APPENDIX C.
THE INHERITANCE OF FUNCTIONALLY-WROUGHT MODIFICATIONS: A SUMMARY
The assertion that changes of structure caused by changes of function are transmitted to descendants is continually met by the question – Where is the evidence? When some facts are assigned in proof, they are pooh-poohed as insufficient. If after a time the question is raised afresh and other facts are named, there is a like supercilious treatment of them. Successively rejected in this way, the evidences do not accumulate in the minds of opponents; and hence produce little or no effect. When they are brought together, however, it turns out that they are numerous and weighty. We will group them into negative and positive.
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Negative evidence is furnished by those cases in which traits otherwise inexplicable are explained if the structural effects of use and disuse are transmitted. In the foregoing chapters and appendices three have been given.
(1) Co-adaptation of co-operative parts comes first. This has been exemplified by the case of enlarged horns in a stag, by the case of an animal led into the habit of leaping, and in the case of the giraffe (cited in "The Factors of Organic Evolution"); and it has been shown that the implied co-adaptations of parts cannot possibly have been effected by natural selection.
(2) The possession of unlike powers of discrimination by different parts of the human skin, was named as a problem to be solved on the hypothesis of natural selection or the hypothesis of panmixia; and it was shown that neither of these can by any twisting yield a solution. But the facts harmonize with the hypothesis that the effects of use are inherited.
(3) Then come the cases of those rudimentary organs which, like the hind limbs of the whale, have nearly disappeared. Dwindling by natural selection is here out of the question; and dwindling by panmixia, even were its assumptions valid, would be incredible. But as a sequence of disuse the change is clearly explained.
Failure to solve any one of these three problems would, I think, alone prove the Neo-Darwinian doctrines untenable; and the fact that we have three unsolved problems seems to me fatal.
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From this negative evidence, turn now to the positive evidence. This falls into several groups.
There are first the facts collected by Mr. Darwin, implying functionally-altered structures in domestic animals. The hypothesis of panmixia is, as we have seen, out of court; and therefore Mr. Darwin's groups of evidences are reinstated. There is the changed ratio of wing-bones and leg-bones in the duck; there are the drooping ears of cats in China, of horses in Russia, of sheep in Italy, of guinea-pigs in Germany, of goats and cattle in India, of rabbits, pigs, and dogs in all long-civilized countries. Though artificial selection has come into play where drooping has become a curious trait (as in rabbits), and has probably caused the greater size of ears which has in some cases gone along with diminished muscular power over them; yet it could not have been the initiator, and has not been operative on animals bred for profit. Again there are the changes produced by climate; as instance, among plants, the several varieties of maize established in Germany and transformed in the course of a few generations.
Facts of another class are yielded by the blind inhabitants of caverns. One who studies the memoir by Mr. Packard on The Cave Fauna of North America, &c., will be astonished at the variety of types in which degeneration or loss of the eyes has become a concomitant of life passed in darkness. A great increase in the force of this evidence will be recognized on learning that absence or extreme imperfection of visual organs is found also in creatures living in perpetual night at the bottoms of deep oceans. Endeavours to account for these facts otherwise than by the effects of disuse we have seen to be futile.
Kindred evidence is yielded by decrease of the jaws in those races which have had diminished use of them – mankind and certain domestic animals. Relative smallness in the jaws of civilized men, manifest enough on comparison, has been proved by direct measurement. In pet dogs – pugs, household spaniels – we find associated the same cause with the same effect. Though there has been artificial selection, yet this did not operate until the diminution had become manifest. Moreover there has been diminution of the other structures concerned in biting: there are smaller muscles, feeble zygomata, and diminished areas for insertion of muscles – traits which cannot have resulted from selection, since they are invisible in the living animal.
