But Goethe did not merely endeavour to search for such far-reaching laws, he also occupied himself most actively for a long time with numerous individual researches, especially in comparative anatomy. Among these, none is perhaps more interesting than the discovery of the _mid jawbone in man_. As this is, in several respects, of importance to the theory of development, I shall briefly explain it here. There exist in all mammals two little bones in the upper jaw, which meet in the centre of the face, below the nose, and which lie between the two halves of the real upper jawbone. These two bones, which hold the four upper cutting teeth, are recognized without difficulty in most mammals; in man, however, they were at that time unknown, and celebrated comparative anatomists even laid great stress upon this want of a mid jawbone, as they considered it to const.i.tute the princ.i.p.al difference between men and apes-the want of a mid jawbone was, curiously enough, looked upon as the most human of all human characteristics. But Goethe could not accept the notion that man, who in all other corporeal respects was clearly only a mammal of higher development, should lack this mid jawbone.

By the general law of induction as to the mid jawbone he arrived at the special deductive conclusion that it must exist in man also, and Goethe did not rest until, after comparing a great number of human skulls, he really found the mid jawbone. In some individuals it is preserved throughout a whole lifetime, but usually at an early age it coalesces with the neighbouring upper jawbone, and is therefore only to be found as an independent bone in very youthful skulls. In human embryos it can now be pointed out at any moment. In man, therefore, the mid jawbone actually exists, and to Goethe the honour is due of having first firmly established this fact, so important in many respects; and this he did while opposed by the celebrated anatomist, Peter Camper, one of the most important professional authorities. The way by which Goethe succeeded in establishing this fact is especially interesting; it is the way by which we continually advance in biological science, namely, by way of induction and deduction. _Induction_ is the inference of a general law from the observation of numerous individual cases; _deduction_, on the other hand, is an inference from this general law applied to a single case which has not yet been actually observed. From the collected empirical knowledge of those days, the inductive conclusion was arrived at that all mammals had mid jawbones. Goethe drew from this the deductive conclusion, that man, whose organization was in all other respects not essentially different from mammals, must also possess this mid jawbone; and on close examination it was actually found. The deductive conclusion was confirmed and verified by experience.

Even these few remarks may serve to show the great value which we must ascribe to Goethe's biological researches. Unfortunately most of his labours devoted to this subject are so hidden in his collected works, and his most important observations and remarks so scattered in numerous individual treatises-devoted to other subjects-that it is difficult to find them out. It also sometimes happens that an excellent, truly scientific remark is so much interwoven with a ma.s.s of useless philosophical fancies, that the latter greatly detract from the former.

Nothing is perhaps more characteristic of the extraordinary interest which Goethe took in the investigation of organic nature than the lively way in which, even in his last years, he followed the dispute which broke out in France between Cuvier and Geoffroy de St. Hilaire. Goethe, in a special treatise which was only finished a few days before his death, in March, 1832, has given an interesting description of this remarkable dispute and its general importance, as well as an excellent sketch of the two great opponents. This treatise bears the t.i.tle "Principes de Philosophic Zoologique par M. Geoffroy de Saint Hilaire"; it is Goethe's last work, and forms the conclusion of the collected edition of his works. The dispute itself was, in several respects, of the highest interest. It turned essentially upon the justification of the theory of development. It was carried on, moreover, in the bosom of the French Academy, by both opponents, with a personal vehemence almost unheard of in the dignified sessions of that learned body; this proved that both naturalists were fighting for their most sacred and deepest convictions. The conflict began on the 22nd of February, and was followed by several others; the fiercest took place on the 19th of July, 1830. Geoffroy, as the chief of the French nature-philosophers, represented the theory of natural development and the monistic conception of nature. He maintained the mutability of organic species, the common descent of the individual species from common primary forms, and the unity of their organization-or the unity of the plan of structure, as it was then called.

Cuvier was the most decided opponent of these views, and according to what we have seen, it could not be otherwise. He endeavoured to show that the nature-philosophers had no right to rear such comprehensive conclusions on the basis of the empirical knowledge then possessed, and that the unity of organization-or plan of structure of organisms-as maintained by them, did not exist. He represented the teleological (dualistic) conception of nature, and maintained that "the immutability of species was a necessary condition for the existence of a scientific history of nature," Cuvier had the great advantage over his opponent, that he was able to bring towards the proof of his a.s.sertions things obvious to the eye; these, however, were only individual facts taken out of their connection with others. Geoffroy was not able to prove the higher and general connection of individual phenomena which he maintained, by equally tangible details. Hence Cuvier, in the eyes of the majority, gained the victory, and decided the defeat of the nature-philosophy and the supremacy of the strictly empiric tendency for the next thirty years.

