m< OU_160737m
OSMANIA UNIVERSITY LIBRARY
Call No. | / Accession No '
Author
Title fvi^oloc '. ^Vck Jh r* U>w have
areas of common interest? What other sciences
or areas of study might be represented by
circles in the above diagram? Where would
you draw each?
for the individual as a person, as a knowing,
thinking, and otherwise reacting organism.
Differences in Emphasis among the Sci-
ences. The distinction between related sci-
ences is usually not a matter of hard and
fast differences, with clear lines separating
the sciences in question; rather it is one of
varying emphasis. Thus, it is not possible
to draw a line clearly dividing anthropology
from sociology, or to separate sharply soci-
ology from psychology or psychology from
physiology. In each case, one of these spills
over into the other ( or perhaps into several
others), and two or more sciences often
study the same subject matter. For example,
both physiology and psychology are inter-
ested in the functioning of the nervous sys-
tem, though each from a somewhat different
point of view. Psychology, sociology, and
anthropology all concern themselves with
the relationship of the group and the in-
dividual, but again the emphasis differs
for each science. Incidentally, we have a
similar situation in physics and chemistry,
where the emphasis differs but no hard and
fast boundaries can be drawn.
It is easy to get the idea that this is an
unfortunate situation and that the various
sciences should straighten out their titles to
14
UNDERSTANDING HUMAN BEHAVIOR
certain territories or areas of subject mat-
ter. Verbal battles have sometimes been
fought over such issues, but fortunately
for the welfare of science and society no
permanent victories have been won. Areas
of overlap in science can be opportunities
for cooperation, and two groups of scien-
tists, working together, have often attained
insights denied to either group working
alone. Human behavior is obviously a field
that is complex and not so well understood
as we should like it to be. No one has a
monopoly on information about it or on
methods of studying it. It is the concern of
many sciences, including psychology.
APPLIED PSYCHOLOGY
One striking fact about modern psychol-
ogy is, as we mentioned earlier, the increas-
ing number of psychologists, especially
since World War II. A great many more
people are now earning a livelihood as psy-
chologists than were doing so a few short
years ago. This growth is largely due to the
expansion of research and professional serv-
ices concerned with the applications of psy-
chology.
Until recently a majority of psychologists
were engaged in teaching. Now teaching is
still an important field of employment, but
positions concerned with research and ap-
plying psychology to practical problems
are the more numerous.
Psychology is now applied in a number
of situations, varying from those that deal
with children to those that deal with old
people, and from those that deal with peo-
ple who are in great difficulty to those that
deal with people in positions of responsible
leadership. Let us look at some of these
fields in which psychologists are applying
the findings of the science.
-Clinical Psychology. The largest single
group of professional psychologists are
those who work in mental hospitals, mental
health clinics, and the like. Clinical psy-
chologists, as the term implies, deal with
people in difficulty. Some of these persons
may have a serious mental illness, while
others m^ have encountered more than
their share of the problems we all face or
may lack the skill that most of us have de-
veloped for dealing with such problems.
Here it might be wise to make a distinc-
tion between a clinical psychologist and a
psychiatrist. Ordinarily a clinical psycholo-
gist has a Ph.D. in psychology. Having
finished a bachelor of arts degree (and pos-
sibly a master of arts degree also) in psy-
chology or a related field, he goes on to get
the doctor'--; degree in psychology. In the
course of earning this degree, he usually
serves at least one year of internship, which
gives practical experience in dealing with
persons having psychological difficulties.
This is a valuable supplement to classwork.
The psychiatrist, on the other hand, al-
ways has a medical degree. After complet-
ing his premedical training he usually
spends four years in medical school, some
time as an intern, and then some more as a
resident. His area of specialty is the care
and treatment of people with emotional and
mental illness.
Another person who works with mentally
disordered individuals, or with persons in
difficulty, is the psychiatric social worker.
He usually has a master's degree in social
work and specializes in getting information
about and understanding people who have
emotional difficulties.
In many clinics and hospitals the team
approach is used, the team consisting of a
psychiatrist, a clinical psychologist, and a
psychiatric social worker. To some extent
each member of this team specializes in a
particular area, but they combine their
training and talents in investigating the
problems of a particular patient and, after
the diagnosis, in helping him regain his
mental health. Many who work in this field
feel that the team approach is proving its
effectiveness and strengthening our efforts
THE STUDY OF HUMAN BEHAVIOR
15
to combat problems in the area of mental
health.
Counseling Psychology. Another field of
professional specialization in psychology is
known as counseling psychology. Though
counseling and clinical psychology are
closely related, they have two fairly distinct
roles in the general scheme of psychological
services.
We use the word "counseling" to refer to
the function of psychologists whose prin-
cipal job is to deal with people who are
in need of help or advice but not primarily
with people who have emotional difficulties.
A typical example is to be found in the
Veterans Administration, where the coun-
selor acquaints an individual with voca-
tional opportunities and gives him informa-
tion designed to better his vocational ad-
justments. Since a person's vocation influ-
ences so many phases of his life, counseling
psychologists often are called upon to deal
with other problems which the individual
may be facing.
Of course, not all counselors are psy-
chologists. Other people do counseling
teachers, social workers, supervisors, min-
isters, lawyers, physicians, and so forth. But
psychologists counsel too, and the point
that needs to be emphasized is that one
branch of psychology is concerned with
the theory, as well as the practice and tech-
niques, of counseling.
A branch of psychology closely related
to counseling is to be found in the work of
the school psychologist. School psycholgists
often do educational and vocational coun-
seling, but they also give advice and guid-
ance on matters having to do with cur-
riculum planning, teacher training, prob-
lems of parents, and the like.
Psychology in Business and Industry.
Psychologists also practice professionally in
business and industry. Human-relations
problems in business and industry are often
as important as any other sort, and the need
for effective teamwork is probably nowhere
greater than it is in this particular area.
Psychologists participate in the affairs of
business and industry in at least three ways.
In the first place, they have made some real
contributions to business management by
making it possible to do a better job of
selecting, placing, and training employees.
Here the first contribution that comes to
mind is probably that of psychological tests,
but while they have been important, they
are not by any means the whole story. In-
terviews are also useful, and even observa-
tion of behavior over a period of time has
proved worthwhile. Furthermore, psycholo-
gists have been able to improve methods
of training people for their jobs.
In the second place, there are psycholo-
gists who specialize in counseling with the
executives of a business and otherwise help-
ing in their development. They are often
the persons with whom the executive "talks
out" his problems, and they help him
gain insight into his own limitations and
strengths and to improve his skill as an
executive. The emphasis here is primarily
on self-improvement, for in these matters
as in many others, real development must
come from within the individual. '
This process of helping executives and
supervisors to grow and develop is some-
times carried out with groups rather than
with individuals. Through research, psy-
chologists have uncovered some of the
factors that distinguish successful leaders
from those not so successful, and the in-
dustrial psychologist often has the opportun-
ity to translate these findings into a form
and a set of skills that will make them use-
ful to the manager.
The third area in which psychology has
played an increasing role in business and
industry is often called human engineering.
