No More Learning

Of course, few of the cases now credited are as gross as this, but the
principle involved remains the same.

We will take a hypothetical case of a common sort for the sake of
clearness: the mother receives a wound on the arm; when her child is
born it is found to have a scar of some sort at about the same place on
the corresponding arm. Few mothers would fail to see the result of a
maternal impression here. But how could this mark have been transmitted?
This is not a question of the transmission of acquired characters
through the germ-plasm, or anything of that sort, for the child was
already formed when the mother was injured. One is obliged, therefore,
to believe that the injury was in some way transmitted through the
placenta, the only connection between the mother and the unborn child;
and that it was then reproduced in some way in the child.

Here is a situation which, examined in the cold light of reason, puts a
heavy enough strain on the credulity. Such an influence can reach the
embryo only through the blood of the mother. Is it conceivable to any
rational human being, that a scar, or what not, on the mother's body can
be dissolved in her blood, pass through the placenta into the child's
circulation, and then gather itself together into a definite scar on the
infant's arm?

There is just as much reason to expect the child to grow to resemble the
cow on whose milk it is fed after birth, as to expect it to grow to
resemble its mother, because of prenatal influence, as the term is
customarily used, for once development has begun, the child draws
nothing more than nourishment from its mother.

Of course we are accustomed to the pious rejoinder that man must not
expect to understand all the mysteries of life; and to hear vague talk
about the wonder of wireless telegraphy. But wireless telegraphy is
something very definite and tangible--there is little mystery about it.
Waves of a given frequency are sent off, and caught by an instrument
attuned to the same frequency. How any rational person can support a
belief in maternal impressions by such an analogy, if he knows anything
about anatomy and physiology, passes comprehension.

Now we are far from declaring that a reason can be found for everything
that happens. Science does not refuse belief in an observed fact merely
because it is unexplainable. But let us examine this case of maternal
impressions a little further. What can be learned of the time element?

Immediately arises the significant fact that most of the marks,
deformities and other effects which are credited to prenatal influence
must on this hypothesis take place at a comparatively late period in the
antenatal life of the child. The mother is frightened by a dog; the
child is born with a dog-face. If it be asked when her fright occurred,
it is usually found that it was not earlier than the third month, more
likely somewhere near the sixth.

But it ought to be well known that the development of all the main parts
of the body has been completed at the end of the second month. At that
time, the mother rarely does more than suspect the coming of the child,
and events which she believes to "mark" the child, usually occur after
the fourth or fifth month, when the child is substantially formed, and
it is impossible that many of the effects supposed to occur could
actually occur. Indeed, it is now believed that most errors of
development, such as lead to the production of great physical defects,
are due to some cause within the embryo itself, and that most of them
take place in the first three or four weeks, when the mother is by no
means likely to influence the course of embryological development by her
mental attitude toward it, for the very good reason that she knows
nothing about it.

Unless she is immured or isolated from the world, nearly every expectant
mother sees many sights of the kind that, according to popular
tradition, cause "marks. " Why is it that results are so few? Why is it
that women doctors and nurses, who are constantly exposed to unpleasant
sights, have children that do not differ from those of other mothers?

Darwin, who knew how to think scientifically, saw that this is the
logical line of proof or disproof. When Sir Joseph Hooker, the botanist
and geologist who was his closest friend, wrote of a supposed case of
maternal impression, one of his kinswomen having insisted that a mole
which appeared on her child was the effect of fright upon herself for
having, before the birth of the child, blotted with sepia a copy of
Turner's _Liber Studiorum_ that had been lent her with special
injunctions to be careful, Darwin[27] replied: "I should be very much
obliged, if at any future or leisure time you could tell me on what you
ground your doubtful belief in imagination of a mother affecting her
offspring. I have attended to the several statements scattered about,
but do not believe in more than accidental coincidences. W. Hunter told
my father, then in a lying-in hospital, that in many thousand cases he
had asked the mother, before her confinement, whether anything had
affected her imagination, and recorded the answers; and absolutely not
one case came right, though, when the child was anything remarkable,
they afterwards made the cap to fit. "

Any doctor who has handled many maternity cases can call to mind
instances where every condition was present to perfection, for the
production of maternal impression, on the time-honored lines. None
occurred. Most mothers can, if they give the matter careful
consideration, duplicate this experience from their own. Why is it that
results are so rare?

That Darwin gave the true explanation of a great many of the alleged
cases is perfectly clear to us. When the child is born with any peculiar
characteristic, the mother hunts for some experience in the preceding
months that might explain it. If she succeeds in finding any experience
of her own at all resembling in its effects the effect which the infant
shows, she considers she has proved causation, has established a good
case of prenatal influence.

It is not causation; it is coincidence.

If the prospective mother plays or sings a great deal, with the idea of
giving her child a musical endowment, and the child actually turns out
to have musical talent, the mother at once recalls her yearning that
such might be the case; her assiduous practice which she hoped would be
of benefit to her child. She immediately decides that it did benefit
him, and she becomes a convinced witness to the belief in prenatal
culture. Has she not herself demonstrated it?

