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Russell ES. The interpretation of development and heredity. (1930) Oxford. Univ. Press.

   The interpretation of development and heredity (1930): 1 Introductory | 2 Aristotle’s ‘De Generatione Animalium’ | 3 Preformation and Epigenesis | 4 The Germ-Plasm Theory | 5 The Theory of the Gene | 6 Some Modern Epigenetic Theories | 7 Wilhelm Roux and the Mechanics of Development | 8 The Mnemic Theories | 9 Retrospect. The Use and Misuse of Abstraction | 10 The Organismal Point of View | 11 The Physiological Interpretation of the Cell Theory | 12 The Cell and the Organism | 13 The Cell in Relation to Development and Differentiation | 14 The Organism as a Whole in Development and Reproduction
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VIII The Mnemic Theories

Online Editor - Mnemic - relating to the ability to retain memory.

Although Samuel Butler was not the first to enunciate a theory linking up development with memory — this honour belongs to Hering — it is convenient to begin with him, for his point of view is radically different from that adopted in most theories of development, and represents in fact an entirely new method of approach. As we shall see later, the theories of Hering and Semon remain based upon a materialistic conception of the organism and show little methodological advance upon the views current in their time. Butler, on the other hand, whether he was right or wrong, did strike out for himself a new line, and by adopting a frankly psychological standpoint was able to look at heredity and development from a new angle.

Butler was not a professional biologist, and therein lay both his strength and his weakness. He was the cultivated amateur, bringing to bear upon a great problem, whose intricacies he perhaps did not fully realize, a keen, ingenious, and unbiassed mind. We must remember too that when he published his main book on biological problems, Life and Habit ( 1878), the detailed facts about the nature of fertilization had not long been discovered, and had barely had time to filter down from the technical journals to the man in the street; the germplasm theory had not yet been formulated by Weismann; it was still orthodox to believe in the inheritance of acquired characters, and Charles Darwin had even revived the ancient Hippocratic doctrine of pangenesis in order to explain such transmission on a materialistic basis. .

In order to understand Butler’s point of view it is necessary to free one’s mind from such modern conceptions as the germ-plasm theory, the separation of soma and germ-cells, and to hark back to a simpler, almost ‘pre-scientific’ view. It is in fact the very simplicity of Butler’s theory that makes it rather difficult to grasp at the present day. The cell-theory was familiar to him, and he knew that fertilization consisted in the union of two cells, the ovum and the spermatozoon, but there his knowledge stopped. He thought habitually in terms of the organism as a whole and did not, as we do, think of it in terms of cells. Thus for him the hen did really form the egg, just as a plant may form a bud or a tuber ; he did not trouble himself about the cellular details. We shall find it impossible to understand what Butler is driving at unless we can by an effort recover his pre-Weismannian simplicity of outlook.

Butler hit upon the memory-theory of heredity in complete independence of Hering, who preceded him actually by eight years. Only after his book was published did he hear of Hering, and he rendered graceful homage to his predecessor by giving an excellent translation of Hering’s lecture in his Unconscious Memory (1880). Some hint or foreshadowing of Butler’s views is found in Erasmus Darwin’s Zoonomia (i, 1794), as he himself points out, quoting the following passage : ‘Owing to the imperfection of language, the offspring is termed a new animal; but is, in truth, a branch or elongation of the parent, since a part of the embryonic animal is or was a part of the parent, and, therefore, in strict language, cannot be said to be entirely new at the time of its production, and, therefore, it may retain some of the habits of the parent system’ (p. 484).

Butler introduces his theme in Life and Habit by pointing out and illustrating how great a part habit plays in the individual life ; we all know that complex actions and trains of action at first laboriously and consciously learnt become easy and habitual through long-continued practice, reaching finally the unconsciousness and automaticity of perfect habit, or as Butler would say, of perfect knowledge. The analogy of development and habitual action is striking. All goes on as if the embryo had perfect knowledge of the route to follow, and this in Butler’s view can only be because it has already gone through its development countless times before, so that its knowledge has become automatic and unconscious.

Is it conceivable, asks Butler, that the embryo can do all the things that it does without knowing how to do them, and without having done them before ?

‘Shall we say*, he writes, ‘that a baby of a day old sucks (which involves the whole principle of the pump, and hence a profound practical knowledge of the laws of pneumatics and hydrostatics), digests, oxygenizes its blood (millions of years before Sir Humphrey Davy discovered oxygen), sees and hears — all most difficult and complicated operations, involving a knowledge of the facts concerning optics and acoustics, compared with which the discoveries gf Newton sink into utter insignificance ? Shall we say that a baby can do all these things at once, doing them so well and so regularly, without being even able to direct its attention to them, and at the same time not know how to do them, and never have done them before i l

Assuredly not.