In abnormal vision produced by abnormal use of the eyes we have evidence of another kind. That the Germans, among whom congenital short sight is notoriously prevalent, have been made shortsighted by inheritance of modifications due to continual reading of print requiring close attention, is by some disputed. It is strange, however, that if there exists no causal connexion between them, neither trait occurs without the other elsewhere. But for the belief that there is a causal connexion we have the verifying testimony of oculists. From Dr. Lindsay Johnson I have cited cases within his professional experience of functionally-produced myopia transmitted to children; and he asserts that other oculists have had like experiences.
Development of the musical faculty in the successive members of families from which the great composers have come, as well as in the civilized races at large, is not to be explained by natural selection. Even when it is great, the musical faculty has not a life-saving efficiency as compared with the average of faculties; for the most highly gifted have commonly passed less prosperous lives and left fewer offspring than have those possessed of ordinary abilities. Still less can it be said that the musical faculty in mankind at large has been developed by survival of the fittest. No one will assert that men in general have been enabled to survive and propagate in proportion as their musical appreciation was great.
The transmission of nervous peculiarities functionally produced is alleged by the highest authorities – Dr. Savage, president of the Neurological Society, and Dr. Hughlings Jackson. The evidence they assign confirms, and is confirmed by, that which the development of the musical faculty above named supplies.
Here, then, we have sundry groups of facts directly supporting the belief that functionally-wrought modifications descend from parents to offspring.
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Now let us consider the position of those Darwinians who dissent from Darwin, and who make light of all this evidence. We might naturally suppose that their own hypothesis is unassailable. Yet, strange to say, they admit that there is no direct proof that any species has been established by natural selection. The proof is inferential only.
The certainty of an axiom does not give certainty to the deductions drawn from it. That natural selection is, and always has been, operative is incontestable. Obviously I should be the last person to deny that survival of the fittest is a necessity: its negation is inconceivable. The Neo-Darwinians, however, judging from their attitude, apparently assume that firmness of the basis implies firmness of the superstructure. But however high may be the probability of some of the conclusions drawn, none of them can have more than probability; while some of them remain, and are likely to remain, very questionable. Observe the difficulties.
(1) The general argument proceeds upon the analogy between natural selection and artificial selection. Yet all know that the first cannot do what the last does. Natural selection can do nothing more than preserve those of which the aggregate characters are most favourable to life. It cannot pick out those possessed of one particular favourable character, unless this is of extreme importance.
(2) In many cases a structure is of no service until it has reached a certain development; and it remains to account for that increase of it by natural selection which must be supposed to take place before it reaches the stage of usefulness.
(3) Advantageous variations, not preserved in nature as they are by the breeder, are liable to be swamped by crossing or to disappear by atavism.
Now whatever replies are made, their component propositions cannot be necessary truths. So that the conclusion in each case, however reasonable, cannot claim certainty: the fabric can have no stability like that of its foundation.
When to uncertainties in the arguments supporting the hypothesis we add its inability to explain facts of cardinal significance, as proved above, there is I think ground for asserting that natural selection is less clearly shown to be a factor in the origination of species than is the inheritance of functionally-wrought changes.
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If, finally, it is said that the mode in which functionally-wrought changes, especially in small parts, so affect the reproductive elements as to repeat themselves in offspring, cannot be imagined – if it be held inconceivable that those minute changes in the organs of vision which cause myopia can be transmitted through the appropriately-modified sperm-cells or germ-cells; then the reply is that the opposed hypothesis presents a corresponding inconceivability. Grant that the habit of a pointer was produced by selection of those in which an appropriate variation in the nervous system had occurred; it is impossible to imagine how a slightly-different arrangement of a few nerve-cells and fibres could be conveyed by a spermatozoon. So too it is impossible to imagine how in a spermatozoon there can be conveyed the 480,000 independent variables required for the construction of a single peacock's feather, each having a proclivity towards its proper place. Clearly the ultimate process by which inheritance is effected in either case passes comprehension; and in this respect neither hypothesis has an advantage over the other.
APPENDIX D.