She has not. But if she would examine the child's heredity, she would
probably find a taste for music running in the germ-plasm. Her study and
practice had not the slightest effect on this hereditary disposition; it
is equally certain that the child would have been born with a taste for
music if its mother had devoted eight hours a day for nine months to
cultivating thoughts of hatred for the musical profession and repugnance
for everything that possesses rhythm or harmony.

It necessarily follows, then, that attempts to influence the inherent
nature of the child, physically or mentally, through "prenatal culture,"
are doomed to disappointment. The child develops along the lines of the
potentialities which existed in the two germ-cells that united to become
its origin. The course of its development can not be changed in any
specific way by any corresponding act or attitude of its mother, good
hygiene alone need be her concern.

It must necessarily follow that attempts to improve the race on a large
scale, by the general adoption of prenatal culture as an instrument of
eugenics, are useless.

Indeed, the logical implication of the teaching is the reverse of
eugenic. It would give a woman reason to think she might marry a man
whose heredity was most objectionable, and yet, by prenatal culture,
save her children from paying the inevitable penalty of this weak
heritage. The world has long shuddered over the future of the girl who
marries a man to reform him; but think what it means to the future of
the race if a superior girl, armed with correspondence school lessons in
prenatal culture, marries a man to reform his children!

Those who practice this doctrine are doomed to disillusion. The time
they spend on prenatal culture is not cultivating the child; it is
merely perpetuating a fallacy. Not only is their time thus spent
wasted, but worse, for they might have employed it in ways that really
would have benefited the child--in open-air exercise, for instance.

To recapitulate, the facts are:

(1) That there is, before birth, no connection between mother and child,
by which impressions on the mother's mind or body could be transmitted
to the child's mind or body.

(2) That in most cases the marks or defects whose origin is attributed
to maternal impression, must necessarily have been complete long before
the incident occurred which the mother, after the child's birth,
ascribes as the cause.

(3) That these phenomena usually do not occur when they are, and by
hypothesis ought to be, expected. The explanations are found after the
event, and that is regarded as causation which is really coincidence.

Pre-natal care as a euthenic measure is of course not only legitimate
but urgent. The embryo derives its entire nourishment from the mother;
and its development depends wholly on its supply of nourishment.
Anything which affects the supply of nourishment will affect the embryo
in a general, not a particular way. If the mother's mental and physical
condition be good, the supply of nourishment to the embryo is likely to
be good, and development will be normal. If, on the other hand, the
mother is constantly harassed by fear or hatred, her physical health
will suffer, she will be unable properly to nourish her developing
offspring, and it may be its poor physical condition when born,
indicates this.

Further, if the mother experiences a great mental or physical shock, it
may so upset her health that her child is not properly nourished, its
development is arrested, mentally as well as physically, and it is born
defective. H. H. Goddard, for example, tells[28] of a high-grade
imbecile in the Training School at Vineland, N. J. "Nancy belongs to a
thoroughly normal, respectable family. There is nothing to account for
the condition unless one accepts the mother's theory. While it sounds
somewhat like the discarded theory of maternal impression, yet it is not
impossible that the fright and shock which the mother received may have
interfered with the nutrition of the unborn child and resulted in the
mental defect. The story in brief is as follows. Shortly before this
child was born, the mother was compelled to take care of a sister-in-law
who was in a similar condition and very ill with convulsions. Our
child's mother was many times frightened severely as her sister-in-law
was quite out of her mind. "

It is easily understandable that any event which makes such an
impression on the mother as to affect her health, might so disturb the
normal functioning of her body that her child would be badly nourished,
or even poisoned. Such facts undoubtedly form the basis on which the
airy fabric of prenatal culture was reared by those who lived before the
days of scientific biology.

Thus, it is easy enough to see the real explanation of such cases as
those mentioned near the beginning of this discussion. The mothers who
fret and rebel over their maternity, she found, are likely to bear
neurotic children. It is obvious (1) that mothers who fret and rebel are
quite likely themselves to be neurotic in constitution, and the child
naturally gets its heredity from them: (2) that constant fretting and
rebellion would so affect the mother's health that her child would not
be properly nourished.

When, however, she goes on to draw the inference that "self-control,
cheerfulness and love . . . will practically insure you a child normal in
physique and nerves," we are obliged to stop. We know that what she says
is not true. If the child's heredity is bad, neither self-control,
cheerfulness, love, nor anything else known to science, can make that
heredity good.

At first thought, one may wish it were otherwise. There is something
inspiring in the idea of a mother overcoming the effect of heredity by
the sheer force of her own will-power. But perhaps in the long run it is
as well; for there are advantages on the other side. It should be a
satisfaction to mothers to know that their children will not be marked
or injured by untoward events in the antenatal days; that if the
child's heredity can not be changed for the better, neither can it be
changed for the worse.

The prenatal culturists and maternal-impressionists are trying to place
on her a responsibility which she need not bear. Obviously, it is the
mother who is most nearly concerned with the bogy of maternal
impressions, and it should make for her peace of mind to know that it is
nothing more than a bogy. It is important for the expectant mother to
keep herself in as nearly perfect condition as possible, both physically
and mentally. Her bodily mechanism will then run smoothly, and the child
will get from her blood the nourishment needed for its development.
Beyond that there is nothing the mother can do to influence the
development of her child.

