That the morphological conception of a Species is not a positive but only a relative conception, and that it has no other absolute or positive value than those other similar system-categories--sports, varieties, races, tribes, families, cla.s.ses--is now acknowledged by every systematiser who forms an honest and unprejudiced judgment of the practical systematic distinction of species. From the very nature of the case there are no limits to arbitrary discretion in this department, and there are no two systematists who are at one in every instance; this one separating forms as true varieties which that one does not. (Compare on this point "History of Creation," vol. i., p.

273.) The conception of variety or species has a different value in every small or large department of systematic Zoology and Botany.

But the conception of species has just as little any fixed physiological value. In respect to this we must especially insist that the question of hybrid offspring, the last corner of refuge of all the defenders of the constancy of species, has at present lost all significance as bearing on the conception of species. For we know now, through numerous and reliable experiences and experiments, that two different true varieties can frequently unite and produce fertile hybrids (as the hare and rabbit, lion and tiger, many different kinds of the carp and trout tribes, of willows, brambles, and others); and in the second place, the fact is equally certain that descendants of one and the same species which, according to the dogma of the old schools, could always effect a fertile union under certain circ.u.mstances, either cannot effect such a union or produce only barren hybrids (the Porto-Santo rabbit, the different races of horses, dogs, roses, hyacinths, &c.; see "History of Creation," vol. i., p.

146).

For a certain proof that the conception of species rests on a subjective abstraction and has a merely relative value--like the conception of genus, family, order, cla.s.s, &c.--no cla.s.s of animals is of so much importance as that of the Sponges. In it the fluctuating forms vary with such unexampled indefiniteness and variability as to make all distinction of species quite illusory. Oscar Schmidt has already pointed this out in the siliceous sponges and keratose sponges; and I, in my monograph, in three volumes, on the Calcareous Sponges (the result of five years of most accurate investigations of this small animal group), have pointed out that we may at pleasure distinguish 3, or 21, or 111, or 289, or 591 different species. I also believe that I have thus convincingly demonstrated how all these different forms of the calcareous sponges may quite naturally, and without any forcing, be traced to a single common parent-form, the simple--and not hypothetical, but existing at this present day--the simple Olynthus. Hence I think I have here produced the most positive a.n.a.lytical evidence of the transformation of species, and of the unity of the derivation of all the species of a given group of animals, that is generally possible.

Properly, I might spare myself these disquisitions on the question of species, for Virchow does not go into this main question of the theory of descent--but this is very characteristic of his att.i.tude. And just as he nowhere thoroughly discusses the doctrine of transformation, neither does he enter generally on the refutation of any of the other certain proofs of the doctrine of descent which we in fact possess at the present day. Neither the morphological nor the physiological arguments for the theory of descent, neither the rudimentary organs nor the embryonic forms, neither the paleontological nor the chronological argument are anywhere closely examined and tested as to their worth or their worthlessness as "certain proofs." On the contrary, Virchow takes them quite easily, sets them aside, and declares that "certain proofs" of the doctrine of descent do not exist, but remain to be discovered. To be sure, he does not indicate where they are to be sought, nor can he indicate it. How is this strange conduct to be explained? How is it possible that a distinguished naturalist should resist the most important step forward of modern natural science without in any way specially investigating it, without even practically testing and refuting the most weighty arguments in its favour? To this question there is but one answer.

Virchow is not generally intimate with the modern doctrine of evolution, and does not possess that knowledge of natural science which is indispensable for any well-grounded judgment on it.

After collecting and carefully reading all that Virchow, during many years, had written against evolution, I arrived at the conviction that he had not thoroughly read either Darwin's great work on the Origin of Species, nor any other work on the theory of descent, nor had he thought the matter out with such attention as so serious and intricate a subject absolutely demands. Virchow did with these works as it has been his well-known custom to do with many others--he hastily turned over the pages, caught at a few leading words, and without any farther trouble he has discoursed upon them, and, which is worst of all, has perpetuated these discourses through the press.