ON ALLEGED "SPONTANEOUS GENERATION," AND ON THE HYPOTHESIS OF PHYSIOLOGICAL UNITS
[The following letter, originally written for publication in the North American Review, but declined by the Editor in pursuance of a general rule, and eventually otherwise published in the United States, I have thought well to append to this first volume of the Principles of Biology. I do this because the questions which it discusses are dealt with in this volume; and because the further explanations it furnishes seem needful to prevent misapprehensions.]
The Editor of the North American Review
Sir,
It is in most cases unwise to notice adverse criticisms. Either they do not admit of answers or the answers may be left to the penetration of readers. When, however, a critic's allegations touch the fundamental propositions of a book, and especially when they appear in a periodical having the position of the North American Review, the case is altered. For these reasons the article on "Philosophical Biology," published in your last number, demands from me an attention which ordinary criticisms do not.
It is the more needful for me to notice it, because its two leading objections have the one an actual fairness and the other an apparent fairness; and in the absence of explanations from me, they will be considered as substantiated even by many, or perhaps most, of those who have read the work itself – much more by those who have not read it. That to prevent the spread of misapprehensions I ought to say something, is further shown by the fact that the same two objections have already been made in England – the one by Dr. Child, of Oxford, in his Essays on Physiological Subjects, and the other by a writer in the Westminster Review for July, 1865.
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In the note to which your reviewer refers, I have, as he says, tacitly repudiated the belief in "spontaneous generation;" and that I have done this in such a way as to leave open the door for the interpretation given by him is true. Indeed the fact that Dr. Child, whose criticism is a sympathetic one, puts the same construction on this note, proves that your reviewer has but drawn what seems to be a necessary inference. Nevertheless, the inference is one which I did not intend to be drawn.
In explanation, let me at the outset remark that I am placed at a disadvantage in having had to omit that part of the System of Philosophy which deals with Inorganic Evolution. In the original programme will be found a parenthetic reference to this omitted part, which should, as there stated, precede the Principles of Biology. Two volumes are missing. The closing chapter of the second, were it written, would deal with the evolution of organic matter – the step preceding the evolution of living forms. Habitually carrying with me in thought the contents of this unwritten chapter, I have, in some cases, expressed myself as though the reader had it before him; and have thus rendered some of my statements liable to misconstructions. Apart from this, however, the explanation of the apparent inconsistency is very simple, if not very obvious. In the first place, I do not believe in the "spontaneous generation" commonly alleged, and referred to in the note; and so little have I associated in thought this alleged "spontaneous generation" which I disbelieve, with the generation by evolution which I do believe, that the repudiation of the one never occurred to me as liable to be taken for repudiation of the other. That creatures having quite specific structures are evolved in the course of a few hours, without antecedents calculated to determine their specific forms, is to me incredible. Not only the established truths of Biology, but the established truths of science in general, negative the supposition that organisms having structures definite enough to identify them as belonging to known genera and species, can be produced in the absence of germs derived from antecedent organisms of the same genera and species. If there can suddenly be imposed on simple protoplasm the organization which constitutes it a Paramœcium, I see no reason why animals of greater complexity, or indeed of any complexity, may not be constituted after the same manner. In brief, I do not accept these alleged facts as exemplifying Evolution, because they imply something immensely beyond that which Evolution, as I understand it, can achieve. In the second place, my disbelief extends not only to the alleged cases of "spontaneous generation," but to every case akin to them. The very conception of spontaneity is wholly incongruous with the conception of Evolution. For this reason I regard as objectionable Mr. Darwin's phrase "spontaneous variation" (as indeed he does himself); and I have sought to show that there are always assignable causes of variation. No form of Evolution, inorganic or organic, can be spontaneous; but in every instance the antecedent forces must be adequate in their quantities, kinds, and distributions, to work the observed effects. Neither the alleged cases of "spontaneous generation," nor any imaginable cases in the least allied to them, fulfil this requirement.
