§ 3. Rudimentary Organs
Darwin attached great importance to the existence in man of so-called rudimentary organs, which he regarded as convincing evidence of man’s descent from the lower forms of animal life. Nineteenth century science, being ignorant of the functional purpose served by many organs, arbitrarily pronounced them to be useless organs, and chose, in consequence, to regard them all as the atrophied and (wholly or partially) functionless remnants of organs that were formerly developed and fully functional in remote ancestors of the race. Darwin borrowed this argument from Lamarck. It may be stated thus: Undeveloped and functionless organs are atrophied organs. But atrophy is the result of disuse. Now disuse presupposes former use. Consequently, rudimentary organs were at one time developed and functioning, viz. in the remote ancestors of the race. Since, therefore, these selfsame organs are developed and functional in the lower forms of life, it follows that the higher forms, in which these organs are reduced and functionless, are descended from forms similar to those in which said organs are developed and fully functional.
This argument, however, fairly bristles with assumptions that are not only wholly unwarranted, but utterly at variance with actual facts. In the first place, it wrongly assumes that all reduced organs are functionless, and, conversely, that all functionless organs are atrophied or reduced. Facts, however, prove the contrary; for we find frequent instances of reduced organs which function, and, vice versa, of well-developed organs which are functionless. The tail, for example, in cats, dogs, and certain Catarrhine monkeys, though it discharges neither the prehensile function that makes it useful in the Platyrrhine monkey, nor the protective function that makes it useful to horses and cattle in warding off flies, is, nevertheless, despite its inutility or absence of function, a quite fully developed organ. Conversely, the reduced or undeveloped fin-like wings of the penguin are by no means functionless, since they enable this bird to swim through the water with great facility.
To save his argument from this antagonism of the facts, Darwin resorts to the ingenious expedient of distinguishing between rudimentary organs and nascent organs. Rudimentary organs are undeveloped organs, which are wholly, or partially, useless. They have had a past, but have no future. Nascent organs, on the contrary, are undeveloped organs, which “are of high service to their possessors” (“Descent of Man,” ch. I, p. 28, 2nd ed.). They “are capable of further development” (ibidem), and have, therefore, a future before them. He gives the following examples of rudimentary organs: “Rudimentary organs ... are either quite useless, such as teeth which never cut through the gums, or almost useless, such as the wings of an ostrich, which serve merely as sails.” (“Origin of Species,” 6th ed., ch. XIV, p. 469.) As an example of a nascent organ, he gives the mammary glands of the oviparous Duckbill: “The mammary glands of the Ornithorhynchus may be considered, in comparison with the udders of a cow, as in a nascent condition.” (Op. cit., ch. XIV, p. 470.)
Darwin admits that it is hard to apply this distinction in the concrete: “It is, however, often difficult to distinguish between rudimentary and nascent organs; for we can judge only by analogy whether a part is capable of further development, in which case alone it deserves to be called nascent.” (Op. cit., ch. XIV, p. 469.) For Darwin “judging by analogy” meant judging on the assumption that evolution has really taken place; for he describes rudimentary organs as being “of such slight service that we can hardly suppose that they were developed under the conditions which now exist.” (“Descent of Man,” ch. I, p. 29.)
He is somewhat perplexed about applying this distinction to the penguin: “The wing of the penguin,” he admits, “is of high service, acting as a fin; it may, therefore, represent the nascent state: not that I believe this to be the case; it is more probably a reduced organ, modified for a new function.” (“Origin of Species,” 6th ed., ch. XIV, pp. 469, 470.) In other words, there is scarcely any objective consideration by which the validity of this distinction can be checked up in practice. Like homology and convergence, like palingenesis and cænogensis, the distinction between rudimentary and nascent organs is a convenient device, which can be arbitrarily manipulated according to the necessities of a preconceived theory. It is “scientific” sanction for the privilege of blowing hot and cold with the same breath.
