How to Live Part 29

These physical, mental and moral peculiarities are not scattered evenly through the population, but exist on certain family lines only.

For instance, one-tenth of the deaths that occur in the United States are from tuberculosis. But this does not mean that one-tenth of all families die of the disease. On the contrary, some families lose more than half their numbers from it, while other families lose almost none at all. The 10 per cent. is simply the average of all. The percentage is high among the Irish, and low among the Jews. Life insurance companies take consideration of this fact in examining applicants for insurance. A family history of tuberculosis counts against even a healthy applicant, not because of a belief that tuberculosis is directly inheritable, but because non-resistant types, especially light-weights, are known to be transmitted. A profound influence toward checking this malady would evidently be exerted if the matings on the family lines exhibiting the characteristic of susceptibility were to cease, and thus the perpetuation of susceptible types checked.

The same is true of crime. The 80,000 prisoners constantly supported in the United States are recruited not evenly from the general population, but mainly from certain family breeds.[59] Criminality among "The Jukes" is a rule, among Jonathan Edwards' descendants, the exception.

The same is true of mental abilities of different kinds. Galton showed that the prominent English judges, statesmen, chancellors, etc., were furnished by certain family lines only, and were not drawn evenly from all families.[60] The same is true of feeble-mindedness.[61]

[Sidenote: Socially n.o.ble and Ign.o.ble Traits]

The question of what traits are desirable and what traits are undesirable might seem, on first thought, rather a difficult matter to determine. Few of us would like to have our neighbor's taste in the matter const.i.tuted as a standard of judgment upon our own traits. There is one standard of judgment, however, that is so broad and impersonal and so founded on the elements in society to which all individuals are subject, that it can justly serve as a line of division between the desirability and undesirability, broadly speaking, of individual traits for perpetuation. This is the measurement by the standard of social worth and service commonly designated as "fitness."[62] Above this dividing line may be roughly grouped the genius, the specially skilled, the mediocre, who are a service to society, or at least not a burden.

Below this line may be grouped those feeble-minded, paupers, criminals, insane, weak and sick, who are a burden, economically and socially. That is, a person's traits are desirable of perpetuation if so balanced as to render the individual not a burden to others.

It must undoubtedly be true that many families possess, inherently, traits of ability which have never had an opportunity to exhibit themselves. This may account for the apparently sudden appearance of great men and women without obvious hereditary background. It is plainly possible, furthermore, to bring about a special combination of two family lines, the mental traits on neither of which exhibit remarkableness, but which, when combined, bring an extremely happy result.

Mental ability does not depend upon education. Education can only enable an individual to utilize more fully his inherent ability; it cannot increase capacity.

The same is true, of course, of physical capacity. Sandow has an extraordinary muscular ability, developed by certain exercises. Similar exercises will not, however, develop all men into Sandows, no matter how constant their faith and persistent their efforts. Sandow was, we may a.s.sume, hereditarily gifted with a superior muscular capacity, which his exercises have enabled him to fully develop. It is true, however, that few people ever realize their full physical and mental capacities, owing to lack of opportunity, inclination, etc., and that there generally exist untold possibilities for improvement for those who wish to get the most out of themselves.

[Sidenote: A Majority of Sterling Traits]

It is apparent that the make-up of an individual is the result of a very complex combination of traits. For this reason, the makeup is not likely to fall heir to all "bad" traits, any more than it is to all "good"

traits. Even the feeble-minded, who have fallen heir to such an intensely undesirable trait--or rather, to the lack of intensely desirable traits--in many instances have simultaneously inherited many desirable traits, such as kindness, gentleness and generosity, often lacking in those possessed of scholarly capacities. Many women of the border-line type of feeble-mindedness, where mental incapacity often pa.s.ses for innocence, possess the qualities of charm felt in children, and are consequently quickly selected in marriage. If a mentally able man possess as an ideal of womanhood other traits than mental capacity, no amount of schooling for his child can make up for the difference between the mental capacity of the offspring of such a mating, and the offspring of a mating with an able-minded woman. Although the trait of able-mindedness is dominant, so that the mating of an able and a feeble mind will result in fairly able-minded offspring, who may even be above the average, mentally, such offspring carry in their own germ plasm the defect derived from their feeble-minded parent, which defect may then be pa.s.sed on to future generations through the germ plasm from which their children get their inheritance. A mother's hereditary influence on the child is just as important a factor as the father's, generally speaking.

Where feeble-mindedness exists on a family line, care should be exercised by the able-minded members of that line not to mate with another line possessing cases of feeble-mindedness, lest the offspring then fall heir to feeble-mindedness, which can skip a generation. An appreciation of what is feeble-minded, and a realization of its inheritability can not help but modify a man or a woman's admiration for the traits or lack of traits which it embraces.

