Kitabı oku: «The Old Riddle and the Newest Answer», sayfa 12

XVII
"AUDI ALTERAM PARTEM"

WE have heard Mr. Carruthers' declaration, based upon his survey of palæontological botany, "The whole evidence is against Evolution, and there is none in favour of it."

Remarkably enough, at almost the same period²⁷⁴ Professor Huxley concluded a discussion of palæontological evidence with a precisely contrary pronouncement – "The whole evidence is in favour of Evolution, and there is none against it." On other occasions, also, he distinctly maintained that it is just this line of enquiry which conclusively establishes Evolution as no longer a theory, but an historical fact. To such a conclusion, he tells us,²⁷⁵ "an acute and critical-minded investigator is led by the facts of palæontology;" – and, again, "If the doctrine of Evolution had not existed, palæontologists must have invented it, so irresistibly is it forced upon the mind by the study of the remains of the Tertiary mammalia."

Such declarations clearly challenge consideration, especially when it is remembered how strict were the views which Professor Huxley professed as to the necessity of proofs for our beliefs, – "that it is wrong for a man to say he is certain of the objective truth of any proposition unless he can produce evidence which logically justifies that certainty."²⁷⁶

We therefore turn naturally to his lectures on Evolution, wherein he treats the palæontological argument ex professo, and we find that his verdict is based upon a few selected instances, such as that of the reptilian birds already mentioned, which he considers favourable to Evolution, and one which he terms demonstrative, – namely that of the Horse. This he treats in some detail; in regard of it he delivers the positive judgment which we have just heard, and it therefore in a special manner demands our attention.

As furnishing evidence for the history of the horse, two features are of special importance, his limbs, and his teeth. Of these we may confine our attention to the former, as being, at once, sufficient for our purpose, and within the scope of ordinary observation.

The horse family, or Equidae, belong to the tribe of Ungulates, or hoofed animals, some points of whose anatomy require to be considered in relation to our own.

Taking first the fore-limbs. What we call the "knee" of a horse is in reality the wrist, – the true knee, or rather elbow, being what we call the "shoulder." Below the knee comes the "cannon bone," corresponding to the middle bone of the hand, and below it the "pastern," "coronary," and "coffin" bones, representing the joints of the solitary middle-finger, while the hoof is its greatly enlarged and thickened nail. Similarly, in the hind-limbs; the "hock" is veritably the ankle, and again the lateral digits are suppressed, the middle toe alone remaining.

It thus appears that an Ungulate such as the horse, is an extreme modification of the general Mammalian plan, his members being highly specialized for a certain kind of work. His leg and hoof, as the theory of genetic Evolution declares, have been gradually fashioned to their present shape from an original limb in the common Mammalian ancestor, which by other modifications has equally produced the totally different members possessed by other mammals.

That the horse is descended from a race bearing more than one digit on each extremity, seems to be indicated by the splint-bones which are found on the cannon-bone of both fore and hind legs, and which represent the second and fourth finger and toe, and also by recorded occurrences of polydactyle horses, one of which has a distinguished place in history as Julius Cæsar's charger.²⁷⁷

That the animal as we now know him is the lineal descendant of various other ungulates, in whom the digits were gradually reduced from the normal number of five, to their present solitary representative, Professor Huxley and other Evolutionists hold to be demonstrated by the discovery in due succession of various equine specimens, in which this diminution is gradually exhibited.

The remains of these animals are all found in Tertiary strata, of which, it will be remembered, there are three great divisions, the Eocene, Miocene, and Pliocene, the first named being the most ancient, and the last the most recent.

The genus Equus, or at least our modern horse, Equus caballus, can be traced no further back than the Post-tertiary period. The succession of forms leading up thither commences at the bottom of the Eocene, and extends to the upper Pliocene.

