Creation or Evolution? A Philosophical Inquiry

by George Ticknor Curtis

The question here is, not whether descent of organisms from organisms, with modifications upon modifications, is a supposable theory, but whether it is so satisfactorily shown that it can be said to exclude the hypothesis of a special creation of each organism. There may be parts of structure in one animal which seem to have no functional use, although we should be cautious in making the assumption that they are of no use because we have not yet discovered that use. But let it be assumed that these apparently useless parts in one animal correspond to parts which in another animal are functionally useful. If there was established for these two separately created animals a like system of procreation and gestation, that system, affected at the same time by a law of growth imposed by the special type of the species, might in one species lead to the presence of parts of which we can not recognize the use, and might in other species lead to the presence of parts of which we can see the use. It does not help to a better explanation to say that there has been an accumulation of modifications upon modifications in the course of an unknown descent of one organism from another. Why did these modifications stop short of the production of a species or of several species in which no resemblance of parts more or less functionally useful could be found? The supposition is that the modifications have been going on through millions of years. Time enough, therefore, has elapsed for the destruction of all uniformity of structure; and the causes of modification are as immeasurable as the period through which they are supposed to have been operating. The imaginary ancestral stock, wherever it is placed in the line of remote descent, had, in its first distinctive existence, a peculiar structure, which it bequeaths to its offspring. In the countless generations of its descendants, modifications of that structure take place, until a new animal is evolved. What preserved any unity of type from the modifying influences? It was not choice on the part of the several descending species; not a conscious exertion to preserve something; it was nothing but the propinquity of descent, which by the law of heredity transmitted certain resemblances. But why was that law so potent that it could preserve a certain unity of type, and at the same time so powerless as not to prevent the modifications which the successive organisms have undergone in all other respects? Or, to reverse the terms of the question, why were the causes of modification sufficiently powerful to produce distinct species, and yet not powerful enough to eliminate the resemblances which we find obtaining throughout the whole group of animals to which these several species belong? It would seem that here we are not to lose sight of the fact that, in the animal kingdom, procreation never takes place between a male and a female of distinct species, and that we have no reason to believe that it ever did take place. Now, although the evolution hypothesis supposes that, starting from an ancestral stock, the modifications of structure have been produced in offspring descended from parents of that same stock, which have transmitted acquired peculiarities to their immediate progeny, and so on indefinitely, yet there must have been a time when the diverging species became distinct and peculiar organisms, and when it became impossible for any crossing of these organisms to take place. All the supposed modifications, therefore, have taken place within the limits of an actual descent of one kind of animal from another, each successive pair belonging to the species from which they were individually generated. In this descent of lives from lives, there came about changes which in progress of time led to two animals as wide asunder as the man and the ostrich, or as the man and the horse, and yet the causes which were powerful enough to produce these widely diverging species were not powerful enough to break up all unity of plan in some one or more respects. If naturalists of the evolution school would explain how there has come to be, for example, in the skeleton of the vertebrata, a bony structure called the spine, in which a certain resemblance and a certain function obtain throughout the whole class, and yet one species creeps upon its belly, another walks on four legs, and another on two, and one flies in the air and another never can do so, and how this could be without any design or special interposition of a creating power, but that the whole of this uniformity amid such diversity has arisen from acquired habits among the different descendants from an aboriginal stock that had no such habits in either mode of locomotion, and no organs for such modes of life, they would at least be able to commend their theory to a better appreciation of its claims than is now possible to those who want "grounds more relative" than a naked hypothesis.

3. The argument from embryology requires for its appreciation a careful statement of its abstract proposition, and a statement of it in a concrete form. As an abstract proposition, embryology, or the comparison of the development of different organisms under their embryonic stages, shows that in the earliest stage of any organism it has the greatest number of characters in common with all other organisms in their earliest stage; that at a later stage its structure is like the structures displayed at corresponding phases by a less extensive number of organisms; that at each subsequent stage the developing embryo becomes more and more distinguished from the groups of embryos that it previously resembled; and that this divergence goes on, until we reach the species of which the embryo is a member, in which the class of similar forms is finally narrowed to that species.

