If they exist, why do not ordinary brothers become as much
alike as identical twins?
alike as identical twins?
Applied Eugenics by Roswell H. Johnson and Paul Popenoe
[5]
[Illustration: THE EFFECT OF NURTURE IN CHANGING NATURE
FIG. 2. --Corn of a single variety (Leaming Dent) grown in two
plots: at the left spaced far apart in hills, at the right crowded. The
former grows to its full potential height, the latter is stunted. The
size differences in the two plots are due to differences in environment,
the heredity in both cases being the same. Plants are much more
susceptible to nutritional influences on size than are mammals, but to a
less degree nutrition has a similar effect on man. Photograph from A. F.
Blakeslee. ]
"If now these resemblances are due to the fact that the two members of
any twin pair are treated alike at home, have the same parental models,
attend the same school and are subject in general to closely similar
environmental conditions, then (1) twins should, up to the age of
leaving home, grow more and more alike, and in our measurements the
twins 13 and 14 years old should be much more alike than those 9 and 10
years old. Again (2) if similarity in training is the cause of
similarity in mental traits, ordinary fraternal pairs not over four or
five years apart in age should show a resemblance somewhat nearly as
great as twin pairs, for the home and school condition of a pair of the
former will not be much less similar than those of a pair of the latter.
Again, (3) if training is the cause, twins should show greater
resemblance in the case of traits much subject to training, such as
ability in addition or multiplication, than in traits less subject to
training, such as quickness in marking off the A's on a sheet of printed
capitals, or in writing the opposites of words. "
The data were elaborately analyzed from many points of view. They showed
(1) that the twins 12-14 years old were not any more alike than the
twins 9-11 years old, although they ought to have been, if environment
has great power to mold the character during these so-called "plastic
years of childhood. " They showed (2) that the resemblance between twins
was two or three times as great as between ordinary children of the same
age and sex, brought up under similar environment. There seems to be no
reason, except heredity, why twins should be more alike. The data showed
(3) that the twins were no more alike in traits subject to much training
than in traits subject to little or no training. Their achievement in
these traits was determined by their heredity; training did not
measurably alter these hereditary potentialities.
"The facts," Professor Thorndike wrote, "are easily, simply and
completely explained by one simple hypothesis; namely, that the nature
of the germ-cells--the conditions of conception--cause whatever
similarities and differences exist in the original natures of men, that
these conditions influence mind and body equally, and that in life the
differences in modification of mind and body produced by such
differences as obtain between the environments of present-day New York
City public school children are slight. "
"The inferences," he says, "with respect to the enormous importance of
original nature in determining the behavior and achievements of any man
in comparison with his fellows of the same period of civilization and
conditions of life are obvious. All theories of human life must accept
as a first principle the fact that human beings at birth differ
enormously in mental capacities and that these differences are largely
due to similar differences in their ancestry. All attempts to change
human nature must accept as their most important condition the limits
set by original nature to each individual. "
Meantime other investigators, principally followers of Karl Pearson in
England, were working out correlation coefficients in other lines of
research for hundreds of different traits. As we show in more detail in
Chapter IV, it was found, no matter what physical or mental trait was
measured, that the coefficient of correlation between parent and child
was a little less than . 5 and that the coefficient between brother and
brother, or sister and sister, or brother and sister, was a little more
than . 5. On the average of many cases the mean "nature" value, the
coefficient of direct heredity, was placed at . 51. This gave another
means of measuring nurture, for it was also possible to measure the
relation between any trait in the child and some factor in the
environment. A specific instance will make this clearer.
Groups of school children usually show an appalling percentage of
short-sightedness. Now suppose it is suggested that this is because they
are allowed to learn to read at too early an age. One can find out the
age at which any given child did learn to read, and work out the
coefficient of correlation between this age and the child's amount of
myopia. If the relation between them is very close--say . 7 or . 8--it
will be evident that the earlier a child learns to read, the more
short-sighted he is as he grows older. This will not prove a relation of
cause and effect, but it will at least create a great suspicion. If on
the contrary the correlation is very slight, it will be evident that
early reading has little to do with the prevalance of defective vision
among school children. If investigators similarly work out all the other
correlations that can be suggested, finding whether there is any
regular relation between myopia and overcrowding, long hours of study,
general economic conditions at home, general physical or moral
conditions of parents, the time the child spends out of doors, etc. , and
if no important relation is found between these various factors and
myopia, it will be evident that no factor of the environment which one
can think of as likely to cause the trouble really accounts for the poor
eyesight of school children.
[Illustration: HEIGHT IN CORN AND MEN
FIG. 3. --An unusually short and an unusually tall man,
photographed beside extreme varieties of corn which, like the men, owe
their differences in height indisputably to heredity rather than to
environment. No imaginable environmental differences could reverse the
positions of these two men, or of these two varieties of corn, the
heredity in each case being what it is. The large one might be stunted,
but the small one could not be made much larger. Photograph from A. F.
Blakeslee. ]
This has actually been done,[6] and none of the conditions enumerated
has been found to be closely related to myopia in school children.
Correlations between fifteen environmental conditions and the goodness
of children's eyesight were measured, and only in one case was the
correlation as high as . 1. The mean of these correlations was about
. 04--an absolutely negligible quantity when compared with the common
heredity coefficient of . 51.
Does this prove that the myopia is rather due to heredity? It would, by
a process of exclusion, if every conceivable environmental factor had
been measured and found wanting. That point in the investigation can
never be reached, but a tremendously strong suspicion is at least
justified. Now if the degree of resemblance between the prevalence of
myopia in parents and that in children be directly measured, and if it
be found that when the parent has eye trouble the child also has it,
then it seems that a general knowledge of heredity should lead to the
belief that the difficulty lies there, and that an environmental cause
for the poor vision of the school child was being sought, when it was
all the time due almost entirely to heredity. This final step has not
yet been completed in an adequate way,[7] but the evidence, partly
analogical, gives every reason to believe in the soundness of the
conclusion stated, that in most cases the schoolboy must wear glasses
because of his heredity, not because of overstudy or any neglect on the
part of his parents to care for his eyes properly during his childhood.
[Illustration: WHY MEN GROW SHORT OR TALL
FIG. 4. --Pedigree charts of the two men shown in the preceding
illustration. Squares represent men and circles women; figures
underlined denote measurement in stocking feet. It is obvious from a
comparison of the ancestry of the two men that the short one comes from
a predominantly short family, while the tall one gains his height
likewise from heredity. The shortest individual in the right-hand chart
would have been accounted tall in the family represented on the left.
After A. F. Blakeslee. ]
The extent to which the intelligence of school children is dependent on
defective physique and unfavorable home environment is an important
practical question, which David Heron of London attacked by the methods
we have outlined. He wanted to find out whether the healthy children
were the most intelligent. One is constantly hearing stories of how the
intelligence of school children has been improved by some treatment
which improved their general health, but these stories are rarely
presented in such a way as to contribute evidence of scientific value.
It was desirable to know what exact measurement would show. The
intelligence of all the children in fourteen schools was measured in its
correlation with weight and height, conditions of clothing and teeth,
state of nutrition, cleanliness, good hearing, and the condition of the
cervical glands, tonsils and adenoids. It could not be found that mental
capacity was closely related to any of the characters dealt with. [8] The
particular set of characters measured was taken because it happened to
be furnished by data collected for another purpose; the various items
are suggestive rather than directly conclusive. Here again, the
correlation in most cases was less than . 1, as compared with the general
heredity correlation of . 5.
The investigation need not be limited to problems of bad breeding.
Eugenics, as its name shows, is primarily interested in "good breeding;"
it is particularly worth while, therefore, to examine the relations
between heredity and environment in the production of mental and moral
superiority.
If success in life--the kind of success that is due to great mental and
moral superiority--is due to the opportunities a man has, then it ought
to be pretty evenly distributed among all persons who have had favorable
opportunities, provided a large enough number of persons be taken to
allow the laws of probability full play. England offers a good field to
investigate this point, because Oxford and Cambridge, her two great
universities, turn out most of the eminent men of the country, or at
least have done so until recently. If nothing more is necessary to
ensure a youth's success than to give him a first-class education and
the chance to associate with superior people, then the prizes of life
ought to be pretty evenly distributed among the graduates of the two
universities, during a period of a century or two.
This is not the case. When we look at the history of England, as Galton
did nearly half a century ago, we find success in life to an unexpected
degree a family affair. The distinguished father is likely to have a
distinguished son, while the son of two "nobodies" has a very small
chance of becoming distinguished. To cite one concrete case, Galton
found[9] that the son of a distinguished judge had about one chance in
four of becoming himself distinguished, while the son of a man picked
out at random from the population had about one chance in 4,000 of
becoming similarly distinguished.
The objection at once occurs that perhaps social opportunities might
play the predominant part; that the son of an obscure man never gets a
chance, while the son of the prominent man is pushed forward regardless
of his inherent abilities. This, as Galton argued at length, can not be
true of men of really eminent attainments. The true genius, he thought,
frequently succeeds in rising despite great obstacles, while no amount
of family pull will succeed in making a mediocrity into a genius,
although it may land him in some high and very comfortable official
position. Galton found a good illustration in the papacy, where during
many centuries it was the custom for a pope to adopt one of his nephews
as a son, and push him forward in every way. If opportunity were all
that is required, these adopted sons ought to have reached eminence as
often as a real son would have done; but statistics show that they
reached eminence only as often as would be expected for nephews of great
men, whose chance is notably less, of course, than that of sons of great
men, in whom the intensity of heredity is much greater.
Transfer the inquiry to America, and it becomes even more conclusive,
for this is supposed to be the country of equal opportunities, where it
is a popular tradition that every boy has a chance to become president.
Success may be in some degree a family affair in caste-ridden England;
is it possible that the past history of the United States should show
the same state of affairs?
Galton found that about half of the great men of England had
distinguished close relatives. If the great men of America have fewer
distinguished close relatives, environment will be able to make out a
plausible case: it will be evident that in this continent of boundless
opportunities the boy with ambition and energy gets to the top, and that
this ambition and energy do not depend on the kind of family he comes
from.
Frederick Adams Woods has made precisely this investigation. [10] The
first step was to find out how many eminent men there are in American
history. Biographical dictionaries list about 3,500, and this number
provides a sufficiently unbiased standard from which to work. Now, Dr.
Woods says, if we suppose the average person to have as many as twenty
close relatives--as near as an uncle or a grandson--then computation
shows that only one person in 500 in the United States has a chance to
be a near relative of one of the 3,500 eminent men--provided it is
purely a matter of chance. As a fact, the 3,500 eminent men listed by
the biographical dictionaries are related to each other not as one in
500, but as one in five. If the more celebrated men alone be considered,
it is found that the percentage increases so that about one in three of
them has a close relative who is also distinguished. This ratio
increases to more than one in two when the families of the forty-six
Americans in the Hall of Fame are made the basis of study. If all the
eminent relations of those in the Hall of Fame are counted, they average
more than one apiece. Therefore, they are from five hundred to a
thousand times as much related to distinguished people as the ordinary
mortal is.
To look at it from another point of view, something like 1% of the
population of the country is as likely to produce a man of genius as is
all the rest of the population put together,--the other 99%.