Following Professor Huxley's guidance, we trace the pedigree downwards, thus:

Firstly, there is the true horse. Next we have the American Pliocene form, Pliohippus. In the conformation of its limbs it presents some very slight deviations from the ordinary horse. Then comes Protohippus, which represents the European Hipparion, having one large digit and two small ones on each foot… But it is more valuable than Hipparion, for certain peculiarities tend to show that the latter is rather a member of a collateral branch, than a form in the direct line of succession. Next, in the backward order in time, is the Miohippus, [Miocene], which corresponds pretty nearly with the Anchitherium of Europe. It presents three complete toes – one large median and two smaller lateral ones; and there is a rudiment of that digit which answers to the little finger of the human hand. The European record stops here: in the American Tertiaries, the series of ancestral equine forms is continued into the Eocene. An older Miocene form, Mesohippus, has three toes in front, with a large splint-like rudiment representing the little finger, and three toes behind. The radius and ulna, tibia and fibula,²⁷⁸ are distinct. Most important of all is the Orohippus, from the Eocene. Here we find four complete toes on the front limb, three toes on the hind-limb, a well developed ulna, a well developed fibula.

Here, when the lecture which we are considering was delivered, the series terminated: – and upon the facts as above given Professor Huxley thus commented:

Thus, it has become evident that, so far as our present knowledge extends, the history of the horse-type is exactly and precisely that which could have been predicted from a knowledge of the principles of Evolution. And the knowledge we now possess justifies us completely in the anticipation, that when the still lower Eocene deposits, and those which belong to the Cretaceous Epoch have yielded up their remains, we shall find, first, a form with four complete toes and a rudiment of the innermost or first digit in front, with probably a rudiment of the fifth digit in the hind foot; while, in still older forms, the series of the digits will be more and more complete, until we come to the five-toed animals, in which, if the doctrine of Evolution is well founded, the whole series must have taken its origin.

Finally he was able to add in a note that since the delivery of the lecture, Professor Marsh had discovered a new genus of Equine Mammals, Eohippus, corresponding very nearly to his description of what might first be looked for. "This," adds Professor Huxley, "is what I mean by demonstrative evidence of Evolution… In fact, the whole evidence is in favour of Evolution, and there is none against it."

That these facts are indeed most remarkable and deserving of all attention, cannot be questioned. But before we can agree that they are conclusive and demonstrative in Professor Huxley's sense a good many considerations require to be carefully weighed.

(i.) It is obvious, in the first place, that here as in all other instances which we have seen, the one thing is lacking which is really wanted in order to prove Evolution, namely evidence of one species gradually shading off into another. The creatures of which we have heard, are each isolated from the rest, and indeed very much isolated, for each belongs to a different genus,²⁷⁹ which shows that the differences between them are substantial. They are, in fact, farther apart from one another, than the zebra or the donkey from the horse, for both of these are classed in the genus equus, – or than the Bengal tiger is from the domestic pussy-cat, both belonging to the genus felis.

These various ungulate forms thus stand a long way from one another, and if they were once connected together by a bridge, or rather a causeway, we ought certainly to find some traces of it, and not always of those particular types which require to be united. If we suppose the very distinct species actually known to have been the piers of such a bridge, yet what has become of the arches? Till some vestiges of these be found, or, at least, some positive evidence that arches there actually were, can it be said that the story of the fossil equidae furnishes convincing testimony on behalf of the supposed evolution? Affinities these various forms undoubtedly exhibit: it has yet to be shown that affinities necessarily imply descent.

There is, however, something even more remarkable. We have seen that Professor Huxley prognosticated beforehand the discovery of Eohippus, and specified pretty nearly the features it would be found to present. In the same way, Professor Marsh²⁸⁰ anticipates and describes a still more remote ancestral form, for which, though it has not yet been found, he has provided an appellation, Hippops. But if either Professor really believes in Evolution, why does he take for granted that we shall chance upon one particular form, standing like a solitary outpost by itself, and not upon any other trace of the stream of life whereof it was but one transient phase? Such predictions may be evidence that the occurrence of these progressive forms is regulated by something analogous to Bode's Law of interplanetary distances, and that their discovery may be looked for at certain intervals. But the very fact that their actual position can be so accurately specified serves to show that it is very definitely fixed.