There is another and somewhat similar fallacy which deserves a passing
word, although it is of more concern to the livestock breeder than to
the eugenist. It is called telegony and is, briefly, this: that
conception by a female results in a definite modification of her
germ-plasm from the influence of the male, and that this modification
will be shown in the offspring she may subsequently bear to a second
male. The only case where it is often invoked in the human race is in
miscegenation. A white woman has been married to a Negro, for instance,
and has borne one or more mulatto offspring. Subsequently, she mates
with a white man; but her children by him, instead of being pure white,
it is alleged, will be also mulattoes. The idea of telegony, the
persistent influence of the first mating, may be invoked to explain this
discrepancy.

It is a pure myth. There is no good evidence[29] to support it, and
there is abundant evidence to contradict it. Telegony is still believed
by many animal breeders, but it has no place in science. In such a case
as the one quoted, the explanation is undoubtedly that the supposed
father is not the real one; and this explanation will dispose of all
other cases of telegony which can not be explained, as in most instances
they can be, by the mixed ancestry of the offspring and the innate
tendency of all living things to vary.

Now to sum up this long chapter. We started with a consideration of the
germ-plasm, the physical basis of life; pointing out that it is
continuous from generation to generation, and potentially immortal; that
it is carefully isolated and guarded in the body, so that it is not
likely to be injured by any ordinary means.

One of the logical results of this continuity of the germ-plasm is that
modifications of the body of the parent, or acquired characters, can
hardly be transferred to the germ-plasm and become a part of the
inheritance. Further the experimental evidence upholds this position,
and the inheritance of acquired body characters may be disregarded by
eugenics, which is therefore obliged to concern itself solely with the
material already in existence in the germ-plasm, except as that material
may be changed by variation which can neither be predicted nor
controlled.

The evidence that the germ-plasm can be permanently modified does not
warrant the belief; and such results, if they exist at all, are not
large enough or uniform enough to concern the eugenist.

Pre-natal culture and telegony were found to be mere delusions. There is
no justification for hoping to influence the race for good through the
action of any kind of external influences; and there is not much danger
of influencing it for ill through these external influences. The
situation must be faced squarely then: if the race is to be improved, it
must be by the use of the material already in existence; by endeavor to
change the birth-and death-rates so as to alter the relative proportions
of the amounts of good and bad germ-plasm in the race. This is the only
road by which the goal of eugenics can be reached.




CHAPTER III

DIFFERENCES AMONG MEN


While Mr. Jefferson, when he wrote into the Declaration of Independence
his belief in the self-evidence of the truth that all men are created
equal, may have been thinking of legal rights merely, he was expressing
an opinion common among philosophers of his time. J. J. Rousseau it was
who made the idea popular, and it met with widespread acceptance for
many years. It is not surprising, therefore, that the phrase has long
been a favorite with the demagogue and the utopian. Even now the
doctrine is by no means dead. The American educational system is based
largely on this dogma, and much of the political system seems to be
grounded on it. It can be seen in the tenets of labor unions, in the
practice of many philanthropies--traces may be found almost anywhere one
turns, in fact.

Common enough as applied to mental qualities, the theory of human
equality is even more widely held of "moral" qualities. Men are
considered to be equally responsible for their conduct, and failure to
conform to the accepted code in this respect brings punishment. It is
sometimes conceded that men have had differing opportunities to learn
the principles of morality; but given equal opportunities, it is almost
universally held that failure to follow the principles indicates not
inability but unwillingness. In short, public opinion rarely admits that
men may differ in their inherent capacity to act morally.

In view of its almost universal and unquestioned, although half
unconscious, acceptance as part of the structure of society, it becomes
of the utmost importance that this doctrine of human equality should be
examined by scientific methods.

Fortunately this can be done with ease. Methods of mental and physical
measurement that have been evolved during the last few decades offer
results that admit of no refutation, and they can be applied in hundreds
of different places.

[Illustration: DISTRIBUTION OF 10-YEAR-OLD SCHOOL CHILDREN

FIG. 8. --The graph shows that 10-year-old children in
Connecticut (1903) are to be found in every grade, from the first to the
eighth. The greatest number is in the fourth grade, and the number who
are advanced is just about the same as the number who are retarded. ]

It will not be worth while to spend any time demonstrating that all
individuals differ, at birth and during their subsequent life,
physically. The fact is patent to all. It carries with it as a necessary
corollary mental differences, since the brain is part of the body;
nevertheless, we shall demonstrate these mental differences
independently.

We present in Fig. 8 a graph from E. L. Thorndike, showing the number of
10-year-old children in Connecticut (1903) in each school grade. If the
children are all intellectually equal, all the 10-year-olds ought to be
in the same grade, or near it. Numerous explanations of their wide
distribution suggest themselves; as a working hypothesis one might adopt
the suggestion that it is because the children actually differ in innate
ability to the extent here indicated. This hypothesis can be tested by
a variety of mental measurements. S. A. Courtis' investigation of the
arithmetical abilities of the children in the schools of New York City
will be a good beginning. He measured the achievements of pupils in
responding to eight tests, which were believed to give a fair idea of
the pupil's capacity for solving simple arithmetical problems. The
results were, on the average, similar to the result he got in a certain
eighth-grade class, whose record is shown in Fig. 9. It is evident that
some of the children were good in arithmetic, some were poor in it; the
bulk of them were neither good nor bad but half way between, or, in
statistical language, mediocre.

