§ 1. Definition of Heredity, Inheritance, Nurture, Development. § 2. Heredity a Condition of Evolution. § 3. Modifications and Heredity. § 4. The Organism as a Historic Being. § 5. Nature and Nurture. § 6. The Other Side of Heredity. § 7. Heredity and Personality.
THE water-vapour in the atmosphere condenses into rain which falls on the hills; in the cold night it is changed into ice, and next morning into running water again; at midday it changes once more into water-vapour. So the same material in the domain of the inorganic passes from form to form, and nothing is lost. A mineral changes into something else and great aggregates are slowly transformed. They say the solid earth on which we tread in tracts of fluent heat began. There is a similar sort of flux in the realm of organisms, in everyday metabolism, in wear and tear, in senescence. And so from hour to hour we ripe and ripe, and then from hour to hour we rot and rot, and thereby hangs a tale.
But apart from remarkable cases like Uranium liberating Helium and giving origin to Radium, which liberating more Helium may give origin to Lead, there is nothing in the domain of things to compare with sequence of generations that marks the realm of organisms. Individuals grow old and die; oftener perhaps they do not grow old, but are devoured; in any case they give place to others in the production of which they often share. The corporeal individuality ceases to exist as such, yet part of it or something that was wrapped up with it continues, or may continue into another individuality. This is the genetic relationheredity, which has to be considered as a condition of evolution, and likewise as a factor in determining the individual life.
§ 1. Definition of Heredity, Inheritance, Nurture, Development.
A few definitions, representing condensed discussions, may be useful to start with. Heredity is the relation of organic continuity between successive generations, which secures the general persistence of resemblance between offspring and their parents, between progeny and their ancestors; it implies the continuance of a specific dynamic organisation of which the germ-cells are usually the vehicle. In brief, heredity is the genetic relation between ancestors and descendants.
Some use the word heredity to include all the causes or factors which determine the resemblance between individuals who are related to one another. But this resemblance is not wholly due to heredity. Others would say that heredity is the fact that like begets like; but it is more than that, including indeed the possibility of variations. Others would say that heredity is the past living on in the present, but perhaps inheritance is the fitter word to denote that fact. All these definitions suggest part of the truth, but it seems clearest to regard heredity as the organic relation between successive generations,a relation which secures persistence of characteristics and yet allows new ones to emerge.
Whatever definition of heredity is adopted, it must be clearly understood that heredity is no mysterious force or principle; it is a flesh-and-blood linkage, a continuity of germ-plasm, binding one generation to another. In pre-Darwinian days, men always spoke of heredity with a capital letter, as if it were a power that did things, as many people still talk of Evolution, but one of Darwin's many services was that he showed the linkage between generations to be amenable to scientific experiment and description.
In mankind one generation may influence its successors by tradition and institutions, by literature and art, and in similar ways which are outside heredity in the biological sense. For the extra-organismal legacies the term social heritage may be usefully restricted,a usage which would leave Galton's term natural inheritance for all that is handed on by means of the germ-cells, namely the egg-cell and the sperm-cell. The natural inheritance includes all that the organism is or has to start with in virtue of its hereditary relation to parents and ancestors.
In most mammals, where the unborn offspring is carried by the mother for a more or less prolonged periodthe two being bound together in a very intimate ante-natal partnership or symbiosisthe natural inheritance of the offspring may be influenced by peculiarities in the available maternal nurture. The same is true in all cases where the parents, plants as well as animals, nurture the offspring. It is plain, though often forgotten, that ante-natal dints or imprints are not in the strict sense part of the natural inheritance. The word nurture, which Galton raised to the rank of a technical term, includes all manner of extrinsic influences, environmental, nutritional, and functional, which play upon the organism, or with which the organism plays. Modifications, as we have seen, are structural changes in the body of the organism directly induced in the individual lifetime by peculiarities in function or environment (including food, etc.), which transcend the limit of organic elasticity and thus persist after the inducing conditions have ceased to operate. They may be illustrated by the tanning of the skin under a tropical sun, or by the fattening of cattle, or by a callosity due to pressure. They are dints due to peculiarities in nurture, and have not been convincingly shown to be transmissible as such or in any representative degree. Finally, it may be noted that development is the realisation of the normal inheritance in appropriate nurture.
§ 2. Heredity a Condition of Evolution.
Heredity is not so much a factor in evolution, as a condition of evolution. There would be heredity though there were no evolution, but there could be no evolution if there were not heredity. What is the rôle of Heredity?