To excuse this conduct, and to account for Virchow's enigmatical position in the battle of evolution, we must consider what changes this highly-gifted and meritorious man has gone through in the course of the last thirty years. The most important and fruitful part of his life and labours was indisputably during the eight years when he resided in Wurzburg, from 1848 to 1856. There Virchow, with all the keenness of his youthful intellect, with a sacred enthusiasm for scientific truth, with indefatigable powers of work and the rarest insight, worked out that glorious reform of scientific medicine which will shine through all time as a star of the first magnitude in the history of medical science. In Wurzburg, Virchow elaborated that comprehensive application of the cellular theory to pathology which culminates in the conception that the cell is an independent living elementary organism, and that our human organism, like that of all the higher animals, is merely a congeries of cells--a highly fertile conception, which Virchow now denies as resolutely as he then supported it. In Wurzburg, twenty-five years since, I sat devoutly at his feet, and received from him with enthusiasm that clear and simple doctrine of the mechanics of all vital activity--a truly monistic doctrine, which Virchow now undoubtedly opposes where formerly he defended it. In Wurzburg, finally, he wrote those incomparable critical and historical leading articles which are the ornament of the first ten yearly series of his "Archives" of pathological anatomy. All that Virchow effected as the great pioneer of reform in medicine, and by which he won imperishable honour in the scientific treatment of disease,--all this was either carried out or preconceived in Wurzburg; and even the celebrated "Cellular Pathology," a course of lectures which he delivered during the first year and a half after quitting Wurzburg for Berlin, consists only of the collected and matured fruits of which the blossoms are due to Wurzburg.

In the autumn of 1856 Virchow left Wurzburg to settle in Berlin. The exchange of a narrow sphere of labours for a wider one, of small means and appliances for greater ones, proved unfavourable in this case, as in many similar cases. Since he has been in Berlin, in a "great Inst.i.tution," and with luxurious appliances, all the scientific results which Virchow has as yet brought to light are not to be compared, either as to quality or quant.i.ty, to the grand and immortal achievements which he himself effected in the little inst.i.tute of Wurzburg with the scantiest means--a new proof of the maxim enunciated by me, and hitherto never confuted, that "the scientific results of an inst.i.tute are in inverse proportion to its size." (See "The Aim and Methods of Modern Evolution."[14])

Still more grave is the circ.u.mstance that, since settling in Berlin, Virchow has more and more exchanged his theoretical scientific activity for practical political life. It is well known how prominent a part he plays there in the Prussian Chamber of Representatives, how he raised himself to be the leader of the party of progress, and, to give this political position a broader basis, took part in the representation of the citizens of the capital; how he has taken a most active interest, as city commissioner, in all the petty anxieties and concerns which the charge of such a city as Berlin entails. I am far from blaming, as many have blamed, the political and civic activity to which Virchow has indefatigably devoted his best powers. If a man feels in himself the inclination and vocation with strength and talent enough, to play a conspicuous political part, by all means let him do so; but verily I do not envy him; for the satisfaction which is derived from the most successful and fruitful political activity is not, to my taste, to be compared with that pure and disinterested satisfaction of the mind which results from absorption in serious and difficult scientific labours. In the turmoil of the political and social struggle, even the most splendid civic crown will be dulled by the stifling dust of practical life, which never reaches the ethereal heights of pure science and never rests on the laurels of the thoughtful investigator. However, as I have said, that is a matter of taste. If Virchow really believes that he is doing a greater service to humanity by his practical political life in Berlin than he formerly did by his theoretical scientific work in Wurzburg, that is his affair; but for all that, in his former sphere he was incomparable, and cannot be replaced; in the latter this is not the case.

If a distinguished man, be he never so remarkable for uncommon power of work and universal gifts, pa.s.ses the whole day in the friction of political party-struggles, and throws himself as well into all the petty and wearisome details of daily civic life, it is impossible for him to maintain the requisite feeling for the progress of science--particularly when it advances so rapidly and incessantly as is the case in our day. It is therefore quite intelligible that Virchow should soon have lost this feeling, and in the course of the last two decades have become more and more estranged from science. And this estrangement has at last led to so complete a change in his fundamental views, to such a metapsychosis, that the present Virchow of 1878 is hardly in a position to understand the youthful Virchow of 1848.