[Illustration: VARIATION IN ABILITY

FIG. 9. --Diagram to show the standing of children in a single
class in a New York City school, in respect to their ability in
arithmetic. There are wide divergences in the scores they made. ]

The literature of experimental psychology and anthropology is crammed
with such examples as the above. No matter what trait of the individual
be chosen, results are analogous. If one takes the simplest traits, to
eliminate the most chances for confusion, one finds the same conditions
every time. Whether it be speed in marking off all the A's in a printed
sheet of capitals, or in putting together the pieces of a puzzle, or in
giving a reaction to some certain stimulus, or in making associations
between ideas, or drawing figures, or memory for various things, or
giving the opposites of words, or discrimination of lifted weights, or
success in any one of hundreds of other mental tests, the conclusion is
the same. There are wide differences in the abilities of individuals, no
two being alike, either mentally or physically, at birth or any time
thereafter.

[Illustration: ORIGIN OF A NORMAL PROBABILITY CURVE

FIG. 10. --When deviations in all directions are equally
probable, as in the case of shots fired at a target by an expert
marksman, the "frequencies" will arrange themselves in the manner shown
by the bullets in compartments above. A line drawn along the tops of
these columns would be a "normal probability curve. " Diagram by C. H.
Popenoe. ]

Whenever a large enough number of individuals is tested, these
differences arrange themselves in the same general form. It is the form
assumed by the distribution of any differences that are governed
absolutely by chance.

Suppose an expert marksman shoots a thousand times at the center of a
certain picket in a picket fence, and that there is no wind or any
other source of constant error that would distort his aim. In the long
run, the greatest number of his shots would be in the picket aimed at,
and of his misses there would be just as many on one side as on the
other, just as many above as below the center. Now if all the shots, as
they struck the fence, could drop into a box below, which had a
compartment for each picket, it would be found at the end of his
practice that the compartments were filled up unequally, most bullets
being in that representing the middle picket and least in the outside
ones. The intermediate compartments would have intermediate numbers of
bullets. The whole scheme is shown in Fig. 11. If a line be drawn to
connect the tops of all the columns of bullets, it will make a rough
curve or graph, which represents a typical chance distribution. It will
be evident to anyone that the distribution was really governed by
"chance," i. e. , a multiplicity of causes too complex to permit detailed
analysis. The imaginary sharp-shooter was an expert, and he was trying
to hit the same spot with each shot. The deviation from the center is
bound to be the same on all sides.

[Illustration: FIG. 11. --The "Chance" or "Probability" Form of
Distribution. ]

Now suppose a series of measurements of a thousand children be taken in,
let us say, the ability to do 18 problems in subtraction in 10 minutes.
A few of them finish only one problem in that time; a few more do two,
more still are able to complete three, and so on up. The great bulk of
the children get through from 8 to 12 problems in the allotted time; a
few finish the whole task. Now if we make a column for all those who did
one problem, another column beside it for all those who did two, and so
on up for those who did three, four and on to eighteen, a line drawn
over the tops of the columns make a curve like the above from
Thorndike.

Comparing this curve with the one formed by the marksman's spent
bullets, one can not help being struck by the similarity. If the first
represented a distribution governed purely by chance, it is evident that
the children's ability seems to be distributed in accordance with a
similar law.

With the limited number of categories used in this example, it would not
be possible to get a smooth curve, but only a kind of step pyramid. With
an increase in the number of categories, the steps become smaller. With
a hundred problems to work out, instead of 18, the curve would be
something like this:

[Illustration: FIG. 12. --Probability curve with increased
number of steps. ]

And with an infinite number, the steps would disappear altogether,
leaving a perfectly smooth, flowing line, unmarred by a single step or
break. It would be an absolutely _continuous_ distribution.

If then, the results of all the tests that have been made on all mental
traits be studied, it will be found that human mental ability as shown
in at least 95% of all the traits that have been measured, is
distributed throughout the race in various degrees, in accordance with
the law of chance, and that if one could measure all the members of the
species and plot a curve for these measurements, in any trait, he would
get this smooth, continuous curve. In other words, human beings are not
sharply divided into classes, but the differences between them shade off
into each other, although between the best and the worst, in any
respect, there is a great gulf.
If this statement applies to simple traits, such as memory for numbers,
it must also apply to combinations of simple traits in complex mental
processes. For practical purposes, we are therefore justified in saying
that in respect of any mental quality,--ability, industry, efficiency,
persistence, attentiveness, neatness, honesty, anything you like,--in
any large group of people, such as the white inhabitants of the United
States, some individuals will be found who show the character in
question in a very low degree, some who show it in a very high degree;
and there will be found every possible degree in between.