(a) Heredity involves arrangements which secure the persistence of a specific dynamic organizationholding fast that which is good. This rôle is achieved by a simple devicethe continuity of the germ-plasm or essential germinal material, a luminous conception mainly due to Galton and Weismann. It amounts to this, that in the course of development, often very early, some germinal material containing the intact inheritance is kept apart from specialisation and goes to form the germ-cells which become the starting-points of another generation. As Galton pointed out, in development the bulk of the germinal material of the fertilised egg-cell goes to form the body of the embryo, undergoing in a most puzzling way differentiation into nerve and muscle, blood, and bone; but a certain residue is kept apart from the development of the body to form the primordium of the reproductive organs of the offspring, whence will be launched in due time another similar vessel on the adventurous voyage of life. Thus in a sense the child is as old as the parent, for when the parent is developing, a residue of unspecialised germinal material, retaining the heritable qualities in their intactness, is kept apart, and will eventually give rise to the germ-cells which form the starting-point of the child. As Weismann put it: In each development a portion of the specific germ-plasm contained in the parent egg-cell is not used up in the construction of the body of the offspring, but is reserved unchanged for the formation of the germ-cells of the following generation. So it comes to be that the parent is rather the trustee of the germ-plasm than the producer of the child. In a new sense the child is a chip of the old block. Or, as Bergson puts it, in less static metaphor, life is like a current passing from germ to germ through the medium of a developed organism. It appears that too rigid a contrast has been made between body-cells and germ-cells; for groups of body-cells in plants, sponges, polyps, worms, Tunicates, and various other groups are able to develop into perfect organisms. It is safer to say that the germ-cells are those cells which carry the whole inheritance without allowing any of it to find expression until appropriate conditions and stimuli are forthcoming. They carry the whole inheritance in a form little liable to extrinsic influence and yet readily admitting of development. The general idea of germinal continuity is one of the most important contributions to post-Darwinian biology. It accounts for the inertia of the main mass of the inheritance, which is carried on with little change from generation to generation. For men do not gather grapes off thorns or figs off thistles. Similar material to start with; similar conditions in which to develop; therefore like begets like.
(b) The second rôle of the hereditary relation is that it allows of the emergence of the new and of the handing-on of the new. On the whole it makes for persistence, for inertia, but it also admits of the origin and entailment of novelties. An antithesis is often made between heredity and variation, but that is not well thought-out; the hereditary relation includes both the tendency to persistence and opportunities for variation; the antithesis is between the persistence of complete hereditary resemblance and the entailment of variations.
(c) The third rôle of the hereditary relation is to shelter the specific organisation from the influence of parental modifications. It is not certain that the shelter is quite complete; but it is indubitable that most of the dints made on the individual body are not entailed. An organism which becomes subjected to a lasting change of temperature may, as the direct result thereof, acquire some adaptive peculiarity of great advantage; it would please our idea of economy to know that this individual gain could be handed on. An organism forced into a new habitat changes its functions adaptively and acquires, as the direct result thereof, a new dexterity. It would please our idea of economy to know that this gain could be entailed. So far as we know, this does not occur, and the reason is probably that such entailment of gains would involve also an entailment of losses, and that both are inconsistent with the arrangements which secure what is much more important, namely, the persistence of the specific organisation and of the germinal changes which it from time to time exhibits. If any organisms ever showed a strong tendency to transmit somatic modifications, the probability is that they would be eliminated.
Our personal conviction, detailed evidence for which we have given elsewhere (Heredity, rev. ed., 1919), is that there is at present no good case warranting belief in the transmission of exogenous somatic modifications. But several biologists for whom we have the greatest respect think otherwise, and, without any indecision on our own part, we would refer to the works cited in the bibliography under the names of Hartog, MacBride, and Semon.
§ 3. Modifications and Heredity.
In the absence of any convincing evidence that exogenous modifications acquired by parents can be transmitted to their offspring, either as such or in any representative degree, we have to face the question whether individual modifications have any evolutionary interest at all. It may be answered, first, that deeply-saturating modifications may influence the blood and other fluids of the body, or may alter the rhythm of metabolism so that the production of internal secretions is affected, and that these internal changes in the somatic environment may act as liberating stimuli on the germ-plasm and provoke variations. Prolonged exercise, e.g., in dancing, may lead to an exaggerated production of muscle-forming substance; the myogenic metabolism may be enhanced; this may be spread through the body, e.g., from limbs to heart; it is conceivable that it might affect the germ-plasm specifically.
The second answer is that suggested by Profs. Mark Baldwin, Lloyd Morgan, and H. F. Osborn, that an adaptive modification may serve as a protective screen for the individual until, perhaps, a germinal variation in the same direction has time to arise and establish itself. What is not organically entailed may be acquired afresh in each successive generation. In an area where a dark skin was of survival value, acquired tanning might save many individual lives until, perhaps, a germinal variation in the direction of inborn swarthiness had time to appear and establish itself.