(ii.) Moreover, a very grave difficulty at once suggests itself, of which Professor Huxley makes no mention. The horse as we now have him, Equus caballus, is a native of the Old World, and has been introduced to America only since the time of Columbus. There had, it is true, been horses in America previously, – belonging to the genus Equus, perhaps even to the species caballus, – they had, however, been long extinct, and no memory of them remained. But, as will be noticed, the pedigree given by Professor Huxley consists almost entirely of American animals, to which category belong all whose names terminate in -hippus, and these cannot with any reason be assigned as progenitors to the European horse. As Sir J. W. Dawson observes:²⁸¹

In America a series of horse-like animals has been selected, beginning with the Eohippus of the Eocene – an animal the size of a fox, and with four toes in front and three behind – and these have been marshalled as the ancestors of the fossil horses of America… Yet all this is purely arbitrary, and dependent merely on a succession of genera more and more closely resembling the modern horse being procurable from successive Tertiary deposits often widely separated in time and place. In Europe, on the other hand, the ancestry of the horse has been traced back to Palæotherium– an entirely different form – by just as likely indications, the truth being that as the group to which the horse belongs culminated in the early Tertiary times, the animal has too many imaginary ancestors. Both genealogies can scarcely be true, and there is no actual proof of either. The existing American horses, which are of European origin, are, according to the theory, descendants of Palæotherium, not of Eohippus; but if we had not known this on historical evidence, there would have been nothing to prevent us from tracing them to the latter animal. This simple consideration alone is sufficient to show that such genealogies are not of the nature of scientific evidence.

(iii.) Even apart from this fundamental difficulty, there is much diversity as to the precise genealogy. We may compare together the lines of ancestry favoured – (1) by Professor Huxley, (2) In a case exhibited in our Museum of Natural History to illustrate the subject, (3) By Mr. Mivart,²⁸² (4) By Mr. Lydekker,²⁸³ (5) In The Evolution of the Horse, a pamphlet issued, January, 1903, by the American Museum. This last gives the very latest version of the pedigree, but, naturally, of the American Horse alone.

It will be observed, that whereas Hipparion is disallowed by Professor Huxley as not being in the direct line of descent, in all the other genealogies he appears as the immediate ancestor of Equus. Also that in all these tables, Old World and New World forms are used indifferently to supply progenitors for the same successor. Also that there is no agreement at all as to the earlier ancestry. It would likewise appear that even the existence of Eohippus himself is not beyond question, for in our Museum galleries and guide-book his name always has a note of interrogation appended. The American authorities give an anticipatory sketch of the limbs of the ancestor which still remains to be discovered.

There is something even more remarkable.

Huxley's lecture exhibiting the pedigree we have been considering was delivered in 1876. We have already seen that six years earlier he had declared himself satisfied, after much search, that though other genealogies might be doubtful, we had in the case of the Horse something really satisfactory. But the pedigree of 1870 – which he thus indicated as scientifically established – was totally different from that of 1876, and was acknowledged as erroneous by the very acceptance of the latter. In 1870 the ancestry presented for Equus consisted of Hipparion, Anchitherium, and Plagiolophus. Of these, Hipparion was in 1876 specifically disallowed as a direct ancestor: Anchitherium was displaced by Miohippus, and although we are told that these creatures "correspond pretty nearly," the Horse cannot be descended from both, especially as they dwelt in different hemispheres. Finally Plagiolophus disappears from the amended pedigree altogether. Nothing could more vividly illustrate the danger of such speculations than that an authority so clear-headed and conscientious as Professor Huxley should thus proclaim his acceptance of a genealogy which he had on after information to renounce. Nor to him alone have such misadventures happened. Mr. Darwin too thought the claim of Hipparion to ancestral equine rank to be beyond dispute. "No one will deny," he wrote,²⁸⁴ "that the Hipparion is intermediate between the existing horse and certain older ungulate forms." Yet, as we see, this has been denied by his champion Huxley himself.