This might still be due in some degree to family influence, to the
prestige of a famous name, or to educational advantages afforded the
sons of successful men. Dr. Woods' study of the royal families of Europe
is more decisive. [11]
In the latter group, the environment must be admitted--on the whole--to
be uniformly favorable. It has varied, naturally, in each case, but
speaking broadly it is certain that all the members of this group have
had the advantage of a good education, of unusual care and attention. If
such things affect achievement, then the achievements of this class
ought to be pretty generally distributed among the whole class. If
opportunity is the cause of a man's success, then most of the members of
this class ought to have succeeded, because to every one of royal blood,
the door of opportunity usually stands open. One would expect the heir
to the throne to show a better record than his younger brothers,
however, because his opportunity to distinguish himself is naturally
greater. This last point will be discussed first.
Dr. Woods divided all the individuals in his study into ten classes for
intellectuality and ten for morality, those most deficient in the
qualities being put in class 1, while the men and women of preeminent
intellectual and moral worth were put in class 10. Now if preeminent
intellect and morality were at all linked with the better chances that
an inheritor of succession has, then heirs to the throne ought to be
more plentiful in the higher grades than in the lower. Actual count
shows this not to be the case. A slightly larger percentage of
inheritors is rather to be found in the lower grades. The younger sons
have made just as good a showing as the sons who succeeded to power; as
one would expect if intellect and morality are due largely to heredity,
but as one would not expect if intellect and morality are due largely to
outward circumstances.
Are "conditions of turmoil, stress and adversity" strong forces in the
production of great men, as has often been claimed? There is no evidence
from facts to support that view. In the case of a few great commanders,
the times seemed particularly favorable. Napoleon, for example, could
hardly have been Napoleon had it not been for the French revolution. But
in general there have been wars going on during the whole period of
modern European history; there have always been opportunities for a
royal hero to make his appearance; but often the country has called for
many years in vain. Circumstances were powerless to produce a great man
and the nation had to wait until heredity produced him. Spain has for
several centuries been calling for genius in leadership in some lines;
but in vain. England could not get an able man from the Stuart line,
despite her need, and had to wait for William of Orange, who was a
descendant of a man of genius, William the Silent. "Italy had to wait
fifty years in bondage for her deliverers, Cavour, Garibaldi and Victor
Emmanuel. "
"The upshot of it all," Dr. Woods decides, "is that, as regards
intellectual life, environment is a totally inadequate explanation. If
it explains certain characters in certain instances, it always fails to
explain many more, while heredity not only explains all, or at least
90%, of the intellectual side of character in practically every
instance, but does so best when questions of environment are left out of
discussion. "
Despite the good environment almost uniformly present, the geniuses in
royalty are not scattered over the surface of the pedigree chart, but
form isolated little groups of closely related individuals. One centers
in Frederick the Great, another in Queen Isabella of Spain, a third in
William the Silent, and a fourth in Gustavus Adolphus. Furthermore, the
royal personages who are conspicuously low in intellect and morality are
similarly grouped. Careful study of the circumstances shows nothing in
the environment that would produce this grouping of genius, while it is
exactly what a knowledge of heredity leads one to expect.
In the next place, do the superior members of royalty have
proportionately more superior individuals among their close relatives,
as was found to be the case among the Americans in the Hall of Fame? A
count shows at once that they do. The first six grades all have about an
equal number of eminent relatives, but grade 7 has more while grade 8
has more than grade 7, and the geniuses of grade 10 have the highest
proportion of nearer relatives of their own character. Surely it cannot
be supposed that a relative of a king in grade 8 has on the average a
much less favorable environment than a relative of a king in grade 10.
Is it not fair, then, to assume that this relative's greater endowment
in the latter case is due to heredity?
Conditions are the same, whether males or females be considered. The
royal families of Europe offer a test case because for them the
environment is nearly uniformly favorable. A study of them shows great
mental and moral differences between them, and critical evidence
indicates that these differences are largely due to differences in
heredity. Differences of opportunity do not appear to be largely
responsible for the achievements of the individuals.
But, it is sometimes objected, opportunity certainly is responsible for
the appearance of much talent that would otherwise never appear. Take
the great increase in the number of scientific men in Germany during the
last half century, for example. It can not be pretended that this is due
to an increased birth-rate of such talent; it means that the growth of
an appreciation of scientific work has produced an increased amount of
scientific talent. J. McKeen Cattell has argued this point most
carefully in his study of the families of one thousand American men of
science (_Popular Science Monthly_, May, 1915). "A Darwin born in China
in 1809," he says, "could not have become a Darwin, nor could a Lincoln
born here on the same day have become a Lincoln had there been no Civil
War. If the two infants had been exchanged there would have been no
Darwin in America and no Lincoln in England. " And so he continues,
urging that in the production of scientific men, at least, education is
more important than eugenics.
This line of argument contains a great deal of obvious truth, but is
subject to a somewhat obvious objection, if it is pushed too far. It is
certainly true that the exact field in which a man's activities will
find play is largely determined by his surroundings and education. Young
men in the United States are now becoming lawyers or men of science, who
would have become ministers had they been born a century or two ago. But
this environmental influence seems to us a minor one, for the man who is
highly gifted in some one line is usually, as all the work of
differential psychology shows, gifted more than the average in many
other lines. Opportunity decides in just what field his life work shall
lie; but he would be able to make a success in a number of fields.
Darwin born in America would probably not have become the Darwin we
know, but it is not to be supposed that he would have died a "mute,
inglorious Milton": it is not likely that he would have failed to make
his mark in some line of human activity. Dr. Cattell's argument, then,
while admissible, can not properly be urged against the fact that
ability is mainly dependent on inheritance.
We need not stop with the conclusion that equality of training or
opportunity is unable to level the inborn differences between men. We
can go even farther, and produce evidence to show that equality of
training _increases the differences_ in results achieved.
This evidence is obtained by measuring the effects of equal amounts of
exercise of a function upon individual differences in respect to
efficiency in it. Suppose one should pick out, at random, eight
children, and let them do problems in multiplication for 10 minutes.
After a number of such trials, the three best might average 39 correct
solutions in the 10 minutes, and the three poorest might average 25
examples. Then let them continue the work, until each one of them has
done 700 examples. Here is equality in training; does it lead to uniform
results?
Dr. Starch made the actual test which we have outlined and found that
the three best pupils gained on the average 45 in the course of doing
700 examples; while the three poorest gained only 26 in the same course
of time.
Similar tests have been made of school children in a number of
instances, and have shown that equality of training fails to bring about
equality of performance. All improve to some extent; but those who are
naturally better than their comrades usually become better still, when
conditions for all are the same. E. L. Thorndike gives[12] the following
tabular statement of a test he conducted:
THE EFFECT OF EQUAL AMOUNTS OF PRACTICE UPON INDIVIDUAL DIFFERENCES
IN THE MENTAL MULTIPLICATION OF A THREE-PLACE BY A THREE-PLACE
NUMBER
Amount done Percentage of
per unit of correct figures
time in answers
Hours of Practice
|
| First 5 Examples First 5 Examples
| | |
| | Last 5 or 10 | Last 5 or 10
| | Examples | Examples
| | | | |
| | | Gain | | Gain
Initial highest five individuals 5. 1 85 147 61 70 78 18
" next five " 5. 1 56 107 51 68 78 10
" " six " 5. 3 46 68 22 74 82 8
" " six " 5. 4 38 46 8 58 70 12
" " five " 5. 2 31 57 26 47 67 20
" " one individual 5. 2 19 32 13 100 82 -18
Similar results have been obtained by half a dozen other experimenters,
using the tests of mental multiplication, addition, marking A's on a
printed sheet of capitals, and the like. It would be a mistake to
conclude too much from experiments of such restricted scope; but they
all agree in showing that if every child were given an equal training,
the differences in these traits would nevertheless be very great.
And although we do not wish to strain the application of these results
too far, we are at least justified in saying that they strongly indicate
that inborn mediocrity can not be made into a high grade of talent by
training. Not every boy has a chance to distinguish himself, even if he
receives a good education.
We are driven back to the same old conclusion, that it is primarily
inborn nature which causes the achievements of men and women to be what
they are. Good environment, opportunity, training, will give good
heredity a chance to express itself; but they can not produce greatness
from bad heredity.
These conclusions are familiar to scientific sociologists, but they have
not yet had the influence on social service and practical attempts at
reform which they deserve. Many popular writers continue to confuse
cause and effect, as for example H. Addington Bruce, who contributed an
article to the _Century Magazine_, not long ago, on "The Boy Who Goes
Wrong. " After alleging that the boy who goes wrong does so because he is
not properly brought up, Mr. Bruce quotes with approval the following
passage from Paul Dubois, "the eminent Swiss physician and philosopher:
"If you have the happiness to be a well-living man, take care not to
attribute the credit of it to yourself. Remember the favorable
conditions in which you have lived, surrounded by the relatives who
loved you and set you a good example; do not forget the close friends
who have taken you by the hand and led you away from the quagmires of
evil; keep a grateful remembrance for all the teachers who have
influenced you, the kind and intelligent school-master, the devoted
pastor; realize all these multiple influences which have made you what
you are. Then you will remember that such and such a culprit has not in
his sad life met with these favorable conditions; that he had a drunken
father or a foolish mother, and that he has lived without affection,
exposed to all kinds of temptation. You will then take pity upon this
disinherited man, whose mind has been nourished upon malformed mental
images, begetting evil sentiments such as immoderate desire or social
hatred. "
Mr. Bruce indorses this kind of talk when he concludes, "The blame for
the boy who goes wrong does not rest with the boy himself, or yet with
his remote ancestors. It rests squarely with the parents who, through
ignorance or neglect, have failed to mold him aright in the plastic days
of childhood. "
Where is the evidence of the existence of these plastic days of
childhood?
If they exist, why do not ordinary brothers become as much
alike as identical twins? How long are we to be asked to believe, on
blind faith, that the child is putty, of which the educator can make
either mediocrity or genius, depending on his skill? What does the
environmentalist _know_ about these "plastic days"? If a boy has a
drunken father or foolish mother, does it not suggest that there is
something wrong with his pedigree? With such an ancestry, we do not
expect him to turn out brilliantly, no matter in what home he is brought
up. If a boy has the kind of parents who bring him up well; if he is,
as Dr. Dubois says, surrounded by relatives who love him and set him a
good example, we at once have ground for a suspicion that he comes of a
pretty good family, a stock characterized by a high standard of
intellectuality and morality, and it would surprise us if such a boy did
not turn out well. But he turns out well because what's bred in the bone
will show in him, if it gets any kind of a chance. It is his nature, not
his nurture, that is mainly responsible for his character.
CHAPTER II
MODIFICATION OF THE GERM-PLASM
Every living creature was at some stage of its life nothing more than a
single cell. It is generally known that human beings result from the
union of an egg-cell and a sperm-cell, but it is not so universally
understood that these germ-cells are part of a continuous stream of
germ-plasm which has been in existence ever since the appearance of life
on the globe, and which is destined to continue in existence as long as
life remains on the globe.
The corollaries of this fact are of great importance. Some of them will
be considered in this chapter.