We have seen a similar mental change occur contemporaneously in our greatest naturalist, Carl Ernst von Baer. This gifted and profound thinker and biologist, whose name marks a new epoch in the history of evolution, had in his later years become wholly incompetent even to understand those most important problems of his youthful labours which opened up new paths of inquiry. While in his early years he laid down principles of the greatest value to our modern doctrine of evolution, and even went very near to adopting this hypothesis into his system, at a later period he utterly denied it, and by his writings on Darwinism proved that he was no longer generally capable of mastering this difficult problem. As I am one of Von Baer's warmest admirers, and in my "Evolution of Man," as well as in the "History of Creation," and in other places, have most emphatically expressed that sincere esteem, I thought I might venture to forbear from calling attention to the discrepancy between the lucid, monistic principles of Von Baer in his youth, and the confused dualistic views of his old age. But as many opponents of Darwinism--and among them particularly the Old Catholic philosopher of Munich, Huber, who has written a series of articles in the "Augsburger Zeitung"--have made constant capital out of the harmless talk of the feeble old Von Baer, I must in this place explicitly declare that this dualistic prating of the old man is quite incapable of shaking the monistic principles of the young and enterprising pioneers of science, or of giving them the lie.

In his autobiography Von Baer gives us the explanation of this striking contradiction. In 1834 he entirely and for ever abandoned the province of the history of development, at which for twenty years he had laboured incessantly, and where he had earned splendid laurels.

To escape from the haunting and importunate ideas of the science which had so wholly absorbed him, he fled from Konigsberg to Petersburg, and subsequently busied himself in scientific inquiries of a quite different character. Twenty-five long years pa.s.sed by, and when Darwin's work appeared in 1859, Von Baer had too long undergone a metapsychosis to be able to understand it. In Von Baer, as in Virchow, the course of this remarkable metapsychosis is highly instructive, and will itself afford to the thoughtful psychologist an interesting evidence of the doctrine of evolution.

However, the lack of comprehension of our modern evolution-hypothesis is easier to explain in Virchow's case than in Von Baer's, for this reason: morphological knowledge was greatly lacking to Virchow, while Von Baer possessed it in the highest degree. Now morphology is precisely that very department of inquiry in which our theory of descent has its deepest and strongest roots, and has matured the most glorious fruits of knowledge. The study of organic forms, or morphology, is thus, more than any other science, interested in the doctrine of descent, because through this doctrine it first obtained a practical knowledge of effective causes, and was able to raise itself from the humble rank of a descriptive study of _forms_ to the high position of an a.n.a.lytical science of _form_. It is true that by the beginning of this century the most comprehensive branch of morphology--_i.e._, comparative anatomy--which was founded by Cuvier and splendidly developed by Johannes Muller, had laid the foundations on which to build a truly philosophical science of form. The enormous ma.s.s of various empirical material, which had been acc.u.mulated by descriptive systematists and by the dissections of zootomists since the time of Linnaeus and Pallas, had already been abundantly matured and utilised in many ways for philosophic purposes by the synthetic principles of comparative anatomy. But even the most important universal laws of organisation--of which the old system of comparative anatomy was one--had to take refuge in mystical ideas of a plan of structure and of creative final causes (_causae finales_); they were incapable of arriving at a true and clear perception of effective mechanical causes (_causae efficientes_). This last, most difficult, and grandest problem, Charles Darwin was the first to solve in 1859, by setting Lamarck's theory of descent, which was already fifty years old, on a firm footing by his own theory of selection. By this hypothesis it was first made possible to fit together the rich materials which had been previously ama.s.sed, into the splendid edifice of the mechanical science of form. (See my "General Morphology," vol. i. chap. iv.)

