Are the Effects of Use and Disuse Inherited?

MARKED EFFECTS OF USE AND DISUSE ON THE INDIVIDUAL

These are, to some extent, an argument against the cumulative inheritance of such effects. When a nerve atrophies from disuse, or a duct shrivels, or bone is absorbed, or a muscle becomes small or flabby, it proves, so far, that the average effect of use through enormous ages is not transmitted. When the fibula of a dog's leg thickens by 400 per cent. to a size "equal to or greater than" that of the removed tibia which previously did the work,[69 - Variation of Animals and Plants under Domestication, ii. 286.] it shows that in spite of disuse for countless generations, the "almost filiform" bone has retained a potentiality of development which is fully equal to that possessed by the larger one which has been constantly used. When, after being reared on the ailanthus, the caterpillars of the Bombyx hesperus die of hunger rather than return to their natural food, the inherited effect of ancestral habit does not seem to be particularly strong. Neither is there any strongly-inherited effect of long-continued ancestral wildness in many animals which are easily tamed.

WOULD NATURAL SELECTION FAVOUR USE-INHERITANCE?

If use-inheritance is really one of the factors of evolution, it is certainly a subordinate one, and an utterly helpless one, whenever it comes into conflict with the great ruling principle of Selection. Would this dominant cause of evolution have favoured a tendency to use-inheritance if such had appeared, or would it have discouraged and destroyed it? We have already seen that use-inheritance is unnecessary, since natural selection will be far more effective in bringing about advantageous modifications; and if it can be shown that use-inheritance would often be an evil, it then becomes probable that on the whole natural selection would more strongly discourage and eliminate it as a hostile factor than it might occasionally favour such a tendency as a totally unnecessary aid.

USE-INHERITANCE AN EVIL

Use-inheritance would crudely and indiscriminately proportion parts to actual work done – or rather to the varying nourishment and growth resulting from a multiplicity of causes – and this in its various details would often conflict most seriously with the real necessities of the case, such as occasional passive strength, or appropriate shape, lightness and general adaptation. If its accumulated effects were not corrected by natural or sexual selection, horns and antlers would disappear in favour of enlarged hoofs. The elephant's tusks would become smaller than its teeth. Men would have callosities for sitting on, like certain monkeys, and huge corns or hoofs for walking on. Bones would often be modified disastrously. Thus the condyle of the human jaw would become larger than the body of the jaw, because as the fulcrum of the lever it receives more pressure. Some organs (like the heart, which is always at work) would become inconveniently or unnecessarily large. Other absolutely indispensable organs, which are comparatively passive or are very seldom used, would dwindle until their weakness caused the ruin of the individual or the extinction of the species. In eliminating various evil results of use-inheritance, natural selection would be eliminating use-inheritance itself. The displacement of Lamarck's theory by Darwin's shows that the effects of use-inheritance often differ from those required by natural selection; and it is clear that the latter factor must at least have reduced use-inheritance to the very minor position of comparative feebleness and harmlessness assigned to it by Darwin.

Use-inheritance would be ruinous through causing unequal variation in co-operative parts – of which Mr. Spencer may accept his own instances of the jaws and teeth, and the cave-crab's lost eyes and persistent eye-stalks, as typical examples. That the variation would be unequal seems almost self-evident from the varying rapidity and extent of the effects of use and disuse on different tissues and on different parts of the general structure. The optic nerve may atrophy in a few months from disuse consequent on the loss of the eye. Some of the bones of the rudimentary hind legs of the whale are still in existence after disuse for an enormous period. Evidently use-inheritance could not equally modify the turtle and its shell, or the brain and its skull; and in minor matters there would be the same incongruity of effect. Thus, if the molar teeth lengthened from extra use the incisors could not meet. Unequal and indiscriminate variation would throw the machinery of the organism out of gear in innumerable ways.

Use-inheritance would perpetuate various evils. We are taught, for instance, that it perpetuates short-sight, inferior senses, epilepsy, insanity, nervous disorders, and so forth. It would apparently transmit the evil effects of over-exertion, disuse, hardship, exposure, disease and accident, as well as the defects of age or immaturity.