Early investigators tended naturally to look on the germ-cells as a
product of the body. Being supposedly products of the body, it was
natural to think that they would in some measure reproduce the character
of the body which created them; and Darwin elaborated an ingenious
hypothesis to explain how the various characters could be represented in
the germ-cell. The idea held by him, in common with most other thinkers
of his period, is still held more or less unconsciously by those who
have not given particular attention to the subject. Generation is
conceived as a direct chain: the body produces the germ-cell which
produces another body which in turn produces another germ-cell, and so
on.
But a generation ago this idea fell under suspicion. August Weismann,
professor of zoology in the University of Freiburg, Germany, made
himself the champion of the new idea, about 1885, and developed it so
effectively that it is now a part of the creed of nearly every
biologist.
Weismann caused a general abandonment of the idea that the germ-cell is
produced by the body in each generation, and popularized the conception
of the germ-cell as a product of a stream of undifferentiated
germ-plasm, not only continuous but (potentially at least) immortal.
The body does not produce the germ-cells, he pointed out; instead, the
germ-cells produce the body.
The basis of this theory can best be understood by a brief consideration
of the reproduction of very simple organisms.
"Death is the end of life," is the belief of many other persons than the
Lotus Eaters. It is commonly supposed that everything which lives must
eventually die. But study of a one-celled animal, an Infusorian, for
example, reveals that when it reaches a certain age it pinches in two,
and each half becomes an Infusorian in all appearance identical with the
original cell. Has the parent cell then died? It may rather be said to
survive, in two parts. Each of these daughter cells will in turn go
through the same process of reproduction by simple fission, and the
process will be continued in their descendants. The Infusorian can be
called potentially immortal, because of this method of reproduction.
The immortality, as Weismann pointed out, is not of the kind attributed
by the Greeks to their gods, who could not die because no wound could
destroy them. On the contrary, the Infusorian is extremely fragile, and
is dying by millions at every instant; but if circumstances are
favorable, it _can_ live on; it is not inevitably doomed to die sooner
or later, as is Man. "It dies from accident often, from old age never. "
Now the single-celled Infusorian is in many respects comparable with the
single-celled germ of the higher animals. The analogy has often been
carried too far; yet it remains indisputable that the germ-cells of men
reproduce in the same way--by simple fission--as the Infusorian and
other one-celled animals and plants, and that they are organized on much
the same plan. Given favorable circumstances, the germ-cell should be
expected to be equally immortal. Does it ever find these favorable
circumstances?
The investigations of microscopists indicate that it does--that
evolution has provided it with these favorable circumstances, in the
bodies of the higher animals. Let us recall in outline the early history
of the fertilized germ-cell, the _zygote_ formed by the union of ovum
and spermatozoon. These two unite to form a single cell, which is
essentially the same, physiologically, as other germ-cells. It divides
in two similar cells; these each divide; the resulting cells again
divide, and so the process continues, until the whole body--a fully
developed man,--has been produced by division and redivision of the one
zygote.
But the germ-cell is obviously different from most of the cells that
make up the finished product, the body. The latter are highly
differentiated and specialized for different functions--blood cells,
nerve cells, bone cells, muscle cells, and so on, each a single cell but
each adapted to do a certain work, for which the original,
undifferentiated germ-cell was wholly unfit. It is evident that
differentiation began to take place at some point in the series of
divisions, that is to say, in the development of the embryo.
Th. Boveri, studying the development of a threadworm, made the
interesting discovery that this differentiation began at the first
division. Of the two daughter-cells produced from the zygote, one
continued dividing at a very slow rate, and without showing any
specialization. Its "line of descent" produced only germ-cells. The
products of division of the other daughter-cell began to differentiate,
and soon formed all the necessary kinds of cells to make up the body of
the mature worm. In this body, the cells from the first daughter-cell
mentioned were inclosed, still undifferentiated: they formed the
germ-cells of the next generation, and after maturity were ready to be
ejected from the body, and to form new threadworms.
Imagine this process taking place through generation after generation of
threadworms, and one will realize that the germ-plasm was passed on
directly from one generation to the next; that in each generation it
gave rise to body-plasm, but that it did not at any time lose its
identity or continuity, a part of the germ-plasm being always set aside,
undifferentiated, to be handed on to the next generation.
In the light of this example, one can better understand the definition
of germ-plasm as "that part of the substance of the parents which does
not die with them, but perpetuates itself in their offspring. " By
bringing his imagination into play, the reader will realize that there
is no limit to the backward continuity of this germ-plasm in the
threadworm. Granted that each species has arisen by evolution from some
other, this germ-cell which is observed in the body of the threadworm,
must be regarded as part of what may well be called a stream of
germ-plasm, that reaches back to the beginning of life in the world. It
will be equally evident that these is no foreordained limit to the
forward extension of the stream. It will continue in some branch, as
long as there are any threadworms or descendants of threadworms in the
world.
The reader may well express doubt as to whether what has been
demonstrated for the threadworm can be demonstrated for the higher
animals, including man. It must be admitted that in many of these
animals conditions are too unfavorable, and the process of embryology
too complicated, or too difficult to observe, to permit as distinct a
demonstration of this continuity of the germ-plasm, wherever it is
sought. But it has been demonstrated in a great many animals; no facts
which impair the theory have been discovered; and biologists therefore
feel perfectly justified in generalizing and declaring the continuity of
germ-plasm to be a law of the world of living things.
Focusing attention on its application to man, one sees that the race
must represent an immense network of lines of descent, running back
through a vast number of different forms of gradually diminishing
specialization, until it comes to a point where all its threads merge in
one knot--the single cell with which it may be supposed that life on
this globe began. Each individual is not only figuratively, but in a
very literal sense, the carrier of the heritage of the whole race--of
the whole past, indeed. Each individual is temporarily the custodian of
part of the "stuff of life"; from an evolutionary point of view, he may
be said to have been brought into existence, primarily to pass this
sacred heritage on to the next generation. From Nature's standpoint, he
is of little use in the world, his existence is scarcely justified,
unless he faithfully discharges this trust, passing on to the future
the "Lamp of Life" whose fire he has been created to guard for a short
while.
Immortality, we may point out in passing, is thus no mere _hope_ to the
parent: it is a _real possibility_. The death of the huge agglomeration
of highly specialized body-cells is a matter of little consequence, if
the germ-plasm, with its power to reproduce not only these body-cells,
but the mental traits--indeed, we may in a sense say the very soul--that
inhabited them, has been passed on. The individual continues to live, in
his offspring, just as the past lives in him. To the eugenist, life
everlasting is something more than a figure of speech or a theological
concept--it is as much a reality as the beat of the heart, the growth of
muscles or the activity of the mind.
This doctrine of the continuity of germ-plasm throws a fresh light on
the nature of human relationships. It is evident that the son who
resembles his father can not accurately be called a "chip off the old
block. " Rather, they are both chips off the same block; and aside from
bringing about the fusion of two distinct strains of germ-plasm, father
and mother are no more responsible for endowing the child with its
characters except in the choice of mate, than is the child for "stamping
his impress" on his parents. From another point of view, it has been
said that father and son ought to be thought of as half-brothers by two
different mothers, each being the product of the same strain of paternal
germ-plasm, but not of the same strain of maternal germ-plasm.
Biologically, the father or mother should not be thought of as the
_producer_ of a child, but as the trustee of a stream of germ-plasm
which produces a child whenever the proper conditions arise. Or as Sir
Michael Foster put it, "The animal body is in reality a vehicle for ova
or sperm; and after the life of the parent has become potentially
renewed in the offspring, the body remains as a cast-off envelope whose
future is but to die. " Finally to quote the metaphor of J. Arthur
Thomson, one may "think for a moment of a baker who has a very precious
kind of leaven; he uses much of this in baking a large loaf; but he so
arranges matters by a clever contrivance that part of the original
leaven is always carried on unaltered, carefully preserved for the next
baking. Nature is the baker, the loaf is the body, the leaven is the
germ-plasm, and each baking is a generation. "
When the respective functions and relative importance, from a genetic
point of view, of germ-plasm and body-plasm are understood, it must be
fairly evident that the natural point of attack for any attempt at race
betterment which aims to be fundamental rather than wholly superficial,
must be the germ-plasm rather than the body-plasm. The failure to hold
this point of view has been responsible for the disappointing results of
much of the sociological theory of the last century, and for the fact
that some of the work now carried on under the name of race betterment
is producing results that are of little or no significance to true race
betterment.
On the other hand, it must be fairly evident, from the pains which
Nature has taken to arrange for the transmission of the germ-plasm from
generation to generation, that she would also protect it from injury
with meticulous care. It seems hardly reasonable to suppose that a
material of this sort should be exposed, in the higher animals at least,
to all the vicissitudes of the environment, and to injury or change from
the chance of outward circumstances.
In spite of these presumptions which the biologist would, to say the
least, consider worthy of careful investigation, the world is full of
well-intentioned people who are anxious to improve the race, and who in
their attempts to do so, wholly ignore the germ-plasm. They see only the
body-plasm. They are devoted to the dogma that if they can change the
body (and what is here said of the body applies equally to the mind) in
the direction they wish, this change will in some unascertainable way be
reproduced in the next generation. They rarely stop to think that man is
an animal, or that the science of biology might conceivably have
something to say about the means by which his species can be improved;
but if they do, they commonly take refuge, deliberately or
unconsciously, in the biology of half a century ago, which still
believed that these changes of the body could be so impressed on the
germ-plasm as to be continued in the following generation.
Such an assumption is made to-day by few who have thoroughly studied the
subject. Even those who still believed in what is conventionally called
"the inheritance of acquired characteristics" would be quick to
repudiate any such application of the doctrine as is commonly made by
most of the philanthropists and social workers who are proceeding
without seeking the light of biology. But the idea that these
modifications are inherited is so widespread among all who have not
studied biology, and is so much a part of the tradition of society, that
the question must be here examined, before we can proceed confidently
with our program of eugenics.
The problem is first to be defined.
It is evident that all characters which make up a man or woman, or any
other organism, must be either germinal or acquired. It is impossible to
conceive of any other category. But it is frequently hard to say in
which class a given character falls. Worse still, many persons do not
even distinguish the two categories accurately--a confusion made easier
by the quibble that _all_ characters must be acquired, since the
organism starts from a single cell, which possesses practically none of
the traits of the adult.
What we mean by an inborn character is one whose expression is due to
something which is present in the germ-plasm; one which is inherent and
due to heredity. An acquired character is simply a modification, due to
some cause external to the germ-plasm acting on an inborn character. In
looking at an individual, one can not always say with certainty which
characters are which; but with a little trouble, one can usually reach a
reliable decision. It is possible to measure the variation in a given
character in a group of parents and their children, in a number of
different environments; if the degree of resemblance between parent and
offspring is about the same in each case, regardless of the different
surroundings in which the children may have been brought up, the
character may properly be called germinal. This is the biometric method
of investigation. In practice, one can often reach a decision by much
simpler means: if the character is one that appears at birth, e. g. ,
skin color, it is usually safe to assume that it is a germinal
character, unless there is some evident reason for deciding otherwise,
as in the case of a child born with some disease from which the mother
had been suffering for the previous few months. In general, it is more
difficult to decide whether a mental trait is germinal, than whether a
physical one is; and great care should be used in classification.