The immeasurable step which Darwin thus made in organic morphology can be adequately appreciated only by those who, like myself, were brought up in the school of the old teleological morphology, and whose eyes were suddenly opened by the theory of selection to a comprehension of that greatest of all biological riddles, the creation of specific forms. The dogma of creation, the mystic and dualistic doctrine of the isolated creation of each separate variety, was annihilated at one blow; the belief in trans.m.u.tation has now for ever taken its place--the mechanistic and monistic doctrine of the metamorphosis of organic forms, of the descent of all the species of one natural cla.s.s from a common parent-form. How complete a change the science of mechanical morphology has by this means been compelled to undergo, I have endeavoured to point out in my "General Morphology;" and any one who wishes to convince himself clearly of what an enormous revolution has been brought about, particularly in comparative anatomy, may compare the "Outlines of Comparative Anatomy" (Grundzuge der vergleichenden Anatomie), by Carl Gegenbaur, 1870, and the latest edition of his "Elements" (Grundrisses), with the old text-books of that science.

Virchow has no suspicion even of all these immeasurable strides in morphology, for this department always lay out of his ken. His great reforms in pathology were founded in the province of physiology, and more especially in cellular physiology. But within the last twenty years these two main branches of biological inquiry have grown more and more apart. The great Johannes Muller was the last biologist who was able to keep these departments of organic inquiry together, and who won equally immortal honours in both divisions of the subject.

After Muller's death in 1858 they fell asunder. Physiology, as the science especially of the functions or living activity of the organism, addressed itself more and more to exact and experimental methods: morphology, on the contrary, as the science of the forms and structure of animals and plants, could naturally make but very small use of this method; it must take refuge more and more in the history of evolution, and so const.i.tute an historical natural science. It was on this very historical and genetic method of morphology, in contradistinction to the exact and experimental method of physiology, that I based my Munich address; and if Virchow in his answer had really and thoroughly refuted this position, instead of fighting with mere phrases and denunciations, this radical opposition would have been well worthy of the fullest discussion. At the same time I have no wish to reproach Virchow for being wholly fettered by the one-sided views of the modern school-physiology, nor because morphology lies so far out of his ken that he has not been able to form an independent judgment of its aims and methods; but when, in spite of all this, he on every occasion lets fall a disparaging judgment of it, we must dispute his competence. It is true that in his Munich address he emphasises the statement, "That which graces me best is that I know my ignorance," by printing it in italics. I only regret that I am forced to deny his possession of this very grace. Virchow does not know how ignorant he is of morphology, else he would never have uttered his annihilating verdict on it, else he would not continually designate the study of the theory of descent as dilettanteism and vain dreaming, as "a fanciful private speculation which is now making its way in several departments of natural science." In truth, Virchow does me greatly too much honour when he designates as my "personal crotchet"

an idea which for the last ten years has been the most precious common possession of all morphological science. If Virchow were not so unfamiliar with the literature of morphology, he must have known that it is penetrated throughout by this principle of descent, that every morphological inquiry which conscientiously pursues a well-considered problem now a.s.sumes the doctrine of descent as granted and indisputable. Of all this he is ignorant, and so it is intelligible that he should continue to demand "certain proofs" of this hypothesis, although those proofs have long since been produced.

FOOTNOTES:

[12] Vol. ii., p. 334 of translation.

[13] London: C. Kegan Paul & Co. 1879.

[14] Jena, Zeitschriften fur Naturwissenschaft, 1875. Vol. x.

Supplement.

CHAPTER III.

THE SKULL THEORY AND THE APE THEORY.

Inasmuch as Virchow persists in treating the theory of descent as an "unproved hypothesis," inasmuch as he ignores all the forcible evidences of that hypothesis, he deprives himself of the right of speaking a decisive word in this, the most important scientific dispute of the present day. Virchow is, in fact, simply incompetent in the great question of evolution, as he is deficient in the greater part of that knowledge--more especially morphological knowledge--which is indispensable to forming a judgment upon it. Hence on the turning-point of the whole matter--viz., the problem as to the origin of species--he can have no opinion, as he has never turned his attention to the systematic treatment of species: those transitions of one species into another, which he asks to see, abound on all sides, as is well known to every systematic naturalist. Only consider, for example, the genera of Rubus and Salix among the living plants of the present period, and the Ammonites and Brachiopoda among extinct animals. Hence, too, Virchow can have no independent views as to the historical development of the higher from the lower animals, because the abundant living forms of the lower animals are almost unknown to him, and because he has hardly any conception of the marvellous strides which hundreds of industrious workers have made in this very department within the last twenty years. But there can be no doubt, indeed it is already universally acknowledged, that it is precisely the comparative anatomy of the lower--nay, of the very lowest animals--that has solved the greatest riddles of life, and removed the greatest obstacles from the path of the doctrine of descent. He simply ignores the fact that true Monads actually exist, and have been positively identified by many different observers as structureless "organisms without organs," and he turns out the poor Bathybius with a kick. And yet I believe that in "Kosmos"[15] I have conclusively proved that Monads must retain their vast elementary importance whether the Bathybius actually exists or not.

