As to the course of living nature, the development theory is there at once repudiated in the now clearly established fact, that the first germinal vesicles are different in the different tribes of animals. A non-identity of type is discoverable in the minutest microscopical beginnings of organic life. And “by no change of conditions can two ova of animals of the same species be developed into different animal species; neither by any provision of identical conditions can two ova of different species be developed into animals of the same kind.” Corresponding to these differences in their fœtal forms, there are in all the stages toward parturition a similarity of progress in the various organs and appendages in the same kinds of animals. Fishes, birds, quadrupeds, all manifest a divergence from each other in the first action of the respirating organs—in the nervous system—and in all the apparatus connected with the movements of the heart and blood-vessels. There is no structural interchange, in the minutest part, that distinguishes the orders of the perfect animal in any of the antecedent fœtal conditions; the organic contrivances within the egg being as complete and as thoroughly prospective to the future use and habits of the bird, as are the petals of the flower inclosed within the bud, the arms of the giant oak within the acorn, or man in his evolving capacity toward intellectual being.
What is thus true in all the rudimentary stages of organic development is strikingly confirmed by the unalterable condition of all living nature. Plants and animals never diverge, beyond small ascertained limits, from the fixed characters of their families, resisting the effects of every kind of influence, whether proceeding from natural causes or human interference. The lapse of three thousand years has left the embalmed carcasses of men and animals, in Egypt, wrapped and swathed in a material woven from the same species of plants which still flourish on the banks of the Nile. The crocodile and the ibis still drink of its waters. Nothing changed in form or appearance, the swarthy Arab repairs to its cooling fountains to quench his thirst. Nature has been tortured in a thousand ways, to cause her to depart from her long beaten paths; but she is obdurate on every point. Man would improve her kinds, and hybrids are produced; but there the variety ends. Crosses are constantly attempted; but “the hitherto and no farther” is soon approached. Our fruit-bearing trees are coaxed with all the appliances of horticultural skill; and yet in all their seminal and floral organs, the texture of their leaves and bark, the structure of their roots and stem, the rudimentary stock remains one and the same. Domestication has, indeed, wrought wonderful changes and improvements in the breed of many creatures. Horses, oxen, sheep, pigs, dogs, and poultry of all sorts, are increased in bulk, tamed, ameliorated in habit and disposition. But the skeletons of all continue essentially as they were in their natural state; and even the individuals the most widely removed from the primitive type, as exemplified in the canine race, never present any real difference of form in the important organs.—When again abandoned to their own guidance, and the restraints imposed by man are removed, the domesticated animals, one and all, return to their former condition, and speedily resume the instincts and appearance of the jungle and the forest.
If such are the unvarying laws of physiology now, the presumption is that they have been the same in all past ages. Creatures are brought from the extremities of the earth—the polar, temperate, and tropical denizens, all mixed up and crossed with each other—food, climate, and treatment, all changed—and, through all, the type of every species continues as before—no transmutation of one kind into another under all the violent tutoring agencies to which they have been subjected. For thousands of years such has been the unswerving course of nature. Would it not clearly be a solecism in reasoning to argue differently over the geological epochs, however indefinite in extent, because, in the far-off regions of space, our eyes can note no change in the relative position of the stars? The things will not compare. Time and space are not co-ordinate terms. And an appeal from positive knowledge to supposed, assumed ignorance does not meet the question.
Meanwhile, the amplitude of the current epoch, if we may so speak, gives scope and verge enough for all the requirements of the problem to be solved, the conditions of the argument to be established, the process of reasoning to be employed. An experience not merely of six thousand years, but an experience embracing a uniformity of results in all the hundreds of thousands of instances into which animate nature is divided, in all the countless species of plants and animals which have existed successively throughout the whole of that period, furnishes proof of such a cumulative kind as approaches, if not to demonstration, at least to the nearest possible degree of certainty. There is no instance of a single transmutation of a vegetable species into another species, of algæ into fuci or conversely, of grasses into cereals, of endogens into exogens, of the pine into the oak; and the same of animal species, where, through all the living tribes, the fixity of family law has maintained its steady, unchanging course since Adam gave names to them, down to the present hour. What link in the chain is wanting? The course of creation is verified and complete. The exception would be a miracle. And we are not at liberty, upon just principles of ratiocination, to refuse our assent, where all the facts, indefinite as to number, are exclusively on one side, and none upon the other. Our belief in the case is defined and restrained by the absolute uniformity of stubborn, unbending nature; and an appeal from the known to the unknown, from the human to the geological epochs, is just to relinquish reason for the dominion of imagination, the evidences of the senses for the visions of fancy. The shark, rapacious as ever, holds the empire of the seas—the lion, the domain of the forest—the eagle, the region of the air—and man, progressive man, alone looks unto the heavens and blesses his Maker.
