From The Contemporary Review.

ON THE HEREDITARY TRANSMISSION OF

ACQUIRED PSYCHICAL HABITS.

BY DR. W. D. CARPENTER.

been subsequently shown to have an application far more extensive than they had themselves anticipated.

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The Physiology of mental Habit cannot

THERE cannot, I think, be a question be rightly understood without a prelimithat in the minds of all the more progres-nary study of bodily Habit; and it will be sive thinkers of the present day, the shown that we may pass from one of doctrine of Evolution, whether accepted these categories to the other by a series thoroughly or only tentatively, is giving a of steps so gradational, that it is impossidirection to their inquiries, and a form to ble to draw a distinct line of separation their speculations. Believing, as I do, between them. The readers of my previthat the future advance of Psychology will ous Papers in this Review will not need to depend in great measure upon the sa- be reminded that I hold it absolutely gacity and fearlessness with which this essential to a sound Psychology, to look at principle is pushed forward, I am desirous Man's nature as a whole; and, so far from of showing that the doctrine of the em- attempting to mark out distinct spheres bodiment in the Constitution of one gen- for Mind and Body, Spirit and Matter, to eration, of congenital tendencies to certain endeavour to trace the subtle threads by forms of Psychical action, which are the which, in our present state of existence; resultants of the experience of previous their operations are inextricably connected. generations, has a sound Physiological "What God hath joined together, let not basis. It will appear, in the course of my Man put asunder." I do not pretend to exposition, that this doctrine is really explain" any Mental phenomenon by much older than the able writers to whom Physiology: I merely affirm that the Phyit is generally attributed; and that while siological method affords, in many inSir John Sebright and Mr. Thomas An- stances, a valuable clue to the study of drew Knight had most explicitly advanced Mental phenomena; and that wherever the principle of the hereditary transmis- any form of Mental activity is distinctly sion of acquired Habits, so that they be- related to Bodily, the investigation of the come "secondary instincts" before it was material conditions of that activity is an taken up by Mr. Herbert Spencer and essential part of Psychological Science. made part of the basis of his Philosophy, There is no part of our composite nathe probability that such acquired Habits ture as to which this is more obvious than tend to produce structural modifications it is in the formation of Habits; which, as in the Organic mechanism, analogous to I pointed out twenty years ago, is entirely those of which the original Instinctive pro- conformable to the general laws of Nutripensities are the expressions, had been tion. The demand for Nutrition in the distinctly shown before Professor Bain living organism, that is, for the conformularized it in language which appears tinual replacement, by new tissue, of that to me more positive and explicit than we which has become effete, arises from the have at present a right to use. I have no limitation of the term of life of each part, other motive than the suum cuique in mak- which is for the most part brief in proporing this reclamation. The future his- tion to its activity. Thus in a Tree, the torian of what I am convinced will be leåf-cells, which do the greater part of the bereafter regarded as a most remarkable work of assimilating the nutrient mateEpoch in the History of Philosophy, will rials, last only for a season; whilst the be able to assign to these two most able solid trunk, to the growth of which the thinkers and writers the great merit to functional activity of the leaves is subwhich they are unquestionably entitled; servient, may eudure for centuries. So in without overlooking the preparation which the Animal body, while there is a conhad been made for them by previous tinual "shedding" and reproduction of thinkers, who, in their respective spheres, the assimilating and secreting cells by were patiently collecting and generalizing which the plastic material of the blood is facts, or developing principles, which have prepared, there is a far greater perma

nence in the framework of the Skeleton, | since pointed out, the Formative power is the bones, cartilages, ligaments, and ten- often exercised, not only in maintaining dons, whose functions are purely mechani- the original type, but also in keeping up cal. In the case of the Nervo-muscular some acquired peculiarity; as, for example, apparatus, to whose action all the rest of in the perpetuation of a scar left after the the Organism ministers, the duration of healing of a wound. For the tissue of the life of each competent integer seems a cicatrix grows and assimilates nutrient essentially to depend upon the use that is material, exactly as do the normal tissues made of it; varying inversely as its func- which surround it; and thus a scar on a tional activity. Thus, the greater the Child's face which is as long as his own amount of Nervo-muscular energy put finger, will still be as long as his finger forth, the greater will be the "waste of when he becomes a Man. tissue, and the greater the demand for its replacement by the Nutritive process.