(iv.) The materials available for the reconstruction of these various equine forms, are far less satisfactory than might easily be supposed. As a rule, each is known to us only by small fragments of its skeleton, so that we can have no assurance as to what the whole animal was really like, or even that all parts assigned to one creature really belonged to him. We can accordingly feel no certainty that if we could see any of these as a whole we should find it possible to suppose that the horse descended from it. Thus in Hippidium, an American genus closely allied to Equus, it is at least doubtful whether the digits did not terminate in claws.²⁸⁵ One species of Hippidium is known only by a solitary tooth. Of Hyracotherium only the skull has been found: of Orohippus only parts of jaws and teeth and a forefoot: of Epihippus, "only incomplete specimens."²⁸⁶ Accordingly, Professor Williamson, speaking of the discoveries of Professor Marsh and others, thus expresses himself:²⁸⁷

Beyond all question, some of the gaps that have hitherto separated the three animals [Anchitherium, Hipparion, and Equus] are filled up by these discoveries; but I want yet more evidence before I can arrive at the conclusion that the doctrine of Evolution is proved by these facts beyond the possibility of question. It appears to me that before I can unhesitatingly give to the testimony of these fossil horses the full value I am asked to do, I must know more about them than is at present possible. It will not be enough that the limbs and teeth of these creatures indicate transmutation, but such transmutation must be evidenced by every part of the animal. This demand is especially applicable to the stages which intervene between the Hipparion and the horse… Myriads of individuals must have existed to effect the gradual shading of the one into the other in every part of its body.

(v.) It should likewise be remarked that in one not unimportant particular, the plates so commonly given to illustrate the horse's ancestry do not fairly represent the facts. It would appear from them that all the animals were much of a size, which doubtless greatly assists the imagination in picturing them as all in one line of descent. But as a matter of fact they differed in stature extremely, and the remoter supposed progenitors were comparative pigmies. Hyracotherium, for instance, was "about the size of a hare,"²⁸⁸ and according to Professor Cope, Orohippus was the exact counterpart of this diminutive steed. The hypothetical Hippops, which Professor Marsh locates in the lower Tertiary or upper Secondary rocks, can, he thinks,²⁸⁹ now "be predicated with certainty;" and amongst other things it "probably was not larger than a rabbit, perhaps much smaller." Sometimes, so far as evidence goes, it even seems that in respect of size there was deterioration instead of advance as the lineage progressed. Thus Epihippus, found in the Upper Eocene, is considerably smaller than Protorohippus, found in the Middle Eocene; "but," says the American pamphlet,²⁹⁰ "no doubt there were others of larger size living at the same time," which will scarcely be called convincing.

(vi.) Worthy of notice also is "the remarkable circumstance that in the line of evolution culminating in the modern Horse, a parallel series of generically identical or closely allied forms occurs in the Tertiaries of both Europe and North America, from which it has been suggested that on both continents a parallel development of the same genera has simultaneously taken place."²⁹¹ And, as we have seen, while the American pedigree must have been entirely different from the European, it terminates equally in both continents with the genus Equus, if not actually with Equus caballus.²⁹² But, on any mechanical system of evolution, it is impossible to suppose that developments conducted along separate roads could thus be brought to meet in one terminus.²⁹³ Mr. Darwin did not conceive it possible that the same species should be produced twice over, "if even the very same conditions of life, organic and inorganic should recur,"²⁹⁴ and the production of genuine horses, not only in widely diverse circumstances, but through totally different ancestors, must appear still less conceivable. Consequently, says Mr. Mivart,²⁹⁵ "it follows from this generic identity, that classification will be no longer Darwinian, but one more Aristotelian, and will regard, not the origin but the outcome of development, whether of the individual or the species."

(vii.) There is, however, another consideration more serious than any of the above. In order to set the theory of genetic Evolution upon a sound and substantial basis, it is not sufficient to show that the last ungulate is lineally descended from the first, —Equus from Eohippus, Hyracotherium, Phenacodus, or Hippops, – but that this first ungulate himself – whichever it was – has been, or at least may have been, similarly developed from a non-ungulate Mammalian ancestor, the common parent of all the protean forms assumed by his progeny. To develop all these from one original, through a graduated series in each case, by the infinitesimal process of descent with modification, would require a period of time inconceivably long – immensely longer than that required to change one ungulate into another. Ungulates, as has been said, are a highly specialized type of Mammals, and although they walked on the nails of five digits instead of only one, a vast amount of Evolution would be required to bring them even to this point, from that whence all Mammals are said to have started. There must also have existed, while this development was in progress, a teeming and multitudinous mammalian life, as raw material for its operations – and of this at least some trace should remain.