There must therefore be a real continuity of experience between the embryo and its parents, and, through the endless chain of ancestors, right back to the dawn of life. The kernel of Butler’s theory is this extension of habit and memory beyond the confines of the individual life. To explain development as being due to habit:

‘. . . we must suppose the continuity of life and sameness between living beings, whether animals or plants, and their descendants, to be far closer than we have hitherto believed ; so that the experience of one person is not enjoyed by his successor, so much as that the successor is bona fide but a part of the life of his progenitor, imbued with all his memories, profiting by all his experiences — which are, in fact, his own — and only unconscious of the extent of his own memories and experiences owing to their vastness and already infinite repetitions* (ibid., p. 50).

It will be readily admitted that there is continuity in the life of the individual from ovum to old age :

‘Nor, if we admit personal identity between the ovum and the octogenarian, is there any sufficient reason why we should not admit it between the impregnate ovum and the two factors of which it is composed, which two factors are but offshoots from two distinct personalities, of which they are as much part as the apple is of the apple-tree; so that an impregnate ovum cannot without a violation of first principles be debarred from claiming personal identity with both its parents, and hence, by an easy chain of reasoning, with each of the impregnate ova from which its parents were developed.

1 Life and Habit . Fifield reprint, 1910, p. 54.

‘So that each ovum when impregnate should be considered not as descended from its ancestors, but as being a continuation of the personality of every ovum in the chain of its ancestry, which every ovum it actually is quite as truly as the octogenarian is the same identity with the ovum from which he has been developed.

‘This process cannot stop short of the primordial cell, which again will probably turn out to be but a brief resting-place. We therefore prove each one of us to be actually the primordial cell which never died nor dies, but has differentiated itself into the life of the world, all living beings whatever being one with it, and members one of another’ (ibid., pp. 85-6).

It is a little unfortunate that Butler uses the words ‘personal identity’ to describe what is neither more nor less than continuity of organic experience — the emphasis should be laid on ‘continuity’ rather than upon ‘personality’. But the meaning of the words is perfectly clear, and is nowhere more vividly brought out than in the following passage from Luck and Cunning (188 7) where the race is declared to be ‘one long individual, living indeed in pulsations, so to speak, but no more losing continued personality by living in successive generations than an individual loses it by living in consecutive days’ (Fifield reprint, 1909, p. 25). Instead of continuity of germ-plasm we have here continuity of living experience.

It is important to note that the egg or embryo is regarded as actually partaking in the life of its producer, as actually sharing the hereditary experience of the parent organism. Butler does not seem to have realized the fact that the germcells live as it were a life of their own and go through a special development, separate from the differentiation of the soma, and having reference chiefly to their future destiny as eggs or sperms. If he did recognize the fact, he seems to have thought it of subordinate importance. His conception is that the gametes actually share in the experience of the parents, just as a bulb, or tuber, or cutting of a plant may be assumed to ‘know whatever the plant knows’. There is no question of an influence exerted by the soma upon the germcells (such as is required in the theories of Hering and Semon), for Butler did not separate the two. This is the point where, in the light of modern conceptions, Butler’s theory is difficult to follow. One must however make the required effort to grasp his thought. It emerges fairly clearly from the following, apparently cryptic, sentence : ‘A moth becomes each egg that she lays, and that she does so, she will in good time show by doing, now that she has got a fresh start, as near as may be what she did when first she was an egg, and then a moth, before’ ( Life and Habit , p. 99).

The egg or embryo (and also the spermatozoon) is to be regarded as a bud of the parent, summarizing all the experience of that parent — all its developmental tendencies and all its instincts — up to the time when it leaves the body of the parent. As the parent itself was produced from egg and sperm, the chain of experience is continuous back to the previous generation, and so, generation by generation, right back to the primordial form from which life has sprung. It is in this simple sense that we are to interpret Butler’s conclusion in the last pages of Life and Habit that ‘the small, structureless, impregnate ovum from which we have each one of us sprung, has a potential recollection of all that has happened to each one of its ancestors prior to the period at which any such ancestor has issued from the bodies of its progenitors — provided that is to say, a sufficiently deep, or sufficiently often-repeated, impression has been made to admit of its being remembered at all’ (p. 297).