The assumption that atrophy and reduction are the inevitable consequence of disuse, or diminution of use, in so far as this decreases the flow of nourishing blood to unexercised parts, is certainly erroneous. Yet Darwin made it the premise of his argument from so-called rudimentary organs. “The term ‘disuse’ does not relate,” he informs us, “merely to lessened action of muscles, but includes a diminished flow of blood to the part or organ, from being subjected to fewer alternations of pressure, or from being in any way less habitually active.” (“Origin of Species,” 6th ed., p. 469.) As a matter of fact, however, we have many instances in which use has failed to develop and disuse to reduce organs in certain types of animals. As an example in point, we may cite the case of right-handedness among human beings. From time immemorial, the generality of mankind have consistently used the right hand in preference to the left, without any atrophy or reduction of the left hand, or over-development of the right hand, resulting from this racial practice. “The superiority of one hand,” says G. Elliot Smith, “is as old as mankind.” (Smithson. Inst. Rpt. for 1912, p. 570.) It is true that only about 6,000 years of human existence are known to history, but, if one accepts the most conservative estimates of glaciologists, man has had a much longer prehistory, the lowest estimates for the age of man being approximately 30,000 years. Thus W. J. Sollas tells us that the Glacial period, in which man first appeared, came to an end about 7,000 years ago, and that the men buried at Chapelle-aux-Saints in France lived about 25,000 years ago. His figures agree with those of C. F. Wright, who bases his calculations on the Niagara Gorge. The Niagara River is one of the postglacial streams, and the time required to cut its gorge has been calculated as 7,000 years. Gerard De Geer, the Swedish scientist, gives 20,000 years ago as the end of glacial and the commencement of recent or postglacial time. He bases his estimates on the sediments of the Yoldia Sea in Sweden. His method consists in the actual counting of certain seasonally-laminated clay layers, presumably left behind by the receding ice sheet of the continental glacier. The melting is registered by annual deposition, in which the thinner layers of finer sand from the winter flows alternate with thicker layers of coarser material from the summer flows. In warm years, the layers are thicker, in colder years they are thinner, so that these laminated Pleistocene clays constitute a thermographic as well as a chronological record. De Geer began his study of Pleistocene clays in 1878, and in 1920 he led an expedition to the United States, for the purpose of extending his researches. (Cf. Science, Sept. 24, 1920, pp. 284-286.) At that time, he claimed to have worked out the chronology of the past 12,000 years. His figure of 20,000 years for postglacial time, while very displeasing to that reckless foe of scientific caution and conservatism, Henry Fairfield Osborn, tallies very well with the estimates of Sollas and Wright. H. Obermaier, basing his computation on Croll’s theory that glaciation is caused by variations in the eccentricity of the earth’s orbit about the sun, which would bring about protracted winters in the hemisphere having winter, when the earth was farthest from the sun (with consequent accumulation of ice), gives 30,000 years ago as the date of the first appearance of man on earth. Father Hugues Obermaier, it may be noted, like Abbé Henri Breuil, is one of the foremost authorities on the subject of prehistoric Man. Both are Catholic priests.
All such computations of the age of man are, of course, uncertain and theoretical. Evolutionists calculate it in hundreds of thousands, and even millions, of years. After giving such a table of recklessly tremendous figures, Osborn has the hypocritical meticulosity to add that, for the sake of precision (save the mark!) the nineteen hundred and some odd years of the Christian era should be added to his figures. But, even according to the most conservative scientific estimates, as we have seen, man is said to have been in existence for 30,000 years, and the prevalence of right-handedness among men is as old as the human race. One would expect, then, to find modern man equipped with a gigantic right arm and a dwarfed left arm. In other words, man should exhibit a condition comparable to that of a lobster, which has one large and one small chela. Yet, in spite of the fact that the comparative inaction of the human left hand is supposed to have endured throughout a period of, at least, 30,000 years, this state of affairs has not resulted in the faintest trace of atrophy or retrogression. Bones, muscles, tendons, ligaments, nerves, blood vessels, and all parts are of equal size in both arms and both hands. Excessive exercise may overdevelop the musculature of the right arm, but this is an individual and acquired adaptation, which is never transmitted to the offspring, e.g. the child of a blacksmith does not inherit the muscular hypertrophy of his father. Disuse, therefore, has not the efficacy which Lamarck and Darwin ascribed to it.
In fine, it must be recognized, once for all, that organisms are not-molded on a Lamarckian basis of use, nor yet on a Darwinian basis of selected utility. Expediency, in other words, is not the sole governing principle of the organic world. Neither instinctive habitude nor the struggle for existence succeeds in forcing structural adaptation of a predictable nature. Animals with different organic structure have the same instincts, e.g. monkeys with, and without, prehensile tails alike dwell in trees; while animals having the same organic structure may have different instincts, e.g. the rabbit, which burrows, and the hare, which does not, are practically identical in anatomical structure. Again, some animals are highly specialized for a function, which other animals perform without specialized organs, as is instanced in the case of moles, which possess a special burrowing apparatus, and prairie-dogs, which burrow without a specialized apparatus. Any system of evolution, which ignores the internal or hereditary factors of organic life and strives to explain all in terms of the environmental factors, encounters an insuperable obstacle in this remorseless resistance of conflicting facts.