Persons possessing weak physical makeups may possess strong mental capacities, and vice-versa. Persons of superior mental capacities may lack loftiness of character. It might happen that in so mating as to prevent the perpetuation of an undesirable trait, physical, mental or moral, a desirable trait would be lost along with it. In any mating transaction, therefore, choice must necessarily compromise upon the favorable hereditary action of a majority of the traits on the two family lines. One must relinquish any quest for perfection. After eliminating the individuals possessing the grossly unsocial traits below the dividing line of social fitness, one must choose with respect to a majority of socially fit traits, in addition to the elements of personal congeniality and affinity. The two last-named elements, however, generally serve as useful narcotics in blinding the mating individuals to the existence of the compromise, and the real becomes the ideal.

[Sidenote: Successive Generations and Fraternities]

Each trait in the mosaic of one person is transmitted or not transmitted to a child according to the mating of that particular trait--mating with trait or lack of trait--rather than according to the mating of the two persons as a whole. That is, when a man and woman marry and bear offspring, it is not the mating of two units, but it is the mating of myriads of pairs of units--the units being the const.i.tuent traits and lack of traits (contained in some mysterious way in the germ plasm), each trait-mating producing its own trait-offspring. The collection of these trait-offspring makes up the child.

It has been observed that traits differ with respect to their action in mating. Given a specific type of trait-mating, say of a trait with like trait, or trait with the lack of that trait, some types always reappear in the next generation or else are lost entirely from the family line unless reinfused, whereas other types of traits may not reappear in the next generation, but still appear in a generation further removed.

Another type of trait is transmissible only by one s.e.x of a family line, and can not be transmitted by the other s.e.x.

From these facts, it is readily understandable how important becomes the consideration of the marriage of relatives, such as cousins,[63] who are, of course, individuals of the same family line, whose mating brings together like groups of traits, thus strengthening the existence of these traits, whether desirable or undesirable. Cousin marriages, when the family possess traits of mental ability, may result in children who are geniuses; but cousin marriages, when the family line possesses traits of mental inability, may result disastrously with respect to offspring. Family lines possessing traits of mental weakness should most a.s.suredly join only to family lines possessing traits of strength in those regards.

In calculating the inheritability of traits, it is also necessary to consider that certain physical, mental and moral traits flower at the arrival of certain ages only. It is necessary to look along the whole line of a life, as traits may exist at one age and not at another. A boy's beard does not appear until p.u.b.erty. Likewise, other physical and mental and moral traits sometimes do not manifest themselves until specific ages, according to the type of the family breed. Because a parent dies before the development of the trait does not preclude its transmissibility to his offspring. Huntington's ch.o.r.ea, an extremely undesirable trait, does not develop until middle life, but is transmissible to offspring even though the father dies from some other cause before the period when the disease in his own person would be expected to appear.

[Sidenote: Results of Specific Matings]

[Sidenote: Andalusian Fowl]

We can best understand the laws governing the inheritance of traits by taking a few concrete cases. The first case is that of an Andalusian fowl. We shall consider the two species, pure bred black and pure bred white, and confine ourselves to observing the inheritance of the single characteristic, plumage _color_. Of course, as long as the black mate only with the black their children will be black, and as long as the white mate with white the children will be white. But if a white mates with a black, the children will not be either black or white, but blue.

All will be blue. But the most interesting facts appear in the next generation, when these hybrid blue fowls mate with black or white, or with each other. The original of the cross between the white and the black is an entirely new color blue, which may be considered a sort of amalgam of black and white. But a cross between the blue and the black will not be any new color, but will be either black or blue--and the chances are even. That is, in the long run about half of the children of the blue and black parents will be blue and half will be black. None of the children will be white. So also crossing the blue with the white will result in half of the children being blue and half, white. Still more curious is the result of mating blue with blue. One might imagine that in this case all the children would be blue, but only half will be blue, while a quarter will be black and a quarter white.

[Sidenote: Laws of Chance]

These laws are a curious mixture of chance and certainty. In certain circ.u.mstances, as we have seen, we can predict with certainty that the offspring will be black, white, blue, or whatever the case may be. In other circ.u.mstances we can only state what the _chances_ are. But these chances can be definitely stated as one in two, one in four or whatever it may be, and where there are large numbers of offspring this amounts to a practical certainty that definite proportions will have this or that color, or other characteristics.

Two parents are like two baskets or bundles of traits from which the child takes its traits at random. In the wonderful play of Maeterlinck's, called the "Bluebird," we are taken to the "land before birth," where the children are waiting to be born, having selected their parents to be. Of course, this is only a pleasant fancy, like the advice of Oliver Wendell Holmes to children to choose good grandparents, but it is a useful fancy which will help us to understand the laws of heredity. The child of the Andalusian fowl takes its color from its two parents on the same principle as a lottery in which it would take two beans, white or black as the case might be, from each of two baskets.