As the world of work becomes more com-
plex and the machines and processes with
which we have to deal become more in-
volved, the problems of the control of the
means of production or transportation be-
16
UNDERSTANDING HUMAN BEHAVIOR
EFFICIENCY OF
VARIOUS DIALS
This experiment * throws some light on the work of the human engineer.
The purpose was to determine which of several types of dials would give
the most useful readings of an altimeter (instrument for measuring altitude).
Each dial was presented to the subjects with twelve different settings. They
were printed in a test booklet, with space provided in each case for indicat-
ing the correct reading. As far as possible, the printed designs were of the
same size, with the same legibility of printing, the same number of grada-
tions, etc. The order of presentation of the different dials was also varied
systematically to reduce the practice effect. The subjects were 97 United
States Air Force cadets and 79 college students without aircrew experience.
The accompanying figure presents the various types of dials used and also
the results obtained. Dial A was one commonly in use at the time of the
experiment, and, as can be seen, it showed up poorly both in errors and
time for interpretation. It is interesting to note that at least in some cases the
results of this study are quite different from what would be predicted by
so-called "common sense."
Errors of 1,000 feet or more, per cent
Interpretation time, seconds
17.4
J7.5
162
J7.J
10.7
10.7
117
1.8
LEGEND
1 97 AAF pilots
I I 79 college students
900
23,000 rr
800
22.900 -^
700 -;
72,800
[i] 3
^
| 27.800~
600
22.700
~
1
500 -z
22,600 -^
400-=
22,500 -^
Errors of 1,000 feet or more, per cent
Interpretation time, seconds
14.1
13.0
6.9
,03
0.4
U 1 9
M.9
(0.4
I 0.0
I 0.0
I 0.0
Speed and accuracy in reading altitude from different types of instruments.
(Note that instrument I proved most satisfactory under these conditions.)
(W. F. Grether, Instrument Reading: /, The Design of Long-scale Indica-
tors for Speed and Accuracy of Quantitative Readings, Journal of Applied
Psychology, 33:365, 1949. Courtesy of the publisher.)
* W. F. Grether, "Instrument Reading: I. The Design of Long-scale Indicators for Speed
and Accuracy of Quantitative Readings/' Journal of Applied Psychology, 1949, 33:363-372.
THE STUDY OF HUMAN BEHAVIOR
17
come more difficult. Indeed, in many in-
stances, more information can be given to
the operator of a machine than he is able
to perceive and use. Consider, for example,
a large airplane. It has a number of engines,
and each engine has a number of instru-
ments reporting on its performance. Clearly,
more information can be fed into the cock-
pit of the plane than any individual could
ever assimilate in any reasonable length
of time. Indeed, more information can be
displayed in the cockpit than a crew of
several men are able to assimilate. The
problem is to make this information as
usable as possible.
There is a question, for instance, as to
what sort of design an instrument ought
to have. Should it be black on white, or
white on black? Should it be large or small?
Where should it be located? These and
many more complex questions are of in-
terest to the human engineer.
Perhaps nowhere can we find a better il-
lustration of the difference between psy-
chology and "common sense." The common-
sense approach to this problem would be
to figure out which of these would seem
to be the most serviceable and to use it.
The psychologist, on the other hand, uses
the experimental approach. He experiments
with various kinds of cockpits and instru-
ments and controls, and by holding other
variables constant, determines not which
one looks as though it would work best but
rather which one really does work best.
There is no doubt of the superiority of the
psychologist's approach to this sort of prob-
lem.
Problems of this sort are to be found in
many aspects of the world of work, and the
contributions to their solution by psycholo-
gists may ultimately touch the lives of all
of us.
" Psychology and Attitude Measurement.
Finally, among the applied fields we have
chosen to discuss, there is the field in
which the attitudes of individuals or groups
are measured. Such attitude measurement
has been used extensively in public-opin-
ion polling (of which the so-called "Gallup
poll" is an example) and in market re-
search.
We are all familiar in a general way with
polling procedures. Questions are carefully
designed and studied and, when considered
satisfactory, are asked of a great many peo-
ple. Their responses are carefully noted,
and conclusions are drawn concerning the
attitudes of a larger group of people with
regard to the matter being studied. This
technique may be used to determine the
feeling of people toward the several presi-
dential hopefuls or toward a new brand of
detergent.
Complexity of the Field of Psijchology.
By now it is apparent that modern psy-
chology is not a simple field, with all psy-
chologists having the same interests and
skills. The various sorts of psychologists
have a number of things in common, but
they also have their own special interests.
The complexity of the field can be seen
from a study of the American Psychological
Association. This is the scientific and pro-
fessional organization of American psychol-
ogists. Minimum requirements for associate
membership are two years of graduate
study in psychology (or one year of grad-
uate study plus one year of experience in
professional work that is psychological in
nature) and employment in a job that is
primarily psychological (or continuation of
graduate study in psychology). More and
more the Ph.D. degree is being required
of people who are recognized as psycholo-
gists. In 1956 the association had about
15,000 members, in 1957 16,000.
At present the association is organized
into seventeen divisions, some set up pri-
marily on the basis of applied interests and
others primarily on the basis of subject
matter. These divisions are as follows:
UNDERSTANDING HUMAN BEHAVIOR
General Psychology
The Teaching of Psychology
Experimental Psychology
Evaluation and Measurement
Developmental Psychology
Abnormal and Social Psychology
The Society for the Psychological Study of
Social Issues
Esthetics
Clinical Psychology
Consulting Psychology
Industrial and Business Psychology
Educational Psychology
School Psychologists
Counseling Psychology
Psychologists in Public Service
Military Psychology
Maturity and Old Age
This list emphasizes the point made earlier
that some psychologists are essentially re-
search scientists, others arc primarily teach-
ers of psychology, and still others are prac-
ticing in various fields of applied psychol-
ogy. Psychology is thus both a science and
an ai t or a profession.
WHAT PSYCHOLOGY IS NOT
So far we have been talking about what
psychology is and how it relates to science
in general. Let us look now at some of the
popular misconceptions of psychology and
see wherein these are in error.
Psychology and the Mysterious. Many
people imagine that psychology is some-
thing magical or mysterious and that some-
how psychologists have a superior or al-
most superhuman way of looking into the
thoughts and feelings of a person. The no-
tion is, in other words, that there is a psy-
chological method or approach, and that
anyone who knows how to use this and
uses it successfully has an advantage over
anyone who lacks it.
Psychology, however, is no more myste-
Figure 1.6. Some people seem to think that
psychologists have insight into human behavior
that is little short of magical or mysterious.
Others hold that we learn about human be-
havior only from experience and that psycholo-
gists really have nothing to contribute to our
understanding of this subject. Neither of these
extreme positions is correct.
THE STUDY OF HUMAN BEHAVIOR
rious than medicine or engineering or the
other sciences. It is an ordinary, everyday,
hard-working science. It has no magic, no
mysterious ways, and no dark or hidden
routes by which it gets its knowledge.
Whatever psychologists have learned, they
have learned through observation, through
careful reflection upon what they have ob-
served, and through the checking of their
conclusions with other persons in this and
other fields. Psychology is neither magical
nor mysterious.
