BIOLOGICAL
PSYCHOLOGY
NATURE VS. NURTURE

Founder of the Trait
Theory
◦ Predispositions to
respond, in a same or
similar manner, to
different stimuli
◦ After meeting Freud,
Allport felt there was too
much emphasis on inner
drives
Gordon Allport
Trait Theories of Personality
 Personalities
described by main
characteristics (traits)
 Traits (honesty,
laziness, ambition,
outgoing) thought to
be stable throughout
life
Key Ideas of Trait Theory

We are psychophysical beings
 Mind and body function together

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Personality develops from both mental and
biological influence
Each person is unique
 Everything is a characteristic of us and no one else

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Heredity (genetics) provides “raw materials”
Environment shapes, expands, or limits heredity
(raw materials)
Key Ideas of Trait Theory


In other words: individual combination of genes
(except for identical twins) + the environment =
personality
Two personalities
 Childhood (more biological)
 Adulthood (more environmental)
 Childhood personality does not determine adult
personality!
Other Trait Theorists
Dimensions of
personality
1. Extraversion vs.
introversion (E)
2. Neuroticisms vs.
emotional stability (N)
3. Psychoticism vs.
impulse control (P)
 Predisposed to each
 Collectively makes up
personality

Hans Eyesenck

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Extraversion vs.
introversion (E)
Extraverts
◦ Lower level of cortical
(brain) arousal
◦ Seeks stimulation

Introverts
◦ Higher level of cortical
arousal
◦ Shies away from stimuli
Hans Eyesenck
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
Neurotic vs. emotional
stability (N)
Neurotic
◦ Greater brain activity in
sympathetic branch of
autonomic nervous
system
◦ Alarm system – “fight,
flight, or freeze”
◦ Overreacts to even mild
stress

Emotional stability
◦ More subdued responses
◦ More “level headed”
Hans Eyesenck


Psychoticism vs. Impulse
control (P)
Psychoticism
◦
◦
◦
◦
◦
◦
◦

Aggressive
Anti-social
Tough minded
Cold
Ego-centric
Cruel, hostile, insensitive
Men tend to score higher
(hormonal)
Impulse control
◦ Can channel aggression into
appropriate activity
Hans Eyesenck


Heredity plays greater
role than environment
Descriptors of E
◦ Sociable, lively, active,
assertive, sensation
seeking, carefree,
dominant, venturesome
Hans Eyesenck

Descriptors of N
◦ Anxious, depressed,
guilt feelings, low
self-esteem, tense,
irrational, shy, moody

Descriptors of P
◦ Aggressive, cold,
egocentric,
impersonal,
impulsive, anti-social,
creative, toughminded
Robert McCrae and Paul Costa
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“Big Five” factors
of personality
Stability
Extraversion
Openness
Agreeableness
Conscientiousness

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Stability (calm or anxious, secure or
insecure, self-satisfied or self-pitying)
Extraversion (sociable or retiring, fun-loving
or sober, affectionate or reserved)
Openness (imaginative or practical, variety
or routine, independent or conforming)
Agreeableness (soft-hearted or ruthless,
trusting or suspicious, helpful or
uncooperative)
Conscientiousness (organized or
disorganized, careful or careless, disciplined
or impulsive)
The Big Five
According to Big Five
trait theory:
 Traits are stable
over time
 Can be attributed to
genetics
 Describes
personality equally
across different
cultures
 Predicts other
attributes
The Big Five
Correlations with the Big Five:
Which behaviors correlate?
Protested injustice
- Emotionally stable, open
Fell in love at first sight
- Extraverted
Have not been in therapy
- Emotionally stable
Been in therapy
- Open
Thrown a large party
- Extraverted
Kept a diary
- Open
Listen to music by self in
dark
- Open
Correlations with the Big Five:
Which behaviors correlate?
Read fewer than 12 books per
year
- Extraverted
Never cheated on a test
- Conscientious
Never pulled all-nighter to finish
assignment
- Conscientious
Not likely to become addicted to
Internet
-Extraverted
Dated a person of a different
race
- Open
Written a poem spontaneously
- Open
Arnold Buss and Robert Plomin

Temperament
◦ Building blocks of
personality
◦ Everyone has levels
of all three
◦ Primarily biological;
can be adapted by
environment


First Temperament
Emotionality
◦ Level of excitability for unpleasant feelings
Sensitive to
any emotion
unemotional
Arnold Buss and Robert Plomin