It seems to some quite incredible that the same modification should be hammered on for a thousand generations without inducing germinal changes in the same direction, but the difficulty is to find any direct or indirect evidence. It is likely enough that the long continuance of a particular modification might produce a metabolic change which might affect the germ-plasm, but the point is whether the effect on the germ-plasm would be to provoke a variation in the same direction as the modification. Mr. J. T. Cunningham and others have suggested that a well-defined modification may be followed by the liberation of some very specific hormone from the affected tissues, which might be carried to the germ-cells and there find a nidus for subsequent operations. But this remains a conceivable interpretation of what we do not know to be a fact.
(c) Another consideration must not be forgotten, that it is in the personal life of the creature that the germinal variations are expressed, used, and subjected to criticism. The germ-cell or implicit individuality determines the cards, but it is the developed organism that plays them. It is highly probable that the adult creature sometimes seeks out a situation where its idiosyncrasy tells. Prof. James Ward has emphasised the importance of this organic selection. Environment selects organisms, but an organism may also select its environment.
§ 4. The Organism as a Historic Being.
The central idea in heredity is the persistence of a specific organisation and the associated specific activity. The past lives on in the present. The category of organism includes the conception of the creature as a historic being. Let us think over this idea.
(a) There is, in the first place, the remarkable persistence of the main body of the inheritance, with but rare divergence. There is racial inertia; the entailment of what is called specificity. As was said of old time, All flesh is not the same flesh: but there is one kind of flesh of men, another flesh of beasts, another of fishes, and another of birds This is confirmed by modern research, which has demonstrated, for instance, that the ciliated epithelium lining the windpipe of a dog is different from that from a rabbit. A fish can often be identified from a few scales, a bird by a single feather. This specificity goes through and through: thus Reichert and Brown (1909) have shown that the various species of mammals, so far as they have been tried, differ in the minutiæ of their hæmoglobin crystals. In this way it is possible to distinguish the blood of a domestic dog from that of a wolf, or even from that of the Australian dingo; red fox, grey fox, and Arctic fox are crystallographically specific! Every creature has its own particular kind of colloidal substratum and its own particular chemical routine taking place therein. The largest fact of inheritance is the persistence of specificity, and we have here the reason why new departures of great moment are not likely to occur from specialised types. The relatively generalised types are most likely to be strikingly inventive.
The antiquity of the various parts of the hereditary framework is one of the most impressive facts of biology. Galton has used the illustration of modern buildings in Italy which have sometimes been built out of the pillaged edifices of ancient times; hero is an antique column and there a lintel unified afresh.
(b) The persistence of antiques is often seen with diagrammatic vividness in the case of vestigial structures, which linger on in dwindled expression for ages after they have ceased to be of any use. As Darwin said, they are like the unsounded letters in many words, quite functionless but of historical interest. They have often been compared to the vestigial structures in clothes, buttons without corresponding holes, and holes without corresponding buttons. So is it with the deeply-buried remnants of the long lost hind limbs that some of the whales still exhibit, or with the minute comb-like vestige of a gill in the spiracle of a skate. The animal world is full of these interesting relics as if the past were loath to relinquish its lien on the present. Man is an antiquarian in spite of himself, a walking museum of relics. A good instance is the vestigial third eyelid, larger in some races than others, occasionally with a supporting cartilage, but quite useless. It is the remnant of the nictitating membrane that in most birds and mammals does important work in cleaning the eye. Similarly, the muscle which moves the trumpet or pinna of the ear in many mammals, such as dog and donkey, and is useful in locating sounds, is vestigial in man, who moves his head about so readily. Some men have it larger than others; some may even become able to move their ears by wasting attention on the senseless effort. It may be noted that there is no great evidence of imperfection in the fact that vestigial organs are sometimes troublesome; it is too much to expect that there should be no tax on the stability of what is useful.
Another instance of the past living on in the present is to be found in the persistence of ancient habits that have outlived their utility. According to Darwin, there is anecho of the distant past when the dog before it settles itself to sleep turns round and round in the imaginary herbage of the hearthrug. The hand of the past is upon it in the passivity of sleepiness, and it does needlessly what its ancestors did to a purpose. So in the donkey we see signs of its original desert life in its strong dislike to cross the smallest stream of water. We are told that some Scottish cows transported to unwonted conditions on an American ranch hid their calves in the thicket, and went to feed in the open in the old approved fashion of wild cattle. The novel circumstances were really primitive and they awakened a long dormant instinct. Many examples of this sort have been collected by Robinson in his Wild Traits in Tame Animals, and while there is need for criticism, there can be no doubt as to the persistence with which the past lives on in the present. Many outcrops that seem quite perplexing in man are probably anachronistic stirrings of ancestral habits.