Now it is unquestionably during the period of growth, that the influence of exBut the Age of the Animal body has a ternal agencies is most strongly exerted in very important relation to the activity of modifying the Constitution of the individthe Nutritive operations; for whilst the ual; for when this has been once fixed, it Plant grows by mere addition and extension, either succumbs to a change of conditions, the Animal grows (at least in all but the or dominates over them, having little lowest Plant-like forms) by the production power of adaptation to them. To such of additional tissue in the intimate substance early modifiability of Constitution I should of every part and organ; and thus, during refer the following case, cited by Sir the whole passage of the Human or any Charles Lyell (Principles of Geology, 11th similar Organism from its earliest embry-Edit. vol. ii. p. 297) as one of "inherited onic stage to its full maturity, there is a instincts": "Some of our countrymen continual pulling-down and rebuilding of engaged about the year 1825 in conducting every part of the fabric, which produces a one of the principal mining associations in demand for Nutrition that is far out of Mexico, that of Real del Monte, carried proportion to the actual increase. Every-out with them some English greyhounds one knows the appetite of a rapidly grow- of the best breed, to hunt the hares which ing boy; and yet of the excess of food abound in that country. The great platwhich he takes in a given time beyond form which is here the scene of sport is at what would be required by the adult, an elevation of about 9,000 feet above the probably not one hundredth part goes to level of the sea, and the mercury in the supply the material for the mere addition barometer stands habitually at the height of weight which he acquires during that of about 19 inches. It was found that the time, all the rest being used up in that greyhounds could not support the fatigues process of reconstruction, which is a neces- of a long chase in this attenuated atmossary condition of the enlargement of the phere, and before they could come up with Organism as a whole. their prey, they lay down gasping for breath; but these same animals have produced whelps which have grown up, and are not in the least degree incommoded by the want of density in the air, but run down the hares with as much ease as the fleetest of their race in this country."

The Formative power, then, ordinarily exerts itself (1) in keeping up the Nutrition of every integral part of the body, so as to maintain it in the condition proper to it at each period of life; (2) in that continual rebuilding which is actively going on during the period of growth; and (3) in that original production which is required for the development of new parts and organs at some particular stage of life; as that of the apparatus for the Reproduction of the race, when the organism of the individual is approaching its maturity.

But, further, as Sir James Paget long

Again, it cannot be doubted that in the exercise of the Reproductive function, a formative capacity is transmitted to the germ, in virtue of which (the requisite external conditions being supplied) it devel ops itself into an Organism possessing the characters of its species, and sometimes the individual characters of one or other of its

parents, or of both in combination. Of not only comes to tolerate what would have the limiting conditions of that Hereditary | been in the first instance absolutely poiTransmission which is certainly a general sonous, but that it comes to be dependent tendency, Physiology can at present give upon a repetition of the dose for the power very little account; and I shall only sug- of sustaining its ordinary activity, and gest that while a great deal of discussion that the want of such repetition produces has taken place as to whether the male or an almost unbearable craving, which is the female parent exerts the greater influ- as purely Physical as that of hunger or ence over the character of the offspring, thirst. Now all these "nervine stimuwe are as yet entirely ignorant of how far lants" further agree in this, that while the union of two different natures may they excite or misdirect the Automatic produce as in the combination of an activity of the Mind, they weaken the acid and a base a resultant essentially controlling power of the Will; and this dissimilar to either of them. This much, is exactly the condition which, intensified however, may be confidently affirmed, that and fixed into permanence, constitutes Inwhere general constitutional taints, that is to sanity. We have a larger experience of the say, abnormal habitudes of Nutrition, have results of habitual Alcoholic excess, than we been acquired, these tend to propagate have in regard to any other "nervine stimuthemselves hereditarily; and that they do lant;" and all such experience is decidedso with the most certainty, when both par- ly in favour of the hereditary transmission ents partake of them. It may also be of that acquired perversion of the normal affirmed that every repetition of such, nutrition of the nervous system which it transmission tends to increase the mis- has induced. That this manifests itself chief; so that by "breeding in and in," sometimes in congenital Idiocy, sometimes the injurious external conditions remaining the same, a very slight original departure from healthy nutrition may become intensified in successive generations into a most serious abnormality. Of this we have an example in the production of Cretinism, which may be characterized as idiocy connected with bodily deformity. This is not essentially connected, as some have supposed, with goitre; for it presents itself in some localities where goitre does not prevail, whilst elsewhere goitre prevails without developing itself into cretinism. But in the Vallais of the Alps the con- were drunkards, seven idiotic children ditions of the two appear concurrent; and the result of their conjoint action through a succession of generations becomes most distressingly apparent.

