Evolution

EVOLUTION

I. Evolution in Biology.

IN the former half of the 18th century, the term “evolution” was introduced into biological writings, in order to denote the mode in which some of the most eminent physiologists of that time conceived that the generation of living things took place; in opposition to the hypothesis advocated, in the preceding century, by Harvey in that remarkable work which would give him a claim to rank among the founders of biological science, even had he not been the discoverer of the circulation of the blood.

One of Harvey’s prime objectsis to defend and establish, on the basis of direct observation, the opinion already held by Aristotle; that, in the higher animals at any rate, the formation of the new organism by the process of generation takes place, not suddenly, by simultaneous accretion of rudiments of all or the most important of the organs of the adult; nor by sudden metamorphosis of a formative substance into a miniature of the whole, which subsequently grows; but by epigenesis, or successive differentiation of a relatively homogeneous rudiment into the parts and structures which are characteristic of the adult.

“Et primò, quidem, quoniam per epigenesin sive partium suρer-exorientium additamentum pullum fabricari certum est: quaenam pars ante alias omnes exstruatur, et quid de illa ejusque generandi modo observandum veniat, dispiciemus. Ratum sane est et in ovo manifesté apparet quod A ristoteles de perfectorum animalium generatione enuntiat: nimirum, non omnes partes simul fieri, sed ordine aliam post aliam; primùmque existere particulam genitalem, cujus vntute postea (tanquam ex principio quodam) reliquae omnes partes prosiliant. Qualem in plantarum seminibu3 (fabis, putà, aut glandibus) gemmam sive apicem protuberantem cernimus, totius futurae arboris principium. Estque hoec particula velut filius emancipatus seorsurnque collocatus, et principium per se vivens; unde postea membrorum ordo describitur; et quaecunque ad absolvendum animal pertinent, disponuntur . Quoniam enim nulla pars se ipsam generat; sed postquam generata est, se ipsam jam auget; ideo eam primum oriri necesse est, quae principium augendi contineat (sive enim planta, sive animal est, oeque omnibus inest quod vim habeat vegetandi, sive nutriendi), simulque reliquas omnes partes suo quamque ordine distinguat et formet; proindeque in eadem primogenita particula anima primario inest, sensus, motusque, et totius vitae auctor et principium.” (Exercitatio 51.)

Harvey proceeds to contrast this view with that of the “Medici,” or followers of Hippocrates and Galen, who, “badly philosophizing,” imagined that the brain, the heart, and the liver were simultaneously first generated in the form of vesicles; and, at the same time, while expressing his agreement with Aristotle in the principle of epigenesis, he maintains that it is the blood which is the primal generative part, and not, as Aristotle thought, the heart.

In the latter part of the 17th century, the doctrine of epigenesis thus advocated by Harvey was controverted on the ground of direct observation by Malpighi, who affirmed that the body of the chick is to be seen in the egg before the punctum sanguineum makes its appearance. But from this perfectly correct observation a conclusion which is by no means warranted was drawn; namely, that the chick as a whole really exists in the egg antecedently to incubation; and that what happens in the course of the latter process is no addition of new parts, “alias post alias natas,” as Harvey puts it, but a simple expansion or unfolding of the organs which already exist, though they are too small and inconspicuous to be discovered. The weight of Malpighi’s observations therefore fell into the scale of that doctrine which Harvey terms metamorphosis, in contradistinction to epigenesis.

The views of Malpighi were warmly welcomed on philosophical grounds by Leibnitz, who found in them a support to his hypothesis of monads, and by Malebranche; while, in the middle of the 18th century, not only speculative considerations, but a great number of new and interesting observations on the phenomena of generation, led the ingenious Bonnet, and Haller, the first physiologist of the age, to adopt, advocate, and extend them.

Bonnet affirms that, before fecundation, the hen’s egg contains an excessively minute but complete chick; and that fecundation and incubation simply cause this germ to absorb nutritious matters, which are deposited in the interstices of the elementary structures of which the miniature chick, or germ, is made up. The consequence of this intussusceptive growth is the “development” or “evolution” of the germ into the visible bird. Thus an organized individual (tout organise) “is a composite body consisting of the original, or elementary , parts and of the matters which have been associated with them by the aid of nutrition;” so that, if these matters could be extracted from the individual (tout), it would, so to speak, become concentrated in a point, and would thus be restored to its primitive condition of a germ; “just as, by extracting from a bone the calcareous substance which is the source of its hardness, it is reduced to its primitive state of gristle or membrane.”

“Evolution” and “development” are, for Bonnet, synonymous terms; and since by “evolution” he means simply the expansion of that which was invisible into visibility, he was naturally led to the conclusion, at which Leibnitz had arrived by a different line of reasoning, that no such thing as generation, in the proper sense of the word, exists in nature. The growth of an organic being is simply a process of enlargement, as a particle of dry gelatine may be swelled up by the intussusception of water; its death is a shrinkage, such as the swelled jelly might undergo on desiccation. Nothing really new is produced in the living world, but the germs which develop have existed since the beginning of things; and nothing really dies, but, when what we call death takes place, the living thing shrinks back into its germ state.

The two parts of Bonnet’s hypothesis, namely, the doctrine that all living things proceed from pre-existing germs, and that these contain, one inclosed within the other, the germs of all future living things, which is the hypothesis of “emboîtement;” and the doctrine that every germ contains in miniature all the organs of the adult, which is the hypothesis of evolution or development, in the primary senses of these words, must be carefully distinguished. In fact, while holding firmly by the former, Bonnet more or less modified the latter in his later writings, and, at length, he admits that a “germ” need not be an actual miniature of the organism; but that it may be merely an “original preformation” capable of producing the latter.

But, thus defined, the germ is neither more nor less than the “particula genitalis” of Aristotle, or the “primordium vegetale” or “ovum” of Harvey; and the “evolution” of such a germ would not be distinguishable from “epigenesis.”

Supported by the great authority of Haller, the doctrine of evolution, or development, prevailed throughout the whole of the 18th century, and. Cuvier appears to have substantially adopted Bonnet’s later views, though probably he would not have gone all lengths in the direction of “emboîtement.” In a well-known note to Laurillard’s Éloge, prefixed to the last edition of the Osserneηs fossiles, the “radical de l’être” is much the same thing as Aristotle's “particula genitalis” and Harvey’s “ovum.”

Bonnet’s eminent contemporary, Buffon, held nearly the same views with respect to the nature of the germ, and expresses them even more confidently.

“Ceux qui ont era que le coeur étoit le premier formé, se sont trompés; ceux qui disent que c’est le sang se trompent aussi: tout est formé en même temps. Si l’on ne consulte que l’observation, le poulet se voit dans l’oeuf avant qui’il ait été couvé.”

“J’ai ouvert une grande quantité d’oeufs à differens temps avant et après l’incubation, et je me suis convaincu par mes yeux que le poulet existe en entier dans le milieu de la cicatrale au moment qu’il sort du corps de la poule.”

The “moule intérieur” of Buffon is the aggregate of elementary parts which constitute the individual, and is thus the equivalent of Bonnet?, germ, as defined in the passage cited above. But Buffon further imagined that innumerable “molecules organiques” are dispersed throughout the world, and that alimentation consists in the appropriation by the parts of an organism of those molecules which are analogous to them. Growth, therefore, was, on this hypothesis, partly a process of simple evolution, and partly of what has been termed syngenesis. Buffon’s opinion is, in fact, a sort of combination of views, essentially similar to those of Bonnet, with others, somewhat similar to those ot ’ the “Medici” whom Harvey condemns. The “molecules organiques” are physical equivalents of Leibnitz’s “monads.”

It is a striking example of the difficulty of getting people to use their own powers of investigation accurately, that this form of the doctrine of evolution should have held its ground so long; for it was thoroughly and completely exploded, not long after its enunciation, by Caspar Frederick Wolff, who in his Theoria Generationis, published in 1759, placed the opposite theory of epigenesis upon the secure foundation of fact, from which it has never been displaced. But Wolff had no immediate successors. The school of Cuvier was lamentably deficient in embryologists; and it was only in the course of the first thirty years of the present century, that Prévost and Dumas in France, and, later on, Döllinger, Pander, Von Bär, Rathke, and Remak in Germany, founded modern embryology; and, at the same time, proved the utter incompatibility of the hypothesis of evolution as formulated by Bonnet and Haller, with easily demonstrable facts.

Nevertheless, though the conceptions originally denoted by “evolution” and “development” were shown to bo untenable, the words retained their application to the process by which the embryos of living beings gradually make their appearance; and the terms “Development,” “Entwickelung,” and “Evolutio” are now indiscriminately used for the series of genetic changes exhibited by living beings, by writers who would emphatically deny that “Development” or “Entwickelung” or “Evolutio,” in the sense in which these words were usually employed by Bonnet or Haller, ever occurs.

Evolution, or development, is, in fact, at present employed in biology as a general name for the history of the steps by which any living being has acquired the morphological and the physiological characters which distinguish it. As civil history may be divided into biography, which is the history of individuals, and universal history, which is the history of the human race, so evolution falls naturally into two categories,—the evolution of the individual, and the evolution of the sum of living beings. It will be convenient to deal with the modern doctrine of evolution under these two heads.

1. The Evolution of the Individual.

No exception is, at this time, known to the general law, established upon an immense multitude of direct observations, that every living thing is evolved from a particle of matter in which no trace of the distinctive characters of the adult form of that living thing is discernible. This particle is termed a germ. Harvey says—

“Omnibus viventibus primordium insit, ex quo et a quo proveniant. Liceat hoc nobis primordium végétale nominare; nempe substantiam quandam corpoream vitam habentem potentia; vel quoddam per se existens, quod aptum sit, in vegetativam formam, ab interno principio operante, mutari. Quale nempe primordium, ovum est et plantarum semen; tale etiam viviparorum conceptus et insectorum vermis ab Aristotele dictus: diversa scilicet diversorum viventium primordia.”

The definition of a germ as “matter potentially alive, and having within itself the tendency to assum ∣ definite living form,” appears to meet all the reqιr.ements of modern science. For, notwithstanding it might be justly questioned whether a germ is not merely potentially, but rather actually, alive, though its vital manifestations are reduced to a minimum, the term “potential” may fairly be used in a sense broad enough to escape the objection. And the qualification of “potential” has the advantage of reminding us that the great characteristic of the germ is not so much what it is, but what it may, under suitable conditions, become. Harvey shared the belief of Aristotle—whose writings he so often quotes, and of whom he speaks as his precursor and model, with the generous respect with which one genuine worker should regard another—that such germs may arise by a process of “equivocal generation” out of not-living matter; and the aphorism so commonly ascribed to him, " omne vivum ex ovo,” and which is indeed a fair summary of his reiterated assertions, though incessantly employed against the modern advocates of spontaneous generation, can be honestly ≡o used only by those who have never read a score of pages of the Exercitationes. Harvey, in fact, believed as implicitly as Aristotle did in the equivocal generation of the lower animals. But, while the course of modern investigation has only brought out into greater prominence the accuracy of Harvey’s conception of the nature and mode of development of germs, it has as distinctly tended to disprove the occurrence of equivocal generation, or abiogenesis, in the present course of nature. In the immense majority of both plants and animals, it is certain that the germ is not merely a body in which life is dormant or potential, but that it is itself simply a detached portion of the substance of a pre-existing living body; and the evidence has yet to be adduced which will satisfy any cautious reasoner that

“omne vivum ex vivo” is not as well established a law of the existing course of nature as “omne vivum ex ovo.”

-Hn all instances which have yet been investigated, the substance of this germ has a peculiar chemical composition, consisting of at fewest four elementary bodies, viz., carbon, hydrogen, oxygen, and nitrogen, united into the ill-defined compound known as protein, and associated with much water, and very generally, if not always, with sulphur and phosphorus in minute proportions. Moreover, up to the present time, protein is known only as a product and constituent of living matter. Again, a true germ is either devoid of any structure discernible by optical means, or, at most, it is a simple nucleated cell.

In all cases, the process of evolution consists in a succession of changes of the form, structure, and functions of the germ, by which it passes, step by step, from an extreme simplicity, or relative homogeneity, of visible structure, to a greater dr less degree of complexity or heterogeneity; and the course of progressive differentiation is usually accompanied by growth, which is effected by intussusception. This intussusception, however, is a very different process from that imagined either by Buffon, or by Bonnet. The substance by the addition of which the germ is enlarged is, in no case, simply absorbed ready-made from the not-living world and packed between the elementary constituents of the germ, as Bonnet imagined; still less does it consist of the “molecules organiques” of Buffon. The new material is, in great measure, not only absorbed but assimilated, so that it becomes part and parcel of the molecular structure of the living body into which it enters. And, so far from the fully developed organism being simply the germ plus the nutriment which it has absorbed, it is probable that the adult contains neither in form, nor in substance, more than an inappreciable fraction of the constitutents of the germ, and that it is almost wholly made up of assimilated and metamorphosed nutriment. In the great majority of cases, at any rate, the full grown organism becomes what it is by the absorption of not-living matter, and its conversion into living matter of a specific type. As Harvey says (Ex. 45), all parts of the body are nourished “ab eodem succo alibili, aliter aliterque cambiato,” “ut plantae omnes ex eodem communi nutrimento (sive rore seu terrae humore).”

In all animals and plants above the lowest, the germ is a nucleated cell, using that term in its broadest sense; and the first step in the process of the evolution of the individual is the division of this cell into two or more portions. The process of division is repeated, until the organism, from being unicellular, becomes multicellular. The single cell becomes a cell-aggregate; and it is to the growth and metamorphosis of the cells of the cell-aggregate thus produced, that all the organs and tissues of the adult owe their origin.

In certain animals belonging to every one of the chief groups into which the Metazoa are divisible, the cells of the cell-aggregate which results from the process of yelk division, and which is termed a morula, diverge from one another in such a manner as to give rise to a central space, around which they dispose themselves as a coat or envelope; and thus the morula becomes a vesicle filled with fluid, the planula. The wall of the planula is next pushed in on one side, or invaginated, whereby it is converted into a double walled sac with an opening, the blastospore, which leads into the cavity lined by the inner wall. This cavity is the primitive alimentary cavity, or archenterom · the inner, or invaginated, layer is the hypoblast, the outer the epiblast; and the embryo, in this stage, is termed a gastrula. In all the higher animals, a layer of cells makes its appearance between the hypoblast and the epiblast, and is termed the mesoblast. In the further course of development, the epiblast becomes the ectoderm or epidermic layer of the body; the hypoblast becomes the epithelium of the middle portion of the alimentary canal; and the mesoblast gives rise to all the other tissues, except the central nervous system, which originates from an ingrowth of the epiblast.

With more or less modification in detail, the embryo has been observed to pass through these successive evolutional stages in sundry Sponges, Coelenterates, Worms, Echinoderms, Tunicates, Arthropods, Mollusks, and Vertebrates; and there are valid reasons for the belief, that all animals of higher organization than the Protozoa agree in the general character of the early stages of their individual evolution. Each, starting from the condition of a simple nucleated cell, becomes a cell-aggregate; and this passes through a condition which represents the gastrula stage, before taking in the features distinctive of the group to which it belongs. Stated in this form, the “gastraea theory” of Haeckel appears to the present writer to be one of the most important and best founded of recent generalizations.

So far as individual plants and animals are concerned, therefore, evolution is not a speculation but a fact; and it takes place by epigenesis.

“Animal. . . per epigenesin procreatur, materiam simul attrahit, parat, concoquit, et eadem utitur; formatur simul et augetur. . . . primum futuri corporis concrementum . . . prout augetur, dividitur sensim et distinguitur in partes, non simul omnes, sed alias post alias natas, et ordine quasque suo emergentes.”

In these words, by the divination of genius, Harvey, in the 17th century, summed up the outcome of the work of all those who, with appliances he could not dream of, are continuing his labours in the 19th century.

Nevertheless, though the doctrine of epigenesis, as understood by Harvey, has definitively triumphed over the doctrine of evolution as understood by his opponents of the 18th century, it is not impossible that, when the analysis of the process of development is carried still further, and the origin of the molecular components of the physically gross, though sensibly minute, bodies which we term germs is traced, the theory of development will approach more nearly to metamorphosis than to epigenesis. Harvey thought that impregnation influenced the female organism as a contagion; and that the blood, which he conceived to be the first rudiment of the germ, arose in the clear fluid of the “colliquamentum” of the ovum by a process of concrescence, as a sort of living precipitate. We now know, on the contrary, that the female germ or ovum, in all the higher animals and plants, is a body which possesses the structure of a nucleated cell; that impregnation consists in the fusion of the substance of another more or less modified nucleated cell, the male germ, with the ovum; and that the structural components of the body of the embryo are all derived, by a process of division, from the coalesced male and female germs. Hence it is conceivable, and indeed probable, that every part of the adult contains molecules derived both from the male and from the female parent; and that, regarded as a mass of molecules, the entire organism may be compared to a web of which the warp is derived from the female and the woof from the male. And each of these may constitute one individuality, in the same sense as the whole organism is one individual, although the matter of the organism has been constantly changing. The primitive male and female molecules may play the part of Buffon’s “moules organiques,” and mould the assimilated nutriment, each according to its own type, into innumerable new molecules. From this point of view, the process, which, in its superficial aspect, is epigenesis, appears, in essence, to be evolution, in the modified sense adopted in Bonnet’s later writings; and development is merely the expansion of a potential organism or “original preformation” according to fixed laws.

2. The Evolution of the Sum of Living Beings.

The notion that all the kinds of animals and plants may have come into existence by the growth and modification of primordial germs is as old as speculative thought; but the modern scientific form of the doctrine can be traced historically to the influence of several converging lines of philosophical speculation and of physical observation, none of which go further back than the 17th century. These are :—

1. The enunciation by Descartes of the conception that the physical universe, whether living or not living, is a mechanism, and that, as such, it is explicable on physical principles.

2. The observation of the gradations of structure, from extreme simplicity to very great complexity, presented by living things, and of the relation of these graduated forms to one another.

3. The observation of the existence of an analogy between the series of gradations presented by the species which compose any great group of animals or plants, and the series of embryonic conditions of the highest members of that group.

4. The observation that large groups of species of widely different habits present the same fundamental plan of structure; and that parts of the same animal or plant, the functions of which are very different, likewise exhibit modifications of a common plan.

5. The observation of the existence of structures, in a rudimentary and apparently useless condition, in one species of a group, which are fully developed and have definite functions in other species of the same group.

6. The observation of the effects of varying conditions in modifying living organisms.

7. The observation of the facts of geographical distribution.

8. The observation of the facts of the geological succession of the forms of life.

1. Notwithstanding the elaborate disguise which fear of the powers that were led Descartes to throw over his real opinions, it is impossible to read the Principes de lα Philosophie without acquiring the conviction that this great philosopher held that the physical world and all things in it, whether living or not living, have originated by a process of evolution, due to the continuous operation of purely physical causes, out of a primitive relatively formless matter.

The following passage is especially instructive :—

“Et tant s’en faut que je veuille que l’on croie toutes les choses que j’écrirai, que même je pretends en proposer ici quelques unes que je crois absolument être fausses; à savoir, je ne doute point ?ue le monde n’ait été créé au commencement avec autant de per-ection qu’il en a; en sorte que le soleil, la .terre, la lune, et les étoiles ont été dès lors; et que la terre n’a pas eu seulement en soi les semences des plantes, mais que les plantes même en ont couvert une partie; et qu’ Adam et Eve n’ont pas été créés enfans mais en âge d’hommes parfaits. La religion chrétienne veut que nous le croyons ainsi, et la raison naturelle nous persuade entièrement cette vérité; car si nous considérons la toute puissance de Dieu, nous devons juger que tout ce qu’il a fait a eu dès le commencement toute la perfection qu’il devoit avoir. Mais néanmoins, comme on connôitroit beaucoup mieux quelle a ete la nature d Adam et celle des arbres de Paradis si on avoit examiné comment les enfants se forment peu à peu dans le ventre de leurs mères et comment les plantes sortent de leurs semences, que si on avoit seulement considéré quels ils ont été quand Dieu les a créés: tout de même, nous ferons mieux entendre quelle est généralement la nature de toutes les ehoses qui sont an monde si nous pouvons imaginer quelques principes qui soient fort intelligibles et fort simples, desquels nous puissions voir clairement que les astres et la terre et enfin tout ce monde visible auroit pu être produit ainsi que de quelques semences (bien que nous sachions qu’il n'a pas été produit en cette façon) que si nous la décrivions seulement comme il est, ou bien comme nous croyons qu’il a été créé. Et parceque je pense avoir trouvé des principes qui sont tels, je tacherai ici de les expliquer.”