Goethe of course supported Geoffroy's views. How deeply interested he was, even in his 81st year, in this great contest is proved by the following anecdote related by Soret:-

"Monday, Aug. 2nd, 1830.-The news of the outbreak of the revolution of July arrived in Weimar to-day, and has caused general excitement. In the course of the afternoon I went to Goethe. 'Well?' he exclaimed as I entered, 'what do you think of this great event? The volcano has burst forth, all is in flames, and there are no more negotiations behind closed doors.' 'A dreadful affair,' I answered; 'but what else could be expected under the circ.u.mstances, and with such a ministry, except that it would end in the expulsion of the present royal family?' 'We do not seem to understand each other, my dear friend,' replied Goethe. 'I am not speaking of those people at all; I am interested in something very different, I mean the dispute between Cuvier and Geoffroy de Saint Hilaire, which has broken out in the Academy, and which is of such great importance to science.' This remark of Goethe's came upon me so unexpectedly, that I did not know what to say, and my thoughts for some minutes seemed to have come to a complete standstill. 'The affair is of the utmost importance,' he continued, 'and you cannot form any idea of what I felt on receiving the news of the meeting on the 19th. In Geoffroy de Saint Hilaire we have now a mighty ally for a long time to come. But I see also how great the sympathy of the French scientific world must be in this affair, for, in spite of the terrible political excitement, the meeting on the 19th was attended by a full house. The best of it is, however, that the synthetic treatment of nature, introduced into France by Geoffroy, can now no longer be stopped. This matter has now become public through the discussions in the Academy, carried on in the presence of a large audience; it can no longer be referred to secret committees, or be settled or suppressed behind closed doors.'"

In my book on "The General Morphology of Organisms" I have placed as headings to the different books and chapters a selection of the numerous interesting and important sentences in which Goethe clearly expresses his view of organic nature and its constant development. I will here quote a pa.s.sage from the poem ent.i.tled, "The Metamorphosis of Animals"

(1819).

"All members develop themselves according to eternal laws, And the rarest form mysteriously preserves the primitive type, Form therefore determines the animal's way of life, And in turn the way of life powerfully reacts upon all form.

Thus the orderly growth of form is seen to hold Whilst yielding to change from externally acting causes."[3]

Here, clearly enough, the contrast between two different organic constructive forms is intimated, which are opposed to one another, and which by their interaction determine the form of the organism; on the one hand, a common inner original type, firmly maintaining itself, const.i.tutes the foundation of the most different forms; on the other hand, the externally active influence of surroundings and mode of life, which influence the original type and transform it. This contrast is still more definitely pointed out in the following pa.s.sage:-

"An inner original community forms the foundation of all organization; the variety of forms, on the other hand, arises from the necessary relations to the outer world, and we may therefore justly a.s.sume an original difference of conditions, together with an uninterruptedly progressive transformation, in order to be able to comprehend the constancy as well as the variations of the phenomena of form."

The "original type" which const.i.tutes the foundation of every organic form "as the inner original community" is the _inner constructive force_, which receives the original direction of form-production-that is, the tendency to give rise to a particular form-and is propagated by _Inheritance_. The "uninterruptedly progressive transformation," on the other hand, which "springs from the necessary relations to the outer world," acting as an _external formative force_, produces, by _Adaptation_ to the surrounding conditions of life, the "infinite variety of forms" (Gen. Morph. i. 154; ii. 224). The internal formative tendency of _Inheritance_, which retains the unity of the original type, is called by Goethe in another pa.s.sage the _centripetal force_ of the organism, or its tendency to specification; in contrast with this he calls the external formative tendency of _Adaptation_, which produces the variety of organic forms, the _centrifugal force_ of organisms, or their tendency to variation.

The pa.s.sage in which he clearly indicates the "equilibrium" of these two extremely important organic formative tendencies, runs as follows: "The idea of _metamorphosis_ resembles the vis centrifuga, and would lose itself in the infinite, if a counterpoise were not added to it: I mean the tendency to _specification_, the strong power to preserve what once has come into being, a vis centripeta, which in its deepest foundation cannot be affected by anything external."