Psychology and "Common Sense." Some
people go to the opposite extreme and as-
sume that psychology is essentially nothing
more than common sense. To them, psy-
chology is simply what wise people have
discovered from their experience, whether
they have ever had formal training in the
subject or not.
It would, of course, be overstating the
case to say that psychologists have a mo-
nopoly of knowledge of human behavior.
We have already acknowledged the role of
the other sciences in studying human be-
havior, and we tnust further recognize that
nonscientific endeavors, such as religion,
literature, and the law, also have useful
contributions to make to this understanding.
We are not maintaining, in other words,
that only psychologists understand any-
thing about human behavior.
The fact nevertheless remains that sci-
1 entific psychology and the "psychology"
i of common sense are often rather different.
For one thing, there are statements that
are accepted by common sense but not
accepted by psychology. One example of
this is the common notion that those who
are insane or seriously mentally ill have
"lost their minds." In other words, insane
people are considered to be unable to
reason adequately or accurately. This com-
mon-sense idea of insanity is far from the
truth. Although intellectual abilities are
sometimes disturbed in mental illness, a
great many individuals who are insane are
not suffering from lack of ability to reason.
If given an intelligence test, they do as well
on it as ever. In such cases, the difficulty is
not in the intellectual realm at all but rather
in the field of emotion. Thus, psychology
must insist that insanity cannot be regarded
as the "loss of mind."
On the other hand, a good many things
that are accepted by psychology are not
accepted by common sense. An example
relates to the phenomenon of color. The
common-sense view of color is that the color
is in the object which we see. Thus, if we
see yellow flowers and blue flowers in a
vase on our desk, common sense says the
yellowness and the blueness are actually
in the flowers themselves. From the stand-
point of modern science this view is en-
tirely unacceptable. We have every reason
at present to believe that the color is not
in the object but rather in the pcrceiver.
The object reflects to our eyes light waves
of a certain length, and the color which we
see depends upon the length of the par-
ticular light waves. Thus, if long light waves
strike our eyes we get a seilsation which
we call red, while if short light waves
strike our eyes we get a sensation which
we call violet. Light waves of intermediate
length may lead to blue or green or yellow.
But there is no serious reason to believe
that the flowers themselves are colored.
Color is our response to light waves which
they reflect.
Thus, it can be seen that psychology,
while it sometimes agrees with common
sense, is not just common sense. It does not
agree with all that common sense holds,
and common sense sometimes mistakenly
holds to what psychology has shown to be
untrue.
Psychology and the Pseudo Sciences.
People sometimes confuse psychology with
a whole group of endeavors which have
come to be known as pseudo sciences.
(These are called pseudo sciences because
the term pseudo means "false/*) Among
20
UNDERSTANDING HUMAN BEHAVIOR
these pseudo sciences are phrenology, physi-
ognomy, numerology, palmistry, and astrol-
ogy-
Why do we call them false sciences? In
the first place, as will be clear when we
examine them in some detail, the claims
made by them simply do not fit with the
other established facts about the nature of
the world and of man. In the second place,
they are untrue to, or inconsistent with, the
spirit of science and the scientific method.
In other words, they do not stick close to
the facts but rather rely on essences for
their explanations. They do not depend pri-
marily on observation but rather on a priori
reasoning and predetermined conclusions
and prejudices. Instead of being objective
they select evidence supporting their posi-
tions, while overlooking, neglecting, or even
denying the facts that do not fit their pre-
conceptions.
Let us look more closely at some of these
endeavors. Phrenology goes back about 150
to 175 years. A celebrated anatomist by the
name of Gall got the idea that he could re-
late the contours of the brain to the mental
life of the individual. He further believed
that the contour of the skull reflects ac-
curately the contour of the brain. He went
on to map out the brain area, finding
thirty-nine "propensities" and "faculties,"
as he called them, each with its own local-
ized area. Thus, he concluded that the in-
tellectual faculties are mainly concentrated
in the forehead and that emotional factors
are located toward the back part of the
head. Gall believed that the size of an area
was a measure of the strength of the par-
ticular faculty, and hence he advocated
careful mapping of these areas.
We now know that Gall's suppositions
were without foundation, although different
parts of the brain and even of the cerebrum
do have different functions. There is no
reason to believe that we actually have the
faculties which he designated (or any fac-
ulties, for that matter) or that they were
located as he thought they were. Further-
more, the contours of the brain cannot be
inferred from the shape of the skull, nor
is the size of a brain area correlated with
the strength of a faculty. All Gall's major
assumptions are false. Hence, phrenology
is a pseudo science.
Much the same remarks can be made
about physiognomy. This pseudo science
did not restrict itself to the shape of the
skull but considered facial features and
the shape of the body as a whole. For ex-
ample, one physiognomist held that a per-
son with a misshapen or a deformed body
is also likelv fo have a personality similarly
warped. More specifically, it has been held
by some physiognomists that a square jaw
means determination, a high forehead
means intelligence (a view which they
might share with the phrenologists), and
so forth. Now, the truth is that the claims
of physiognomy, like those of phrenology,
do not stand up when carefully investigated.
There is no serious reason to believe that
any of the teachings of physiognomy cor-
respond to the facts.
Likewise, numerology attempts to de-
termine the character of the individual (and
sometimes his future) from the combina-
tions of numbers connected with his name
or other things in his life. Palmistry at-
tempts to predict his character and his fu-
ture from the lines on the palm. And finally,
astrology makes predictions about him
from the stars under which he was born.
The claims made by these endeavors are
false almost without exception. There is
no trustworthy evidence that the numbers
really influence a person's life or that the
life line on a palm has anything to do with
how long he will live. Likewise, the stars
under which he was born have no real in-
fluence on his personality. Psychologists
have had a great deal to do with showing
through experiment and other careful study
how these claims have no basis in fact. They
involve a priori reasoning and "essences."
THE STUDY OF HUMAN BEHAVIOR
21
It is easy to understand that psychologists
do not like to be classed with these pseudo
sciences. This is partly because the con-
clusions of the pseudo sciences are false,
but it is even more because they violate
the fundamental spirit of science in their
ways of investigation and their methods of
arriving at conclusions.
SUMMARY
All of us have an interest in human be-
havior. Part of this interest comes from the
fact that we need to understand, predict,
and control the actions of other people.
Part of it comes from our need for self-
understanding and self-control.
Psychology is the scientific study of the
behavior of living organisms, with especial
attention given to human behavior. It is
to be distinguished from anthropology and
sociology in that they focus their attention
largely on the group, while psychology
studies primarily the individual. It is to be
distinguished from physiology in that physi-
ology emphasizes the various systems of
the body and how they interact and also
how the organism adjusts to its physical en-
vironment, whereas psychology studies the
individual as a person, as a thinking, re-
membering, imagining, feeling, and react-
ing individual.
Actually all these sciences overlap in sub-
ject matter. No hard and fast lines can be
drawn to separate psychology from any of
the others, but there are differences in de-
gree and in emphasis. This makes it pos-
sible for scientists from several areas to
concentrate on the same problem.