It seems that Von Baer formulated this generalization of embryologic development into an "embryologic law," which, according to Mr. Spencer, becomes a support to the hypothesis of evolution in this way: Species that had a common ancestry will exhibit a parallelism in the embryonic development of their individual members. As the embryos of the ancestral stock were developed in their growth, so the embryos of the descended species would be developed at corresponding phases in a similar way. As one species diverged from its ancestral stock, there would come about modifications in the development of its embryos, and thus a later ancestral stock would be formed, which would in turn transmit to its descendants in the development of the embryo less and less resemblances, and so on, until finally the individual animal, at birth, would structurally resemble only the individual infants of its own race.

Here, then, is another remarkable instance of the force of an adopted theory. First, we have a comparison of the embryonic development of different animals from their seminal germs which displays certain phenomena of resemblances and departures. Next, we have the assumption of an ancestral stock, the common origin of all the organisms in the development of whose embryos among its descendants an embryologic law was to work, starting from the visible resemblance of all the germs, then exhibiting structural changes into later ancestral stocks, and so on, until the resemblances are reduced to those which obtain only among individuals of the same species. So that, without the hypothesis, the assumption of an ancestral stock of all the organisms, formed somehow in the course of descent from a germ that gave rise to an animal of some kind, we have nothing to which to apply the embryologic law. We are to infer the embryologic law from the parallelism of embryonic development which prevails in the whole series of animal generation, or from its divergences, or from both, and then we draw from this law the inference that the whole series of animals came from some common stock. The difficulty with this whole theory is, as I have more than once suggested, that we have no means, aside from the theory itself, of connecting lives with lives, in the generation of one distinct species out of another. Without some proof of the fact that the human fœtus was a diverging growth out of some ancestral stock that was the same as that from which the fœtus of another animal was a different diverging growth, the embryologic law is no help to us whatever. If this kinship of the human fœtus with the fœtus of some other animal can not be found, by tracing the intermediate links which carry them respectively back to their common ancestor, between what animals in respect to their embryonic development can such kinship be found, excepting upon the theoretical assumption of a common origin of the whole vertebral class? If there was such a common ancestral stock, where is it to be placed, what was its character, when did the law of embryologic development begin to operate upon its descendants? Until some facts can be adduced which will have a satisfactory tendency to show the kinship of one animal with another by reason of ancestral descent from a common ancestral stock that was unlike either of them, the phenomena of embryologic development have no tendency to displace the hypothesis of special creations; for, on the latter hypothesis, the phenomena of resemblances and differences in the growth from the germ into the fœtus and from the fœtus into the newly born infant, evinced by any range of comparison of the different species, would be the same. If man was a special creation, and one of the higher quadrumana was also a distinct and separate creation, the establishment for each of a like process of procreation and gestation would produce all the resemblances of fœtal growth that obtain between them, and the ordained differences of their animal destinies would explain all the divergences. Let us see if this is not a rational conclusion.

It is exceedingly difficult for the common reader of such a work as that of Mr. Spencer, on which I am now commenting, to avoid the influence of the perpetual assertion that facts are explicable upon one hypothesis alone. At each step in the argument, the array of facts terminates with the assertion that, upon the hypothesis of design, the facts are inexplicable; and yet we are furnished with no reasoning that has a tendency to show that the facts necessarily exclude the hypothesis of design, or, in other words, that the facts are inconsistent with that hypothesis. It is essential to understand what is the true scope of the hypothesis of special creation; for, without a definite idea of what that term implies, we have no proper means of comparing the facts of animal resemblances or differences with the rationality of the hypothesis that they resulted from an intentional design. Recollecting, then, that we are now pursuing the resemblances and divergences that are found in a comparison of the embryologic development of different species of animals, let us endeavor to understand the meaning of what I have suggested at the close of the last preceding paragraph; namely, the establishment for a large class of animals of a like general system of procreation and gestation, and the ordination of different destinies for the different species of animals belonging to that class. I have said that the two branches of this hypothesis would account for the resemblances in the embryological growth of different animals, and would explain the divergences which obtain among their embryological developments. The first inquiry is, whether this hypothesis presents a true philosophic idea of special creation. The next inquiry is, whether it affords a satisfactory explanation of the phenomena of comparative embryologic development.