Would it not be better on the whole if each individual took a fresh start as far as possible on the advantageous typical lines laid down by natural selection? Through the long stages of evolution from primæval protoplasm upwards, such species as were least affected by use-inheritance would be most free to develop necessary but seldom-used organs, protective coverings such as shells or skulls, and natural weapons, defences, ornaments, special adaptations, and so forth; and this would be an advantage – for survival would obviously depend on the importance of a structure or faculty in deciding the struggle for existence and reproduction, and not on the total amount of its using or nourishment. If natural selection had on the whole favoured this officious ally and frequent enemy, surely we should find better evidence of its existence.

Without laying undue stress upon the evil effects of use-inheritance, a careful examination of them in detail may at least serve to counter-balance the optimistic a priori arguments for belief in that plausible but unproven factor of evolution.

The benefits derivable from use-inheritance are largely illusory. The effects of use, indeed, are generally beneficial up to a certain point; for natural selection has sanctioned or evolved organs which possess the property or potentiality of developing to the right extent under the stimulus of use or nourishment. But use-inheritance would cumulatively alter this individual adaptability, and would tend to fix the size of organs by the average amount of ancestral use or disuse rather than by the actual requirements of the individual. Of course under changed conditions involving increased or lessened use of parts it might become advantageous; but even here it may prove a decided hindrance to adaptive evolution in some respects as well as an unnecessary aid in others. Thus in the case of animals becoming heavier, or walking more, it would lengthen the legs although natural selection might require them to be shortened. In the Aylesbury duck and the Call duck, if use-inheritance has increased the dimensions of the bones and tendons of the leg, natural selection has had to counteract this increase so far as length is concerned, and to effect 8 per cent. of shortening besides. If use-inheritance thickens bones without proportionally lengthening them, it would hinder rather than help the evolution of such structures as the long light wings of birds, or the long legs and neck of the giraffe or crane.

VARIED EFFECTS OF USE AND DISUSE

The changes which we somewhat roughly and empirically group together as the effects of "use and disuse" are of widely diverse character. Thus bone, as the physiological fact, thickens under alternations of pressure (and the consequent increased flow of nourishment), but atrophies under a steadily continued pressure; so that if the use of a bone involved continuous pressure, the effect of such use would be a partial or total absorption of that bone. Darwin shows that bone lengthens as well as thickens from carrying a greater weight, while tension (as seen in sailors' arms, which are used in pulling) appears to have an equally marked effect in shortening bones (Descent of Man, p. 32). Thus different kinds of use may produce opposite results. The cumulative inheritance of such effects would often be mischievous. The limbs of the sloth and the prehensile tail of the spider monkey would continually grow shorter, while the legs of the evolving elephant or rhinoceros might lengthen to an undesirable extent. Such cumulative tendencies of use-inheritance, if they exist, are obviously well kept under by natural selection.

Although the ultimate effect of use is generally growth or enlargement through increased flow of blood, the first effect usually is a loss of substance, and a consequent diminution of size and strength. When the loss exceeds the growth, use will diminish or deteriorate the part used, while disuse would enlarge or perfect it. Teeth, claws, nails, skin, hair, hoofs, feathers, &c., may thus be worn away faster than they can renew themselves. But this wearing away usually stimulates the repairing process, and so increases the rate of growth; that is, it will increase the size produced, if not the size retained. Which effect of use does use-inheritance transmit in such cases – the increased rate of growth, or the dilapidation of the worn-out parts? We can hardly suppose that both these effects of use will be inherited. Would shaving destroy the beard in time or strengthen it? Will the continued shearing of sheep increase or lessen the growth of wool? What will be the ultimate effect of plucking geese's quills, and of the eider duck's abstraction of the down from her breast? If the mutilated parts grow stronger or more abundantly, why were the motmot's feathers alleged to be narrowed by the inherited effects of ancestral nibbling?

The "use" or "work" or "function" of muscles, nerves, bones, teeth, skin, tendon, glands, ducts, eyes, blood corpuscles, cilia, and the other constituents of the organism, is as widely different as the various parts are from each other, and the effects of their use or disuse are equally varied and complicated.