Second Temperament
Activity
◦ Physical energy and vigor
Constant
movement
unmoving
Arnold Buss and Robert Plomin
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Third Temperament
Sociability
◦ Preference for contact/interaction with others
Want to be
around others
Don’t like to be
around others
Arnold Buss and Robert Plomin

Reflection: Looking at the Big Five and
Three Temperaments, which ones do
you see having the greatest impact on
your life?
Assessing Our Traits
Untangling Nature and
Nurture
Behavior Genetics: the study of the interaction
of genes and environment on behavior
“Nature” = role genes
have on a trait
 “Nurture” = role life
experience has on trait
 Eysneck, McCrae and
Costa, and Buss and
Plomin all used twin
studies in research

Nature vs. Nurture
Biological Theories of Personality
What % of the
variation in a
population is
attributable to
genes? heritability
 Not sure; BUT
temperaments do
seem to be stable
from infants to old
age.

Percentage of trait variation in a group
that can be attributed to genetic
differences (can be inherited)
 In other words, what role do genetics
play?

◦ 0% means genes play no role
◦ 100% means genes play entire role

Depends on the population
Heritability
Heritability
Sara is very
outgoing
and
agreeable
Suzy is timid
and nonconforming
If this pair of IDENTICAL twins is my population,
what percent of the personality differences is
attributable to genetic differences between them?
The heritability is 0%.
Joe and Hank are
not related. At
birth, both were
placed in identical
environments that
were maintained
identical until they
were 10 years old.
At 10, Joe is
outgoing and
friendly.
At 10, Hank is
withdrawn and
shy.
In this (very small) population, what is the heritability of
their personality traits? In other words, what percentage of
the difference is attributable to genes?
Heritability
100%
Trait
Creativity
Extraversion
Autism
Depression
Sleep quality
TV viewing
Religious beliefs
Religious conservatism
Divorce
Height
Population
adolescents
adults
general
general
general
3-5 year olds
general
women
general
women
Heritability
25%
30-50%
90-95%
40-55%
35%
10-45%
0%
40%
55%
92%
How heritable is that trait?
http://www.peele.net/lib/genes.html The Stanton Peele Addiction Website
Twin Studies
Identical Twins
Same genes,
Same environment
vs.
Fraternal Twins
Different genes,
Same environment
Therefore, greater differences between the two groups indicate
greater heritability (“Nature”). The trait might appear to have a large
genetic component.
Twin Studies
Increased risk of schizophrenia if twin
develops disease
60%
% increase
50%
40%
30%
20%
10%
0%
Fraternal twins
Identical twins
Criticism:
1) Do fraternal twins
really have equally
similar environments to
identical twins?
Differences in looks or
inborn temperament
may cause people to
treat you differently.
2) Identical twins may
share a placenta but
fraternal twins do not.
Thus, we can’t
eliminate prenatal
environments as the
cause of the
differences between
the two groups.
Twin Studies
Identical Twins Reared Together
Same genes,
Same environment
v.
Identical Twins Reared Apart
Same genes,
Different environment
Greater difference between these two groups indicates greater role of
the environment (“nurture”).
Twin Studies
Similarity of IQ Test Scores in Twins
Correlation
0.9
0.8
0.7
0.6
0.5
Identical twins reared
together
Identical twins reared
apart
Criticisms:
1) Adoption
agencies try to
place twins in
similar families so
the variation in
environment may
be small, and
2) There is a very
limited sample.
Is child more
like adoptive
parents…
Adoptive Parents - Nurture
Adoption Studies
…or biological
parents?
Biological Parents - Nature
Adoption Studies
Similarity of Temperament Between Adopted
Children and their Parents
0.5
0.4
0.3
0.2
0.1
0
Biological parents
Adoptive parents
Correlation Coefficient
Correlation Coefficient
Similarity of Values Between Adopted
Children and their Parents
0.6
0.5
0.4
0.3
0.2
0.1
0
Biological parents

Adoptive parents
Note: Two related siblings that grow up in the same family are
strikingly different in personality (as I’m sure many of you can
attest to).
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Nature?
Nurture?
Both?
Twins?
Genetic engineering?
Genetic engineering?
Examples of theories?
What is your opinion of the nature vs.
nurture theory of psychology? In other
words, do you believe nature is dominant,
nurture is dominant, or it’s a combination
of both?
 Please explain your answer!

Reflection