(c) Another set of illustrations of the past living on in the present is afforded by the facts that are now familiar in regard to the staying power of certain unit-characters or Mendelian characters that are relatively superficial in nature, and cannot be regarded as forming part of the main framework of the inheritance. When we consider how the Haps-burg lip has persisted for four centuries in Austria and Spain, how night-blindness has continued to crop out for ten generations and in hundreds of individuals in one family history beginning with 1637, or how brachydactylism (having the fingers all thumbs) may last for six generations, we realise that the hand of the past is living indeed,and inexorable. We have already mentioned the laciniate variety of the Greater Celandine (Chelidonium majus), which suddenly appeared about 1590 and has been breeding true ever since, and it is this sort of fact that we must include in our conception of the living organism, of Animate Nature, and of man in particular. That the innate defects as well as the excellences of the fathers are continued in the children far beyond the third and fourth generation is well known.
(d) Another general illustration of the past living on in the present is to be found in the way in which the individual development tends to recapitulate the racial evolution. Long before the evolution idea was accepted, the suggestion was made, e.g., by Meckel, Von Baer, and Louis Agassiz, that the stages in individual development correspond to grades of organisation in the animal kingdom. In post-Darwinian days, Haeckel recognised the importance of the recapitulation doctrine and stated it clearly in the light of evolution. He called it the fundamental law of biogenesis, and stated it in the familiar words: Ontogeny is a recapitulation of Phylogeny. He also emphasised the contrast between palingenetic characters, which correspond to those of the ancestral stock, and kainogenetic characters, which are relatively recent additions. The latter, he said, may disguise the former in a perplexing way; in any case, the recapitulation is general, not exact, and often shows great condensation. Fritz Müller was another who did much to illustrate and corroborate the recapitulation-idea, e.g., in his Für Darwin (1864).
The recapitulation doctrine has suffered considerably at the hands of its friends, who have sometimes stated it in an exaggerated fashion. When Prof. Milnes Marshal said, Every animal in its own development repeats its history, climbs up its own genealogical tree, he was speaking picturesquely, for the recapitulation is general, not detailed; it often shows telescoping; and it is truer of stages in organogenesis than of stages in the development of the embryo as a whole.
It has also to be remembered that one term in the comparison, the phylogeny, is very imperfectly known, so that assertions as to the exactness of the recapitulation must be taken with reserve. Needless to say, one must beware of the vicious circle of arguing from the development to the presumed ancestor, and then from the ancestor to its recapitulative rehabilitation in development.
Another saving clause is that the individual development, especially when there are larval stages, may have its recapitulatory features obscured by secondary adaptations to relatively recent conditions of life. Thus one does not look for recapitulation in the life-history of insects which have sub-aquatic larvaæ, for these have been secondarily adapted to a habitat which was not that of the ancestral stock. We may also recall the idea that life-histories have been adaptively altered by lengthening out one chapter and telescoping another.
Another saving clause concerns specificity, the individuality and uniqueness of every well-defined type. Increased precision of embryological work has shown that from very early stages in ontogeny an organism is itself and no other. An expert can distinguish an embryo chick a few days old from an embryo duck, before either of them shows any avian characters. There is only a technical difficulty in the way of distinguishing even the cells of an embryo mouse from those of an embryo rabbit, or those of an onion from those of a lily: the number of chromosomes is different. But a recognition of specificity from first to last is not inconsistent with admitting a significant correspondence between steps in individual development and steps in racial evolution. A tadpole is from the first in several ways an Amphibian and not a Fish, and yet in its two-chambered heart and branchial circulation it is for a time distinctively piscine.
One reason why the ontogenetic recapitulation of phylogeny must be general, not precise, is that the successive gains made in the course of racial evolution are not superposed one upon another, but must be severally incorporated into the organisation and unified with it. The additions from millennium to millennium are not like new wings added to a house, for the tenements which we call individuals are continually dissolved, and there is re-unification at the start of each new life. We must remember too that antique characters gradually disappear, thus ancestral birds had teeth, but no embryo bird shows any trace of them. These saving-clauses are of importance, but the broad fact remains that the organism's inheritance, garnered for ages, does in many cases express itself in a step-to-step development, from the general to the special, which is in some measure a recapitulation of stages in what is believed to have been the racial evolution. Some illustrations must be given.