To make the distinction, one ought to be familiar with an individual
from birth, and to have some knowledge of the conditions to which he was
exposed, in the period between conception and birth,--for of course a
modification which takes place during that time is as truly an acquired
character as one that takes place after parturition. Blindness, for
example, may be an inborn defect. The child from conception may have
lacked the requisites for the development of sight. On the other hand,
it may be an acquired character, due to an ill-advised display of
patriotism on July 4, at some time during childhood; or even to
infection at the moment of birth. Similarly small size may be an inborn
character, due to a small-sized ancestry; but if the child comes of a
normal ancestry and is stunted merely because of lack of proper care and
food, the smallness is an acquired character. Deafness may be congenital
and inborn, or it may be acquired as the result, say, of scarlet fever
during childhood.
Now the inborn characters (excepting modifications _in utero_) are
admittedly heritable, for inborn characters must exist potentially in
the germ-plasm. The belief that acquired characters are also inherited,
therefore, involves belief that in some way the trait acquired by the
parent is incorporated in the germ-plasm of the parent, to be handed on
to the child and reappear in the course of the child's development. The
impress on the parental _body_ must in some way be transferred to the
parental _germ-plasm_; and not as a general influence, but as a specific
one which can be reproduced by the germ-plasm.
This idea was held almost without question by the biologists of the
past, from Aristotle on. Questionings indeed arose from time to time,
but they were vague and carried no weight, until a generation ago
several able men elaborated them. For many years, it was the question of
chief dispute in the study of heredity. The last word has not yet been
said on it. It has theoretical bearings of immense importance; for our
conception of the process of evolution will be shaped according to the
belief that acquired characters are or are not inherited. Herbert
Spencer went so far as to say, "Close contemplation of the facts
impresses me more strongly than ever with two alternatives--either that
there has been inheritance of acquired characters, or there has been no
evolution. " But its practical bearings are no less momentous. Again to
quote Spencer: "Considering the width and depth of the effects which the
acceptance or non-acceptance of one or the other of these hypotheses
must have on our views of life, the question, Which of them is true?
demands beyond all other questions whatever the attention of scientific
men. A grave responsibility rests on biologists in respect of the
general question, since wrong answers lead, among other effects, to
wrong belief about social affairs and to disastrous social actions. "
Biologists certainly have not shirked this "grave responsibility" during
the last 30 years, and they have, in our opinion, satisfactorily
answered the general question. The answer they give is not the answer
Herbert Spencer gave.
But the popular mind frequently lags a generation behind, in its grasp
of the work of science, and it must be said that in this case the
popular mind is still largely under the influence of Herbert Spencer and
his school. _Whether they know it or not_, most people who have not made
a particular study of the question still tacitly assume that the
acquirements of one generation form part of the inborn heritage of the
next, and the present social and educational systems are founded in
large part on this false foundation. Most philanthropy starts out
unquestioningly with the assumption that by modifying the individual for
the better, it will thereby improve the germinal quality of the race.
Even a self-styled eugenist asks, "Can prospective parents who have
thoroughly and systematically disciplined themselves, physically,
mentally and morally, transmit to their offspring the traits or
tendencies which they have developed? " and answers the question with the
astounding statement, "It seems reasonable to suppose that they have
this power, it being simply a phase of heredity, the tendency of like to
beget like. "
The right understanding of this famous problem is therefore fraught with
the most important consequences to eugenics. The huge mass of
experimental evidence that has been accumulated during the last quarter
of a century has, necessarily, been almost wholly based on work with
plants and lower animals. Even though we can not attempt to present a
general review of this evidence, for which the reader must consult one
of the standard works on biology or genetics, we shall point out some of
the considerations underlying the problem and its solution.
In the first place, it must be definitely understood that we are dealing
only with specific, as distinguished from general, transmission. As the
germ-cells derive their nourishment from the body, it is obvious that
any cause profoundly affecting the latter might in that way exercise an
influence on the germ-cells; that if the parent was starved, the
germ-cells might be ill-nourished and the resulting offspring might be
weak and puny. There is experimental evidence that this is the case; but
that is not the inheritance of an acquired character. If, however, a
white man tanned by long exposure to the tropical sun should have
children who were brunettes, when the family stock was all blond; or if
men whose legs were deformed through falls in childhood should have
children whose legs, at birth, appeared deformed in the same manner;
then there would be a distinct case of the transmission of an acquired
characteristic. "The precise question," as Professor Thomson words it,
"is this: Can a structural change in the body, induced by some change in
use or disuse, or by a change in surrounding influence, affect the
germ-cells in such a _specific_ or representative way that the offspring
will through its inheritance exhibit, even in a slight degree, the
modification which the parent acquired? " He then lists a number of
current misunderstandings, which are so widespread that they deserve to
be considered here.
(1) It is frequently argued (as Herbert Spencer himself suggested) that
unless modifications are inherited, there could be no such thing as
evolution. Such pessimism is unwarranted. There _is_ abundant
explanation of evolution, in the abundant supply of germinal variations
which every individual presents.
(2) It is common to advance an _interpretation_ of some observation, in
support of the Lamarckian doctrine, as if it were a _fact_.
Interpretations are not facts. What is wanted are the facts; each
student has a right to interpret them as he sees fit, but not to
represent his interpretation as a fact. It is easy to find structural
features in Nature which _may be interpreted_ as resulting from the
inheritance of acquired characters; but this is not the same as to say
and to prove that they _have resulted_ from such inheritance.
(3) It is common to beg the question by pointing to the transmission of
some character that is not proved to be a modification. Herbert Spencer
cited the prevalence of short-sightedness among the "notoriously
studious" Germans as a defect due to the inheritance of an acquired
character. But he offered no evidence that this is an acquirement rather
than a germinal character. As a fact, there is reason to believe that
weakness of the eyes is one of the characteristics of that race, and
existed long before the Germans ever became studious--even at a time
when most of them could neither read nor write.
(4) The reappearance of a modification may be mistaken for the
transmission of a modification. Thus a blond European family moves to
the tropics, and the parents become tanned. The children who grow up
under the tropical sun are tanned from infancy; and after the
grandchildren or great-grandchildren appear, brown from childhood, some
one points to the case as an instance of permanent modification of
skin-color. But of course the children at the time of birth are as white
as their distant cousins in Europe, and if taken back to the North to be
brought up, would be no darker than their kinsmen who had never been in
the tropics. Such "evidence" has often been brought forward by careless
observers, but can deceive no one who inquires carefully into the facts.
(5) In the case of diseases, re-infection is often mistaken for
transmission. The father had pneumonia; the son later developed it;
ergo, he must have inherited it. What evidence is there that the son in
this case did not get it from an entirely different source? Medical
literature is heavily burdened with such spurious evidence.
(6) Changes in the germ-cells _along with_ changes in the body are not
relevant to this discussion. The mother's body, for example, is poisoned
with alcohol, which is present in large quantities in the blood and
therefore might affect the germ-cells directly. If the children
subsequently born are consistently defective it is not an inheritance of
a body character but the result of a direct modification of the
germ-plasm. The inheritance of an acquired modification of the body can
only be proved if some particular change made in the parent is inherited
as such by the child.
(7) There is often a failure to distinguish between the possible
inheritance of a particular modification, and the possible inheritance
of indirect results of that modification, or of changes correlated with
it. This is a nice but crucial point on which most popular writers are
confused. Let us examine it through a hypothetical case. A woman, not
herself strong, bears a child that is weak. The woman then goes in for
athletics, in order better to fit herself for motherhood; she
specializes on tennis. After a few years she bears another child, which
is much stronger and better developed than the first. "Look," some one
will say, "how the mother has transmitted her acquirement to her
offspring. " We grant that her improved general health will probably
result in a child that is better nourished than the first; but that is a
very different thing from heredity. If, however, the mother had played
tennis until her right arm was over-developed, and her spine bent; if
these characteristics were nowhere present in the ancestry and not seen
in the first child; but if the second child were born with a bent spine
and a right arm of exaggerated musculature, we would be willing to
consider the case on the basis of the inheritance of an acquired
character. We are not likely to have such a case presented to us.
To put the matter more generally, it is not enough to show that _some_
modification in the parent results in _some_ modification in the child.
For the purposes of this argument there must be a similar modification.
(8) Finally, data are frequently presented, which cover only two
generations--parent and child. Indeed, almost all the data alleged to
show the inheritance of acquired characteristics are of this kind. They
are of little or no value as evidence. Cases covering a number of
generations, where a _cumulative_ change was visible, would be of
weight, but on the rare occasions when they are forthcoming, they can be
explained in some other way more satisfactorily than by an appeal to the
theory of Lamarck. [13]
If the evidence currently offered to support a belief in the inheritance
of acquired characters is tested by the application of these
"misunderstandings," it will at once be found that most of it
disappears; that it can be thrown out of court without further
formality. The Lamarckian doctrine is now held mainly by persons who
have either lacked training in the evaluation of evidence, or have never
examined critically the assumptions on which they proceed. Medical men
and breeders of plants or animals are to a large extent believers in
Lamarckism, but the evidence (if any) on which they rely is always
susceptible of explanation in a more reasonable way. It must not be
forgotten that some of the ablest intellects in the world have been
assidously engaged in getting at the truth in the case, during the last
half-century; and it is certainly worthy of consideration that not in a
single case has the transmission of an acquired body character ever
been proved beyond dispute. Those who still hold a belief in it (and it
is fair to say that some men of real ability are among that number) too
often do so, it is to be feared, because it is necessary for the support
of some theoretical doctrine which they have formulated. Certainly there
are few men who can say that they have carefully examined the evidence
in the case, and accept Lamarckism because the evidence forces them to
do so. It will be interesting to review the various classes of alleged
evidence, though we can cite only a few cases from the great number
available (most of them, however, dealing with plants or lower animals).
Nearly all the evidence adduced can be put in one of these four classes:
(1) Mutilations.
(2) Diseases.
(3) Results of use or disuse.
(4) Physico-chemical effects of environment.
The case in regard to mutilations is particularly clear cut and leaves
little room for doubt. The noses and ears of oriental women have been
pierced for generations without number, yet girls are still born with
these parts entire. Circumcision offers another test case. The evidence
of laboratory experiments (amputation of tails) shows no inheritance. It
may be said without hesitation that mutilations are not heritable, no
matter how many generations undergo them.
(2) The transmissibility of acquired diseases is a question involved in
more of a haze of ignorance and loose thinking. It is particularly
frequent to see cases of uterine infection offered as cases of the
inheritance of acquired characters. To use the word "heredity" in such a
case is unjustified. Uterine infection has no bearing whatever on the
question.
Taking an historical view, it seems fairly evident that if diseases were
really inherited, the race would have been extinct long ago. Of course
there are constitutional defects or abnormalities that are in the
germ-plasm and are heritable: such is the peculiar inability of the
blood to coagulate, which marks "bleeders" (sufferers from hemophilia, a
highly hereditary disease). And in many cases it is difficult to
distinguish between a real germinal condition of this sort, and an
acquired disease.
The inheritance of an acquired disease is not only inconceivable, in the
light of what is known about the germ-plasm, but there is no evidence to
support it. While there is most decidedly such a thing as the
inheritance of a tendency to or lack of resistance to a disease, it is
not the result of incidence of the disease on the parent. It is possible
to inherit a tendency to headaches or to chronic alcoholism; and it is
possible to inherit a lack of resistance to common diseases such as
malaria, small-pox or measles; but actually to inherit a zymotic disease
as an inherent genetic trait, is impossible,--is, in fact, a
contradiction of terms.