But even as regards the higher animals--nay, even as to the comparative anatomy of the highest next to man, the apes--Virchow stands apart, not understanding the views of modern morphology.

We must here examine more closely into this, because it is precisely in this department that Virchow's only morphological experiments have been made; viz., his investigations as to the skulls of apes and of men. This is precisely the one only point on which he has sought a closer acquaintance with morphology, and precisely here it is most clearly to be seen how little he is acquainted with the recent advances our science has made, and that he has hardly any conception of the extraordinary importance to that science of the theory of descent.

The skull theory, as is well known, has for a long time been a very favourite theme, not only with prominent naturalists, but also with talented amateurs. Undoubtedly the skull, viewed as the bony capsule which encloses our most important organ of sense, our brain, has a special claim to morphological importance; for the general conformation of the skull corresponds on the whole to the development of the brain, and its inner surface gives an approximate idea of the outer surface of the brain. In this correspondence lies the only sound kernel of the sickly, overgrown fancies of phrenology. The various development of the skull allows of an approximate inference as to the various degrees of development of the brain and of the mental faculties. The comparative study of the skulls of the vertebrate animals had excited the lively interest of morphologists by the end of the last century, when comparative anatomy was beginning to const.i.tute a special science; and the genetic inquiry as to the morphological significance and development of the skull soon grew out of it. It was no less a man than our greatest German poet who first answered this question, and propounded the theory that the skull was neither more nor less than the modified foremost end of the vertebral column, and that the separate groups of bones which lie behind one another in the human skull, as in that of all the higher vertebrata, answer to the separate modified vertebrae. This "vertebral theory" of the skull, which Von Goethe and Oken simultaneously and independently attempted to prove, aroused universal interest and maintained its ground for seventy years, while many attempts were made to improve and enlarge upon it in detail.

A quite new light was thrown on this, as on every other morphological question, as soon as Darwin in 1859 had once more put into our hands the torch of the doctrine of descent. The inquiry as to the origin of the skull now a.s.sumed a real and tangible form. Since all vertebrate animals, from fishes up to man, agree so completely as to their essential internal structure that they can be rationally conceived of no otherwise than as branches of one stock and as descendants of one parent-form, the distinctly formulated question as to the skull theory which now started into prominence was this: "How, historically, has the skull of man and of the higher animals originated from that of the lower animals? How is the development of the bones of the skull from the vertebrae to be proved?" The answer to these difficult questions was supplied by the first comparative anatomist of the present day, by Carl Gegenbaur. After Huxley had pointed out that the ontogenesis or individual development of the skull by no means favoured the older hypothesis of Goethe and Oken, Gegenbaur brought forward evidence that the fundamental idea of that theory was correct; that the skull does in fact correspond to a series of coalescent vertebrae, but that the separate bones of the skull are not to be regarded as representing parts of such modified vertebrae. The skull-bones of all recent vertebrate animals are rather, for the most part, dermal bones, which have come into closer connection as supplementary to the cartilaginous primitive skull. We can even now trace the number and position of the original vertebrae, from which this primitive skull originated, by the number of the vertebral arches (gill-arches) which are attached to it, as well as by the number and position of those vertebrae, from nine to ten. Of all the recent vertebrata, the cartilaginous fishes, or Selachians, have most nearly preserved the form and structure of this primordial skull. These Selachians, the Rays and Sharks, are on the whole the creatures which throw the clearest light on the history of the lineage of the vertebrata and on the organisation of our primeval fish-natured ancestors. It is one of the particular merits of Gegenbaur that he clearly and firmly established the place in nature of the Selachians as the common ancestors of all vertebrate animals from fish up to man.

