(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[{253}] [{254}]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 [{255}]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[{256}] 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[{257}] 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[{258}] 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 fingers[300] 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 specimens[301] are about half as large again as[{259}] the largest of our modern elephants. Professor Ray Lankester has recently declared[302] 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]