Hume was so impressed with the force of this argument, as to maintain, upon the ground of it, the absolute impossibility of establishing the truth of a single miraculous event, or of any event that did not harmonize with the existing course of nature. The Laws of Nature have been so uniform, within the entire range of human experience, as that no testimony or reasoning of man, says that subtile dialectitian, can invalidate their authority, or render credible any alleged case of discrepancy or of deviation.—The author of the “Vestiges,” for the first time, has cast the whole weight of this evidence aside, or holds it as even scarcely relevant in a question of proof. And thus outstripping, as he does, both the measure and the requirements of the Christian’s faith, he may be safely left to the logic of its most merciless adversary in dealing with the phenomenal or imaginary transmutations of the geological epochs.
But the facts of geology, from its remotest periods, are in themselves no less strongly opposed to this extravagant, untenable hypothesis. This might be presumed from the distinct teachings of geology, as already stated, against the theory of a scale of beings becoming more perfect as we ascend from the faunas of the older to those of the newer formations. The families of the various formations are distinct, and consist of real non-interchanging forms of structure, whether they die out and disappear with a particular formation, or are carried forward and intermixed with the fossils of another. The fishes of the silurian rocks, are as perfect after their kind as those of the Devonian, Carboniferous, or Cretaceous deposits; and not less perfect than they are genuine types of all their successors. The sauroids of the old red sandstone have reptilian resemblances, but yet the saurians of the oolite age have no affinities of true kindred descent; while, again, of all the mammalia of the tertiary period, there is not one that boasts a likeness, in habit or organization, to a single creature of an antecedent or posterior epoch. “Thus between the palæotherium and the species of our own days,” says Cuvier, “we should be able to discover some intermediate forms: and yet no such discovery has ever been made. Since the bowels of the earth have not preserved monuments of this strange genealogy, we have a right to conclude, that the ancient and now extinct species were as permanent in their forms and characters as those which exist at present: or at least, that the catastrophe which destroyed them did not leave sufficient time for the production of the changes that are alleged to have taken place.” Agassiz, in his own department of fishes, is equally opposed in all his deductions to the transformation of species from one formation to another, which he asserts, “the imagination invents with as much facility as the reason refutes.” Professor Owen, after minutely examining the organic structure of the nine orders of fossil reptiles, declares no less strongly against the theory, and adds—“The nearest approximation to the organization of fishes is made by the Ichthyosaurus, an extinct genus which appears to have been introduced into the ancient seas subsequent to the deposition of the strata inclosing the remains of the thecodont lizards. But by no known forms of the fossil animals can we diminish the wide interval which divides the most sauroid of fishes from an Ichthyosaurus.”[12]
The development theory is not more at fault in the rudimentary structure and primitive size of animals, as brought to light by the deepest researches of geology, than it is in the perfection and complication of the several organs with which they were endowed. These organs in the earlier types ought, upon the principles of this theory, to have all partaken of the simplicity and sameness of the germinal vesicles; varying, indeed, in their complexity, as in their completeness, in proportion as we ascend among the fossiliferous strata. But the facts are not so. Nay, so far otherwise, that in the very earliest specimens of Nature’s workmanship we find the mechanism of the parts as minute, varied, and multiplied, as in those of her most recent productions. Examine the eye of the Trilobite, the oldest of crustaceans, and the distinguishing type of the lowest of the fossiliferous rocks. These creatures swarmed in the Silurian seas. Their destiny was not fulfilled by the close of the tertiary periods, for they still exist. But in none of her subsequent creations has Nature displayed greater elaboration in the parts, or more skillful adaptive contrivance in their arrangement, than in the visual organ of this palæozoic family. The eye of the trilobite is formed of four hundred spherical lenses, arranged in distinct compartments on the surface of the cornea, which again projects conically upward, so as to enable the animal while resting, or seeking its food at the bottom of the waters, to take in the largest possible field of view—this, as it might require, either for the purpose of defense or attack. Fishes, birds, and mammals, have all, it is well known, an optical apparatus precisely adjusted to their respective habits and the element in which they live. Fishes and fowls have their eyes differently constructed.—The bat, which preys in the dark,—the eagle, which soars in the blaze of the sun,—and the mole, which burrows in the earth, have each peculiar and appropriate organisms. But in none is there greater complication or perfection, than what is manifested in the eye of these earliest and still living tribes of the waters.