On each side of the neck of the embryo reptile, bird, and mammal there are branchial pouches or gill-clefts which correspond to those which have a respiratory function in amphibians and fishes, and may or do persist throughout life. In reptiles, birds, and mammals these pouches are on the whole transient, like fleeting reminiscences. The first seems to persist as the Eustachian tube from the auditory passage to the back of the mouth, and the thymus gland is connected with another; but the rest pass away without persistent result. They are echoes of the past. In embryos of the chick and of some reptiles, dwindling and transient traces of gills in connection with the gill-clefts have been recently discovered (Boyden, 1918).
Similarly, the embryos of higher Vertebrates show for a time a notochord,a primitive skeletal axis derived from the roof of the embryonic gut, and thus of endodermic origin. It persists throughout life in lancelets and lampreys, serving as the dorsal axis of the animal, as the forerunner of the backbone which, from fishes onwards, develops from the mesodermic sheath of the notochord. The notochord does not become the backbone, though perhaps serving as a sort of tissue-scaffolding for it, and every stage of the replacement of the notochord by its substitute the backbone is seen in fishes. Yet on to man himself the notochord continues to appear in development, a veritable antique; it has its short day and passes, leaving but an unimportant trace behind.
In the establishment of the brain, the skull, the heart, the kidneys, and other important structures in higher animals, the foundations are laid down on old-fashioned lines, not directly suggestive of what is to follow. In the individual organogenesis there is often a recapitulation of historical stages. The development of many an organ appears to the observer to be circuitous, as if the old paths had to some extent to be retrod, and yet the progress of a hundred thousand years may be condensed into one day.
Another aspect of the same fact is that the developing embryos of, say, bird and reptile are for some days very much alike, moving on parallel lines along the great highway of Amniote development; but, sooner or later, about the sixth day in the case of the chick, their paths diverge and become distinctively avian and saurian. Thus does the past live again in the present with compelling force. How are we to think of it?
Ontogeny is the making explicit of the germinal organisation, which is what it is because of phylogeny. The way in, which an embryo moves towards a goal as if it had its future consciously in view is due to the fact that it is constitutionally determined by the past, which lives on in the present in a manner peculiar to and characteristic of living creatures. The ages that have gone have bent the bow in the plane along which the arrow of the individual flies. But ontogeny must not be thought of as the uncoiling of a wound-up spring, or as the unpacking of a marvellous treasure-box, or as a series of metabolisms which start one another in succession and enter into increasingly complex inter-relations; ontogeny is a function of the individuality which is somehow condensed within the germ-cell. Perhaps it is not, after all, very different from behaviour! The fundamental fact which we are so far from understanding is that the fertilised ovum is at once the repository of ages of organic inventions and a unified individuality in the one-cell stage of its becoming.
If we adhere to the conclusion that evolution has been a series of discoveries or inventions of the genuinely new, the further question Is how the gains have become enregistered in the germinal organisation, which must be thought of as becoming increasingly complex. There are two ways in which this enregistering may he thought of. (1) On the one hand it is conceivable that the individual acquirements and experiences of the fully developed individual may in some definite way affect the germinal organisation, and thus the progeny. In this way Lamarckians have thought of the germ-cells as being continually enriched by the gains of the individual organism, or reduced by its losses, and that in a quite definite and representative manner. There are very few known facts which lend support to this view, but it seems premature to foreclose the question by any dogmatic denial of the possibility that individually acquired modifications can leave representative imprints on the organisation, or, as some would say, on the unconscious memory of the germ-cells. It is possible that an increase of knowledge will show us that there is some hidden truth in the Lamarckian position; but the facts do not point that way at present. Deserving of consideration here are the remarkable facts of cellular habit or momentum in metabolism, expounded notably by Prof. J. G. Adami (1918, p. 55 and p. 166). Professor Adami calls attention to facts like the following. Once the cells of the body of a rabbit have got accustomed to producing a counteractive or anti-toxin to ricin (a poison from the castor-oil plant), they may go on producing this antiricin for weeks or months after the original stimulus. There is an. organic momentum. In the horse a single toxin unit of tetanus can lead in the process of immunisation to the production of 1,000,000 anti-toxin units. A cold in the head may continue for weeks after the causative agent has disappeared, and thorough sterilisation of the nose has been effected. The cells form a habit, it may be an entirely new habit, and it lasts, an acquired cell variation becoming, if I may so express it, converted into a cell-heredity. But the difficulty is to pass from such cases to the generations of multicellular animals.