USE-INHERITANCE IMPLIES PANGENESIS

How could the transmission of these varied effects to offspring be accounted for? Is it possible to believe, with Mr. Spencer, that the effects of use and disuse on the parts of the personal structure are simultaneously registered in corresponding impressions on the seminal germs? Must we not feel, with Darwin apparently,[70 - Variation of Animals and Plants under Domestication, ii. 388, 398, 367; Life and Letters, iii. 44.] that the only intelligible explanation of use-inheritance is the hypothesis of Pangenesis, according to which each modified cell, or physiological unit, throws off similarly-modified gemmules or parts of itself, which ultimately reproduce the change in offspring? If we reject pangenesis, it becomes difficult to see how use-inheritance can be possible.

PANGENESIS IMPROBABLE

The more important and best-known phenomena of heredity do not require any such hypothesis, and leading facts (such as atavism, transmission of lost parts, and the general non-transmission of acquired characters) are so adverse to it that Darwin has to concede that many of the reproductive gemmules are atavistic, and that by continuous self-multiplication they may preserve a practical "continuity of germ-substance," as Weismann would term it. The idea that the relationship of offspring to parent is one of direct descent is, as Galton tells us, "wholly untenable"; and the only reason he admits some supplementary traces of pangenesis into his "Theory of Heredity,"[71 - Contemporary Review, Dec., 1875, pp. 94, 95.] is that he may thus account for the more or less questionable cases of the transmission of acquired characters. But there appears to be no necessity even for this concession. We ought therefore to dispense with the useless and gratuitous hypothesis that cells multiply by throwing off minute self-multiplying gemmules, as well as by the well-known method of self-division. If pangenesis occurs, the transmission of acquired characters ought to be a prominent fact. The size, strength, health and other good or evil qualities of the cells could hardly fail to exercise a marked and corresponding effect upon the size and quality of the reproductive gemmules thrown off by those cells. The direct evidence tends to show that these free gemmules do not exist. Transfusion of blood has failed to affect inheritance in the slightest degree. Pangenesis, with its attraction of gemmules from all parts of the body into the germ-cells, and the free circulation of gemmules in the offspring till they hit upon or are attracted by the particular cell or cells, with which alone they can readily unite, seems a less feasible theory and less in conformity with the whole of the facts than an hypothesis of germ-continuity which supposes that the development of the germ-plasm and of the successive self-dividing cells of the body proceeds from within. Darwin's keen analogy of the fertilization of plants by pollen renders development from without conceivable, but as there are no insects to convey gemmules to their destination, each kind of gemmule would have to be exceedingly numerous and easily attracted from amongst an inconceivable number of other gemmules. Arguments against pangenesis can also be drawn from the case of neuter insects – a fact which seems to have escaped Darwin's notice, although he had seen how strongly that case was opposed to the doctrine which is the essential basis of the theory of pangenesis.

SPENCER'S EXPLANATION OF USE-INHERITANCE

Mr. Spencer's explanation of the inheritance of the effects of use and disuse (p. 36) is that "while generating a modified consensus of functions and of structures, the activities are at the same time impressing this modified consensus on the sperm-cells and germ-cells whence future individuals are to be produced" – a proposition which reads more like metaphysics than science. Difficult to understand or believe in ordinary instances, such consensus-inheritance seems impossible in cases like that of the hive-bee. Can we suppose that the consensus of the activities of the working bee impresses itself on the sperm-cells of the drones and on the germ-cells of the carefully secluded queen? Büchner thinks so, for he says: "Although the queens and drones do not now work, yet the capacities inherited from earlier times still remain to them, especially to the former, and are kept alive and fresh by the impressions constantly made upon them during life, and they are thus in a position to transmit them to posterity." Surely it is better to abandon a cherished theory than to be compelled to defend it by explanations which are as inconsistent as they are inadequate. New capacities are developed as well as old ones kept fresh. The massacre or expulsion of the drones would have to impress itself on the germ-cells of an onlooking queen, and the imprisonment of the queen on the sperm-cells of the drones – and in such a way, moreover, as to be afterwards developed into action in the neuters only. And use-inheritance all the while is being thoroughly overpowered by impression-inheritance – by the full transmission of that which is merely seen in others! If such a law prevails, one may feel cold because an ancestor thought of the frosty Caucasus. None of this absurdity would arise if it were clearly seen that a parent is only a trustee – that transmission and development are perfectly distinct – that parental modifications are irrelevant to those transmitted to offspring.