[Illustration: THE EFFECT OF NURTURE IN CHANGING NATURE
FIG. 2. --Corn of a single variety (Leaming Dent) grown in two
plots: at the left spaced far apart in hills, at the right crowded. The
former grows to its full potential height, the latter is stunted. The
size differences in the two plots are due to differences in environment,
the heredity in both cases being the same. Plants are much more
susceptible to nutritional influences on size than are mammals, but to a
less degree nutrition has a similar effect on man. Photograph from A. F.
Blakeslee. ]
"If now these resemblances are due to the fact that the two members of
any twin pair are treated alike at home, have the same parental models,
attend the same school and are subject in general to closely similar
environmental conditions, then (1) twins should, up to the age of
leaving home, grow more and more alike, and in our measurements the
twins 13 and 14 years old should be much more alike than those 9 and 10
years old. Again (2) if similarity in training is the cause of
similarity in mental traits, ordinary fraternal pairs not over four or
five years apart in age should show a resemblance somewhat nearly as
great as twin pairs, for the home and school condition of a pair of the
former will not be much less similar than those of a pair of the latter.
Again, (3) if training is the cause, twins should show greater
resemblance in the case of traits much subject to training, such as
ability in addition or multiplication, than in traits less subject to
training, such as quickness in marking off the A's on a sheet of printed
capitals, or in writing the opposites of words. "
The data were elaborately analyzed from many points of view. They showed
(1) that the twins 12-14 years old were not any more alike than the
twins 9-11 years old, although they ought to have been, if environment
has great power to mold the character during these so-called "plastic
years of childhood. " They showed (2) that the resemblance between twins
was two or three times as great as between ordinary children of the same
age and sex, brought up under similar environment. There seems to be no
reason, except heredity, why twins should be more alike. The data showed
(3) that the twins were no more alike in traits subject to much training
than in traits subject to little or no training. Their achievement in
these traits was determined by their heredity; training did not
measurably alter these hereditary potentialities.
"The facts," Professor Thorndike wrote, "are easily, simply and
completely explained by one simple hypothesis; namely, that the nature
of the germ-cells--the conditions of conception--cause whatever
similarities and differences exist in the original natures of men, that
these conditions influence mind and body equally, and that in life the
differences in modification of mind and body produced by such
differences as obtain between the environments of present-day New York
City public school children are slight. "
"The inferences," he says, "with respect to the enormous importance of
original nature in determining the behavior and achievements of any man
in comparison with his fellows of the same period of civilization and
conditions of life are obvious. All theories of human life must accept
as a first principle the fact that human beings at birth differ
enormously in mental capacities and that these differences are largely
due to similar differences in their ancestry. All attempts to change
human nature must accept as their most important condition the limits
set by original nature to each individual. "
Meantime other investigators, principally followers of Karl Pearson in
England, were working out correlation coefficients in other lines of
research for hundreds of different traits. As we show in more detail in
Chapter IV, it was found, no matter what physical or mental trait was
measured, that the coefficient of correlation between parent and child
was a little less than . 5 and that the coefficient between brother and
brother, or sister and sister, or brother and sister, was a little more
than . 5. On the average of many cases the mean "nature" value, the
coefficient of direct heredity, was placed at . 51. This gave another
means of measuring nurture, for it was also possible to measure the
relation between any trait in the child and some factor in the
environment. A specific instance will make this clearer.
Groups of school children usually show an appalling percentage of
short-sightedness. Now suppose it is suggested that this is because they
are allowed to learn to read at too early an age. One can find out the
age at which any given child did learn to read, and work out the
coefficient of correlation between this age and the child's amount of
myopia. If the relation between them is very close--say . 7 or . 8--it
will be evident that the earlier a child learns to read, the more
short-sighted he is as he grows older. This will not prove a relation of
cause and effect, but it will at least create a great suspicion. If on
the contrary the correlation is very slight, it will be evident that
early reading has little to do with the prevalance of defective vision
among school children. If investigators similarly work out all the other
correlations that can be suggested, finding whether there is any
regular relation between myopia and overcrowding, long hours of study,
general economic conditions at home, general physical or moral
conditions of parents, the time the child spends out of doors, etc. , and
if no important relation is found between these various factors and
myopia, it will be evident that no factor of the environment which one
can think of as likely to cause the trouble really accounts for the poor
eyesight of school children.
[Illustration: HEIGHT IN CORN AND MEN
FIG. 3. --An unusually short and an unusually tall man,
photographed beside extreme varieties of corn which, like the men, owe
their differences in height indisputably to heredity rather than to
environment. No imaginable environmental differences could reverse the
positions of these two men, or of these two varieties of corn, the
heredity in each case being what it is. The large one might be stunted,
but the small one could not be made much larger. Photograph from A. F.
Blakeslee. ]
This has actually been done,[6] and none of the conditions enumerated
has been found to be closely related to myopia in school children.
Correlations between fifteen environmental conditions and the goodness
of children's eyesight were measured, and only in one case was the
correlation as high as . 1. The mean of these correlations was about
. 04--an absolutely negligible quantity when compared with the common
heredity coefficient of . 51.
Does this prove that the myopia is rather due to heredity? It would, by
a process of exclusion, if every conceivable environmental factor had
been measured and found wanting. That point in the investigation can
never be reached, but a tremendously strong suspicion is at least
justified. Now if the degree of resemblance between the prevalence of
myopia in parents and that in children be directly measured, and if it
be found that when the parent has eye trouble the child also has it,
then it seems that a general knowledge of heredity should lead to the
belief that the difficulty lies there, and that an environmental cause
for the poor vision of the school child was being sought, when it was
all the time due almost entirely to heredity. This final step has not
yet been completed in an adequate way,[7] but the evidence, partly
analogical, gives every reason to believe in the soundness of the
conclusion stated, that in most cases the schoolboy must wear glasses
because of his heredity, not because of overstudy or any neglect on the
part of his parents to care for his eyes properly during his childhood.
[Illustration: WHY MEN GROW SHORT OR TALL
FIG. 4. --Pedigree charts of the two men shown in the preceding
illustration. Squares represent men and circles women; figures
underlined denote measurement in stocking feet. It is obvious from a
comparison of the ancestry of the two men that the short one comes from
a predominantly short family, while the tall one gains his height
likewise from heredity. The shortest individual in the right-hand chart
would have been accounted tall in the family represented on the left.
After A. F. Blakeslee. ]
The extent to which the intelligence of school children is dependent on
defective physique and unfavorable home environment is an important
practical question, which David Heron of London attacked by the methods
we have outlined. He wanted to find out whether the healthy children
were the most intelligent. One is constantly hearing stories of how the
intelligence of school children has been improved by some treatment
which improved their general health, but these stories are rarely
presented in such a way as to contribute evidence of scientific value.
It was desirable to know what exact measurement would show. The
intelligence of all the children in fourteen schools was measured in its
correlation with weight and height, conditions of clothing and teeth,
state of nutrition, cleanliness, good hearing, and the condition of the
cervical glands, tonsils and adenoids. It could not be found that mental
capacity was closely related to any of the characters dealt with. [8] The
particular set of characters measured was taken because it happened to
be furnished by data collected for another purpose; the various items
are suggestive rather than directly conclusive. Here again, the
correlation in most cases was less than . 1, as compared with the general
heredity correlation of . 5.
The investigation need not be limited to problems of bad breeding.
Eugenics, as its name shows, is primarily interested in "good breeding;"
it is particularly worth while, therefore, to examine the relations
between heredity and environment in the production of mental and moral
superiority.
If success in life--the kind of success that is due to great mental and
moral superiority--is due to the opportunities a man has, then it ought
to be pretty evenly distributed among all persons who have had favorable
opportunities, provided a large enough number of persons be taken to
allow the laws of probability full play. England offers a good field to
investigate this point, because Oxford and Cambridge, her two great
universities, turn out most of the eminent men of the country, or at
least have done so until recently. If nothing more is necessary to
ensure a youth's success than to give him a first-class education and
the chance to associate with superior people, then the prizes of life
ought to be pretty evenly distributed among the graduates of the two
universities, during a period of a century or two.
This is not the case. When we look at the history of England, as Galton
did nearly half a century ago, we find success in life to an unexpected
degree a family affair. The distinguished father is likely to have a
distinguished son, while the son of two "nobodies" has a very small
chance of becoming distinguished. To cite one concrete case, Galton
found[9] that the son of a distinguished judge had about one chance in
four of becoming himself distinguished, while the son of a man picked
out at random from the population had about one chance in 4,000 of
becoming similarly distinguished.
The objection at once occurs that perhaps social opportunities might
play the predominant part; that the son of an obscure man never gets a
chance, while the son of the prominent man is pushed forward regardless
of his inherent abilities. This, as Galton argued at length, can not be
true of men of really eminent attainments. The true genius, he thought,
frequently succeeds in rising despite great obstacles, while no amount
of family pull will succeed in making a mediocrity into a genius,
although it may land him in some high and very comfortable official
position. Galton found a good illustration in the papacy, where during
many centuries it was the custom for a pope to adopt one of his nephews
as a son, and push him forward in every way. If opportunity were all
that is required, these adopted sons ought to have reached eminence as
often as a real son would have done; but statistics show that they
reached eminence only as often as would be expected for nephews of great
men, whose chance is notably less, of course, than that of sons of great
men, in whom the intensity of heredity is much greater.
Transfer the inquiry to America, and it becomes even more conclusive,
for this is supposed to be the country of equal opportunities, where it
is a popular tradition that every boy has a chance to become president.
Success may be in some degree a family affair in caste-ridden England;
is it possible that the past history of the United States should show
the same state of affairs?
Galton found that about half of the great men of England had
distinguished close relatives. If the great men of America have fewer
distinguished close relatives, environment will be able to make out a
plausible case: it will be evident that in this continent of boundless
opportunities the boy with ambition and energy gets to the top, and that
this ambition and energy do not depend on the kind of family he comes
from.
Frederick Adams Woods has made precisely this investigation. [10] The
first step was to find out how many eminent men there are in American
history. Biographical dictionaries list about 3,500, and this number
provides a sufficiently unbiased standard from which to work. Now, Dr.
Woods says, if we suppose the average person to have as many as twenty
close relatives--as near as an uncle or a grandson--then computation
shows that only one person in 500 in the United States has a chance to
be a near relative of one of the 3,500 eminent men--provided it is
purely a matter of chance. As a fact, the 3,500 eminent men listed by
the biographical dictionaries are related to each other not as one in
500, but as one in five. If the more celebrated men alone be considered,
it is found that the percentage increases so that about one in three of
them has a close relative who is also distinguished. This ratio
increases to more than one in two when the families of the forty-six
Americans in the Hall of Fame are made the basis of study. If all the
eminent relations of those in the Hall of Fame are counted, they average
more than one apiece. Therefore, they are from five hundred to a
thousand times as much related to distinguished people as the ordinary
mortal is.
To look at it from another point of view, something like 1% of the
population of the country is as likely to produce a man of genius as is
all the rest of the population put together,--the other 99%.