When we say that a certain endeavor is
a science, we refer primarily not to a set of
facts or a body of knowledge but to a set of
attitudes and values and, in particular, to
certain methods for acquiring knowledge.
A science proceeds from observations, care-
fully checked, recorded, and confirmed. It
insists on objectivity, on drawing conclu-
sions on the basis of what is observed and
not on the basis of what the scientist wants
to find or believe. It stays as close to the
actual observations as practicable, though
it is admitted that observations never in-
terpret themselves and the scientist has to
go at least somewhat beyond them to inter-
pret them. Finally, though a scientist may
be interested in information that can be
used, another important motive is a desire
to know simply for the sake of knowing.
Scientists customarily use two kinds of
observation: (1) the experiment, which in-
volves control of all the relevant conditions
except the independent variable, which is
allowed to change or forced to change; and
(2) naturalistic observation, which is the
observing of events as they occur. If it
were practicable, scientists would use ex-
periments in all their observations, because
they permit better control of variables, but
since this is often impossible, they must
make use of naturalistic observation.
Psychology is both a science and a profes-
sion. As a science, it is interested in under-
standing more and more about the be-
havior of the organism. As a profession, it is
concerned with applications of this knowl-
edge to the prediction and control of be-
havior.
It is easy to believe that psychology is
magical or mysterious, or, on the other
hand, that it is nothing more than ordinary
common sense. Likewise, psychology is
sometimes associated with pseudo sciences
like phrenology. All these are false concep-
tions, as psychologists have been able to
demonstrate.
22
UNDERSTANDING HUMAN BEHAVIOR
QUESTIONS
1. What is a science? In what ways does it
differ from nonscientific endeavors?
2. What do we mean by saying that a scientist
often wants to know for the sake of knowing?
3. What is an experiment? How does it differ
from other types of observation?
4. Compare and contrast (a) "armchair" the-
orizing and experiment; (/;) "armchair" the-
orizing and naturalistic observation.
5. What is the law of parsimony, and what is
its importance?
6. Just what is psychology? Name several
problems that are distinctively psychological
in character.
7. In what applied areas are psychologists
found today? Describe the principal work of
each area.
8. What is anthropology? On what kinds of
problems would both psychologists and an-
thropologists work?
9. What is sociology? On what kinds of prob-
lems would both psychologists and sociologists
work?
10. What is physiology? On what kinds of
problems would both psychologists and physi-
ologists work?
11. In the experiment on remembering favor-
able and unfavorable material, what was the
independent variable? What was the depend-
ent one? What other variables did the experi-
menters attempt to control?
12. Do the > iine for the experiment on the
efficiency of * ions dials,
13. What aiguments can you give to prove
that psychology is not just "common sense"?
14. How would you demonstrate the inaccu-
racy of the claims of phrenology? What are the
chief differences between psychology and
phrenology? (Consider both conclusions and
methods of arriving at conclusions.)
SUGGESTED READINGS
Britt, Steuart Henderson: Social Psychology of
Modern Life, rev. ed., Rinehart, New York,
1949, chap. 2.
(An interesting and informative treatment
of the scientific method in psychology.)
Brown, C. W., and E. E. Ghiselli: Scientific
Method in Psychology, McGraw-Hill, New
York, 1955.
(Application of the scientific method to
many psychological problems.)
Chapanis, A., W. R. Garner, and C. T. Morgan:
Applied Experimental Psychology, Wiley, New
York, 1949.
(A discussion of the scientific design of
equipment for human use.)
Daniel, R. S., and C. M. Louttit: Professional
Problems in Psychology, Prentice-Hall, Englc-
wood Cliffs, N.J., 1953.
(The nature and growth of the profession
of psychology.)
Gray, J. Stanley: Psychology Applied 1o Hu-
man Affairs, 2d ed., McGraw-Hill, New York,
1954.
(Application of psychology to contempo-
rary problems.)
Marcuse, F. L.: Areas of Psychology, Harper,
New York, 1954.
(An introduction to the various fields or
branches of psychology.)
Ogg, Elizabeth: "Psychologists in Action,"
Public Affairs Pamphlet 229, 1955.
(A survey of the activities of the profes-
sional psychologist. )
Watson, Robert I.: Psychology as a Profession,
Studies in Psychology series, Random House,
New York, 1954.
(Applications of psychology to the prob-
lems of today; the nature of the profession
of psychologist.)
THE STUDY OF HUMAN BEHAVIOR
2 HEREDITY
AND ENVIRONMENT
In order to study behavior more efficiently,
the psychologist often separates the biologi-
cal and cultural factors. In his separation
of these factors, he does not mean to imply
that some characteristics are biologically in-
herited and that others are acquired by liv-
ing in a certain society. Rather, our traits
and characteristics are the products of the
interaction of our heredity and our environ-
. ment.
In this chapter we shall discover why the
emphasis is to be put on the word "interac-
tion." We shall see what the facts are that
make it incorrect to think that any trait of a
living creature is entirely hereditary or com-
pletely environmental. On the contrary, it
is more correct to say that all traits and
characteristics are both hereditary and en-
vironmental.
HEREDITY VERSUS ENVIRONMENT
During the nineteenth century biology
emerged and took its place among the sci-
ences. By the end of the century, both the
facts and theories of biology were having
considerable impact on the thinking of sci-
entists about human nature. Of particular
importance was Darwin's theory of evolu-
tion, which stressed the survival of those in-
herited characteristics through which ani-
mals adapted to their environments. The
Darwinian emphasis on heredity led biolo-
gists, physicians, and even people generally
to consider heredity as the most important
factor in determining human traits and char-
acteristics. By the close of the nineteenth
century, too much emphasis (as we see it
now) had been placed on man's heredity
as the molder of his character and per-
sonality.
24
In time, opinion began to shift away from
this view. Many scientists, especially the
sociologists, came to feel that too much
emphasis had been placed on heredity.
Gradually, during the early decades of the
twentieth century, a case was made for en-
vironment as the more influential factor in
growth and development. By the time of
World War I, many sociologists were ex-
pressing the belief that heredity is relatively
unimportant in the elaboration of character
and personality. They admitted, however,
that for some physical traits, such as eye
color and shape of face, heredity had some
importance.
As so often is the case, the full swing of
the pendulum put too much emphasis on
environment, just as heredity had been ac-
corded too much importance by biologists
and physicians. Caught in the middle were
several groups to whom the issue was of
some practical significance. The educators
were one such group. They did not know
whether to go along with the emphasis of
physicians and biologists on heredity, or
whether to join those sociologists who
stressed environment. To seek a resolution
of the problem, one group of educators set
up a study committee. 1 The purpose of the
committee was to determine which is more
important heredity or environment. At
least they wanted to find out which traits
and characteristics of the human being are
accounted for by heredity and which are
accounted for by environment.
When the committee got into the prob-
lem, assembling and organizing the relevant
scientific facts, it became apparent to them,
as it had to some biologists and some soci-
ologists, that it is impossible to separate the
influences of heredity from those of environ-
ment. Rather, the two always go along to-
gether.
