Popular Science Monthly/Volume 14/January 1879/Heredity
| HEREDITY. |
By GEORGE ILES.
HAWTHORNE in his masterpiece, the "Scarlet Letter," makes his heroine, Hester Prynne, a woman who has sinned, resolutely refuse to tell the name of her partner in guilt when the Puritan inquisitors urge her to do so. The ministers of justice and vengeance then turn to her child, and sharply scrutinize her features, to find if possible some trace of her father's look, that the wrong done may be punished. Here, too, they are unsuccessful—the face of the little elf tells no story that they can read, gives them no clew in their task of detection; they are obliged to withdraw, baffled and surly. This incident in the greatest of American romances is true to experience; while the inheritance from parents of form and character is general, yet it is not universal, and while some of the exceptions, when explained, afford very interesting studies of the play of natural forces, too subtile to be noticed by simple inspection of their results, yet many anomalies exist in heredity which the science of to-day is quite incompetent to explain.
The inheritance of the peculiarities of physical structure is a matter of daily and hourly observation, and the minute fidelity of it is at times very remarkable. Agassiz placed on record cases where traces of surgical operations had been transmitted. Sometimes parent and child are not only alike in form and feature, but even in tricks of tone and gesture, handwriting and gait.
The predisposition to certain diseases, like gout or insanity, often developed after maturity, is transmissible; and also the liability to die about a certain age. The famous Turgots, for more than a century, rarely exceeded fifty years of age; and insanity often appears after the meridian of life in several successive generations of a family. The remarkable faithfulness of reproduction in the majority of cases is a fact somewhat parallel to the growth and maintenance of an organism, wherein, with the constant succession of cells each of brief existence, substantial identity is kept up. There do not seem to be very marked differences in babes, yet from the same food one will become a man of muscle and energy, another of nerve and brain, a third a portly man of ease-loving habits. All the original peculiarities of each tiny human nucleus pick out from a common nourishment elements like themselves, rejecting the rest.
Inheritance is not only physical, but intellectual as well; great ability in mathematics, painting, music, and other departments of effort, has clearly been received at birth in many thousands of examples. The Bach family for two hundred years maintained exalted rank in music. The direct succession of very able men in the families of Pitt, Napier, Fox, Herschel, Darwin, and many more, is evidence that mind and will are as transmissible as complexion and stature. This is more apparent in a country like England, where the institutions and customs favor and confirm the results of heredity, than in America, where there is no law of entail, and as yet little of the ambitious founding of families.
There is abundant testimony to prove that heredity can be moral as well as physical and intellectual. The Stuarts were as constant in the presentation of certain moral traits as the family of the Churchills or the American Adamses are in others. Imprudence, penuriousness, dishonesty, or good judgment, once thoroughly established in a stock, persists with quite as much tenacity as the familiar eyes or nose. The inheritance by posterity of the changes wrought on individuals by their experience is the basis of the modern explanation of the growth of instinct and the evolution of human intelligence. Darwin has developed this theory in a masterly manner. He gives as an illustration that between the finished skill of the honey-bee and the rude capabilities of the humble-bee stand the intermediate powers of the Mexican melipona. This last insect constructs a comb of wax, almost regular in form, consisting of cylindrical cells, in which the larvae are hatched, and a certain number of large cells to hold its store of honey. The latter cells are nearly spherical and situated at a considerable distance from each other. Now, any slight variation of organization or instinct, by which the melipona would construct its cells more uniformly and compactly, would economize its wax and labor, and bring it up toward the plane of the honey-bee. The generations of insects succeed each other so rapidly that no modification can be detected among species low in the scale. Honey-bees, however, are not possessed of unadaptable and rigid instincts, for they have been observed to spring arches and buttresses in their hives to avoid glass rods purposely inserted. An organism's advantage plainly lies in an increase of its skill and ingenuity, and any slight advance made by individuals is preserved by heredity, persists in tendencies and habit, and becomes fixed as instinct.
