Creation or Evolution? A Philosophical Inquiry

by George Ticknor Curtis

In what way, then, are these substitutions unaccountable as results of design, and why are they any more congruous with the supposition that the mammalian type arose out of the lower vertebrate type? In the first place, it is necessary to have a distinct conception of what is meant by design. In the present case, it means that for a certain large group of animals there was established a system of reproduction by the sexual union of male and female, each contributing a cellular substance peculiar to itself, in the formation of a compound cellular substance in which the separate substances are united, and which is to be developed into the fœtus by a law of growth; and as a further design there is wrapped up in the compound germ of each distinct species of animal a typical plan of ultimate form and structure. This typical plan can not be detected in the germ itself, as it is too subtile and obscure even for the microscope; but we have every reason to believe that it is there in all its distinctness of original purpose, because at a later stage of the embryonic development we find a distinct species of animal is the result. This is a conclusion that must be adopted by the evolutionist, as well as by the believer in special creations, because it has nothing to do with the question of how distinct species came to exist. Whether they were designedly and separately created, or were evolved out of one another, the reproductive process by which the individuals of the same species are brought into being alike involves the conclusion that, in the ante-fœtal germ of that species, there is somehow involved, in a form so minute that it can not be seen, the type of animal which is to belong to that species, and to no other. Here, then, we have the grand and compound design which is to obtain throughout a whole group of different animals; namely, that they shall multiply in the production of individuals of their own types, by a sexual union, in which the male and the female each contributes a cellular substance of its own to the formation of a compound germ, and in that germ there is made to reside the typical form and structure of a distinct organism, so minute that we can not see it, but which we must conclude from the result has been put there to be developed by a law of growth ordained for the accomplishment of a certain distinct order of beings. But the very obscurity of this type, in the earliest stage of embryonic development, leads to the conclusion that while it will never be lost, so long as its life is preserved, it will unfold itself in ways that will be equally beyond our ken, until the point is reached where it is no longer obscured, but where it is revealed in all its distinctness of outline and its peculiarity of structure. What is certain and invariable is, that the type peculiar to the species is at some time in the growth of the individual animal perfectly developed. But in the modes of its development through different embryonic stages, there will be variations and substitutions of organs in the different species, but in each distinct species these variations and substitutions will be uniformly the same, because the law of development imposed by the distinct type, while it may operate differently among different species, will always operate in the same way in the same species. Thus in one animal the development from the original type which was implanted in its seminal ante-fœtal germ may at one stage exhibit an organ for which at a later stage another organ will be substituted; and in another animal a seemingly corresponding organ may serve a different purpose, or may altogether abort. These embryologic phenomena, varying in different species, but occurring uniformly in the same species, are necessarily among the most obscure of all the phenomena of animal life, on account of the fact that they take place where we can not watch the changes or modifications as they are taking place during actual fœtal life. But they are no more explicable upon the hypothesis of the descent of distinct animals from a common stock, than they are upon the hypothesis of distinct creations of species. Upon the former hypothesis, the assumed propinquity of descent implies the preservation of the same mode of embryonic development until it becomes varied by the operation of causes that bring about a new habit of development, and then a fixation in this new habit after a new species or a new ancestral stock is formed; so that in each distinct species there comes at length to be a uniform process of substituting and suppressing organs, or changing the functions of organs. But how are we to account for the operation of causes that have preserved a parallelism of development, along with the operation of causes that have produced the different modes of development, when all the species are supposed to be derived from a common ancestral stock, which first began to procreate and to develop its descendants in one and the same way? What are the facts which will enable us to say that the mammalian type arose out of the lower vertebrate types, when we compare the different modes of their embryologic development? How are we to estimate the chances for a preservation of so much resemblance as exists between the two in their embryologic lives, and the chances for the variations that are observable? What we can safely conclude is that there is a law which holds each species in a constant repetition of its own fœtal growth, according to its unvarying development in the same series of changes, substitutions, or suppressions. But we can not safely conclude that this species became formed in the supposed process of descent from a remote ancestral stock, which may or may not have originally exhibited the same series of changes, substitutions, or suppressions. If the ancestors of the mammalian vertebrates were the kind of animal supposed, we have to find, in order to justify the supposed descent, those states which represent the correspondence between the mode in which the ancestral stock developed its own embryos, when compared with the mode in which the type of the lower vertebrata developed its embryos, so as to make it reasonably certain that these subsidiary organs derived their several substitutions or suppressions from the process of descent, and not from any special mode of development ordained for each distinct species. We may imagine these states through which the mammalian embryo has passed, but as yet we have only a theory which suggests their existence without facts to support it. The truth would seem to be that this whole subject of comparative embryology, upon the hypothesis of the kinship of all organized beings, or the descent of many distinct species from a common stock, is involved in very great difficulties; not the least of which is the difficulty of explaining how the diverging descendants from that stock came to be endowed with habits of embryologic life and growth that resulted in the production of very different modes of development, and at the same time preserved for each new species its own peculiar mode of development. To say, for example, that the mammalian embryo passed through states representing, more or less distinctly, those which its remote ancestors had in common with the lower vertebrata, and that it developed certain subsidiary organs in like ways with the lower vertebrata, is merely to state a theory, which, without some evidence that the mammalian embryo was a formation resulting from a connection of lives with lives back to a common ancestor whose embryo was developed as those of the lower vertebrata are, amounts to nothing. Often as this want of evidence has been adverted to, it must be here again pointed out: for the whole argument from embryology, like that derived from a comparison of the forms of mature animals, lacks the support of facts that are essential to show the connection of life with life which descent from a common ancestral stock necessarily implies.