1 Intelligence: Its Nature and Nurture, Thirty-
ninth Yearbook of the National Society for the
Study of Education, 1940.
Figure 2.1. Julian Huxley, the noted biologist, is the
grandson of the distinguished nineteenth century
biologist Thomas Huxley. His brother is Aldous
Huxley, noted critic and novelist. Does this illustri-
ous family tend to show the greater significance of
heredity in the production of genius? Can a case be
made here for the interaction of heredity and en-
vironment? (International News Photos.)
HEREDITARY AND ENVIRONMENTAL INFLUENCES ON
TRAITS
Today we know that all traits the social,
the psychological, and the physicalare a
product of the interaction and the interrela-
tion of heredity and environment. Certainly,
no trait can develop without some inherit-
ance, nor, on the other hand, can any trait
or characteristic develop unless the proper
environment is provided. It is obvious that
the hereditary factors present in the egg of
a chicken cannot produce a human being.
It should also be obvious that, if the right
environment is not provided, these same
factors cannot be made to produce a
chicken.
It is correct to think of every organism
HEREDITY AND ENVIRONMENT
25
and also of each part of every organism as
a joint function of three factors: .heredity,
environment, and time. Each of these fac-
tors is indispensable. If there is no heredity,
all the time and environment in the world
cannot produce a living organism. On the
other hand, if there is no place (environ-
ment) in which to grow and develop, no
amount of time and heredity can bring
forth a living organism. Likewise, in addi-
tion to the other two factors, a life span
(time) is necessary for the very existence
of every living plant and animal.
In order to clarify our thinking, let us
set up a concise expression for the interac-
tion of these factors.
P = /(H,E,T)
P is the individual person who is some
function ( / ) or product of the three factors
heredity (H), environment (E), and time
(T). This is a way of saying that all three
factors are essential and must work to-
gether for an organism to survive and de-
velop. Note in the formula that if any one
of the three (H, or E, or T) is reduced to
zero (is nonexistent), the result is zero,
which means that there will be no person.
Also, we can think of P as the whole person
or as any part of the person, i.e., any trait
or characteristic.
In order to understand some of the im-
portant implications of this formula, we
must now see what is technically meant
by the terms heredity and environment.
HEREDITY
A human body is composed of many small
cells, each of which has a nucleus. Within
each nucleus are a number of small rodlike
or threadlike objects named chromosomes.
Particularly important for our discussion
is the fact that in these chromosomes are
some tiny submicroscopic particles called
genes. These genes are the unit carriers of
heredity. They are the units that largely
direct the growth and development of the
human being, Biologists have good reason
to believe that the genes are giant organic
molecules, which somehow act as the blue-
prints for the building of the organism.
Under their influence and given the proper
environment, a fertilized egg (one cell)
can divide and grow into a human being
composed of billions of cells. Furthermore,
these billions of cells are formed into tissues
and organs which have definite places and
functions in the life of the organism. How
the minute genes manage to do what they
do is still one of nature's closely guarded
secrets. In any case, what we mean by the
word "hereditary" is gene-directed.
Let us consider now the role of the genes
in human heredity. For a human being to
be conceived, an egg from the mother must
be fertilized by a sperm cell from the
father. Once the egg has been fertilized, a
brand-new individual is begun. From the
mother comes half the number of genes
needed and from the father the other half.
Hence, both mother and father contribute
an equal amount of heredity to the new
individual. If these genes are to direct the
growth of this new individual, a specific,
proper environment must be present. In
the case of the human being, the proper
place is the mother's uterus. If the fertilized
egg is left in a normal uterus for seven to
nine months, an infant more or less ready
to take its place in the outside environment
will develop. Were we to remove the egg
from the uterus at the time of conception
and place it in a test tube, it would soon
die. Even our common sense tells us that
a test tube is not the proper place for an
egg to develop. So we see that we must
have both the necessary genes and also the
proper environment for the development
of a new individual.
Chromosomes. As a rule, each of the bil-
lions of cells in the human body has a nu-
cleus containing 48 chromosomes. In each
chromosome are something like 1,000 genes.
26
UNDERSTANDING HUMAN BEHAVIOR
Actually, it is better to speak of the 48
chromosomes as 24 pairs, because they are
found in pairs and also because there are
a few cells in the body that contain 24
chromosomes ( one from each pair ) instead
of the full 48.- These cells, which prove to
be the exceptions to the rule of 48, are the
egg cells in the female and the sperm cells
in the male. But nature has provided well.
When the sperm cell fertilizes the egg cell,
its 24 chromosomes pair up with the egg's
24 and form the 48 needed by the new in-
dividual. Thus, nature gains variety by
letting two different lines of heredity con-
tribute equally to the new offspring. The
baby will be somewhat like both its mother
and father and yet not exactly like either
of them.
Reductive cell division. How does it come
about that the egg and sperm each contain
only 24 chromosomes rather than the typi-
cal 48? In the female ovaries, where eggs
are produced, and in the male tcstcs, where
sperm cells are made, mother cells with 48
chromosomes each divide into daughter
cells that have only 24. This process is called
reductive cell division. During this division
the 48 chromosomes of the mother cell line
up in 24 pairs. One member of each pair
goes to each daughter cell. However, for
each individual pair it is a matter of pure
chance as to which member of the pair goes
to which of the two daughter cells. Because
of this random process, millions of different
combinations of chromosomes are possible.
It is unlikely that any two eggs produced
by the same woman would have exactly the
same 24 chromosomes.
With the exception of one pair, each
chromosome in a pair carries genes which
match the genes on the other member of the
pair. That is to say, each member of a
given pair has genes controlling the growth
2 For many years, biologists have* set the num-
ber of chromosomes at 48. A very recent count,
however, has found 46 (23 pairs). With cither
number, genetic theory and principles are the same.
Every cell in our body has
48 chromosomes (or 24 pairs)
(A pair of
chromosomes
showing genes;
each
chromosome
has about
1,000 genes)
except the egg cell
and the sperm cell,
each of which has only 24
(1 from each pair)
and development of the same specific set
of features and characteristics as the other
member of the pair. Biologists have sorted
out these 24 pairs and designated them by
the first 24 letters of the alphabet, A through
X. Thus, either member of any woman's A
pair can match up with either member of
any man's A pair and the developing child
that receives this new A pair (along with
the other pairs) will be assured of those
human features that are transmitted by the
A pair.
The one exception to the simple match-
ing of pairs occurs in the twenty-fourth pair.
Where both of the A's, B's, C's, etc., are
the same in shape and size, the two mem-
bers of the last pair may be different. Biolo-
gists note this fact by labeling this pair
HEREDITY AND ENVIRONMENT
27
(8 chromosomes
48 chromosomes
48 chromosomes
24 chromosomes
ORDINARY CELL DIVISION
REDUCTIVE CELL DIVISION
XX when the two members are alike and
XY when they are different. The X chromo-
some is a full-sized chromosome, but the Y
is dwarfed.
