Applied Eugenics Part 10

Prediction is possible only when uniform sequences are found. How are such sequences to be found in heredity, if they do not appear when a parent and his offspring are examined? Obviously it is necessary to examine _a large number_ of parents and their offspring,--to treat the problem by statistical methods.

But, it may be objected, a uniformity gained by such methods is spurious. It is merely shutting the eyes to the ma.s.s of contradictions which are concealed by an apparent statistical uniformity.

This objection would be valid, if the statistical results were used for prediction _in individual cases_. The statistician, however, expressly warns that his conclusions must not be used for such prediction. They are intended to predict only general trends, only average results; and for this purpose they are wholly legitimate. Moreover, evolution itself is a problem of statistics, and therefore the statistical method of studying heredity may offer results of great value to eugenics, even though it can not furnish in individual cases the prediction which would be desirable.

From this standpoint, we return to attack the problem of the relation between parent and offspring. We noted that there is no uniform sequence in a single family, and ill.u.s.trated this by the case of brown eyes. But if a thousand parents and their offspring be selected and some trait, such as eye-color, or stature, or general intelligence, be measured, a uniformity at once appears in the fact of regression. Its discoverer, Sir Francis Galton, gives this account of it:

[Ill.u.s.tration: FINGER-PRINTS OF TWINS

FIG. 25.--Above are the finger-prints, supplied by J. H. Taylor of the Navy Department, of the two young sailors shown in Fig. 24. The reader might examine them once or twice without seeing any differences.

Systematic comparison reveals that the thumbs of the left hands and the middle fingers of the right hands particularly are distinguishable.

Finger-prints as a means of identification were popularized by Sir Francis Galton, the founder of eugenics, and their superiority to all other methods is now generally admitted. In addition to this practical usefulness, they also furnish material for study of the geneticist and zoologist. The extent to which heredity is responsible for the patterns is indicated by the resemblance in pattern in spite of the great variability in this tract.]

"If the word 'peculiarity' be used to signify the difference between the amount of any faculty possessed by a man, and the average of that possessed by the population at large, then the law of regression may be described as follows: each peculiarity in a man is shared by his kinsmen, but on the _average_ in a less degree. It is reduced to a definite fraction of its amount, quite independently of what its amount might be. The fraction differs in different orders of kinship, becoming smaller as they are more remote. When the kinship is so distant that its effects are not worth taking into account, the peculiarity of the man, however remarkable it may have been, is reduced to zero in his kinsmen.

This apparent paradox is fundamentally due to the greater frequency of mediocre deviations than of extreme ones, occurring between limits separated by equal widths."

As to the application of this law, let Galton himself speak: "The Law of Regression tells heavily against the full hereditary transmission of any gift. Only a few out of many children would be likely to differ from mediocrity so widely as their Mid-Parent [i. e., the average of their two parents], allowing for s.e.xual differences, and still fewer would differ as widely as the more exceptional of the two parents. The more bountifully the parent is gifted by nature, the more rare will be his good fortune if he begets a son who is as richly endowed as himself, and still more so if he has a son who is endowed yet more largely. But the law is evenhanded; it levies an equal succession-tax on the transmission of badness as of goodness. If it discourages the extravagant hopes of a gifted parent that his children on the average will inherit all his powers, it not less discountenances extravagant fears that they will inherit all his weakness and disease.

"It must be clearly understood that there is nothing in these statements to invalidate the general doctrine that the children of a gifted pair are much more likely to be gifted than the children of a mediocre pair."

To this it should be added that progeny of very great ability will arise more frequently in proportion to the quality of their parents.

It must be reiterated that this is a statistical, not a biological, law; and that even Galton probably goes a little too far in applying it to individuals. It will hold good for a whole population, but not necessarily for only one family. Further, we can afford to reemphasize the fact that it in no way prevents the improvement of a race by selection and a.s.sortative mating.

Stature is the character which Dr. Galton used to get an exact measurement of the amount of regression. More recent studies have changed the value he found, without invalidating his method. When large numbers are taken it is now abundantly proved that if parents exceed the average stature of their race by a certain amount their offspring will, in general, exceed the racial average by only one-half as much as their parents did. This is due, as Galton said, to the "drag" of the more remote ancestry, which when considered as a whole must represent very nearly mediocrity, statistically speaking.