We must never lose sight of the one grand postulate of an infinite Creator. This postulate must be conceded to the believers in special creations, because any idea of creation implies a creating power. If we conceive of creation without a Creator, we must stop all argument. Now, the hypothesis of creation, as I have more than once said, implies a being of boundless faculties. There can be absolutely no limitation to the power of such a being, either in respect to the methods by which he will accomplish his objects, or to the number and variety of these objects, or to the purposes for which they are to exist. If we narrow our conception of creating power to anything less than an infinite faculty; if we suppose it to be restricted in any direction; if we argue about it as if there were things that it can not do, we shall be without the means of reasoning soundly upon anything that it is supposed to have done. It is quite otherwise when we are reasoning about the operation and effect of secondary causes. There is no secondary cause—no imaginable operation of a fixed quality of substance—no action of any of the properties of substance—that is not limited. The scope of its action may be very wide; within its sphere it may be enormously potent; but in its very nature it is bounded.[86] It is not so with the First Cause of all things; not so with the Infinite Power which, upon the hypothesis of a First Cause, has established all the physical laws of the universe and all the properties of matter. So that, when we reason about the methods of that infinite creating power, if we find a general system established, or a pattern repeated through a very large class of organisms, the proper inference is, not that the power was limited, but that it has been exercised to the whole extent of what was useful, and in that direction has been exercised no further; and if we find variations or additional structures incorporated with the repetition of a general pattern, the proper inference is that the unlimited creating power has put forth all the additional exertion and skill needful for the formation of new beings.

What, then, does the establishment of a like system of procreation and gestation imply, upon the supposition of the distinct creation of species? It implies a certain parallel embryonic development, from the germ to the fœtus and from the fœtus to the new-born infant, throughout a large group of different animals; and this parallelism would in certain stages of the embryonic growth display identity or close similarity of form and structure. But as in each species of animal the distinct creation would necessarily imply a distinct destiny, the parallelism of embryonic form and structure would cease at the point of development at which the characteristic structure of the species would begin to unfold itself. The general system of procreation and gestation common to a whole class of different animals, and the ordained diversity of species, would present the same phenomena of resemblances and differences in the embryonic development that are supposed to be explicable only by the hypothesis of a descent of all the species from a common ancestral stock through the process of evolution.