This pair of chromosomes is important
because the sex of the offspring depends on
it. If a child receives an X from its mother
and an X from its father so that it has a
matched XX pair, the child is a girl. If it
receives an X from the mother and a Y
from the father, it is a boy. Every woman
and girl has two X's, and every man and boy
has an X and a Y. We see, then, that we al-
ways receive an X from our mother and
either an X or a Y from our father. Hence,
any complaints about our sex should be
made to our father, not our mother.
Ordinary cell division. One egg and one
sperm cell unite to begin one new human
being. This fertilized egg divides by what is
called ordinary cell division into two cells.
Each of these cells has its own nucleus with
48 chromosomes. Moreover, these cells, usu-
ally stick together. The process of cell di-
vision continues, and with each new divi-
sion the number of cells is doubled. Be-
fore long, billions of cells have been pro-
duced. Under the direction of the genes
and in the ideal environment of the uterus,
these cells form a human infant.
Twins. Most of the time the fertilization
of one egg by one sperm cell produces one
offspring. Once in a while, however, the
first two cells into which the fertilized egg
divides do not stick together. Instead, each
of these two cells then multiplies independ-
ently and produces an infant. These two in-
fants are identical twins. The important
point is that they come from one egg and
one sperm cell and are, therefore, two in-
dividuals with exactly the same heredity
(genes). Identical twins (triplets, etc.) are,
in fact, the only cases known where two
(or more) people have identical heredity.
Since they are identical in heredity, they
are always of the same sex. We shall see
28
UNDERSTANDING HUMAN BEHAVIOR
later that these facts are valuable to the
psychologist who is trying to study experi-
mentally the influences of heredity and en-
vironment.
Occasionally two eggs instead of one are
ready at the same time for fertilization
within the mother. In this case two different
sperm cells may fertilize these two eggs
and two infants result. These twins are
called fraternal twins and may be two boys
or two girls or a boy and a girl. Moreover,
these twins are not of the same heredity.
They arc no more related than any other
two brothers and sisters born at different
times.
The relatedness of relatives. On the aver-
age, brothers and sisters are related to each
other in heredity about as much as they arc
to cither parent; that is, on the average,
siblings (all the children of the same par-
ents) have 24 chromosomes in common.
Some siblings have more than 24 in com-
mon, and some less than 24. Since kinship
depends upon the possession of common
chromosomes, some siblings are more (or
less) related than others. One of the ex-
tremes in relationship is, of course, the
case of identical twins ( all 4(8 chromosomes
in common). The other extreme, which
probably never occurs (but is theoretically
possible ) , is the case of a brother and a sis-
ter who have no chromosomes in common.
Biologically speaking, these two siblings
would not be akin to each other at all. This
remarkable state of affairs might arise if,
by chance, 24 of the mother's chromosomes
went to the boy and a different set en-
tirely went to the girl and if the father's
chromosomes were similarly divided. In the
usual case, however, the girl receives one
or more of the chromosomes that also went
to the boy. Consequently, our best bet is
what our common sense tells us, that broth-
ers and sisters are related. Or to emphasize
the point in another way, we may say that
there is no known case of siblings who are
not related, even though it is possible ge-
netically for them not to be related.
We have presented these extremes simply
to set the limits of kinship. We may now say
that, biologically speaking, we are related
to only those people who share with us at
least one chromosome. We have also ^oen
that we receive 24 chromosomes from our
mother and 24 from our father. Thus, we
are always related half and half to our two
parents there are no exceptions. Our par-
ents, of course, received their chromosomes
from their parents, which means that our
chromosomes came to us (through our par-
ents) from our four grandparents. On the
average, then, we received 12 from each
of our gr a rd parents. However, because
which chrj-riosomes are passed on is a
matter of chance, some of us received more
than 12 from a particular grandparent (e.g.,
our mother's father) and some received
fewer. Thus we may be more or less re-
lated to a particular grandparent, just as
we are to our siblings. Moreover, as in the
case of siblings, it is theoretically possible
for us to have received as many as 24 or as
few as none from any one of our grandpar-
ents. Again it is not very likely that we
possess no kinship at all to one of our grand-
parents, and even less likely that we are un-
related to two of them.
The likelihood of no kinship increases
as we trace our lineage back through
more and more generations. From each of
our 8 great-grandparents we receive, on
the average, 6 chromosomes. This far back,
the possibility of our not being related to
one of them is not so remote. From our
great-great-grandparents we receive on the
average 3 from each. From the next genera-
tion back, we average only 1% from each.
And from our ancestors six generations
back, we are given on the average only %
chromosome from each. Since a chromo-
some is usually transmitted all in one piece,
we have at last come to a generation of
ancestors in which some of the individuals
are definitely not akin to us. These facts
make highly questionable our attempt to
trace our family trees back very far. Many
HEREDITY AND ENVIRONMENT
29
great grandparents
grandparents
m X^.^Trw i
parents
an individual
Figure 2.2. On the average, how many chromosomes does a person receive
from each generation of his ancestors? In this drawing the chromosomes are
represented as ovals and may he traced hack for three generations. A count
will show that the typical individual represented received 24 from each of
his parents, 12 from each grandparent, and 6 from each great-grandparent.
people who glory in a supposed kinship
with some historic personage are only fool-
ing themselves. The possibility that they
have a chromosome in common with that
person is too remote to consider seriously.
Dominant and Recessive Genes. Genetics
is the name biologists give to the special
study of heredity. As the name indicates,
genetics is the science that deals with the
genes. The first laws of heredity were for-
mulated about a hundred years ago by an
Austrian monk, Gregor Johann Mendel 3
3 V. Grant, "The Development of a Theory of
Heredity," American Scientist, 44(2):158-179.
( 1822-1884). He learned about inheritance
by growing and crossing several varieties
of garden peas. His work was neglected
until about 1900, when his laws were re-
discovered and the science of genetics be-
gan to flourish.
One of the most important findings of
genetics is that some gens are dominant
and_spmg_are recessive^ To illustrate the
meaning of these terms, let us first take a
classical example from Mendel's work with
the color of pea flowers. Some of these
flowers are white and some are red. If the
flower contains only the genes for red, it
UNDERSTANDING HUMAN BEHAVIOR
is called pure red. If it has only genes for
white, it is called pure white. If it contains
j genes for both red and white, it is called a
'hybrid.
In Figure 2.4 we see that the crossing
(mating) of a pure red flower and a pure
white produces offspring that are all red in
color and that are designated as hybrid red.
In Figure 2.5 we observe that, if two of
these hybrid reds are crossed, the result, on
the average, is three red and one white off-
spring out of every four. Further, by subse-
quent breeding experiments, we can show
that one of these reds is pure red like its
red grandparent and the one white flower
is pure white like the other grandparent.
The other two reds, however, are hybrids
like their parents.
The foregoing illustrations show that,
though the hybrid red looks like the pure
red, it breeds differently. It must carry a
gene for white because, when cross-bred, it
has white offspring. Because the gene
for white is not expressed when paired with
the gene for red, it is called "recessive."
