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CHAPTER XIII. ·
THE ORGANIC SIMILARITY OF ANIMALS.
THERE is sufficient similarity in the general structure of animals, and of analogy in some of their parts, though in other respects the animals may be widely different in appearance and habits, to convince us that this is not accidental; and, therefore, out of the School of Transmutation, it is said that there is a general plan which, on the whole, is sustained throughout the organic world. This plan seems to have been worked on a type with reference to a future advancement, and this advancement, in the opinion of many great physiologists, pointed towards the coming man, who was to be the crown and consummation of the vertebrated animals.
Agassiz, in his Principles of Zoology, has thus expressed it: There is a manifest progress in the succession of beings on the surface of the earth. This progress consists in an increasing similarity of the living fauna and among the vertebrates, especially in their increasing resemblance to man. But this connection is not the consequence of a direct lineage between the faunas of different ages. There is nothing like parental descent connecting them. The fishes of the Palæozoic age are in no respect the ancestors of the reptiles of the Secondary age, nor does man descend
from the mammals which preceded him in the Tertiary age; the link by which they are connected is of a higher and immaterial nature; and their connection is to be sought in the view of the Creator himself, whose aim in forming the earth, in allowing it to undergo the successive changes which geology has pointed out, and in creating successively all the different types of animals which have passed away, was to introduce man upon the surface of the earth. Man is the end towards which all the animal crea. tion has tended from the first appearance of the first Palæozoic fishes.'
This is said, in substance, also by the illustrious Cuvier; and Professor Owen has expressed similar sentiments. * The recognition of an ideal exemplar for the vertebrated animals proves that the knowledge of such a being as man must have existed before man appeared. For the Divine mind that planned the archetype also foreknew all its modifications. The archetypal idea was manifested in the flesh, under divers modifications upon this planet, long prior to the existence of those animal species that actually exemplify it.
As a short illustration of this prophetic aspect of organic appearances, take the following remarks of Hugh Miller: • Of the earliest known vertebrates, the placoidal fishes of the upper Silurian rocks, we possess only fragments, which, however, sufficiently indicate that they belonged to fishes furnished with the two pair of fins, now so generally recognized as the homologues of the fore and hinder limbs of quadrupeds.
* With the second carliest vertebrates, the ganoid fishes of the Old Red Sandstone, we are more directly acquainted, and kuow that they exhibited the true typical form-a verte
bral column terminating in a brain-protecting skull, and that in the acanth, celecanth, and dipterian families, they had the limb-like fins. In the upper part of the system, the earliest reptiles have the first-known traces of the typical foot, with its five digits. Higher still, in one of the deposits of the Trias, we are startled by what seems to be the impression of a human hand of an uncouth massive shape, but with thumbs apparently set in opposition, as in man, to the other fingers. We next trace the type upwards among the wonderfully developed reptiles of the Secondary periods. Then among the mammals of the Tertiary ages, higher and yet higher forms appear; the mute prophecies of the coming being will each approach clearer, fuller, more expressive, and at length receive their fulfilment in* the advent of man.'
All this of course is viewed in a very different light by the Transmutationists, with whom it is obviously essential to deny any plan in the general arrangements of the organic world. For if it be conceded that there is a plan, this would necessarily imply a presiding intelligent mind, able to arrange and carry out the plan ; whereas the very essence of their system is that all living beings are the result of a non-intelligent sequence of events—of accidental circumstances benefiting and improving 'favoured' races, and leaving the rest to perish.
All these organic similarities and homologues of parts are with them evidences of descent. If the placoidal fishes of the upper Silurian have fins which were homologues of the fore and hinder limbs of quadrupeds, they interpret this that the fish is the ancestor of the quadruped, and that the quadruped derived his limbs from the fins of
* Testimony of the Rocks.
the fish. In the tail of the cow, giraffe, fox, lorse, &c., they see the tail of the fish ‘worked up' for these different animals; modified, and altered indeed, but still made out of the fish's tail: and thus similitudes and homologues are all family-marks, and all bespeak one ancestral origin.
When several characters,' says Mr Darwin, let them be ever so trijling, occur together throughout the large group of beings having different habits, we may feel almost sure on the theory of descent, that the character has been inherited from a common ancestor' (458).
Mr Darwin might have said more than this, for 'on the Theory of Descent,' that is, taking for granted that that Theory is true, we may be quite sure that these characters’ have been inherited from a common ancestor. The postulate, however, is not conceded, and Mr Darwin has first to prove that his Theory is true.
However, thus more at length does he explain to us his views on this particular branch of his Theory :
We have seen that the members of the same class, independently of their habits of life, resemble each other in the general plan of their organization. This resemblance is often expressed by the term “unity of type,' or by saying that the several parts and organs in the different species of the class are homologues. The whole subject is included under the term morphology. What can be more curious than that the hand of a man formed for grasping, that of a mole for digging, the leg of a horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include simi. lar bones, in the same relative position ? The parts may change to almost any extent in form and size, and yet they always remain connected together in the same order.
We never find, for instance, the bones of the arm and forearm, or of the thigh and leg, transposed. Hence the same name can be given to the homologous bones in widely different animals.
Nothing can be more hopeless than to attempt to explain this similarity of pattern in members of the same class, by utility, or by doctrine of final causes. On the ordinary view of the independent creation of each being we can only say that it is--that it has so pleased the Creator to construct each animal and plant.
“The explanation is manifest on the theory of Natural Selection of successive slight modifications—in changes of this nature there will be little or no tendency to modify the original pattern, or to transpose parts--the bones of the limbs might be shortened or widened to any extent, and become gradually enveloped in thick membrane, so as to serve as a fin-or a webbed foot might have all its bones, or certain bones, lengthened to any extent, and the membrane connecting them increased to any extent, so as to serve as a wing, &c. If we suppose that the ancient progenitor, the archetype as it may be called, of all mammals had its limbs constructed on the general pattern, for whatever portion they served, we can at once perceive the plain signification of the homologous construction of the limbs throughout the whole class,' &c. (466-7).
This passage, which clearly explains the demands of the Theory on Morphology, shows also the necessary exclusion of creation from the system of the Transmutationists, who reject with disdain the idea of referring the commencement of life of an organized being to an operation and a power which our understanding cannot grasp. The whole reasoning, however, goes on the assumption that Natural