Metamorphosis, according to Goethe, consists not merely, as the word is now generally understood, in the changes of form which the organic individual experiences during its individual development, but, in a wider sense, in the transformation of organic forms in general. His idea of metamorphosis is almost synonymous with the theory of development.

This is clear, among other things, from the following pa.s.sage:-"The triumph of physiological metamorphosis manifests itself where the whole separates and transforms itself into families, the families into genera, the genera into species, and then again into other varieties down to the individual. This operation of nature goes on ad infinitum; she cannot rest inactive, but neither can she keep and preserve all that she has produced. From seeds there are always developed varying plants, exhibiting the relations of their parts to one another in an altered manner."

Goethe had, in truth, discovered two great mechanical forces of nature, which are the active causes of organic formations, his two organic formative tendencies-on the one hand the conservative, centripetal, and internal formative tendency of Inheritance or specification; and on the other hand the progressive, centrifugal, and external formative tendency of Adaptation, or metamorphosis. This profound biological intuition could not but lead him naturally to the fundamental idea of the Doctrine of Filiation, that is, to the conception that the organic species resembling one another in form are actually related by blood, and that they are descended from a common original type. In regard to the most important of all animal groups, namely that of Vertebrate animals, Goethe expresses this doctrine in the following pa.s.sage (1796):-"Thus much then we have gained, that we may a.s.sert without hesitation that all the more perfect organic natures, such as fishes, amphibious animals, birds, mammals, and man at the head of the last, were all formed upon one original type, which only varies more or less in parts which are none the less permanent, and still daily changes and modifies its form by propagation."

This sentence is of interest in more than one way. The theory that all "the more perfect organic natures," that is all Vertebrate animals, are descended from one common prototype, that they have arisen from it by propagation (Inheritance) and transformation (Adaptation), may be distinctly inferred. But it is especially interesting to observe that Goethe admits no exceptional position for man, but rather expressly includes him in the tribe of the other Vertebrate animals. The most important special inference of the Doctrine of Filiation, that man is descended from other Vertebrate animals, may here be recognized in the germ.(3)

This exceedingly important fundamental idea is expressed by Goethe still more clearly in another pa.s.sage (1807), in the following words:-"If we consider plants and animals in their most imperfect condition, they can scarcely be distinguished. But this much we can say, that the creatures which by degrees emerge as plants and animals out of a common phase, where they are barely distinguishable, arrive at perfection in two opposite directions; so that the plant in the end reaches its highest glory in the tree, which is immovable and stiff, the animal in man, who possesses the greatest elasticity and freedom." This remarkable pa.s.sage not only indicates most explicitly the genealogical relationship between the vegetable and animal kingdoms, but contains the germ of the monophyletic hypothesis of descent, the importance of which I shall have to explain hereafter. (Compare Chapter XVI. and the Pedigree, p. 398.)

At the time when Goethe in this way sketched the fundamental features of the Theory of Descent, another German philosopher, Gottfried Reinhold Trevira.n.u.s, of Bremen (born 1776, died 1837), was zealously engaged at the same work. As Wilhelm Focke has recently shown, Trevira.n.u.s, even in the earliest of his greater works, "The Biology or Philosophy of Animate Nature," which appeared at the beginning of the present century, had already developed monistic views of the unity of nature, and of the genealogical connection of the species of organisms, which entirely correspond with our present view of the matter. In the first three volumes of the Biology, which appeared successively in 1802, 1803, and 1805 (therefore several years before Oken's and Lamarck's princ.i.p.al works), we find numerous pa.s.sages which are of interest in this respect.

I shall here quote only a few of the most important.

In speaking of the princ.i.p.al question of our theory, the question of the origin of organic species, Trevira.n.u.s makes the following remarks:-"Every form of life can be produced by physical forces in one of two ways: either by coming into being out of formless matter, or by modification of an already existing form by a continued process of shaping. In the latter case the cause of this modification may lie either in the influence of a dissimilar male generative matter upon the female germ, or in the influence of other powers which operate only after procreation. In every living being there exists the capability of an endless variety of form-a.s.sumption; each possesses the power to adapt its organization to the changes of the outer world, and it is this power put into action by the change of the universe that has raised the simple zoophytes of the primitive world to continually higher stages of organization, and has introduced a countless variety of species into animate nature."