This might still be due in some degree to family influence, to the
prestige of a famous name, or to educational advantages afforded the
sons of successful men. Dr. Woods' study of the royal families of Europe
is more decisive. [11]
In the latter group, the environment must be admitted--on the whole--to
be uniformly favorable. It has varied, naturally, in each case, but
speaking broadly it is certain that all the members of this group have
had the advantage of a good education, of unusual care and attention. If
such things affect achievement, then the achievements of this class
ought to be pretty generally distributed among the whole class. If
opportunity is the cause of a man's success, then most of the members of
this class ought to have succeeded, because to every one of royal blood,
the door of opportunity usually stands open. One would expect the heir
to the throne to show a better record than his younger brothers,
however, because his opportunity to distinguish himself is naturally
greater. This last point will be discussed first.
Dr. Woods divided all the individuals in his study into ten classes for
intellectuality and ten for morality, those most deficient in the
qualities being put in class 1, while the men and women of preeminent
intellectual and moral worth were put in class 10. Now if preeminent
intellect and morality were at all linked with the better chances that
an inheritor of succession has, then heirs to the throne ought to be
more plentiful in the higher grades than in the lower. Actual count
shows this not to be the case. A slightly larger percentage of
inheritors is rather to be found in the lower grades. The younger sons
have made just as good a showing as the sons who succeeded to power; as
one would expect if intellect and morality are due largely to heredity,
but as one would not expect if intellect and morality are due largely to
outward circumstances.
Are "conditions of turmoil, stress and adversity" strong forces in the
production of great men, as has often been claimed? There is no evidence
from facts to support that view. In the case of a few great commanders,
the times seemed particularly favorable. Napoleon, for example, could
hardly have been Napoleon had it not been for the French revolution. But
in general there have been wars going on during the whole period of
modern European history; there have always been opportunities for a
royal hero to make his appearance; but often the country has called for
many years in vain. Circumstances were powerless to produce a great man
and the nation had to wait until heredity produced him. Spain has for
several centuries been calling for genius in leadership in some lines;
but in vain. England could not get an able man from the Stuart line,
despite her need, and had to wait for William of Orange, who was a
descendant of a man of genius, William the Silent. "Italy had to wait
fifty years in bondage for her deliverers, Cavour, Garibaldi and Victor
Emmanuel. "
"The upshot of it all," Dr. Woods decides, "is that, as regards
intellectual life, environment is a totally inadequate explanation. If
it explains certain characters in certain instances, it always fails to
explain many more, while heredity not only explains all, or at least
90%, of the intellectual side of character in practically every
instance, but does so best when questions of environment are left out of
discussion. "
Despite the good environment almost uniformly present, the geniuses in
royalty are not scattered over the surface of the pedigree chart, but
form isolated little groups of closely related individuals. One centers
in Frederick the Great, another in Queen Isabella of Spain, a third in
William the Silent, and a fourth in Gustavus Adolphus. Furthermore, the
royal personages who are conspicuously low in intellect and morality are
similarly grouped. Careful study of the circumstances shows nothing in
the environment that would produce this grouping of genius, while it is
exactly what a knowledge of heredity leads one to expect.
In the next place, do the superior members of royalty have
proportionately more superior individuals among their close relatives,
as was found to be the case among the Americans in the Hall of Fame? A
count shows at once that they do. The first six grades all have about an
equal number of eminent relatives, but grade 7 has more while grade 8
has more than grade 7, and the geniuses of grade 10 have the highest
proportion of nearer relatives of their own character. Surely it cannot
be supposed that a relative of a king in grade 8 has on the average a
much less favorable environment than a relative of a king in grade 10.
Is it not fair, then, to assume that this relative's greater endowment
in the latter case is due to heredity?
Conditions are the same, whether males or females be considered. The
royal families of Europe offer a test case because for them the
environment is nearly uniformly favorable. A study of them shows great
mental and moral differences between them, and critical evidence
indicates that these differences are largely due to differences in
heredity. Differences of opportunity do not appear to be largely
responsible for the achievements of the individuals.
But, it is sometimes objected, opportunity certainly is responsible for
the appearance of much talent that would otherwise never appear. Take
the great increase in the number of scientific men in Germany during the
last half century, for example. It can not be pretended that this is due
to an increased birth-rate of such talent; it means that the growth of
an appreciation of scientific work has produced an increased amount of
scientific talent. J. McKeen Cattell has argued this point most
carefully in his study of the families of one thousand American men of
science (_Popular Science Monthly_, May, 1915). "A Darwin born in China
in 1809," he says, "could not have become a Darwin, nor could a Lincoln
born here on the same day have become a Lincoln had there been no Civil
War. If the two infants had been exchanged there would have been no
Darwin in America and no Lincoln in England. " And so he continues,
urging that in the production of scientific men, at least, education is
more important than eugenics.
This line of argument contains a great deal of obvious truth, but is
subject to a somewhat obvious objection, if it is pushed too far. It is
certainly true that the exact field in which a man's activities will
find play is largely determined by his surroundings and education. Young
men in the United States are now becoming lawyers or men of science, who
would have become ministers had they been born a century or two ago. But
this environmental influence seems to us a minor one, for the man who is
highly gifted in some one line is usually, as all the work of
differential psychology shows, gifted more than the average in many
other lines. Opportunity decides in just what field his life work shall
lie; but he would be able to make a success in a number of fields.
Darwin born in America would probably not have become the Darwin we
know, but it is not to be supposed that he would have died a "mute,
inglorious Milton": it is not likely that he would have failed to make
his mark in some line of human activity. Dr. Cattell's argument, then,
while admissible, can not properly be urged against the fact that
ability is mainly dependent on inheritance.
We need not stop with the conclusion that equality of training or
opportunity is unable to level the inborn differences between men. We
can go even farther, and produce evidence to show that equality of
training _increases the differences_ in results achieved.
This evidence is obtained by measuring the effects of equal amounts of
exercise of a function upon individual differences in respect to
efficiency in it. Suppose one should pick out, at random, eight
children, and let them do problems in multiplication for 10 minutes.
After a number of such trials, the three best might average 39 correct
solutions in the 10 minutes, and the three poorest might average 25
examples. Then let them continue the work, until each one of them has
done 700 examples. Here is equality in training; does it lead to uniform
results?
Dr. Starch made the actual test which we have outlined and found that
the three best pupils gained on the average 45 in the course of doing
700 examples; while the three poorest gained only 26 in the same course
of time.
Similar tests have been made of school children in a number of
instances, and have shown that equality of training fails to bring about
equality of performance. All improve to some extent; but those who are
naturally better than their comrades usually become better still, when
conditions for all are the same. E. L. Thorndike gives[12] the following
tabular statement of a test he conducted:
THE EFFECT OF EQUAL AMOUNTS OF PRACTICE UPON INDIVIDUAL DIFFERENCES
IN THE MENTAL MULTIPLICATION OF A THREE-PLACE BY A THREE-PLACE
NUMBER
Amount done Percentage of
per unit of correct figures
time in answers
Hours of Practice
|
| First 5 Examples First 5 Examples
| | |
| | Last 5 or 10 | Last 5 or 10
| | Examples | Examples
| | | | |
| | | Gain | | Gain
Initial highest five individuals 5. 1 85 147 61 70 78 18
" next five " 5. 1 56 107 51 68 78 10
" " six " 5. 3 46 68 22 74 82 8
" " six " 5. 4 38 46 8 58 70 12
" " five " 5. 2 31 57 26 47 67 20
" " one individual 5. 2 19 32 13 100 82 -18
Similar results have been obtained by half a dozen other experimenters,
using the tests of mental multiplication, addition, marking A's on a
printed sheet of capitals, and the like. It would be a mistake to
conclude too much from experiments of such restricted scope; but they
all agree in showing that if every child were given an equal training,
the differences in these traits would nevertheless be very great.
And although we do not wish to strain the application of these results
too far, we are at least justified in saying that they strongly indicate
that inborn mediocrity can not be made into a high grade of talent by
training. Not every boy has a chance to distinguish himself, even if he
receives a good education.
We are driven back to the same old conclusion, that it is primarily
inborn nature which causes the achievements of men and women to be what
they are. Good environment, opportunity, training, will give good
heredity a chance to express itself; but they can not produce greatness
from bad heredity.
These conclusions are familiar to scientific sociologists, but they have
not yet had the influence on social service and practical attempts at
reform which they deserve. Many popular writers continue to confuse
cause and effect, as for example H. Addington Bruce, who contributed an
article to the _Century Magazine_, not long ago, on "The Boy Who Goes
Wrong. " After alleging that the boy who goes wrong does so because he is
not properly brought up, Mr. Bruce quotes with approval the following
passage from Paul Dubois, "the eminent Swiss physician and philosopher:
"If you have the happiness to be a well-living man, take care not to
attribute the credit of it to yourself. Remember the favorable
conditions in which you have lived, surrounded by the relatives who
loved you and set you a good example; do not forget the close friends
who have taken you by the hand and led you away from the quagmires of
evil; keep a grateful remembrance for all the teachers who have
influenced you, the kind and intelligent school-master, the devoted
pastor; realize all these multiple influences which have made you what
you are. Then you will remember that such and such a culprit has not in
his sad life met with these favorable conditions; that he had a drunken
father or a foolish mother, and that he has lived without affection,
exposed to all kinds of temptation. You will then take pity upon this
disinherited man, whose mind has been nourished upon malformed mental
images, begetting evil sentiments such as immoderate desire or social
hatred. "
Mr. Bruce indorses this kind of talk when he concludes, "The blame for
the boy who goes wrong does not rest with the boy himself, or yet with
his remote ancestors. It rests squarely with the parents who, through
ignorance or neglect, have failed to mold him aright in the plastic days
of childhood. "
Where is the evidence of the existence of these plastic days of
childhood?
If they exist, why do not ordinary brothers become as much
alike as identical twins? How long are we to be asked to believe, on
blind faith, that the child is putty, of which the educator can make
either mediocrity or genius, depending on his skill? What does the
environmentalist _know_ about these "plastic days"? If a boy has a
drunken father or foolish mother, does it not suggest that there is
something wrong with his pedigree? With such an ancestry, we do not
expect him to turn out brilliantly, no matter in what home he is brought
up. If a boy has the kind of parents who bring him up well; if he is,
as Dr. Dubois says, surrounded by relatives who love him and set him a
good example, we at once have ground for a suspicion that he comes of a
pretty good family, a stock characterized by a high standard of
intellectuality and morality, and it would surprise us if such a boy did
not turn out well. But he turns out well because what's bred in the bone
will show in him, if it gets any kind of a chance. It is his nature, not
his nurture, that is mainly responsible for his character.
CHAPTER II
MODIFICATION OF THE GERM-PLASM
Every living creature was at some stage of its life nothing more than a
single cell. It is generally known that human beings result from the
union of an egg-cell and a sperm-cell, but it is not so universally
understood that these germ-cells are part of a continuous stream of
germ-plasm which has been in existence ever since the appearance of life
on the globe, and which is destined to continue in existence as long as
life remains on the globe.
The corollaries of this fact are of great importance. Some of them will
be considered in this chapter.
Early investigators tended naturally to look on the germ-cells as a
product of the body. Being supposedly products of the body, it was
natural to think that they would in some measure reproduce the character
of the body which created them; and Darwin elaborated an ingenious
hypothesis to explain how the various characters could be represented in
the germ-cell. The idea held by him, in common with most other thinkers
of his period, is still held more or less unconsciously by those who
have not given particular attention to the subject. Generation is
conceived as a direct chain: the body produces the germ-cell which
produces another body which in turn produces another germ-cell, and so
on.