The fact that the hybrid is red indicates
that the gene for red dominates the gene
for white. For that reason, it is called "domi-
Figure 2.3. What is peculiar about the heredity of this individual? By counting
the chromosomes, drawn as ovals, we discover that this individual received 24
from each parent, just as ice all do. However, from his paternal grandmother
he received 15 and from his paternal grandfather only 9, making up the 24
from his father. Even more unusual, he received 24 chromosomes from his ma-
ternal grandfather and none at all from his maternal grandmother. Thus, he is
not genetically related to his own mothers mother! Such an occurrence as this
is very unlikely, but it does illustrate one remote possibility in heredity.
grandparents
parents
an individual
HEREDITY AND ENVIRONMENT
31
PARENTS
pure red
pure white
OFFSPRING
Figure 2.4. If we cross a pure red sweet pea
with a pure white sweet pea, we obtain a hy-
brid red offspring. This hybrid looks exactly
like the pure red parent but differs in that it
carries the recessive genes for whiteness as well
as the dominant genes for redness. Since we
cannot tell by looking at a flower whether or
not it is a pure red or hybrid red, how can we
determine this fact?
hybrid reds
Figure 2.5. When two hybrids are
crossed, we obtain what is known
as the ft Mendelian ratio" What is
this ratio? Will it hold every time
four offspring are produced? Why
was the discovery of this ratio im-
portant for the science of genetics?
(For further discussion of this ratio,
see Figure 2.6.)
hybrid red
hybrid red
pure red
hybrid red
hybrid red pure white
UNDERSTANDING HUMAN BEHAVIOR
nant." A dominant gene is one that, when
paired with a recessive gene, dominates;
i.e., its character shows up in the offspring.
It dominates but does not eliminate the
recessive gene. Whenever in later genera-
tions two recessive genes come together,
the recessive characteristic again appears.
If we let R stand for the dominant red
gene in our pea and w for the recessive
white, we have in Figure 2.6 a picture of
hew the genes pair off. Figure 2.6 is a
combination of the facts of Figures 2.4 and
.5. In this figure one R and one iv have
been enclosed in parentheses simply to al-
low us to follow them more easily from
generation to generation.
This same rule of dominants and reces-
sives holds for human genes as well as for
those of the pea plant. Human character-
istics, however, are seldom determined by a
single pair of genes. Rather, we must think
in terms of complex groups of genes pairing
with each other. This is the reason that sim-
ple human examples are hard to find. It
would be convenient, for example, if we
could say simply that brown eyes arc con-
FIRST CROSS -
(as seen in
Fig. 2.4)
R(R)
pure red
w(w)
pure white
All offspring are hybrid reds
being either Rw, R(w), (R)w,
or (R)(w). If we take any two
of these hybrid reds and cross
them, we get the following:
SECOND CROSS -
(as seen in
Fig. 2.5)
>- Rw
hybrid red
(R)
hybrid red
(w)
R(R)
pure red
(R)w
hybrid red
w(R)
hybrid red
w(w)
pure white
trolled by a single dominant gene and blue
eyes by a single recessive one. Such a state-
ment would allow us to follow Figures 2.4,
2.5, and 2.6, changing only "pure red flower"
to "pure brown eyes" and "pure white
flower" to "pure blue eyes." Unhappily, such
a statement is not true. Although brown
eyes are usually dominant and blue eyes
usually recessive, eye color in the human
being is so complex that we need further
genetic laws to handle them. Some of these
laws exist, but we must leave their study to
the course in genetics.
It is sufficient for us in this introduction
to genetics u see that human heredity fol-
lows define e patterns and laws. Further-
more, these principles hold generally for all
living organisms, plants and animals alike.
The So-called "Purely" Hereditary Traits.
In the last section we seemed to ignore the
part environment plays in the determina-
tion of the characteristics of redness and
whiteness in pea plants or brownness and
blueness in human eyes. Actually we merely
considered environment to be held constant.
This is not to say, however, that environ-
ment is unimportant. If E and T in the
formula P = /(//,E,T) are held constant
between two individuals, they nevertheless
influence the growth and development of
both individuals. However, any difference
between these two people will be attrib-
Figure 2.6. A first cross between a pure red and
a pure white pea plant. All offspring of this
cross are hybrid reds. A second cross between
two of these hybrids shows the Mendelian ratio
of 1-2-1; i.e., one pure dominant, two hybrids,
and one pure recessive. With only a few sec-
ond-cross offspring this ratio may show chance
variations. However, with large numbers of
offspring the ratio holds. This ratio was dis-
covered by Grcgor Mendel. (The parentheses
are used simply to identify one of the R's and
one of the w's. )
HEREDITY AND ENVIRONMENT
utablc to H which has varied (i.e., H is
different for each of them). In identical
twins we have it the other way around;
H and T are constant (they have exactly
the same genes and age), while only E
can vary and be different for each of them.
In the example of the pea plants we are
assuming that all the plants are grown in
the same soil, with the same climate, etc.
Also we are comparing them after the same
lapse of time in each case. In a later section,
we give a number of examples that show
how changes in environment can affect
traits ordinarily called "hereditary." For the
time being we shall simply reaffirm that all
traits and characteristics are both hereditary
and environmental.
ENVIRONMENT
Each of us realizes that he lives in an
environment. Whenever the word is men-
tioned, we probably think of the house we
live in, of the school we attend, of all the
objects we own, of the grass and the trees in
our yard, and even of the air we breathe.
All these elements, and many more, are a
part of our external, physical environment.
But it would be a great mistake if we were
to limit our use of the word to only this sort
of environment.
The most useful way for us to define the
word "environment" is to say that it-in -
eludes aJL the_ conditions in ^he _ world that
influence injiny way ouTjbghavior, fflowtH,
development, or life processs=-except the
genes (and even genes can be considered
to provide environment for other genes).
According to this broad definition, not only
are there a multitude of factors in our en-
vironment at any one time, but there are
also a great number of other factors that
are potentially capable of influencing us.
However, our actual environment consists
in only those factors in the world around
us which do exert their influence. In order
to examine more closely the composition of
our environment, let us divide it into three
parts: the external, physical environment;
the internal environment; and the social en-
vironment.
The External, Physical Environment. We
have already listed a few of the elements
that make up our external, physical en-
vironmenthouses, trees, air, etc. It would
take a list almost without end to exhaust
everything that could possibly become a
part of this environment. We get around
this difficulty by using the general term ex-
ternal stimuli. Since we take up the topic
of stimuli in a later chapter, it is enough
to say here that a stimulus is anything which
is able to stimulate or excite the receptors
in any one of the several sense organs ( eye,
ear, skin, etc.). It is through our sense or-
gans that the external world ordinarily in-
fluences us...
To some extent our every action is de-
termined by what we see, hear, or feel.. Life
is a continual and continuous responding to
stimulation. We change and mold and shape
our external environment at the same time
that it molds and shapes and changes us.
Moreover, certain external factors must be
in the environment if genes are to exert
their influence on human characteristics.
For example, in Europe during World War
II some children could not find enough
food and were permanently stunted in
growth. Although a boy might have inher-
ited the genes that with the right environ-
ment (a better diet) would have allowed
him to be 6 feet tall, under wartime con-
ditions he might stop growing at a height
of barely 5 feet.