The development of intelligence among mankind is accounted for in the same manner: efforts at first painfully made by our ancestors in new paths were at last rewarded by the facility that comes with repetition; their immediate descendants were born with new aptitudes and an organization with a wider range of powers; the acquisitions thus gained and transmitted have grown into the varied faculties of the men and women of to-day. "Mankind," Comte says, "is as one man, always living and always learning." The passing away of one generation and the birth of another do not interfere with the constant progress of the race.
The method applied to the explication of the growth of instinct and intelligence has been used by Darwin in approaching the problem of the origin of the conscience from the side of natural history. He deems it to have had its beginning-when an animal could contrast the transient pleasure given by the gratification of a passion-with the abiding pain afterward felt. An enlargement of memory must have come before the immediate and remote effects of actions could be compared in consciousness, and the greater good recognized and chosen.
This theory of conscience, which holds it to have been created by the experiences of the race confirming habits best suited for social life, well accords with the theory of morals which takes benefit or utility, in its largest sense, as the test and sanction of right conduct.
While the manifestations of heredity in their obvious effects are interesting, yet the laws brought to light by an examination of some results apparently exceptional and contradictory are of still deeper interest. A single great law may underlie a large group of problems, yet many other principles of minor weight may coöperate with it and obscure its direct force. The study of residual phenomena is ever fraught with increased knowledge and the unfailing testimony that where law seems to be at fault it is only so from our ignorance of the varied energies at work, which are constantly revealed to the patient searcher for truth. In the science of heredity many apparent anomalies have been resolved in allowing for the action of forces newly discovered or applied.
The study of the unconscious powers of the mind has of late years attracted much attention; observation has found that there may lie latent in a man tendencies and forces whose existence he may never suspect, but which he is capable of transmitting to children who shall palpably develop them. Insanity, gout, and melancholia, frequently skip a generation and reappear when hopes have been entertained that the evil trait had died out in the family. A son may resemble his mother very markedly, and have children with the features and character of his father. The evidence of heredity is thus borne out frequently in the long-run, when to a contracted view it would seem at fault. An individual inherits not only from his parents but from all their predecessors in the line of life, and just what of them shall appear evidently in him, and what be hidden in unconsciousness, none can tell. The surface forces of the man may be like the momentum of a tree falling down a mountain-slope, but the inner and dormant powers never to be manifested during a lifetime may as far transcend the energies actually shown as the force of the fire which the tree may feed excels that of its mere bodily impact in descent.
The dormancy of traits accounts for atavism or the reversion of an organism to the form and character of ancestral stock. Pigeons, dogs, and horses, frequently relapse, so to speak, to the inferior type from which they have been bred, and so exhibit a wide divergence from their immediate parents. Reversion of this kind has been noticed in the silkworm after a hundred generations. So long in Nature does an organism retain substantially the same form, that when art produces a rapid modification of structure, or desires to seize upon a valuable and marked variety, repeated and careful selection is required to give it permanence.
The principle of atavism explains the curious resemblance often seen in a human family between uncle and nephew; the likeness in such cases is derived from some common ancestor, the grandfather most usually.
Mr. Galton, in his work on "Hereditary Genius," adopts the statistical method to prove that illustrious men arise oftenest from families displaying eminent talent, and have relatives approaching to themselves in ability in a degree proportioned to the nearness of kinship. A man of genius is much more likely to have a remarkable father or son, than a nephew or cousin. Great men, Galton says, seem to arise like islands, isolated and unaccountable; but this is an illusion—they are given to us usually by parents unknown from the necessarily narrow limitations of fame; islands are but the tops of hills whose whole extent is hidden by obscuring ocean. Yet the exceptions to this rule are very numerous: why should Cromwell, Milton, Goethe, and so many others, leave behind them unworthy children? Was it from unfortunate mating with an inferior mother, or because the vitality, physical and mental, was too much drawn upon by the individual life for worthy continuation? How can it be explained that men like Burns and Faraday should come up from families in which even enthusiastic biographers can find nothing to distinguish them from their neighbors?
