Creation or Evolution? A Philosophical Inquiry

by George Ticknor Curtis

Let us now see what is the state of the proof. It may assist the reader to understand the Darwinian pedigree of man if I present it in a tabulated form, such as we are accustomed to use in exhibiting to the eye the pedigree of a single animal. Stated in this manner, the Darwinian pedigree of man may be traced as follows:

I. A marine animal of the maggot form.
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II. Group of lowly-organized fishes.
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III. Ganoids and other fishes.
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IV. The Amphibians.
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V. The ancient Marsupials.
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VI. The Quadrumana and all the higher mammals.
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VII. The Lemuridæ.
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VIII. The Simiadæ.
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IX. Old World Monkeys.	New World Monkeys.
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X. Man.

These ten classes or groups of animals are supposed to be connected together by intermediate diversified forms, which constitute the transitions from one of the classes or groups to the other; and in reading the table downward it must be remembered that we are reading in fact through an ascending scale of beings, from the very lowest organized creature to the highest. The whole, taken together, forms a chain of evidence; and, according to the rational rules of evidence, each distinct fact ought to be proved to have existed at some time before our belief in the main hypothesis can be challenged. I know of no reason why the probable truth of a scientific hypothesis should be judged by any other rules of determination than those which are applied to any other subject of inquiry; and, while I am ready to concede that in matters of physical science it is allowable to employ analogy in constructing a theory, it nevertheless remains, and must remain, true that where there are numerous links in a supposed chain of proofs that are established by nothing but an inference drawn from an analogous fact, the collection of supposed proofs does not exclude the probable truth of every other hypothesis but that which is sought to be established, as it also does not establish the theory in favor of which the supposed facts are adduced. Upon these principles of evidence I propose now to examine the Darwinian pedigree of man.

I. The group of marine animals described as resembling the larvæ of existing Ascidians; that is to say, an aquatic animal in the form of a grub, caterpillar, or worm, which is the first condition of an insect at its issuing from the egg. These assumed progenitors of the Vertebrata are reached, according to Mr. Darwin, by "an obscure glance into a remote antiquity," and they are described as "apparently" existing, and as "resembling" the larvæ of existing Ascidians. We are told that these animals were provided with branchiæ, or gills, for respiration in water, but with the most important organs of the body, such as the brain and heart, imperfectly or not at all developed. This simple and crude animal "we can see," it is said, "in the dim obscurity of the past," and that it "must have been the early progenitor of all the Vertebrata."[35] It is manifest that this creature is a mere hypothesis, constructed, no doubt, by the aid of analogy, but existing only in the eye of scientific imagination. Why is it placed in the water? For no reason, apparently, but that its supposed construction is made to resemble that of some creatures which have been found in the water, and because it was necessary to make it the progenitor of the next group, the lowly-organized fishes, in order to carry out the theory of the subsequent derivations. It might have existed on the land, unless at the period of its assumed existence the whole globe was covered with water. If it had existed on the land, the four subsequent forms, up to and including the Marsupials, might have been varied to suit the exigencies of the pedigree without tracing the descent of the Marsupials through fishes and the Amphibians.

II. The group of lowly-organized fishes. These are said to have been "probably" derived from the aquatic worm (I), and they are described to have been as lowly organized as the lancelet, which is a known fish of negative characters, without brain, vertebral column, or heart, presenting some affinities with the Ascidians, which are invertebrate, hermaphrodite marine creatures, permanently attached to a support, and consisting of a simple, tough, leathery sack, with two small projecting orifices. The larvæ of these creatures somewhat resemble tadpoles, and have the power of swimming freely about. These larvæ of the Ascidians are said to be, in their manner of development, related to the Vertebrata in the relative position of the nervous system, and in possessing a structure closely like the chorda dorsalis of vertebrate animals.[36] Here, again, it is apparent that a group of lowly-organized fish-like animals, of which there are no remains, have been constructed by a process of scientific reasoning from a certain class of marine creatures that are known. As a matter of pure theory, there can be no serious objection to this kind of construction, especially if it is supported by strong probabilities furnished by known facts. But when a theory requires this kind of reasoning in order to establish an important link in a chain of proofs, it is perfectly legitimate and necessary criticism that we are called upon to assume the former existence of such a link; and, indeed, the theorists themselves, with true candor and accuracy, tell us that they are arguing upon probabilities from the known to the unknown, or that a thing "must have existed" because analogies warrant the assumption that it did exist. In a matter so interesting, and in many senses important, as the evolution theory of man's descent, it is certainly none too rigid to insist on the application of the ordinary rules of belief.

