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.