By _zoophytes_, Trevira.n.u.s here means organisms of the lowest order and of the simplest character, namely, those neutral primitive beings which stand midway between animals and plants, and on the whole correspond with our _protista_. "These zoophytes," he remarks in another pa.s.sage, "are the original forms out of which all the organisms of the higher cla.s.ses have arisen by gradual development. We are further of opinion that every species, as well as every individual, has certain periods of growth, of bloom, and of decay, but that the decay of a species is _degeneration_, not dissolution, as in the case of the individual. From this it appears to us to follow that it was not the great catastrophes of the earth (as is generally supposed) which destroyed the animals of the primitive world, but that many survived them, and it is more probable that they have disappeared from existing nature, because the species to which they belonged have completed the circle of their existence, and have become changed into other kinds."

When Trevira.n.u.s, in this and other pa.s.sages, points to _degeneration_ as the most important cause of the transformation of the animal and vegetable species, he does not understand by it what is now commonly called degeneration. With him "degeneration" is exactly what we now call _Adaptation_ or _modification_, by the action of external formative forces. That Trevira.n.u.s explained this trans-transformation of organic species by Adaptation, and its preservation by Inheritance, and thus the whole variety of organic forms by the interaction of Adaptation and Inheritance, is clear also from several other pa.s.sages. How profoundly he grasped the mutual dependence of all living creatures on one another, and in general the _universal connection between cause and effect_-that is, the monistic causal connection between all members and parts of the universe-is further shown, among others, by the following remarks in his Biology:-"The living individual is dependent upon the species, the species upon the fauna, the fauna upon the whole of animate nature, and the latter upon the organism of the earth. The individual possesses indeed a peculiar life, and so far forms its own world. But just because its life is limited it const.i.tutes at the same time an organ in the general organism. Every living body exists in consequence of the universe, but the universe, on the other hand, exists in consequence of it."

It is self-evident that so profound and clear a thinker as Trevira.n.u.s, in accordance with this grand mechanical conception of the universe, could not admit for man a privileged and exceptional position in nature, but a.s.sumed his gradual development from lower animal forms. And it is equally self-evident, on the other hand, that he did not admit a chasm between organic and inorganic nature, but maintained the absolute unity of the organization of the whole universe. This is specially attested by the following sentence:-"Every inquiry into the influence of the whole of nature on the living world must start from the principle, that all living forms are products of physical influences, which are acting even now, and are changed only in degree, or in their direction." Hereby, as Trevira.n.u.s himself says, "The fundamental problem of biology is solved,"

and we add, solved in a purely mechanical or monistic sense.

Neither Trevira.n.u.s nor Goethe is commonly considered the most eminent of the German nature-philosophers, but Lorenz Oken, who, in establishing the vertebral theory of the skull, came forward as a rival to Goethe, and did not entertain a very kindly feeling towards him. Although they lived for some time in the same neighbourhood, yet the natures of these two men were so very different, that they could not well be drawn towards each other. Oken's "Manual of the Philosophy of Nature," which may be designated as the most important production of the nature-philosophy school then existing in Germany, appeared in 1809, the same year in which Lamarck's fundamental work, the "Philosophie Zoologique," was published. As early as 1802, Oken had published an "Outline of the Philosophy of Nature." As we have already intimated, in Oken's as in Goethe's works, a number of valuable and profound thoughts are hidden among a ma.s.s of erroneous, very eccentric, and fantastic conceptions. Some of these ideas have only quite recently and gradually become recognized in science, many years after they were first expressed. I shall here quote only two thoughts, which are almost prophetic, and which at the same time stand in the closest relation to the theory of development.

One of the most important of Oken's theories, which was formerly very much decried, and was most strongly combatted, especially by the so-called "exact experimentalists," is the idea that the phenomena of life in all organisms proceed from a common chemical substance, so to say, from a general simple _vital-substance_, which he designated by the name _Urschleim_, or _original slime_. By it he meant, as the name indicates, a mucilaginous substance, an alb.u.minous combination, which exists in a semi-fluid condition of aggregation, and possesses the power, by adaptation to different conditions of existence in the outer world and by interaction with its material, of producing the most various forms. Now, we need only change the expression "original slime"