None but those who have thoroughly studied the comparative morphology of the vertebrata, who have sought the genetic issue from that labyrinth of intricate morphological problems at the hands of the theory of descent, can duly value the immeasurable service which Gegenbaur has done by this and other "Investigations into the Comparative Anatomy of the Vertebrata." These investigations are as much distinguished by a profound knowledge and careful working out of the wonderfully-extensive empirical materials for the subject, as by their critical ac.u.men and philosophic grasp. At the same time they set in the clearest light the immeasurable value of the theory of descent in the causal explanation of the most difficult morphological problems. Gegenbaur might, therefore, with perfect right, enunciate this axiom in the Introduction to his "Comparative Anatomy." "The theory of descent will at once find a touchstone of proof in comparative anatomy. Up to this time no experience in comparative anatomy has transpired which contradicts that theory; on the contrary, they all lead up to it. Thus it will receive back from science that which it has given to scientific method: clearness and certainty." In point of fact we can adduce no morphological investigations which better support this declaration than those very phylogenetic researches "as to the cranium of the Selachians, as a basis for the critical examination of the genesis of the cranium of the vertebrata," 1872. As Virchow had formerly thoroughly studied the old skull-hypothesis, and in his admirable discourse on "Goethe as a Naturalist," 1861, had given an excellent exposition of it; as moreover he had produced most valuable contributions to the normal and pathological anatomy of the human skull, we might have expected that he would have received Gegenbaur's grand reform of the theory of the skull, and historical solution of the skull-problem, with the greatest interest, and have made it the clue to his own further researches. But we seek in vain through Virchow's latest contributions to the study of the human skull, for any indication of his knowing or appreciating Gegenbaur's investigations. On the contrary, we see him persistently moving, without any clear goal in view, on that trodden and devious path of investigation which finds the highest aim of craniological science in the measuring of skulls, or craniometry.

We are far from undervaluing the full significance of the results of exact and careful descriptions and measurements of various conformations of the skull as an empirical basis for a true and scientific study of the skull--_i.e._, for comparative and genetic craniology. But still we must say that the way and method by which this skull measurement has, for ten years now, been pursued by numerous craniologists can never yield corresponding scientific results; on the contrary, though it is cried up as the "exact morphology" of the skull, it simply loses itself in the domains of harmless trifling. A large amount of time has in the last ten years been squandered in disputes as to the best method of measuring skulls, while the craniologists concerned have not, in the first place, answered the obviously most important question: What end they propose to gain by this specialist measuring, what proposition they mean to prove by it? Most of those numerous skull measurers know nothing beyond the perfect human skull, or at most the skulls of a few other mammalia, while the comparative morphology and historical development of the crania of the lower vertebrata are wholly unknown to them; and yet these last contain the true key to the comprehension of the others. One single month devoted by these "exact skull measurers" to the study of Gegenbaur's theory of the skull, and to testing the hypothesis by the skulls of Selachians, would have yielded them more fruit and have given them more light than long years of describing and measuring human skulls, however various.

Virchow himself affords the most striking example of the usual results of this so-called "exact method" of studying skulls. In his popular essay on "The Skulls of Men and Apes," 1870, he concludes with this notable proposition:--"It is therefore self-evident that Man can never by any progressive development have originated from the Apes." Every evolutionist who is familiar with the surprising facts of comparative morphology will draw from them the opposite conclusion: "It is self-evident that Man could only have originated from the progressive development of the Ape (organism)."