If we read between the lines of this singular exhibition of force of one kind and weakness of another, it is clear that Descartes believed that he had divined the mode in which the physical universe had been evolved; and the Traité de l ’ homme and the essay Sur les Passions afford abundant additional evidence that he sought for, and thought he had found, an explanation of the phenomena of physical life by deduction from purely physical laws.

Spinoza abounds in the same sense, and is as usual perfectly candid—·

“Naturae leges et regulae, secundum quas omnia fiunt et ex unis formis in alias mutantur, sunt ubique et semper eadem. ’

Leibnitz’s doctrine of continuity necessarily led him in the same direction; and, of the infinite multitude of monads with which he peopled the world, each is supposed to be the focus of an endless process of evolution and involution. In the Protogcea, xxvi., Leibnitz distinctly suggests the mutability of species—

“Alii mirantur in saxis passim species videri quas vel in orbe cognito, vel saltem in vicinis locis nustra quaeras. Ita Cornua Ammonis, quae ex nautilorum numero habeantur, passim et forma et magnitudine (nam et pedali diametro aliquando reperiuntur) ab omnibus illis naturis discrepare dicunt, quas praebet mare. Sed quis absconditos ejus recessus aut subterraneas abyssos pervestigavit? quam multa nobis animalia antea ignota offert novus orbis? Et credibile est per magnas illas conversiones etiam animalium species plurimum immutatas.”

Thus in the end of the 17th century the seed was sown which has at intervals brought forth recurrent crops of evolutional hypotheses, based, more or less completely, on general reasonings.

Among the earliest of these speculations is that put forward by Benoit de Maillet in his Telliamed, which, though printed in 1735, was not published until twenty three years later. Considering that this book was written before the time of Haller, or Bonnet, or Linnaeus, or Hutton, it surely deserves more respectful consideration than it usually receives. For De Maillet not only has a definite conception of the plasticity of living things, and of the. production of existing species by the modification of their predecessors; but he clearly apprehends the cardinal maxim of modern geological science, that the explanation of the structure of the globe is to be sought in the deductive application to geological phenomena of the principles established inductively by the study of the present course of nature. Somewhat later, Maupertuis suggested a curious hypothesis as to the causes of variation, which he thinks may be sufficient to account for the origin of all animals from a single pair. Robinet followed out much the same line of thought as De Maillet, but less soberly; and Bonnet’s speculations in the Palingenesie, which appeared in 1769, have already been mentioned. Buffon (1753-1778), at first a partisan of the absolute immutability of species, subse-

cpιently appears to have believed that larger or smaller groups of species have been produced by the modification of a primitive stock; but he contributed nothing to the general doctrine of evolution.

Erasmus Darwin (Zοonοmia, 1794), though a zealous evolutionist, can hardly be said to have made any real advance on his predecessors; and, notwithstanding that Goethe (1791-4) had the advantage of a wide knowledge of morphological facts, and a true insight into their signification, while he threw all the power of a great poet into the expression of his conceptions, it may be questioned whether he supplied the doctrine of evolution with a firmer scientific basis than it already possessed. Moreover, whatever the value of Goethe’s labours in that field, they were not published before 1820, long after evolutionism had taken a new departure from the works of Treviranus and Lamarck—the first of its advocates who were equipped for their task with the needful large and accurate knowledge of the phenomena of life, as a whole. It is remarkable that each of these writers seems to have been led, independently and contemporaneously, to invent the same name of “Biology” for the science of the phenomena of life; and thus, following Buffon, to have recognized the essential unity of these phenomena, and their contradistinction from those of inanimate nature. And it is hard to say whether Lamarck or Treviranus has the priority in propounding the main thesis of the doctrine of evolution; for though the first volume of Treviranus’s Biologie appeared only in 1802, he says, in the preface to his later work, the Erscheinungen und Gesetze des organischen Lehens, dated 1831, that he wrote the first volume of the Biologie “nearly five-and-thirty years ago,” or about 1796.

Now, in 1794, there is evidence that Lamarck held doctrines which present a striking contrast to those which are to be found in the Philosophie Zoologique, as the following passages show :—

685. Quoique mon unique objet dans cet article n’ait été que de traiter de la cause physique de l’entretien de la vie des êtres organiques, malgré cela j'ai osé avancer en débutant, que l’existence de ces êtres étonnants n'appartiennent nullement à la nature; que tout ce qu on peut entendre par le mot nature, ne pouvoit donner la vie, c’est-à-dire, que toutes les qualités de la matière, jointes à toutes les circonstances possibles, et même à l’activité répandue dans l’univers, ne pouvaient point produire un être muni du mouvement organique, capable de reproduire son semblable, et sujet à la mort.

686. Tous les individus de cette nature, qui existent, proviennent d’individus semblables qui tous ensemble constituent l’espèce entière. Or, je crois qu’il est aussi impossible à l’homme de connôitre la cause physique du premier individu de chaque espèce, que d’assigner aussi physiquement la cause de l’existence de la matière ou de l’univers entier. C’est au moins ce que le résultat de mes connaissances et de mes réflexions me portent à penser. S’il existe beaucoup de variétés produites par l’effet des circonstances, ces variétés ne dénaturent point les espèces; mais on se trompe, sans doute souvent, en indiquant comme espèce, ce qui n’est que variété; et alors je sens que cette erreur peut tirer à conséquence dans les raisonnements que l’on fait sur cette matière.

The first three volumes of Treviranus’s Biologie, which contains his general views of evolution, appeared between 1802 and 1805. The Recherches sur l'organisation des corps vivants, which sketches out Lamarck’s doctrines, was published in 1802; but the full development of his view s, in the Philosopjhie Zoologique, did not take place until 1809.

The Biologie and the Philosop>his Zoologique are both very remarkable productions, and are still worthy of attentive study, but they fell upon evil times. The vast authority of Cuvier was employed in support of the traditionally respectable hypotheses of special creation and of catastrophism; and the wild speculations of the Discours sur les Devolutions de la Surface du Globe were held to be models of sound scientific thinking, while the really much more sober and philosophical hypotheses of the Hydrogeologie were scouted. For many years it was the fashion to speak of Lamarck with ridicule, while Treviranus was altogether ignored.

Nevertheless, the work had been done. The conception of evolution was henceforward irrepressible, and it incessantly reappears, in one shape or another, up to the year 1858, when Mr Darwin and Mr Wallace published their Theory of Natural Selection. The Origin of Species appeared in 1859; and it is within the knowledge of all whose memories go back to that time, that, henceforward, the doctrine of evolution has assumed a position and acquired an importance which it never before possessed. In the Origin of Species, and in his other numerous and important contributions to the solution of the problem of biological evolution, Mr Darwin confinée himself to the discussion of the causes which have brought about the present condition of living matter, assuming such matter to have once come into existence. On the other hand, Mr Spencer and Professor Haeckel have dealt with the whole problem of evolution. The profound and vigorous writings of Mr Spencer embody the spirit of Descartes in the knowledge of our own day, and may be regarded as the “Principes des Philosophie” of the 19th century; while, whatever hesitation may not unfrequently be felt by less daring minds, in following Haeckel in many of his speculations, his attempt to systematize the doctrine of evolution and to exhibit its influence as the central thought of modern biology, cannot fail to have a far-reaching influence on the progress of science.

If we seek for the reason of the difference between the scientific position of the doctrine of evolution a century ago, and that which it occupies now, we shall find it in the great accumulation of facts, the several classes of .which have been enumerated above, under the second to the eighth heads. For those which are grouped under the second to the seventh of these classes, respectively, have a clear significance on the hypothesis of evolution, while they are unintelligible if that hypothesis be denied. And those of the eighth group are not only unintelligible without the assumption of evolution, but can be proved never to be discordant with that hypothesis, while, in some cases, they are exactly such as the hypothesis requires. The demonstration of these assertions would require a volume, but the general nature of the evidence on which they rest may be briefly indicated.

2. The accurate investigation of the lowest forms of animal life, commenced by Leeuwenhoek and Swammerdam, and continued by the remarkable labours of Reaumur, Trembley, Bonnet, and a host of other observers in the latter part of the 17th and the first half of the 18th centuries, drew the attention of biologists to the gradation in the complexity of organization which is presented by living beings, and culminated in the doctrine of the “échelle des êtres,” so powerfully and clearly stated by Bonnet; and, before him, adumbrated by Locke and by Leibnitz. In the then state of knowledge, it appeared that all the species of animals and plants could be arranged in one series; in such a manner that, by insensible gradations, the mineral passed into the plant, the plant into the polype, the polype into the worm, and so, through gradually higher forms of life, to man, at the summit of the animated world.

But, as knowledge advanced, this conception ceased to be tenable in the crude form in which it was first put forward. Taking into account existing animals and plants alone, it became obvious that they fell into groups which were more or less sharply separated from one another; and, moreover, that even the species of a genus can hardly ever be arranged in linear series. Their natural resemblances and differences are only to be expressed by disposing them as if they were branches springing from a common hypothetical centre.

Lamarck, while affirming the verbal proposition that animals form a single series, was forced by his vast acquaintance with the details of zoology to limit the assertion to such a series as may be formed out of the abstractions constituted by the common characters of each group.

Cuvier on anatomical, and Von Baer on embryological grounds, made the further step of proving that, even in this limited sense, animals cannot be arranged in a single series, but that there are several distinct plans of organization to be observed among them, no one of which, in its highest and most complicated modification, leads to any of the others.

The conclusions enunciated by Cuvier and Von Baer have been confirmed in principle by all subsequent research into the structure of animals and plants. But the effect of the adoption of these conclusions has been rather to substitute a new metaphor for that of Bonnet than to abolish the conception expressed by it. Instead of regarding living things as capable of arrangement in one series like the steps of a ladder, the results of modern investigation compel us to dispose them as if they were the twigs and branches of a tree. The ends of the twigs represent individuals, the smallest groups of twigs species, larger groups genera, and so on, until we arrive at the source of all these ramifications of the main branch, which is represented by a common plan of structure. At the present moment, it is impossible to draw up any definition, based on broad anatomical or developmental characters, by which any one of Cuvier’s great groups shall be separated from all the rest. On the contrary, the lower members of each tend to converge towards the lower members of all the others, The same may be said of the vegetable world. The apparently clear distinction between flowering and flowerless plants has been broken down by the series of gradations between the two exhibited by the Lycopodiaceoe, Iihizocarpece, and Gymnospermeoe. The groups of Pungi, Lichenece, and Algoe have completely run into one another, and, when the lowest forms of each are alone considered, even the animal and vegetable kingdoms cease to have a definite frontier.

If it is permissible to speak of the relations of living forms to one another metaphorically, the similitude chosen must undoubtedly be that of a common root, whence two main trunks, one representing the vegetable and one the animal world, spring; and, each dividing into a few main branches, these subdivide into multitudes of branchlets and these into smaller groups of twigs.

As Lamarck has well said —

Il n’y a que ceux qui se sont longtemps et fortement occupés de la détermination des espèces, et qui ont consulté de riches collections, qui peuvent savoir jusqu’à quel point les espèces, parmi les corps vivants se fondent les unes dans les autres, et qui ont pu se convaincre que, dans les parties où nous voyons des espèces isoles, cela n'est ainsi que pareequ’il nous en manque d’autres qui en sont plus voisines et que nous n’avons pas encore recueillies.

Je ne veux pas dire pour cela que les animaux qui existent forment une série très-simple et partout également nuancée; mais je dis qu'ils forment une série rameuse, irrégulièrement graduée et qui Λ a point de discontinuité dans ses parties, ou qui, du moins, n en a tou i ours pas eu, s’il est vrai que, par suite de quelques especes perdues il s’en trouve quelque part. Il en resuite que les espèces qui terminent chaque rameau de la série générale tiennent, au moins d’un côté à d’autres espèces voisines qui se nuancent avec elles. Voilà ce que l’état bien, connu des choses me met maintenant a portée de démontrer. Je n’ai besoin d’aucune hypothèse ni d’aucune supposition pour cela: j’en atteste toutes naturalistes observateurs.

3. In a remarkable essay Meckel remarks

“There is no good physiologist who has not been struck by the observation that the original form of all organisms is one and the same, and that out of this one form, all, the lowest as well as the highest, are developed in such a manner that the latter pass through the permanent forms of the former as transitory stages. Aristotle, Haller, Harvey, Kielmeyer, Autenrieth, and many others have either made this observation incidentally, or, especially the latter, have drawn particular attention to it, and drawn therefrom results of permanent importance for physiology.”

Meckel proceeds to exemplify the thesis, that the lower forms of animals represent stages in the course of the development of the higher, with a large series of illustrations.

After comparing the Salamanders and the perennibranchiate Urodela with the Tadpoles and the Frogs, and enunciating the law that the more highly any animal is organized the more quickly does it pass through the lower stages, Meckel goes on to say—

“From these lowest Vertebrata to the highest, and to the highest forms among these, the comparison between the embryonic conditions of the higher animals and the adult states of the lower can be more completely and thoroughly instituted than if the survey is extended to the Invertebrata, inasmuch as the latter are in many respects constructed upon an altogether too dissimilar type; indeed they often differ from one another far more than the lowest vertebrate does from the highest mammal; yet the following pages will show that the comparison may be also extended to them with interest. I n fact, there is a period when, as Aristotle long ago said, the embryo of the highest animal has the form of a mere worm, and, devoid of internal and external organization, is merely an almost structureless lump of polype-substance. Notwithstanding the origin of organs, it still for a certain time, by reason of its want of an internal bony skeleton, remains worm and mollusk, and only later enters into the series of the Vertebrata, although traces of the vertebral column even in the earliest periods testify its claim to a place in that series.”— Op. cit. pp. 4, 5.

If Meckel’s proposition is so far qualified, that the comparison of adult with embryonic forms is restricted within the limits of one type of organization; and, if it is further recollected, that the resemblance between the permanent lower form and the embryonic stage of a higher form is not special but general, it is in entire accordance with modern embryology; although there is no branch of biology which has grown so largely, and improved its methods so much since Meckel’s time, as this. In its original form, the doctrine of “arrest of development,” as advocated by Geoffroy Saint-Hilaire and Serres, was no doubt an over-statement of the case. It is not true, for example, that a fish is a reptile arrested in its development, or that a reptile was ever a fish; but it is true that the reptile embryo, at one stage of its development, is an organism which, if it had an independent existence, must be classified among fishes; and all the organs of the reptile pass, in the course of their development, through conditions which are closely analogous to those which are permanent in some fishes.

4. That branch of biology which is termed Morphology is a commentary upon, and expansion of, the proposition that widely different animals or plants, and widely different parts of animals or plants, are constructed upon the same plan. From the rough comparison of the skeleton of a bird with that of a man by Belon, in the sixteenth century (to go no further back), down to the theory of the limbs and the theory of the skull at the present day; or, from the first demonstration of the homologies of the parts of a flower by C. F. Wolff, to the present elaborate analysis of the floral organs, morphology exhibits a continual advance towards the demonstration of a fundamental unity among the seeming diversities of living structures. And this demonstration has been completed by the final establishment of the cell theory, which involves the admission of a primitive conformity, not only of all the elementary structures in animals and plants respectively, but of those in the one of these great divisions of living things with those in the other. No a priori difficulty can be said to stand in the way of evolution, when it can be shown that all animals and all plants proceed by modes of development, which are similar in principle, from a fundamental protoplasmic material.

5. The innumerable cases of structures, which are rudimentary and apparently useless, in species, the close allies of which possess well developed and functionally important homologous structures, are readily intelligible on the theory of evolution, while it is hard to conceive their raison Tetre on any other hypothesis. However, a cautious reasoner will probably rather explain such cases deductively from the doctrine of evolution, than endeavour to support the doctrine of evolution by them. For it is almost impossible to prove that any structure, however rudimentary, is useless—that is to say, that it plays no part whatever in the economy; and, if it is in the slightest degree useful, there is no reason why, on the hypothesis of direct creation, it should not have been created. Nevertheless, double-edged as is the argument from rudimentary organs, there is probably none which has produced a greater effect in promoting the general acceptance of the theory of evolution.

6. The older advocates of evolution sought for the causes of the process exclusively in the influence of varying conditions, such as climate and station, or hybridization, upon living forms. Even Treviranus has got no further than this point. Lamarck introduced the conception of the action of an animal on itself as a factor in producing modification. Starting from the well-known fact that the habitual use of a limb tends to develop the muscles of the limb, and to produce a greater and greater facility in using it, he made the general assumption that the effort of an animal to exert an organ in a given direction tends to develop the organ in that direction. But a little consideration showed that, though Lamarck had seized what, as far as it goes, is a true cause of modification, it is a cause the actual effects of which are wholly inadequate to account for any considerable modification in animals, and which can have no influence at all in the vegetable world; and probably nothing contributed so much to discredit evolution, in the early part of this century, as the floods of easy ridicule which were poured upon this part of Lamarck’s speculation. The theory of natural selection, or survival of the fittest, was suggested by Wells in 1813, and further elaborated by Matthew in 1831. But the pregnant suggestions of these writers remained practically unnoticed and forgotten, until the theory was independently devised and promulgated by Darwin and Wallace in 1858, and the effect of its publication was immediate and profound.

Those who were unwilling to accept evolution, without better grounds than such as are offered by Lamarck or tho author of that particularly unsatisfactory book, the Vestiges of the Natural History of the Creation, and who therefore preferred to suspend their judgment on the question, found in the principle of selective breeding, pursued in all its ap- · plications with marvellous knowledge and skill by Mr Dar-· win, a valid explanation of the occurrence of varieties and races; and they saw clearly that, if the explanation would apply to species, it would not only solve the problem of their evolution, but that it would account for the facts of teleology, as well as for those of morphology; and for the persistence of some forms of life unchanged through long epochs of time, while others undergo comparatively rapid metamorphosis.

How far “natural selection” suffices for the production of species remains to be seen. Few can doubt that, if not the whole cause, it is a very important factor in that operation; and that it must play a great part in the sorting out of varieties into those which are transitory aud those which are permanent.

But the causes and conditions of variation have yet to be thoroughly explored; and the importance of natural selection will not be impaired, even if further inquiries should prove that variability is definite, and is determined in certain directione rather than in others, by conditions inherent in that which varies. It is quite conceivable that every species tends to produce varieties of a limited number and kind, and that the effect of natural selection is to favour the development of some of these, while it opposes the development of others along their predetermined lines of modification.

7. No truths brought to light by biological investigation were better calculated to inspire distrust of the dogmas intruded upon science in the name of theology, than those which relate to the distribution of animals and plants on the surface of the earth. Very skilful accommodation was needful, if the limitation of sloths to South America, and of the ornithorhynchus to Australia, was to be reconciled with the literal interpretation of the history of the deluge; and, with the establishment of the existence of distinct provinces of distribution, any serious belief in the peopling of the world by migration from Mount Ararat came to an end.

Under these circumstances, only one alternative was left for those who denied the occurrence of evolution; namely, the supposition that the characteristic animals and plants of each great province were created, as such, within the limits in which we find them. And as the hypothesis of “specific centres,” thus formulated, was heterodox from the theological point of view, and unintelligible under its scientific aspect, it may be passed over without further notice, as a phase of transition from the creational to the evolutional hypothesis.

8. In fact, the strongest and most conclusive arguments in favour of evolution are those which are based upon the facts of geographical, taken in conjunction with those of geological, distribution.

Both Mr Darwin and Mr Wallace lay great stress on the close relation which obtains between the existing fauna of any region and that of the immediately antecedent geological epoch in the same region; and rightly, for it is in truth inconceivable that there should be no genetic connection between the two. It is possible to put into words the proposition, that all the animals and plants of each geological epoch were annihilated, and that a new set of very similar forms was created for the next epoch, but it may be doubted if any one who ever tried to form a distinct mental image of this process of spontaneous generation on the grandest scale, ever really succeeded in realizing it.

Within the last twenty years, the attention of the best palaeontologists has been withdrawn from the hodman’s work of making o new species” of fossils, to the scientific task of completing our knowledge of individual species, and tracing out the succession of the forms presented by any given type in time.

Those who desire to inform themselves of the nature and extent of the evidence bearing on these questions may consult the works of Riitimeyer, Gaudry, Kowalewsky,

Marsh, and the writer of the present article. It must suffice, in this place, to say that the successive forms of the Equine type have been fully worked out; while those of nearly all the other existing types of Ungulate mammals and of the Carnivora have been nearly as closely followed through the Tertiary deposits; the gradations between birds and reptiles have been traced; and the modifications undergone by the Crocodilia, from the Triassic epoch to the present day, have been demonstrated. On the evidence of palaeontology, the evolution of many existing forms of animal life from their predecessors is no longer an hypothesis, but an historical fact; it is only the nature of the physiological factors to which that evolution is due which is still open to discussion. (τ. π. h.)