[Illustration: NORMAL VARIABILITY CURVE FOLLOWING LAW OF CHANCE

FIG. 13. --The above photograph (from A. F. Blakeslee), shows
beans rolling down an inclined plane and accumulating in compartments at
the base which are closed in front by glass. The exposure was long
enough to cause the moving beans to appear as caterpillar-like objects
hopping along the board. Assuming that the irregularity of shape of the
beans is such that each may make jumps toward the right or toward the
left, in rolling down the board, the laws of chance lead to the
expectation that in very few cases will these jumps all be in the same
direction, as is demonstrated by the few beans collected in the
compartments at the extreme right and left. Rather the beans will tend
to jump in both right and left directions, the most probable condition
being that in which the beans make an equal number of jumps to the right
and left, as is shown by the large number accumulated in the central
compartment. If the board be tilted to one side, the curve of beans
would be altered by this one-sided influence. In like fashion a series
of factors--either of environment or of heredity--if acting equally in
both favorable and unfavorable directions, will cause a group of men to
form a similar variability curve, when classified according to their
relative height. ]

The consequences of this for race progress are significant. Is it
desired to eliminate feeble-mindedness? Then it must be borne in mind
that there is no sharp distinction between feeble-mindedness and the
normal mind. One can not divide sheep from goats, saying "A is
feeble-minded. B is normal. C is feeble-minded. D is normal," and so on.
If one took a scale of a hundred numbers, letting 1 stand for an idiot
and 100 for a genius, one would find individuals corresponding to every
single number on the scale. The only course possible would be a somewhat
arbitrary one; say to consider every individual corresponding to a grade
under seven as feeble-minded. It would have to be recognized that those
graded eight were not much better than those graded seven, but the
drawing of the line at seven would be justified on the ground that it
had to be drawn somewhere, and seven seemed to be the most satisfactory
point.

In practice of course, students of retardation test children by
standardized scales. Testing a hundred 10-year-old children, the
examiner might find a number who were able to do only those tests which
are passed by a normal six-year-old child. He might properly decide to
put all who thus showed four years of retardation, in the class of
feeble-minded; and he might justifiably decide that those who tested
seven years (i. e. , three years mental retardation) or less would, for
the present, be given the benefit of the doubt, and classed among the
possibly normal. Such a procedure, in dealing with intelligence, is
necessary and justifiable, but its adoption must not blind students, as
it often does, to the fact that the distinction made is an arbitrary
one, and that there is no more a hard and fast line of demarcation
between imbeciles and normals than there is between "rich men" and "poor
men. "

[Illustration: CADETS ARRANGED TO SHOW NORMAL CURVE OF VARIABILITY

FIG. 14. --The above company of students at Connecticut
Agricultural College was grouped according to height and photographed by
A. F. Blakeslee. The height of each rank, and the number of men of that
height, is shown by the figures underneath the photograph. The company
constitutes what is technically known as a "population" grouped in
"arrays of variates"; the middle rank gives the median height of the
population; the tallest array (5 ft. , 8 in. ) is the mode. If a line be
drawn connecting the upper ends of the rows, the resulting geometric
figure will be a "scheme of distribution of variates" or more briefly a
"variability curve," such as was shown in several preceding figures. The
arrangement of homogeneous objects of any kind in such form as this is
the first step in the study of variation by modern statistical methods,
and on such study much of the progress of genetics depends. ]

[Illustration: FIG. 15. --Height is one of the stock examples of
a continuous character--one of which all grades can be found. As will be
seen from the above diagram, every height from considerably under five
feet to considerably over six feet can be found in the army, but extreme
deviations are relatively rare in proportion to the amount of deviation.
The vertical columns represent the total number of individuals of a
given height in inches. From Davenport. ]

If a group of soldiers be measured as the children were measured for
arithmetical ability, their height will be distributed in this same
curve of probability. Fig. 14 shows the cadets of Connecticut
Agricultural College; it is obvious that a line drawn along the tops
of the files would again make the step-pyramid shown in Figures 10, 11
and 13. If a larger number were taken, the steps would disappear and
give place to a smooth curve; the fact is well shown in a graph for the
heights of recruits to the American Army (Fig. 15).

The investigation in this direction need not be pursued any farther. For
the purpose of eugenics, it is sufficient to recognize that great
differences exist between men, and women, not only in respect of
physical traits, but equally in respect of mental ability.

This conclusion might easily have been reached from a study of the facts
in Chapter I, but it seemed worth while to take time to present the fact
in a more concrete form as the result of actual measurements. The
evidence allows no doubt about the existence of considerable mental and
physical differences between men.

The question naturally arises, "What is the cause of these differences? "

The study of twins showed that the differences could not be due to
differences in training or home surroundings. If the reader will think
back over the facts set forth in the first chapter, he will see clearly
that the fundamental differences in men can not be due to anything that
happens after they are born; and the facts presented in the second
chapter showed that these differences can not be due in an important
degree to any influences acting on the child prior to birth.




CHAPTER IV

THE INHERITANCE OF MENTAL CAPACITIES


We have come to the climax of the eugenist's preliminary argument; if
the main differences between human beings are not due to anything in the
environment or training, either of this or previous generations, there
can be but one explanation for them.

They must be due to the ancestry of the individual--that is, they must
be matters of heredity in the ordinary sense, coupled with the
fortuitous variations which accompany heredity throughout the organic
world.