But, so far as we know, the first Ungulates made their appearance upon earth quite as soon as did any other mammals from which they could possibly have sprung. Phenacodus, is in fact described as,²⁹⁶ "The most primitive Eocene mammal yet discovered." He appears in the Lower Tertiary; while the Secondary and Mesozoic rocks beneath, – the whole period covered by which would be none too long for the evolution of Tertiary mammals generally, – are practically devoid of mammalian remains altogether, exhibiting only a few small marsupials, from which we can no more suppose Phenacodus and the huge and various beasts who were his Eocene contemporaries to have developed, than from opossums the size of shrew-mice.

It also complicates matters not a little to find that when placental mammals first show themselves all over the world at the beginning of the Eocene, – while this highly specialized order of the Ungulates seems to have been much the most numerous, it had a host of contemporaries, of extreme diversities of structure: – as for instance Unguiculates (or clawed animals) allied to the Hyena and the Fox, Rodents (gnawing animals) akin to the Squirrel, as well as Whales and Bats. Of the Cetaceans, Sir J. W. Dawson tells us:²⁹⁷

The oldest of the whales are in their dentition more perfect than any of their successors, since their teeth are each implanted by two roots, and have serrated crowns, like those of the seals. The great Eocene whales of the South Atlantic (Zeuglodon) which have these characters, attained the length of seventy feet, and are undoubtedly the first of the whales in rank as well as in time. This is perhaps one of the most difficult facts to explain on the theory of Evolution… "We may question," says Gaudry,²⁹⁸ "these strange and gigantic sovereigns of the Tertiary oceans as to their progenitors – they leave us without reply." … Their silence is the more significant as one can scarcely suppose these animals to have been nurtured in any limited or secluded space in the early stages of their development.

The Bats, as is obvious, would require quite as much transformation from the generalized mammalian type as the Whales themselves, though in quite another direction. But they appear with their wings fully developed, in the Eocene, in both Hemispheres.

Gaudry thinks [writes Sir J. W. Dawson]²⁹⁹ that it is "natural to suppose" that there must have been species existing previously with shorter fingers³⁰⁰ and rudimentary wings; but there are no facts to support this supposition, which is the more questionable since the supposed rudimentary wings would be useless, and perhaps harmful to their possessors. Besides, if from the Eocene to the present, the Bats have remained the same, how long would it take to develop an animal with ordinary feet, like those of a shrew, into a bat?

Such instances are by no means singular, nor are like difficulties confined to the Eocene. In the Miocene above, about the time when Anchitherium flourished, there appeared a family with whom he might claim relationship, for they were not only akin to the Ungulates but Perissodactyles, or "odd-toed," like himself. These were the "Proboscideae" – "the beasts that bear between their eyes a serpent for a hand," in other words the Elephants and their allies. These, like other families, amongst their earliest representatives included the giants of their race, for some of their Miocene specimens³⁰¹ are about half as large again as the largest of our modern elephants. Professor Ray Lankester has recently declared³⁰² that we now understand the genetic affinities of these creatures, whose faces have been pulled out into trunks with the nose at the extremity, and in support of his statement he adduces the features of the cranium as exhibited in certain recently-discovered specimens. But how far can conclusions be called final which are based upon such partial evidence?³⁰³ As M. Gaudry, convinced Evolutionist as he is, acknowledges, in regard of this very matter:³⁰⁴

Like the Mastodons, the Dinotheria appeared suddenly. Whence did they come? from what quadrupeds did they spring? At present we do not know… The points of difference [from other mammals] taken as a whole, and compared with the points of resemblance, are too great to enable us to point to any relationship between the Proboscideans and animals of other orders as yet known to us.

Such then are some of the still unanswered questions connected with the genesis of the Horse, "the most famous instance of geological evidence"³⁰⁵ which Professor Huxley selects as proving Evolution to demonstration. It is by no means easy to understand how it could ever be supposed to merit any such description. In view of the various difficulties recited above it can hardly be thought that there is satisfactory evidence even of the modicum of Evolution for which alone are such arguments brought, namely within the limits of the Equidæ. Even were the reality of this established to the full, how would such evidence compare with that we have heard, drawn not from one corner of Organic Nature, but from a review of the great lines of its history?³⁰⁶

We find indeed that while Professor Huxley declares palæontology to be the main support of Evolution, other authorities tell us the exact contrary.