III. The Ganoids and other fishes like the Lepidosiren. These, we are told, "must have been developed" from the preceding (II). The Ganoids, it is said, were fishes covered with peculiar enameled bony scales. Most of them are said to be extinct, but enough is known about them to lay the foundation for their "probable" development from the first fishes that are supposed to have been derived from the aquatic worm (I). There is a reason for arguing the existence of these first fishes as a true fish with the power of locomotion, because the next ascending group of animals is to be the Amphibians. In a fish, the swim-bladder is an important organ; and it is an organ that plays an important part in the Darwinian theory, furnishing, it is claimed, a very remarkable illustration that an organ constructed originally for one purpose, flotation, may be converted into one for a widely different purpose, namely, respiration. As the Amphibians, which as a distinct group were to come next after the fishes in the order of development, must be furnished with a true air-breathing lung, their progenitors, which inhabited the water only, must be provided with an organ that would undergo, by transitional gradations, conversion into a lung. But what is to be chiefly noted here is that it is admitted that the prototype, which was furnished with a swim-bladder, was "an ancient and unknown prototype"; and it is a mere inference that the true lungs of vertebrate animals are the swim-bladder of a fish so converted, by ordinary generation, from the unknown prototype because the swim-bladder is "homologous or 'ideally similar' in position and structure with the lungs of the higher vertebrate animals."[37] One might ask here without presumption, why the Omnipotent God should not have created in the vertebrate animals a lung for respiration, as well as have created or permitted the formation of a swim-bladder in a fish; and looking to the probabilities of the case, it is altogether too strong for the learned naturalist to assert that "there is no reason to doubt that the swim-bladder has actually been converted into lungs or an organ used exclusively for respiration"; especially as we are furnished with nothing but speculation to show the intermediate and transitionary modifications between the swim-bladder and the lung. While we may not assume "that the Creator works by intellectual powers like those of man," in all respects, it is surely not presumptuous to suppose that an Omnipotent and All-wise Being works by powers that are competent to produce anything that in his infinite purposes he may see fit specially to create.

IV. The Amphibians. Here we come to what is now a very numerous group, of which it is said that the first specimens received, among other modifications, the transformation of the swim-bladder of their fish progenitors into an air-breathing lung. We are told that from the fishes of the last preceding group (III) "a very small advance would carry us on to the Amphibians."[38] But whether the advance from an animal living in the water and incapable of existing out of that element, to an animal capable of living on the land as well as in the water, was small or large, we look in vain, at present, for the facts that constitute that advance.

V. The Ancient Marsupials. These were an order of mammals such as the existing kangaroos, opossums, etc., of which the young, born in a very incomplete state of development, are carried by the mother, while sucking, in a ventral pouch. They are supposed to have been the predecessors, at an earlier geological period, of the placental mammals, namely, the highest class of mammals, in which the embryo, after it has attained a certain stage, is united to the mother by a vascular connection called the placenta, which secures nourishment that enables the young to be born in a more complete state. There is a third and still lower division of the great mammalian series, called the Montremata, and said to be allied to the Marsupials. But the early progenitors of the existing Marsupials, classed as the Ancient Marsupials, are supposed to constitute the connection between the Amphibians and the placental mammals; that is to say, an animal which produced its young by bringing forth an egg, from which the young is hatched, became converted into an animal which produced its young from a womb and nourished it after birth from the milk supplied by its teats, the young being born in a very incomplete state of development and carried by the mother in a ventral pouch while it is sucking. The steps of variation and development by which this extraordinary change of structure, of modes of reproduction and formation of organs, as well as habits of life, took place, are certainly not yet discovered; and it is admitted, in respect to forms "now so utterly unlike," that the production of the higher forms by the process of evolution "implies the former existence of links binding closely together all these forms."[39] In other words, we are called upon to supply by general reasoning links of which we have as yet no proof.