(Urschleim) into _Protoplasm_, or _cell-substance_, in order to arrive at one of the grandest results which we owe to microscopic investigations during the last ten years, more especially to those of Max Schultze. By these investigations it has been shown that in all living bodies, without exception, there exists a certain quant.i.ty of mucilaginous alb.u.minous matter, in a semi-fluid condition; and that this nitrogen-holding carbon-compound is exclusively the original seat and agent of all the phenomena of life, and of all production of organic forms. All other substances which appear in the organism, besides these, are either formed by this active matter of life, or have been introduced from without. The organic egg, the original cell out of which every animal and plant is first developed, consists essentially only of one round little lump of such alb.u.minous matter. Even the yolk of an egg is nothing but alb.u.men, mixed with granules of fat. Oken was therefore right when, more divining than knowing, he made the a.s.sertion-"Every organic thing has arisen out of slime, and is nothing but slime in different forms. This primitive slime originated in the sea, from inorganic matter in the course of planetary-evolution."

Another equally grand idea of the same philosopher is closely connected with his theory of primitive slime, which coincides with the extremely important _Protoplasm theory_. For Oken, as early as 1809, a.s.serted that the primitive slime produced in the sea by spontaneous generation, at once a.s.sumed the form of microscopically small bladders, which he called "_Mile_," or "_Infusoria_." "Organic nature has for its basis an infinity of such vesicles." These little bladders arise from original semi-fluid globules of the primitive slime, by the fact of their periphery becoming condensed. The simplest organism, as well as every animal and every plant of higher kind, is nothing else than "an acc.u.mulation (synthesis) of such infusorial bladders, which by various combinations a.s.sume various forms, and thus develop into higher organisms." Here again we need only translate the expression _little bladder_, or _infusorium_, by the word _cell_, and we arrive at the Cell theory, one of the grandest biological theories of our century.

Schleiden and Schwann, about thirty years ago, were the first to furnish experiential proof that all organisms are either simple cells, or acc.u.mulations (syntheses) of such cells, and the more recent protoplasm theory has shown that protoplasm (the original slime) is the most essential (and sometimes the only) const.i.tuent part of the genuine cell.

The properties which Oken ascribes to his Infusoria are exactly the properties of cells, the properties of elementary beings, by whose acc.u.mulation, combination, and varying development, the higher organisms are formed.

These two extremely fruitful thoughts of Oken, on account of the absurd form in which he expressed them, were at first little heeded, or entirely misunderstood, and it was reserved for a much later era to establish them by actual observation. The supposition that the individual species of plants and animals originated from common prototypes by a slow and gradual development of the higher organisms out of lower ones, was of course most closely connected with these ideas.

Man's descent from lower organisms was likewise a.s.serted by Oken-"Man has been developed, not created." Although many arbitrary perversities and extravagant fancies may be found in Oken's philosophy of nature, they must not prevent us paying our just admiration to these grand ideas, which were so far in advance of their age. This much is clearly evident from the statements of Goethe and Oken which we have quoted, and from the views of Lamarck and Geoffroy which have to be discussed next, that during the first decade of our century no doctrine approached so nearly to the natural Theory of Descent, newly established by Darwin, as the much decried "Natur-philosophie."

CHAPTER V.

THEORY OF DEVELOPMENT ACCORDING TO KANT AND LAMARCK.

Kant's Dualistic Biology.-His Conception of the Origin of Inorganic Nature by Mechanical Causes, of Organic Nature by Causes acting for a Definite Purpose.-Contradiction of this Conception with his leaning towards the Theory of Descent.-Kant's Genealogical Theory of Development.-Its Limitation by his Teleology.-Comparison of Genealogical Biology with Comparative Philology.-Views in favour of the Theory of Descent entertained by Leopold Buch, Bar, Schleiden, Unger, Schaafhausen, Victor Carus, Buchner.-French Nature-philosophy.-Lamarck's Philosophie Zoologique.-Lamarck's Monistic (mechanical) System of Nature.-His Views of the Interaction of the Two Organic Formative Tendencies of Inheritance and Adaptation.-Lamarck's Conception of Man's Development from Ape-like Mammals.-Geoffroy St. Hilaire's, Naudin's, and Lecoq's Defence of the Theory of Descent.-English Nature-philosophy.-Views in favour of the Theory of Descent, entertained by Erasmus Darwin, W. Herbert, Grant, Freke, Herbert Spencer, Hooker, Huxley.-The Double Merit of Charles Darwin.

