant's cosmogony which establish its kinship with the planetesimal hypothesis are closely connected with one of the most elusive and most questionable details of his system of dynamics---namely, his "force of repulsion." It is this and this alone which (to his mind) explains why particles, as they fall towards the center of attraction, are " deflected sideways " and thus have their rectilinear motion converted into movement of revolution. It is likewise the establishment of an equilibrium between repulsive and attractive forces that, as he conceives, gives shape and determinate limits of size, not only to planets, but to all coherent and individuated masses of matter.[17] This notion of a Zuruckstossungskraft,, which he took over from Newton, but the use of which to explain revolutional motion Newton would never have sanctioned, was a favorite one with Kant from the beginning of his career to the end; lie reverts to it so late as 1786, in his " Metaphysical Foundations of Natural Science." It is in the " Physical Monadology," 1756, that we get the most definite account of it. We there learn the quantitative formula for this force, when acting between any two bodies; while attraction decreases in proportion to the square of the distance, repulsion decreases
( 551) in proportion to the cube.[18] Kant seeks, by reasonings both obscure and peculiar, to establish an a priori necessity that these two forces—emanating from identical points and perfectly analogous save in the direction of the motion of the external particles they affect—should yet differ in the ratio in which their potency decreases with distance. But in the "Universal Natural History" the disciple of Newton bases no calculations, such as could be compared with the actual positions and densities of the heavenly bodies, upon this quantitative formula—of which, possibly, he had not yet bethought himself. In fact, in his cosmogony he wholly fails to indicate even an approximate law of the action of repulsive force. When the plot of the world-story threatens to come to a standstill or to issue in a hopeless entanglement, " repulsion " like a deus ex machina appears upon the scene to set things right and ensure a happy ending. Precisely the same particles, under what (so far as one can judge from Kant's language) might be similar physical conditions, and at approximately equal distances, figure now as attracting, now as repelling, one another, as the exigencies of the hypothesis require. That a theorist who improvised laws of dynamics in so easy-going a manner proves to have anticipated a very recent conception of planetary evolution, must, I think, be regarded rather as evidence of good luck than of scientific good management.
What, now, was, for Kant himself, the bearing of his doctrine of cosmic evolution upon biology ? Descartes, holding the theory of animal automatism, had undoubtedly regarded the formation of organisms as part of that mechanical process of the redistribution of matter which also explained the formation of suns and planets. Such a view was not necessarily equivalent to a belief in the transformation of species. There is no necessary logical connection (though there is a natural affinity) between a mechanistic physiology and transformism—any more than between a vitalistic physiology and the doctrine of the fixity of species. Thus the question concerning the relation of cosmic evolutionism to biology is merely the genetic form of the issue of vitalism versus mechanism; in it the problems of the theory of descent need not be directly implicated. Upon this question a view current in Kant's time was that the gradual genesis of inorganic things might well be ex-
( 552) -plained from mechanical principles, but that no such explanation could be given of the origin and the characters of living beings. Such was the position taken by the author of the introduction to the " Universal History," whom we have already seen Kant quoting.
The manner of the original formation of plants and animals, in which the wisdom of the Creator principally appears, has never been accounted for by any philosopher with any tolerable success; matter and the laws of motion having nothing at all to do in these things, whatever they have in the inanimate parts of the world.[19]
And this was substantially the attitude which Kant adopted, in the one passage of the " Allgemeine Naturgeschichte " in which he definitely discusses the matter.
We are in a position to say: "Give me matter and I will construct a world." For given matter endued with the essential force of attraction, and [all astronomical phenomena] ... can be traced back to the simplest mechanical causes, which causes we may confidently hope to discover.... But can we boast of any such advantage with respect to the meanest plant or insect? Are we in a position to say: " Give me matter and I will show you how a caterpillar is generated "? Do we not in this case, from the very first step in our quest, remain in ignorance of the true inner constitution of the object in question and of the complexity of the manifold parts composing it? It should surprise no one, therefore, when I venture to say that the formation of all the heavenly bodies, the cause of their motions, in short, the origin of the entire present constitution of the universe, will become completely intelligible, before the generation of a single herb or caterpillar can be made wholly clear from mechanical principles.
This passage is, perhaps, capable of being construed as expressing rather an ignoramus than an ignorabimus. But considering it in conjunction with the uniform tenor of Kant's subsequent writings, we are justified, I think, in saying that he at no time admitted the possibility of bringing organisms within the compass of a scheme of cosmic evolution based -upon mechanistic principles. e was, in short, throughout his career a vitalist, though in later life a curiously inconsistent one. The notion of an original " spontaneous generation " of life out of the inorganic always roused his aversion. Yet, as I have remarked, a vitalist may without inconsistency be a transformist; living beings, once produced by non-mechanical. causes, may still conceivably change their forms in the course of natural descent. But Kant throughout most of his life looked upon the theories of spontaneous generation and of the transformation of species with so blinding a hostility that he could scarcely tell them apart. We shall find that some thirty-five years of reflection were required before he was able to make so simple a discrimination as to recognize that, from the point of view of his own biological philosophy, the two stood upon a different, even though both stood upon an unsound, footing.
2. The Review of Moscati on Man's Upright Posture.—In 1771
( 553) Kant wrote a review of a disquisition by an Italian anatomist, Moscati,[20] on the difference between the structure of man and that of the lower animals. Moscati's principal contention was that the upright posture is not " natural " to man, and was not his primitive attitude. Upon this Kant remarks in part as follows:
Here we have once more the natural man upon all fours-an acute anatomist having traced him back to that condition. Dr. Moscati shows that the upright gait of man is forced and contrary to nature, and that his structure is such that this position, when it has become necessary and habitual, entails upon man various disorders and diseases-clear proof enough that he has been led by reason and imitation to depart from his primitive animal posture. In his inner constitution man is not formed otherwise than as are all the quadrupeds. .. . Paradoxical as this conclusion of our Italian physician may seem, yet in the hands of so acute and philosophical an anatomist it attains to almost complete certainty (erhält or beinahe eine völlige Gewissheit). We see from this that nature's first care was for the preservation of man as an animal, in his own interest and that of the species; and for this purpose the posture which was best adapted to his internal structure, to the position of the foetus, and to protection against dangers, was the four-footed one; but we see also that there lay in man a germ of reason, through the development of which he was to become fitted, for society. He consequently assumed the posture most suitable to this, that of a biped. By virtue of this, man, on the one hand infinitely surpasses the animals; but, on the other hand, he is obliged to endure certain disorders that afflict him in consequence of his having raised his head so proudly above his former comrades.
Here, then, Kant readily accepts the doctrine that man was originally a four-footed animal, which, pari passu with its unique development of rationality and of the social instincts, assumed the upright attitude. His promptness in making the views of Moscati his own certainly indicates a general predisposition to evolutionary ways of thinking; and, if we had no other expressions of Kant's dealing with the subject more directly, it would be not unnatural to construe this assertion of the descent of civilized man from quadrupedal ancestors as equivalent to an assertion of the mutability of species. Yet the latter doctrine, it must be noted, is nowhere expressed or directly implied in the review of Moscati; and it will presently become clear that Kant would not have regarded it as a legitimate inference from any of his admissions about the earlier condition of humanity. From the time of publication of this review to the end of his life Kant seems to have remained what may be called an anthropological evolutionist; but he deliberately refused to flake the transition from this position to a general biological evolutionism.