What light does the theory of ancestral habit throw upon the problems of development ? In the first place, it accounts for the orderly succession of stages in ontogeny, for the embryo goes through these as by routine, each stage awakening the memory of what to do next. On the memory theory:

‘Each step of normal development will lead the impregnate ovum up to, and remind it of, its next ordinary course of action, in the same way as we, when we recite a well-known passage, are led up to each successive sentence by the sentence which has immediately preceded it. . . . Hence, though the ovum immediately after impregnation is instinct with all the memories of both parents, not one of these memories can normally become active till both the ovum itself, and its surroundings, are sufficiently alike what they respectively were, when the occurrence now to be remembered last took place. The memory will then immediately return, and the creature will do as it did on the last occasion that it was in like case as now. This ensures that similarity of order shall be preserved in all the stages of development, in successive generations’ (pp. 297-8).

It accounts also for heredity, and in particular for the fact that the offspring as a rule resembles its own parents more than any chance pair of the stock, for on the memory theory we should expect ‘that the offspring should, as a general rule, resemble its own most immediate progenitors ; that is to say, that it should remember best what it has been doing most recently’ (p. 168).

In particular — and this is one of the strongest points of the mnemic theory — it explains why in the first period of development structure is formed in advance of functioning, and why in a general way the embryo repeats in ontogeny the ancestral history of its race. As Butler writes:

‘The self-development of each new life in succeeding generations — the various stages through which it passes (as it would appear, at first sight, without rhyme or reason) — the manner in which it prepares structures of the most surpassing intricacy and delicacy, for which it has no use at the time when it prepares them — and the many elaborate instincts which it exhibits immediately on, and indeed before, birth — all point in the direction of habit and memory, as the only causes which could produce them.

‘Why should the embryo of any animal go through so many stages — embryological allusions to forefathers of a widely different type? And why, again, should the germs of the same kind of creature always go through the same stages ? . . .

‘The creature goes through so many intermediate stages between its earliest state as life at all, and its latest development, for the simplest of all reasons, namely, because this is the road by which it has always hitherto travelled to its present differentiation; this is the road it knows, and into every turn and up and down of which, it has been guided by the force of circumstances and the balance of considerations’

(PP- 12 5 “ 6 )*

It accounts for the fact that the development of the individual is only a shortened and sketchy epitome of the developmental history of its ancestors, not recapitulating this in full, but taking short cuts and telescoping stages. ‘In its earliest stages the embryo should be simply conscious of a general method of procedure on the part of its forefathers, and should, by reason of long practice, compress tedious and complicated histories into a very narrow compass, remembering no single performance in particular’ (p. 169).

Butler was of course an ardent Lamarckian 1 and believed firmly that advance in evolution takes place only by the effort of the organism itself. Such effort, he conceived, as did Roux about the same time (see above, p. 108), made its mark upon succeeding generations, so that what was originally acquired by pain and striving made its appearance more easily in succeeding generations and finally without any effort at all — in the absence of the functional stimulus, as Roux would say.

In general, Butler conceived normal development to be a blind and automatic repetition of ancestral routine, out of which sleep-like progression the embryo is stirred only when it encounters unusual or difficult circumstances, such as it has in the person of its ancestors rarely or never met with before. When it is thus stirred out of its routine it has to cope actively with the unusual situation, with the results that we see in regulatory development.

‘When events are happening to it which have ordinarily happened to its forefathers, and which it would therefore remember, if it was possessed of the kind of memory which we are here attributing to it, it acts precisely as it would act if it were possessed of such memory.

‘When, on the other hand, events are happening to it, which, if it has the kind of memory we are attributing to it, would baffle that memory, or which have rarely or never been included in the category of its recollections, it acts precisely as a creature acts when its recollection is disturbed , or when it is required to do something which it has never done before ’ {Life and Habit, p. 132).

The mnemic theory is of course peculiarly adapted to explain the historical or routine aspect of development; it does not by itself explain the driving force or hormic impulse behind development, nor the initiative shown by the embryo in adapting itself to unusual conditions. At the most it gives a reasoned account of why the developmental impulse follows such and such routine paths, is so curiously indirect, and yet is so orderly a succession of events. Butler’s own theory of evolution by effort supplies, to some extent at least, this missing element in the mnemic conception.

1 See Evolution Old and New , London, 1879.

Butler made his memory theory rather more difficult than it needed to be by bringing in consciousness as a necessary accompaniment of the organism’s original effort — of that effort which, through practice, throughout a long series of generations, becomes in time habitual and unconscious.

He really had no warrant in experience for assuming that ‘organic’ or growth-activities, as distinct from behaviouractivities, are ever consciously performed, for the only actions which we consciously will are behaviour-actions carried out vis-a-vis a sensed environment. Nor is evidence lacking that the phenomena of habit and learning can be manifested by tissues and organs, as is seen in many cases of functional adaptation, where there is not the slightest justification for assuming conscious guidance.