This brings us to that question which, in the popular treatment of the theory of descent, is justly considered as its most important outcome and as the keystone of the evolutionist edifice--to the well-known proposition, "Man is descended from the Ape." While we simply ignore all the misrepresentation, distortion, and misinterpretation which this ape, or pithecoid hypothesis, has met with on all sides, we will only remark that this fundamental proposition, in the sense of our modern doctrine of evolution, can rationally have only this plain meaning: that the human species as a whole was long since developed from the order of apes, indeed actually from one (or perhaps more) long since extinct form of ape; the immediate progenitors of man in the long series of his vertebrate ancestry were apes or ape-like animals. Of course none of the now surviving species of apes is to be regarded as the unaltered posterity of that primeval parent-form.

Virchow, however, understanding the "ape question" in this sense, answers it, as Bastian also does, with the most positive contradiction. "We cannot teach the doctrine that man is descended from apes or from any other animal, for we cannot regard it as a real acquisition of science" (p. 31). Although I myself, in direct opposition to this view, and in agreement with almost all my professional colleagues, look upon the descent of man from apes as one of the surest of phylogenetic hypotheses, I will here expressly admit that the _relative_ certainty of this, as of all other historical hypotheses of descent, is not comparable with the _absolute_ certainty of the general theory of descent. It is now ten years since I first explicitly stated (in my "Natural History of Creation," vol. ii. p.

358): "The pedigree of the human race, like that of every animal or plant, remains in detail a more or less approximate general hypothesis. This, however, in no way affects the application of the theory of descent to man. In this, as in all researches into the derivation of our organism, we must distinguish between the _general theory_ of descent and the _specific hypothesis_ of descent. The general theory of descent claims full and permanent value, because it is inductively based on the whole range of common biological phenomena and on their internal causal connection. Each special hypothesis of descent, on the other hand, is conditional as to its specific value on the existing state of our biological information, and on the extent of those objective empirical grounds on which we deductively found the hypothesis, by our subjective inferences." And I must here emphatically add that I have on every opportunity repeated that reservation, and have always insisted on the difference which exists between the absolute certainty of trans.m.u.tation in general and the relative certainty of each individual specific pedigree. So that when Semper and others of my opponents a.s.sert that I teach my specific genealogies as "infallible dogmas," it is simply false. I have, on the contrary, pointed out on all occasions that I regard them only as _heuristic or provisional hypotheses_, and as a means of investigating the actual relations of cognate races of organic forms more and more approximately.

Since the conception of the natural animal system as a hypothetical genealogical tree, and the phylogenetic interpretation of morphological affinity which that conception involves, afford in fact the only rational interpretation of that affinity in general, my first genealogical attempts soon found many imitators, and at the present time numerous industrious labourers in the different departments of systematic zoology are endeavouring to find in the construction of such hypothetical genealogies the shortest and completest expression of the modern conception of structural affinity. If Virchow had not been as ignorant of the true significance and method of systematic morphology as he is of its progress and scientific contents, he must certainly have known this, and then he would surely have withheld his mockery of all these grave phylogenetic studies as "personal crotchets" and worthless dreams.

What mighty strides towards a mechanical morphology we have made by this phylogenetic working out of the system, and how much light and life it has at once thrown into the system that before was dead and cold, can only be known to those who have long and deeply studied specific systematisation and the grouping of species; Virchow has not the remotest suspicion of it. Moreover, these attempts have now proceeded so far, that a large proportion of the phylogenetic hypotheses are regarded as very nearly certain, and can hardly undergo any further essential modifications; while the greater number of them are still in an unfixed state, and one systematist tries to improve them in this direction, and another in that.

The following phylogenetic hypotheses are held to be almost certain:----The descent of many-celled animals from single-celled, of the Medusae from the hydroid Polyps, of the jointed from the unjointed worms, of the sucking from the gnawing insects, of amphibious animals from fishes, of birds from reptiles, of the placental mammalia from the marsupials, and so forth. I personally consider the descent of man from the apes as equally certain; nay, I regard this most important and pregnant genealogical hypothesis as one of those which, up to the present time, rest on the best empirical basis.

