BIOLOGICAL PSYCHOLOGY

NATURE VS. NURTURE

Gordon Allport

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

Trait Theories of PersonalityPersonalities

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 Personality develops from both mental and

biological influence Each person is unique

Everything is a characteristic of us and no one else 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

Hans Eyesenck

Dimensions of personality

1. Extraversion vs. introversion (E)

2. Neuroticisms vs. emotional stability (N)

3. Psychoticism vs. impulse control (P)

Predisposed to eachCollectively makes up

personality

Hans Eyesenck

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

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

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, tough-minded

Robert McCrae and Paul Costa“Big Five” factors

of personalityStabilityExtraversionOpennessAgreeablenessConscientiousness

The Big Five

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

Correlations with the Big Five:Which behaviors correlate?Protested injustice

- Emotionally stable, openFell in love at first sight

- ExtravertedHave not been in therapy

- Emotionally stableBeen in therapy

- OpenThrown a large party

- ExtravertedKept a diary

- OpenListen 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

- ConscientiousNot likely to become addicted to

Internet-Extraverted

Dated a person of a different race- Open

Written a poem spontaneously- Open

Arnold Buss and Robert PlominTemperament

◦Building blocks of personality

◦Everyone has levels of all three

◦Primarily biological; can be adapted by environment

Arnold Buss and Robert Plomin

First TemperamentEmotionality

◦Level of excitability for unpleasant feelings

Sensitive to unemotionalany emotion

Arnold Buss and Robert Plomin

Second TemperamentActivity

◦Physical energy and vigor

Constant unmoving

movement

Arnold Buss and Robert Plomin

Third TemperamentSociability

◦Preference for contact/interaction with others

Want to be Don’t like to be

around others around others

Assessing Our Traits

Reflection: Looking at the Big Five and Three Temperaments, which ones do you see having the greatest impact on your life?

Untangling Nature and Nurture

Behavior Genetics: the study of the interaction of genes and environment on behavior

Nature vs. Nurture

“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

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.

Heritability

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

HeritabilitySara is very outgoing and agreeable

Suzy is timid and non-conforming

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%.

Heritability

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?

100%

How heritable is that trait?

Trait Population HeritabilityCreativity adolescents 25%Extraversion adults 30-50%Autism general 90-95%Depression general 40-55%Sleep quality general 35%TV viewing 3-5 year olds 10-45%Religious beliefs general 0%Religious conservatism women 40%Divorce general 55%Height women 92%

http://www.peele.net/lib/genes.html The Stanton Peele Addiction Website

Identical Twins vs. Fraternal TwinsSame genes, Different genes,Same environment 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

Twin StudiesCriticism: 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.

Increased risk of schizophrenia if twin develops disease

0%

10%

20%

30%

40%

50%

60%

Fraternal twins Identical twins

% in

crea

se

Twin StudiesIdentical Twins Reared Together v. Identical Twins Reared Apart

Same genes, Same genes,Same environment Different environment

Greater difference between these two groups indicates greater role of the environment (“nurture”).

Twin Studies

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.

Similarity of IQ Test Scores in Twins

0.5

0.6

0.7

0.8

0.9

Identical twins rearedtogether

Identical twins rearedapart

Corr

elat

ion

Adoption Studies

Is child more like adoptive parents…

…or biological parents?

Adoptive Parents - Nurture Biological Parents - Nature

Adoption Studies

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).

Similarity of Values Between Adopted Children and their Parents

0

0.1

0.2

0.3

0.4

0.5

Biological parents Adoptive parents

Corr

elat

ion

Coef

ficie

nt

Similarity of Temperament Between Adopted Children and their Parents

0

0.1

0.2

0.3

0.4

0.5

0.6

Biological parents Adoptive parentsCo

rrel

atio

n Co

effic

ient

Examples of theories?

Nature?Nurture?Both?Twins?Genetic engineering?Genetic engineering?

Reflection

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!