If, accepting these alleged cases of "spontaneous generation," I had assumed, as your reviewer seems to do, that the evolution of organic life commenced in an analogous way; then, indeed, I should have left myself open to a fatal criticism. This supposed "spontaneous generation" habitually occurs in menstrua that contain either organic matter, or matter originally derived from organisms; and such organic matter, proceeding in all known cases from organisms of a higher kind, implies the pre-existence of such higher organisms. By what kind of logic, then, is it inferrible that organic life was initiated after a manner like that in which Infusoria are said to be now spontaneously generated? Where, before life commenced, were the superior organisms from which these lowest organisms obtained their organic matter? Without doubting that there are those who, as the reviewer says, "can penetrate deeper than Mr. Spencer has done into the idea of universal evolution," and who, as he contends, prove this by accepting the doctrine of "spontaneous generation"; I nevertheless think that I can penetrate deep enough to see that a tenable hypothesis respecting the origin of organic life must be reached by some other clue than that furnished by experiments on decoction of hay and extract of beef.
From what I do not believe, let me now pass to what I do believe. Granting that the formation of organic matter, and the evolution of life in its lowest forms, may go on under existing cosmical conditions; but believing it more likely that the formation of such matter and such forms, took place at a time when the heat of the Earth's surface was falling through those ranges of temperature at which the higher organic compounds are unstable; I conceive that the moulding of such organic matter into the simplest types, must have commenced with portions of protoplasm more minute, more indefinite, and more inconstant in their characters, than the lowest Rhizopods – less distinguishable from a mere fragment of albumen than even the Protogenes of Professor Haeckel. The evolution of specific shapes must, like all other organic evolution, have resulted from the actions and reactions between such incipient types and their environments, and the continued survival of those which happened to have specialities best fitted to the specialities of their environments. To reach by this process the comparatively well-specialized forms of ordinary Infusoria, must, I conceive, have taken an enormous period of time.
To prevent, as far as may be, future misapprehension, let me elaborate this conception so as to meet the particular objections raised. The reviewer takes for granted that a "first organism" must be assumed by me, as it is by himself. But the conception of a "first organism," in anything like the current sense of the words, is wholly at variance with conception of evolution; and scarcely less at variance with the facts revealed by the microscope. The lowest living things are not properly speaking organisms at all; for they have no distinctions of parts – no traces of organization. It is almost a misuse of language to call them "forms" of life: not only are their outlines, when distinguishable, too unspecific for description, but they change from moment to moment and are never twice alike, either in two individuals or in the same individual. Even the word "type" is applicable in but a loose way; for there is little constancy in their generic characters: according as the surrounding conditions determine, they undergo transformations now of one kind and now of another. And the vagueness, the inconstancy, the want of appreciable structure, displayed by the simplest of living things as we now see them, are characters (or absences of characters) which, on the hypothesis of Evolution, must have been still more decided when, as at first, no "forms," no "types," no "specific shapes," had been moulded. That "absolute commencement of organic life on the globe," which the reviewer says I "cannot evade the admission of," I distinctly deny. The affirmation of universal evolution is in itself the negation of an "absolute commencement" of anything. Construed in terms of evolution, every kind of being is conceived as a product of modifications wrought by insensible gradations on a pre-existing kind of being; and this holds as fully of the supposed "commencement of organic life" as of all subsequent developments of organic life. It is no more needful to suppose an "absolute commencement of organic life" or a "first organism," than it is needful to suppose an absolute commencement of social life and a first social organism. The assumption of such a necessity in this last case, made by early speculators with their theories of "social contracts" and the like, is disproved by the facts; and the facts, so far as they are ascertained, disprove the assumption of such a necessity in the first case. That organic matter was not produced all at once, but was reached through steps, we are well warranted in believing by the experiences of chemists. Organic matters are produced in the laboratory by what we may literally call artificial evolution. Chemists find themselves unable to form these complex combinations directly from their