Huxley, in particular, fifteen years ago, in his celebrated "Man's Place in Nature," 1863, so admirably proved the undoubted "descent of man from apes," and so clearly discussed all the relations that had to be taken into consideration, that very little was left to others to do. The result of his comparative morphological investigations is contained in this proposition----" If we take up a system of organs, be it which we will, the comparison of its modifications throughout the series of apes leads us to the same conclusion: that in every single visible character man differs less from the higher apes than these do from the lower members of the same order." It is therefore impossible for any objective zoologist, according to the principles of comparative systematisation, to ascribe to man any other place in the animal world than in the order of apes; and it is quite immaterial whether we designate this individual group as the Order of Apes, or, with Linnaeus, as the Primates. For the phylogenetic construction of the system, the common descent of man and of apes from one common parent-form, necessarily follows from this inevitable grouping, and on this proposition only all the general inferences of the "ape-hypothesis" depend. As to what that common parent-form of men and apes may have been, very different views might probably be brought on opposite sides; but any one who knows the collected facts that bear upon the matter, and estimates them impartially, must, in conclusion, arrive at the certain conviction that that hypothetical and long-since extinct parent-form can only have been genuine apes; that is to say, of the placental mammalian type, such as when we see them now living before our eyes we unhesitatingly cla.s.s, on the ground of their zoological characters, as true apes, in the order of Apes or Primates.

In this, and all other sound phylogenetic hypotheses, we may most easily attain to a conviction of their truth by taking into consideration and comparison the other possible hypotheses. But in fact no single opponent of the ape-hypothesis has been able to combat it with any other phylogenetic hypothesis that has the faintest glimmer of probability. Not one opponent has suggested, or can suggest, any other animal form that can serve as our nearest ancestor than the ape. No one has ever reproached me by saying that Mother Nature has endowed me with too little imagination; on the contrary, I am often accused of having a superfluity of that gift of the G.o.ds; but I have often and repeatedly exerted my imagination to picture to myself any known or unknown animal-form as the nearest parent-form to man in the place of the apes, and have always found myself under the necessity of falling back upon the stock of apes. Let me conceive of the outward conformation and the internal structure of the nearest mammalian ancestors of men as I will, I am always forced to acknowledge that this hypothetical parent-form ranges under the zoologically-conceived order of apes, and cannot possibly be separated from the Simiadoe or Primates. If, in spite of this, any one chooses, out of a "personal crotchet," to accept some other series of unknown animal ancestors of man that have nothing to do with apes, that is but a mere empty hypothesis floating in the air. Our ape-hypothesis, on the other hand, is objectively and thoroughly proved by the essential agreement of the internal bodily structure of man and of apes, and by the ident.i.ty of their embryonic development, as I have fully shown in my "Evolution of Man" (chaps. xix. and xxvi.) The mode and manner in which he here puts palaeontology in the foreground, and throws on the theory of descent the task of producing an unbroken gradation of fossil transitional forms between the apes and man, is very indicative of Virchow's ignorance of this zoological question--in which I, as a professional zoologist, must decisively declare his incompetence. The reasons why such a solution of the problem is not to be expected, the extraordinary imperfection of the palaeontological record, the natural impediments to the palaeontological evidence of the genealogical table, have been so lucidly unfolded by Darwin himself (chaps. ix. and x. of the "Origin of Species") that I am obliged once more to come to the conclusion that Virchow has never read it with any attention.

Besides, long before Darwin, the gifted Lyell, the great originator of modern geology, showed clearly and convincingly how, for many reasons, the greater part of the fossil series must remain most imperfect, and these reasons were at a later period so often and so fully discussed (by myself among others, in chap. xv. of the "History of Creation,"

vol. ii. pp. 24-32) that it is wholly superfluous once more and in this place to state these well-known and time-worn questions. It only shows how little Virchow was acquainted with geology and palaeontology, and what a limited judgment he can form of these historical causal relations.

FOOTNOTES:

[15] Vol. i. p. 293.

CHAPTER IV.

THE CELL-SOUL AND CELLULAR PSYCHOLOGY.

No attack in Virchow's Munich address surprised me so much, and none so plainly betrayed the subversion of his most important scientific views, as that which he directed against my observations on psychology and cellular physiology. A mystic dualism in his fundamental views is here revealed, which stands in the sharpest contrast to the mechanical monism formerly upheld by the famous pathologist of Wurzburg.