The wide unlikeness frequently observed between parents and children in talent and character suggests an analogy with a familiar fact in chemistry. A compound's color, weight, and other properties, may be changed almost beyond recognition by adding or eliminating a single element. It is somewhat so in human nature; a father of warm passions or strong acquisitive impulses may transmit all his traits to a son, except prudence; and the omission may cause much sympathy for a reputable and worthy man's being afflicted with a boy so unlike himself. If the lack in inheritance be in perseverance and application, of what value are splendid talents without them?
A lens externally not to be distinguished from a perfect one may, from some slight defect in composition or handling, give images blurred and distorted, instead of true and beautiful. A chain is no stronger than its weakest link, and a small lack or discordance in the elements of character may exclude it from the exacting demands of high place. We often hear regrets that men of genius so rarely have living descendants, but we must not overrate the persistence of ordinary families: taking the first eleven names of acquaintances that occurred to me, I found that three of them were in a fair way of being the last of their race; every old person can recollect the dying out of many once numerous families.
Ribot, the French authority on heredity, alleges two causes as among the chief at work in cases where the law of transmission does not obviously manifest itself. The first is the disproportion of an initiatory force to the amount of energy it may liberate or direct, as in the slight agencies by which fires are lit or explosions set off. The accidental surroundings of a mother before the birth of her child may affect it for life in a way altogether disproportioned to the forces at work. The military excitements in which Madame Bonaparte lived just prior to Napoleon's birth are well known. Anxiety, grief, elation, an unusual degree of physical health or debility at such times are productive of very striking effects, quite capable of masking the likeness between parent and child in form and disposition. The Greeks believed so strongly in the potency of prenatal conditions that they not only guarded mothers who were bearing with the kindest care, but used even to surround them with beautiful works of art, that imagination might act a favorable part.
The second cause which Ribot thinks often tends to obscure the evidence of heredity is the transformation in development of characteristics which are the same at root. Thus a consumptive father has a son who suffers from rheumatism or paralysis. Here the transmission has simply been that of a feeble constitution, which gives way in the first circumstances of severe trial—those favoring rheumatism, paralysis, or other disease. The crystal of life, to use Galton's figure, is disturbed, and reposes on a new facet. In cases where talent appears conspicuously in a family, it may be that energy and patience, productive of but ordinary results in a father, are directed by his son to supplying some new public want, or filling 'a position created by some sudden national emergency. The constructive powers of Stephenson were less remarkable than his dogged perseverance; and when the world needed steam locomotion he was the man to give it, and surmount the immense difficulties in the way. His strong will is not a rare trait of character, but, joined to his ingenuity, it won him success in his great opportunity. Had Charles I. been a good king, Cromwell would probably have died a brewer. Unbending will was also his chief characteristic, but at Huntingdon it could have enjoyed but narrow play.
Readers of the Monthly may remember Galton's paper on "Twins," published in January, 1876. In that paper, based on wide and carefully made comparisons, it was proved that in the production of character original constitution is a much more important factor than either education or surroundings. The resemblance of twins when it occurs, as it frequently does very strongly, continues through life in a large proportion of cases. The same author has confirmed his opinion that Nature is more powerful than nurture in moulding men, by collecting elaborate testimony from all the illustrious Englishmen of science now living, who say for the most part that their tastes were either innate or manifested themselves very early under the influence of training, and in some few cases were developed in antagonism to a particular kind of education imparted to them.
Galton thinks that the natural differences among men are far wider than commonly supposed: from a careful study of the statistics of Cambridge examinations, he estimates that the capacity in mathematics of a senior wrangler is to the lowest in the scale of students taking honors as three hundred to one. Similar results have been arrived at by comparisons made in other branches of learning. From all this, it would seem that the popular mind not only underrates the natural differences of men, but also exaggerates the real limits of the improvability of the masses of mankind. Education can only call out one's powers, not bestow them where they are lacking; and supreme minds almost seem to be independent of education, or, at least, always able to get all they need. The task of diffusing information is comparatively an easy one, but the absorption and vitalization of it in the receiving minds is a matter quite beyond the teacher's skill. While we should not expect too much from instruction, we may rightly expect a great deal if it be wisely given; and here it may be fitting to draw attention to a danger in our modern schemes of education, very ably pointed out by Johnson in his recent work on China. The increasing uniformity in methods of instruction, while it may tend to the adoption of the one best plan for an average scholar, has a disadvantage in repressing individuality, and abolishing the many special kinds of teaching for which some teachers are peculiarly fit, and by which some of the best kinds of scholars, different from the average, are notably benefited. The narrow line of a great circle is undoubtedly the shortest path for a ship to take, but, if we would explore new seas and find new truths, the sharply-defined curve of economic navigation must be departed from; and the more diverse the tracks of the ship-master, the more of the deep waters of the unknown will he map out for us.