The general amount of regression in heredity, then, is one-half. If it be expressed as a decimal, .5, the reader will at once note its ident.i.ty with the coefficient of correlation which we have so often cited in this book as a measure of heredity. In fact, the coefficient of correlation is nothing more than a measure of the regression, and it is probably simpler to think of it as correlation than it is to speak of a Law of Regression, as Sir Francis did.

This correlation or regression can, of course, be measured for other ancestors as well as for the immediate parents. From studies of eye-color in man and coat-color in horses, Karl Pearson worked out the necessary correlations, which are usually referred to as the law of Ancestral Inheritance. Dr. Galton had pointed out, years before, that the contributions of the several generations of individuals probably formed a geometrical series, and Professor Pearson calculated this series, for the two cases mentioned, as:

Parents Grandparents G-Grandparents G-G-Grandparents

.6244 .1988 .0630 .0202 ... etc.

In other words, the two parents, together, will on the average of a great many cases be found to have contributed a little more than three-fifths of the hereditary peculiarities of any given individual; the four grandparents will be found responsible for a little less than one-fifth, and the eight great-grandparents for about six hundredths, and so on, the contribution of each generation becoming smaller with ascent, but each one having, in the average of many cases, a certain definite though small influence, until infinity.

It can not be too strongly emphasized that this is a statistical law, not a biological law. It must not be applied to predict the character of the offspring of any one particular mating, for it might be highly misleading. It would be wholly unjustified, for example, to suppose that a certain man got three-tenths of his nature from his father, because the Law of Ancestral Heredity required it: in point of fact, he might get one-tenth or nine-tenths, none or all of a given trait. But, when dealing with a large population, the errors on one side balance the errors on the other, and the law is found, in the cases to which it has been applied, to express the facts.[51]

While, therefore, this Galton-Pearson law gives no advice in regard to individual marriages, it is yet of great value to applied eugenics. In the first place, it crystallizes the vague realization that remote ancestry is of much less importance than immediate ancestry, to an individual, while showing that every generation has a part in making a man what he is. In the second place, it is found, by mathematical reasoning which need not here be repeated, that the type of a population may be quickly changed by the mating of like with like; and that this newly established type may be maintained when not capable of further progress. Regression is not inevitable, for it may be overcome by selection.

To put the matter in a more concrete form, there is reason to think that if for a few generations superior people would marry only people on the average superior in like degree (superior in ancestry as well as individuality), a point would be reached where all the offspring would tend to be superior, mediocrities of the former type being eliminated; and this superiority could be maintained as long as care was taken to avoid mating with inferior. In other words, the Galton-Pearson Law gives statistical support for a belief that eugenic marriages will create an improved breed of men. And this, it seems to us, is the most important implication of that law for eugenics, although it is an implication that is generally ignored.

We do not propose to discuss further the laws of heredity; but it is likely that the reader who has made no other study of the subject may by this time find himself somewhat bewildered. "Can we talk only in generalities?" he may well ask; "Does eugenics know no laws of heredity that will guide me in the choice of a wife? I thought that was the purpose of eugenics!"

We reply: (1) The laws of heredity are vastly complicated in man by the complex nature of most of his characters. The definite way in which some abnormalities are inherited is known; but it has not been thought necessary to include an account of such facts in this work. They are set forth in other books, especially Davenport's _Heredity in Relation to Eugenics_. The knowledge of how such a trait as color-blindness is inherited may be of importance to one man out of a thousand in choosing a wife; but we are taking a broader view of eugenics than this. As far as the great ma.s.s of human characters go, they are, in our opinion, due to so many separately inheritable factors that it is not safe to dogmatize about exactly how they will behave in heredity. Such knowledge, desirable as it may be, is not necessary for race progress.

(2) But it is possible, with present knowledge, to say that human traits, mental as well as physical, are inherited, in a high degree.

Even before the final details as to the inheritance of all traits are worked out--a task that is never likely to be accomplished--there is ample material on which to base action for eugenics. The basal differences in the mental traits of man (and the physical as well, of course) are known to be due to heredity, and little modified by training. It is therefore possible to raise the level of the human race--the task of eugenics--by getting that half of the race which is, on the whole, superior in the traits that make for human progress and happiness, to contribute a larger proportion to the next generation than does the half which is on the whole inferior in that respect. Eugenics need know nothing more, and the smoke of controversy over the exact way in which some trait or other is inherited must not be allowed for an instant to obscure the known fact that the level can be raised.