in a predisposition to Insanity, which requires but a very slight exciting cause to develop it, and sometimes in a strong craving for alcoholic drinks, which the unhappy subject of it strives in vain to resist, is the concurrent testimony of all who have directed their attention to the enquiry. Thus Dr. Howe, in his Report on the Statistics of Idiocy in Massachusetts, states that the habits of the parents of 300 idiots having been learned, 145, or nearly one half, were found to be habitual drunkards. In one instance, in which both parents

were born to them. Dr. Down, whose experience of Idiocy is greater than that of any other man in this country, has assured me that he does not consider Dr. Howe's statement as at all exaggerated. Sir W. A. F. Browne, the first Medical Lunacy Commissioner for Scotland, thus wrote when himself in charge of a large asylum:-"The drunkard not only injures and enfeebles his own nervous system, but entails mental disease upon his family. His daughters are nervous and hysterical; his sons are weak, wayward, eccentric, and sink under the pressure of excitement, of some unforeseen exigency, that it or the ordinary calls of duty. Dr. Howa

There is one class of cases, moreover, in which a particular abnormal form of Nutrition that is distinctly acquired by the individual, exerts a most injurious influence upon the offspring-that, namely, which is the result of habitual Alcoholic excess. There can be no reasonable question that the continual action of what have been termed "nervine stimulants" modifies the nutrition of the Nervous system; for in no other way can we account for the fact. unfortunately but too familiar

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remarks that the children of drunkards lead unwary readers to believe that much are deficient in bodily and vital energy, has been definitely ascertained, which is and are predisposed by their very organ-merely assumed), I shall here reproduce, ization to have cravings for alcoholic stimu- from the fifth edition of my Human lants. If they pursue the course of their Physiology," my former account of the fathers, which they have more temptation rationale of Habit, with some additional ilto follow, and less power to avoid, than lustrations. the children of the temperate, they add to The Spinal Cord, with its afferent and their hereditary weakness, and increase efferent nerves, constitutes the apparatus the tendency to idiocy or insanity in their for the performance of those "Reflex' constitution; and this they leave to their movements which do not involve Sensachildren after them. The experiences of tion; depending merely on a sort of reflecthose who, like Hartley Coleridge, have tion by the Nerve-centres, along the moinherited the craving for alcoholic excite- tor or efferent nerves, of the impressions ment, together with the weakness of Will brought to these centres by the excitor or which makes them powerless to resist it, afferent. Now these "reflex" movements, whilst all their better nature prompts the some (as the acts of Breathing and Swalstruggle, must satisfy any one who care- lowing, with Sucking which is compoundfully weighs them, how closely connected ed of both) are obviously dependent on their Psychical state is with the Physical the congenital arrangement of the Nervous constitution which they inherit, and how apparatus which is the instrument of their small is their own moral responsibility for performance; whilst others, for which the errors which are mainly attributable to capacity is acquired subsequently, belong the vices of their progenitors. As I heard to Hartley's category of secondarily autoRobert Collyer (of Chicago) well say in matic. In the acquirement of such as, for an admirable sermon 66 on The thorn in example, the habit of erect progression, the flesh: "-"In the far-reaching influ- common to every normally constituted ences that go to every life, and away back- Human being-not only consciousness ward as certainly as forward, children are but volitional effort may be involved; and sometimes born with appetites fatally yet, when once acquired, they may be perstrong in their nature. As they grow up, formed through the instrumentality of the the appetite grows with them, and speed- Spinal Cord alone, as when soldiers conily becomes a master, the master a tyrant, tinue to march during sleep, or fowls move and by the time he arrives at his manhood on several steps after their heads have the man is a slave. I heard a man say been cut off. This is now generally adthat for eight-and-twenty years the soul mitted by Physiologists to be the true exwithin him had had to stand, like an un-planation of the results of Pflüger's expersleeping sentinel, guarding his appetite iments on the decapitated Frog; though for strong drink. To be a man at last the purposive nature of the movements it under such a disadvantage, not to men- executes was at first supposed by many to tion a saint, is as fine a piece of grace as indicate that the Spinal Cord is the seat can well be seen. There is no doctrine of Consciousness and Will. Thus if a certhat demands a larger vision than this oftain spot of the thigh of a decapitated the depravity of human nature. Old Dr. frog be touched with acetic acid, the dorMason used to say that as much grace as sal surface of the foot of the same side would make John a saint would barely moves to the spot, so as to rub off the keep Peter from knocking a man down." With such evidence of the hereditary transmission of general diatheses, or modes of Nutrition, of which we can distinctly trace the acquirement in the history of the progenitor, we seem fully justified in applying the same doctrine to such particular habits as may be regarded, from the Physiologist's point of view, in the light of expressions of special modifications of Nervous organization. As I do not consider that any advance has been made in our positive knowledge on this subject, beyond the stage to which I had brought it twenty years ago (although the language used by some later writers might