Notwithstanding the mystery and obscurity in which the process of animal procreation is involved—a mystery and obscurity which will perhaps never be fully solved—we can see enough to warrant some definite conclusions. One of these conclusions is that, in the formation of the germ which becomes developed into the fœtus, the male and female parent each contributes some cellular substance to the compound which constitutes that germ. We may safely infer this, because the individual animal becomes a union of characteristics belonging to both the parents, although the traits that are peculiar to one of the parents may be more or less marked in their different offspring, so that in one of the descendants the paternal and in another the maternal traits will predominate. But in every descendant from the same pair there is more or less of the peculiarities of each parent plainly discernible. The inference, therefore, may be safely drawn that the male and the female parent each contributes to the formation of the ante-fœtal germ some cellular substance, in which resides the typical characteristic of animal organism which each parent possesses. The compound germ that is thus formed is endowed with the mysterious principle of animal life which admits of growth and development; and whether after its formation the female parent bestows most or bestows least upon the product, that product consists of a union of cellular substances contributed by both the male and the female parent in the sexual act of procreation. This compound resultant germ, in the earliest stage of its formation, like the separate cells of which it is a union, exhibits no visible difference when we compare the ante-fœtal germ of one animal with that of a different animal. Perhaps we shall never be able to detect either chemical or mechanical differences in the cellular substances or in the earliest stage of the compound product which has resulted from their union. But in that compound product there resides a contributory cellular substance derived from each of the parents; and it is a just inference from this fact, and from what we learn when we trace the further development, that there is a peculiar and typical structure impressed upon and inwrapped in this compound germ, which is to grow into a fœtal development by a law of its own. There will at the same time be a particular law of development for each distinct species of animal, and a general law of development for a great variety of species among whom there obtains a common process of the sexual union and of the contribution of male and female cellular substance. When the fœtus becomes formed, there will still be marked resemblances in the different species, before the stage is reached at which the characteristic structure of each species is to begin to unfold itself. But at some time the fundamental difference of structure originally lodged in the cellular substances of which the compound ante-fœtal germ was composed, and impressed upon that germ as the type which was gradually to unfold itself into a distinct being, will begin to exert its force. The resemblances of structure will become less and less, as the fœtus of the different animals approaches to the time of birth. Organs, or appearances of organs, which at one stage of the comparison have seemed to indicate descent from a common ancestral stock, but which may have been only the result of a common process of fœtal development, will be found to be varied by force of the original diversity of structure and destiny that was made to reside in the seminal substance of each distinct species of animal; and, at length, this original and intentional peculiarity of structure and being would become perfected at or before the period when birth is to take place, leaving only those resemblances which must obtain in all organisms constructed in certain respects upon a uniform plan, and brought into being by a common process of procreation and gestation.

Let us now see whether this reasoning involves any such unphilosophical or unscientific belief as is supposed. Passing by the often-repeated assertion that the facts of comparative embryologic development are reconcilable only with the belief in evolution, let us advert to some of those facts. "The substitutions," says Mr. Spencer, "of organs and the suppression of organs, are among those secondary embryological phenomena which harmonize with the belief in evolution, but can not be reconciled with any other belief. There are cases where, during its earlier stages of development, an embryo possesses organs that afterward dwindle away, as there arise other organs to discharge the same functions. And there are cases where organs make their appearance, grow to certain points, have no functions to discharge, and disappear by absorption." The concrete illustration of this substitution and suppression of organs is thus given by Mr. Spencer:

"We have a remarkable instance of this substitution in the successive temporary appliances for aërating the blood which the mammalian embryo exhibits. During the first phase of its development, the mammalian embryo circulates its blood through a system of vessels distributed over what is called the area vasculosa, a system of vessels homologous with one which, among fishes, serves for aërating the blood until the permanent respiratory organs come into play. After a time, there buds out from the mammalian embryo a vascular membrane called the allantois, homologous with one which, in birds and reptiles, replaces the first as a breathing apparatus. But while, in the higher oviparous vertebrates, the allantois serves the purpose of a lung during the rest of embryonic life, it does not do so in the mammalian embryo. In implacental mammals it aborts, having no function to discharge; and in the higher mammals it becomes "placentiferous, and serves as the means of intercommunication between the parent and the offspring"—becomes an organ of nutrition more than of respiration. Now, since the first system of external blood-vessels, not being in contact with a directly oxygenated medium, can not be very serviceable to the mammalian embryo as a lung; and since the second system of external blood-vessels is, to the implacental embryo, of no greater avail than the first; and since the communication between the embryo and the placenta among placental mammals might as well or better have been made directly, instead of by metamorphosis of the allantois—these substitutions appear unaccountable as results of design. But they are quite congruous with the supposition that the mammalian type arose out of lower vertebrate types. For, in such case, the mammalian embryo, passing through states representing, more or less distinctly, those which its remote ancestors had, in common with the lower vertebrata, develops these subsidiary organs in like ways with the lower vertebrata."[87]