NATURE OR NURTURE?!
It is considered by many that any defects at birth can be effectively cured through some effort in the future, and such changes will then be transmitted to any offspring.
There is no lack
of efforts to improve the race, by this method of
!direct change
of the environment. It involves two assumptions, which are sometimes made
explicitly, sometimes merely taken for granted. These are:
!That changes in
a man's surroundings, or, to use the more technical biological term, in his
nurture, will change the nature that he has inherited.
!That such
changes will further be transmitted to his children.
Any one who
proposes methods of race betterment, as we do in the present book, must meet
these two popular beliefs. We shall therefore examine
!the first of
them in this chapter, and the second in Chapter II.
Galton adopted
and popularised Shakespeare's antithesis of nature and nurture to describe a
man's inheritance and his surroundings, the two terms including everything that
can pertain to a human being. The words are not wholly suitable, particularly
since nature has two distinct meanings,--human nature and external nature. The
first is the only one considered by Galton. Further, nurture is capable of
subdivision into those environmental influences which do not undergo much
change,--e.g., soil and climate,--and those forces of civilisation and
education which might better be described as culture. The evolutionist has
really to
!deal with the
three factors of germ-plasm, physical surroundings and culture. But Galton's
phrase is so widely current that we shall continue to use it, with the
implications that have just been outlined.
The antithesis
of nature and nurture is not a new one; it was met long ago by biologists and
settled by them to their own satisfaction. The whole body of experimental and
observational evidence in biology tends to show that the characters which the
individual inherits from his
ancestors remain
remarkably constant in all ordinary conditions to which they may be subjected.
Their constancy is roughly proportionate to the place of the animal in the
scale of evolution; lower forms are more
!easily changed
by outside influence, but as one ascends to the higher forms, which are more differentiated,
it is found more and more difficult to effect any change in them. Their
characters are more definitely fixed at birth.[1]
It is with the
highest of all forms, Man, that we have now to deal. The student in biology is
not likely to doubt that the differences in men
!are due much
more to inherited nature than to any influences brought to bear after birth,
even though these latter influences include such powerful ones as nutrition and
education within ordinary limits.
But the
biological evidence does not lend itself readily to summary treatment, and we
shall therefore examine the question by statistical methods.[2] These have the
further advantage of being more easily
understood; the
problem of nature vs. nurture can not be solved in general terms; a moment's
thought will show that it can be understood only by examining
!one trait at a
time. The problem is to decide whether the differences between the people met
in everyday life are due more to inheritance or to outside influences, and these
differences must naturally be examined separately; they can not be lumped
together.
To ask whether
nature in general contributes more to a man than nurture
is futile; but
it is not at all futile to ask whether the differences in
a given human
trait are more affected by differences in nature than by differences in
nurture. It is easy to see that a verdict may be sometimes given to one side,
sometimes to the other. Albinism in animals, for instance, is a trait which is
known to be inherited, and which is very slightly affected by differences of
climate, food supply, etc. On the other hand, there are factors which, although
having inherited bases, owe their expression almost wholly to outside
influences. Professor Morgan, for example, has found a strain of fruit flies
whose offspring in cold weather are usually born with supernumerary legs. In
hot weather they are practically normal. If this
!strain were
bred only in the tropics, the abnormality would probably not be noticed; on the
other hand, if it were bred only in cold regions, it would be set down as one
characterised by duplication of limbs. The heredity factor would be the same in
each case, the difference in appearance being due merely to temperature.
Mere inspection
does not always tell whether some feature of an individual is more affected by
changes in heredity or changes in
surroundings. On
seeing a swarthy man, one may suppose that he comes of a swarthy race, or that
he is a fair-skinned man who has lived long in
the desert. In
the one case the swarthiness would be inheritable, in the other not. Which
explanation is correct, can only be told by examining a number of such
individuals under critical conditions, or by an
examination of
the ancestry. A man from a dark-skinned race would become little darker by
living under the desert sun, while a white man would
!take on a good
deal of tan.
The limited
effect of nurture in changing nature is in some fields a
matter of common
observation. The man who works in the gymnasium knows that exercise increases
the strength of a given group of muscles for a
while, but not
indefinitely. There comes a time when the limit of a man's hereditarypotentiality is reached, and no amount of exercise will add another milli-meter
to the circumference of his arm. Similarly the handball or tennis player some
day reaches his highest point, as do
runners or race
horses. A parallel case is found in the students who take a college
examination. Half a dozen of them may have devoted the same amount of time to
it--may have crammed to the limit--but they will still receive widely different
marks. These
commonplace cases show that nurture has seemingly some power to mold the
individual, by giving his inborn possibilities a
!chance to
express themselves, but that nature says the first and last word. Francis Galton, the father of eugenics, hit on an ingenious and more convincing
illustration by studying the history of twins.[3]
There are,
everyday observation shows, two kinds of twins--ordinary twins and the
so-called identical twins. Ordinary twins are merely brothers, or sisters, or
brother and sister, who happen to be born two
at a time,
because two ova have developed simultaneously. The fact that they were born at
the same time does not make them alike--they differ quite as widely from each
other as ordinary brothers and sisters do.