But a generation ago this idea fell under suspicion. August Weismann,
professor of zoology in the University of Freiburg, Germany, made
himself the champion of the new idea, about 1885, and developed it so
effectively that it is now a part of the creed of nearly every
biologist.
Weismann caused a general abandonment of the idea that the germ-cell is
produced by the body in each generation, and popularized the conception
of the germ-cell as a product of a stream of undifferentiated
germ-plasm, not only continuous but (potentially at least) immortal.
The body does not produce the germ-cells, he pointed out; instead, the
germ-cells produce the body.
The basis of this theory can best be understood by a brief consideration
of the reproduction of very simple organisms.
"Death is the end of life," is the belief of many other persons than the
Lotus Eaters. It is commonly supposed that everything which lives must
eventually die. But study of a one-celled animal, an Infusorian, for
example, reveals that when it reaches a certain age it pinches in two,
and each half becomes an Infusorian in all appearance identical with the
original cell. Has the parent cell then died? It may rather be said to
survive, in two parts. Each of these daughter cells will in turn go
through the same process of reproduction by simple fission, and the
process will be continued in their descendants. The Infusorian can be
called potentially immortal, because of this method of reproduction.
The immortality, as Weismann pointed out, is not of the kind attributed
by the Greeks to their gods, who could not die because no wound could
destroy them. On the contrary, the Infusorian is extremely fragile, and
is dying by millions at every instant; but if circumstances are
favorable, it _can_ live on; it is not inevitably doomed to die sooner
or later, as is Man. "It dies from accident often, from old age never. "
Now the single-celled Infusorian is in many respects comparable with the
single-celled germ of the higher animals. The analogy has often been
carried too far; yet it remains indisputable that the germ-cells of men
reproduce in the same way--by simple fission--as the Infusorian and
other one-celled animals and plants, and that they are organized on much
the same plan. Given favorable circumstances, the germ-cell should be
expected to be equally immortal. Does it ever find these favorable
circumstances?
The investigations of microscopists indicate that it does--that
evolution has provided it with these favorable circumstances, in the
bodies of the higher animals. Let us recall in outline the early history
of the fertilized germ-cell, the _zygote_ formed by the union of ovum
and spermatozoon. These two unite to form a single cell, which is
essentially the same, physiologically, as other germ-cells. It divides
in two similar cells; these each divide; the resulting cells again
divide, and so the process continues, until the whole body--a fully
developed man,--has been produced by division and redivision of the one
zygote.
But the germ-cell is obviously different from most of the cells that
make up the finished product, the body. The latter are highly
differentiated and specialized for different functions--blood cells,
nerve cells, bone cells, muscle cells, and so on, each a single cell but
each adapted to do a certain work, for which the original,
undifferentiated germ-cell was wholly unfit. It is evident that
differentiation began to take place at some point in the series of
divisions, that is to say, in the development of the embryo.
Th. Boveri, studying the development of a threadworm, made the
interesting discovery that this differentiation began at the first
division. Of the two daughter-cells produced from the zygote, one
continued dividing at a very slow rate, and without showing any
specialization. Its "line of descent" produced only germ-cells. The
products of division of the other daughter-cell began to differentiate,
and soon formed all the necessary kinds of cells to make up the body of
the mature worm. In this body, the cells from the first daughter-cell
mentioned were inclosed, still undifferentiated: they formed the
germ-cells of the next generation, and after maturity were ready to be
ejected from the body, and to form new threadworms.
Imagine this process taking place through generation after generation of
threadworms, and one will realize that the germ-plasm was passed on
directly from one generation to the next; that in each generation it
gave rise to body-plasm, but that it did not at any time lose its
identity or continuity, a part of the germ-plasm being always set aside,
undifferentiated, to be handed on to the next generation.
In the light of this example, one can better understand the definition
of germ-plasm as "that part of the substance of the parents which does
not die with them, but perpetuates itself in their offspring. " By
bringing his imagination into play, the reader will realize that there
is no limit to the backward continuity of this germ-plasm in the
threadworm. Granted that each species has arisen by evolution from some
other, this germ-cell which is observed in the body of the threadworm,
must be regarded as part of what may well be called a stream of
germ-plasm, that reaches back to the beginning of life in the world. It
will be equally evident that these is no foreordained limit to the
forward extension of the stream. It will continue in some branch, as
long as there are any threadworms or descendants of threadworms in the
world.
The reader may well express doubt as to whether what has been
demonstrated for the threadworm can be demonstrated for the higher
animals, including man. It must be admitted that in many of these
animals conditions are too unfavorable, and the process of embryology
too complicated, or too difficult to observe, to permit as distinct a
demonstration of this continuity of the germ-plasm, wherever it is
sought. But it has been demonstrated in a great many animals; no facts
which impair the theory have been discovered; and biologists therefore
feel perfectly justified in generalizing and declaring the continuity of
germ-plasm to be a law of the world of living things.
Focusing attention on its application to man, one sees that the race
must represent an immense network of lines of descent, running back
through a vast number of different forms of gradually diminishing
specialization, until it comes to a point where all its threads merge in
one knot--the single cell with which it may be supposed that life on
this globe began. Each individual is not only figuratively, but in a
very literal sense, the carrier of the heritage of the whole race--of
the whole past, indeed. Each individual is temporarily the custodian of
part of the "stuff of life"; from an evolutionary point of view, he may
be said to have been brought into existence, primarily to pass this
sacred heritage on to the next generation. From Nature's standpoint, he
is of little use in the world, his existence is scarcely justified,
unless he faithfully discharges this trust, passing on to the future
the "Lamp of Life" whose fire he has been created to guard for a short
while.
Immortality, we may point out in passing, is thus no mere _hope_ to the
parent: it is a _real possibility_. The death of the huge agglomeration
of highly specialized body-cells is a matter of little consequence, if
the germ-plasm, with its power to reproduce not only these body-cells,
but the mental traits--indeed, we may in a sense say the very soul--that
inhabited them, has been passed on. The individual continues to live, in
his offspring, just as the past lives in him. To the eugenist, life
everlasting is something more than a figure of speech or a theological
concept--it is as much a reality as the beat of the heart, the growth of
muscles or the activity of the mind.
This doctrine of the continuity of germ-plasm throws a fresh light on
the nature of human relationships. It is evident that the son who
resembles his father can not accurately be called a "chip off the old
block. " Rather, they are both chips off the same block; and aside from
bringing about the fusion of two distinct strains of germ-plasm, father
and mother are no more responsible for endowing the child with its
characters except in the choice of mate, than is the child for "stamping
his impress" on his parents. From another point of view, it has been
said that father and son ought to be thought of as half-brothers by two
different mothers, each being the product of the same strain of paternal
germ-plasm, but not of the same strain of maternal germ-plasm.
Biologically, the father or mother should not be thought of as the
_producer_ of a child, but as the trustee of a stream of germ-plasm
which produces a child whenever the proper conditions arise. Or as Sir
Michael Foster put it, "The animal body is in reality a vehicle for ova
or sperm; and after the life of the parent has become potentially
renewed in the offspring, the body remains as a cast-off envelope whose
future is but to die. " Finally to quote the metaphor of J. Arthur
Thomson, one may "think for a moment of a baker who has a very precious
kind of leaven; he uses much of this in baking a large loaf; but he so
arranges matters by a clever contrivance that part of the original
leaven is always carried on unaltered, carefully preserved for the next
baking. Nature is the baker, the loaf is the body, the leaven is the
germ-plasm, and each baking is a generation. "
When the respective functions and relative importance, from a genetic
point of view, of germ-plasm and body-plasm are understood, it must be
fairly evident that the natural point of attack for any attempt at race
betterment which aims to be fundamental rather than wholly superficial,
must be the germ-plasm rather than the body-plasm. The failure to hold
this point of view has been responsible for the disappointing results of
much of the sociological theory of the last century, and for the fact
that some of the work now carried on under the name of race betterment
is producing results that are of little or no significance to true race
betterment.
On the other hand, it must be fairly evident, from the pains which
Nature has taken to arrange for the transmission of the germ-plasm from
generation to generation, that she would also protect it from injury
with meticulous care. It seems hardly reasonable to suppose that a
material of this sort should be exposed, in the higher animals at least,
to all the vicissitudes of the environment, and to injury or change from
the chance of outward circumstances.
In spite of these presumptions which the biologist would, to say the
least, consider worthy of careful investigation, the world is full of
well-intentioned people who are anxious to improve the race, and who in
their attempts to do so, wholly ignore the germ-plasm. They see only the
body-plasm. They are devoted to the dogma that if they can change the
body (and what is here said of the body applies equally to the mind) in
the direction they wish, this change will in some unascertainable way be
reproduced in the next generation. They rarely stop to think that man is
an animal, or that the science of biology might conceivably have
something to say about the means by which his species can be improved;
but if they do, they commonly take refuge, deliberately or
unconsciously, in the biology of half a century ago, which still
believed that these changes of the body could be so impressed on the
germ-plasm as to be continued in the following generation.
Such an assumption is made to-day by few who have thoroughly studied the
subject. Even those who still believed in what is conventionally called
"the inheritance of acquired characteristics" would be quick to
repudiate any such application of the doctrine as is commonly made by
most of the philanthropists and social workers who are proceeding
without seeking the light of biology. But the idea that these
modifications are inherited is so widespread among all who have not
studied biology, and is so much a part of the tradition of society, that
the question must be here examined, before we can proceed confidently
with our program of eugenics.
The problem is first to be defined.
It is evident that all characters which make up a man or woman, or any
other organism, must be either germinal or acquired. It is impossible to
conceive of any other category. But it is frequently hard to say in
which class a given character falls. Worse still, many persons do not
even distinguish the two categories accurately--a confusion made easier
by the quibble that _all_ characters must be acquired, since the
organism starts from a single cell, which possesses practically none of
the traits of the adult.
What we mean by an inborn character is one whose expression is due to
something which is present in the germ-plasm; one which is inherent and
due to heredity. An acquired character is simply a modification, due to
some cause external to the germ-plasm acting on an inborn character. In
looking at an individual, one can not always say with certainty which
characters are which; but with a little trouble, one can usually reach a
reliable decision. It is possible to measure the variation in a given
character in a group of parents and their children, in a number of
different environments; if the degree of resemblance between parent and
offspring is about the same in each case, regardless of the different
surroundings in which the children may have been brought up, the
character may properly be called germinal. This is the biometric method
of investigation. In practice, one can often reach a decision by much
simpler means: if the character is one that appears at birth, e. g. ,
skin color, it is usually safe to assume that it is a germinal
character, unless there is some evident reason for deciding otherwise,
as in the case of a child born with some disease from which the mother
had been suffering for the previous few months. In general, it is more
difficult to decide whether a mental trait is germinal, than whether a
physical one is; and great care should be used in classification.