II. Evolution in Philosophy. Definition.— The modern biological doctrine of evolution, which regards the higher forms of life as gradually arising out of the lower, owes its chief philosophic significance to the fact that it renders definite and precise one part of a general theory of the world viewed as an orderly succession of events or as a process of becoming. This theory is put forward as an answer to one of the two problems of philosophy conceived as an interpretation of real existence. The first of these problems concerns itself with what may be called the statical aspect of the world, and inquires into the ultimate nature of all reality (matter and mind), viewed as coexistent and apart from time. The second problem treats of the dynamical aspect of the world, and has to do with the process by which the totality of things has come to be what it is, and is still being transformed. It is this latter problem which the various theories of evolution seek to solve.

The most general meaning of evolution may be defined as follows: Evolution includes all theories respecting the origin and order of the world which regard the higher or more complex forms of existence as following and depending on the lower and simple forms, which represent the course of the world as a gradual transition from the indeterminate to the determinate, from the uniform to the varied, and which assume the cause of this process to be immanent in the world itself that is thus transformed. All theories of evolution, properly so called, regard the physical world as a gradual progress from the simple to the complex, look upon the development of organic life as conditioned by that of the inorganic world, and view the course of mental life both of the individual and of the race as correlated with a material process. This definition covers roughly the principal historical systems bearing the name of evolution, as well as others which have hardly as yet been characterized by this title.

It is clear by this definition that we cannot now press the etymological force of the word. Evolution has no doubt often been conceived as an unfolding of something already contained in the original, and this view is still commonly applied to organic evolution both of the individual and.of the species. It will be found that certain metaphysical systems of evolution imply this idea of an unfolding of something existing in germ or at least potentially in the antecedent. On the other hand, the modern doctrine of evolution, with its ideas of elements which combine, and of causation as transformation of energy, does not necessarily imply this notion. It may be remarked that some of the arguments brought against the modern doctrine rest on the fallacious assumption that the word is still used in its etymological sense, and that consequently that which evolves must contain in some shape what is evolved (e.y., inorganic matter must contain life and consciousness).

Evolution is thus almost synonymous with progress, though the latter term is usually confined to processes of development in the moral as distinguished from the physical world. Further, this idea, as Mr Spencer remarks, has rather a subjective than an objective source, since it points to an increased value in existence as judged by our feelings. At the same time, inasmuch as conscious and more particularly human life is looked on by the evolutionist as the highest phase of all development, and since man’s development is said to be au increase in well-being and happiness, we do not greatly err when we speak of evolution as a transition from the lower to the higher, from the worse to the better. Another respect in which the whole process of evolution may be said to be a progress is in its relation to our perceptions as aesthetic spectators, the higher phases of the process being the more varied, the fuller, and the more perfect. Apart from these subjective estimates, evolution is first of all as a whole a progress from the lower to the higher, in the sense that it is a substitution of a complex for a simple type of existence; and it is such a progress, secondly, in the narrow sense of organic development if not in the wider sense of cosmic development, inasmuch as all advance implies a larger measure of adaptation and so of permanence.

Problems solved by Evolution.— The hypothesis of evolution aims at answering a number of questions respecting the becoming or genesis of things. Of these the first is the problem of explaining change, that is to say, of accounting for that incessant process of transformation which the world manifests. The form which this question has commonly taken is, “What is motion, and how does it arise 1” The second inquiry relates to the factor of intelligible order in the world, to the existence of general classes of things, including minds, of universal laws, and finally to that appearance of a rational end towards which things tend. Thirdly, it is necessary to account for the origin of organic beings which appear to be subordinated to different principles from those which control inorganic bodies. Lastly, we have the apparent mystery of a genesis of conscious minds in dependence on physical bodies. These are the principal inquiries which the various theories of evolution aim more or less completely at answering. As a subordinate question, we may mention the meaning of human history, and its relation to physical processes.

Evolution, Creation, and Emanation.— In seeking to answer these questions, the hypothesis of an evolution of the cosmos with all that it contains competes, in part at least, with two other principal doctrines respecting the origin of the world. These are the theory of direct creation by a personal Deity and that of emanation.

It is clear that the doctrine of evolution is directly antagonistic to that of creation. Just as the biological doctrine of the transmutation of species is opposed to that of special creations, so the idea of evolution as applied to the formation of the world as a whole, is opposed to that of a direct creative volition. It substitutes within the ground which it covers the idea of a natural and necessary process for that of an arbitrary volitional process.

The theory of a personal Creator answers the questions enumerated above by referring the form of the world to an act of direct creation. As an extreme doctrine, it views matter as well as form as the product of divine volition; in a modified form, it conceives the Deity as simply fashioning the uncreated material of the world; and in a still more restricted form, it regards the universal laws or forms which are impressed on things as co-eternal with the Deity. Advancing knowledge has gradually limited the sphere of direct creative activity, by referring the present order of the world to the action of secondary causes. Hence this theory only now competes with the hypothesis of evolution at one or two pointe, more especially the production of living forms, the origin of the human mind, and the nature of history,—which last is conceived as somehow controlled by divine action in the shape of Providence. The question how far the doctrine of evolution, in its most extended and elaborate form, absolutely excludes the idea of creative activity need not be dwelt on here. It is sufficient to say that the theory of evolution, by assuming an intelligible and adequate principle of change, simply eliminates the notion of creation from those regions of existence to which it is applied.

The doctrine of emanation, which had its origin in the East, and was developed by the Neoplatouists, Gnostics, and Cabalists, is a philosophic transformation of the idea of an original creation of the world. It regards the world as a product of the divine nature, and so far it is a theory of creation. On the other hand, it conceives of this production as necessary, and analogous rather to a physical than to a moral action. In this respect it agrees with the doctrine of evolution. It further coincides with this doctrine in the recognition of a scale of existence. It differs from this last inasmuch as it reverses the order of evolution, by making the original stage the most perfect and all later stages a succession of degradations. In one respect, the theory of emanation has a curious relation to that of evolution. As we have seen, the process of evolution is from the indeterminate to the determinate. This is often expressed as a progress from the universal to the particular. Thus the primordial matter assumed by the early Greek physicists may be said to be the universal substance out of which particular things arise. The doctrine of emanation again regards the world as a process of particularization. Yet the resemblance bereis more apparent than real. The universal is, as Mr Spencer remarks, a subjective idea; and the general forms, existing ante res, which play so prominent apart in Greek and mediaeval philosophy, do notin the least correspond to the homogeneous matter of the physical evolutionists. The one process is a logical operation, the other a physical. The theory of emanation, which had its source in certain moral and religious ideas, aims first of all at explaining the origin of mental or spiritual existence as an effluence from the divine and absolute spirit. In the next place, it seeks to account for the general laws of the world, for the universal forms of existence, as ideas which emanate from the Deity. By some it was developed into a complete philosophy of the world, in which matter itself is viewed as the lowest emanation from the absolute. In this form it stands in sharp antithesis to the doctrine of evolution, both because the former views the world of particular things and events as essentially unreal and illusory; and because the latter, so far as it goes, looks on matter as eternal, and seeks to explain the general forms of things as we perceive them by help of simpler assumptions. In certain theories known as doctrines of emanation, only mental existence is referred to the absolute source, while matter is viewed as eternal and distinct from the divine nature. In this form the doctrine of emanation approaches, as we shall see, certain forms of the evolution theory.

Forms of Doctrine of Evolution.— Let us now see how the doctrine of evolution deals with the problems of becoming as above defined. And here it becomes necessary to distinguish between different w ays of formulating and interpreting the idea of evolution. The various modes of conceiving and interpreting the idea of a natural evolution of things depend on the answers given to thι¾e principal questions respecting the nature and causes of the process. These are :—I. How far is the process a real objective one? II. What is the nature of that reality which makes the content, so to speak, of the process of evolution? and III. How is the process effected?

I. First of all, very different views may be taken of the reality of the process of becoming, generation, and transformation. On the oneside we have the extreme view of theElea-tics, that there is no such thing as change or individual object, that real being is one and unchangeable, and that what appears like the formation and destruction of things is an illusion of the senses. At the other extreme we have the view that all reality consists in the process of becoming, or selfrealization, and that nothing persists save this law of evolution itself. Between these two extremes there lie a number of intermediate conceptions, as that of a varying and progressive activity, of a persistent force, or of a gradual manifestation of an unchanging substance. The reality of the process is viewed in a peculiar light from the stand-point of modern Subjective Idealism, which regards time as nothing but a mental form. It is to be added that the process of cosmic evolution may present different degrees of reality. Thus to the ancient atomists the real part of the process is the combination of atoms. There is no absolute generation or destruction of things. Further, the evolution of the world of sensible qualities (colour, <tc.) of things, is illusory, and has only a subjective existence in our sensations. The modern scientific doctrine of evolution carries out this view of its reality, both by its conception of the material world as objectively real only in its forces and movements, and by its doctrine of the conservation of energy, which teaches that amid all change and transformation there is something (though not necessarily a metaphysical thing) which persists.

II. Secondly, the view of evolution will vary according to the conception of that substance or real thing which enters into the process and constitutes its essential content. We have said that the problems of being and becoming (esse and fieri) are distinct, yet they cannot be discussed in perfect isolation. More particularly our idea of becoming must be determined by our notion of that existing reality which underlies the process.

It follows from our definition of evolution that its main problem is to conceive of material and mental development in their mutual relation. There are various ways of effecting this result First of all, the material and the mental may be regarded from a dualistic point of view as perfectly distinct kinds of reality. According to this view, physical evolution as taking place in the inorganic world, and mental evolution as unfolded in man’s history, are two unconnected processes. Further, the fact of their correlation in organic development must either be left unexplained altogether, or can only be referred to the arbitrary action of some supernatural power.

Opposed to this dualistic conception of reality there are the monistic conceptions, which conceive of all parts of the process of evolution as homogeneous and identical. Of these the first is the materialistic, which assumes but one substance, and regards mind as but a property or particular manifestation of matter. On this view, mental evolution is simply one phase of material, and the whole course of cosmic evolution may be described as a production of mind out of matter.

The next monistic conception is the spiritualistic, which assumes but one substance—mind, and resolves the reality of the material world into a spiritual principle. According to this way of looking at the world-process, material and mental evolution are but two continuous phases of one spiritual movement. From the operation of inanimate nature up to human history it is the same spiritual reality which manifests itself.

Finally, there is the monistic conception in the narrow modern sense, viz., that which views the material and the mental as two sides of one and the same reality. Accord ing to this view, physical evolution as manifested in the material world, and mental evolution as seen in human life, may each be regarded as a two-sided process. The first is simply that part of the process in which the material side is most conspicuous; the second, that in which the mental side is so. This monistic conception shows itself in a number of forms,—from the crude semi-mythological conception of a cosmic organism or world-animal, which is at once body and soul, up to the metaphysical doctrine of one substance with two attributes.

III. In the third place, the form of the doctrine of evolution will vary according to the conception of the force or activity which effects the process. This point, though closely related to the last, is not identical with it. It is one thing to understand what it is that evolves itself, another thing to comprehend how the process is brought about. The latter point is of even greater importance for studying the various theories of evolution than the former.

There are two strongly contrasted modes of viewing all action or change. The first is drawn from the region of physical events, and views the change as conditioned by antecedents or efficient causes. This way of looking at change gives the mechanical view of evolution. The second is drawn from the region of our conscious volitions regarded as themselves undetermined by antecedent causes, and conceives of change as related to and determined by some end or purpose. This gives the teleological view of evolution. Although there is a natural affinity between the mechanical and the materialistic conception of evolution on the one side, and between the teleological and the spiritualistic on the other, they are not exactly co-extensive. The teleological view does no doubt imply the acceptance of a spiritual or quasi-spiritual principle; it refers the form and order of the world to the action of an intelligence (conscious or unconscious) which combines particular events as means to some comprehensive end. The mechanical view, on the other hand, does not necessarily imply the acceptance of a material principle as the one reality. It is applicable to mind as well as to body. Thus, on the determinist theory, mental development is as much a mechanical process as physical development.

Adopting this distinction between the mechanical and teleological conception of evolution as the essential one, we may roughly classify the various systems of evolution under the three heads :— (a), those in which the mechanical view predominates; (δ), those in which the teleological view predominates; and (c), those in which the two views are combined in some larger conception.

(a) The mechanical interpretation may first of all be combined with a dualistic theory. Such would be Descartes’s doctrine of evolution if it had been fully worked out on its mental side. It has been observed, however, that the mechanical view is naturally allied to the materialistic theory. Systems of evolution which arise out of this combination seek to resolve all appearance of order and purpose in the physical world into the combined effect of elementary forces or actions. They adopt a mechanical conception of organic bodies and their processes. Finally, they regard mental life and its evolution as a process of combination exactly analogous to that of physical evolution and closely correlated with a certain mode of this process. In this way they lead to a materialistic conception of man’s origin and development as conditioned by physical circumstances and organic changes.

This thorough-going materialistic way of viewing the origin and formation of the world finds its greatest obstacle in the genesis of conscious life. Hence it has from the earliest been modified in one or two ways so as to provide a primordial source of sensation and thought, without, however, abandoning a strictly mechanical view of the process. The first and crude form in which this modification presents itself is that of an original, thin, quasi-material substance (as ether), which may serve as the raw material, so to speak, of individual minds. The formation of these minds, however, is regarded as a strictly mechanical process, and related to that of physical evolution in t.ιe narrow sense. This theory of the origin of mental existence clearly approaches one of the forms of the doctrine of emanation already referred to. We have only to conceive of the primordial mental substance as the infinite being, transcending our finite world, and the doctrine becomes one of emanation. The second modification of this view consists in the theory that all parts of matter are endowed with sensibility, but that the sensations are not themselves (as teleological factors) the productive force in the process, but are rather the appendages of the real factors. The world forms itself according to strictly mechanical laws of combination, and the evolution of the various grades of mind in the organic region takes place by a composition of elementary feelings exactly similar to the process of material combination.

Before leaving the systems which are based on the mechanical view, a bare allusion must be made to a recent suggestion that all things consist ultimately of mental substance (“mind-stuff”), which combines itself both in the material world and in the region of conscious mind according to strictly mechanical principles.

(ό) The second mode of viewing the process of evolution subordinates the idea of physical cause to that of final cause. The force which effects the continual production and transformation of things is conceived of more or less distinctly after the analogy of a rational impulse towards an end, and the process is regarded as determined or conditioned by this element of purpose.

This teleological view of evolution may be found in a number of systems of nature, which look on the material world as at once bodily and vital or spiritual, though it is often difficult to say whether any particular system should be called dualistic or monistic (in the narrow sense). Thus we have the evolution of the physical world referred to a vital principle which pervades all matter, and of which the essential nature is productivity, to a formative plastic principle which moulds the dead material into various shapes, to an organizing cosmic force, and so on. In all these conceptions, which appear to aim more especially at an explanation of organic forms and life, the element of purpose appears in a nascent shape. Nature is personified as a worker who aims unconsciously and instinctively at some dimly descried end, such as the most various production, the progressive manifestation of life, and so on. In some of these systems, notably in the Aristotelian, the genesis of conscious mind is explained along with that of organic life by means of the supposition that mind is but the formative principle of the individual organism.

The idea of purpose becomes more definite, and, at the same time, a further step is taken towards the explanation of mental life as a development out of physical, in those systems which project a distinct spiritual principle into nature. The way in which this is frequently done is by means of the theory of a world-soul which animates the whole of the material world and directs all parts of its evolution. When this spiritual principle is regarded not only as the formative force, but also as the substantial source of conscious mental life, which has eternally coexisted, with matter, we have, as already remarked, a pantheistic conception of evolution which, like another and cognate conception already referred to, approximates to one form of the emanation theory.

The full development of this way of regarding the world ana its evolution as the work of a spiritual principle aiming towards an end is to be found in certain doctrines of Objective Idealism, which resolve all material existence into a mode of mental existence—will and thought. These theories clearly simplify the conception of evolution to the utmost, by the identification both of the substantial reality which enters into all parts of the world-process, and of the rationale of all parts of the process itself. In the systems now referred to, the mechanical idea is wholly taken up into the teleological. Purpose is the highest law of things, and it is one purpose which manifests itself through all stages of the world’s evolution,—in the region of inorganic nature, of organic life, and of human history. The first genesis of conscious life is explained as a particular moment in this process. In some spiritualistic systems an attempt is made to combine the mechanical (causal) and teleological ideas under the notion of logical development. Yet as a rule the teleological way of conceiving the process predominates.

(c) The systems which seek to combine the teleological and the mechanical view of evolution are for the most part based on the monistic idea that the material and the mental are two equally real aspects of one thing. It is clear that this conception of reality provides a way of doing justice to both modes of looking at evolution. In this manner the systems now spoken of are able to regard all parts of evolution as identical in nature, being alike links in a chain of purposeful effects.

This way of regarding the world in its process of evolution will vary according to the particular view of the one reality underlying material and mental phenomena. Thus we may have a universalistic conception of evolution as the two-sided activity of one undivided substance. This idea passes easily into a pantheistic view of the worldprocess as determined by a divine reason which is also the principle of necessity. In the second place, we may have an individualistic conception of this two-sided process, according to which the world arises out of the unceasing activity of an indefinite number of elements endowed with motion and sensation, and so comprehending a mechanical and a teleological factor. It has already been remarked, however, that this conception may be combined with a strictly mechanical view of evolution.

History of the Idea of Evolution.— The doctrine of evolution in its finished and definite form is a modern product. It required for its formation an amount of scientific knowledge which could only be very gradually acquired. It is vain, therefore, to look for clearly defined and systematic presentations of the idea among ancient writers. On the other hand, nearly all systems of philosophy have discussed the problems underlying evolution. Such questions as the origin of the cosmos as a whole, the production of organic beings and of conscious minds, and the meaning of the observable grades of creation, have from the dawn of speculation occupied men’s minds; and the answers to these questions often imply a vague recognition of the idea of a gradual evolution of things. Accordingly, in tracing the antecedents of the modern philosophic doctrine we shall have to glance at most of the principal systems of cosmology, ancient and modern. Yet since in these systems the two inquiries into the esse and fieri of the world are rarely distinguished with any precision, it will be necessary to indicate very briefly the general outlines of the system so far as they are necessary for understanding their bearing on the problems of evolution.

Mythological Interpretation.— The problem of the origin of the world was the first to engage man’s speculative activity. Nor was this line of inquiry pursued simply as a step in the more practical problem of man’s final destiny, The order of ideas observable in children suggests the reflection that man began to discuss the “whence” of existence before the “whither.” At first, as in the case of the child, the problem of the genesis of things was conceived anthropomorphically: the question “How did the world arise Δ first shaped itself to the human mind under the form “Who made the world Δ As long as the problem was conceived in this simple manner there was, of course, no room for the idea of a necessary self-conditioned evolution. Yet the first indistiuct germ of such an idea appears to emerge in combination with that of creation in some of the ancient systems of theogony. (See article Cosmogony.) Thus, for example, in the myth of the ancient Parsees, the gods Ormuz and Ahriman are said to evolve themselves out of a primordial matter. It may be supposed that these crude fancies embody a dim recognition of the physical forces and objects personified under the forms of deities, and a rude attempt to account for their genesis as a natural process. These first unscientific ideas of a genesis of the permanent objects of nature took as their pattern the process of organic reproduction and development, and this, not only because these objects were regarded as personalities, but also because this particular mode of becoming would most impress these early observers. This same way of looking at the origin of the material world is illustrated in the Egyptian notion of a cosmic egg out of which issues the god (Phta) who creates the world.

Indian Philosophy.— Passing from mythology to speculation properly so called, w e find in the early systems of philosophy of India theories of emanation which approach in some respects the idea of evolution. Brahma is conceived as the eternal self-existent being, which on its material side unfolds itself to the world by gradually condensing itself to material objects through the gradations of ether, fire, water, earth, and the elements. At the same time this eternal being is conceived as the all-embracing worldsoul from which emanates the hierarchy of individual souls. In the later system of emanation of Sankhja there is a more marked approach to a materialistic doctrine of evolution. If, we are told, we follow the chain of causes far enough back we reach unlimited eternal creative nature or matter. Out of this “principal thing” or “original nature” all material and spiritual existence issues, and into it will return. Yet this primordial creative nature is endowed with volition with regard to its own development. Its first emanation as plastic nature contains the original soul or deity out of which all individual souls issue.