Identical twins
have their origin in a different phenomenon--they are believed to be halves of
the same egg-cell, in which two growing-points
!appeared at a
very early embryonic stage, each of these developing into a separate
individual. As would be expected, these identical twins are always of the same
sex, and extremely like each other, so that sometimes their own mother can not
tell them apart. This likeness extends to all sorts of traits:--they have lost
their milk teeth on the same day in one case, they even fell ill on the same
day with the same disease, even though they were in different cities.
Now Galton
reasoned that if environment really changes the inborn character, then these
identical twins, who start life as halves of the
same whole,
ought to become more unlike if they were brought up apart; and as they grew
older and moved into different spheres of activity,
they ought to
become measurably dissimilar. On the other hand, ordinary twins, who start
dissimilar, ought to become more alike when brought up in the same family, on
the same diet, among the same friends, with the same education. If the course
of years shows that identical twins remain as like as ever and ordinary twins
as unlike as ever, regardless of
changes in
conditions, then environment will have failed to demonstrate that it has any
great power to modify one's inborn nature in these
!traits.
With this view,
Galton collected the history of eighty pairs of identical twins, thirty-five
cases being accompanied by very full
details, which
showed that the twins were really as nearly identical, in childhood, as one
could expect to find. On this point, Galton's inquiries were careful, and the
replies satisfactory. They are not,
however, as he
remarks, much varied in character. "When the twins are children, they are
usually distinguished by ribbons tied around the wrist or neck; nevertheless
the one is sometimes fed, physicked, and whipped by mistake for the other, and
the description of these little
domestic
catastrophes was usually given by the mother, in a phraseology, that is
sometimes touching by reason of its seriousness. I have one case in which a
doubt remains whether the children were not changed in their bath, and the
presumed A is not really B, and vice versa. In another
case, an artist
was engaged on the portraits of twins who were between three and four years of
age; he had to lay aside his work for three weeks, and, on resuming it, could
not tell to which child the respective
likeness he had
in hand belonged. The mistakes become less numerous on the part of the mother
during the boyhood and girlhood of the twins, but are almost as frequent as
before on the part of strangers. I have many instances of tutors being unable
to distinguish their twin pupils. Two
!girls used
regularly to impose on their music teacher when one of them wanted a whole
holiday; they had their lessons at separate hours, and the one girl sacrificed
herself to receive two lessons on the same day, while the other one enjoyed
herself from morning to evening. Here is a brief and comprehensive account:
'Exactly alike in all, their schoolmasters could never tell them apart; at
dancing parties they constantly changed partners without discovery; their close
resemblance is scarcely diminished by age."
Not a single
case was found in which originally dissimilar
characters
became assimilated, although submitted to exactly the same
!influences.
Reviewing the evidence in his usual cautious way, Galton declared, "There
is no escape from the conclusion that nature prevails enormously over nurture,
when the differences of nurture do not exceed what is commonly to be found
among persons of the same rank in society and in the same country."
This kind of
evidence was a good start for eugenics but as the science grew, it outgrew such
evidence. It no longer wanted to be told, no matter how minute the details,
that "nature prevails enormously over nurture." It wanted to know
exactly how much. It refused to be satisfied with the statement that a certain
quantity was large; it demanded that it be measured or weighed. So Galton, Karl
Pearson and other
!mathematicians
devised means of doing this, and then Professor Edward L. Thorndike of Columbia
University took up Galton's problem again, with more refined methods.
The tool used by
Professor Thorndike was the coefficient of correlation, which shows the amount
of resemblance or association between any two things that are capable of
measurement, and is expressed in the form of a decimal fraction somewhere
between 0 and the unit 1. Zero shows that there is no constant resemblance at
all between the two things concerned,--that they are wholly independent of each
other, while 1
shows that they
are completely dependent on each other, a condition that rarely exists, of
course.[4] For instance, the correlation between the
!right and left
femur in man's legs is .98.
Professor
Thorndike found in the New York City schools fifty pairs of twins of about the
same age and measured the closeness of their resemblance in eight physical
characters, and also in six mental characters, the latter being measured by the
proficiency with which the subjects performed various tests. Then children of
the same age and sex, picked at random from the same schools, were measured in
the same way.
!It was thus
possible to tell how much more alike twins were than ordinary children in the
same environment.[5]
!
"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 analysed 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
obtained 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 behaviour and achievements of any man in
comparison with his fellows of the same period of civilisation 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."
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