We turn now to a consideration of Butler’s philosophic standpoint. Here again we find the amateur, full of brilliant ideas, but unable to weave them into a fully coherent system.

He was definitely anti-materialist, and combated the materialistic side of Charles Darwin’s doctrine of evolution, preferring to it the older teleological views of Erasmus Darwin and Lamarck. He took the ordinary, everyday, ‘commonsense’ view of living things, seeing them as active, striving individuals, beating out a livelihood by means of their own efforts. Survival he considered was not a matter of luck, as Charles Darwin’s theory seemed to imply, but a matter of the organism’s own ingenuity — and this gave the title to his last book on biological problems, Luck or Cunning ( i 8 87 ).

We do not find in Butler’s writings any formal statement of his philosophical position. It may best be described as psychobiological. He was convinced that it was hopeless to explain life in terms of matter only, and that instead of regarding living things as on a level with inorganic objects, differing only by degree of material complexity, it was necessary rather to assimilate the inorganic to the organic.

‘The only thing of which I am sure’, he wrote in Unconscious Memory (1880), ‘is, that the distinction between the organic and inorganic is arbitrary; that it is more coherent with our other ideas, and therefore more acceptable, to start with every molecule as a living thing, and then deduce death as the breaking up of an association or corporation, than to start with inanimate molecules and smuggle life into them; and that, therefore, what we call the inorganic must be regarded as up to a point living, and instinct, within certain limits, with consciousness, volition, and power of concerted action’ (Fifield reprint, 1910, p. 15).

Later, in 1887, he definitely accepts a sort of pampsychism, refusing to think of soul in isolation from body, or of body in isolation from soul.

‘All body’, he writes, in Luck and Cunning , ‘is more or less ensouled. As it gets farther and farther from ourselves, indeed, we sympathize less with it; nothing, wc say to ourselves, can have intelligence unless we understand all about it — as though intelligence in all except ourselves meant the power of being understood rather than that of understanding. We are intelligent, and no intelligence, so different from our own as to baffle our powers of comprehension, deserves to be called intelligence at all. The more a thing resembles ourselves, the more it thinks as we do — and thus by implication tells us that we are right — the more intelligent we think it ; and the less it thinks as we do, the greater fool it must be; if a substance does not succeed in making it clear that it understands our business, we conclude that it cannot have any business of its own, much less understand it, or indeed understand anything at all.

‘But letting this pass, so far as we are concerned, XMVwrusv navrwv fidrpov avOpwiros, we are body ensouled, and soul embodied, ourselves, nor is it possible for us to think seriously of anything so unlike ourselves as to consist either of soul without body, or body without soul’ (Fifield reprint, 1909, p. 80).

There is noticeable in these two quotations a certain measure of approach to the ‘organic theory 5 of Nature later elaborated from a different standpoint by Whitehead (see below, p. 179 et seq.), and it is hardly fanciful to see in the following two (also from Luck and Cunning) a distinctly Bergsonian turn of thought.

‘Action may be regarded as a kind of middle term between mind and matter; it is the throe of thought and thing, the quivering clash and union of body and soul; commonplace enough in practice; miraculous, as violating every canon on which thought and reason are founded, and we theorize about it, put it under the microscope, and vivisect it’ (p. 79).

‘All change is qua us absolutely incomprehensible and miraculous; the smallest change baffles the greatest intellect if its essence, as apart from its phenomena, be inquired into’ (p. 76).

Before leaving Samuel Butler, it is interesting to note that he did consider — and reject — the materialistic alternative to his memory theory. It was pointed out to him by a critical friend that the accurate repetition of the developmental cycle might be simply explained by assuming, as in the germplasm theory, identity of starting-point. If the antecedents were identical we should expect identical consequences. Butler discusses this possibility at some length in Unconscious Memory .

‘I endeavoured to see’, he writes, ‘how far I could get on without volition and memory, and reasoned as follows: A repetition of like antecedents will be certainly followed by a repetition of like consequents, whether the agents be men and women or chemical substances’ (p. 153).

There are all sorts of inorganic cycles, in which memory clearly plays no part:

‘Who will attribute memory to the hands of a clock, to a piston-rod, to air or water in a storm or in course of evaporation, to the earth and planets in their circuits round the sun, or to the atoms of the universe, if they too be moving in a cycle vaster than we can take account of. And if not, why introduce it into the embryonic development of living beings, when there is not a particle of evidence in support of its actual presence, when regularity of action can be ensured just as well without it as with it, and when at the best it is considered as existing under circumstances which it baffles us to conceive, inasmuch as it is supposed to be exercised without any conscious recollection. Surely a memory which is exercised without any consciousness of recollecting is only a periphrasis for the absence of any memory at all’ (p. 160).