Another flaw in the Darwinian argument from rudimentary organs is that it confounds, in many cases, apparent, with real inutility (or absence of function). Darwin and his followers frequently argued out of their ignorance, and falsely concluded that an organ was destitute of a function, merely because they had failed to discover its utility. Large numbers, accordingly, of highly serviceable organs were catalogued as vestigial or rudimentary, simply because nineteenth century science did not comprehend their indubitable utility. With the advance of present-day physiology, this list of “useless organs” is being rapidly depleted, so that the scientific days of the rudimentary organ appear to be numbered. At any rate, in arbitrarily pronouncing many important and functioning organs to be useless vestiges of a former stage in the history of the race, the Darwinians were not the friends of Science, but rather its reactionary enemies, inasmuch as they sought to discourage further investigation by their dogmatic decision that there was no function to be found. In so doing, however, they were merely exploiting the ignorance of their times in the interest of a preconceived theory, which whetted their appetite for discovering, at all costs, the presence in man of functionless organs.
Their anxiety in this direction led them to consider the whole group of organs constituting a most important regulatory and coördinative system in man and other vertebrates as so many useless vestigial organs. This system is called the cryptorhetic system and is made of internally-secreting, ductless glands, now called endocrine glands. These glands generate and instill into the blood stream certain chemical substances called hormones, which, diffusing in the blood, produce immediate stimulatory, and remote metabolic effects on special organs distant from the endocrine gland, in which the particular hormone is elaborated. As examples of such endocrine glands, we may mention the pineal gland (epiphysis), the pituitary body (hypophysis), the thyroid glands, the parathyroids, the islelets of Langerhans, the adrenal bodies (suprarenal capsules), and the interstitial cells of the gonads. The importance of these alleged useless organs is now known to be paramount. Death, for instance, will immediately ensue in man and other animals, upon extirpation of the adrenal bodies.
The late Robert Wiedersheim, it will be remembered, declared the pineal gland or epiphysis to be the surviving vestige of a “third eye” inherited from a former ancestor, in whom it opened between the parietal bones of the skull, like the median or pineal eye of certain lizards, the socket of which is the parietal foramen formed in the interparietal suture. If the argument is based on homology alone, then the coincidence in position between the human epiphysis and the median optic nerve of the lizards in question has the ordinary force of the evolutionary argument from homology. But when one attempts to reduce the epiphysis to the status of a useless vestigial rudiment, he is in open conflict with facts; for the pineal body is, in reality, an endocrine gland generating and dispersing a hormone, which is very important for the regulation of growth in general and of sexual development in particular. Hence this tiny organ in the diencephalic roof, no larger than a grain of wheat, is not a functionless rudiment, but an important functioning organ of the cryptorhetic system. We have no ground, therefore, on this score for inferring that our pineal gland functioned in former ancestors as a median eye comparable to that of the cyclops Polyphemus of Homeric fame.
In like manner, the pituitary body or hypophysis, which in man is a small organ about the size of a cherry, situated at the base of the brain, buried in the floor of the skull, and lying just behind the optic chiasma, was formerly rated as a rudimentary organ. It was, in fact, regarded as the vestigial remnant of a former connection between the neural and alimentary canals, reminiscent of the invertebrate stage. “The phylogenetic explanation of this organ generally accepted,” says Albert P. Mathews, “is that formerly the neural canal connected at this point with the alimentary canal. A probable and almost the only explanation of this, though an explanation almost universally rejected by zoölogists, is that of Gaskell, who has maintained that the vertebrate alimentary canal is a new structure, and that the old invertebrate canal is the present neural canal. The infundibulum, on this view, would correspond to the old invertebrate œsophagus, the ventricle of the thalamus to the invertebrate stomach, and the canal originally connected posteriorly with the anus. The anterior lobe of the pituitary body could then correspond to some glandular adjunct of the invertebrate canal, and the nervous part to a portion of the original circumœsophageal nervous ring of the invertebrates.” (“Physiological Chemistry,” 2nd ed., 1916, pp. 641, 642.)
This elaborate piece of evolutionary contortion calls for no comment here. We are only interested in the fact that this wild and weird speculation was originally inspired by the false assumption that the hypophysis was a functionless organ. As a matter of fact, it is the source of two important hormones. The one generated in its anterior lobe is tethelin, a metabolic hormone, which promotes the growth of the body in general and of the bony tissue in particular. Hypertrophy and overfunction of this gland produces giantism, or acromegaly (enlargement of hands, feet, and skull), while atrophy and underfunction of the anterior lobe results in infantilism, acromikria (diminution of extremities, i. e. hands, feet, head), obesity, and genital dystrophy (i. e. suppression of secondary sexual characters). The posterior lobe of the pituitary body constitutes, with the pars intermedia, a second endocrine gland, which generates a stimulatory hormone called pituitrin. This hormone stimulates unstriated muscle to contract, and thereby regulates the discharge of secretions from various glands of the body, e. g. the mammary glands, bladder, etc. Hence the hypophysis, far from being a useless organ, is an indispensable one. Moreover, it is an integral and important part of the cryptorhetic system.