The teleological view of nature, which explains the phenomena of the organic world by the action of a personal Creator acting for a definite purpose, necessarily leads, when carried to its extreme consequences, either to utterly untenable contradictions, or to a twofold (dualistic) conception of nature, which most directly contradicts the unity and simplicity of the supreme laws which are everywhere perceptible. The philosophers who embrace teleology must necessarily a.s.sume two fundamentally different natures: an _inorganic_ nature, which must be explained by causes acting _mechanically_ (causae efficientes), and an _organic_ nature, which must be explained by _causes acting for a definite purpose_ (causae finales). (Compare p. 34.)

This dualism meets us in a striking manner when considering the conceptions of nature formed by Kant, one of the greatest German philosophers, and his ideas of the coming into being of organisms. A closer examination of these ideas is forced upon us here, because in Kant we honour one of the few philosophers who combine a solid scientific culture with an extraordinary clearness and profundity of speculation. The Konigsberg philosopher gained the highest celebrity, not only among speculative philosophers as the founder of critical philosophy, but acquired a brilliant name also among naturalists by his mechanical cosmogeny. Even in the year 1755, in his "General History of Nature, and Theory of the Heavens,"(22) he made the bold attempt "to discuss the const.i.tution and the mechanical origin of the whole universe, according to Newton's principles," and to explain them mechanically by the natural course of development, to the exclusion of all miracles. This cosmogeny of Kant, or "cosmological gas theory,"

which we shall briefly discuss in a future chapter, was at a later day fully established by the French mathematician Laplace and the English astronomer Herschel, and enjoys at the present day almost universal recognition. On account of this important work alone, in which exact knowledge is coupled with most profound speculation, Kant deserves the honourable name of a natural philosopher in the best and purest sense of the word.

If we read Kant's Criticism of the Teleological Faculty of Judgment, his most important biological work, we perceive that in contemplating organic nature he always maintains what is essentially the teleological or dualistic point of view; whilst for inorganic nature he, unconditionally and without reserve, a.s.sumes the mechanical or monistic method of explanation. He affirms that in the domain of inorganic nature all the phenomena can be explained by mechanical causes, by the moving forces of matter itself, but not so in the domain of organic nature. In the whole of Anorganology (in Geology and Mineralogy, in Meteorology and Astronomy, in the physics and chemistry of inorganic natural bodies), all phenomena are said to be explicable merely by _mechanism_ (causa efficiens), without the intervention of a final purpose. In the whole domain of Biology, on the other hand-in Botany, Zoology, and Anthropology-mechanism is not considered sufficient to explain to us all their phenomena; but we are supposed to be able to comprehend them only by an a.s.sumption of a _final cause_ acting for a definite purpose (causa finalis). In several pa.s.sages Kant emphatically remarks that, from a strictly scientific point of view, _all_ phenomena, without exception, require a mechanical interpretation, and that _mechanism alone can offer a true explanation_. But at the same time he thinks, that in regard to living natural bodies, animals and plants, our human power of comprehension is limited, and not sufficient for arriving at the real cause of organic processes, especially at the origin of organic forms. The _right_ of human reason to explain all phenomena mechanically is unlimited, he says, but its _power_ is limited by the fact that organic nature can be conceived only from a teleological point of view.

Some pa.s.sages are, however, very remarkable, in which Kant in a surprising manner deviates from this mode of viewing things, and expresses, more or less distinctly, the fundamental idea of the Theory of Descent. He even a.s.serts the necessity of a genealogical conception of the series of organisms, if we at all wish to understand it scientifically. The most important and remarkable of these pa.s.sages occurs in his "Methodical System of the Teleological Faculty of Judgment" (-- 79), which appeared in 1790 in the "Criticism of the Faculty of Judgment." Considering the extraordinary interest which this pa.s.sage possesses, both for forming a correct estimate of Kant's philosophy, as well as for the Theory of Descent, I shall here insert it _verbatim_.