The answer is that we must bring memory in to account for development, for it is one of the antecedents. If we deny this psychical element in development we must by analogy deny it also in human behaviour.

If the repetition of the course of development were exact we might perhaps believe it to be mechanical.

‘The fact . . . that on each repetition of the action there is one memory more than on the last but one, and that this memory is slightly different from its predecessor, is seen to be an inherent and, ex hypothesi , necessarily disturbing factor in all habitual action — and the life of an organism should be regarded as the habitual action of a single individual, namely, of the organism itself, and of its ancestors’ (p. 167).

If we observed the resemblance between successive generations to be as close as that between distilled water and distilled water through all time, and if we observed that perfect unchangeablencss in the action of living beings which we see in what we call chemical and mechanical combinations, we might indeed suspect that memory had as little place among the causes of their action as it can have in anything, and that each repetition, whether of a habit or the practice of an art, or of an embryonic process in successive generations, was an original performance, for all that memory had to do with it. I submit however that in the case of the reproductive forms of life we see just so much variety in spite of uniformity, as is consistent with a repetition involving not only a perfect similarity in the agents and their circumstances, but also the little departure therefrom that is inevitably involved in the supposition that a memory of like presents as well as of like antecedents (as distinguished from a memory of like antecedents only) has played a part in their development — a cyclonic memory, if the expression may be pardoned’ (p. 173).

One is reminded of a subtle and profound remark in Evolution , Old and New: ‘It is not in the bond or nexus of our ideas that something utterly inanimate and inorganic should scheme, design, contrive, and elaborate structures which can make mistakes; it may elaborate low unerring things, like crystals, but it cannot elaborate those which have the power to err’ (Jonathan Cape reprint, p. 29).

Samuel Butler’s psychological or psychobiological point of view found few adherents in scientific circles, though Hartog and Darbishire in this country showed much sympathy with and understanding of his views. 1 Strongest support came from that fine philosopher James Ward, who discussed the memory theory in his Realm of Ends (2nd edit., 1912) and also in a valuable little essay Heredity and Memory (Cambridge, 1913), in which he pointed out that the memory theory could be properly used only by those who adopt, as did Butler, a frankly psychological attitude. Referring to Semon’s theory, he wrote :

‘Records or memoranda alone are not memory, for they presuppose it. They may consist of physical traces, but memory, even when called “unconscious”, suggests mind; for, as we have seen, the automatic character implied by this term “unconscious” presupposes foregone experience. . . . The mnemic theory then, if it is to be worth anything, seems to me clearly to require not merely physical records or “engrams”, but living experience or tradition. The mnemic theory will work for those who can accept a monadistic or pampsychist interpretation of the beings that make up the world, who believe with Spinoza and Leibniz that “all individual things are animated albeit in divers degree”. But quite apart from difficulties of detail, I do not see how in principle it will work otherwise’ (pp. 55-6).

Hering’s views, which we have hitherto passed over, are contained in a lecture, delivered in 1870, entitled ‘Ueber das Gedachtniss als eine allgemeine Funktion der organisirten Materie’ (Vienna). 2

Ewald Hering was a highly skilled physiologist who did excellent work on visual sensations, and his exposition, though short, is better documented than Butler’s and carries more conviction to the professional mind. It is written from the point of view of the physiologist.

His philosophical position is that of psycho-physical parallelism. The physiologist, he maintains, must treat the organism as purely material, though the psychologist has an

1 Marcus Hartog, Problems of Life and Reproduction , London, 1913; A. D. Darbishire, An Introduction to a Biology , London, 1917. See also C. J. Patten, The Memory Factor in Biology , London, 1926. F. Darwin’s views are considered below (pp. 129-30).

Reprinted in Ostwald’s ‘Klassiker der exakten Wissenschaften’, No. 148, 1921. Translated in Butler’s Unconscious Memory (1880, pp. 97-133), also with two other lectures in Memory, Open Court Pub. Co., 4th edit., 1913, Chicago and London.

equal right to regard only the psychical side. Material and psychical events in the living thing are functions one of the other. The physiologist may even on occasion shift his attention to the psychical side, provided he does this advisedly and does not confuse psychical with physical concepts. What the material aspect of life does not reveal to his inquiry he may find displayed in the mirror of consciousness.