We need not limit ourselves, however, to the argument by exclusion, for
it is not difficult to present direct evidence that the differences
between men are actually inherited by children from parents. The
problem, formally stated, is to measure the amount by which the likeness
of individuals of like ancestry surpasses the likeness of individuals of
different ancestry. After subtraction of the necessary amount for the
greater likeness in training, that the individuals of like ancestry will
have, whatever amount is left will necessarily, represent the actual
inheritance of the child from its ancestors--parents, grandparents, and
so on.

Obviously, the subtraction for environmental effects is the point at
which a mistake is most probable. We may safely start, therefore, with a
problem in which no subtraction whatever need be made for this cause.
Eye color is a stock example, and a good one, for it is not conceivable
that home environment or training would cause a change in the color of
brothers' eyes.

The correlation[30] between brothers, or sisters, or brothers and
sisters--briefly, the fraternal resemblance--for eye-color was found by
Karl Pearson, using the method described in Chapter I, to be . 52. We are
in no danger of contradiction if we state with positiveness that this
figure represents the influence of ancestry, or direct inheritance, in
respect to this particular trait.

Suppose the resemblance between brothers be measured for stature--it
is . 51; for cephalic index, that is, the ratio of width of skull to length
of skull--it is . 49; for hair color--it is . 59. In all of these points,
it will be admitted that no home training, or any other influence except
heredity, can conceivably play an important part. We could go on with a
long list of such measurements, which biometrists have made; and if they
were all summed up it would be found that the fraternal correlation in
these traits as to the heritability of which there can be no dispute, is
about . 52. Here is a good measure, albeit a technical one, of the
influence of heredity from the near ancestry. It is possible, too, to
measure the direct correlation between a trait in parent and the same
trait in offspring; the average of many cases where only heredity can be
thought to have had any effect in producing the result, is . 49. By the
two methods of measurement, therefore, quite comparable results are
obtained.

So much work has been done in this subject that we have no hesitation in
affirming . 5 to represent approximately the average intensity of
heredity for physical characters in man. If any well-marked physical
character be measured, in which training and environment can not be
assumed to have had any part, it will be found, in a large enough number
of subjects, that the resemblance, measured on a scale from 0 to 1, is
just about one-half of unity. Of course, perfect identity with the
parents is not to be expected, because the child must inherit from both
parents, who in turn each inherited from two parents, and so on.

So far, it may be said, we have had plain sailing because we have
carefully chosen traits in which we were not obliged to make any
subtraction whatever for the influence of training. But it is evident
that not all traits fall in that class.

This is the point at which the inheritance of mental traits has been
most often questioned. Probably no one will care to dispute the
inheritance of such physical traits as eye-color. But in considering the
mind, a certain school of popular pseudo-psychological writers question
the reality of mental inheritance, and allege that the proofs which the
geneticist offers are worthless because they do not make account of the
similarity in environment or training. Of course, it is admitted that
some sort of a mental groundwork must be inherited, but extremists
allege that this is little more than a clean slate on which the
environment, particularly during the early years of childhood, writes
its autograph.

We must grant that the analysis of the inheritance of mental traits is
proceeding slowly. This is not the fault of the geneticist, but rather
of the psychologist, who has not yet been able to furnish the geneticist
with the description of definite traits of such a character as to make
possible the exhaustive analysis of their individual inheritance. That
department of psychology is only now being formed.

We might even admit that no inherited "unit character" in the mind has
yet been isolated; but it would be a great mistake to assume from this
admission that proof of the inheritance of mental qualities, in general,
is lacking.

The psychologists and educators who think so appear either to be swayed
by metaphysical views of the mind, or else to believe that resemblance
between parent and offspring is the only evidence of inheritance that
can be offered. The father dislikes cheese, the son dislikes cheese.
"Aha, you think that that is the inheritance of a dislike for cheese,"
cries the critic, "but we will teach you better. " An interesting example
of this sort of teaching is furnished by Boris Sidis, whose feelings are
outraged because geneticists have represented that some forms of
insanity are hereditary. He declaims for several pages[31] in this
fashion:

"The so-called scientific method of the eugenists is radically faulty,
in spite of the rich display of colored plates, stained tables,
glittering biological speculations, brilliant mathematical formulae and
complicated statistical calculations. The eugenists pile Ossa on Pelion
of facts by the simple method of enumeration which Bacon and the
thinkers coming after him have long ago condemned as puerile and futile.
From the savage's belief in sympathetic, imitative magic with its
consequent superstitions, omens, and taboos down to the articles of
faith and dogmas of the eugenists we find the same faulty, primitive
thought, guided by the puerile, imbecile method of simple enumeration,
and controlled by the wisdom of the logical _post hoc, ergo propter
hoc_. "

Now if resemblance between parent and offspring were, as Dr. Sidis
supposes, the only evidence of inheritance of mental traits which the
eugenist can produce, his case would indeed be weak. And it is perfectly
true that "evidence" of this kind has sometimes been advanced as
sufficient by geneticists who should have known better. But this is not
the real evidence which genetics offers. The evidence is of numerous
kinds, and several lines might be destroyed without impairing the
validity of the remainder. It is impossible to review the whole body of
evidence here, but some of the various kinds may be indicated, and
samples given, even though this involves the necessity of repeating some
things we have said in earlier chapters. The reader will then be able to
form his own opinion as to whether the geneticists' proofs or the mere
assurances of those who have not studied the subject are the more
weighty.