The same story may be repeated of the thyroid glands. These consist of two lobes located on either side of the windpipe, just below the larynx (Adam’s apple), and joined together across the windpipe by a narrow band or isthmus of their own substance. Gaskell homologized them with a gland in scorpions, and Mathew says that, if his surmise is correct, “the thyroid represents an accessory sexual organ of the invertebrate.” (Op. cit., p. 654.) They are, however, endocrine glands, that generate a hormone known as thyroxin, which regulates the body-temperature, growth of the body in general, and of the nervous system in particular, etc., etc. Atrophy or extirpation of these glands causes cretinism in the young and myxoedema in adults. Without a sufficient supply of this hormone, the normal exercise of mental powers in human beings is impossible. The organ, therefore, is far from being a useless vestige of what was formerly useful.
George Howard Parker, the Zoölogist of Harvard, sums up the case against the Darwinian interpretation of the endocrine glands as follows: “The extent to which hormones control the body is only just beginning to be appreciated. For a long time anatomists have recognized in the higher animals, including man, a number of so-called ductless glands, such as the thyroid gland, the pineal gland, the hypophysis, the adrenal bodies, and so forth. These have often been passed over as unimportant functionless organs whose presence was to be explained as an inheritance from some remote ancestor. But such a conception is far from correct. If the thyroids are removed from a dog, death follows in from one to four weeks. If the adrenal bodies are excised, the animal dies in from two to three days. Such results show beyond doubt that at least some of these organs are of vital importance, and more recent studies have demonstrated that most of them produce substances which have all the properties of hormones.” (“Biology and Social Problems,” 1914, pp. 43, 44.)
Even the vermiform appendix of the cæcum, which since Darwin’s time has served as a classic example of a rudimentary organ in man, is, in reality, not a functionless organ. Darwin, however, was of opinion that it was not only useless, but positively harmful. “With respect to the alimentary canal,” he says, “I have met with an account of only a single rudiment, namely, the vermiform appendage of the cæcum. ... Not only is it useless, but it is sometimes the cause of death, of which fact I have lately heard two instances. This is due to small hard bodies, such as seeds, entering the passage and causing inflammation.” (“Descent of Man,” 2nd ed., ch. I, pp. 39, 40.) The idea that seeds cause appendicitis is, of course, an exploded superstition, the hard bodies sometimes found in the appendix being fecal concretions and not seeds—“The old idea,” says Dr. John B. Deaver, “that foreign bodies, such as grape seeds, are the cause of the disease, has been disproved.” (Encycl. Americana, vol. 2, p. 76.) What is more germane to the point at issue, however, is that Darwin erred in denying the utility of the vermiform appendix. For, although this organ does not discharge in man the important function which its homologue discharges in grain-eating birds and also in herbivorous mammals, it subserves the secondary function of lubricating the intestines by means of a secretion from its muciparous glands.
Darwin gives the semilunar fold as another instance of a vestigial organ, claiming that it is a persistent rudiment of a former third eyelid or membrana nictitans, such as we find in birds. “The nictitating membrane, or third eyelid,” he says, “with its accessory muscles and other structures, is especially well developed in birds, and is of much functional importance to them, as it can be rapidly drawn across the whole eyeball. It is found in some reptiles and amphibians, and in certain fishes as in sharks. It is fairly well developed in the two lower divisions of the mammalian series, namely, in the monotremata and marsupials, and in some higher mammals, as in the walrus. But in man, the quadrumana, and most other mammals, it exists, as is admitted by all anatomists, as a mere rudiment, called the semilunar fold.” (Op. cit., ch. I, pp. 35, 36.) Here Darwin is certainly wrong about his facts; for the so-called third eyelid is not well developed in the two lower divisions of the mammalian series (i.e. the monotremes and the marsupials) nor in any other mammalian type. “With but few exceptions,” says Remy Perrier, “the third eyelid is not so complete as among the birds; (in the mammals) it never covers the entire eye. For the rest, it is not really perceptible except in certain types, like the dog, the ruminants, and, still more so, the horse. In the rest (of the mammals) it is less developed.” (“Elements d’anatomie comparée,” Paris, 1893, p. 1137.) Moreover, Darwin’s suggestion leaves us at sea as to the ancestor, from whom our “rudimentary third eyelid” has been inherited. His mention of birds as having a well developed third eyelid is not very helpful, because all evolutionists agree in excluding the birds from our line of descent. The reptiles are more promising candidates for the position of ancestors, but, as no trace of a third eyelid could possibly be left behind in the imperfect record of the fossiliferous rocks (soft parts like this having but slight chance of preservation), we do not really know whether the palæozoic reptiles possessed this particular feature, or not. Nor can we argue from analogy and induction, because not all modern reptiles are equipped with third eyelids. Hence the particular group of palæozoic reptiles, which are supposed to have been our progenitors, may not have possessed any third eyelid to bequeath to us in the reduced and rudimentary form of the plica semilunaris. If it be replied, that they must have had this feature, because otherwise we would have no ancestor from whom we could inherit our semilunar fold, it is obvious that such argumentation assumes the very point which it ought to prove, namely: the actuality of evolution. Rudiments are supposed to be a proof for evolution, and not, vice versa, evolution a proof for rudiments.