The Internal Environment. We have men-
tioned food as a part of our external en-
vironment. We see food, taste it, and re-
spond to it by eating it. Once it is in our
stomachs and intestines, it is in between our
external and internal environments. We say
"in between" because until it is digested and
absorbed into our blood stream it is not
properly spoken of as internal environment,
34
UNDERSTANDING HUMAN BEHAVIOR
If it were not for the fact that it is inside
our digestive tract, it would be best to con-
sider it as an external stimulus,
Once food and water are in the blood
stream (and in the lymph fluids), they
affect every cell in the body and are defin-
itely part of the internal environment. The
same thing can be said for the vitamins we
eat and the hormones produced by the
glands. This aspect of our internal environ-
ment is treated more fully in Chapter 9*
If we accept the concept of inter-- 1 en-
vironment, we must be prepared to admit
that it is nearly impossible to tell where our
environment leaves off and we begin. Or to
put it another way, we must say that we
cannot draw a sharp line between ourselves
and our environment.
The Social Environment. Psychologists
generally recognize our social environment
to be extremely important in shaping our
individual behavior and personality. In
using the word "social" we mean to include
all the other human beings who in any way
influence us. Some people influence us by
direct, daily contact our families, our
friends, our school and business acquaint-
ances, etc. Other people have as much or
more influence through indirect contact-
over radio and television, in books and other
publications, and in many other ways.
Especially in personality is each of us a
result of the interaction of our genes and
our social environment. Because of this in-
teraction, each of us is unique. Even in the
cases of individuals who have some genes
in common or similar social environments,
Figure 2.7. Which aspects of this scene can
be considered as the external environment of
these students? What things are actually stimu-
lating them at the moment and what are po-
tential stimuli? Can you describe the social en-
vironment as it is depicted here? (Standard Oil
Company, New Jersey.)
the interaction produces wide variations in
personality. Siblings, who have both simi-
lar social environment and some genes in
common, also show this wide variation.
Even where heredity is the same (identical
twins), and the social environment is al-
lowed to vary, personalities show remark-
able differences.
The reason we ordinarily think of identi-
cal twins as having inherited the same per-
sonality is that they most often have very
nearly the same social environment as well
as the same genes_. However, on close anal-
ysis such identical twins show consistent
individual J inferences in personality (note
the case of twin T and twin C on page 36).
In the rare instances where identical twins
have been separated at birth and reared
in extremely different social environments,
their adult personalities have been quite
different (note the case of Mabel and Mary
on page 37). In the next section we shall
examine several more examples of inter-
action, some of which show the effect on
the total personality and some the effect
on one or two characteristics.
HEREDITY AND ENVIRONMENT
35
These babies are identical twins, 38 weeks old.
Since they have exactly the same heredity and
have been reared together, they are about as
much alike as two human beings can be. It is
not surprising that they are responding quite
similarly in the test situation. However, one
infant is reaching with its right hand and the
other with its left. The reason is that they are
"mirror-image" twins the left side of one twin
is identical with the right side of the other one.
(Courtesy of Dr. Arnold Gesell.)
IDENTICAL TWINS
REARED TOGETHER-
TWIN T
AND TWIN C
Because they have exactly the same heredity, identical twins reared to-
gether can be expected to show great similarity in nearly all respects. On the
other hand, since there are at least small differences in their environment,
we can also expect to see some individual differences between them. Such
similarities and differences are shown in the study of twin T and twin C.*
These identical twin girls were studied for fourteen years by the Yale Clinic
of Child Development.
From time to time in this study the method of co-twin control was used.
Twin T would be given training in such activities as stair climbing, manual
coordination, block building, and vocabulary, while twin C was left untrained
as a control. At first in each task twin T would tend to excel, but as C reached
the proper level of maturation, she soon equaled T's performance.
As would be expected, these twins were very much alike in physical
growth and appearance, in intelligence, and in many other characteristics.
However, closer study showed a number of persistent and durable dif-
ferences. T was quicker, C more deliberate. In drawing a picture T preferred
to use straight lines and angles, while C preferred curved lines. T appeared
a little brighter, C was a bit better in a social situation. T was more prompt
in attention, while C was more alert.
Although these differences were slight, they added up to a distinctive per-
sonality for each of the two girls. Certainly they were not so unlike as most
people, but each had her unique personality. Of interest is the fact that some
of their differences showed up in infancy. This fact points up the importance
of the, prenatal environment in the development of temperament. Other of
the differences showed up later.
We should remember that interaction of heredity and environment pro-
duced everything about these twins, including both their differences and
their similarities. However, since their heredity was identical, we must con-
* A. Getell and H. Thompson, "Learning and Growth in Identical Infant Twins: An Ex-
perimental Study by the Method of Co-twin Control/' Genetic Psycho/ogy Monograph, 6:1-
124, 1929.
UNDERSTANDING HUMAN BEHAVIOR
elude the environmental variations accounted for the differences they pos-
sessed. Certainly such differences exist, for since two people cannot occupy
the same identical space at the same time, they must have at least slightly
different environments. In the mother's uterus, for example, if one twin is on
the left side the other must be on the right side. Also, in growing up even
twins will receive, at least occasionally, different treatment. Very important
in the case of twin T and twin C were the co-twin control observations. The
training that twin T received constituted environmental stimulation which
twin C did not have.
We can conclude from this study that even identical twins reared together
can be expected Jo show^mall differences in addition to a great amount of
Mabel and Mary * were identical twin's e pa rated early in life. Mabel
lived in the country and participated in all the rural activities, including hard
farm chores. She was permitted to finish only eight grades in the small
IDENTICAL TWINS , . , . __ __. . . .
REARED APART country school near her home. Mary grew up in a medium-sized city, where
MABEL AND MARY ner ma ' n interest was the study of music. She attended three years of high
school in this city and then finished her fourth year in a large-city school.
After graduation she became a music teacher. Both girls had the advantage
of living in relatively prosperous homes.
At the age of twenty-nine Mabel and Mary were studied by a psychologist.
In intelligence they were separated by 17 IQ points on the Stanford-Binet Test
(see Chapter 17 for information about this test). Mary was rated as high
average in intelligence and Mabel was low average. In personality Mabel,
who was still a farm woman, was slow and phlegmatic, and yet was con-
sidered an aggressive leader in her community. Mary was excitable, nearly
neurotic. In manner Mabel was almost masculine, while the music teacher
Mary was quite ladylike. This difference in manner showed up in their walk-
Mabel had a firm, manlike stride, Mary a very feminine step.
Even in physical appearance these twins differed. Mabel had hard muscles
and weighed 138 pounds. Mary's muscles were soft and not well developed,
and she weighed 110 pounds.
Over-all, they were unlike in behavior and appeared to be as strikingly
dissimilar in personality as the psychological tests had indicated. They did
not seem to be identical twins at all, although undoubtedly there was a fam-
ily resemblance.
Mabel and Mary illustrate how widely two persons, even with heredity
constant between them, can vary in personality and appearance if reared
r separately. We have already seen in the study of twin T and twin C how
identical Heredity and rather small variations in environment can produce
small but real differences in personality.
In these studies we again see proof that ajperson is a result of the inter-
action of both heredjty_and environment. These