It is in regarding this mirror, in consulting the data of his own experience, that he becomes aware of the importance of memory and habit. But he finds too that memory is not always conscious — the chain of recollections is continuous, but only at times conscious. ‘Between the “me” of to-day and the “me” of yesterday lie night and sleep, abysses of unconsciousness; nor is there any bridge but memory with which to span them’ (Butler’s transl.). Yet memory does span them and the bond of union lies in our unconscious world.

‘Thus the cause which produces the unity of the single phenomena of consciousness must be looked for in unconscious life. As we know nothing of this except what we learn from our investigations of matter, and since in a purely empirical consideration matter and the unconscious must be regarded as identical, the physiologist may justly define memory in a wider sense to be a faculty of the brain, the results of which to a great extent belong to both consciousness and unconsciousness’ (Open Court trans., p. 9).

The physiologist must, if he wishes to use this concept of memory in a scientific and objective manner, return to the mechanistic point of view and regard memory as a property of organized matter; he must disregard its psychical aspect. From this point of view, memory depends upon a material trace or impression made upon living matter by the original situation which is later ‘remembered’. The evidence from experience ‘clearly shows that after the extinction of conscious sensations, some material vestiges still remain in our nervous system, implying a change of its molecular and atomic structure, by which the nervous substance is enabled to reproduce such physical processes as are connected with the corresponding physical processes of sensation and perception’

(p. 7). Such recollected perceptions may arise in the absence of the external stimulus which originally called them forth.

Habit and memory play a part not only in behaviour-life, but also in other organic activities. A muscle grows stronger by use and increases in size ; this law of functional adaptation holds good for most organs and tissues, and is clearly a manifestation of organic memory. In cell division and multiplication we see another manifestation of the same power of organic memory or reproduction, and the most striking of all in the development of the individual organism. Hering considered, as did most biologists of his time, that there was ample evidence of the transmissibility of acquired characters. Every organism, he thought, adds a small heritage of personal acquisition to the hereditary equipment of its gametes. How this comes about is difficult to understand ; it may be through the instrumentality of the all-pervading nervous system or by way of the body fluids, but it is certain that the destinies of the growing organism are in some way re-echoed in the germ-cells. We have to do here not with any immaterial influence; the specific material structure of the germ determines its future development, and the parental organism can affect this development only by influencing materially, it may be in an infinitesimal degree, the specific germinal architecture.

‘If’, then, ‘in a parental organism by long habit or constant practice something grows to be second nature, so as to permeate, be it ever so feebly, its germinal cells, and if the germinal cells commence an independent life, they increase and grow till they form a new being, but their single parts still remain the substance of the parental being, they are bones of its bones, and flesh of its flesh. If, then, the filial organisms reproduce what they experienced as' a smaller part of a greater whole, this fact is marvellous indeed, but no more so than when an old man is surprised by reminiscences of his earliest childhood’ (pp. 16-17).

If the parents’ acquired characters can thus be reproduced by each offspring, how much more will it reproduce those characters which have for countless generations been developed by its ancestors, and so have been deeply impressed upon the organic memory of the germ-cells. ‘Thus every organized being of our present time is the product of the unconscious memory of organized matter. Constantly increasing and dividing, constantly assimilating new and excreting waste matter, constantly recording new experiences in its memories, to be reproduced again and again, each has taken richer and more perfect shape the longer it has lived’

(p. 1 8).

It is a natural consequence of this ancestral memory that the developing organism should run through in a summary way the principal stages of the evolution of its race.

It will be seen that Hering’s views on heredity and memory are in practice not very different from those later propounded by Butler. They were, however, definitely grounded in a mechanistic conception of life — hence the insistence that memory depends on material traces, and is to be considered as a function of organized matter ; hence too the supposition that the soma must in some way exercise a material influence upon the germ-cells. We shall see presently how Richard Semon some thirty years later developed these mechanistic assumptions of Hering’s theory.

In passing, it is worth noting, in justice to Hering, that in a later essay (1898) he protested against a too facile application of mechanistic conceptions to physiology, and pointed out that ‘Life can he fully understood only from life, and a physics and a chemistry which have sprung up solely from the domain of inanimate nature are adequate only to the explanation of such things as are common to the living and the dead.’ 1

Hering stated his mnemic theory merely in outline; it was left to the zoologist Richard Semon to develop and elaborate Hering’s conception. 2 It is not necessary to examine Semon’s views in detail; his treatment of the theme is analytic and of a Germanic thoroughness, but the fundamental ideas are the

1 Open Court publication, 1913, p. 45.

R. Semon, DieMneme , Leipzig, 1904. English translation by L. Simon from third German edition (1911), London, 1921. The mnemic idea was developed to some extent by Haeckel (1876), also by E. D. Cope (1885, 1889, and 1896), and particularly by H. B. Orr (1893).

same as Hering’s. He sets out to prove that all ‘reproductive’ processes, whether of heredity, habit, or memory, are due to one and the same property of organized matter — the mneme. Repetition of a train of events is of course not confined to the organic world, but it is a peculiarity of mnemic reproduction that it is independent of a complete repetition of the original conditions. Often a very small portion of the original situation suffices to cause a reproduction of the original reaction.