elements; but they succeed in forming them indirectly, by successive modifications of simpler combinations. In some binary compound, one element of which is present in several equivalents, a change is made by substituting for one of these equivalents an equivalent of some other element; so producing a ternary compound. Then another of the equivalents is replaced, and so on. For instance, beginning with ammonia, N H3, a higher form is obtained by replacing one of the atoms of hydrogen by an atom of methyl, so producing methyl-amine, N (C H3 H2); and then, under the further action of methyl, ending in a further substitution, there is reached the still more compound substance dimethyl-amine, N (C H3) (C H3) H. And in this manner highly complex substances are eventually built up. Another characteristic of their method is no less significant. Two complex compounds are employed to generate, by their action upon one another, a compound of still greater complexity: different heterogeneous molecules of one stage, become parents of a molecule a stage higher in heterogeneity. Thus, having built up acetic acid out of its elements, and having by the process of substitution described above, changed the acetic acid into propionic acid, and propionic into butyric, of which the formula is
this complex compound, by operating on another complex compound, such as the dimethyl-amine named above, generates one of still greater complexity, butyrate of dimethyl-amine
See, then, the remarkable parallelism. The progress towards higher types of organic molecules is effected by modifications upon modifications; as throughout Evolution in general. Each of these modifications is a change of the molecule into equilibrium with its environment – an adaptation, as it were, to new surrounding conditions to which it is subjected; as throughout Evolution in general. Larger, or more integrated, aggregates (for compound molecules are such) are successively generated; as throughout Evolution in general. More complex or heterogeneous aggregates are so made to arise, one out of another; as throughout Evolution in general. A geometrically-increasing multitude of these larger and more complex aggregates so produced, at the same time results; as throughout Evolution in general. And it is by the action of the successively higher forms on one another, joined with the action of environing conditions, that the highest forms are reached; as throughout Evolution in general.
When we thus see the identity of method at the two extremes – when we see that the general laws of evolution, as they are exemplified in known organisms, have been unconsciously conformed to by chemists in the artificial evolution of organic matter; we can scarcely doubt that these laws were conformed to in the natural evolution of organic matter, and afterwards in the evolution of the simplest organic forms. In the early world, as in the modern laboratory, inferior types of organic substances, by their mutual actions under fit conditions, evolved the superior types of organic substances, ending in organizable protoplasm. And it can hardly be doubted that the shaping of organizable protoplasm, which is a substance modifiable in multitudinous ways with extreme facility, went on after the same manner. As I learn from one of our first chemists, Prof. Frankland, protein is capable of existing under probably at least a thousand isomeric forms; and, as we shall presently see, it is capable of forming, with itself and other elements, substances yet more intricate in composition, that are practically infinite in their varieties of kind. Exposed to those innumerable modifications of conditions which the Earth's surface afforded, here in amount of light, there in amount of heat, and elsewhere in the mineral quality of its aqueous medium, this extremely changeable substance must have undergone now one, now another, of its countless metamorphoses. And to the mutual influences of its metamorphic forms under favouring conditions, we may ascribe the production of the still more composite, still more sensitive, still more variously-changeable portions of organic matter, which, in masses more minute and simpler than existing Protozoa, displayed actions verging little by little into those called vital – actions which protein itself exhibits in a certain degree, and which the lowest known living things exhibit only in a greater degree. Thus, setting out with inductions from the experiences of organic chemists at the one extreme, and with inductions from the observations of biologists at the other extreme, we are enabled deductively to bridge the interval – are enabled to conceive how organic compounds were evolved, and how, by a continuance of the process, the nascent life displayed in these became gradually more pronounced. And this it is which has to be explained, and which the alleged cases of "spontaneous generation" would not, were they substantiated, help us in the least to explain.
It is thus manifest, I think, that I have not fallen into the alleged inconsistency. Nevertheless, I admit that your reviewer was justified in inferring this inconsistency; and I take blame to myself for not having seen that the statement, as I have left it, is open to misconstruction.