(2) The known facts point to the conclusion that the organic materials of progress are supplied from within, from the fountain of change that there is in the germ-cell. If the metaphor be permissible, and we cannot get beyond metaphors yet, the germ-cell is the blind artist whose many inventions are expressed, embodied, and exercised in the developed organism, the seeing artist who, beholding the work of the germ-cell, either pronounces it, in the light of the success which it brings, to be good, or else, when it spells ruin, curses it effectively by sinking with it into extinction. There is no difficulty in understanding how a germinal mutation, having arisen, comes to stay. That is provided for in the continuity of the germ-plasm. It is probably, then, by the entailment of the results of intrinsic germinal experiments, and not by the imprinting of the results of individual experiences, that the steps made in phylogeny become registered in the germ-cells, and thus made expressible in the ontogeny for long ages to come.
§ 5. Nature and Nurture.
Development is always the result of an interaction between inherited nature (the germinal organisation and activity), and appropriate nurture (air, moisture, space, warmth, food, light, exercise, education, and much else). The two are complementary. Though the direction of development is mainly intrinsic, the degree of expression which the inheritance attains is conditioned by nurture. Theoretically, the point is of interest that there is what may be called an external heritage in relation to which the natural inheritance must develop. For we are ever apt to isolate too much, forgetting that the actuality is an association of organisms in a definite region. It is of obvious practical importance that the best possible nurture be secured. Otherwise promising variations may remain like sleeping buds, an inherited talent may remain hidden in a napkin in the ground. Hereditary characters are like seeds requiring soil and sunshine and rain. Negatively too it is always possible that alterations of nurture may prevent the actualism of inherited predispositions of a deteriorative sort. In Man's case nurture is very modifiable and largely under control; much is made that is not born, and it rests with Man to determine whether it be ameliorative or the reverse. But it must never be forgotten that the direct effect seems to be restricted to the individual.
§ 6. The Other Side of Heredity.
The past lives on in the present, that, is what is meant by heredity. There is an inexorableness in the persistence, the so-called transmission, of all sorts of inborn peculiarities, except sterility of course, not only to the third and fourth generation, but far further. Sometimes it is a trivial feature like a shock of white hair; sometimes it is a deadly vice of blood; sometimes it is all bodily, leaving the spirit unblemished, as in certain cripples; sometimes it is a blot on the brain that affects the character, now in this way and again in that, but always perniciously. There is no gainsaying the fatalistic impression that the study of heredity forces upon us, and since heredity is the relation of organic or genetic continuity between successive generations, there can be no other side to it. But there is another side to the fatalism.
There is a growing solidarity among men and women of good-will; there is a wider recognition of the social or racial aspect of parentage; there is an increasing control of life. So that, while words are easy and actual doing is difficult, it is not speaking unadvisedly with our lips to say, that the reappearance of an evil past is not inevitable in the future: it may be blocked in the present. The transmission of defects and weaknesses of a misery-bringing, race-weakening sort can be in some measure checked. A man, who is captain of his soul, need not submit to the lien that ancestry has over him. Brave words, of course; but history is full of brave deeds. One does not wish to say much about the way in whichby a survival of Nature's régime in the Kingdom of Manrotten stocks come of themselves to an end; for the tragedy is that they often taint sound stocks by the way.
Moreover, it is ungrateful to forget that the hereditary relation, which depresses us when we lose perspective, secures the entailment of all manner of wholesome human qualities. The true inwardness of heredity is a holding fast of that which is good.
For characters that blend, if the occurrence of blending characters be granted, it may remain true what Galton stated in his Law of Filial Regression,that there is a regular regression or deviation which brings the offspring of extraordinary parents in a definite ratio nearer the average of the stock. This succession-tax is even-handed; the offspring of under-average parents come nearer the mean just as do those of extraordinarily gifted parents.
The hereditary relation is such that it admits of variability, for the temptation to make a quite misleading antithesis between heredity and variation should be avoided. There is a strong specific inertiathe first law of motion, as it were; but there is a copious fountain of changethe second law, as it were. Phrase it as we may, there is something like creativeness, which is always supplying the new raw material of progress. Unless we have quite misunderstood evolution, it implies an emergence of novelties. It is like original thinking.
The quality of the nurture, largely in our own hands, determines the degree to which the buds of good qualities in our inheritance may be made to unfold, and the buds of bad qualities may be kept more or less dormant.
There is an undeniable moulding power in changes of function and environment, and though the resulting modifications of our plastic organism do not seem to be genetically persistent, i.e., transmissible as such or in any representative degree, they can be re-impressed, if desirable, on each successive generation. This is part of the biology of education.
Lastly, it must be recognised that in our social heritage, which is as supreme as our natural inheritance is fundamental, there are ever-widening opportunities for transcending the trammels of protoplasm. Wherefore, Sursum corda: Let us lift up our hearts.