The mnemic property is regarded purely from the physiological point of view. Any stimulus acting upon irritable organic substance not only produces an immediate physical effect but leaves behind it an enduring physical trace or engram. Subsequent stimuli of a similar or associated kind elicit an ecphoric response. The main object of Semon’s book is ‘to deduce from a common property of all irritable organic substance — namely, that of retaining revivable traces or engrams — a number of mnemic laws, equally valid for the reproductions commonly grouped under memory, habit, or training, and also for those which come under the head of ontogenetic development, inherited periodicity, and regeneration — laws common, in fact, to every kind of organic reproduction’ (p. 13).

The principle mnemic laws are as follows:

'The First Mnemic Law , or Law of Engraphy. All simultaneous excitations within an organism form a coherent simultaneous excitation-complex which acts engraphically; that is, it leaves behind a connected engram-complex constituting a coherent unity.

“The Second Mnemic Law , or Law of Ecphory. The partial recurrence of the energetic condition, which has previously acted engraphically, acts ecphorically on the whole simultaneous engram-complex; or, as it may be more explicitly stated : the partial recurrence of the excitation-complex, which left behind the engram-complex, acts ecphorically on this simultaneous engram-complex, whether the recurrence be in the form of an original or of a mnemic excitation.

‘Association is the nexus of the single components of an engramcomplex. The engram-association is a result of engraphy and becomes manifest in ecphory* (pp. 273-4).

The more purely psychological side of Semon’s inquiry into mnemic phenomena was further pursued (from a paraUelistic standpoint) in two subsequent publications, 1 but we are here concerned only with the application of the mnemic principle to the problems of development and heredity. Semon was firmly convinced that the engraphic effects of stimuli in the individual could be, at least in certain cases, transmitted to its descendants, and he discussed in a very useful volume 2 the general evidence for the transmission of acquired characters. Exactly how this engraphic effect reaches the germ-cells is not made clear, but Semon holds that ‘somatic induction’ is more probable than ‘parallel induction’ — in other words, that the effect on the germ-cells is mediated through the somatic modification rather than imposed simultaneously on soma and germ-cells. The germcells appear to pass through a period of special sensitiveness to impressions from the soma.

The germ-cells contain the complete inherited engramstock of the species, and development is due to the ecphory of these material predispositions. Semon does not enter into much detail concerning this ‘engrammatic’ conception of the germ-plasm, nor does he definitely locate the engram-stock in any particular constituent of the germ-cell. His general position is that ‘each germ-cell, or its equivalent, which initiated each individuality phase, possesses the entire inherited engram-stock. Most probably neither the cell nor the nucleus of the cell is the smallest unit able to possess it. For the sake of brevity, we shall call the smallest unit able to contain the entire inherited engram-stock the “mnemic protomer” ; whether it be the cell, or whether it be a more minute morphological unit, we shall leave future research to decide’ (p. 116). The facts of regeneration show that such mnemic protomers must exist widely distributed throughout the developing organism.

There is an obvious resemblance between Semon’s protomers and Weismann’s ids, but Semon was fully aware of the

1 Die mnemiscben Empjindungen , Leipzig, 1909, 2nd edit., 1922; Bewusstseins vorgang und Gebirnprozess , Wiesbaden, 1920.

Das Problem der Vererbung *erworbener EigenscbafterC , Leipzig, 1912.

danger of postulating morphologically distinct representative particles. ‘Useful as such symbolic ideas may be for purposes of Mendelian research’, he writes, ‘the materialization of symbols in the shape of morphologically isolable units appears to me a very dangerous procedure’ (p. 252). Semon adopted the same general philosophical position as Hering — that for the purposes of science attention must be focussed on the material side of organic happenings. Like Semon he stated the essentially psychological concept of the mneme in terms of material traces or engrams.

An interesting variant of the mnemic theory is that propounded by the late Prof. Rignano, 1 where the idea is applied to the organism regarded as a developing physico-chemical system.