Finally, the basic assumption of Darwin that the semilunar fold is destitute of function is incorrect; for this crescent-shaped fold situated in the inner or nasal corner of the eye of man and other mammals serves to regulate the flow of the lubricating lacrimal fluid (which we call tears). True this function is secondary compared with the more important function discharged by the nictitating membrane in birds. In the latter, the third eyelid is a pearly-white (sometimes transparent) membrane placed internal to the real eyelids, on the inner side of the eye, over whose surface it can be drawn like a curtain to shield the organ from excessive light, or irritating dust; nevertheless, the regulation of the flow of lacrimal humor is a real function, and it is therefore entirely false to speak of the semilunar fold as a functionless rudiment.
The coccyx is likewise cited by Darwin as an example of an inherited rudiment in man. “In man,” he says, “the os coccyx, together with certain other vertebræ hereafter to be described, though functionless as a tail, plainly represents this part in other vertebrate animals.” (Op. cit., ch. I, p. 42.) That it serves no purpose as a tail, may be readily admitted, but that it serves no purpose whatever, is quite another matter. As a matter of fact, it serves for the attachment of several small muscles, whose functioning would be impossible in the absence of this bone. Darwin himself concedes this; for he confesses that the four vertebræ of the coccyx “are furnished with some small muscles.” (Ibidem.) We may, therefore, admit the homology between the human coccyx and the tails of other vertebrates, without being forced to regard the latter as a useless vestigial organ. It may be objected that the attachment of these muscles might have been provided for in a manner more in harmony with our ideas of symmetry. To this we reply that Helmholtz criticized the human eye for similar reasons, when he said that he would remand to his workshop for correction an optical instrument so flawed with defects as the human eye. But, after all, it was by the use of these selfsame imperfect eyes that Helmholtz was enabled to detect the flaws of which he complained. When man shall have fully fathomed the difficulties and obstructions with which organic morphogeny has to contend in performing its wonderful work, and shall have arrived at an elementary knowledge of the general laws of morphogenetic mechanics, he will be more inclined to admire than to criticize. It is a mistake to imagine that the finite works of the Creator must be perfect from every viewpoint. It suffices that they are perfect with respect to the particular purpose which they serve, and this purpose must not be narrowly estimated from the standpoint of the created work itself, but from that of its position in the universal scheme of creation. All such partial views as the Helmholtzian one are false views.
Another consideration which Darwin and his partisans have failed to take into account is the possibility of an ontogenetic, as well as a phylogenetic, explanation of rudimentary organs. That is to say, rudimentary organs might, so far as a priori reasons are concerned, be the now useless vestiges of organs formerly developed and functional in the fœtus, and need not necessarily be interpreted as traces of organs that functioned formerly in remote racial ancestors. That there should be such things as special fœtal organs, which atrophy in later adult life, is a possibility that ought not to excite surprise. During its uterine existence, the fœtus is subject to peculiar conditions of life, very different from those which prevail in the case of adult organisms—e.g. respiration and the digestive process are suspended, and there is a totally different kind of circulation. What, then, more natural than that the fœtus should require special organs to adapt it to these special conditions of uterine life? Such organs, while useful and functional in the earlier stages of embryonic development, will, so soon as birth and maturity introduce new conditions of life, become superfluous, and therefore doomed, in the interest of organic economy, to ultimate atrophy and degeneration, until nothing is left of them but vestigial remnants.
The thymus may be cited as a probable instance of such an organ. This organ, which is located in front of the heart and behind the breastbone, in the region between the two lungs, consists, at the period of its greatest development in man, of a two-lobed structure, 5 cm. long and 4 cm. wide, with a thickness of 6 mm. and a maximum weight of 35 grams. It is supplied with numerous lymphoid cells, which are aggregated to form lymphoid follicles (cf. Gray’s “Anatomy,” 20th ed., 1918, pp. 1273, 1274; Burton-Opitz’ “Physiology,” 1920, p. 964). This organ is a transitory one, well developed at birth, but degenerating, according to some authors, after the second year of life (cf. Starling’s “Physiology,” 3rd ed., 1920, p. 1245); according to others, however, not until the period of full maturity, namely, puberty. (Cf. Gray’s “Anatomy,” loc. cit.) W. H. Howell cites both opinions, without venturing to decide the matter (cf. his “Physiology,” 8th ed., 1921, pp. 869, 870). It was at one time classified as a rudimentary or functionless organ. Later on, however, it was thought by certain observers to be an endocrine gland, yielding a secretion important for the growth of young mammals. This took it out of the class of useless vestigial organs, but the recent discovery that it is indispensable to birds as furnishing a secretion necessary for the formation of the tertiary envelopes (egg membrane and shell) of their eggs, has tended to revive the idea of its being a vestigial organ inherited from the lower vertebrates.