Mr. Bernard Shaw speaks of the unbreathable atmosphere of fatalism which is the characteristic blight of Darwinism We have sought to show that as regards heredity there is air to breathe. It appears to us, moreover, that the fatalists assume a knowledge which they do not possess. A human inheritance is a very wonderful thing; it is very difficult to tell how much or how little a man has got. The son is told that he is handicapped by his father's defects, but it is quite possible that the father's innate defects were fewer and his excellences greater than ever transpired. For the fullness or sparseness of nurture determines the degree of expression which the inheritance attains in development. Of course there are limits. He that will to Cupar maun to Cupar. Though thou shalt bray a fool in a mortar, yet will not his folly depart from him. Our possibilities are hereditarily pre-determined, but can this be said of our actual personalities? The higher the organism the greater its unpredictability within certain limits, the greater the power of the higher nature to modify what has undergone automatisation or enregistration, the greater the capacity of selecting and altering the environment. We do not know all the evil that is in our inheritance, therefore we should not take too many risky chances. We do not know all the good that is in our inheritance, therefore we should give it every chance. Biology and history, as well as our conscience, give the lie to the mechanistic fatalism which asserts that we have not, in any measure, freedom of self-development.
§ 7. Heredity and Personality.
The greatest advance in the modern study of heredity has been the disclosure of unit-characters or Mendelian characters. It is certain that there are numerous hereditary characters which behave in a distinctive and independent way in inheritance, being distributed as indivisible entities according to a definite scheme. They are clear-cut, either there or not there; they do not blend or intergrade; and they are infallibly present in a certain proportion of the offspring. They seem to be represented in the germ-cells by definite determinants, factors, or genes, the nature of which is unknown. Some have likened them to ferments; others to differences in the ultra-microscopic architecture. It is quite likely that several factors may be concerned in one character, or that one factor may influence more than one character. The gist of the Mendelian discovery is, in Pearl's words, this: Hereditary differences behave, in the main, as discrete units, which are shuffled about and re-distributed to individuals in the course of the hereditary process, to a considerable extent independently of each other; and in typical cases this re-distribution follows the simplest of statistical laws of dispersal, the point binomial. In illustration of characters that exhibit Mendelian inheritance, the following may be cited, the dominant condition which prevails over its alternative in the first cross-bred generation being named first in each case:Hornlessness and the presence of horns in cattle, normal hair and long Angora hair in rabbits and guinea-pigs, kinky hair and straight hair in man, crest and no crest in poultry, extra toes in poultry and the normal number four, bandless shell in wood-snail and banded shell; yellow cotyledons in peas and green ones, round seeds in peas and the wrinkled form, absence of awn in wheat and its presence, susceptibility to rust in wheat and immunity to this disease, two-rowed ears of barley and six-rowed ears, markedly dentate margin in nettle leaves and slightly toothed margin. Why one character should be dominant and its alternative recessive we do not know. It is often supposed that a dominant character implies something plus, the presence of a definite factor while the corresponding recessive character implies the absence of that factor. But it is difficult to hold to this consistently.
The modern study of heredity suggests that our personality is made up of many strands which go back into antiquity and which have a unique combination for each, individual. The strands are ancient, but the individual, as Jennings (1911) says, is a new knot. And it seems an important fact that a good deal is known in regard to the intimate material processes of the interweaving. There is a fresh unification at the beginning of each individual life,a fresh unification that implies some measure of unpredictability and freedom from the past.
The strands of each individual knot diverge before and behind us. Those in my knot have come from a hundred others, and may later untie in a hundred still diverse. Of my characteristics I may say, like Iago of his purse, twas mine, tis his, and has been slave to thousands Our characteristics exist elsewhere in humanity and will continue to exist after that particular knot which forms the present self has been untied (Jennings, 1911, p. 906).
There is a certain organic immortality which is the lot of all, our strands live on. It holds as well and in the same sense for him who leaves no children of his own as for the parent. Each of us is but a knot in a continuous web of strands that have, in other combinations, built up many persons, and will, in still new combinations, build up many persons. Thus as we have before taken part in the development of brute and of man, we may hope to take part in the development of superman (Jennings, p. 910).
It has been said that to find any enlightenment in the persistence of strands of personality in collateral lineages shows a very tawdry conception of what personality means and a very limited appreciation of the sanctities of human relationships. But this criticism is not quite fair: the biologist whom we quoted and with whom we agree was simply; making a biologist's contribution to one of the riddles of existencethe apparent wastefulness of fine flowers that bear no seed. It is very unlikely that the same flowers will ever appear again; the really fine individuality is unique. But it is not unlikely that approximations to the same pattern will recur. There is a conservatism in evolution, which retains qualities on collateral lines even when a particular lineage comes to an end. Mongrelising makes for mediocrity, but eugenic marriages make for masterpieces. One can hardly reproach the order of Nature for cases where remediable social conditions have prevented fine personalities from the venture of parenthood. The deliberate or coerced celibacy of fine types may have implied in some cases an enrichment of the social heritage, but it is very unsound biologically.