Instructors sometimes err in being too early in their work, as well as too uniform in their methods; so that matters of great moment lose the bloom of novelty before the reason needed to grasp them matures. One of the compensations for an education coming late in life by one's own effort or otherwise is, that the wonderfulness and suggestiveness of truths come to the mind undampened by any early and useless familiarity.
In the cause of education it is to be regretted that men of the greatest natural endowments can so rarely describe their processes of thought, or analyze their methods of arriving at results. The intuitive perceptions derived from inheritance or long personal experience are of coalescent quality, and are of too rapid awakening to be capable of explanation and record in consciousness. The most original thinkers are, therefore, seldom gifted with the teaching-talent; just as orators and statesmen are not often eminent as authorities in elocution or political economy. Few of the ways and means of intellectual acumen can be reduced to rule and definitely expressed, yet the error is perennial of regarding logic as reason, and calculations, necessarily imperfect from the extent and complexity of the forces at work, as sound judgment.
The modern view that human intelligence is due to the experiences of the race organized in the brain gives an explanation to a very interesting group of facts. When the education of an individual is totally unlike that received by his line of progenitors, it cannot take deep root in his nature. Every conscientious Christian missionary laments the difficulty of making a really deep impression on a pagan mind. The momentum of ages cannot be changed in direction in a single-life, and, if it could, the pledges of human progress, which after all are based on human permanence, would be done away. In the conflict between inherited instincts and personally-acquired convictions, it is as if the man were attempting to fight all his ancestry at once, and he is usually worsted in the fray. Natural historians are familiar with the survival in animals of habits once useful to them in the distant past, but in their changed conditions no longer so. Some reptiles now living on land possess the remnants of organs once used in their perfection by their remote ancestry in aquatic life. In a somewhat parallel way, the superstitions of our progenitors persist in many persons of undoubted common-sense. Madame de Staël said, when asked if she believed in ghosts, "No, but I am afraid of them." When we consider the great problems of life and death in hours of calm reason, our reflections are apt to take a direction very different from that along which our instinctive feelings may impel us in seasons of pain and distress. It is a poor apology for a crude theological belief that our instincts declare it to be true, however much reason may contradict it. Instinct has no infallibility: in the human mind it is simply the register of thoughts and experiences during the long, primitive ages of our race; and our own opinions formed by personal accumulation since birth more probably point toward truth, than the lines of feeling laid down in our fibres in times of struggling intelligence and fierce strifes with natural powers, awful and unknown. In the conflict between instinct and reason, it would be strange indeed to contemn that reason which is only a better instinct than we have now, in the making. The study of race-impulses in an individual makes clear why it is that a man will do generous, heroic deeds, from which it is impossible for him to derive advantage. He acts as he does not from calculation, but from instinctive incitements inherited from parentage of noble blood; the line of race-benefit may not always coincide with that of individual good, but the impetus of ancestral forces transcends self-regard, and leaves the account of debit and credit apparently unbalanced. Not only are human instincts at times noble and heroic, but also, unfortunately more often, cruel and destructive. When a war breaks out, or any great public dissension arises, how speedily can the thin plating of civilization be abraded away, exposing the old barbarism of the under-nature! The sanguinary and destructive instincts of a people, once thoroughly let loose, can overturn in a few days a social fabric painfully wrought by generations. Of popular outbreaks of fury history has many terrible records, and none more so than of those revolts against order which, as in the French Revolution, had a core of justice in them. The natural differences among men in ability are very marked; much less so are their different capabilities of enjoying the rewards of skill and power: hence inevitably arise discontent and the ignoble spirit of envy; any artificial increase of the gulfs drawn by Nature between one man and another excites this discontent and envy by a conviction of injustice, and endangers order. From these causes the artificial enrichment of nobles and clergy by exemption from taxation has again and again deluged Europe with blood; and the enormous accumulations of property in private hands by bequest and increment have even in America excited concern. In considering this subject. Mill proposed that there should be a moderate limit to the amount one might legally receive by gifts and bequests; and the same thinker, and others of equal eminence, have declared their conviction that land shall at some future time, near or remote, be redistributed on some equitable plan.