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I pass now to the second allegation – that in ascribing to certain specific molecules, which I have called "physiological units," the aptitude to build themselves into the structure of the organism to which they are peculiar, I have abandoned my own principle, and have assumed something beyond the re-distribution of Matter and Motion. As put by the reviewer, his case appears to be well made out; and that he is not altogether unwarranted in so putting it, may be admitted. Nevertheless, there does not in reality exist the supposed incongruity.
Before attempting to make clear the adequacy of the conception which I am said to have tacitly abandoned as insufficient, let me remove that excess of improbability the reviewer gives to it, by the extremely-restricted meaning with which he uses the word mechanical. In discussing a proposition of mine he says: —
"He then cites certain remarks of Mr. Paget on the permanent effects wrought in the blood by the poison of scarlatina and small-pox, as justifying the belief that such a 'power' exists, and attributes the repair of a wasted tissue to 'forces analogous to those by which a crystal reproduces its lost apex.' (Neither of which phenomena, however, is explicable by mechanical causes.)"
Were it not for the deliberation with which this last statement is made, I should take it for a slip of the pen. As it is, however, I have no course left but to suppose the reviewer unaware of the fact that molecular actions of all kinds are now not only conceived as mechanical actions, but that calculations based on this conception of them, bring out the results that correspond with observation. There is no kind of re-arrangement among molecules (crystallization being one) which the modern physicist does not think of. and correctly reason upon, in terms of forces and motions like those of sensible masses. Polarity is regarded as a resultant of such forces and motions; and when, as happens in many cases, light changes the molecular structure of a crystal, and alters its polarity, it does this by impressing, in conformity with mechanical laws, new motions on the constituent molecules. That the reviewer should present the mechanical conception under so extremely limited a form, is the more surprising to me because, at the outset of the very work he reviews, I have, in various passages, based inferences on those immense extensions of it which he ignores; indicating, for example, the interpretation it yields of the inorganic chemical changes effected by heat, and the organic chemical changes effected by light (Principles of Biology, § 13).
Premising, then, that the ordinary idea of mechanical action must be greatly expanded, let us enter upon the question at issue – the sufficiency of the hypothesis that the structure of each organism is determined by the polarities of the special molecules, or physiological units, peculiar to it as a species, which necessitate tendencies towards special arrangements. My proposition and the reviewer's criticism upon it, will be most conveniently presented if I quote in full a passage of his from which I have already extracted some expressions. He says: —
"It will be noticed, however, that Mr. Spencer attributes the possession of these 'tendencies,' or 'proclivities,' to natural inheritance from ancestral organisms; and it may be argued that he thus saves the mechanist theory and his own consistency at the same time, inasmuch as he derives even the 'tendencies' themselves ultimately from the environment. To this we reply, that Mr. Spencer, who advocates the nebular hypothesis, cannot evade the admission of an absolute commencement of organic life on the globe, and that the 'formative tendencies,' without which he cannot explain the evolution of a single individual, could not have been inherited by the first organism. Besides, by his virtual denial of spontaneous generation, he denies that the first organism was evolved out of the inorganic world, and thus shuts himself off from the argument (otherwise plausible) that its 'tendencies' were ultimately derived from the environment."
This assertion is already in great measure disposed of by what has been said above. Holding that, though not "spontaneously generated," those minute portions of protoplasm which first displayed in the feeblest degree that changeability taken to imply life, were evolved, I am not debarred from the argument that the "tendencies" of the physiological units are derived from the inherited effects of environing actions. If the conception of a "first organism" were a necessary one, the reviewer's objection would be valid. If there were an "absolute commencement" of life, a definite line parting organic matter from the simplest living forms, I should be placed in the predicament he describes. But as the doctrine of Evolution itself tacitly negatives any such distinct separation; and as the negation is the more confirmed by the facts the more we know of them; I do not feel that I am entangled in the alleged difficulty. My reply might end here; but as the hypothesis in question is one not easily conceived, and very apt to be misunderstood, I will attempt a further elucidation of it.