Early Greek Physicists.— Passing by Buddhism, which, though teaching the periodic destruction of our world by fire, &c., does not seek to determine the ultimate origin of the cosmos, we come to those early Greek physical philosophers who distinctly set themselves to eliminate the idea of divine interference with the world by representing its origin and changes as a natural process. The early Ionian physicists, including Thales, Anaximander, and Anaximenes, seek to explain the world as generated out of a primordial matter which is at the same time the universal support of things. This substance is endowed with a generative or transmutative force by virtue of which it passes into a succession of forms. They thus resemble modern evolutionists, since they regard the world with its infinite variety of forms as issuing from a simple mode of matter. More especially the cosmology of Anaximander resembles the modern doctrine of evolution in its conception of the indeterminate (to απfψοv) out of which the particular forms of the cosmos are differentiated. Again, Anaximander may be said to prepare the way for more modern conceptions of material evolution by regarding his primordial substance as eternal, and by looking on all generation as alternating with destruction, each step of the process being of course simply a transformation of the indestructible substance. Once more, the notion that this indeterminate body contains potentially in itself the fundamental contraries—hot, cold, etc.,—by the excretion or evolution of which definite substances were generated, is clearly a forecasting of that antithesis of potentiality and actuality which from Aristotle downwards has been made the basis of so many theories of development. In conclusion, it is noteworthy that though resorting to utterly fanciful hypotheses respecting the order of the development of the world, Anaximander agrees with modern evolutionists in conceiving the heavenly bodies as arising out of an aggregation of diffused matter, and in assigning to organic life an origin in the inorganic materials of the primitive earth (pristine mud). The doctrine of Anaximenes, who unites the conceptions of a determinate and indeterminate original substance adopted by Thales and Anaximander in the hypothesis of a primordial and all generating air, is a clear advance on these theories, inasmuch as it introduces the scientific idea of condensation and rarefaction as the great generating or transforming agencies. For the rest, his theory is chiefly important as emphasizing the vital character of the original substance. The primordial air is conceived as animated. Anaximenes seems to have inclined to a view of cosmic evolution as throughout involving a quasi-spiritual factor. This idea of the air as the original principle and source of life and intelligence is much more clearly expressed by a later writer, Diogenes of Apollonia. Diogenes made this conception of a vital and intelligent air the ground of a teleological view of climatic and atmospheric phenomena. It is noteworthy that he sought to establish the identity of organic and inorganic matter by help of the facts of vegetal and animal nutrition. Diogenes distinctly taught that the world is of finite duration, and will be renewed out of the primitive substance.

Pythagoreans. —We may pass by that curious mode of conceiving the world as a development out of numbers regarded as active principles which was adopted by the Pythagoreans, since it is too remote from modern conceptions of cosmic evolution. Eleatics.— The Eleatics, Xenophanes, Parmenides, and Zeno need to be referred to here simply on the ground of their denial of all plurality and individuality in objects and of any real process of change, development, or transformation in the world. It may be added, however, that both Xenophanes and Parmenides have their way of regarding the origin of the cosmos and of animal and human life, though these conjectures are put forward as matters of “opinion,” having to do with the illusory impressions of the senses only.

Heraclitus.— The next Greek thinker, Heraclitus, deserves a prominent place in a history of the idea of evolution. This writer distinctly sides with the Ionian physicists, as against the Eleatics, by asserting the reality of motion, change, and generation. He differs from the former, as Grote observes, by regarding the problem of change rather as one of ontology than of physics. Heraclitus conceives of the incessant process of flux in which all things are involved as consisting of two sides or moments—generation and decay—which are regarded as a confluence of opposite streams. In thus making transition or change, viewed as the identity of existence and nonexistence the leading idea of his system, Heraclitus anticipated in some measure Hegel’s peculiar doctrine of evolution as a dialectic process.Tβ' s * S ^ ,rou ^^ 0u ^ ^ , ∙ L ass ≡∙lle, Die Philosophie Herαkleitοs, ] At the same time, we may find expressed in figurative language the germs of thoughts which enter into still newer doctrines of evolution. For example, the notion of conflict (πόλεμος) as the father of all things and of harmony as arising out of a union of discords, and again of an endeavour by individual things to maintain themselves in permanence against the universal process of destruction and renovation, cannot but remind one of certain fundamental ideas in Mr Darwin’s theory of evolution. According to Grote, it is doubtful how far Heraclitus intended to supply by his idea of fire a physical, as distinguished from a metaphysical, doctrine of the worldprocess.

Empedocles.— Empedocles took an important step in the direction of modern conceptions of physical evolution by teaching that all things arise, not by transformations of some primitive form of matter, but by various combinations of a number of permanent elements. Further, by maintaining that the elements are continually being combined and separated by the two forces love and hatred, which appear to represent in a figurative way the physical forces of attraction and repulsion, Empedocles may be said to have made a considerable advance in the construction of the idea of evolution as a strictly mechanical process. It may be observed, too, that the hypothesis of a primitive compact mass (sphcerus), in which love (attraction) is supreme, has some curious points of similarity to, and contrast with, that notion of a primitive nebulous matter with which the modern doctrine of cosmic evolution usually sets out. Empedocles tries to explain the genesis of organic beings, and, according to Lange, anticipates the idea of Mr Darwin that adaptations abound, because it is their nature to perpetuate themselves. He further recognizes a progress in the production of vegetable and animal forms, though this part of his theory is essentially crude and unscientific. More important in relation to the modern problems of evolution is his thoroughly materialistic way of explaining the origin of sensation and knowledge by help of his peculiar hypothesis of effluvia and pores. The supposition that sensation thus rests on a material process of absorption from external bodies naturally led up to the idea that plants and even inorganic substances are pre-cipient, and so to an indistinct recognition of organic life as a scale of intelligence.

Anaxagoras.— The doctrine of Homoemeries, propounded by Anaxagoras, agrees with that of Empedocles in assigning the origin of things to combinations and redistributions of certain primordial forms of matter. Yet these are less simple than the elements of the other thinker. Moreover, the idea that the diversity of things arises from a preponderance of certain elements, and not from the mere fact of various combination, removes the theory of Anaxagoras further from modern conceptions of cosmic evolution tnan that of Empedocles. According to Grote’s interpretation, Anaxagoras, in his conception of nous as the originator of movement and order which manifests itself as the vital principle in plants as well as in animals and man, would appear to lean rather to a monistic and purely materialistic than to a dualistic conception of evolution.

Atσmists. — In the theory of Atomism taught by Leucippus and Democritus we have the basis of the modern mechanical conceptions of cosmic evolution. Here the endless harmonious diversity of our cosmos, as well as of other worlds supposed to co-exist with our own, is said to arise through the various combination of indivisible material elements differing in figure and magnitude only. The force which brings the atoms together in the forms of objects is inherent in the elements, and all their motions are necessary. The origin of things, which is also their substance, is thus laid in the simplest and most homogeneous elements or principles. The real world thus arising consists only of diverse combinations of atoms, having the properties of magnitude, figure, weight, and hardness, all other qualities being relative only to the sentient organism. The problem of the genesis of mind is practically solved by identifying the soul, or vital principle, with heat or fire which pervades in unequal proportions, not only man and animals, but plants and nature as a whole, and through the agitation of which by incoming effluvia all sensation arises.

The Sophists— Critias. — Of the Sophists there is but one whose doctrine need concern us here, namely, Critias. In a fragment of his writings we meet with a speculation on the past development of man, which is curious as distinctly recognizing the upward direction of human history, and so as contrasting with the prevailing view of this history as a gradual deterioration. Critias tells us there was a time when the life of man was lawless (άτακτος) and beast-like (θηριώόης), when he was a slave of force, and when no honour was paid to the good nor punishment administered to the bad. Laws having arisen, evil actions which could no longer be done overtly were still practised in secret, and at this stage a wise man arose who sought to instil terror into the minds of the people, and so conceived the Deity, who is made the more terrible by being localized in the region whence proceed thunder and lightning.

Plato.— Plato needs to be referred to here only because of the strongly marked opposition of his philosophy to the teaching of evolution. It is true (as Zeller remarks) that Plato’s whole philosophy was directed less to the explanation of becoming than to the consideration of being. So far, however, as the highly mythical cosmology of the Timoeus may be taken as indicating Plato’s way of looking at the successive order of the world, we see that it widely deviates from that of the evolutionist. Thus the notion of the Demiurgus is distinctly contradictory of the idea of a natural process of evolution. Again, the supposition that the world of particular things is somehow determined by pre-existing universal ideas lends itself rather to a theory of emanation as a descent from the more perfect to the less perfect than to a doctrine of evolution. It became the basis of that doctrine of universal essences or types which for ages interfered with a scientific explanation of organic forms. Again Plato exactly reverses the order of evolution in his way of looking at the scale of organic beings and souls, since he sets out with the highest and most perfect, the divine cosmos, and passes downwards to man and the lower animals viewed as successive degradations.

Early Platonists.— Among the early followers of Plato, Speusippus deserves mention here in so far as he assimilated the course of the world to the development of the individual by regarding it as a progress from imperfection to perfection. Xenocrates again appears to have viewed the whole of the cosmos as a graduated scale of animate existence.

Aristotle.— Aristotle is much nearer a conception of evolution than his master. It is true he sets out with a transcendent Deity, and follows Plato in viewing the creation of the cosmos as a process of descent from the more to the less perfect according to the distance from the original self-moving agency. Yet on the whole Aristotle leaus to a teleological theory of evolution, which he interprets dualistually by means of certain metaphysical distinctions. Thus even his idea of the relatiou of the divine activity to the world shows, as Zeller and Lange remark, a tendency to a pantheistic notion of a divine thought which gradually realizes itself in the process of becoming. Aristotle’s distinction of form and matter, and his conception of becoming as a transition from actuality to potentiality, provides a new ontological way of conceiving the process of material and organic evolution. To Aristotle the whole of nature is instinct with a vital impulse towards some higher manifestation. Organic life presents itself to him as a progressive scale of complexity determined by its final end, namely, man. In some respects Aristotle approaches the modern view of evolution. Thus, though he looked on species as fixed, being the realization of an unchanging formative principle (φυσις), he seems, as Ueberweg observes, to have inclined to entertain the possibility of a spontaneous generation in the case of the lowest organisms. Aristotle’s teleological conception of organic evolution often approaches modern mechanical conceptions. Thus he says that nature fashions organs in the order of their necessity, the first being those essential to life. So, too, in his psychology he speaks of the several degrees of mind as arising according to a progressive necessity. In his view of touch and taste, as the two fundamental and essential senses, he may remind one of Mr Spencer’s doctrine. At the same time Aristotle precludes the idea of a natural development of the mental series by the supposition that man contains, over and above a natural finite soul inseparable from the body, a substantial and eternal principle (νουs) which enters into the individual from without. Aristotle’s brief suggestions respecting the origin of society and governments in the Politics show a leaning to a naturalistic interpretation of human history as a development conditioned by growing necessities.

Strato.— Of Aristotle’s immediate successors one deserves to be noticed here, namely, Strato of Lampsacus, who developed his master’s cosmology into a system of naturalism. Strato appears to reject Aristotle’s idea of an original source of movement and life extraneous to the world in favour of an immanent principle. All parts of matter have an inward plastic life whereby they can fashion themselves to the best advantage, according to their capability, though not with consciousness.

The Stoics.— In the cosmology of the Stoics we have the germ of a monistic and pantheistic conception of evolution. All things are said to be developed out of an original being, which is at once material (fire) and spiritual (the Deity), and in turn they will dissolve back into this primordial source. At the same time the world as a developed whole is regarded as an organism which is permeated with the divine Spirit, and so we may say that the world-process is a self-realization of the divine Being. The formative principle or force of the world is said to contain the several rational germinal forms of things. Individual things are supposed to arise out of the original being, as animals and plants out of seeds. Individual souls are an efflux from the all-compassing world-soul. The necessity in the world’s order is regarded by the Stoics as identical with the divine reason, aud this idea is used as the basis of a teleological and optimistic view of nature. Very curious, in relation to modern evolutional ideas, is the Stoical doctrine that our world is but one of a series of exactly identical ones, all of which are destined to be burnt up and destroyed.

The Epicureans—Lucretius.— The Epicureans differed from the Stoics by adopting a purely mechanical view of the world-process. Their fundamental conception is that of Democritus; they seek to account for the formation of the cosmos, with its order and regularity, by setting out with the idea of an original (vertical) motion of the atoms, which somehow or other results in movements towards and from one another. Our world is but one of an infinite number of others, and all the harmonies and adaptations of the universe are regarded as a special case of the infinite possibilities of mechanical events. Lucretius regards the primitive atoms (first beginnings or first bodies) as seeds out of which individual things are developed. All living and sentient things are formed out of insentient atoms (e.y., worms spring out of dung). The peculiarity of organic and sentient bodies is due to the minuteness and shape of their particles, and to their special motions and combinations. So, too, mind consists but of extremely fine particles of matter, and dissolves into air when the body dies. Lucretius traces, in the fifth book of his poem, the progressive genesis of vegetal and animal forms out of the mother-earth. He vaguely anticipates the modern idea of the world as a survival of the fittest when he says that many races may have lived aud died out, and that those which still exist have been protected either by craft, courage, or speed. Lucretius touches on the development of man out of a primitive, hardy, beast-like condition. Pregnant hints are given respecting a natural development of language which has its germs in sounds of quadrupeds and birds, of religious ideas out of dreams and waking hallucinations, and of the art of music by help of the suggestion of natural sounds. Lucretius thus recognizes the whole range of existence to which the doctrine of evolution may be applied.

Neo-Platonisls.— In the doctrines of the Neo-Platonists, of whom Plotinus is the most important, we have the worldprocess represented after the example of Plato as a series of descending steps, each being less perfect than its predecessors, since it is further removed from the first cause. The system of Plotinus, Zeller remarks, is not strictly speaking one of emanation, since there is no communication of the divine essence to the created world; yet it resembles emanation inasmuch as the genesis of the world is conceived as a necessary physical effect, and not as the result of volition. In Proclus we find this conception of an emanation of the world out of the Deity, or the absolute, made more exact, the process being regarded as threefold—(1) persistence of cause in effect, (2) the departure of effect from cause, and (3) the tendency of effect to revert to its cause.

The Fathers.— The speculations of the fathers respecting the origin and courso of the world seek to combine Christian ideas of the Deity with doctrines of Greek philosophy. The common idea of the origin of things is that of an absolute creation of matter and mind alike. The course of human history is regarded by those writers who are most concerned to refute Judaism as a progressive divine education. Among the Gnostics we meet with the hypothesis of emanation, as, for example, in the curious cosmic theory of Valentinus.

Middle Ages—Early Schoolmen.— In the speculative writings of the Middle Ages, including those of the schoolmen, we find no progress towards a more accurate and scientific view of nature. The cosmology of this period consists for the most part of the Aristotelian teleological view of nature combined with the Christian idea of the Deity and His relation to the world. In certain writers, however, there appears a more elaborate transformation of the doctrine of creation into a system of emanation. According to John Scotus Erigena, the nothing out of which the world is created is the divine esseuce. Creation is the act by which God passes through the primordial causes, or universal ideas, into the region of particular things (processio), in order finally to return to himself (reversio). The transition from the universal to the particular is of course conceived as a descent or degradation. A similar doctrine of emanation is to be found in the writings of Bernhard of Chartres, who conceives the process of the unfolding of the world as a movement in a circle from the most general to the individual, and from this back to the most general. This movement is said to go forth from God to the animated heaven, stars, visible world, and man, which represent decreasing degrees of coguition.

Arab Philosophers.— Elaborate doctrines of emanation, largely based on Neo-Platonic ideas, are also propounded by some of the Arabic philosophers, as by Alfarabi and Avicenna. The leading thought is that of a descending series of intelligences, each emanating from its predecessor, and having its appropriate region in the universe.

Jewish Philosophy.— In the Jewish speculations of the Middle Ages may be found curious forms of the doctrine of emanations, uniting the Biblical idea of creation with elements drawn from the Persians and the Greeks. In the later and developed form of the Cabala, the origin of the world is represented as a gradually descending emanation of the lower out of the higher. Among the philosophic Jews, the Spanish Avicebron, in his Fons Vitee, expounds a curious doctrine of emanation. Here the divine will is viewed as an efflux from the divine wisdom, as the intermediate link between God, the first substance and all things, and as the fountain out of which all forms emanate. At the same time all forms, including the higher intelligible ones, are said to have their existence only in matter. Matter is the one universal substance, body and mind being merely specifications of this. Thus Avicebron approaches, as M. Munk observes, a pantheistic conception of the world, though he distinctly denies both matter and form to God.

Later Scholastics.— Passing now to the later schoolmen, a bare mention must be made of Thomas, who elaborately argues for the absolute creation of the world out of nothing, and of Albertus Magnus, who reasons against the Aristotelian idea of the past eternity of the world. More importance attaches to Duns Scotus, who brings prominently forward the idea of a progressive development in nature by means of a process of determination. The original substance of the world is the materia primo-prima, which is the immediate creation of the Deity. This serves Duns Scotus as the most universal basis of existence, all angels ιavmg material bodies. This matter is differentiated into particular things (which are not privations but perfections) through the addition of an individualizing principle (hoecceitas) to the universal (quidditas). The whole world is represented by the figure of a tree, of which the seeds and roots are the first indeterminate matter, the leaves the accidents, the twigs and branches corruptible creatures, the blossoms the rational soul, and the fruit pure spirits or angels. It is also described as a bifurcation of two twigs, mental and bodily creation out of a common root. One might almost say that Duns Scotus recognizes the principle of a gradual physical evolution, only that he chooses to represent the mechanism by which the process is brought about by means of quaint scholastic fictions.

Revival of Learning.— The period of the revival of learning, which was also that of a renewed study of nature, is marked by a considerable amount of speculation respecting the origin of the universe. In some of these we see a return to Greek theories, though the influence of physical discoveries, more especially those of Copernicus, Kepler, and Galileo, is distinctly traceable.

Telesio.— An example of a return to early Greek speculation is to be met with in Bernardino Telesio. By this writer the world is explained as a product of three principles,—dead matter, and two active forces, heat and cold. Terrestrial things arise through a confluence of heat, which issues from the heavens, and cold, which comes from the earth. Both principles have sensibility, and thus all products of their collision are sentient, that is, feel pleasure and pain. The superiority of animals to plants and metals in the possession of special organs of sense is connected with the greater complexity and heterogeneity of their structure.

Giordano Bruno.— In the system of Giordano Bruno, who sought to construct a philosophy of nature on the basis of new scientific ideas, more particularly the doctrine of Copernicus, we find the outlines of a theory of cosmic evolution conceived as an essentially vital process. Matter and form are here identified, and the evolution of the world is presented as the unfolding of the world-spirit to its perfect forms according to the plastic substratum (matter) which is but one of its sides. This process of change is conceived as a transformation, in appearance only, of the real unchanging substance (matter and form). All parts of matter are capable of developing into all forms; thus the materials of the table and chair may, under proper circumstances, be developed to the life of the plant or of the animal. The elementary parts of existence are the minima, or monads, which are at once material and mental. On their material side they are not absolutely unextended, but spherical. Bruno looked on our solar system as but one out of an infinite number of worlds. His theory of evolution is essentially pantheistic, and he does not employ his hypothesis of monads in order to work out a more mechanical conception.

Campanella.— A word must be given to one of Bruno’s contemporary compatriots, namely Campanella, who gave poetic expression to that system of universal vitalism which Bruno developed. He argues, from the principle quie-quid est in effectibus esse et in causis, that the elements and the whole world have sensation, and thus he appears to derive the organic part of nature out of the so-called “inorganic.”

Boehme.— Another writer of this transition period deserves a passing reference here, namely, Jacob Boehme the mystic, who by his conception of a process of inner diremption as the essential character of all mind, and so of God, prepared the way for later German theories of the origin of the world as the self-differentiation and self-externalization of the absolute spirit.

Hobbes and Gassendi.— The influence of an advancing study of nature, which was stimulated if not guided by Bacon’s writings, is seen in the more careful doctrines of materialism worked out almost simultaneously by Hobbes and Gassendi. These theories, however, contain little that bears directly on the hypothesis of a natural evolution of things. In the view of Hobbes, the difficulty of the genesis of conscious minds is solved by saying that sensation and thought are part of the reaction of the organism on external movement. Yet Hobbes appears (as Clarke points out) to have vaguely felt the difficulty; and in a passage of his Physics (chap. 25, sect. 5) he says that the universal existence of sensation in matter cannot be disproved, though he shows that when there are no organic arrangements the mental side of the movement (phantasma) is evanescent. The theory of the origin of society put forth by Hobbes, though directly opposed in most respects to modern ideas of social evolution, deserves mention here by reason of its enforcing that principle of struggle (bellum omnium contra omnes) which has played so conspicuous a part in recent doctrines of evolution. Gassendi, with some deviations, follows Epicurus in his theory of the formation of the world. The world consists of a finite number of atoms, which have in their own nature a self-moving force or principle. These atoms, which are the seeds of all things, are, however, not eternal but created by God. Gassendi distinctly argues against the existence of a worldsoul or a principle of life in nature.