"It is desirable to examine the great domain of organized nature by means of a methodical comparative anatomy, in order to discover whether we may not find in it something resembling a system, and that too in connection with the mode of generation, so that we may no longer be compelled to stop short with a mere consideration of forms as they are-which gives us no insight into their generation-and need no longer give up in despair all hope of gaining a full insight into this department of nature. The agreement of so many kinds of animals in a certain common plan of structure, which seems to be visible not only in their skeletons, but also in the arrangement of the remaining parts-so that a wonderfully simple typical form, by the shortening and lengthening of some parts, and by the suppression and development of others, might be able to produce an immense variety of species-gives us a ray of hope, though feeble, that here perhaps some result may be obtained, by the application of the principle of the _mechanism of nature_, without which, in fact, no science can exist. This a.n.a.logy of forms (in so far as they seem to have been produced in accordance with a common prototype, notwithstanding their great variety) strengthens the supposition that they have an actual blood-relationship, due to origination from a common parent; a supposition which is arrived at by observation of the graduated approximation of one cla.s.s of animals to another, beginning with the one in which the principle of purposiveness seems to be most conspicuous, that is man, and extending down to the polyps, and from these even down to mosses and lichens, and arriving finally at raw matter, the lowest stage of nature observable by us. From this matter and its forces the whole apparatus of Nature seems to have descended according to mechanical laws (such as those which she follows in the production of crystals); yet this apparatus, as seen in organic beings, is so incomprehensible to us, that we feel ourselves compelled to conceive for it a different principle. But it would seem that the archaeologist of Nature is at liberty to regard the great _Family_ of creatures (for as a Family we must conceive it, if the above-mentioned continuous and connected relationship has a real foundation) as having sprung from the immediate results of her earliest revolutions, judging from all the laws of their mechanism known to or conjectured by him."

If we take this remarkable pa.s.sage out of Kant's "Criticism of the Teleological Faculty of Judgment," and consider it by itself, we cannot but be astonished to find how profoundly and clearly the great thinker, even in 1790, had recognized the inevitable necessity of the Doctrine of Descent, and designated it as the only possible way of explaining organic nature by mechanical laws-that is, by true scientific reasoning. On account of this one pa.s.sage taken by itself, we might place Kant beside Goethe and Lamarck, as one of the first founders of the Doctrine of Descent; and considering the high authority which Kant's Critical Philosophy most justly enjoys, this circ.u.mstance might perhaps induce many a philosopher to decide in favour of the theory. But as soon as we consider this pa.s.sage in connection with the other train of thoughts in the "Criticism of the Faculty of Judgment," and balance it against other directly contradictory pa.s.sages, we see clearly that Kant, in these and some similar (but weaker) sentences, went beyond himself, and abandoned the teleological point of view which he usually adopts in Biology.

Directly after the admirable pa.s.sage which I have just quoted, there follows a remark which completely takes off its edge. After having quite correctly maintained the origin of organic forms out of raw matter by mechanical laws (in the manner of crystallization), as well as a gradual development of the different species by descent from one common original parent, Kant adds, "But he (the archaeologist of nature, that is the palaeontologist) must for this end ascribe to the common mother an organization ordained purposely with a view to the needs of all her offspring, otherwise the possibility of suitability of form in the products of the animal and vegetable kingdoms (_i.e._ teleological adaptation) cannot be conceived at all." This addition clearly contradicts the most important fundamental thought of the preceding pa.s.sage, viz., that a purely mechanical explanation of organic nature becomes possible through the Theory of Descent. And that the teleological conception of organic nature predominated with Kant, is shown by the heading of the remarkable -- 79, which contains the two contradictory pa.s.sages cited: "_Of the Necessary Subordination of the Mechanical to the Teleological Principle, in the explanation of a thing as a purpose or object of Nature._"

He expresses himself most decidedly against the mechanical explanation of organic nature in the following pa.s.sage (-- 74): "It is quite certain that we cannot become sufficiently acquainted with organized creatures and their hidden potentialities by aid of purely mechanical natural principles, much less can we explain them; and this is so certain, that we may boldly a.s.sert that it is absurd for man even to conceive such an idea, or to hope that a Newton may one day arise able to make the production of a blade of gra.s.s comprehensible, according to natural laws ordained by no intention; such an insight we must absolutely deny to man." Now, however, this impossible Newton has really appeared seventy years later in Darwin, whose Theory of Selection has actually solved the problem, the solution of which Kant had considered absolutely inconceivable!