Thus Dr. Oscar Riddle, while admitting that the thymus gland in man has some influence on the growth of the bones, contends that the newly-discovered function of this gland in birds is much more important, since without it none of the vertebrates, excepting mammals, could reproduce their young. “It thus becomes clear,” he says, “that though the thymus is almost without use in the human being, it is in fact a sort of ‘mother of the race.’ The higher animals could not have come into existence without it. For even while our ancestors lived in the water, it was the thymus of these ancestors which made possible the production of the egg-envelopes within which the young were cradled and protected until they were ready for an independent life.” (Science, Dec. 28, 1923, Suppl. XIII, XIV.)
This conclusion, however, is far too hasty. For, even if we disregard as negligible the minor function, that Riddle assigns to the thymus in man, there remains another possibility, which H. H. Wilder takes into account, namely, that the thymus may, in certain cases, be a temporary substitute for the lymphatic vessels. Having called attention to certain determinate channels found in some of the lower vertebrates, he tells us that these “can well be utilized as adjuncts of the lymphatic system until their function can be supplied by definite lymphatic vessels.” He then resumes his discussion of the lymph nodules in mammals as follows: “Aside from the solitary and aggregated nodules, both of which appear to be centers of origin of lymphocytes, there are numerous other places in which the cellular constituents of the blood are developed. Many of these, as in the case of the aggregated nodules of the intestines, are developed within the wall of the alimentary canal and are therefore endodermic in origin. These include the tonsils, the thymus, and thyroid glands, the associated epithelial bodies, and, perhaps, the spleen.... In their function as formative nidi for the cellular elements of the blood these organs form physiologically important auxiliaries to the vascular system as a whole, but belong elsewhere in their anatomical developmental affinities.” (“History of the Human Body,” 2nd ed., 1923, p. 395—italics mine.)
This being the case, it is much more reasonable to interpret the thymus as an ontogenetic (embryonic), rather than a phylogenetic (racial) rudiment. It has been observed that, in the case of reptiles which lack definite lymphatic glands (which function in man as formative centers of lymphocytes or white blood corpuscles), the thymus is extraordinarily developed and abounds in lymphoid cells. It has also been observed that the formation of lymphocytes in the lymphatic glands is regulated by the digestive process; for, after digestion, the activity of these glands increases and the formation of leucocytes is accelerated. Since, then, the lymphatic glands appear to require the stimulus of the digestive process to incite them to action, it is clear that in the fœtus, which lacks the digestive process, the lymphatic glands will not be stimulated to action, and that the task of furnishing lymphocytes will devolve upon the thymus. After birth, the digestive process commences and the lymphatic glands become active in response to this stimulus. As the function of forming lymphocytes is transferred from the thymus to the lymphatic glands, the former is gradually deprived of its importance, and, in the interest of organic economy, it begins to atrophy, until, at the end of the child’s second year, or, at latest, when the child has reached sexual maturity, nothing but a reduced vestige remains of this once functional organ. “The thymus,” says Starling, “forms two large masses in the anterior mediastinum which in man grow up to the second year of life and then rapidly diminish, so that only traces are to be found at puberty. It contains a large amount of lymphatic tissue and is therefore often associated with the lymphatic glands as the seat of the formation of lymph corpuscles.... In certain cases of arrested development or of general weakness in young people, the thymus has been found to be persistent.” (“Physiology,” 3rd ed., 1920, p. 1245.)
In the light of these facts, it is utterly unreasonable to regard the thymus as a practically useless rudiment inherited from the lower vertebrates. “That they have an important function in the young animal,” says Albert Mathews, “can hardly be doubted.” (“Physiological Chemistry,” 1916, p. 675.) In fact, the peculiar nature of their development in the young and their atrophy in the adult forces such a conclusion upon us. The thymus, therefore, is, in all probability, an ontogenetic, and not a phylogenetic, rudiment. It might conceivably be exploited as a biogenetic recapitulation of a reptilian stage in man, just as the so-called fish-kidney of the human embryo is exploited for evolutionary interpretation. The principles by which such a view may be refuted have been given previously. But, in any case, it is folly to interpret the thymus as a rudiment in the racial, rather than embryonic sense. Moreover, the possibility of an ontogenetic interpretation of rudiments must not be restricted to the thymus, but must be accepted as a general and legitimate alternative for the phylogenetic interpretation.