Descartes. —In the philosophy of Descartes we meet with a dualism of mind and matter which does not easily lend itself to the conception of evolution. His doctrine that consciousness is confined to man, the lower animals being unconscious machines (automata), excludes all idea of a progressive development of mind. Yet Descartes, in his Principia Philosophia, laid the foundation of the modern mechanical conception of nature and of physical evolution. In the third part of this work he inclines to a thoroughly natural hypothesis respecting the genesis of the physical world, and adds in the fourth part that the same kind of explanation might be applied to the nature and formation of plants and animals. He is indeed careful to keep right with the orthodox doctrine of creation by saying that he does not believe the world actually arose in this mechanical way out of the three kinds of elements which he here supposes, but that he simply puts out his hypothesis as a mode of conceiving how it might have arisen. Descartes’s account of the mind and its passions is thoroughly materialistic, and to this extent he works in the direction of a materialistic explanation of the origin of mental life.

Spinoza.— In Spinoza’s pantheistic theory of the world, which regards thought and extension as but two sides of one substance, the problem of becoming is submerged in that of being. Although Spinoza’s theory attributes a mental side to all physical events, he rejects all teleological conceptions ami explains the order of things as the result of an inherent necessity. He recognizes gradations of things according to the degree of complexity of their movements and that of their conceptions. To Spinoza (as Kuno Fischer observes) man differs from the rest of nature in the degree only and not in the kind of his powers. So far Spinoza approaches the conception of eVolution. He may be said to furnish a further contribution to a metaphysical conception of evolution in his view of all finite individual things as the infinite variety to which the unlimited productive power of the universal substance gives birth. Mr F. Pollock has taken pains to show in more than one essay how nearly Spinoza approaches certain ideas contained in the modern doctrine of evolution, as for example that of self-preservation as the determining force in things.

Cudworth.— One or two English writers belonging to the latter part of the 17th century must be glanced at here. Of these the first is Cudworth, who, in his work The True. Intellectual System of the Universe, elaborately criticises the various “atheistic” modes of explaining the origin and form of the world as a natural process. Cudworth emphasizes especially the difficulty of explaining the rise of consciousness, and seeks to show how the early Greek atomical physiologists were driven to assume a spiritual principle over and above their material elements. He dwells on the signs of purpose in nature, and argues that no fortuitous combination of elements could have sufficed to produce that balance of male and female individuals on which the preservation of species depends. Yet though thus an anti-evolutionist, Cudworth provides a way of interpreting the evolution of life by means of an immanent principle, since he refers the forms of nature to a plastic principle, which does not involve consciousness, though it may be called a drowsy unawakened cognition.

Locke.— In Locke we find, with a retention ∩f certain anti-evolutionist ideas, a marked tendency to this mode of viewing the world. To Locke the universe is the result of a direct act of creation, even matter being limited in duration and created. Even if matter were eternal it would, ho thinks, be incapable of producing motion; and if motion is itself conceived as eternal, thought can never begin to be. The first eternal being is thus spiritual or “cogitative,” and contains in itself all the perfections that can ever after exist. He repeatedly insists on the impossibility of senseless matter putting on sense. Yet while thus placing himself at a point of view opposed to that of a gradual evolution of the organic world, Locke prepared the way for this doctrine in more ways than one. First of all, his genetic method as applied to the mind’s ideas—which laid the foundations of English analytical psychology—was a step in the direction of a conception of mental life as a gradual evolution. Again he works towards the same end in his celebrated refutation of the scholastic theory of real specific essences. In this argument he emphasizes the vagueness of the boundaries which mark off organic species with a view to show that these do not correspond to absolutely fixed divisions in the objective world, that they are made by the mind, not by nature. This idea of the continuity of species is developed more fully in a remarkable passage (Essay, bk. iii. ch vi. § 12), where he is arguing in favour of the hypothesis, afterwards elaborated by Leibnitz, of a graduated series of minds (species of spirits) from the Deity down to the lowest animal intelligence. He here observes that “all quite down from us the descent is by easy steps, and a continued series of things, that in each remove differ very little from one another.” Thus man approaches the beasts, and the animal kingdom is nearly joined with the vegetable, and so on down to the lowest and “most inorganical parts of matter.” Finally, it is to be observed that Locke had a singularly clear view of organic arrangements (which of course he explained according to a theistic teleology) as an adaptation to the circumstances of the environment or to “the neighbourhood of the bodies that surround us.” Thus he suggests that man has not eyes of a microscopic delicacy, because he would receive no great advantage from such acute organs, since though adding indefinitely to his speculative knowledge of the physical world they would not practically benefit their possessor (e.g., by enabling him to avoid things at a convenient distance). Idea of Progress in History.— Before leaving the 17th century we must just refer to the writers who laid the foundations of the essentially modern conception of human history as a gradual upward progress. According to Prof. Flint, there were four men who in this century seized and mado prominent this idea, namely, Bodin, Bacon, Descartes, and Pascal. The former distinctly argues against the idea of a deterioration of man in the past. In this way we see that just as advancing natural science was preparing the way for a doctrine of physical evolution, so advancing historical research was leading to the application of a similar idea to the collective human life.

English Writers of the 18i∕r Century—Hume.— The theological discussions which make up so large a part of the English speculation of the last century cannot detain us here. There is, however, one writer who sets forth so clearly the alternative suppositions respecting the origin of the world that he claims a brief notice. We refer to David Hume, In his Dialogues concerning Natural Pe-ligion he puts forwards tentatively, in the person of one of his interlocutors, the ancient hypothesis that since the world resembles an animal or vegetal organism rather thau a machine, it might more easily be accounted for by a process of generation than by an act of creation. Later on he develops the materialistic view of Epicurus, only modifying it so far as to conceive of matter as finite. Since a finite number of particles is only susceptible of finite transpositions, it must happen (he says), in an eternal duration that every possible order or position will be tried an infinite number of times, and hence this world is to be regarded (as the Stoics maintained) as an exact reproduction of previous worlds. The speaker seeks to make intelligible the appearance of art and contrivance in the world as a result of a natural settlement of the universe (which passes through a succession of chaotic conditions) into a stable condition, having a constancy in its forms, yet without its several parts losing their motion and fluctuation.

Priestley.— The English materialists of the latter part of the century did little to work out the idea of evolution. Priestley needs to be mentioned here only by reason of his clear recognition of human progress.

Monboddo.— Of other British writers of the period, Lord Monboddo must be named on account of his curious speculations respecting the origin of man. In his Ancient Metaphysics (vol. iii.), Monboddo conceives man as gradually elevating himself from an animal condition, in which his mind is immersed in matter, to a state in which mind acts independently of body. In his equally voluminous work, The Origin and Progress of Language, Monboddo brings man under the same species as the orang-outang. He traces the gradual elevation of man to the social state, which he conceives as a natural process determined by “the necessities of human life.” He looks on language (which is not “natural” to man in the sense of being necessary to his self-preservation) as a consequence of his social state.

French Writers of the 18th Century.— Let us now pass to the French writers of the last century. Here we are first struck by the results of advancing physical speculation in their bearing on the conception of the world. Careful attempts, based on new scientific truths, are made to explain the genesis of the world as a natural process. Maupertuis, who, together with λ oltaire, introduced the new idea of the universe as based on Newton’s discoveries, sought to account for the origin of organic things by the hypothesis of sentient atoms. Buffon the naturalist speculated, not only on the structure and genesis of organic beings, but also on the course of formation of the earth and solar system, which he conceived after the analogy of the development of organic beings out of seed. Diderot, too, in his varied intellectual. activity, found time to speculate on the genesis of sensation and thought out of a combination of matter endowed with an elementary kind of sentience. De la Mettrie worked out a materialistic doctrine of the origin of things, according to which sensation and consciousness are nothing but a development out of matter. He sought (L , homme-machines to connect man in his original condition with the lower animals, and emphasized (Hhomme-plantd) the essential unity of plan of all living things. Helvetius, in his work on man, referred all differences between our species and the lower animals to certain peculiarities of organization, and so prepared the way for a conception of human development out of lower forms as a process of physical evolution. Charles Bonnet met the difficulty of the origin of conscious beings much in the same way as Leibnitz, by the supposition of eternal minute organic bodies to which are attached immortal souls. Yet though in this way opposing himself to the method of the modern doctrine of evolution, he aided the development of this doctrine by his view of the organic world as an ascending scale from the simple to the complex. Robinet, in his treatise De la Nature, worked out the same conception of a gradation in organic existence, connecting this with a general view of nature as a progress from the lowest inorganic forms of matter up to man. The process is conceived as an infinite series of variations or specifications of one primitive and common type. Man is the chef T oeuvre of nature, which the gradual progression of beings was to have as its last term, and all lower creations are regarded as pre-conditions of man’s existence, since nature “could only realize the human form by combining in all imaginable ways each of the traits which was to enter into it.” The formative force in this process of evolution (or “metamorphosis”) is conceived as an intellectual principle (idee generatrice^. Robinet thus laid the foundation of that view of the world as wholly vital, and as a progressive unfolding of a spiritual formative principle, which was afterwards worked out by Schelling. It is to be added that Robinet adopted a thorough-going materialistic view of the dependence of mind on body, going even to the length of assigning special nerve-fibres to the moral sense. The system of Holbach seeks to provide a consistent materialistic view of the world and its processes. Mental operations are identified with physical movements, the three conditions ot physical movement, inertia, attraction, and repulsion, being in the moral world self-love, love, and hate. He left open the question whether the capability of sensation belongs to all matter, or is confined to the combinations of certain materials. He looked on the actions of the individual organism and of society aβ determined by the needs of selfpreservation. He conceived of man as a product of nature that had gradually developed itself from a low condition, though he relinquished the problem of the exact mode of his first genesis and advance as not soluble by data of experience. Holbach thus worked out the basis of a rigorously materialistic conception of evolution.

The question of human development which Holbach touched on was one which occupied many minds both in and out of France during the past century, and more especially towards its close. The foundations of this theory of history as an upward progress of man out of a barbaric and animal condition were laid by Vico in his celebrated work Principii di Scienza Nuova. In France the doctrine was represented by Turgot and Condorcet.

Of the English writers who discussed the question of man’s development we have already spoken. The German speculations on the subject will be touched on presently.

German Writers of the 18th Century—Leibnitz.— In Leibnitz we find, if not a doctrine of evolution in the strict sense, a theory of the world which is curiously related to the modern doctrine. The chief aim of Leibnitz is no doubt to account for the world in its static aspect as a co-existent whole, to conceive the ultimate reality of things in such a way as to solve the mystery of mind and matter. Ytt by his very mode of solving the problem he is led on to consider the nature of the worldprocess. By placing substantial reality in an infinite number of monads whose essential nature is force or activity, which is conceived as mental (representation), Leibnitz was carried on to the explanation of the successive order of the world. He prepares the way, too, for a doctrine of evolution by his monistic idea of the substantial similarity of all things, inorganic and organic, bodily and spiritual, and still more by his conception of a perfect gradation of existence from the lowest “inanimate” objects, whose essential activity is confused representation, up to the highest organized being—man—with his clear intelligence. Turning now to Leibnitz’s conception of the world as a process, we see first that he supplies, in his notion of the underlying reality as force which is represented as spiritual {quelque chose eV analogique au sentiment et à l ’ appetit), both a mechanical and a teleological explanation of its order. More than this, Leibnitz supposes that the activity of the monads takes the form of a self-evolution. It is the following out of an inherent tendency or impulse to a series of changes, all of which were virtually pre-existent, and this process cannot be interfered with from without. As the individual monad, so the whole system which makes up the world is a gradual development. In this case, however, we cannot say that each step goes out of the other as in that of individual development. Each monad is an original independent being, and is determined to take this particular point in the universe, this place in the scale of beings. We see how different this metaphysical conception is from that scientific notion of cosmic evolution in which the lower stages are the antecedents and conditions of the higher. It is probable that Leibnitz’s notion of time and space, which approaches Kant’s theory, led him to attach but little importance to the successive order of the world. Leibnitz, in fact, presents to us an infinite system of perfectly distinct though parallel developments, which on their mental side assume the aspect of a scale, not through any mutual action, but solely through the determination of the Deity. Even this idea, however, is incomplete, for Leibnitz fails to explain the physical aspect of development. Thus he does not account for the fact that organic beings—which have always existed as preformations (in the case of animals as animaux spermatiques) —come to be developed under given conditions. Yet Leibnitz prepared the way for a new conception of organic evolution. The modern monistic doctrine, that all material things consist of sentient elements, and that consciousness arises through a combination of these, was a natural transformation of Leibnitz’s theory. Lessing.— Of Leibnitz’s immediate followers we may mention Lessing, who in his Education of the Human Pace brought out the truth of the process of gradual development underlying human history, even though he expressed this in a form inconsistent with the idea of a spontaneous evolution.

Herder.— Herder, on the other hand, Lessing’s contemporary, treated the subject of man’s development in a thoroughly naturalistic spirit. In his Ideen sur Philosophie der Geschichte, Herder adopts Leibnitz’s idea of a graduated scale of beings, at the same time conceiving of the lower stages as the conditions of the higher. Thus man is said to be the highest product of nature, and as such to be dependent on all lower products. All material things are assimilated to one another as organic, the vitalizing principle being inherent in all matter. The development of man is explained in connection with that of the earth, and in relation to climatic variations, &c. Man’s mental faculties are viewed as related to his organization, and as developed under the pressure of the necessities of life. Kant.— Kant’s relation to the doctrine of evolution is a many-sided one. In the first place, his peculiar system of subjective idealism, involving the idea that time is but a mental form to which there corresponds nothing in the sphere of noiimenal reality, serves to give a peculiar philosophical interpretation to every doctrine of cosmic evolution. Kant, like Leibnitz, seeks to reconcile the mechanical and teleological views of nature, only he assigns to these different spheres. The order of the inorganic world is explained by properly physical causes. In his Naturgeschichte des Himmels, in which he anticipated the nebular theory afterwards more fully developed by Laplace, Kant sought to explain the genesis of the cosmos as a product of physical forces and laws. The worlds, or systems of worlds, which fill infinite space are continually being formed and destroyed. Chaos passes by a process of evolution into a cosmos, and this again into chaos. So far as the evolution of the solar system is concerned, Kant held these mechanical causes as adequate. For the world as a whole, however, he postulated a beginning in time (whence his use of the word creation), and further supposed that the impulse of organization which was conveyed to chaotic matter by the Creator issued from a central point in the infinite space-spreading gradually outwards. While in his cosmology Kant thus relies on mechanical conceptions, in his treatment of organic life his mind is, on the contrary, dominated by teleological ideas. An organism was to him something controlled by a formative organizing principle. It was natural, therefore, that he rejected the idea of a spontaneous generation of organisms (which was just then being advocated by his friend Forster), not only as unsupported by experience but as an inadequate hypothesis. Experience forbids our excluding organic activity from natural causes, also our excluding intelligence from purposeful (zu'eckthdtigeη) causes; hence experience forbids our defining the fundamental force or first cause out of which living creatures arose. Just as Kant thus sharply marks off the regions of the inorganic and the organic, so he sets man in strong opposition to the lower animals. His ascription to man of a unique faculty, free-will, forbade his conceiving our species as a link in a graduated series of organic developments. In his doctrine of human development he does indeed recognize an early stage of existence in which our species was dominated by sensuous enjoyment and instinct. He further conceives of this stage as itself a process of (natural) development, namely, of the natural disposition of the species to vary in the greatest possible manner so as to preserve its unity through a process of selfadaptation (A «arte«) to climate. This, he says, must not be conceived as resulting from the action of external causes, but is due to a natural disposition {Anlage). From this capability of natural development (which already involves a teleological idea) Kant distinguishes the power of moral self-development or self-liberation from the dominion of nature, the gradual realization of which constitutes human history or progress. This moral development is regarded as a gradual approach to that rational, social, and political state in which will be realized the greatest possible quantity of liberty. Thus Kant, though he appropriated and gave new form to the idea of human progress, conceived of this as wholly distinct from a natural (mechanical) process. In this particular, as in his view of organic actions, Kant distinctly opposed the idea of evolution as one universal process swaying alike the physical and the moral world.

Schelling.— In the earlier writings of Schelling, containing the philosophy of identity, existence is represented as a becoming, or process of evolution. Nature and mind (which are the two sides, or polar directions, of the one absolute) are each viewed as an activity advancing by an uninterrupted succession of stages. The side of this process which Schelling worked out most completely is the negative side, that is, nature. Nature is essentially a process of organic self-evolution. It can only be understood by subordinating the mechanical conception to the vital, by conceiving the world as one organism animated by a spiritual principle or intelligence {Weltseele). From this point of view the processes of nature from the inorganic up to the most complex of the organic become stages in the self-realization of nature. All organic forms are at bottom but one organization, and the inorganic world shows the same· formative activity in various degrees or potences. Schelling conceives of the gradual self-evolution of nature in a succession of higher and higher forms as brought about by a limitation of her infinite productivity, showing itself in a series of points of arrest. The detailed exhibition of the organizing activity of nature in the several processes of the organic and inorganic world rests on a number of fanciful and unscientific ideas. Schelling’s theory is a bold attempt to revitalize nature in the light of growing physical and physiological science, and by so doing to comprehend the unity of the world under the idea of one principle of organic development. His highly figurative language might leave us in doubt how far he conceived the higher stages of this evolution of nature as following the lower in time. In the introduction to his work Von der Weltseele, however, he argues in favour of the possibility of a transmutation of species in periods incommensurable with ours. The evolution of mind (the positive pole) proceeds by way of three stages,—theoretic, practical, and aesthetical activity. Schelling’s later theosophic speculations do not specially concern us here.

Folloτvers of Schelling.— Of the followers of Schelling a word or two must be said. Heinrich Steffens, in his Anthropologie, seeks to trace out the origin and history of man in connexion with a general theory of the development of the earth, and this again as related to the formation of the solar system. All these processes are regarded as a series of manifestations of a vital principle in higher and higher forms. Oken, again, who carries Schelling’s ideas into the region of biological science, seeks to reconstruct the gradual evolution of the material world out of original matter, which is the first immediate appearance of God, or the absolute. This process is an upward one, through the formation of the solar system and of our earth with its inorganic bodies, up to the production of man. The process is essentially a polar linear action, or differentiation from a common centre. By means of this process the bodies of the solar system separate themselves, and the order of cosmic evolution is repeated in that of terrestrial evolution. The organic world (like the world as a whole) arises out of a primitive chaos, namely, the infusorial slime. A somewhat similar working out of Schelling’s idea is to be found in Oersted’s work entitled The Soul in Nature (Eng. trans.). Of later works based on Schelling’s doctrine of evolution mention may be made of the volume entitled Natur und Idee, by G. F. Carus. According to this writer, existence is nothing but a becoming, and matter is simply the momentary product of the process of becoming, while force is this process constantly revealing itself in these products.

Hegel.— Like Schelling, Hegel conceives the problem of existence as one of becoming. He differs from him with respect to the ultimate motive of that process of gradual evolution which reveals itself alike in nature and in mind. With Hegel the absolute is itself a dialectic process which contains within itself a principle of progress from difference to difference and from unity to unity. “This process (Mr Wallace remarks) knows nothing of the distinctions between past and future, because it implies an eternal present.” This conception of an immanent spontaneous evolution is applied alike both to nature and to mind and history. Nature to Hegel is the idea in the form of hetereity; and finding itself here it has to remove this exteriority in a progressive evolution towards an existence for itself in life and mind. Nature (says Zeller) is to Hegel a system of gradations, of which one arises necessarily out of the other, and is the proximate truth of that out of which it results. There are three stadia, or moments, in· this process of nature—(1) the mechanical moment, or matter devoid of individuality; (2) the physical moment, or matter which has particularized itself in bodies—the solar system; and (3) the organic moment, or organic beings, beginning with the geological organism—or the mineral kingdom, plants, and animals. Yet this process of development is not to be conceived as if one stage is naturally produced out of the other, and not even as if the one followed the other in time. Only spirit has a history; in nature all forms are contemporaneous. Hegel’s interpretation of mind and history as a process of evolution has more scientific interest than his conception of nature. His theory of the development of free-will (the objective spirit), which takes its start from Kant’s conception of history, with its three stages of legal right, morality as determined by motive and instinctive goodness {Sittlichheic), might almost as well be expressed in terms of a thoroughly naturalistic doctrine of human development. So, too, some of his conceptions respecting the development of art and religion (the absolute spirit) lend themselves to a similar interpretation. Yet while, in its application to history, Hegel’s theory of evolution has points of resemblance with those doctrines which seek to explain the world-process as one unbroken progress occurring in time, it constitutes on the whole a theory apart and generis. It does not conceive of the organic as succeeding on the inorganic, or of conscious life as conditioned in time by lower forms. In this respect it resembles Leibnitz’s idea of the world as a development; the idea of evolution is in each case a metaphysical as distinguished from a scientific one. Hegel gives a place in his metaphysical system to the mechanical and the teleological views; yet in his treatment of the world as an evolution the idea of end or purpose is the predominant one.