In connection with Kant and the German philosophers whose theories of development have already occupied us in the preceding chapter, it seems justifiable to consider briefly some other German naturalists and philosophers, who, in the course of our century, have more or less distinctly resisted the prevailing teleological views of creation, and vindicated the mechanical conception of things which is the basis of the Doctrine of Filiation. Sometimes general philosophical considerations, sometimes special empirical observations, were the motives which led these thinking men to form the idea that the various individual species of organisms must have originated from common primary forms. Among them I must first mention the great German geologist, Leopold Buch. Important observations as to the geographical distribution of plants led him to the following remarkable a.s.sertion in his excellent "Physical Description of the Canary Islands":-

"The individuals of genera, on continents, spread and widely diffuse themselves, and by the difference of localities, nourishment, and soil, form varieties; and being in consequence of their isolation never crossed by other varieties, and so brought back to the main type, they in the end become a permanent and a distinct species. Then, perhaps, in other ways, they once more become a.s.sociated with other descendants of the original form-which have likewise become new varieties-and both now appear as very distinct species, no longer mingling with one another. Not so on islands. Being commonly confined in narrow valleys or within the limit of small zones, individuals can reach one another and destroy every commencing production of a permanent variety. Much in the same way the peculiarities or faults in language, originating with the head of some family, become, through the extension of the family, indigenous throughout a whole district. If the district is separated and isolated, and if the language is not brought back to its former purity by constant connection with that spoken in neighbouring districts, a dialect will be the result. If natural obstacles, forests, const.i.tution, form of government, unite the inhabitants of the separate district still more closely, and separate them still more completely from their neighbours, the dialect is fixed, and becomes a completely distinct language." (Uebersicht der Flora auf den Canarien, S. 133.)

We perceive that Buch is here led to the fundamental idea of the Theory of Descent by the phenomena of the geography of plants, a department of biological knowledge which in fact furnishes a ma.s.s of proofs in favour of it. Darwin has minutely discussed these proofs in two separate chapters of his book (the 11th and 12th). Buch's remark is further of interest, because it leads us to the exceedingly instructive comparison of the different branches of language with the species of organisms, a comparison which is of the greatest use to Comparative Philology, as well as to Comparative Botany and Zoology. Just as, for example, the different dialects, provincialisms, branches, and off-shoots of the German, Slavonic, Greco-Latin, and Irano-Indian parent language, are derived from a single common Indo-Germanic parent tongue, and just as their _differences_ are explained by _Adaptation_, and their common _fundamental characters_ explained by _Inheritance_, so in like manner the different species, genera, families, orders, and cla.s.ses of Vertebrate animals are derived from a single common vertebrate form of animal. Here also Adaptation is the cause of differences, Inheritance the cause of community of character. This interesting parallelism in the divergent development of the forms of speech and the forms of organisms has been discussed in the clearest manner by one of our first comparative philologists, the talented Augustus Schleicher, whose premature death, four years ago, remains an irreparable loss, not only to our University of Jena, but to the whole of monistic science.(6)

Among other eminent German naturalists who have expressed their belief in the Theory of Descent more or less distinctly, arriving at their conclusion in very various ways, I must next mention Carl Ernst Bar, the great reformer of animal embryology. In a lecture delivered in 1834, ent.i.tled "The Most General Laws of Nature in All Development," he shows, in the clearest way, that only in a very childish view of nature could organic species be regarded as permanent and unchangeable types, and that really they can be only pa.s.sing series of generations, which have developed by transformation from a common original form. The same conception again received firm support from Baer, in 1859, through a consideration of the laws of the geographical distribution of organisms.

J. M. Schleiden, who founded, thirty years ago, in Jena, a new epoch in Botany by his strictly empirico-philosophical and truly scientific method, ill.u.s.trated the philosophical significance of the conception of organic species in his incisive "Outlines of Scientific Botany,"(7) and showed that it had only a subjective origin in the general _law of specification_. The different species of plants are only the specified productions of the formative tendencies of plants, which arise from the various combinations of the fundamental forces of organic matter.

The eminent botanist, F. Unger, of Vienna, was led by his profound and comprehensive investigations on extinct vegetable species, to a palaeontological history of the development of the vegetable kingdom, which distinctly a.s.serts the principle of the Theory of Descent. In his "Attempt at a History of the World of Plants" (1852), he maintains the derivation of all different species of plants from a few primary forms, and perhaps from a single original plant, a simple vegetable cell. He shows that this view is founded on the genetic connection of all vegetable forms, and is necessary, not merely upon philosophical grounds, but upon those of experience and observation.(8)