The doctrine of organic evolution [says Sir J. W. Dawson]³⁰⁷ is essentially biological rather than geological, and has been much more favoured by biologists than by those whose studies lead them more specially to consider the succession of animals and plants revealed by the rocks of the earth.

Similarly Professor Williamson,³⁰⁸ speaking of the efforts made to obtain evidence on behalf of Evolution, says: "Not only living, but extinct animals have been appealed to; Professor Huxley especially has, with his wonted skilfulness, made use of the latter to buttress the geological side of the structure, which is confessedly its weakest one."

More important than all, – Mr. Darwin himself fully acknowledged that the palæontological evidence is far short of what it should be: – and attempted to meet the difficulty by pleading the imperfection of the geological record: – a plea to be more fully considered presently.

We must not leave unnoticed the method of dealing with the geological record adopted by Professor Haeckel. Of this we have already seen a slight specimen, – in the gratuitous and baseless assertion that the apetalous Dicotyledons date as far back as the Trias, at the very bottom of the Secondary period, by which, were it a fact, a serious Evolutionary void would be filled. In the same manner he draws a perfectly imaginary picture of the submarine forests of primeval days, in which "we may suppose" all the forms of after vegetation to have begun their career as seaweeds.³⁰⁹

But in regard of his favourite doctrine of the bestial origin of man, he goes much further, and prints³¹⁰ an elaborate genealogy upon which Professor Huxley in reviewing him makes no adverse remark. In this he exhibits, as a simple matter of scientific fact, an "Ancestral Series of the human pedigree," which ninety-nine per cent, of his readers will naturally suppose to be based upon palæontological evidence. This wonderful genealogy stands thus:

1. Monera. 2. Single-celled Primeval animals. 3. Many-celled Primeval animals. 4. Ciliated planulæ (Planæada). 5. Primeval Intestinal animals (Gastræada). 6. Gliding Worms (Turbellaria). 7. Soft-worms (Scolecida). 8. Sack worms (Himatega). 9. Acrania. 10. Monorrhina. 11. Primeval fish (Selachii). 12. Salamander fish (Dipneusta). 13. Gilled Amphibia (Sozobranchia). 14. Tailed Amphibia (Sozura). 15. Primeval Amniota (Protamnia). 16. Primary Mammals (Promammalia). 17. Marsupialia. 18. Semi-apes (Prosimiæ). 19. Tailed narrow-nosed Apes. 20. Tail-less narrow-nosed Apes (Men-like Apes). 21. Pithecanthropus (Speechless or Ape-like Man). 22. Talking Man.

The first thing to remark [says M. de Quatrefages]³¹¹ is that not one of the creatures exhibited in this pedigree has ever been seen, either living or fossil. Their existence is based entirely upon theory.³¹² All species, existing or extinct, are said to have been preceded by ancestral forms, which have disappeared leaving no vestige behind… All the ancestral groups more or less ill represented in the actual organic world, do not suffice to fill up the gaps in his pedigree; from one stage to another there is sometimes too broad a gulf. Then Haeckel invents the types themselves, as well as the line of descent to which he assigns them [for example No. 7, The Scolecida, and No. 21, Pithecanthropus].

This kind of "Science" does not deserve to be treated seriously. It will be sufficient to cite another observation of M. de Quatrefages:³¹³

If Darwin erred in regarding our very ignorance as to some degree telling in favour of his notions, he never tried to re-write the missing volumes of the earth's history, to restore the chapters which have been torn out, or to fill the blanks upon pages that have come down to us. But this is just what Haeckel does continually. Whenever a branch or a twig is lacking on his genealogical trees, whenever the transit from one type to another would appear too abrupt, were we to restrict ourselves to creatures actually known, he invents species and groups bodily, to which he unhesitatingly assigns a place in phylogeny, often a part in phylogenesis. Sometimes he calls in ontogeny to countenance the discovery of supposed ancestors: but frequently he does no more than affirm their existence. He thus creates a fauna, entirely hypothetical, of which Vogt rightly said that no man ever saw a trace of it, or ever will.