Of the followers of Hegel who have worked out his peculiar idea of evolution it is hardly necessary to speak. A bare reference may be made to Rosenkranz, who in his work Hegel's Naturphilosophie, seeks to develop Hegel’s idea of an earth-organism in the light of recent science, recognizing in crystallization the morphological element.

Schopenhauer.— Of the other German philosophers immediately following Kant, there is only one who calls for notice here, namely, Arthur Schopenhauer. This writer, by his conception of the world as will which objectifies itself in a series of gradations from the lowest manifestations of matter up to conscious man, gives a slightly new shape to the evolutional view of Schelling, though ha deprives this view of its optimistic character by denying any co-operation of intelligence in the world-process. In truth, Schopenhauer’s conception of the world as the activity of a blind force is at bottom a materialistic and mechanical rather than a spiritualistic and teleological theory. Moreover, Schopenhauer’s subjective idealism, and his view of time as something illusory, hindered him from viewing this process as a sequence of events in time. Thus he ascribes eternity of existence to species under the form of the “Platonic ideas.” As Ludwig Noire observes, Schopenhauer has no feeling for the problem of the origin of organic beings. He says Lamarck’s original animal is something metaphysical, not physical, namely, the will to live. “Every species (according to Schopenhauer) has of its own will, and according to the circumstances under which it would live, determined its form and organization, —yet not as something physical in time, but as something metaphysical out of time.”

Von Baer.— Before leaving the German speculation of the first half of the century, a word must be said of Von Baer, who not only reached those ideas of individual and serial development which are at the basis of the modern doctrine of organic evolution, but who recognized in the law of this development the law of the universe as a whole. In his Entwickelungsgeschichte der Thiere (p. 264) he distinctly tells us that the law of growing individuality is “the fundamental thought which goes through all forms and degrees of animal development and all single relations. It is the same thought which collected in the cosmic space the divided masses into spheres, and combined these to solar systems; the same which caused the weather-beaten dust on the surface of our metallic planet to spring forth into living forms.” Von Baer thus prepared the way for Mr Spencer’s generalization of the law of organic evolution as the law of all evolution.

Early Half of the Century—English Writers.— We may here conveniently break off our review of German evolutionists, returning to the writers of the latter part of the century presently. The thinkers outside Germany who in the first half of the century contributed elements to the growth of the idea of evolution are too unimportant to detain us here. In the English philosophy of this period questions of cosmology play a very inconsiderable part. The development of the analytical psychology, especially by the two Mills, may be referred to. Also an allusion may be made to the discussions respecting the nature of cause. Among these Sir W. Hamilton’s definition of cause (Lectures on Metaphysics, ii. 377) is specially interesting as appearing to tell against the production of mind out of matter.

French Writers—Comte.— Tn France during this period the name of Auguste Comte is the only one that need arrest our attention. Comte’s principles of positivism, which restricted all inquiry to phenomena and their laws, are said by his recent disciples to exclude all consideration of the ultimate origin of the universe, as well as of organic life.

Yet though Comte did not contribute to a theory of cosmic organic evolution, he helped to lay the foundations of a scientific conception of human history as a natural process of development determined by general laws of human nature together with the accumulating influences of the past. Comte does not recognize that this process is aided by any increase of innate capacity; on the contrary, progress is to him the unfolding of fundamental faculties of human nature which always pre-existed in a latent condition; yet he may perhaps be said to have prepared the way for the new conception of human progress by his inclusion of mental laws under biology.

Italian Writers.— In Italy during this period there meet us one or two thinkers who concern themselves with the interpretation of the world-process. Ant. Rosmini follows Campanella in endowing chemical atoms with sensibility and life, and he bases the hierarchy of beings in the universe on the different degrees of this sensibility. At the same time he follows Bruno in speaking of the totality of the world as an organism endowed with a soul which individualizes itself in the innumerable existences of the universe. Spontaneous generation is to Rosmini a necessary consequence of his theory of a universal life. Other Italian writers adopt Hegel’s notion of the world as a self-evolution of the idea. Of these it is enough to mention Terensio Mamiani, who gives an optimistic turn to his conception of evolution by viewing it as a progressive union of the finite with the infinite. Mamiani argues against Darwin, and holds that all specific forms are fixed for all time.

Modern Doctrine of Evolution.— We now approach the period in which the modern doctrine of evolution in its narrow sense has originated. This doctrine is essentially a product of scieutific research and speculation. It is a necessary outcome of the rapid advance of the physical sciences. Its final philosophic form cannot yet be said to be fixed. It may be defined as a natural history of the cosmos including organic beings, expressed in physical terms as a mechanical process. In this record the cosmic system appears as a natural product of elementary matter and its laws. The various grades of life on our planet are the natural consequences of certain physical processes involved in the gradual transformations of the earth. Conscious life is viewed as conditioned by physical (organic and more especially nervous) processes, and as evolving itself in close correlation with organic evolution. Finally, human development, as exhibited in historical and prehistorical records, is regarded as the highest and most complex result of organic and physical evolution. This modern doctrine of evolution is but an expansion and completion of those physical theories which opened the history of speculation. It differs from them in being grounded on exact and verified research. As such, moreover, it is a much more limited theory of evolution than the ancient. It does not concern itself (as yet at least) about the question of the infinitude of worlds in space and in time. It is content to explain the origin and course of development of the world, the solar or, at most, the sidereal system which falls under our own observation. It would be difficult to say what branches of science had done most towards the establishment of this doctrine. We must content ourselves by referring to the progress of physical (including chemical) theory, which has led to the great generalization of the conservation of energy; to the discovery of the fundamental chemical identity of the matter of our planet and of other celestial bodies, and of the chemical relations of organic and inorganic bodies; to the advance of astronomical speculation respecting the origin of the solar system, &c.; to the growth of the new science of geology which has necessitated the conception of vast and unimaginable periods of time in the past history of our globe, and to the rapid march of the biological sciences which has made us familiar with the simplest types and elements of organism; finally, to the recent development of the science of anthropology (including comparative psychology, philology, &c.), and to the vast extension and improvement of all branches of historical study.

English Writers—Darwin.— The honour of working out this theory of evolution on a substanial basis of fact belongs to England. Of the writers who have achieved this result Mr Darwin deserves the first notice. Though modestly confining himself to the problem of accounting for the evolution of the higher organic forms out of the lower, Mr Darwin has done much to further the idea of a gradual evolution of the physical world. The philosophic significance of the hypothesis of natural selection, especially associated with Mr Darwin, is due, as Professor Helmholtz points out, to the fact that it introduces a strictly mechanical conception in order to account for those intricate arrangements known as organic adaptations which had before been conceived only in a teleological manner. By viewing adaptations as conditions of self-preservation, Mr Darwin is able to explain how it is that the seemingly purposeful abounds in organic nature. In so doing he has done much to eliminate the teleological method from biology. It is true that, in his conception of seemingly spontaneous variations and of correlations of growth, he leaves room for the old manner of viewing organic development as controlled by some internal organizing principle. Yet his theory, as a whole, is clearly a heavy blow to the teleological method. Again, Mr Darwin has greatly extended the scope of mechanical interpretation, by making intelligible, apart from the co-operation of intelligent purpose, the genesis of the organic world as a harmonious system of distinct groups, a unity in variety, having certain well-marked typical affinities. How greatly this arrangement has helped to support the idea of an ideal plan, we have had occasion to observe. Mr Darwin in his doctrine of the organic world as a survival refers this appearance of systematic plan to perfectly natural causes, and in so doing lie gives new meaning to theancient theory that the harmony of the world arises out of discord. Once more, Mr Darwin’s hypothesis is of wide philosophic interest, since it helps to support the idea of a perfect gradation in the progress of things. The variations which he postulates are slight, if not infinitesimal, and only effect a sensible functional or morphological change after they have been frequently repeated and accumulated by heredity.

Mr Darwin’s later work, in which he applies his theory of the origin of species to man, is a valuable contribution to a naturalistic conception of human development. The mind of man in its lowest stages of development is here brought into close juxtaposition to the animal mind, and the upward progress of man is viewed as effected by natural causes, chief among which is the action of natural selection. Mr Darwin does not inquire into the exact way in which the mental and the bodily are connected. He simply assumes that, just as the bodily organism is capable of varying in an indefinite number of ways, so may the mental faculties vary indefinitely in correspondence with certain physical changes. In this way he seeks to account for all the higher mental powers, as the use of language and reason, the sentiment of beauty, and conscience.

Finally, Mr Darwin seeks to give a practical and ethical turn to his doctrine. He appears to make the end of evolution the conscious end of man’s action, since he defines the general good as “the rearing of the greatest number of individuals in full health and vigour, and with all their faculties perfect under the conditions to which they are subject. I urther, in his view of the future of the race, - 1r Darwin leans to the idea that the natural process which has effected man’s first progress must continue to be an important factor in evolution, and that, consequently, it is not well to check the scope of this process by undue restraints of population, and a charitable preservation of the incompetent.

Λ. P. Wallace.— Mr A. R. Wallace, who shares with Mr Darwin the honour of establishing the doctrine of natural selection, differs from the. latter in setting much narrower limits to the action of this cause in the mental as well as the physical domain. Thus he would mark off the human faculty of making abstractions, such as space and time, as powers which could not have been evolved in this way. Mr Wallace leans to the teleological idea of some superior principle which has guided man in his upward path, as well as controlled the whole process of organic evolution. This law is connected with the absolute origin of life and organization.

Herbert Spencer.— The thinker who has done more than any one else to elaborate a consistent philosophy of evolution on a scientific basis is Mr Herbert Spencer. First of all he seeks to give greater precision to the conception of this universal process. Evolution is a change from the homogeneous to the heterogeneous, from the indefinite or undetermined to the definite or determined, from the incoherent to the coherent. Again, Mr Spencer seeks to show that the causes of evolution are involved in the ultimate laws of matter, force, and motion, among which he gives great prominence to the modern doctrine of the conservation of energy. Thus the rationale of the process shapes itself to Mr Spencer as a distinctly mechanical problem. He sets out with the assumption of a limited mass of homogeneous matter acted upon by incident forces, and seeks to show how, by help of two laws,—namely, the instability of the homogeneous, and the multiplication of the effects of any such incident force,—the process known as evolution is brought about. This process is illustrated in the genesis of the solar system, for the explanation of which Mr Spencer makes use of the nebular hypothesis, in the formation of our planet, as well as the development of organic and mental life. Mr Spencer does not, however, conceive of this process of evolution as unlimited in time. As in the development of the individual organism, so in that of organic beings as a whole, of the earth, and of the solar system, there is a conflict between the forces of which the action is integrating or consolidating and those of which the action is disintegrating. The process of evolution always tends to an equilibration between these conflicting forces and ultimately to a dissolution of the products of evolution. Thus the solar system is a moving equilibrium which is destined to be finally dissipated into the attenuated matter out of which it arose. Mr Spencer thus approaches the earliest theories of cosmic evolution when he tells us (First Principles, p. 482) that vast periods in which the forces of attraction prevail over those of repulsion, alternate with other vast periods in which the reverse relation holds. The mechanical theory of evolution thus laid down in the First Principles is applied in Mr Spencer’s later works to the explanation of organic, mental, and social evolution. The full explanation of the processes of inorganic evolution finds no place in the writer’s system. Mr Spencer seeks, in the Principles of Biology, to conceive of organic bodies and their actions in mechanical terms. Life Is regarded as essentially a correspondence of internal actions in the organism to external actions proceeding from the environment, and the object of Mr Spencer’s volumes is to explain on mechanical principles the growth of this correspondence from the lowest to the highest. He excludes all consideration of the question how life first arose, though it is clear that he regards the lowest forms of life as continuous in their essential nature with sub-vital processes. It is in the later volumes, dealing with mental and social evolution, that Mr Spencer’s exposition becomes most interesting to the student of philosophy. In the Principles of Psychology, he seeks to deal wit i h mind as an aspect or correlate of life which begins to manifest itself when the process of adjustment to environment, in which all life consists, reaches a certain degree of complexity. Mr Spencer indulges in no hypothesis respecting the universal co-existence of sentience with matter and force. He thinks we must accept the distinctions which common-sense has established, and so limit feeling or consciousness to organic beings endowed with a nervous system. Thus, just as he does not seek to explain the first appearance of life as a whole, so he does not seek to explain the first dawn of mental life. Mr Spencer’s unit of consciousness is the blurred undetermined feeling which answers to a single nervous pulsation or shock. Assuming this he seeks to trace the gradual evolution of consciousness. Sensations arise by a number of rapid successions of such elementary feelings variously combined, and all more composite states of mind arise by a similar process of combination of these feelings. Thus mental evolution is a progressive composition of units of feeling in more and more complex forms, and united by more complex relations. Mr Spencer’s conception of mind thus excludes all fundamental distinctions of faculty. Instinct, memory, reason, the emotions and volitions, alike develop themselves in divergent directions out of a common elementary process. They are, moreover, all related to one and the same biological process, being incidental accompaniments of the actions by which the organism responds and adjusts itself to the forces of its environment. According as these actions are more complex, and consequently less immediate, the mental actions which accompany them vary in character from reflex action up to deliberate volition, from the most simple presentative feeling or sensation up to the most complex representative and re-representative feeling or emotion. It would be impossible to point to all the applications which Mr Spencer has made of his principle of evolution to the questions of psychology. We may just mention among other points of interest his attempt to explain the innate intuitions of space, moral right, <fcc., as mental dispositions handed down from progenitors and embodying the uniform experience of many generations, his ingenious endeavour to account for the coincidence between pleasures and pains and actions beneficial and injurious to the organism, and his conception of the aesthetic interest as a growth out of the play-impulse, which is the tendency of activities that have become developed beyond the immediate needs of existence to vent themselves.

Mr Spencer’s elaboration of the subject of social evolution has not been carried far enough for us to understand the full bearing of his ideas. Yet the fundamental conceptions are given us. The writer regards society, after the analogy of an individual organism, as possessing a number of various structures or organs and functions, and as tending to evolve itself by a series of adjustments to its environment, physical and social. All ideas and institutions display this process of evolution no less than societies as wholes. History is to our author essentially the record of this social evolution. It is to be observed that Mr Spencer attributes to society a certain spontaneous tendency to evolution apart from natural selection. He looks on progress as a gradual process of selfadaptation of man to the conditions of his environment, and anticipates an age when this adjustment will be complete and human happiness perfect. Tn this respect Mr Spencer’s conception of man’s history and destiny wears an optimistic tinge when compared with that very vaguely shadowed forth by Mr Darwin.

To Mr Spencer, as to Mr Darwin, the doctrine of evolution seems to supply the end of conduct. He conceives of morality as essentially an observance of the laws of life, the individual and the collective. At the same time, since Mr Spencer regards the moral sense as a growth out of feelings of pleasure and pain (racial experiences), closely identifies the ends of life and happiness, and distinctly teaches that social evolution or progress makes for an increase of happiness, his ethical doctrine does not materially differ from that of utilitarianism.

So far we have said nothing respecting the metaphysical basis which Mr Spencer seeks to give to his doctrine of evolution. It is generally agreed that this does not really belong to his doctrine of evolution itself. Mr Spencer is a thorough-going realist. From his general scheme of evolution one would be prepared to find him avowing himself a materalist. Yet he seeks to avoid this conclusion by saying that it is one unknowable reality which manifests itself alike in the material and in the mental domain. At the same time, this unknowable is commonly spoken of as force, and in many places seems to be identified with material force. Mr Spencer makes little use of his metaphysical conception in accounting for the evolution of things. He tells us neither why the unknowable should manifest itself in time at all, nor why it should appear as a material world before it appears under the form of mind or consciousness. Indeed Mr Spencer’s doctrine of evolution cannot be said to have received from its author an adequate metaphysical interpretation. The idea of the unknowable hardly suffices to give to his system an intelligible monistic basis. In truth, this system seems in its essence to be dualistic rather than monistic.

Metaphysical Interpretation—Professor Cliford.— Of the very few who have dealt with the metaphysical interpretation of the scientific doctrine of evolution, Professor Clifford deserves special notice. In an essay entitled “On things in themselves,” published in Mind (No. ix.), as well as in other and earlier papers, Mr Clifford, starting from the basis of empirical idealism which asserts that material objects are nothing but states of consciousness, argues that the reality answering to them is in all cases something mental. Thus all existence—including what we call minds as well as bodies—consists in aggregates of elementary “mind stuff,” the elements themselves corresponding to Mr Spencer’s units of feeling. The writer expressly argues that his idea of a continuity of mental existence throughout the physical (phenomenal) world is the direct consequence of the doctrine of evolution. This theory is curious as providing a monistic and quasi-spiritualistic conception of evolution, which is at the same time a mechanical one.

Problems of Organic Evolution.— G. II. Lewes.— Among the writers who have worked on the lines laid down by our two great evolutionists, a high place must be given to Mr G. II. Lewes, who in his biological and psychological writings, and more especially the Problems of Life and Mind, adopts a view of the relations of mind and life or organization closely resembling in its essentials that of Mr Spencer. To Mr Lewes consciousness is but a more complex form of mental life which is correlated with the actions of all the nervous centres, its lowest form being sentience. He appears to look on mind in all its grades as but the other side or face of the bodily processes which it accompanies. Yet he has not so far made use of this monistic conception in explaining the gradual evolution of conscious mental life. Indeed, though Mr Lewes’s writings are pervaded with the idea of organic evolution, his discussion of the nature and laws of organism in his last volume, The Physical Basis of Mind, might seem ever and again, by its sharp separation of organic and inorganic (mechanical) processes, to tell against the supposition of an evolution of life out of inorganic matter.

J. J. Murphy.— The question of the genesis of life and mind receives a peculiar treatment in Mr J. J. Murphy’s Habit and Intelligence. In this work the teachings of the evolutionists are largely accepted, while an attempt is made to reconcile these with a teleological view of nature. The process of inorganic and of organic nature is each recognized as one of evolution; but while the former is viewed as the result of mechanical principles, the latter is said to imply an intelligent or formative principle as well. Mechanical principles do indeed operate in organisms, this is the region of habit; but over and above this, vital processes involve a controlling intelligence. The author adopts the hypothesis that the Creator endowed vitalized matter at the first with intelligence under the guidance of which it organizes itself. Evolution is largely the result of this vital intelligent principle, only a small part being attributable to mechanical causes, such as natural selection.

Evolution and Psychology.— The speculations of Mr Darwin and Mr Spencer have had a powerful influence on recent English psychology, which promises to become comparative, not only in the sense of including a comparison of ethnological mental characteristics, but also in the wider sense of bringing human intelligence into relation to that of the lower animals. Among writers who have laboured in this construction of a theory of mental evolution, mention must be made of the late Mr D. Spalding. Again, Mr Chauncey Wright, in his remarkable essay The Evolution of Self-Consciousness (printed in a collection of his works), made a brilliant attempt to represent man’s highest mental operations as evolved out of simple processes common to man and the lower animals. The influence of evolutional ideas is further traceable in the latest work of Mr A. Bain {Emotions and Will, 3d edition), and in the works of Dr Maudsley and other living psychologists. The relation of the doctrine of evolution to psychology is handled in an essay by Mr J. Sully {Sensation and Intuition, ch. i.).

Anthropology.— The application of the doctrine of evolution to the question of man’s origin and development lias engaged the attention of a number of writers. In a sense all recent anthropologists and historians of culture may be said to have worked in this direction. Special attention must, however, be called to those writers who have sought directly to apply the fundamental ideas of evolution to these problems. Mr Bagehot’s Physics and Politics is remarkable as illustrating the employment of the doctrine of natural selection in order to explain certain aspects of political progress. Still more important is the contribution made by Mr Fiske, in his Cosmic Philosophy, to the theory of man’s origin and development. Mr I iske’s work is a full exposition of Mr Spencer’s doctrine of evolution. In addition to this it contains interesting speculations respecting the steps by which man’s distinguishing intelligence and sociality were first acquired and afterwards developed.