CHAPTER VI

NATURAL SELECTION

Man has risen from the ape chiefly through the action of natural selection. Any scheme of conscious race betterment, then, should carefully examine nature's method, to learn to what extent it is still acting, and to what extent it may better be supplanted or a.s.sisted by methods of man's own invention.

Natural selection operates in two ways: (1) through a selective death-rate and (2) through a selective birth-rate. The first of these forms has often been considered the whole of natural selection, but wrongly. The second steadily gains in importance as an organism rises in the scale of evolution; until in man it is likely soon to dwarf the lethal factor into insignificance. For it is evident that the appalling slaughter of all but a few of the individuals born, which one usually a.s.sociates with the idea of natural selection, will take place only when the number of individuals born is very large. As the reproductive rate decreases, so does the death-rate, for a larger proportion of those born are able to find food and to escape enemies.

When considering man, one realizes at once that relatively few babies or adults starve to death. The selective death-rate therefore must include only those who are unable to escape their enemies; and while these enemies of the species, particularly certain microorganisms, still take a heavy toll from the race, the progress of science is likely to make it much smaller in the future.

The different aspects of natural selection may be cla.s.sified as follows:

{ Lethal { Sustentative { { Non-sustentative Natural selection { { Reproductive { s.e.xual { { Fecundal

The lethal factor is the one which Darwin himself most emphasized.

Obviously a race will be steadily improved, if the worst stock in it is cut off before it has a chance to reproduce, and if the best stock survives to perpetuate its kind. "This preservation of favourable individual differences and variations, and the destruction of those which are injurious, I have called natural selection, or the survival of the fittest," Darwin wrote; and he went on to show that the princ.i.p.al checks on increase were overcrowding, the difficulty of obtaining food, destruction by enemies, and the lethal effects of climate. These causes may be conveniently divided as in the above diagram, into sustentative and non-sustentative. The sustentative factor has acquired particular prominence in the human species, since Malthus wrote his essay on population--that essay which both Darwin and Wallace confess was the starting point of their discovery of natural selection.

There is a "constant tendency in all animated life to increase beyond the nourishment prepared for it," Malthus declared. "It is incontrovertibly true that there is no bound to the prolific plants and animals, but what is made by their crowding and interfering with each others' means of subsistence." His deduction is well known: that as man tends to increase in geometrical ratio, and can not hope to increase his food-supply more rapidly than in arithmetical ratio, the human race must eventually face starvation, unless the birth-rate be reduced.

Darwin was much impressed by this argument and ever since his time it has usually been the foundation for any discussion of natural selection.

Nevertheless it is partly false for all animals, as one of the authors showed[52] some years ago, since a species which regularly eats up all the food in sight is rare indeed; and it is of very little racial importance in the present-day evolution of man. Scarcity of food may put sufficient pressure on him to cause emigration, but rarely death. The importance of Malthus' argument to eugenics is too slight to warrant further discussion.

When the non-sustentative forms of lethal selection are considered, it is seen very clearly that man is not exempt from the workings of this law. A non-sustentative form of natural selection takes place through the destruction of the individual by some adverse feature of the environment, such as excessive cold, or bacteria; or by bodily deficiency; and it is independent of mere food-supply. W. F. R. Weldon showed by a long series of measurements, for example, that as the harbor of Plymouth, England, kept getting muddier, the crabs which lived in it kept getting narrower; those with the greatest frontal breadth filtered the water entering their gills least effectively, and died.

But, it was objected, man is above all this. He has gained the control of his own environment. The b.l.o.o.d.y hand of natural selection may fall on crabs: but surely you would not have us think that Man, the Lord of Creation, shares the same fate?

Biologists could hardly think otherwise. Statisticians were able to supply the needed proof. A selective death-rate in man can not only be demonstrated but it can be actually measured.

"The measure of the selective death-rate." says[53] Karl Pearson, to whom this achievement is due, "is extraordinarily simple. It consists in the fact that the inheritance of the length of life between parent and offspring is found statistically to be about one-third of the average inheritance of physical characters in man. This can only be due to the fact that the death of parent or of offspring in a certain number of cases is due to random and not to const.i.tutional causes." He arrived at the conclusion[54] that 60% of the deaths were selective, in the Quaker families which he was then studying. The exact proportion must vary in accordance with the nature of the material and the environment, but as A. Ploetz found at least 60% of the deaths to be selective in the European royal families and n.o.bility, where the environment is uniformly good, there is no reason to think that Professor Pearson's conclusion is invalid.