On the other hand, the hypothesis of the distinct creation of different species deals with the phenomena of embryologic life in a very different way. It supposes the creation of a pair, male and female, and a law of procreation, designed for the multiplication of individuals of a fixed type. It supposes many such creations, each having in its own peculiar germ the characteristic type of organism that will distinguish the mature animal from all the others. It supposes finally a law of development common to all the species the individuals of which are multiplied by the sexual union of male and female; a law of growth under like conditions, which leads to a parallelism of development until the typical plan of form and structure designed for each distinct animal, and implanted in its germ, begins to take on a mode of development peculiar to that species, and at length the perfect individual of that species is the result. In this hypothesis, therefore, there is no necessity for resorting to any connection with an imaginary ancestral stock of a different type, or for resorting to a theoretical process by which successive generations may be supposed to have gradually arisen out of the ancestral stock by successive changes which have at length resulted in a totally new species. The new species is what is supposed to have been aboriginally created, and to have been placed under its own law for the multiplication of individuals of the same type. In point of simplicity, of comparative certainty, of freedom from accidental causes of variation of which we can predicate no specific result, this hypothesis seems to have a far greater degree of probable evidence in its favor than the theory which entirely lacks the requisite evidence of intermediate connections between the lives of one species with the lives of a remote and different species. For, while it may be truly said that no man ever saw a special creation take place, and while such an act of the infinite power is of a nature that places it beyond the observation of our senses, it is neither inconceivable nor improbable, nor inconsistent with the idea of the divine attributes which we derive from the study of nature. On the other hand, it is not only equally true that no man ever saw, or in the nature of things ever can see, an evolution of distinct species out of other distinct species, but the whole nature of the supposed process of transformation involves an element of chance which forbids all calculation of the results. How, for example, in this very matter of comparative embryological development on the hypothesis of descent of all the species of the vertebrate animals from a common ancestral stock of a different type, are we to account for the fact that the embryo of any one of the descended species has come to be developed in a mode peculiar to itself and differing from the mode in which the embryo of the ancestral stock was developed? The law of sexual union, under which the individuals of the supposed ancestral stock were multiplied, must have imposed on that species an invincible necessity of reproducing in its offspring the same type that constituted the peculiar organism of the parents, whether these parents were or were not the fittest survivors of their race after the severest struggle for existence which they may have had to undergo. If the pair, or the male of that pair, has in the course of that struggle acquired a new organ, or more completely developed an old one, before the act of procreation takes place, how is it that the ovum is developed into the fœtus, and the fœtus into the newly born infant, in an invariable mode peculiar to the species to which the parents belonged? Why did not the same causes of variation which are supposed to have changed the ancestral type into one of a new and entirely distinct character, also vary the mode of fœtal development? When and how did the new organs become fixed in the type which the parents have transmitted to the offspring? And if they became so fixed in the germ which was formed out of the cellular substance contributed by each of the parents, why do we find in every known species participating in this process of reproduction a uniform mode of embryologic development peculiar to the species, and exhibiting its own suppressions and substitutions of organs, irrespective of any newly acquired peculiarities in the individual structures of the parents?