CONCLUSIONS

USE-INHERITANCE DISCREDITED AS UNNECESSARY, UNPROVEN, AND IMPROBABLE

General experience teaches that acquired characters are not usually inherited; and investigation shows that the apparent exceptions to this great rule are probably fallacious. Even the alleged instances of use-inheritance culled by such great and judicious selectors as Darwin and Spencer break down upon examination; for they can be better explained without use-inheritance than with it. On the other hand, the adverse facts and considerations are almost strong enough to prove the actual non-existence of such a law or tendency. There is no need to undertake the apparently impossible task of demonstrating an absolute negative. It will be enough to ask that the Lamarckian factor of use-inheritance shall be removed from the category of accredited factors of evolution to that of unnecessary and improbable hypotheses. The main explanation or source of the fallacy may be found in the fact that natural selection frequently imitates some of the more obvious effects of use and disuse.

MODERN RELIANCE ON USE-INHERITANCE MISPLACED

Modern philanthropy – so far at least as it ever studies ultimate results – constantly relies on this ill-founded belief as its justification for ignoring the warnings of those who point out the ultimately disastrous results of a systematic defiance or reversal of the great law of natural selection. This reliance finds strong support in Mr. Spencer's latest teachings, for he holds that the inheritance of the effects of use and disuse takes place universally, and that it is now "the chief factor" in the evolution of civilized man (pp. 35, 74, iv) – natural selection being quite inadequate for the work of progressive modification. Practically he abandons the hope of evolution by natural selection, and substitutes the ideal of a nation being "modified en masse by transmission of the effects" of its institutions and habits. Use-inheritance will "mould its members far more rapidly and comprehensively" than can be effected by the survival of the fittest alone.

But could we rely upon the aid of use-inheritance if it really were a universal law and not a mere simulation of one? Let us consider some of the features of this alleged factor of evolution, seeing that it is henceforth to be our principal means of securing the improvement of our species and our continued adaptation to the changing conditions of a progressive civilization.

It is curiously uncertain and irregular in its action. It diminishes or abolishes some structures (such as jaws or eyes) without correspondingly diminishing or abolishing other equally disused and closely related parts (such as teeth, or eye-stalks). It thickens ducks' leg-bones while allowing them to shorten. It shortens the disused wing-bones of ducks and the leg-bones of rabbits while allowing them to thicken; and yet in other cases it greatly reduces the thickness of bones without shortening them. It transmits tameness most powerfully in an animal which usually cannot acquire it. It aids in webbing the feet of water-dogs, but fails to web the feet of the water-hen or to remove the web in the feet of upland geese.[72 - Professor Romanes had casts made of the feet of upland geese, and could not detect any diminution as compared with the web of other geese in relation to the toes.] It allows the disused fibula to retain a potentiality of development fully equal to that possessed by the long-used tibia. It lengthens legs because they are used in supporting the body, and shortens arms because they are used in pulling. Whether it enlarges brain if used in one way and diminishes it if used in another, we cannot tell; but it must obviously deaden nervous sensibilities in some cases and intensify them in others. It enlarges hands long before they are used, and thickens soles long before the time for walking on them. At the same time, as if by an oversight, it so delays its transmission of the habit of walking on these thickened soles, that the gradual and tedious acquisition of the non-transmitted habit costs the infant much time and trouble and often some pain and danger. Yet where aided by natural selection, as with chickens and foals, it transmits the habit in wonderful perfection and at a remarkably early date. It transmits new paces in horses in a single generation, but fails to perpetuate the songs of birds. It modifies offspring like parents, and yet allows the formation of two reproductive types in plants, and of two or more types widely different from the parents in some of the higher insects. It is said to be indispensable for the co-ordinated development of man and the giraffe and the elk, but appears to be unnecessary for the evolution and the maintenance of wonderful structures and habits and instincts in a thousand species of ants and bees and termites. It is the only possible means of complex evolution and adaptation of co-operative parts, and yet in Mr. Spencer's most representative case it renders such important parts as teeth and jaws unsuited for each other, and is said to ruin the teeth by the consequent overcrowding and decay. It survives amidst a general "lack of recognised evidence," and only seems to act usefully and healthily and regularly in quarters where it can least easily be distinguished from other more powerful and demonstrable factors of evolution. So little does it care to display its powers where they would be easily verifiable as well as useful that practical breeders ignore it. So slight is its independent power that it seems to allow natural selection or sexual selection or artificial selection to modify organisms in sheer defiance of its utmost opposition, just as readily as they modify organisms in other directions with its utmost help. If it partially perpetuates and extends the pecked-out indentations in the motmot's tail feathers, it on the other hand fails to transmit the slightest trace of mutilation in an almost infinite number of ordinary cases, and even where the mutilation is repeated for a hundred generations; and it apparently repairs rather than transmits the ordinary and oft-repeated losses caused by plucking hair, down and feathers, and the wear and tear of claws, teeth, hoofs and skin.