offending liquid; if the foot be cut off, and the acid be again applied, the leg is again moved in the same manner, but without being able to remove the irritation; and after some fruitless efforts, the other foot is moved towards the spot, and the acid wiped away. Now it is within the experience of most of us, that we ourselves often execute the very same kind of protective movements during profound sleep, when we are functionally in precisely the same condition as the decapitated frog; and however purposive they were when we first learned to perform them, they have come by habit to be purely automatic.

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Now," I remarked (op. cit. p. 494), “in

all these cases it seems reasonable to infer higher class of Secondarily Automatie that the same kind of connection between actions which can only be performed under the excitor and motor nerves comes to be the guidance of Sensation, and which formed by a process of gradual develop- therefore involve some Psychical change, ment, as originally exists in the nervous in each case, as one of the links in the sesystems of those animals whose movements quence, it is impossible not to recognize are entirely automatic; this portion of the the influence of Habit,- that is to say of nervous system of Man being so consti- the Volitional repetition of similar acts tuted, as to grow-to the mode in which it under similar circumstances,—in estabis habitually called into play. Such an lishing a condition of the Nervous apparaidea is supported by all we know of the tus which leads to the performance of such formation and persistence of habits of acts mechanically" (as we say), not only nervo-muscular action. For it is a matter without any intention, but even, it may be, of universal experience, that such habits contrary to a pre-formed intention. Thus are far more readily acquired during the it will probably be within the experience periods of infancy, childhood, and youth, of many of my readers, that they have than they are after the attainment of adult often found themselves winding up their age; and that, the earlier they are ac-watches when they have gone to their quired, the more tenaciously they are re- dressing-rooms to prepare for an evening tained. Now it is whilst the organism is entertainment, just as they would do when growing most rapidly, and the greatest retiring for the night. In fact I have amount of new tissue is consequently be- heard of one rather "absent " gentleman, ing formed, that we should expect such new connections to be most readily established; and it is then, too, that the assimilative processes most readily take-on that new mode of action, which often (as in the maintenance of a cicatrix) becomes so completely a "second nature," as to keep up a certain acquired mode of Nutrition through the whole subsequent life."

A very curious proof of the Hereditary Transmissibility of tendencies to special movements, the secondary acquirement of which tendencies is altogether beyond doubt, is afforded by the following curious fact established by the researches of M. Brown-Sequard. In the course of his masterly experimental investigations on the functions of the Nervous System, he discovered that after a particular lesion of the Spinal Cord of Guinea-pigs, a slight pinching of the skin of the face would throw the animals into a kind of epileptic convulsion. That this artificial epilepsy should be constantly producible in Guineapigs, and not in any other animals experimented on, was in itself sufficiently gingu lar; and it was not less surprising that the tendency to it persisted, after the leison of the spinal cord seemed to have been entirely recovered from. But it was far more wonderful that when these epileptic Guinea-pigs bred together, their offspring showed the same predisposition, without having been themselves subjected to any lesion whatever; whilst no such tendency showed itself in any of the large number of young that were bred by the same accurate observer from parents that had not thus been operated on.

With regard, in the next place, to that

who actually went to bed when he ought to have been dressing for a dinner-party. And it is a common experience of every one who is accustomed to walk day after day in a particular direction, that having set out with the purpose of taking some, other, he has found himself" mechanically" carried on along his usual line, his attention having been occupied in some train of thought, which has for a time withdrawn his movements from the guidance of the Will.

To this category belong the movements of Expression, which have lately been investigated so philosophically by Mr. Darwin. I cannot doubt that he is right in the belief that certain movements of this class were originally "serviceable; as, for example, the winking of the eyes, and the backward withdrawal of the head and body, when a blow is directed towards the face. And I have experienced, like himself, the strong tendency to this action, when my Reason told me that there was no danger whatever. There must, therefore, be some definite arrangement of the Nervous apparatus which is the instrument of these actions; and in the case of those which were obviously "serviceable" in their origin, I agree with him in thinking it probable that the tendency to them comes to be genetically transmitted.

The case is different, however, in regard to those movements of Expression which cannot be shown to have any "purposive character, but are the direct products of a certain Emotional excitement. And with these "gestures," which are often peculiar to individuals, we may connect the "tricks" which are involuntary with many persons,