Dr. Ploetz[55] investigated the relation between length of life in parents, and infant mortality, in about 1,000 families including 5,500 children; half of these were from the n.o.bility and half from the peasantry. The results were of the same order in each case, indicating that environment is a much less important factor than many have been wont to suppose. After discussing Professor Pearson's work, he continued:

It seems to me that a simpler result can be reached from our material in the following way. Since the greater child-mortality of each of our cla.s.ses of children (divided according to the ages at death of their parents) indicates a higher mortality throughout the rest of their lives, the offspring of parents who die young will therefore be eliminated in a higher degree, that is, removed from the composition of the race, than will those whose parents died late. Now the elimination can be non-selective, falling on all sorts of const.i.tutions with the same frequency and degree. In that case it will of course have no connection with selection inside the race. Or it may be of a selective nature, falling on its victims because they differ from those who are not selected, in a way that makes them less capable of resisting the pressure of the environment, and avoiding its dangers. Then we speak of a selective process, of the elimination of the weaker and the survival of the stronger. Since in our examination of the various causes of the difference in infant mortality, in the various age-cla.s.ses of parents, we found no sufficient cause in the effects of the environment, which necessarily contains all the non-selective perils, but found the cause to be in the different const.i.tutions inherited by the children, we can not escape the conclusion that the differences in infant mortality which we observe indicate a strong process of natural selection.

Our tables also permit us to get an approximate idea of the extent of selection by death among children in the first five years of life. The minimum of infant mortality is reached among those children whose parents have attained 85 years of age. Since these represent the strongest const.i.tutions, the mortality of their children would appear to represent an absolute minimum, made up almost wholly of chance, non-selective, unavoidable deaths. As the number of children from marriages, both parties to which reached 85 years of age, is so small as to render any safe conclusions impossible, our only recourse is to take the children of the 85-year-old fathers and the children of the 85-year-old mothers, add them together, and strike an average. But we must recognize that the minimum so obtained is nevertheless still too large, because among the consorts of the long-lived fathers and mothers, some died early with the result of increasing the infant mortality.

The infant mortality with the 85-year-old fathers and mothers is found to be 11.2%-15.4%, average about 13%. The total child-mortality reaches 31-32%, of which the 13% make about 40%.

Accordingly at least 60%, and considering the above mentioned sources of error we may say two-thirds, of the child mortality is selective in character. That accords reasonably well with the 55-74% which Pearson found for the extent of selective deaths in his study.

In general, then, one may believe that more than a half of the persons who die nowadays, die because they were not fit by by nature (i. e., heredity) to survive under the conditions into which they were born.

They are the victims of lethal natural selection, nearly always of the non-sustentative type. As Karl Pearson says, "Every man who has lived through a hard winter, every man who has examined a mortality table, every man who has studied the history of nations has probably seen natural selection at work."

There is still another graphic way of seeing natural selection at work, by an examination of the infant mortality alone. Imagine a thousand babies coming into the world on a given day. It is known that under average American conditions more than one-tenth of them will die during the first year of life. Now if those who die at this time are the inherently weaker, then the death-rate among survivors ought to be correspondingly less during succeeding years, for many will have been cut down at once, who might otherwise have lingered for several years, although doomed to die before maturity. On the other hand, if only a few die during the first year, one might expect a proportionately greater number to die in succeeding years. If it is actually found that a high death-rate in the first year of life is a.s.sociated with a low death-rate in succeeding years, then there will be grounds for believing that natural selection is really cutting off the weaker and allowing the stronger to survive.

E. C. Snow[56] a.n.a.lyzed the infant mortality registration of parts of England and Prussia to determine whether any such conclusion was justified. His investigation met with many difficulties, and his results are not as clear-cut as could be desired, but he felt justified in concluding from them that "the general result can not be questioned.

Natural selection, in the form of a selective death-rate, is strongly operative in man in the early years of life. We a.s.sert with great confidence that a high mortality in infancy (the first two years of life) is followed by a correspondingly low mortality in childhood, and vice-versa.... Our work has led us to the conclusion that infant mortality _does_ effect a 'weeding out' of the unfit."