It is often mischievous as well as anomalous in its action. Under civilization with its division of labour, the various functions of mind and body are very unequally exercised. There is overwork or misuse of one part and disuse and neglect of others, leading to the partial breakdown or degeneration of various organs and to general deterioration of health through disturbed balance of the constitution. The brain, or rather particular parts of it, are often over-stimulated, while the body is neglected. In many ways education and civilization foster nervousness and weakness, and undermine the rude natural health and spirits of the human animal. Alcohol, tobacco, tea, coffee, extra brain work, late hours, dissipation, overwork, indoor life, division of labour, preservation of the weak, and many other causes, all help to injure the modern constitution; so that the prospect of cumulative intensification of these evils by the additional influence of use-inheritance is not an encouraging one. It is true that modern progress and prosperity are improving the people in various respects by their direct action; but if use-inheritance has any share in effecting this improvement it must also transmit increased wants and more luxurious habits, together with such evils as have already been referred to. As depicted by its defenders, use-inheritance transmits evils far more powerfully and promptly than benefits. It transmits insanity and shattered nerves rather than the healthy brain which preceded the breakdown. It perpetuates, and cumulatively intensifies, a deterioration in the senses of civilized men, but it fails to perpetuate the rank vigour of various plants when too well nourished, or the flourishing condition of various animals when too fat or when tamed. It already transmits the short-sight caused by so modern an art as watchmaking, but so fails to transmit the long-practised art of seeing (as it does of walking and talking) that vision is worse than useless to a man until he gradually acquires the necessary but non-transmitted associations of sensation and idea by his own experience. In a well-known case, a blind man on gaining his sight by an operation said that "all objects seemed to touch his eyes, as what he felt did his skin" – so little had the universal experience of countless ages impressed itself on his faculties. Under normal healthy conditions use-inheritance is so slow in its action that "several generations" must elapse before it produces any appreciable effect, and then that effect is only precisely what selection might be expected to bring about without its aid. Strong for evil and slow for good, it can convey epilepsy promptly in guinea pigs, but transmits the acquirements of genius so poorly that our best student of the heredity of genius has to account for the frequent and remarkable deterioration of the offspring by a theory which is strongly hostile to use-inheritance. It would tend to make organisms unworkable by the excessive differences in its rate and manner of action on co-operative parts, and by adapting these parts to the total amount of nourishment received rather than to occasional necessity or actual usefulness. It would tend to stereotype habits and convert reason into instinct.