The number of plates or cylinders which compose the eyes of insects, a higher and more gifted class, differs in different species, amounting in the ant, so provident and wise, to only fifty, in the house-fly to eight thousand, and in the mordella to the amazing number of twenty-five thousand and eighty-eight. And yet how much is all this surpassed by the astounding mechanism displayed in the eye of the cod-fish, in whose crystalline lens there have been detected about five million fibers, every fiber containing about twelve thousand five hundred teeth; and the total number of these teeth or processes reaching the numerical, though to us utterly inconceivable, amount of sixty-two billions five hundred thousand millions! But more than all this. Look at the multiplied appliances furnished to the humblest and lowest of all living creatures for performing the functions of an existence scarcely removed above the vegetable. “The tentacula of polypi,” says Dr. Roget, “are exquisitely sensible, and are frequently seen, either singly or altogether, bending their extremities toward the mouth, when any minute floating body comes in contact with them. When a polypi is expanded, a constant current of water is observed to take place, directed toward the mouth. These currents are never produced by the motions of the tentacula themselves; but are invariably the effects of the rapid vibrations of the cilia placed on the tentacula. Now, of these organs a single flustra foliacæa has been calculated to possess about 400,000,000.” Thus much for the Zoophyte class of animals—placed on the extreme verge of organized bodies—and members of a system of being, according to the development theory, whose primitive productions are of the simplest kind, the monads of a germinating vesicle!
Nor will the development theory do better, when it would account for the diversity of instincts which prevail in the animal kingdom. The instincts, indeed, it assumes as the cause of all their diversity of structural organization. But this is to beg the whole question. Geology carries us back to the beginnings of organic life, when animals, each after their kind, were already perfected, and endowed with a ready-made apparatus for the particular sphere of existence assigned them. The polypi are still a distinct race, unvarying in their instincts, not the least improved in the building art, still piling up reefs, and doing the same thing which they did when first created. The nautilus has lived through all time, swimming his fragile bark as dextrously over the Silurian seas as he now does amidst the breakers of the Pacific. The cephalopoda and the finny tribes then warred against each other, and ever since they meet in mortal conflict. The same with all the great families which were successively brought upon the stage: species and genera have changed, the old withdrawn, and new ones introduced; but in their respective orders—reptiles, insects, birds, and quadrupeds—the type ever continues, and the instincts remain; and there is no nearer an approximation to or crossing of each other’s domains now, than when first summoned into being. Were the development theory true in nature, and the epochs of geology the myriads of ages assumed, the presumption would be, that the old primitive forms would have been all obliterated and figures of creatures substituted, all of the most remote and indistinct analogies. The monodal races, why have they not all passed away? Had the reptiles sprung from fishes, why, upon the principle of progression, should there be fishes still? Had man derived his parentage from the monkey, why are there so many species of the one class, and only a single great family of the other? The vegetable tribes have been equally true to their kind—the fucoids and algæ, still abundant in the seas—the pines of Mar forest, rivaling in coniferous qualities the most gigantic of the oldest relics—and the palms and fern trees of Australia maintaining the very types that flourished in the carboniferous era.