In the last place, it remains for us to consider the Darwinian argument, based upon so-called rudimentary organs, from the standpoint of the science of genetics. Darwin, as we have remarked elsewhere, was ignorant of the non-inheritability of those inconstant individual variations now known as fluctuations. He was somewhat perplexed, when Professor L. Meyer pointed out the extreme variability in position of the “projecting point” on the margin of the human ear, but he still clung to his original contention that this “blunt point” was a surviving vestige of the apex of the pointed ears found in donkeys and horses, etc. “Nevertheless,” he says, “in some cases my original view, that the points are vestiges of the tips of formerly erect and pointed ears, still seems to be probable.” (“Descent of Man,” 2nd ed., ch. I, p. 34.) Darwin, as Ranke points out, was mistaken in homologizing his famous “tubercule” with the apex of bestial ears. “The acute extremity of the pointed animal ear,” says this author, “does not correspond to this prominence designated by Darwin, but to the vertex of the helix.” (“Der Mensch,” II, p. 39.) The feature in question is, moreover, a mere fluctuation due to the degree of development attained by the cartilage: hence its variability in different human beings. In very extreme cases, fluctuations of this sort, may be important enough to constitute an anomaly, and, as anomalies are often interpreted as atavisms and reversions to a primitive type, it may be well to advert to this subject here.
Dwight has an excellent chapter on anatomical variations and anomalies. (Cf. “Thoughts of a Catholic Anatomist,” 1911, ch. IX.) He tells us that “a thigh bone a little more bent, an ear a little more pointed, a nose a little more projecting ... a little more or a little less of anything you please—this is variation.” “An anatomical anomaly,” he says, “is some peculiarity of any part of the body which cannot be expressed in terms of more or less, but is distinctly new.” He divides the latter into two classes, namely: those which consist in the repetition of one or more elements in a series, e.g. the occurrence of supernumerary legs in an insect, and those which consist in the suppression of one or more elements in a series, e.g. the occurrence of eleven pairs of ribs in a man. Variations and anomalies are fluctuational or mutational, according as they are based on changes in the soma alone, or on changes in the germ plasm. Variations, however, are more likely to be non-inheritable fluctuations, and anomalies to be inheritable mutations. We shall speak of the latter presently. In the meantime we may note that the main trouble with interpreting these anatomical irregularities as “reversive” or “atavistic” is that they would connect man with all sorts of quite impossible lines of descent. “In my early days of anatomy,” says Dwight, “I thought that I must be very ignorant, because I could not understand how the occasional appearance in man of a peculiarity of some animal outside of any conceivable line of descent could be called a reversion, as it soon became the custom to call it.... It was only later that I grasped the fact that the reason I could not understand these things was that there was nothing to understand. It was sham science from beginning to end.” (Op. cit., p. 209.) By way of anomaly, almost any human peculiarity can occur in animals, and, conversely, any bestial peculiarity in man, but the resemblance to man of an animal outside of the alleged line of human descent represents a grave difficulty for the theory of evolution, and not an argument in its favor.
The human body is certainly not a mosaic of heterogenetic organs, i.e. a complex of structures inherited from any and every sort of animal, whether extant or extinct; for such a vast number and variety of ancestors could not possibly have coöperated to produce man. Prof. D. Carazzi, in his Address of Inauguration in the Chair of Zoölogy and Comparative Anatomy at the University of Padua, Jan. 20, 1906, excoriated with scathing irony the sham Darwinian science, of which Dwight complains. “But even in the serious works of pure science,” says the Italian zoölogist, “we read, for example, that the over-development of the postauricular muscles sometimes observed in man is an atavistic reminiscence of the muscles of the helix of the ear of the horse and the ass. And so far so good, because it gives evidence of great modesty in recognizing as our ancestors those well-deserving and long-eared quadrupeds. But this is not all; there appear at times in a woman one or more anomalous mammary glands below the pectoral ones; and here, too, they insist on explaining the anomaly as a reversion to type, that is, as an atavistic reminiscence of the numerous mammary glands possessed by different lower mammals; the bitch, for example....
“But the supernumerary mammary glands are not a reversion to type; anomalous mammary glands may appear upon the median line, upon the deltoid, and even upon the knee, regions far-distant from the ‘milk-line.’ So with regard to the postauricular muscles we must say that according to the laws of Darwinism the cases of anomalous development are not interpretable as reversions to type. All these features are not phylogenetic reminiscences, but anomalies of development, of such a nature that, if we should wish to make use of them for establishing the line of human descent, we would have to say that man descends from the swine, from the solipeds and even from the cetaceans, returning, namely, to the old conception of lineal descent, that is, to Buffon’s idea of the concatenation of creatures.” (“Teorie e critiche nella moderna biologia,” 1906.)