How then can we rely upon use-inheritance for the improvement of the race? Even if it is not a sheer delusion, it may be more detrimental as a positive evil than it is advantageous as an unnecessary benefit; and as a normal modifying agent it is miserably weak and untrustworthy in comparison with the powerful selective influences by which nature and society continually and inevitably affect the species for good or for evil. The effects of use and disuse – rightly directed by education in its widest sense – must of course be called in to secure the highly essential but nevertheless superficial, limited, and partly deceptive improvement of individuals and of social manners and methods; but as this artificial development of already existing potentialities does not directly or readily tend to become congenital, it is evident that some considerable amount of natural or artificial selection of the more favourably varying individuals will still be the only means of securing the race against the constant tendency to degeneration which would ultimately swallow up all the advantages of civilization. The selective influences by which our present high level has been reached and maintained may well be modified, but they must not be abandoned or reversed in the rash expectation that State education, or State feeding of children, or State housing of the poor, or any amount of State socialism or public or private philanthropy, will prove permanently satisfactory substitutes. If ruinous deterioration and other more immediate evils, are to be avoided, the race must still be to the swift and the battle to the strong. The healthy Individualism so earnestly championed by Mr. Spencer must be allowed free play. Open competition, as Darwin teaches, with its survival and multiplication of the fittest, must be allowed to decide the battle of life independently of a foolish benevolence that prefers the elaborate cultivation and multiplication of weeds to the growth of corn and roses. We are trustees for the countless generations of the future. If we are wise we shall trust to the great ruling truths that we assuredly know, rather than to the seductive claims of an alleged factor of evolution for which no satisfactory evidence can be produced.

THE END

notes

1

Which originally appeared in the Nineteenth Century for April and May, 1886.

2

Principles of Biology, § 166, footnote. The English jaws are somewhat lighter than the Australian jaws, though I could not undertake to affirm that they are really shorter and smaller. In the typical skulls depicted on p. 68 of the official guide to the mammalian galleries at South Kensington, the typical Caucasian jaw is very much larger than the Tasmanian jaw, although the repulsively obtrusive teeth of the latter convey the contrary idea to the imagination. Mr. Spencer's assumption that the ancient Britons had large jaws appears to me erroneous. (See Professor Rolleston's Scientific Papers and Addresses, i. p. 250.)

3

Romanes, Galton, and Weismann have made great use of this principle in explaining the diminution of disused organs. Weismann has given it the name of Panmixia, —all individuals being equally free to survive and commingle their variations, and not merely selected or favoured individuals. See his Essays on Heredity, &c., p. 90 (Clarendon Press).

4

Inclusive in each case of fixed strengthening wire weighing about a sixteenth of an ounce or less.

5

References of course are to Factors of Organic Evolution.

6

P. 13; and Nineteenth Century, February, 1888, p. 211.

7

Tomes's Dental Surgery, pp. 273-275. Tomes observes that it is as yet uncertain in what way civilization predisposes to caries. But he shows that caries is caused by the lime salts in the teeth being attacked by acids from decomposing food in crevices, from artificial drink such as cyder, from sugar, from medicine, and from vitiated secretions of the mouth. It is evident that in civilized races natural selection cannot so rigorously insist on sound teeth, sound constitutions, and protective alkaline saliva. The reaction of the civilized mouth is often acid, especially when the system is disordered by dyspepsia or other diseases or forms of ill-health common under civilization. The main supply of saliva, which is poured from the cheeks opposite the upper molars, is often acid when in small quantities. But the submaxillary and sub-lingual saliva poured out at the foot of the lower incisors and held in the front part of the jaw as in a spoon, "differs from parotid saliva in being more alkaline" (Foster's Text Book of Physiology, p. 238; Tomes, pp. 284, 685). One observer says that the reaction near the lower incisors is "never acid." Hence (I conclude) the remarkable immunity of the lower incisors and canines from decay, an immunity which extends backwards in a lessening degree to the first and second bicuspids. The close packing of the lower incisors may assist by preventing the retention of decaying fragments of food. Sexual selection may promote caries by favouring white teeth, which are more prone to decay than yellow ones. Acid vitiation of the mucus might account both for caries and (possibly) for the strange infertility of some inferior races under civilization.

8

Origin of Species, pp. 198-9; Variation of Animals and Plants under Domestication, vol. ii. p. 328 footnote, also p. 206.

9

Mr. Spencer weakly argues that an advantageous attribute (such as swiftness, keen sight, courage, sagacity, strength, &c.) cannot be increased by natural selection unless it is "of greater importance, for the time being, than most of the other attributes"; and that natural selection cannot develop any one superiority when animals are equally preserved by "other superiorities." But as natural selection will simultaneously eliminate tendencies to slowness, blindness, deafness, stupidity, &c., it must favour and improve many points simultaneously, although no one of them may be of greater importance than the rest. Of course the more complicated the evolution the slower it will be; but time is plentiful, and the amount of elimination is correspondingly vast.