The law of heredity has an important bearing, not only on questions of education and property, but also on the problem as to the best treatment of the criminal classes. Since the human character is so much dependent on inheritance, and so indelibly impressed by depraved associations in early life, it is thought that all incorrigible offenders, as soon as their state can be proved, should in some right way, by imprisonment or otherwise, be prevented from propagating their kind. Dr. Dugdale, of New York, followed the lines of descent from one Margaret Jukes, through six generations, including in all seven hundred and nine persons—thieves, prostitutes, murderers, and idiots. The Chinese so firmly believe depravity to be a taint of blood, that a criminal's father and grandfather are sometimes required to perish with him; conversely, this nation of ancestor-worshipers deem a man so much indebted to his parents for all that makes him great, that when a citizen is ennobled for eminent services, titles are bestowed upon the ascending line of the family, and not the descending, as with us.
Important as the relations of the law of heredity may be in the various topics adverted to in this paper, none can be so much so as the comprehension of the law, and obedience to it in marriage. The lower animals are carefully bred, while men and women mate with rarely any rational reflection as to their fitness for each other, thus often entailing upon themselves and their offspring woes unspeakable. The plain sense which should forbid the consumptive, syphilitic, or scrofulous, from marrying is disregarded, and the results are terrible. When one's constitution is impaired by some not serious organic ailment, special pains should be taken to avoid the like in selecting a partner for life. Physiologists deem consanguineous unions to result as badly as they often do from the parents inheriting from their one common stock similar weaknesses which unite in their children to form a lower deep of organic deficiency. With very good constitutions, men have been known to marry their sisters with impunity, as some of the Ptolemies did; but, when the stock of the Egyptian monarchs declined in soundness, their close intermarriages resulted in a rapid and frightful degeneracy.
Where there is no blood relationship between parents, they sometimes produce booby children, from having a too close temperamental similarity. The most trustworthy authorities on this subject say that in marriage a moderate difference between the constitutions and characters of the parties, and complementary rather than antagonistic, is best. A. noteworthy consideration in selecting a wife is, that as a mother has much more influence on a child's character than a father, if she has any marked bad trait, as a violent temper, laziness, or vanity, and if that trait be transmitted to her offspring, then the child will be brought up by a woman the least fit of her sex to recognize the child's faults, and eradicate them as far as possible by proper training. In the rearing of young children, close associations have great influence. A professor of McGill University assures me that the infants of his family acquire a resemblance to their nurse in expression, which only disappears when they are removed from her.
A happy and hopeful marriage may be marred in its results from procreation taking place while sickness, anxiety, or grief, has lowered vitality; and the too frequent bearing of children is very seriously detrimental to both mother and progeny.
When a parent transmits a malady, carefulness in living can frequently prevent its development; but when disease or predisposition to it is acquired from a parent together with the carelessness or self indulgence of character which originally induced the disease, then the taint of blood is confirmed and increased. Many persons of weak frame prolong life to old age by prudence and abstemiousness, whereas the conscious possession of a vigorous constitution is a constant temptation to abuses of it. Length of days depends less upon the quantity of vital energy received at birth, than on the jealous care of health and strength.
In these matters, as in all others, we not only need to know much, but to know it so long that we shall act upon our knowledge. The discrepancy between the intellectual acceptance of truth and moral obedience to it is wide as the gap between Ideal and Real.