The believer in special creations has to answer no such questions as these. His hypothesis assumes the creation of a pair of animals of a certain distinct species; a law of procreation and gestation common to a vast multitude of organisms; and a law of embryologic growth peculiar to each species. Whatever peculiarities of structure may have been possessed by the immediate parents of any individual of any one of these different species—peculiarities which did not separate the parents from their race, but only made them the fittest survivors of their race—those peculiarities would or would not descend to their immediate offspring, according to varying and very inappreciable circumstances. But that which constituted the special type of the race, and especially that which constituted its peculiar mode of development during the embryonic stage, would remain unaffected by these incidental and accidental peculiarities of the parents, because, from all that we can discover, that special type was impressed upon the embryo at the earliest stage of its existence, and constituted the living model that was to be developed into the perfect animal of that species, by a law which placed it beyond the influence of any adventitious and non-essential advantages which the male or female parent may have acquired over other individuals of the same race. So that, if the postulate of a special creation of species be assumed as the groundwork of the reasoning, we have to go through with no speculations about a common ancestral stock of all the species, and we have to account for no phenomena that are exposed to chances which might have produced very different results from those which are open to our observation, and results of which we can predicate nothing with any degree of certainty. On the hypothesis of the special creation of a species, and an aboriginal pair of each species, with all that this implies, we can with a high degree of certainty predicate most of the phenomena that we have to observe, and more especially so much of the phenomena of embryologic growth of the different species as are open to our investigation after the life of both mother and embryo has become extinct.

It only remains for me to give to this reasoning a concrete application. Take the case made use of by Mr. Spencer in the passage above cited—that of the "allantois," a vascular membrane, which is said to be in the mammalian embryo homologous with one which in the higher oviparous vertebrates, such as the birds and reptiles, replaces what was at first a breathing apparatus, and becomes for them, during the rest of embryonic life, a sort of lung, or an organ that aërates the blood until the permanent respiratory organs come into play. In the mammalian embryo, the first appliance for aërating the blood is described as a system of vessels distributed over the area vasculosa, and like that which is first observable for the same purpose in fishes. But, as the mammalian embryo continues to grow, a change takes place. There buds out from it the vascular membrane called the "allantois," which is substituted in the place of the first aërating apparatus. Then a further change takes place, as between the higher oviparous vertebrates and the mammalian vertebrates. In the former, the "allantois" continues to perform the breathing function through the rest of the embryonic life. In the mammalian vertebrates it undergoes two changes: In the implacental mammals, it aborts, having no function to discharge; in the placental mammals it becomes modified into another organ, namely, that which serves to convey nutrition from the mother to the offspring. After birth, it is of course ended.

Now, the reasoning, or rather the assertion, that these substitutions are unaccountable as the results of design, appears to me to be singularly inconclusive. It is quite illogical, according to all philosophic meaning of design as applied to the works of the Creator, or to the works of nature, if that term is preferred, to argue that a particular object could have been better accomplished directly, than by a metamorphosis of an organ from one function to another, or by substitution. The metamorphosis, or substitution, which in such cases we find in nature, is of itself the very highest evidence that the indirect method was the best, if we admit the idea of a Creator, because it was the method chosen by a being of infinite perfections for reasons which we may not be able to discover, but which we must presume to have existed, if we concede that hypothesis of attributes which "design" in this case necessarily implies. But how are these metamorphoses and substitutions any more accountable upon the supposition that the mammalian type arose by generation out of the lower vertebrate types which in their embryonic life exhibited the same changes? The doctrine or theory of evolution does not account for them at all; for, while the doctrine supposes, as matters of pure theory, that there were certain states through which the mammalian embryo passed, which represented more or less distinctly those which it had in common with its assumed remote ancestors, the lower vertebrata, it does nothing more than to suggest the theoretical idea that the mammalian embryo came to develop these subsidiary organs in the mode in which they were developed in the embryo of the lower vertebrata, because it was descended from the lower vertebrata. The varying states through which the embryo passed from the lower vertebrata to the mammalian type, are all hypothetical, and there is, therefore, no basis of fact on which to rest the belief in a common mode of development, as resulting from a connection of lives with lives between the mammalian type and the types of birds, reptiles, or fishes.

On the other hand, the hypothesis of the special creation of a species implies the simple fact of a designed process of embryonic development for each species, with substitutions of organs and changes of function in certain organs peculiar to that species; a fact which may well consist in a certain parallelism in the different metamorphoses, and a preservation of the same unvarying changes in the development of each separate embryo. Why these changes should exist, we can not tell; but their existence is very strong proof that they were designed, or made to take place, for some reason, if we admit the hypothesis of a Creator. For that hypothesis, we must look to a wider class of facts, and to the whole phenomena of nature.