Relation to Ethics.— The application of the doctrine of evolution to our ethical and religious ideas has engaged a number of writers. In Mr A. Barratt’s Physical Ethics the development of man’s moral sense out of feelings of pleasure and pain is traced in connexion with his organic and social evolution on which it is said to depend. By conceiving of all matter as endowed with sensibility

(pleasure and pain), Mr Barratt is able to connect man’s moral evolution with the whole process of organic and of cosmic evolution. The idea of a natural growth of the moral sense out of simpler impulses and instincts may also be frequently fυuud in contemporary English literature. On the other hand, this consequence of the evolution theory has been strenuously opposed in the interests of a thoroughgoing intuitive ethics as, for example, by Mr St George Mivart, in his work, The Genesis of Species, and by Mi R. IL Hutton.

Again the question has been discussed whether the doctrine of evolution contributes towards the determination of the end or standard of morals. Mr Sidgwick has shown that it cannot well do this merely by proving how the moral sense has arisen. It is easy, however, to look upon the natural process as a tendency towards an end, and to conceive of our conscious actions as being bound by this tendency, so that the highest end of our existence must be to co-operate with the natural forces. This idea pervades a good deal of contemporary literature. It appears with special distinctness in the writings of Professor Clifford and Mr F. Pollock and in the able work of Miss Siιncox on Natural Law. On the other hand, Mr H. Sidgwick has made an elaborate study of the bearings of evolution on the ethical end, and reduces these to insignificant proportions. This writer criticises Mr Darwin’s definition of the general good, and argues that the idea of a mere quantity of life is inadequate to supply a definite end of conduct Nevertheless life {ζην) is the prime condition of wellbeing (∈υ ζηv), and so far the evolutionist is right in making life a secondary aim. The differentia of wellbeing, however, requires further interpretation, which can only be supplied by the utilitarian principle. At the same time the doctrine of evolution guides us in the pursuit of this ultimate end, in so far as increase of happiness accompanies organic progress, or elevation in the scale of existence. Mr Sidgwick further points out how little the doctrine of evolution assists the utilitarian in dealing with social and political problems.

Relation to Religion.— The bearing of the doctrine of evolution on religion has formed the theme of a host of minor writings. On the whole, Mr Darwin’s doctrine has been said (as it is by the author himself), not only to be compatible with the idea of an original creation of the world, but to supply a higher conception of the divine attributes than the hypothesis of special creations; on the other hand, Mr Spencer’s doctrine, distinctly excluding as it does the idea of creative activity, has called forth strong opposition from a number of theological writers, among whom the most powerful is certainly Professor Martineau. In connexion with the subject of the relation of the evolution doctrine to religious ideas, it is worthy of remark that this doctrine appears to be serving as the starting-point for a new quasi-religious conception of nature. The idea of the cosmos and its forces as the author and source of our being easily lends itself to a kind of pantheistic sentiment towards nature. In Mr Spencer’s own writings it is the unknowable force ever sustaining the evolving worlds which is said to excite this emotion. In the work of Miss Siιncox already referred to, and the occasional papers of Professor Clifford, it is rather visible nature itself which is thus elevated into a religious object.

Recent French Writers.— The French thought of the latter part of the century offers us but little in the way of a discussion of the problems with which evolution has to do. The activity of biological speculation appears to have influenced but a few philosophic minds. Naturalistshave of course discussed the doctrine of evolution, and one of these, E. Quinet, in his work La Creation, seeks to apply Mr Darwin’s theory to problems of art and morality. Thus the ideal of art should, he thinks, be based on the doctrine of evolution, and be “the presentment of superior forms which slumber still in the bosom of actual things,” or the embodiment of “the possible development of the human type in the progress of nature and man.” So the ideas of duty and virtue are to be based on this doctrine. Mau is the only animal which can retrograde, and evil is retrogression in the path laid down by nature. It is an anachronism, or a revolt of man against himself. Among philosophic writers proper, the first place must be given to M. Th. Ribot, who, in his sympathetic exposition of Mr Spencer’s doctrine of evolution in his Recent English Psychology, and in his interesting psychological study On Heredity, shows himself to be deeply pervaded with the new ideas, more especially in their bearing on mental phenomena. M. Ribot regards mental evolution as depending on material, but adds that the recognition of this connexion between the two domains of phenomena is compatible with idealism no less than with materialism. He would eliminate the conception of progress as a subjective one, and says that the idea of historical progress must be taken up into that of an objective cosmic process. M. Ribot makes many interesting applications of his law of mental heredity, which he rightly regards as a factor in mental evolution; as, for example, when he speaks of free-will as expressing the fixed personal factor in conduct,—namely, the inherited character. Of other philosophic writers who have been affected by the English doctrine of evolution, it is sufficient to name the late Léon Dumont, who was one of the first in France to apply the ideas of Mr Darwin and Mr Spencer to problems of psychology; and Professor A. Espinas, who in his work Des Sociétés Animales aims at furthering the theory of man’s psychical derivation from lower types of mind. A writer who appears to be in a lese distinct manner influenced by the idea of evolution is M. Taine, in whose psychological and historical studies the indirect effect of a study of English evolutionists is traceable. On the other hand, the older and teleological view of the world has not wanted its defenders. The most signal supporter of this direction, in the face of the doctrine of evolution, is M. Paul Janet, who, in his earlier work Le Matérialisme Contemporain, and still more in his recent publication Les Causes Finales, draws a sharp line between the regions of the organic and the inorganic, and maintains that the complex arrangements of the latter are only explicable by means of teleological conceptions.

Recent German Writers—Materialists.— In Germany the recent progress of speculation, since the time of the great systems, has exhibited a decided bent towards the problems which group themselves around the doctrine of evolution. First of all the efforts of the materialists directly tended to the formation of a consistent doctrine of cosmic evolution. Their earlier writings appeared just before the epoch-making publication of Mr Darwin, but the ideas of the latter have been incorporated in their later publications. In Moleschott’s Der Kreislauf des Lebens the whole order of things is conceived as a continual flux and exchange of material elements, which accounts for all pβychic life no less than for bodily life, and of which man, equally with the lower animals, is a temporary product. L. Büchner has sought, in his work on Man and his Six Lectures on the Darwinian Theory, to defend the new doctrine of organic evolution as a necessary factor in the materialistic conception of the world. The latter work connects Darwinism with the whole history of materialism. The former is a somewhat feeble attempt to attach man’s ideal aims in the future to the evolutionist’s conception of his past history. The writer appears to think that something equivalent to the process of natural selection is to effect man’s future progress, but the idea is not presented with any definiteness or precision.

Combination of Mechanical and Teleological View of Evolution.— After the materialists we come to a number of writers, who, under the influence of advancing physical and physiological science, have sought to construct a mechanical conception of the order of the world. Some of these have contented themselves with sketching a natural history of the cosmos, others have connected their mechanical conception with peculiar philosophical ideas.

Czolbe.— A curioue combination of the mechanical and teleological conceptions of the world is to be met with in the system of Czolbe. In his first works, Die neue Darstellung des Sensualismus and Die Entstehung des Selbst-Bewusstsein''s, Czolbe regards the world as a product of elementary matter and organic forms both of which are eternal. According to this view, sensation and consciousness are products of particular combinations of movements (circular). To these two original principles he adds, later on, feelings and sensations themselves, which exist in a latent state throughout space, and form a kind of world-soul. Still later, he finds the substantial support of atoms and sensations alike in space, in which feelings are located no lees than the material elements. To Czolbe our visible world, together with conscious minds, is thus a mosaic formed out of these elements, which group themselves according to mechanical laws in bodies and conscious minds. He thus adopts a theory of natural evolution which evades the difficulty of explaining the organic as a product of the inorganic, and mind as a product of matter. But he only achieves this by assuming the eternity cf all organic forms, and by conceiving of the elementary sensations as themselves spatial or “extensional.” Though the mechanical view of the world-order is most prominent in Czolbe, he combines with this a teleological and optimistic view, according to which all things make for the greatest possible perfection of conditioned happiness in every sentient creature.

G. T. Fechner.— Another writer who combines the mechanical view of the world with a curious metaphysical system is G. T. Fechner. Passing by his earlier works, in which he develops his idea of the world as a gradation of souls (including those of plants, an earth spirit, <fcc.), we may best turn to his later work Einige Ideen zur Schopfungs- und Entινickelungs- Geschichte der Organismen. Fechner takes a thoroughly mechanical view of the difference between organic and inorganic matter. But by help of this very difference he seeks to prove that the latter is a product of the former, and not conversely. The great law which determines the evolution of the world is the tendency to greater and greater stability, which law at once supplies a mechanical and a teleological conception of the universe. Organic bodies differ from inorganic in that their molecules are in a less stable condition than those of the latter. Hence we must suppose that the original source of the material world is an organism, namely, a primitive “cosmorganic” condition of our earth. This primitive matter has gradually differentiated itself into the regions of the organic and the inorganic, and the former again into the animal and vegetable kingdoms. Consciousness was breathed into the cosmorganic matter by the Creator and so pressed out, as though from the bellows of an organ, into all living creatures. This process of evolution is directed towards an end, namely, the greatest possible degree of mutual adaptation of parts, or the most stable condition; and conscious action is but the subjective side of this tendency. Lotze.— The mechanical view of the world, as wrought out by modern science, is fully recognized and yet surmounted in the cosmological doctrine put forth by Hermann Lotze in his Mikrokosmus. Lotze defends the mechanical method as applicable to all departments of phenomena, and insists on this way of viewing organic processes. At the same time he holds that the mechanical interpretation of nature is limited at every point. The inadequacy of this view may be seen in the attempt to apply it to the question of the genesis of the world and its order. On the one hand, Lotze accepts the teachings of modern speculation respecting the evolution of the solar system, the genesis of the organic out of the inorganic, the continuity of man with the lower animal world; and his exposition and defence of this idea of evolution as the result of mechanical laws is extremely able and interesting. Again, Lotze seeks to bridge over the gulf between material and spiritual evolution by bringing human development into close relation to the processes of nature as a whole. Yet, while thus doing justice to the mechanical conception of the gradual genesis of the world, Lotze strenuously affirms the limitations of this kind of explanation. In the first place, he maintains that the mechanical processes themselves cannot be understood except by help of ideas respecting the real internal nature of the elements cencerned. This nature he describes as life, and thus he endows all parts of matter with feeling (though he distinctly rejects Czolbe’s idea of a world-soul which includes these feelings). In this internal activity Lotze finds a teleological element, viz., a striving towards self-preservation and development. This idea he seeks to blend with that of mechanical relations among the elements, so as to make the whole upward process of physical evolution the product of purposeful impulses. Thus the first genesis of organisms is represented as a combination of elements (accidentally meeting), through which there is effected a summation of the separate ends of the elements, to a purposeful equilibrium of a composite whole. This may be called the first stage of his teleology. In addition to this, Lotze looks at the world-process as a gradual unfolding of a creative spiritual principle, which he sometimes figuratively describes as the world-soul, more commonly, however, as the infinite substance. This assumption, he says, is necessitated by the very process of cosmic evolution, the absolute beginning and end of which we are wholly unable to conjecture. However far back the evolutionist may go he always has to assume some definite arrangement of parts,—some general laws of action of which he can give no account. The conception of the atomists, that in the beginning of things there was an indefinite number of possibilities, is unthinkable, and the modern doctrine of evolution, by conceiving of the existing world as a survival of certain forms from among many others actually produced, but lacking in the conditions of stability, plainly makes no such absurd supposition. Hence, there must always be a certain order to be accounted for, and science is wholly inadequate to effect this explanation. This conducts to a teleological view of the world-process, as directed by mind towards some end which we cannot distinctly recognize. Lotze’s criticisms of previous attempts to formulate the end of the world-process are not the least valuable part of his discussion of the problems of evolution. He shows that neither the notion of a progressive effort towards the highest unfolding of mental life, nor that of an impulse towards the greatest variety of manifestations of one and the same fundamental form, adequately represents the order of organic forms. Here Lotze shows again a due recognition of the mechanical aspect of the world-process, and argues that the evolution of the organic world is no immediate consequence of the self-evolving ideas, but only the form in which the commands of these ideas are capable of being realized on our earth,—that is to say, with our terrestrial conditions. A somewhat similar view of cosmic and organic evolution, -as at once a mechanical and a teleological process, is to be found in Ulrici’s Gott und die Natur. Mechanical Doctrines of Evolution.— Over against these attempts to carry up a mechanical conception of evolution into a teleological must be set a number of works which content themselves, in the spirit of positive science, with expounding a doctrine of evolution on a strictly mechanical basis. Of these we may first mention C. Radenhausen (Isis), who, in his interesting work Der Mensch und die Welt, expounds the idea of a gradual evolution of the solar system, the earth, and organic life. In the growth of the individual man the past evolution of the world is represented. A temperate statement of the doctrine of modern evolution is to be found in Dr Ch. Wiener’s volume Die Grundzuge der Weltordnung. The problems of the origin of organic life and of the genesis of the nervous system are both said to be as yet insoluble. With this may be compared another interesting presentation of the doctrine of evolution,—namely, H. J. Klein’s Entwickelungsgeschichte des Kosmos. The mechanical causes of evolution are clearly set forth in a work of the Herbartian C. S. Cornelius, Ueber die Entstehung der WeU. Cornelius argues against Czolbe’s hypothesis of the past eternity of organic life. Organisms first arose under some quite special physical conditions. A very curious feature in this volume is the criticism of Mr Darwin’s doctrine of descent, which is said to involve mystical ideas, &c.

Lange.— Among later works touching on the problems of evolution the History of Materialism of Lange deserves mention here. Lange accepts the modern hypothesis of evolution, and justifies the mechanical conception of its various stages. It is true that in his criticism of Mr Darwin’s theory he assumes some internal formative principle (as held to by Nägeli and Kölliker) as supplementary to the factor of utility emphasized by Mr Darwin. Yet he does not appear to regard this process as other than a mode of mechanical action. Lange’s greatest difficulty in view of a consistent materialistic doctrine of evolution is to explain the genesis of conscious life. The difficulty of the atomistic theory, even when we add a rudimentary sensibility to the elements, is to determine “where and how the transition is effected from the manifoldness of the collisions of the atoms to the unity of sensation.” Lange supplements his mechanical view of the world by the Kantian conception of the adaptation of the world by reason of its generalities or uniformities to our intelligence. He argues, with Lotze, that in seeking to frame a theory of physical evolution we must always assume, over and above the eternal atoms, a special initial arrangement of these, without which the order of events would be inconceivable. This modest kind of teleology (he says) is not only not opposed to Mr Darwin’s doctrine; it is its necessary pre-supposition. “The formal purposefulness of the world is nothing else than its adaptation to our understanding.” Lange seems further disposed to accept Kant’s theory of organism as manifesting objective purpose, though he will not allow that this explains anything, all explanations being by way of the principle of mechanical causation.

Noire.— In Ludwig Noiré we have a writer who accepts all the teaching of scientific evolutionists, and at the same time seeks to give to the doctrine a metaphysical and monistic interpretation. In his two volumes Die Welt als Entwickelung des Geistes and Der Monistische Gedanke, Noiré assumes the existence of elementary atoms or “monads” endowed with the twofold properties of motion and sensation. Time and space are not simply forme of intuition, but forms of appearance {Erscheinungsformen') of these fundamental properties. The process of evolution from the simple to the complex, has its ground in the latter property, sensation, which gives its direction to motion (which latter is unchangeable in amount), and which involves a tendency or impulse to further differentiation. The purposefulness of the process of evolution is due to its being the work of a mental principle (sensation). The formation of inorganic bodies is the preliminary step in the process, and involves an obscure mode of consciousness. The genesis of consciousness is said to be effected by means of a certain mode of collision among the atoms, though this point is not made very clear. Noiré’s doctrine of evolution appears to waver somewhat between a mechanical theory (atoms endowed with sensibility, but acting according to strictly mechanical laws) and a distinctly spiritualistic and teleological doctrine, such a3 that of Schelling and Hartmann.

Hartmann.— The writings of E. von Hartmann have a special interest, as illustrating how Mr Darwin’s doctrine of organic development is regarded from the point of view of a thorough-going metaphysical teleology. To Hartmann the world is a manifestation in time—which is real as applying to the activities of this principle—of an ontological principle, styled the unconscious, which is at once will and intelligence. The process of evolution, from the simplest material operations up to conscious human actions, depends on the progressive domination of will, which is the blind force, and answers to the mechanical aspect of the world, by intelligence, which gives to this force form and direction, and answers to the logical and teleological aspect of the world. The end of the process for which this unconscious makes is not, as Hegel says, self-consciousness, but nonexistence, to which consciousness is the immediate precondition. Hartmann has devoted a separate volume to Mr Darwin’s theory {Wahrheit und Iτrthum im Darwinismus), in which he shows himself disposed to accept the principle of natural selection as the mechanical means which the unconscious makes use of in order to effect a certιin amount of the upward organic progress towards which it strives.

Influence of Darwinism in Germany.— We will close the sketch of the recent German discussion of evolution-problems, and so our historical review as a whole, by a brief reference to the philosophic and quasi-philosophic literature which has sprung up in Germany under the direct influence of Mr Darwin’s doctrine. It is not a little curious that, of the two great English evolutionists, the one who has most stimulated German philosophical thought is the writer who has confined himself to questions of natural science, while the writer who has built up the idea of organic descent into a complete cosmological theory is only now beginning to be known in that country.

{a) Darwinism, and Methodology.— First of all, then, a bare allusion must be made to certain criticisms of Mr Darwin’s biological hypothesis as legitimate instruments of a sound natural philosophy. It may surprise some English readers to learn that the doctrine of the descent of species by natural selection has been denounced in Germany as partaking of the vices of a spurious and teleological natural philosophy. The writer who has taken most pains to show up the philosophic unsoundness of Mr Darwin’s procedure is A. Wigand {Der Darwinismus und die Naturforschung Newton’s und Cuvier’s, see especially vol. ii.)

{b) Darwinism and Cosmology.— Turning now to the influences of Darwinism· on German thought, we may best begin with the more circumscribed branches of speculation. Physical speculation in Germany is being slowly affected by Mr Darwin’s theory. A curious example of this is to be met with in a little work by Dr Karl du Prel, entitled Der Kampf ums Dasein am Himmel. This work is of real philosophic interest as illustrating how Mr Darwin’s way of conceiving self-preservation, as the effect of natural superiority in respect of adaptability to the conditions of existence, may be extended beyond the organic world to the cosmos as a whole. Du Prel regards the cosmic bodies as analogous to competing organisms, space standing for the means of existence for which they struggle, and the force of attraction and the fitness of the body’s movement in relation to those of other bodies representing organic efficiency. Those bodies which have these advantages survive, whereas those which lack them are extinguished either by being dissipated or fused with other bodies.

(c) Darwinism and Anthropology.— Passing by the biological speculations respecting the ultimate origin of living forms to which Darwinism has given rise, we pass to those aspects of anthropology which have a peculiar philosophic interest. In a sense it may be said that Mr Darwin’s speculations, especially as carried out by himself in his Descent of Man, have powerfully influenced the whole of recent anthropological speculation; for writers like A. Bastian {Schöpfung und Entstehung and Der Mensch in der Geschichte), who still hold to the doctrine of the fixity of species, and the essential difference between human history and sequences of natural events, are now the exceptions. With anthropology, we must connect that new science of comparative human psychology {Völkerpsychologie) which has sprung up of late years.

Origin of Language.— Of the problems which fall under this science of man’s genesis and development, none has more of philosophic interest than the question of the origin of language. This question, which lies at the very threshold of a proper understanding of the relation of man’s mental nature to that of the lower animals, is touched on by Mr Darwin himself in his Descent of Man. In Germany it is being earnestly discussed by a number of writers, on whom the influence of Mr Darwin’s theory of human descent is very marked. Among the writers who have explicitly applied the method of evolution, as defined by Mr Darwin, to the explanation of language, may be mentioned A. Schleicher, L. Geiger, Dr G. Jäger, Wilhelm Bleek, and Ernest Haeckel. Jäger, who assumes that man is the immediate descendant of ape-like progenitor, connects the first beginnings of human speech with a superiority in the command of the actions of respiration which is involved in man’s erect posture.

(√) Darwinism and Psychology.— From anthropology we pass to psychology. Here the influence of Darwinism meets us too. Among recent psychologists W. Wundt, in his Grundzüge der physiologischen Psychologie, makes frequent use of the doctrine of a gradual evolution of mental dispositions by means of heredity. He would, for example, explain the rapidity with which the space perception is formed in the infant mind by help of such an inherited disposition. Wundt appears to lean to the hypothesis of ultimate sentient elements, by the summation of whose rudimentary feelings arises the unity of consciousness.