Perhaps the most persuasive advocate of the mnemic theory — certainly in this country — was the late Sir Francis Darwin, who dealt with it in his illuminating Presidential Address to the British Association in 1908. 2

He follows Semon on the whole and accepts the engram idea, widening it however to cover the ‘internal conditions’ of Pfeffer and of Klebs, and the ‘physiological states’ of Jennings, from the works of whom, and from his own experiments with plants, he draws a wealth of illustration of mnemic phenomena. He makes the important point that just as the study of movements requires their analysis in terms of stimulus and response, so the same procedure must be adopted in the study of morphological changes. This has the important result ‘that the dim beginnings of habit or unconscious memory that we find in the movements of plants and animals must find a place in morphology’, and particularly in the study of development.

His main conclusions regarding the deep-rooted analogy between habit and development may be summarized as follows:

‘The development of the individual from the germ-cell takes place

1 E. Rignano, Sur la transmtssibilite des carac tires acquis , Paris, 1906, Eng. Trans, by B. C. H. Harvey, Chicago, 1911.

2 British Association Report for 1908, pp. 1-27.

by a series of stages of cell-division and growth, each stage apparently serving as a stimulus to the next, each unit following its predecessor like the movements linked together in an habitual action performed by an animal. My view is that the rhythm of ontogeny is actually and literally a habit. It undoubtedly has the feature which I have described as pre-eminently characteristic of habit, viz., an automatic quality which is seen in the performance of a series of actions in the absence of the complete series of stimuli to which they (the stages of ontogeny) were originally due. This is the chief point on which I wish to insist — I mean that the resemblance between ontogeny and habit is not merely superficial, but deeply seated’ (p. 14).

We may quote also his reference to the theory of recapitulation and its explanation in terms of the mnemic conception.

‘Again, there is the wonderful fact that, as the ovum develops into the perfect organism, it passes through a series of changes which are believed to represent the successive forms through which its ancestors passed in the process of evolution. This is precisely paralleled by our own experience of memory, for it often happens that we cannot reproduce the last-learned verse of a poem without repeating the earlier part; each verse is suggested by the previous one and acts as a stimulus for the next. The blurred and imperfect character of the ontogenetic version of the phylogenetic series may at least remind us of the tendency to abbreviate by omission what we have learned by heart’ (P- is).

He believes of course in the transmissibility of acquired characters and the mnemic connexion of each generation with the next. ‘This can only be possible if the germ-cells are, as it were, in telegraphic communication with the whole body of the organism, so that as ontogeny is changed by the addition of new characters, new engrams are added to the germ-cell’ (p. 17).

His philosophical position is not very clearly defined. While he is inclined to believe that ‘in all living thin gs there is something psychic’ he also believes that ‘the mnemic quality of all living things must depend on the physical changes in protoplasm’ — in practice, then, the attitude of Hering and Semon, rather than that of Butler.

Looking back on the mnemic theories as a whole, we see that the idea has received two quite distinct formulations, one psychological, the other materialistic. The root-idea, which does not achieve really adequate expression in either form of the theory, is undoubtedly a valuable and significant one; there is without question a close analogy between habit and development, and many features of development — its specificity and orderliness, its automatic character and relative independence of environment, the fact of recapitulation — receive illumination, if development be regarded as ancestral habit. The mnemic theory is the only one that gives any explanation of the historical basis of development, and it throws much light upon this important conservative element in form-production. By itself, as Semon admits (p. 14), it does not account for the progressive element in development and evolution; it requires supplementing in this respect by a Lamarckian theory of evolution, as Butler attempted to do. The transmissibility of acquired characters is necessary to the theory, and gives, as Roux has pointed out (see above, p. 108), the possibility of explaining the automatic appearance of form in advance of functioning in the first stage of development.

As we indicated at the beginning of this chapter, Butler’s views both on development and on general biological method are highly original and suggestive. He made a consistent and successful attempt to treat the living thing concretely, as a real psycho-physical unity or individual, and came to grips with the big problem of the relation of the organism to its past and its future. The importance of his views will become more apparent when we consider in the next two chapters some fundamental questions of biological method.

   The interpretation of development and heredity (1930): 1 Introductory | 2 Aristotle’s ‘De Generatione Animalium’ | 3 Preformation and Epigenesis | 4 The Germ-Plasm Theory | 5 The Theory of the Gene | 6 Some Modern Epigenetic Theories | 7 Wilhelm Roux and the Mechanics of Development | 8 The Mnemic Theories | 9 Retrospect. The Use and Misuse of Abstraction | 10 The Organismal Point of View | 11 The Physiological Interpretation of the Cell Theory | 12 The Cell and the Organism | 13 The Cell in Relation to Development and Differentiation | 14 The Organism as a Whole in Development and Reproduction
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