4. We now come to the argument from distribution. This is one of the weakest of the indirect supports of the doctrine of evolution; but, as it is much relied upon, it must be stated with all the force that it is supposed to have. The facts that are relied upon are these: When we survey the whole surface of the globe, so far as it is known to us, we find, in the first place, that the areas which have similar conditions (of soil and climate), and sometimes, where the areas are nearly adjacent, are occupied by quite different faunas. On the other hand, it is said that areas remote from each other in latitude, and contrasted in soil and climate, are occupied by closely allied faunas. The inference drawn is, that there is no manifest predetermined adaptation of the organisms to the areas, or habitats, in which they are found, because we do not find that like organisms are universally or generally found in like habitats, nor very unlike organisms in very unlike habitats. The conclusion is, that the facts of distribution in space do not conform to the hypothesis of design. In other words, the different animals found in different regions were not specially designed for those regions, but some of them have extended into regions of a different character; and when the regions are very unlike there are not found very unlike organisms, but there is a general similarity, or a less extensive variety. There is said, also, to be another important fact, namely, that "the similar areas peopled by dissimilar forms are those between which there are impassable barriers; while the dissimilar areas peopled by similar forms, are those between which there are no such barriers." Hence is drawn the conclusion that "each species of organism tends ever to expand its sphere of existence—to intrude on other areas, other modes of life, other media."[88] A good deal of aid is supposed to be derived for this argument respecting animal life by analogies drawn from the vegetable kingdom; but I can not help thinking that there is much caution to be observed in formulating such analogies into a law of universal application, or into one that relates to the existence of animal organisms. The origin, the multiplication, and the spread of animals involve a principle of life, organization and development which is very different in some important respects from that which obtains in the vegetable world. But, without laying any stress upon this distinction, and without intending to deprive the argument for animal evolution of any aid which it can derive from such supposed analogies, I pass to the specific argument respecting animal distribution. The argument is this: Races of organisms become distributed over different areas, and also through different media. They are thrust by the pressure of overpopulation from their old into new habitats, and as they diverge more widely in space they undergo more and more modifications of structure, by reason of the new conditions on which they enter. Thus, these powerfully incident forces, the new conditions on which the migrating races enter in new regions, vary the structure which they originally brought with them, and which descended to them from the common stock of which they were modified descendants. The widest divergences in space, under such circumstances, will indicate the longest periods of time during which these various descendants from a common stock have been subject to modifying conditions. There will, therefore, come to be, it is said, among organisms of the same group, smaller contrasts of structure in the smaller areas; and, where the varying incident forces vary greatly within given areas, the alterations will become more numerous than in equal areas which are less variously conditioned: that is to say, in the most uniform regions there will be the fewest species, and in the most multiform regions there will be the most numerous species. These hypotheses are said to be in accordance with the facts of distribution in space.[89]

But there are also facts of distribution through different media. The meaning of this is, that, whereas all forms of organisms have descended from some primordial simplest form, which inhabited some one medium, such as the water, its descendants, by migration into some other medium or other media, underwent adaptations to media quite unlike the original medium. In other words, the earth and the air have been colonized from the water. Numerous facts are adduced in support of this conclusion, which are thus summarized:

There are particular habitats in which animals are subject to changes of media. In such habitats exist animals having, in various degrees, the power to live in both media, consequent on various phases of transitional organization. Near akin to these animals, there are some that, after passing their early lives in the water, acquire more completely the structures fitting them to live on land, to which they then migrate. Lastly, we have closely-allied creatures like the Surinam toad and the terrestrial salamander, which, though they belong by their structures to the class Amphibia, are not amphibious in their habits—creatures the larvæ of which do not pass their early lives in the water, and yet go through these same metamorphoses! Must we, then, think that the distribution of kindred organisms through different media presents an insurmountable difficulty? On the contrary, with facts like these before us, the evolution-hypothesis supplies possible interpretations of many phenomena that are else unaccountable. Realizing the way in which such changes of media are in some cases gradually imposed by physical conditions, and in other cases voluntarily commenced and slowly increased in the search after food, we shall begin to understand how, in the course of evolution, there have arisen those strange obscurations of one type by the externals of another type. When we see land-birds occasionally feeding by the water-side, and then learn that one of them, the water-ouzel, an "anomalous member of the strictly terrestrial thrush family, wholly subsists by diving—grasping the stones with its feet and using its wings under water"—we are enabled to comprehend how, under pressure of population, aquatic habits may be acquired by creatures organized for aërial life; and how there may eventually arise an ornithic type, in which the traits of the bird are very much disguised.

Finding among mammals some that, in search of prey or shelter, have taken to the water in various degrees, we shall cease to be perplexed on discovering the mammalian structure hidden under a fish-like form, as it is in the Cetacea. Grant that there has even been going on that redistribution of organisms which we see still resulting from their intrusions on one another's areas, media, and modes of life, and we have an explanation of those multitudinous cases in which homologies of structure are complicated with analogies. And while it accounts for the occurrence, in one medium of organic types fundamentally organized for another medium, the doctrine of evolution accounts also for the accompanying unfitness. Either the seal has descended from some mammal which, little by little, became aquatic in its habits, in which case the structure of its hind-limbs has a meaning; or else it was specially framed for its present habitat, in which case the structure of its hind-limbs is incomprehensible.[90]