All known types, then, of apes and monkeys are too specialized to have been in the direct line of human descent. Man, as Kohlbrugge ironically remarks, appears to have come from an ancestor much more like himself than any species of ape we know of. Moreover, no species of apes or monkeys monopolizes the honors of closest resemblance to man. In many points, the South American monkeys, though more primitive than the anthropoid apes, are more similar to man than the latter.
§ 2. Embryological Resemblances
Much has been made of the so-called biogenetic law as an argument for the bestial origin of mankind. This theory of the embryological recapitulation of racial history was first formulated by Fritz Müller. Haeckel, however, was the one who exploited it most extensively, and who exalted it to the status of “the fundamental law of biogenesis.”[16] The latter’s statement of the principle is as follows: “Die Ontogenesis ist die Palingenesis der Phylogenesis.”—Ontogeny (the development of the individual) is a recapitulation of phylogeny (the development of the race). For a long time this law was received with uncritical credulity by the scientific world, but enthusiasm diminished when more careful studies made it clear that the line of descent suggested by embryology did not agree with what was inferred from comparative anatomy and the sequence of fossil forms. Besides, it was manifest that certain organs in embryos were distinctively embryonic and could never have functioned in adult forms, e.g. the yolk sac and the amnion. “It was recognized,” says T. H. Morgan, “that many embryonic stages could not possibly represent ancestral animals. A young fish with a huge yolk sac attached could scarcely ever have led a happy, free life as an adult individual. Such stages were interpreted, however, as embryonic additions to the original ancestral type. The embryo had done something on its own account. In some animals the young have structures that attach them to the mother, as does the placenta of mammals. In other cases the young develop membranes about themselves—like the amnion of the chick and the mammal—that would have shut off an adult animal from all intercourse with the outside world. Hundreds of such embryonic structures are known to embryologists. These were explained as adaptations and as falsifications of the ancestral records.” (“Critique of the Theory of Evolution,” pp. 16, 17.)
The result has been that this so-called law has fallen into general disrepute among scientists, especially as a means of reconstructing the phylogeny of modern organisms. It is recognized, of course, that comparative embryology can furnish embryological homologies analogous to the homologies of comparative anatomy, but it is now generally acknowledged that the view, which regards the embryological process as an abridged repetition of the various states through which the species has passed in its evolutionary career must be definitively abandoned, and that, as a general law of organic development, the biogenetic principle has been thoroughly discredited. “This law,” says Karl Vogt of Geneva, “which I long held as well-founded, is absolutely and radically false. Attentive study of embryology shows us, in fact, that embryos have their own conditions suitable to themselves, and very different from those of adults.” (Quoted by Quatrefages De Breau, in his “Les Emules de Darwin,” vol. II, p. 13.) “There can no longer be question,” says Prof. M. Caullery of the Sorbonne, “of systematically regarding individual development as a repetition of the history of the stock. This conclusion results from the very progress made under the inspiration received from this imaginary law, the law of biogenesis.” (Smithson. Inst. Rpt. for 1916, p. 325.)
This collapse of the biogenetic law has tumbled into ruins the elaborate superstructure of genealogy which Haeckel had reared upon it. His series of thirty stages extending from the fictitious “cytodes” up to man, inclusively, is even more worthless today than it was when Du Bois-Reymond made his ironic comment: “Man’s pedigree, as drawn up by Haeckel, is worth about as much as is that of Homer’s heroes for critical historians.” (Revue Scientifique, 1877, I, p. 1101.) Haeckel tried in vain to save his discredited law by means of the expedient of cænogenesis, that is, “the falsification of the ancestral record (palingenesis).” That Nature should be guilty of “falsification” is an hypothesis not to be lightly entertained, and it is more credible, as Wasmann remarks, to assume that Haeckel, and not Nature, is the real falsifier, inasmuch as he has misrepresented Nature in his “fundamental biogenetic law.” Cænogenesis is a very convenient device. One can alternate at will between cænogenesis and palingenesis, just as, in comparative anatomy, one can alternate capriciously between convergence and homology, on the general understanding of its being a case of: “Heads, I win; tails, you lose”—certainly, there is no objective consideration to restrain us in such procedure. “Such weapons as Cænogenesis and Convergence,” says Kohlbrugge (in his “Die Morphologische Abstammung des Menschen,” 1908) “are unfortunately so shaped that anyone can use them when they suit him, or throw them aside when they do not. They show, therefore, in the prettiest way the uncertainty even now of the construction of the theory of descent. As soon as we go into details it leaves us in the lurch; it was only while our knowledge was small that everything seemed to fit together in most beautiful order.” (Quoted by Dwight in “Thoughts of a Catholic Anatomist,” p. 187.)
