The Biological Tradition

• Examples from lecture on history:

• The 4 humors (Melancholic, Sanguine)• Phrenology• Body Types

The Biological Tradition

Phineas Gage (1823-1860)

Temperament

• Individual differences in general mood or quality of emotional response that are moderately stable, inherited, and biologically based

Inhibited versus Uninhibited Children(Kagan, 1994)

• Inhibited– Reacts to unfamiliar

people and situations with avoidance, distress, restraint

– Takes longer time to relax in new situations

– Has more fears and phobias

– Is timid and cautious

• Uninhibited– Reacts to unfamiliar

situations with spontaneity and joy

– Takes shorter time to relax in new situations

– Has fewer fears and phobias

– Is not restrained in new situations

Kagan, Arcus, & Snidman (1993)

• At 4-months,– Videotaped behavior during familiar and

novel stimuli (voices, mobiles, balloons)– Rated infants on reactivity (body movement,

crying)

• At 14-months, 21-months, 4.5 years, 8 years– Videotaped behavior and monitored

physiology

High vs. Low Reactive Infants (Kagan et al., 1993)

• High reactive– Show greater fearful

behavior, heart rate acceleration, increased blood pressure

– Smiled and talked less with unfamiliar adult

– Were shy with unfamiliar peer

– Varied within group

• Low reactive– Showed lesser fearful

behavior, heart rate acceleration, increased blood pressure

– Smiled and talked more with unfamiliar adult

– Were less shy with unfamiliar peer

– Varied within group

HEMISPHERE ACTIVATION

Left Hemisphere• Approach-related emotion• Arousal -> happiness, resilience in the face of stress• Underarousal -> vulnerable to sadness and depression

Right Hemisphere• Withdrawal-related emotion• Arousal -> fear, disgust, anxiety• Underarousal -> relaxation

HEMISPHERE ACTIVATION

Davidson’s Evidence from EEG• Reliable from one month to another (r = .66)• More right-sided activation and more intense

negative and less intense positive trait mood• More right-sided activation and more intense

negative affect in response to film clips meant to elicit fear and disgust

• Infants who cried when separated from their mothers had higher right-sided activation

• Inhibited toddlers had low left-sided activation• People with greater left-sided activation had more

natural killer cell activity

Behavioral Genetics

Different ways of estimating genetic influence:

• Experimental animal studies

• Twin studies

• Adoption studies

Heritability

• Twin studies:• Compare identical twins reared together with

those reared apart• Assume the similarity between “Together”

twins due to shared genes and environment• Assume the similarity between “Apart” twins

due only to genes• THEN: • “Similarity of together” - “Similarity of Apart” =

environment, and 1- environment = genes

Heritability

• Another form of twin study:• Compare monozygotic (MZ) together twins

with dyzygotic (DZ) together twins• Assume similarity of MZ due to genes and

environment• Assume similarity of DZ due to 1/2 genes and

environment

Heritability• THEN:

Heritability =

2* (Similarity MZ - Similarity DZ) = 2*((genes + environment) - (1/2 genes +

environment)) =2* (genes +environment - 1/2 genes - environment)

=2*(genes - 1/2 genes) = 2*1/2 genes = genes

Heritability

Heritability is an estimate of the percentage of

the variance in a particular characteristic in a

particular study that resulted from genetic

variation in that study.

Variance

Friendliness0 5 10

*** *

*** **

**

**

3 7

Variance = ((1-5)2 + (3-5)2 + (3-5)2 + ….. (10-5)2) / N-1“ Average deviation”

HERITABILITY

Environment

Genes

Environment

Example: Cloned people reared in very different situations

Example: Identical twins, different pairs have very similar backgrounds

Genes

Environment

Why is “gene” only circle impossible??

Example: Identical twins, different pairs have fairly different backgrounds

30%

60%

0%

HERITABILITY IS NOT

• The chance that an individual will have a certain characteristic

• How much influence genes or environment have on an individual person

• The absolute influence of a gene outside the particular environment in which the estimate was made

Heritability is: an estimate of the percentage of the variance in a particular characteristic in a particular study that resulted from genetic variation in that study.

HERITABILITY

Some results from the major twin studies:

• Intelligence – H = 30% - 70% (some specific cognitive abilities are more heritable than others)

• Activity level, emotional reactivity, sociability-shyness – H = 20% - 50%

• Neuroticism, extraversion, impulsivity, monotony avoidance – H = 23% - 45%

• Depression – H = 13% for male relatives and 30% for female relatives

• Vocational interests – H =0.43

• Religiosity – H =0.49

• Traditionalism – H =0.53

• Attitudes toward drinking alcohol – H = 51%

• Radicalism and toughmindedness – H > 50%

• Aggressive, antisocial, criminal behavior – H about 50%

Schizophrenia and Heritability

• Twin studies:• 0% concordance in identical twins and 6% concordance in

fraternal twins• Adoption Studies:

1% 3%

9% 17%

Not S S

Not S

S

Adopted Family

BiologicalFamily

THE “NATURE-NURTURE” DEBATE

A devil, a born devil, on whose nature

Nurture can never stick; on whom my pains

Humanely taken, all, all lost, quite lost

-The Tempest

NATURE AND NURTURE INTERACTIONS

A Central Theme in Personality and Social Psychology

The dynamic interaction between the person and the situation. People come into the world with some predispositions. They act in accordance with these predispositions and get reactions and feedback from the environment. These reactions and feedback, in turn, inform, drive, and even determine their behavior in the future. The cycle continues.

NATURE AND NURTURE INTERACTIONS

Diathesis-Stress Model

Examples

Schizophrenia (genetic diathesis)

Phobias (environmental diathesis)

Alcoholism (possible genetic/environmental)

Depression (possible genetic/environmental)

Str

ess

Leve

l

Time

Critical Point

Patient Becomes Ill

NATURE AND NURTURE INTERACTIONS

Continuity of Behavior: Two Hypotheses

(Caspi, Bem, & Elder, 1987)

The data on children who tantrum:

Men: downward occupational mobility, erratic work lives, more likely to divorce

Women: married men with lower occupational status, more likely to divorce, ill-tempered mothers

NATURE AND NURTURE INTERACTIONS

Continuity of Behavior: Two Hypotheses

• Cumulative continuity– We make certain choices, deliberate or not deliberate,

that determine what direction our life goes

• Interactional continuity– Early temperament forms an interactional style that

evokes reciprocal, maintaining responses from others. The person acts, the environment reacts, and the person reacts back.

MAIN POINTS• Personality comes from a complex dynamic interaction of

nature and nurture

• Nature contributes to personality through genetics, as well as basic processes such as brain activation, temperment, neuroanatomy, and biochemistry.

• Nurture contributes to personality through influences such as parental relationship, sibling competition, environmental stimulation, and culture.

• Nature and nurture interact from the fetus throughout the life span. Diathesis, cumulative continuity, and interactional continuity are some of the mechanisms through which these interactions occur.