Every individual is a sort of basket containing two beans, as it were.

It took one of these two beans from each parent and will give one to each child.

With this picture of a bean lottery before us it is very easy to understand how the colors of Andalusian fowls are inherited. When two black fowls mate, the offspring must be black, because in this case each parent basket contains a pair of black beans, so to speak, so that the child taking one black bean from each basket will necessarily have a black pair. For the same reason the child of two white fowls must be white, but when a black and white fowl mate, the child takes a white bean from one parent and a black from the other, its own color being resultant or amalgam of the two, which in the case of the Andalusian fowl is blue. Since every such hybrid child has this same combination of a white and a black bean, all these hybrids are alike. All are blue. It is important to remember that this hybrid blue is only a sort of mechanical mixture of black and white, and that the black and white are still separate beans, as it were.

But now suppose a hybrid or blue fowl to mate with a white. This means that the child takes from the white parent or basket one of the two white beans and from the blue parent or basket, one of the two beans, of which one is white and the other, black; the bean taken from the first or white basket must be white, but that taken from the second or blue or hybrid basket may be either white or black. It is a lottery with an even chance of drawing white or black. In the long run, half of the children will draw white and half, black. Those which draw the white will, since they also drew white from the other parent, be wholly white, but those which drew the black will be blue, since they will have one black and one white bean. We see, too, that the white child is just as truly white as though it had not had a hybrid parent; for of the two elements or beans which the hybrid carried, the black one was left behind untaken.

We see that the blue child is a hybrid exactly like its hybrid parent, and not any new kind of cross between the blue and the white. In short, the children of a blue and white are either the one or the other and not a mixture. In the same way if a blue mates with a black, half of the children will be black and half blue.

Finally we come to the mating of a blue with a blue. Here the lottery is to pick a bean from two baskets, each basket containing both white and black beans in equal numbers. When at random one is taken from either of these two baskets there is an even chance that the bean from the father is white or black and an even chance that the bean from the mother is white or black.

Now, what is the chance that the child draws a white bean from both baskets? Evidently it is one chance in four; for there are four ways equally probable in which you can take these beans, viz.: (1) black from the father basket and black from the mother, (2) white from the father and white from the mother, (3) white from the father and black from the mother, (4) black from the father and white from the mother. So the children could draw both white once in four times, both black once in four, and a white and a black in the other two cases. And that is why from two blue Andalusian fowls, on the average you will have one-quarter of the children black, one-quarter white, and the other two-quarters, blue. Again let us stop to emphasize the fact that the black children of these hybrids are just as pure blooded as their black grandparent, and will mate with other pure-blooded black in exactly the same way as though there had never been any white in their ancestry. The white strain has been left behind, or been "bred out."

We have spoken of one character or characteristic--color. The same laws apply to other characters. Often different characters are inherited quite independently of one another. Each of us is a basket or bundle of very many qualities, each quality being a little compartment of the basket with two beans in it. There is, as it were, a pair of beans for every unit trait, whether that trait relates to color, to musical ability, or to any one of hundreds of other kinds.

To summarize the laws of inheritance of the unit character called color, in Andalusian fowl, we have really six ways in which we can consider mating of the three colored fowls (black, white, blue): (1) black may mate with black, in which case all the offspring will be black, (2) white may mate with white, in which case all the offspring will be white, (3) a black may mate with a white, in which case the offspring will all be blue--a hybrid containing both black and blue elements, (4) blue may mate with a black, in which case half the offspring will be pure bred black, and half hybrid blue, (5) a blue may mate with a white, in which case half the offspring will be white and half blue, (6) blue may mate with blue in which case a quarter of the offspring will be white, a quarter black and a half blue.

[Sidenote: Guinea Pigs]

These results are the fundamental laws discovered by Mendel. But the results are not always as clear as in the case of the Andalusian fowl.

In that case the hybrids were not like either parent, but were a new color, blue, so that they were labeled at once and recognizable as hybrids--but this is not generally the case. Take, for instance, guinea pigs. What will be the result of mating an "albino" white with a black guinea pig? Quite exactly the same principle applies as in the case of the Andalusian fowl, but the principle is not as clear to see. All the offspring are hybrid, but they will not be blue: they will be black.