It is undeniable, indeed, that in many cases the young of higher animals pass through stages in which they bear at least a superficial resemblance to adult stages in inferior and less complex organisms. Obviously, however, there cannot be any direct derivation of the embryonic features of one organism from the adult characters of another organism. This preposterous implication of the Müller-Haeckel Law must, as Morgan points out, be entirely eliminated, before it can merit serious consideration. Referring to the spiral cleavage exhibited by annelid, planarian and molluscan eggs, Morgan says: “It has been found that the cleavage pattern has the same general arrangement in the early stages of flat worms, annelids and molluscs. Obviously these stages have never been adult ancestors, and obviously if their resemblance has any meaning at all, it is that each group has retained the same general plan of cleavage possessed by their common ancestor.... Perhaps someone will say, ‘Well! is not this all that we have contended for! Have you not reached the old conclusion in a roundabout way?’ I think not. To my mind there is a wide difference between the old statement that the higher animals living today have the original adult stages telescoped into their embryos, and the statement that the resemblance between certain characters in the embryos of higher animals and corresponding stages in the embryos of lower animals is most plausibly explained by the assumption that they have descended from the same ancestors, and that their common structures are embryonic survivals.” (Op. cit., pp. 22, 23.)
After this admission, however, nothing remains of the law of “recapitulation” except simple embryological homology comparable, in every sense, to adult homology, and adding nothing essentially new to the latter argument for evolution. It is, therefore, ridiculous for evolutionists to speak of branchial (gill) arches and clefts in man. The visceral or pharyngeal arches and grooves appearing in the human embryo are unquestionably homologous with the genuine branchial arches and clefts in a fish embryo. In the latter, however, the grooves become real clefts through perforation, while the arches become the lamellæ of the permanent gills, thus adapting the animal to aquatic respiration. It is, accordingly, perfectly legitimate to refer to these embryonic structures in the young fish as gill arches and gill clefts. In man, however, the corresponding embryonic structures develop into the oral cavity, auditory meatus, ossicles of the ear, the mandible, the lower lip, the tongue, the cheek, the hyoid bone, the styloid process, the thymus, the thyroid and tracheal cartilages, etc. There is no perforation of the grooves, and the arches develop into something quite different than branchial lamellæ. Hence the correct name for these structures in the human embryo is pharyngeal (visceral) arches and grooves, their superficial resemblance to the embryonic structures in the fish embryo being no justification for calling them branchial. In short, the mere fact that certain embryonic structures in the young fish (homologous to the pharyngeal arches and grooves in the human embryo) develop into the permanent gills of the adult fish, is no more significant than the association of homology with divergent preadaptations, which is of quite general occurrence among adult vertebrate types. In all such cases, we have instances of fundamentally identical structures, diverted, as it were, to entirely different purposes or functions (e.g. the arm of a man and the flipper of a whale). Hence the argument drawn from embryological homology is no more cogent than the argument drawn from the homologies of comparative anatomy, which we have already discussed in a previous chapter. The misuse of the term branchial, to prejudge matters in their own favor, is in keeping with the customary policy of evolutionists. It is intended, naturally, to convey the impression that man, in the course of his evolution, has passed through a fish-like stage. At bottom, however, it is nothing more than a verbal subterfuge, that need not detain us further.
The theory of embryological recapitulation is often applied to man, with a view to establishing the doctrine of his bestial ancestry. We have seen one instance of this application, and we shall consider one other, for the purpose of illustrating more fully the principles involved. The claim is made by evolutionists, that man must have passed through a fish or amphibian stage, because, in common with all other mammals, he exhibits, during his embryological development, a typical fish (or, if you prefer, amphibian) kidney, which subsequently atrophies, only to be replaced by the characteristic mammalian kidney. The human embryo, therefore, repeats the history of our race, which must have passed through a fish-like stage in the remote past. In consequence of this phenomenon, therefore, it is inferred that man must have had fish-like ancestors. Let us pause, however, to analyze the facts upon which this inference is based.
In annelids, like the earthworm, the nephridia or excretory tubules are arranged segmentally, one pair to each somite. In vertebrates, however, the nephridial tubules, instead of developing in regular sequence from before backwards, develop in three batches, one behind the other, the anterior batch being called the pronephros, the middle one, the mesonephros and the posterior one, the metanephros. This, according to J. Graham Kerr, holds true not only of the amniotic vertebrates (reptiles, birds, and mammals) but also, with a certain reservation, of the anamniotic vertebrates (fishes and amphibians). “In many of the lower Vertebrates,” says this author, “there is no separation between the mesonephros and metanephros, the two forming one continuous structure which acts as the functional kidney. Such a type of renal organ consisting of the series of tubules corresponding to mesonephros together with metanephros may conveniently be termed the opisthonephros.” (“Textbook of Embryology,” II—Vertebrata, p. 221.) If we accept this view, it is not quite accurate to regard the mesonephros in man as a homologue of the opisthonephros of a fish, seeing that the latter is composed not only of mesonephridia (mesonephric tubules), but also of metanephridia (metanephric tubules). A brief description of the three nephridial systems of vertebrate embryos will serve to further clarify their interrelationship.
(1) The pronephric system: This consists of a collection of tubules called the pronephros, and a pronephric duct leading to the cloaca, or terminal portion of the alimentary canal. The pronephros is a functional organ in the frog tadpole and other larval amphibia. It is also found in a few teleosts, where it is said to persist as a functional organ in the adult. In other fishes, however, and in all higher forms the pronephros atrophies and becomes reduced to a few rudiments.[17]