1. _The analogy from breeding experiments. _ Tame rats, for instance, are
very docile; their offspring can be handled without a bit of trouble.
The wild rat, on the other hand, is not at all docile.

W. E. Castle, of Harvard University, writes:[32] "We have repeatedly
mated tame female rats with wild males, the mothers being removed to
isolated cages before the birth of the young. These young which had
never seen or been near their father were very wild in disposition in
every case. The observations of Yerkes on such rats raised by us
indicates that their wildness was not quite as extreme as that of the
pure wild rat but closely approached it. "

Who can suggest any plausible explanation of their conduct, save that
they inherited a certain temperament from their sire? Yet the
inheritance of temperament is one of the things which certain
psychologists most "view with alarm. " If it is proved in other animals,
can it be considered wholly impossible in man?

2. _The segregation of mental traits. _ When an insane, or epileptic, or
feeble-minded person mates with a normal individual, in whose family no
taint is found, the offspring (generally speaking) will be mentally
sound, even though one parent is not. On the other hand, if two people
from tainted stocks marry, although neither one may be personally
defective, part of their offspring will be affected.

This production of sound children from an unsound parent, in the first
case, and unsound children from two apparently sound parents in the
second case, is exactly the opposite of what one would expect if the
child gets his unsoundness merely by imitation or "contagion. " The
difference can not reasonably be explained by any difference in
environment or external stimuli. Heredity offers a satisfactory
explanation, for some forms of feeble-mindedness and epilepsy, and some
of the diseases known as insanity, behave as recessives and segregate in
just the way mentioned. There are abundant analogies in the inheritance
of other traits in man, lower animals and plants, that behave in exactly
the same manner.

If mental defects are inherited, then it is worth while investigating
whether mental excellencies may not also be.

3. _The persistence of like qualities regardless of difference in
environment. _ Any parent with open eyes must see this in his own
children--must see that they retained the inherited traits even when
they left home and lived under entirely different surroundings. But the
histories of twins furnish the most graphic evidence. Galton, who
collected detailed histories of thirty-five pairs of twins who were
closely alike at birth, and examined their history in after years,
writes:[33] "In some cases the resemblance of body and mind had
continued unaltered up to old age, notwithstanding very different
conditions of life;" in other cases where some dissimilarity developed,
it could be traced to the influence of an illness. Making due allowance
for the influence of illness, yet "instances do exist of an apparently
thorough similarity of nature, in which such differences of external
circumstances as may be consistent with the ordinary conditions of the
same social rank and country do not create dissimilarity. Positive
evidence, such as this, can not be outweighed by any amount of negative
evidence. "

Frederick Adams Woods has brought forward[34] a piece of more exact
evidence under this head. It is known from many quantitative studies
that in physical heredity, the influence of the paternal grandparents
and the influence of the maternal grandparents is equal; on the average
one pair will contribute no more to the grandchildren than the other. If
mental qualities are due rather to early surroundings than to actual
inheritance, this equality of grandparental influence is incredible in
the royal families where Dr. Woods got his material; for the grandchild
has been brought up at the court of the paternal grandfather, where he
ought to have gotten all his "acquirements," and has perhaps never even
seen his maternal grandparents, who therefore could not be expected to
impress their mental peculiarities on him by "contagion. " When Dr. Woods
actually measured the extent of resemblance to the two sets of
grandparents, for mental and moral qualities, he found it to be the same
in each case; as is inevitable if they are inherited, but as is
incomprehensible if heredity is not largely responsible for one's mental
make-up.

4. _Persistence of unlike qualities regardless of sameness in the_
_environment. _ This is the converse of the preceding proposition, but
even more convincing. In the last paragraph but one, we mentioned
Galton's study (cited at some length in our Chapter I) of "identical"
twins, who are so much alike at birth for the very good reason that they
have identical heredity. This heredity was found to be not modified,
either in the body or the mind, by ordinary differences of training and
environment. Some of Galton's histories[35] of ordinary, non-identical
twins were also given in Chapter I; two more follow:

One parent says: "They have been treated exactly alike; both were
brought up by hand; they have been under the same nurse and governess
from their birth, and they are very fond of each other. Their increasing
dissimilarity must be ascribed to a natural difference of mind and
character, as there has been nothing in their treatment to account for
it. "

Another writes: "This case is, I should think, somewhat remarkable for
dissimilarity in physique as well as for strong contrast in character.
They have been unlike in mind and body throughout their lives. Both were
reared in a country house and both were at the same schools until the
age of 16. "

In the face of such examples, can anyone maintain that differences in
mental make-up are wholly due to different influences during childhood,
and not at all to differences in germinal make-up? It is not necessary
to depend, under this head, on mere descriptions, for accurate
measurements are available to demonstrate the point. If the environment
creates the mental nature, then ordinary brothers, not more than four or
five years apart in age, ought to be about as closely similar to each
other as identical twins are to each other; for the family influences in
each case are practically the same. Professor Thorndike, by careful
mental tests, showed[36] that this is not true. The ordinary brothers
come from different egg-cells, and, as is known from studies on lower
animals, they do not get exactly the same inheritance from their
parents; they show, therefore, considerable differences in their psychic
natures. Real identical twins, being two halves of the same egg-cell,
have the same heredity, and their natures are therefore much more
nearly identical.