They will look like the black parent, but they are different. The black color predominates; i.e., black is "dominant" over white, while the white recedes out of sight, or is "recessive." This hybrid black guinea pig is like the hybrid blue Andalusian fowl. It is a hybrid, a combination of white and black, but in the guinea pig the black covers up the white so that _nothing_ in the color reveals the fact that it is a hybrid. Now if the hybrid black offspring of these black and white guinea pigs mate with each other, the result will follow exactly the same Mendelian law as applied to the Andalusian fowl. But this will not be so clear, because now we have two kinds of black instead of a black and a blue. One child in four will be _pure bred_ black like the grandparent and two out of the four will be _hybrid_ black. So to the eye we shall simply have, out of four children, one white and three black. But those three black are not all alike. One is a thoroughbred and two are half-breeds.

But how then are we to distinguish between the one pure bred black, the thoroughbred, and the two blacks that are hybrids so that we can be sure which is which? The only way they can be distinguished is to wait to see what their offspring will be in the next succeeding generations.

The one that is a thoroughbred will behave like a thoroughbred. For instance, if mated with white they will have nothing but black children.

But if one that is hybrid black mate with one that is white, only half of the children will be white; these white children reveal the fact that their black parent was a half breed. Then we can put a tag on that black parent. If proper tags are put on the blacks so as to distinguish between the pure-blooded and the half-blooded--say a blue tag on the hybrids and a black on the thoroughbreds--we shall get exactly the same results as described in the case of the Andalusian fowl, in the six cases mentioned. The same principles apply to qualities of the guinea pigs other than color. Thus, if a long-haired guinea pig mates with a short-haired guinea pig, all the offspring will be short-haired, because short hair is dominant over long hair. Again, if a smooth-coated guinea pig mates with a rough-coated one, the result will be rough coated, because a rough coat is dominant over a smooth coat.

[Sidenote: "Thoroughbred" Humans]

The same principles undoubtedly apply to the human race, although as yet only a few traits have been carefully studied. Eye color is one of these. Imagine a marriage of a thoroughbred, black-eyed Italian with a thoroughbred, blue-eyed Irish. What will be the result? All the children will be black-eyed, black being dominant over blue; but these black eyes are not the genuine article that the Italian parent possessed. They are a blend, and it is only because the black element dominates over or conceals the blue element that we can not see on the surface that there is any blue there. But it may come out in the next generation; for, if these half-blooded individuals marry among themselves one-quarter of their children on the average will be blue-eyed. The other three-quarters will be black-eyed, but only one-quarter will be "really and truly" black-eyed, i.e., black-eyed like the Italian. The remaining half are hybrid black, like the parents. It is only a sort of imitation black so to speak.

The appearance of blue eyes in the second generation is the long observed but formerly mysterious "atavism," or reversion to the grandparent.

Suppose the children of an Italian and an Irish parent intermarry with pure bred Italians. We immediately know what will be the result. All the children will be black-eyed, but among a large number only half will be thoroughbred black-eyed. The other half will be "imitation" black-eyed.

The case is just like the mating of hybrid black guinea pigs with thoroughbred black guinea pigs, or of the blue fowl with the black.

Similarly, if the Irish-Italian hybrids marry with pure Irish, half the offspring will be blue-eyed and half will be hybrid black-eyed.

[Sidenote: Dominants and Recessives]

Black eyes are "dominant" over blue eyes because the black color is due to a pigment, while the blue color is due to the absence of this pigment. In general a quality which is due to the presence of some positive element is dominant over a quality due to the absence of that element. A child inheriting from a blue-eyed person simply draws a blank from that side in the lottery.

In order to understand how these principles of Mendel apply in any given case we need first to know what traits are "dominant" and what are "recessive."

Among traits known to be "dominant" are, besides pigmentation of the eye, certain peculiarities of the skeleton, such as short-fingeredness (two phalanges only on each digit), Huntington's ch.o.r.ea, presenile cataract, congenital thickening of the skin, early absence of hair, diabetes insipidus, stationary night-blindness, liability to periodic outbreak of temper, etc.

Among traits known to be "recessive" are albinism (or lack of pigmentation), a certain degenerative disease of the eye, deafmutism, imbecility, insanity of certain types, certain nervous diseases; also mental traits, such as musical ability.

Suppose now that a normal or "strong-minded" person, if we may use that term as distinct from feeble-minded, marries a feeble-minded person.

a.s.suming that the "strong-minded" person is a "thoroughbred" all of the children will be apparently normal. None will be feeble-minded.

"Strong-mindedness" is dominant over weak-mindedness. Yet all these children that seem to be perfectly normal lack something in their bodies. This deficiency is simply covered up but can crop out in later generations. If two of these hybrids between the weak-minded and the strong-minded marry each other, one-quarter of the children will be feeble-minded, one-quarter thoroughbred strong-minded and the remaining half, though apparently strong-minded, will carry the taint in them just as their parents did. They are half-breeds. On the other hand, if two feeble-minded people marry, all of the children will be feeble-minded.

Certainly we can and ought to forbid and prevent such marriages.