Darwin’s doctrine, however, on the origin and significance of rudimentary organs has been damaged by genetic analysis in a yet more serious fashion. In fact, with the discovery that anomalous suppression and anomalous duplication of organs may result from factorial mutation, this Darwinian conception received what is tantamount to its deathblow. Darwin, it will be remembered, was convinced that the regression of organs was brought about by “increased disuse controlled by natural selection.” (Cf. “Origin of Species,” 6th ed., ch. V.) Such phenomena, he thought, as the suppression of wings in the Apteryx and the reduction of wings in running birds, arose from their “inhabiting ocean islands,” where they “have not been exposed to the attacks of beasts, and consequently lost the power of using their wings for flight.” (“Descent of Man,” 6th ed., ch. I, p. 32.) In some cases, he believed that disuse and natural selection had coöperated ex aequo to produce results of this nature, e.g. the reduction of the eyes in the mole and in Ctenomys; for this reduction, he claims, has some selection-value, inasmuch as reduction of the eyes, adhesion of the lids, and covering with hair tends to protect the unused and useless eye against inflammation. In other cases, however, he is inclined to discount the idea that suppression of organs is an “effect of long-continued disuse,” and to regard the phenomenon as “wholly, or mainly, due to natural selection,” e.g. in the case of the wingless beetles of the island of Madeira. “For during successive generations,” he reasons, “each individual beetle which flew least, either from its wings having been ever so little less developed or from indolent habit, will have had the best chance of surviving from not being blown out to sea; and, on the other hand, those beetles which most readily took to flight would oftenest have been blown to sea, and thus destroyed.” In a third class of instances, however, he assigns the principal rôle to disuse, e.g. in the case of the blind animals “which inhabit the caves of Carniola and Kentucky, because,” as he tells us, “it is difficult to imagine that eyes, though useless, could be injurious to animals living in darkness.” Hence he concludes that, as the obliteration of eyes has no selection-value, under the circumstances prevailing in dark caves, “their loss may be attributed to disuse.” (Cf. “Origin of Species,” 6th ed., ch. V, pp. 128-133.)
Morgan’s comment on these elaborate speculations of Darwin is very caustic and concise. Referring to factorial mutations, which give rise to races of flies having supernumerary and vestigial organs, he says: “In contrast to the last case, where a character is doubled, is the next one in which the eyes are lost. This change took place at a single step. All the flies of this stock, however, cannot be said to be eyeless, since many of them show pieces of eye—indeed the variation is so wide that the eye may even appear like a normal eye unless carefully examined. Formerly we were taught that eyeless animals arose in caves. This case shows that they may also arise suddenly in glass milk bottles, by a change in a single factor.
“I may recall in this connection that wingless flies also arose in our cultures by a single mutation. We used to be told that wingless insects occurred on desert islands because those insects that had the best developed wings were blown out to sea. Whether this is true or not, I will not pretend to say, but at any rate wingless insects may also arise, not through a slow process of elimination, but at a single step.” (“A Critique of the Theory of Evolution,” 1916, pp. 66, 67.)
In directing attention to the fact that a permanent and inheritable reduction of organs to the vestigial state can result from mutation, we do not, of course, intend to exclude the possible occurrence of somatic atrophy due to lack of exercise rather than to germinal change. Thus the blind species of animals in caves may, in some instances, be persistently blind, because of the persistent darkness of the environment in which they live, and not by reason of any inherited factor for blindness. Darwin gives one such instance, namely, that of the cave rat Neotoma. To test such cases, the blind animals would have to be bred in an illuminated environment. If, under this condition, they failed to develop normal eyes, the blindness would be due to a germinal factor, and would be inherited in an illumined, no less than a dark, environment.
In any case, a mutation which suppresses a character is not, as we have seen, a specific change, but merely one of the varietal order, which does not result in the production of a genuine new species. The factorial mutant with a vestigial wing or eye belongs to the same species as its wild or normal parent stock. Moreover, neither disuse nor natural selection has the slightest power to induce mutations of this kind. If mutation be the cause of the blindness of cave animals, then their presence in such caves must be accounted for by supposing that they migrated thither because they found in the cave a most suitable environment for safety, foraging, etc. Darkness alone, however, could never induce germinal, but, at most, merely somatic blindness. The Lamarckian factor of disuse and the Darwinian factor of selection have been definitely discredited as agents which could bring about hereditarily-transmissible modifications.