Again, if the mind is molded during the "plastic years of childhood,"
children ought to become more alike, the longer they are together. Twins
who were unlike at birth ought to resemble each other more closely at 14
than they did at 9, since they have been for five additional years
subjected to this supposedly potent but very mystical "molding force. "
Here again Professor Thorndike's exact measurements explode the fallacy.
They are actually, measurably, less alike at the older age; their inborn
natures are developing along predestined lines, with little regard to
the identity of their surroundings. Heredity accounts easily for these
facts, but they cannot be squared with the idea that mental differences
are the products solely of early training.

5. _Differential rates of increase in qualities subject to much
training. _ If the mind is formed by training, then brothers ought to be
more alike in qualities which have been subject to little or no
training. Professor Thorndike's measurements on this point show the
reverse to be true. The likeness of various traits is determined by
heredity, and brothers may be more unlike in traits which have been
subjected to a large and equal amount of training. Twins were found to
be less alike in their ability at addition and multiplication, in which
the schools had been training them for some years, than they were in
ability to mark off the A's on a printed sheet, or to write the
opposites to a list of words--feats which they had probably never before
tried to do.

This same proposition may be put on a broader basis. [37] "In so far as
the differences in achievement found amongst a group of men are due to
the differences in the quantity and quality of training which they had
had in the function in question, the provision of equal amounts of the
same sort of training for all individuals in the group should act to
reduce the differences. " "If the addition of equal amounts of practice
does not reduce the differences found amongst men, those differences can
not well be explained to any large extent by supposing them to have been
due to corresponding differences in amount of previous practice. If,
that is, inequalities in achievement are not reduced by equalizing
practice, they can not well have been caused by inequalities in previous
practice. If differences in opportunity cause the differences men
display, making opportunity more nearly equal for all, by adding equal
amounts to it in each case should make the differences less.

"The facts found are rather startling. Equalizing practice seems to
increase differences. The superior man seems to have got his present
superiority by his own nature rather than by superior advantages of the
past, since, during a period of equal advantage for all, he increases
his lead. " This point has been tested by such simple devices as mental
multiplication, addition, marking A's on a printed sheet of capitals and
the like; all the contestants made some gain in efficiency, but those
who were superior at the start were proportionately farther ahead than
ever at the end. This is what the geneticist would expect, but fits very
ill with some popular pseudo-science which denies that any child is
mentally limited by nature.

6. _Direct measurement of the amount of resemblance of mental traits in
brothers and sisters. _ It is manifestly impossible to assume that early
training, or parental behavior, or anything of the sort, can have
influenced very markedly the child's eye color, or the length of his
forearm, or the ratio of the breadth of his head to its length. A
measure of the amount of resemblance between two brothers in such traits
may very confidently be said to represent the influence of heredity; one
can feel no doubt that the child inherits his eye-color and other
physical traits of that kind from his parents. It will be recalled that
the resemblance, measured on a scale from 0 to 1, has been found to be
about 0. 5.

Karl Pearson measured the resemblance between brothers and sisters in
mental traits--for example, temper, conscientiousness, introspection,
vivacity--and found it on the average to have the same intensity--that
is, about 0. 5. Starch gets similar results in studying school grades.

Professor Pearson writes:[38]

"It has been suggested that this resemblance in the psychological
characters is compounded of two factors, inheritance on the one hand and
training and environment on the other. If so, one must admit that
inheritance and environment make up the resemblance in the physical
characters. Now these two sorts of resemblance being of the same
intensity, either the environmental influence is the same in both cases
or it is not. If it is the same, we are forced to the conclusion that it
is insensible, for it can not influence eye-color. If it is not the
same, then it would be a most marvelous thing that with varying degrees
of inheritance, some mysterious force always modifies the extent of home
influence, until the resemblance of brothers and sisters is brought
sensibly up to the same intensity! Occam's razor[39] will enable us at
once to cut off such a theory. We are forced, I think, literally forced,
to the general conclusion that the physical and psychical characters in
man are inherited within broad lines in the same manner, and with
approximate intensity. The average parental influence is in itself
largely a result of the heritage of the stock and not an extraneous and
additional factor causing the resemblance between children from the same
home. "

A paragraph from Edgar Schuster[40] may appropriately be added. "After
considering the published evidence a word must be said of facts which
most people may collect for themselves. They are difficult to record,
but are perhaps more convincing than any quantity of statistics. If one
knows well several members of a family, one is bound to see in them
likenesses with regard to mental traits, both large and small, which
may sometimes be accounted for by example on the one hand or unconscious
imitation on the other, but are often quite inexplicable on any other
theory than heredity. It is difficult to understand how the inheritance
of mental capacity can be denied by those whose eyes are open and whose
minds are open too. "

Strictly speaking, it is of course true that man inherits nothing more
than the capacity of making mental acquirements.