In regard to questions with a wider horizon than racial persistence the biologist mustas biologistremain silent, but it is not unscientific to plead for keeping doors open till they must be shut. The personality of a geniuswhether intellectual, artistic, or moralis an amazing fact, perhaps further beyond the individuality of a dog than that is beyond the unity of an amba. It is not the general body of the man that is distinctive, but the greatly increased complexity of the nervous system and the correlated new liberty and integration of thinking and feeling and willing. And this personality is still in process of evolution. Who shall fix its limits?
When, after thousands of years of discussion, all remains dark except in the light of Christianity, why should we continue the unending quest? But it is unlikely that man will ever cease from such adventuring, and it is not to be desired as long as the quest does not interfere with the discharge of his daily duties. As Simmias said in the Phdo, shortly before Socrates was to die: I will tell you my difficulty and Cebes will tell you his. I feel myself (and I daresay that you have the same feeling) how hard or rather impossible is the attainment of any certainty about questions such as these in the present life. And yet I should deem him a coward who did not prove what is said about them to the uttermost, or whose heart failed him before he had examined them on every side. For he should persevere until he has achieved one of two things: either he should discover, or be taught the truth about them; or, if this be impossible I would have him take the best and most irrefragable of human theories, and let this be the raft upon which he sails through lifenot without risk, as I admit, if he cannot find some word of God which will more surely and safely carry him
Heredity, the genetic relation between ancestors and descendants, between the race and the individual, has to be considered as a condition of racial evolution and as a factor in determining the personal life.
Heredity is the relation of organic continuity between successive generations, securing the persistence of resemblance between offspring and their parents, between progeny and their ancestors, and is sustained by the continuance of a specific dynamic organisation of which the germ-cells are usually the vehicle. The natural inheritance includes all that the organism is or has to start with in virtue of its hereditary relation, and is to be distinguished from extra-organismal legacies, such as Man's social heritage; from the results of ante-natal influence as in most mammals and flowering plants; and from exogenous modifications directly due to peculiarities in nurture. Nurture includes all manner of extrinsic influences,environmental, nutritional, and functional. Development is the realisation of the inheritance in appropriate nurture.
Heredity is not so much a factor in, as a condition of evolution. It involves arrangements which secure the persistence of a specific dynamic organizationholding fast that which is good. This is effected by the continuity of the germ-plasm. Nevertheless it admits of the emergence and of the entailment of the new. It serves or tends to prevent the transmission as such of individual somatic modifications either for good or ill. The question arises in what way the personal life counts in evolution.
Although there is not at present any convincing evidence of the transmission of individual modifications as such or in any representative degree, it should be noted that some may serve as variational stimuli; that some may serve as adaptive screens saving the individual until germinal variations in the same direction may emerge and establish themselves; and that it is in the personal life, often of continuous experimenting, that the germinal variations are tested and sifted.
The conception of the organism as a historic being is well illustrated by the facts of heredity and development. There is the inertia of the great mass of the inheritance, much of which is of very ancient origin. There is a striking persistence of vestigial structures and even habits. There is remarkable staying power in unit characters. There is an indubitable recapitulation of phylogeny in ontogeny, especially in organogenesis. The enregistering of past gains is probably to be thought of in the light of the continuity of the germ-plasm, for it seems that organic progress emerges from within and is not impressed from without.
The individual organism is the outcome of a hereditary nature developing in an appropriate nurture. The direction of development is mainly intrinsic, but the degree of expression attained bears some relation to the extrinsic systematisation, what may be called the external heritage. In Man's case in particular, where the nurture is very subtle and very plastic, much may be made that is not born.
A study of the facts of heredity engenders a fatalistic impression: the hand of the past has such a heavy grip. But the other side of heredity must be considered,the persistence of the stable, the continual emergence of the new, the influence of nurture on the individual, and the dominance of the social heritage. It is important to bear in mind that each organism is in some degree a new individuality with some measure of indeterminateness, and made as well as born.
The modern study of heredity forcibly suggests that the personality is a unique combination of many strands which go back into antiquity. The strands are ancient but, as Jennings puts it, each knot is new. It is tied afresh at the beginning of each new life, and this implies some measure of uniqueness and freedom in the self. Our characteristic strands do in some measure exist in other combinations elsewhere, and may last on, unfortunately as well as fortunately, when our particular knot is untied.