To make the distinction, one ought to be familiar with an individual
from birth, and to have some knowledge of the conditions to which he was
exposed, in the period between conception and birth,--for of course a
modification which takes place during that time is as truly an acquired
character as one that takes place after parturition. Blindness, for
example, may be an inborn defect. The child from conception may have
lacked the requisites for the development of sight. On the other hand,
it may be an acquired character, due to an ill-advised display of
patriotism on July 4, at some time during childhood; or even to
infection at the moment of birth. Similarly small size may be an inborn
character, due to a small-sized ancestry; but if the child comes of a
normal ancestry and is stunted merely because of lack of proper care and
food, the smallness is an acquired character. Deafness may be congenital
and inborn, or it may be acquired as the result, say, of scarlet fever
during childhood.
Now the inborn characters (excepting modifications _in utero_) are
admittedly heritable, for inborn characters must exist potentially in
the germ-plasm. The belief that acquired characters are also inherited,
therefore, involves belief that in some way the trait acquired by the
parent is incorporated in the germ-plasm of the parent, to be handed on
to the child and reappear in the course of the child's development. The
impress on the parental _body_ must in some way be transferred to the
parental _germ-plasm_; and not as a general influence, but as a specific
one which can be reproduced by the germ-plasm.
This idea was held almost without question by the biologists of the
past, from Aristotle on. Questionings indeed arose from time to time,
but they were vague and carried no weight, until a generation ago
several able men elaborated them. For many years, it was the question of
chief dispute in the study of heredity. The last word has not yet been
said on it. It has theoretical bearings of immense importance; for our
conception of the process of evolution will be shaped according to the
belief that acquired characters are or are not inherited. Herbert
Spencer went so far as to say, "Close contemplation of the facts
impresses me more strongly than ever with two alternatives--either that
there has been inheritance of acquired characters, or there has been no
evolution. " But its practical bearings are no less momentous. Again to
quote Spencer: "Considering the width and depth of the effects which the
acceptance or non-acceptance of one or the other of these hypotheses
must have on our views of life, the question, Which of them is true?
demands beyond all other questions whatever the attention of scientific
men. A grave responsibility rests on biologists in respect of the
general question, since wrong answers lead, among other effects, to
wrong belief about social affairs and to disastrous social actions. "
Biologists certainly have not shirked this "grave responsibility" during
the last 30 years, and they have, in our opinion, satisfactorily
answered the general question. The answer they give is not the answer
Herbert Spencer gave.
But the popular mind frequently lags a generation behind, in its grasp
of the work of science, and it must be said that in this case the
popular mind is still largely under the influence of Herbert Spencer and
his school. _Whether they know it or not_, most people who have not made
a particular study of the question still tacitly assume that the
acquirements of one generation form part of the inborn heritage of the
next, and the present social and educational systems are founded in
large part on this false foundation. Most philanthropy starts out
unquestioningly with the assumption that by modifying the individual for
the better, it will thereby improve the germinal quality of the race.
Even a self-styled eugenist asks, "Can prospective parents who have
thoroughly and systematically disciplined themselves, physically,
mentally and morally, transmit to their offspring the traits or
tendencies which they have developed? " and answers the question with the
astounding statement, "It seems reasonable to suppose that they have
this power, it being simply a phase of heredity, the tendency of like to
beget like. "
The right understanding of this famous problem is therefore fraught with
the most important consequences to eugenics. The huge mass of
experimental evidence that has been accumulated during the last quarter
of a century has, necessarily, been almost wholly based on work with
plants and lower animals. Even though we can not attempt to present a
general review of this evidence, for which the reader must consult one
of the standard works on biology or genetics, we shall point out some of
the considerations underlying the problem and its solution.
In the first place, it must be definitely understood that we are dealing
only with specific, as distinguished from general, transmission. As the
germ-cells derive their nourishment from the body, it is obvious that
any cause profoundly affecting the latter might in that way exercise an
influence on the germ-cells; that if the parent was starved, the
germ-cells might be ill-nourished and the resulting offspring might be
weak and puny. There is experimental evidence that this is the case; but
that is not the inheritance of an acquired character. If, however, a
white man tanned by long exposure to the tropical sun should have
children who were brunettes, when the family stock was all blond; or if
men whose legs were deformed through falls in childhood should have
children whose legs, at birth, appeared deformed in the same manner;
then there would be a distinct case of the transmission of an acquired
characteristic. "The precise question," as Professor Thomson words it,
"is this: Can a structural change in the body, induced by some change in
use or disuse, or by a change in surrounding influence, affect the
germ-cells in such a _specific_ or representative way that the offspring
will through its inheritance exhibit, even in a slight degree, the
modification which the parent acquired? " He then lists a number of
current misunderstandings, which are so widespread that they deserve to
be considered here.
(1) It is frequently argued (as Herbert Spencer himself suggested) that
unless modifications are inherited, there could be no such thing as
evolution. Such pessimism is unwarranted. There _is_ abundant
explanation of evolution, in the abundant supply of germinal variations
which every individual presents.
(2) It is common to advance an _interpretation_ of some observation, in
support of the Lamarckian doctrine, as if it were a _fact_.
Interpretations are not facts. What is wanted are the facts; each
student has a right to interpret them as he sees fit, but not to
represent his interpretation as a fact. It is easy to find structural
features in Nature which _may be interpreted_ as resulting from the
inheritance of acquired characters; but this is not the same as to say
and to prove that they _have resulted_ from such inheritance.
(3) It is common to beg the question by pointing to the transmission of
some character that is not proved to be a modification. Herbert Spencer
cited the prevalence of short-sightedness among the "notoriously
studious" Germans as a defect due to the inheritance of an acquired
character. But he offered no evidence that this is an acquirement rather
than a germinal character. As a fact, there is reason to believe that
weakness of the eyes is one of the characteristics of that race, and
existed long before the Germans ever became studious--even at a time
when most of them could neither read nor write.
(4) The reappearance of a modification may be mistaken for the
transmission of a modification. Thus a blond European family moves to
the tropics, and the parents become tanned. The children who grow up
under the tropical sun are tanned from infancy; and after the
grandchildren or great-grandchildren appear, brown from childhood, some
one points to the case as an instance of permanent modification of
skin-color. But of course the children at the time of birth are as white
as their distant cousins in Europe, and if taken back to the North to be
brought up, would be no darker than their kinsmen who had never been in
the tropics. Such "evidence" has often been brought forward by careless
observers, but can deceive no one who inquires carefully into the facts.
(5) In the case of diseases, re-infection is often mistaken for
transmission. The father had pneumonia; the son later developed it;
ergo, he must have inherited it. What evidence is there that the son in
this case did not get it from an entirely different source? Medical
literature is heavily burdened with such spurious evidence.
(6) Changes in the germ-cells _along with_ changes in the body are not
relevant to this discussion. The mother's body, for example, is poisoned
with alcohol, which is present in large quantities in the blood and
therefore might affect the germ-cells directly. If the children
subsequently born are consistently defective it is not an inheritance of
a body character but the result of a direct modification of the
germ-plasm. The inheritance of an acquired modification of the body can
only be proved if some particular change made in the parent is inherited
as such by the child.
(7) There is often a failure to distinguish between the possible
inheritance of a particular modification, and the possible inheritance
of indirect results of that modification, or of changes correlated with
it. This is a nice but crucial point on which most popular writers are
confused. Let us examine it through a hypothetical case. A woman, not
herself strong, bears a child that is weak. The woman then goes in for
athletics, in order better to fit herself for motherhood; she
specializes on tennis. After a few years she bears another child, which
is much stronger and better developed than the first. "Look," some one
will say, "how the mother has transmitted her acquirement to her
offspring. " We grant that her improved general health will probably
result in a child that is better nourished than the first; but that is a
very different thing from heredity. If, however, the mother had played
tennis until her right arm was over-developed, and her spine bent; if
these characteristics were nowhere present in the ancestry and not seen
in the first child; but if the second child were born with a bent spine
and a right arm of exaggerated musculature, we would be willing to
consider the case on the basis of the inheritance of an acquired
character. We are not likely to have such a case presented to us.
To put the matter more generally, it is not enough to show that _some_
modification in the parent results in _some_ modification in the child.
For the purposes of this argument there must be a similar modification.
(8) Finally, data are frequently presented, which cover only two
generations--parent and child. Indeed, almost all the data alleged to
show the inheritance of acquired characteristics are of this kind. They
are of little or no value as evidence. Cases covering a number of
generations, where a _cumulative_ change was visible, would be of
weight, but on the rare occasions when they are forthcoming, they can be
explained in some other way more satisfactorily than by an appeal to the
theory of Lamarck. [13]
If the evidence currently offered to support a belief in the inheritance
of acquired characters is tested by the application of these
"misunderstandings," it will at once be found that most of it
disappears; that it can be thrown out of court without further
formality. The Lamarckian doctrine is now held mainly by persons who
have either lacked training in the evaluation of evidence, or have never
examined critically the assumptions on which they proceed. Medical men
and breeders of plants or animals are to a large extent believers in
Lamarckism, but the evidence (if any) on which they rely is always
susceptible of explanation in a more reasonable way. It must not be
forgotten that some of the ablest intellects in the world have been
assidously engaged in getting at the truth in the case, during the last
half-century; and it is certainly worthy of consideration that not in a
single case has the transmission of an acquired body character ever
been proved beyond dispute. Those who still hold a belief in it (and it
is fair to say that some men of real ability are among that number) too
often do so, it is to be feared, because it is necessary for the support
of some theoretical doctrine which they have formulated. Certainly there
are few men who can say that they have carefully examined the evidence
in the case, and accept Lamarckism because the evidence forces them to
do so. It will be interesting to review the various classes of alleged
evidence, though we can cite only a few cases from the great number
available (most of them, however, dealing with plants or lower animals).
Nearly all the evidence adduced can be put in one of these four classes:
(1) Mutilations.
(2) Diseases.
(3) Results of use or disuse.
(4) Physico-chemical effects of environment.
The case in regard to mutilations is particularly clear cut and leaves
little room for doubt. The noses and ears of oriental women have been
pierced for generations without number, yet girls are still born with
these parts entire. Circumcision offers another test case. The evidence
of laboratory experiments (amputation of tails) shows no inheritance. It
may be said without hesitation that mutilations are not heritable, no
matter how many generations undergo them.
(2) The transmissibility of acquired diseases is a question involved in
more of a haze of ignorance and loose thinking. It is particularly
frequent to see cases of uterine infection offered as cases of the
inheritance of acquired characters. To use the word "heredity" in such a
case is unjustified. Uterine infection has no bearing whatever on the
question.
Taking an historical view, it seems fairly evident that if diseases were
really inherited, the race would have been extinct long ago. Of course
there are constitutional defects or abnormalities that are in the
germ-plasm and are heritable: such is the peculiar inability of the
blood to coagulate, which marks "bleeders" (sufferers from hemophilia, a
highly hereditary disease). And in many cases it is difficult to
distinguish between a real germinal condition of this sort, and an
acquired disease.
The inheritance of an acquired disease is not only inconceivable, in the
light of what is known about the germ-plasm, but there is no evidence to
support it. While there is most decidedly such a thing as the
inheritance of a tendency to or lack of resistance to a disease, it is
not the result of incidence of the disease on the parent. It is possible
to inherit a tendency to headaches or to chronic alcoholism; and it is
possible to inherit a lack of resistance to common diseases such as
malaria, small-pox or measles; but actually to inherit a zymotic disease
as an inherent genetic trait, is impossible,--is, in fact, a
contradiction of terms.