The wider consequences of Mr Darwin’s theory in the domain of psychology are briefly indicated by Dr Georg von Giz’ycki, in his little work Die philosophischen Con-sequenzeη der Lamarck-Darwin’ sehen Entwicklungstheorie. He argues against attributing sensation to all material things, which supposition (unlike Professor Clifford) he does not regard as a necessary consequence of the evolution hypothesis. He distinctly seizes the bearing of this doctrine on our conception of mind (animal as well as human) as identical in its fundamental laws, and as presenting to the psychologist a single serial development; and he still further follows Mr Spencer in connecting all mental activity with vital functions essential to the preservation of the individual and of the race. Finally, he adopts the view that the mental organism depends on the laws of the external universe. The harmony or adaptation which we see holding between thoughts and things must be interpreted as the effect of the latter acting on and modifying the former in conformity with themselves.

Darwinism and Ethics and Religion.— Passing now to the region of practical philosophy, we find that Darwinism has occasioned in Germany, as in England, a good deal of curious speculation. Among the many writers who have touched on the aspects of Darwinism we cau only refer to one or two. Among these we may mention Dr Paul Rée, who, in a recent work, Der Ursprung der moralischen Empfindungen, argues that moral dispositions or altruistic impulses have been developed as useful to society, yet rather oddly combines with this idea the pessimistic doctrine that man is not on the whole growing more moral. Again Dr Giz’ycki, in the work just referred to, emphasizes the bearing of the doctrine of human descent on our feeling towards the lower animals as closely linked to ourselves. He goes on to show that this doctrine involves the most definite and stringent form of determinism, and so has a bearing on our ideas of right and wrong, blame, &c. The writer thinks Darwinism by no means excludes a teleological conception of the world as a process striving towards the highest manifestation of mental life, and this idea leading back to that of an absolute first cause of the order of the world, becomes the starting-point for religious and aesthetic aspiration. In Dr G. Jager’s work, Die Darwin’sehe Theorie und ihre Stellung zu Moral und Religion, we find a practical deduction from Darwinism which curiously contrasts with that of Dr Giz’ycki. Jäger argues that this doctrine teaches us to place ourselves in the greatest possible opposition to the lower animals. The aim of morality, as taught by Darwinism, must be to develop to the utmost those excellences which mark off man from the brute. The author seeks to account for the genesis of social institutions and religious ideas, as utilities which benefited those communities possessing them in the struggle for existence.

A work in which are traced the ethical and religious consequences of the doctrine of evolution is The Old Faith and the Λew of David Strauss. According to Strauss, all morality has its root in the recognition and realization of the idea of kind in ourselves and in others. He argues from the fact that nature has produced man as her last and highest achievement, and the lower forms of creatures but as steps in the progress towards man, that our end and aim must be the furtherance of that which marks us off from the brutes. Religion again begins with the sense of unity « ith. nature, and the new doctrine of the cosmos enables us to regard nature as the source whence our life, as all life, springs.

Interpretation of Modern Scientific Doctrine.— A word or two, in conclusion, respecting what is known as the modern doctrine of evolution. It is important to emphasize the fact that this is a scientific doctrine, which has been built up by help of positive research. As such, of course, it embodies the mechanical, as distinguished from the teleological, view of nature’s processes. Yet it still awaits its final philosophic interpretation. We cannot yet say under what head of our historical scheme it is destined to fall.

We think the question of the universal applicability of the doctrine to·physical and mental phenomena may be allowed. There are no doubt wide gaps in our knowledge of both orders. Thus it may reasonably be doubted whether physical theory can as yet enable us fully to see the necessity of that universal process from the homogeneous to the heterogeneous in which evolution consists; yet in a rough and vague way the process is being made theoretically intelligible. Again, the transition from the inorganic to the organic is, as Professor Tyndall has lately told us, far from being conceivable in the present state of our knowledge; and this seems to be implied in the remarkable hypothesis by which Professor Helmholtz and Sir W. Thomson seek to account for the first appearance of life on our planet. Yet we may reason from the general tendencies of research that this step may some day be hypothetically explained in physical and mechanical tenus. Again, in spite of Mr Spencer’s brilliant demonstration of the general continuity of mental life, much remains to be done before all the steps in the process {e.g., from particular to general knowledge, from single feelings to self-consciousness) are made plain. Nevertheless, we may even now dimly see how such mental processes may be knit together in one larger process.

Allowing, then, that the doctnne of evolution as a scientific hypothesis is probably true, the question arises, what is its exact philosophical purport? How far does it help to unify our knowledge, and is it the final explanation of the complex events of our world?

First of all, then, as a unifying generalization, it is clearly limited by the fact of the correlation of mental aτιd physical evolution. These two regions of phenomena may be seen to manifest the same law, yet they cannot be identified. All the laws of physical evolution can never help us to understand the first genesis of mind; and this difficulty is in no way reduced by Mr Spencer’s conception of a perfect gradation from purely physical to conscious life. The dawn of the first confused and shapeless feeling is as much a “mystery” as the genesis of a distinct sensation. Our best exponents of evolution, including Professor Du Bois Reymond (fieber die Grenzen des Naturerkennens, p. 25 $?.), fully recognize this difficulty. We have here much the same “mystery” which meets us in the conversion of a nerve-stir4ulus into a sensation in the developed organism. The sequence 13 unlike any properly physical succession, and so cannot be further explained by being brought under a more general law. Not only so, the doctrine of the conservation of energy, as applied to organic processes, leads to the conclusion that the genesis of mind in general and of every single mental phenomenon is, from a physical point of view, something non-essential.

We may, no doubt, avoid this difficulty, in appearance at least, by assuming that all material processes down to the vibrations of the indivisible atoms are accompanied with a mode of feeling. This may, of course, be proposed as a properly scientific hypothesis, and as involving no metaphysical assumptions respecting the nature of atoms. The great difficulty here would be, how we are to conceive of modes of sensibility that do not enter into a collective consciousness, and which appear to lack all the characteristics of our own conscious life.

Even, however, if this huge difficulty of the genesis of mind is got over, there still remain limits to the explanation effected by the doctrine of evolution. Thus, while it might be able to deduce all the processes of physical evolution from a few assumptions respecting primitive matter and its laws, it would have no such data for resolving all these steps in the mental process which result in a heterogeneous mode of feeling. How, for instance, is it to account on general principles, and by a priori reasoning, for the differentiation of a vague tactual sensibility into what we know as sight and hearing—sensibilities which underlie all our ordinary conceptions of the physical world? Here are manifestly set rigid limits to the explanation effected by the doctrine of evolution, the limits which J. S. Mill has laid down as those of all kinds of explanation of phenomena. The doctrine by no means helps us to resolve all laws of succession into one.

The other limits set to the explanatory power of the modern doctrine have already been hinted at. Thus the doctrine sets out from a given point in time, at which it assumes a definite arrangement of material (and mental) elements to have obtained. “Of the beginning of the universe,” says Professor Clifford, “we know nothing at all.” Again, Professor J. Clerk Maxwell tells us that we must from the first assume an infinite number of molecules exactly alike in their weight and rate of vibration; and he distinctly argues against the supposition that this system of like elements can have been evolved. There is room then for the question, how this particular order of elements arose. And even if we go further back, and make with Mr Spencer the large assumption that these various classée of molecules have been evolved from perfectly homogeneous first elements, one may still ask for an explanation of this original homogeneity. In short, it is plain that every doctrine of evolution must assume some definite initial arrangement, which is supposed to contain the possibilities of the order which we find to be evolved, and no other possibility.

Such being the limits set to the scope of explanation by the idea of evolution, the question arises whether these apparently permanent gaps in our scientific knowledge can be filled up by extra-scientific speculations. One may seek to show the need of such a metaphysical interpretation of evolution by a reference to the very nature of the doctrine. As a scientific truth, it is simply the highest generalization respecting the order of phenomena in time, and as such makes no assumptions with regard to the ultimate nature of that matter, force, and mind, of which it speaks. What, it may be asked, are the realities corresponding to these terms, and how are we to conceive of their mutual relations Ί Each of the supposed deficiencies in the doctrine of evolution just referred to leads us back to those various metaphysical doctrines in which, as we have seen, the idea of evolution has usually clothed itself. In order to understand what Mr Martineau calls the whence as distinguished from the when, and to provide a substantial support for the thread of phenomenal events, it would seem as if we must fall back on some ultimate philosophic assumption respecting the efficient principle in the process.

With respect to metaphysical dualism, it must be said that it leaves us pretty much where we were. The correlation of two distinct substances and their manifestations, in the way required by the doctrine of evolution (whether this correlation be universal or not), needs explanation as much as the correlation of the two sets of phenomena. On the other hand, materialism, spiritualism, and the so-called monism, have each their merits and their drawbacks as helps to the interpretation of evolution. If materialism recommends itself by assuming the fewest possible principles, it is exposed to the objection that it bids us conceive a reality which is wholly distinct from mind. Further, it fails to give any intelligible account of the rise and progress of mental activity. Again, spiritualism assists us in accounting for the genesis of mind, and for the appearance of intelligent order in the world. Yet it is questionable whether this doctrine, assuming as it does some form of unconscious mind (whether as world-soul or as elements of feeling), is not beset with as many difficulties as it resolves. Further, it may be doubted whether the spiritualistic idea, in its common pantheistic form, has yet succeeded in rendering intelligible the fixed mechanical order which marks all stages of evolution. Finally, it may be allowed that the monistic doctrine of one reality with two faces does in appearance lift us over the difficulties which beset the materialistic and the spiritualistic interpretation of evolution. Only is it in truth anything more than a verbal simplification, and does it not rather leave us confined in that dualism where science has to land us 1

It would thus seem that the doctrine of evolution has by no means as yet received its final philosophic character. No one of the metaphysical doctrines which are at our command is so plainly and completely adapted to transform it into a final doctrine of existence, that it must of necessity be accepted at once and by all.

To this we must now add that to many minds this resort to a metaphysical principle as the support of the process .of evolution will not be held to be necessary. A positivist, who thinks that our knowledge of the universe must for ever be limited to phenomena, is at perfect liberty to accept the doctrine of evolution and to regard it as an ultimate expression for the order of the world. Nay more, the empirical idealist—who may perhaps be defined as a positivist that has fully analysed his “phenomena ”—can accept and give a meaning to the doctrine of evolution as formulating the order of sensations, actual and possible, of conscious minds. Mr Spencer somewhere says that, if idealism is true, evolution is a dream. Yet this assertion may be reasonably disputed. It may perhaps seem staggering to be told that evolution postulates vast periods of time in which there existed no mind to experience the sensations into which the world is on the idealistic hypothesis resolved. Yet this difficulty is only apparent, since past physical evolution stands for a projection, so to speak, of now existing minds, and for an order of sensations conceived as possible under other and imaginable circumstances. To the empirical idealist physical evolution stands for an imagined order of perceptions in an indefinite number of minds, mental evolution for actual successions of feeling in many minds, and the transition from the one to the other means the succession of actual states of consciousness on possible or imagined states. The unity of the world-process arises from the ability of the individual mind, which now reflects on these many successions, to gather them up by a series of acts of imagination into a collective ideal experience for itself.

Thus the doctrine of evolution seems to be susceptible of statement in terms of idealism as easily as in terms of realism. In truth, each mode of viewing the process is at once possible and beset with difficulties. The difficulty of giving an idealistic interpretation arises from the popular distinction of mind or perception and something beyond and independent of this. The difficulties of giving a realistic interpretation have in part been stated already in speaking of the different realistic interpretations (materialism and spiritualism). To these must be now added the fundamental obstacle to all realism, which shows itself, in a specially striking way, in relation to the doctrine of evolution,— namely, the difficulty of conceiving in terms of human consciousness something which is independent of, antecedent to, and creative of, this consciousness.

It may be asked, perhaps, whether the doctrine of evolution, by providing a new conception of the genesis of our cognitions, has anything to say to the question of a real independent object. What the doctrine effects with respect to such cognitions as those of space is to show that the bare fact of intuitiveness or innateness does not establish their non-empirical or transcendental origin. Similarly it may be held that the doctrine opens a way of accounting for the growth of the idea of independent realities, supposing this to be now an innate disposition of the mind—viz., by regarding this idea as arising in a succession of many generations, if not out of, yet by help of, certain elements or aspects of experience. It may, however, be maintained that the idea is not even suggested by experience; if so, it would follow from the evolution theory that its present persistence represents a permanent mental disposition to think in a particular way. Even then, however, the question would remain open whether the permanent disposition were an illusory or trustworthy tendency, and in deciding this point the doctrine of evolution appears to offer us no assistance.

As a scientific doctrine, whatever its ultimate interpretation, evolution has a bearing on our practical, i.e., moral and religious ideas. This has already been shown in part by writers from whom we have quoted. Among other results, this doctrine may be said to give new form to the determinist theory of volition, and to establish the relativity of all moral ideas as connected with particular stages of social development. It cannot, as Mr Sidgwick has shown, provide a standard or end of conduct except to those who are already disposed to accept the law sequi naturam as the ultimate rule of life. To such it furnishes an end, though it would still remain to show how the end said to be unconsciously realized by nature, the well-being of individuals and of communities, is to be adjusted to the ends recognized in common-sense morality, including the happiness of all sentient beings. It may be added that the doctrine, by assigning so great an importance to the laws of inheritance as means of raising the degree of organization and life, may be expected to exert an influence on our ideas of the solidarity of the present generation and posterity, and to add a certain solemnity to all the duties of life, prudential morality included.

The bearing of the doctrine of evolution on religious ideas is not so easy to define. Mr Spencer considers the ideas of evolution and of a pre-existing mind incapable of being united in thought (see his rejoinder to Dr Martineau, Contemporary Review, vol· XX. p. 141 sqf Yet, according to others, the idea is by no means incompatible with the notion of an original Creator, though it serves undoubtedly to remove the action of such a being further from our ken. At first sight it might appear that the doctrine as applied to the subjective world, by removing the broad distinction between the human and the animal mind, would discourage the hope of a future life for man’s soul. Yet it may be found, after all, that it leaves the question very much where it was. It may perhaps be said that it favours the old disposition to attribute immortality to those lower forms of mind with which the human mind is found to be continuous. Yet there is nothing inconsistent in the supposition that a certain stage of mental development qualifies a mind for immortality, even though this stage has been reached by a very gradual process of development. And if, as might be shown, the modern doctrine of evolution is susceptible of being translated into terms of Leibnitz’s hypothesis of indestructible monads, which include all grades of souls, then it is clearly not contradictory of the idea of immortality.

Very interesting is the bearing of the doctrine of evolution on that aesthetico-religious sentiment towards the world which has taken the place of older religious emotions in so many minds. First of all by destroying the old anthropocentric view of nature, according to which she is distinct from and subordinated to man, this doctrine favours that pantheistic sentiment which reposes on a sense of ultimate identity between ourselves and the external world. In a sense it may be said that the new doctrine helps to restore the ancient sentiment towards nature as our parent, the source of our life. It is well to add, however, that the theory of evolution, by regarding man as the last and highest product of nature, easily lends support to the idea that all things exist and have existed for the sake of our race. This seems, indeed, to be an essential element in any conception we can form of a rationally evolved universe.

A reference must be made, in closing this article, to the optimistic aspect of the doctrine of evolution. That there is a tone of optimism in much of the more popular exposition of the doctrine of evolution needs not be proved. There is no doubt, too, that both in Mr Darwin’s and Mr Spencer’s theories there are ideas which tend to support a cheerful and contented view of things. The idea of the survival of the fittest, and of evolution as a gradual process of adaptation to environment, lend themselves to this kind of thought. Indeed, Du Bois Reymond, in the lecture on Leibnitz already referred to, seriously argues that the doctrine of evolution provides a scientific equivalent to that philosopher’s remarkable conception of the best of all possible worlds. On the other hand, as the present writer has elsewhere show n, Mr Darwin’s doctrine of evolution contains elements which are fitted to tone dow n our estimate of the value of the world viewed as the seat of conscious sentient life. The pain involved in the renewed struggle for existence is a large drawback from the gains of human progress and of organic development as a whole. More than this, the principle of natural selection appears almost to favour a pessimist view of the world, in so far as it implies the tendency of organic forms to multiply down to the limits of bare existence.

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Principal works used in the historical sketch :—F. Ueberweg, History of Philosophy; J. E. Erdmann, Grundriss der Geschichte der Philosophie; G. H. Lewes, History of Philosophy; C. A. Brandis, Handbuch der Geschichte der griechisch-römischen Philosophie; E. Zeller, Die Philosophie der Greichen; G. Grote, Plato and Aristotle; W. Kaulich, Geschichte der scholastischen Philosophie; A. Stöckl, Geschichte der Philosophie des Mittelalters; Kuno Fischer, Geschichte der neuern Philosophie; J. P. Damiron, Memoirs pour servir à l'Histoire de la Philosophie au 18« Siècle; E. Zeller, Geschichte der deutschen Philosophie. (J. S.) Index to Article Evolution.

Alfarabi, 7⅛8.

Anaxagoras, 756.

Anaximander, 755

Anaximenes, 755.

Anthropology, 766, 769.

Arab philosophers, 758.

Archenterom, 746.

Aristotle, 757

Atomists, 756.

Aτicebron, 758.

Avicenna, 758.

Baer, von, 749, 763.

Barratt, A., 766.

Bastian, 769.

Belon, 750.

Bernhard of Chartres, 758. Biology, evolution in, 744-751. Blastospore, 746.

Boehme, 758.

Bonnet, 744, 745, 760.

Bruno, Giordano, 758.

Biichner, 767.

Buffon, 745, 748, 760.

Campanella, 758.

Carus, 762.

Clifford, 765.

Comte, 763.

Cosmology, 769.

Creation, 752.

Critias, 756.

Cndworth, 759.

Cuvier, 749.

Czolbe, 767.

Darwin, Charles, 749, 764.

Darwin, Erasmus, 748.

Definition, 744, 746, 751.

De Maillet, 748.

Descartes, 747, 759.

Duns Scotus, 75S.

Du Prel, 769.

Eleatics, 755.

Emanation, 752.

Emboîtement, 745.

Empedocles, 756.

Epiblast, 746.

Epigenesis, 744, 747.

Erigena, 758.

Ethics, 766, 770, 772.

Fechner, 767.

Forms of the doctrine, 752,753.

Gassendi, 758.

Gastrula, 747.

Giz’ycki, 770.

Goethe, 748.

Greek physicists, early, 755.

Haeckel, 749, 769.

Haller, 744.

Hartmann, 769.

Harvey, 744, 746.

Hegel, 762.

Helmholtz, 770.

Helvetius, 760.

Heraclitus, 755.

Herder, 761.

Hobbes, 758, 759.

Holbach, 760.

Hume, 760.

Hutton, R. H., 766.

Hypoblast, 746.

Indian philosophy, 755.

Individual, evolution of, 746. Jäger, 769, 770.

Janet, 767.

Jewish philosophy, 758.

Kant, 761.

Lamarck, 748, 749, 750.

Lange, 768.

Language, origin of, 769.

Leibnitz, 744, 748, 760.

Lessing, 761.

Lewes, G. H., 765.

Locke, 759.

Lotze, 768.

Lucretius, 757.

Malebranche, 744.

Malpighi, 744.

Mamiani, 763.

Martineau, 766.

Maxwell, J. Clerk, 771.

Mechanical view, 753, 768.

Meckel, 750.

Mesoblast, 747.

Metaphysics, 765, 771.

Methodology, 769.

Mivart, St George, 766.

Moleschott, 767.

Monboddo, 760.

Monistic view, 754.

Morula, 746.

Murphy, J. J., 766.

Mythological interpretation, 754.

Neo-Platonists, 757.

Noiré, 769.

oersted, 762.

oken, 762.

optimism, 772.

Pessimism, 772.

Philosophical purport, 770.

Philosophy, evolution in, 751 772.

Planula, 746.

Plato, 756.

Platonists, 756.

Problem stated, 752.

Priestley, 760.

Progress, idea of, 759.

Psychology, 766, 770.

Pythagoras, 755.

Quinet, 767.

R.ée, 770.

Religion, 766, 770, 772.

Reymond, Du Bois, 770.

Ribot, 767.

Robinet, 748, 760.

Rosencranz. 763.

Rosmini, 763.

Schelling, 762.

Schoolmen, 757.

Schopenhauer, 763.

Sidgwick, 766.

Spencer, Herbert, 749. 764.

Spinoza, 748, 759.

Steffens, 762.

Stoicism, 757.J

Strato, 757.

Strauss, 770.

Sum of living beings, evolution of, 747.

Systems classified, 753.

Teleological view, 754.

Telesio, 758.

Thomson, Sir W., 770.

Treviranus, 748.

Ulrici, 768.

Vestiges of Creation, 750. wallace, A. R., 749, 764.

Wigand, 769.

Wolff, C. F., 745, 750.

Wundt, 770.