Chapter 9
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Chapter 9. BIOLOGICAL FOUNDATIONS OF PERSONALITY. QUESTIONS TO BE ADDRESSED IN THIS CHAPTER. Are infants born with differences in temperament? If so, what are the biological bases for these differences? How can the study of human evolution inform our understanding of personality today?
Chapter 9

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Slide 1

Chapter 9

BIOLOGICAL FOUNDATIONS

OF PERSONALITY

Slide 2

QUESTIONS TO BE ADDRESSED IN THIS CHAPTER

  • Are infants born with differences in temperament? If so, what are the biological bases for these differences?

  • How can the study of human evolution inform our understanding of personality today?

  • What role do genes play in the formation of personality? How do genes interact with the environment in determining personality?

  • What is the relation between brain processes and personality processes?

Slide 3

TEMPERAMENT

PROSPECTIVE STUDIES

  • The New York Longitudinal Study (NYLS) followed over 100 children from birth to adolescence using parental reports of infants' reactions to a variety of situations to define variations in temperament

  • 3 infant temperament types:

    • Easy = playful and adaptable

    • Difficult = fussy and unadaptable

    • Slow-to-warm-up = low reactivity and mild in responding

Slide 4

TEMPERAMENT

PROSPECTIVE STUDIES

  • The NYLS found a link between differences in infant temperament and later personality

    • Easy babies were least likely to have later maladjustment

    • Difficult babies were most likely to have later maladjustment

    • The parental environment best suited for babies of one temperament type might not be best for those with a different temperament

Slide 5

TEMPERAMENT

CONSTITUTIONAL BASIS

  • Buss & Plomin (1975, 1984) used parental ratings of behavior to define 4 dimensions of temperament:

    • Emotionality

    • Activity

    • Sociability

    • Impulsivity (impulsivity was dropped later - not found to be a distinct dimension via factor analysis)

  • Temperaments show evidence of

    • Stability over time and being largely inherited

Slide 6

TEMPERAMENT

PERSONALITY DEVELOPMENT

Inhibited and Uninhibited Children

  • Jerome Kagan observed children in laboratory settings and identified 2 distinctive temperament profiles:

  • Inhibited child

    • Reacts to unfamiliar people and events with restraint, distress, and avoidance

    • Requires more time to relax in new situations

    • Has more unusual fears (phobias)

  • Uninhibited child

    • Seems to enjoy these very same situations

    • Responds with spontaneity to novel situations, laughing and smiling easily

Slide 7

TEMPERAMENT

PERSONALITY DEVELOPMENT

Inhibited and Uninhibited Children

  • Kagan hypothesized that inherited differences will tend to be stable during development

    • Studied children at 14 months, 21 months, 4.5 years, and 8 years

    • At 14 and 21 months and at 4.5 and 8 years, inhibited kids relative to uninhibited kids showed

      • More fearful behavior

      • Greater heart-rate acceleration

      • Increased blood pressure in response to unfamiliar stimuli and situations

Slide 8

TEMPERAMENT

PERSONALITY DEVELOPMENT

Inhibited and Uninhibited Children

  • Although there is stability in temperament, there also is evidence of change

    • Many inhibited infants did not become fearful

    • Change seemed tied to caretakers who were not overly protective and placed reasonable demands on these children

    • Some uninhibited infants lost their relaxed style

    • The environment appears to play an important role in modulating the expression of biologically based personality styles

Slide 9

TEMPERAMENT

PERSONALITY DEVELOPMENT

  • Schwartz et al. (2003) studied young adults categorized as highly inhibited or uninhibited at 2 years of age

    • Prediction - inhibited adults would be more responsive to pictures of unfamiliar versus familiar faces

    • fMRI was used to identify brain structures activated by visual stimuli

    • When they viewed unfamiliar faces, adults who had been identified as inhibited in childhood showed signifcantly higher levels of reactivity in the amygdala

Slide 11

EVOLUTION AND PERSONALITY

  • 2 types of biological causes of behavior:

  • Proximate causes = biological processes operating within the organism at the time behavior is observed

  • Ultimate causes = why a given biological mechanism has become part of the organism and why it responds to the environment in a certain way

Slide 12

EVOLUTION AND PERSONALITY

  • Ultimate causes are grounded in the view that some biological features are better-suited to a given environment than others

  • Organisms that possess certain biological mechanisms are more likely to survive and reproduce

  • Over generations, the world is increasingly populated by organisms that possess adaptive biological mechanisms, which themselves evolve

Slide 13

EVOLUTION AND PERSONALITY

  • Human functioning today is viewed in terms of evolved solutions to adaptive problems faced by humans over eons (natural selection)

  • Basic elements of human nature can be understood in terms of evolved psychological mechanisms that have adaptive value, specifically, survival and reproductive success

  • Evolved psychological mechanisms are adaptive to life as a hunter-gatherer, but may no longer be generally adaptive (e.g., taste preference for fat)

Slide 14

EVOLUTION AND PERSONALITY

  • Mental modules = multiple information- processing devices, each of which processes information about a specific domain of life

  • For example, attracting a mate is a distinct problem of great evolutionary significance

  • To solve it, we purportedly have evolved a mental module that is activated when we encounter tasks pertaining to mate attraction

Slide 15

EVOLUTION AND PERSONALITY

MATE PREFERENCES AND JEALOUSY

  • Parental Investment Theory (Trivers, 1972)

  • Biological differences between the sexes cause women to invest more in parenting

    • Women can pass their genes on to fewer offspring than can men

    • There are limited time periods during which women are fertile

    • Women have a more limited age range during which they can produce offspring

Slide 16

EVOLUTION AND PERSONALITY

MATE PREFERENCES AND JEALOUSY

  • Women have different and stronger preferences about mating partners than do men

    • Women seek men with potential for providing resources and protection

    • Men focus on the reproductive potential of a woman

  • Are these preferences evident in current patterns of attraction?

Slide 17

EVOLUTION AND PERSONALITY

MATE PREFERENCES AND JEALOUSY

  • Parenthood Probability Theory - Buss

  • Women can always be certain that they are the mothers of their offspring

  • Men cannot be as sure

  • Thus, men are more concerned about sexual rivals and place greater value on chastity in a potential mate than do women

Slide 18

EVOLUTION AND PERSONALITY

MATE PREFERENCES AND JEALOUSY

  • 3 hypotheses from parental investment and parenthood probability theories:

  • A woman's "mate value" for a man will be determined by her reproductive capacity and chastity

  • A man's "mate value" for a woman will be determined by the resources he can provide

  • Men and women will differ in the events that activate jealousy (sexual vs. emotional)

Slide 19

EVOLUTION AND PERSONALITY

MATE PREFERENCES

  • Buss (1989) - 37 samples, > 10,000 individuals from 33 countries on six continents:

  • In all groups, men valued physical attractiveness and youth in potential mates more than did women

    • Mens’ preference for chastity in potential mates was found in 23 of 37 samples

  • In 36 groups, women valued the financial capacity of potential mates more than did men

    • Women preferred ambition and industriousness in potential mates more than did men in 29 of 37 samples

Slide 20

EVOLUTION AND PERSONALITY

JEALOUSY

  • Buss et al. (1992) tested the hypothesis of sex differences in jealousy

  • Undergraduates were asked if they would feel more distressed in response to sexual infidelity or emotional infidelity

    • 60% of men reported greater subjective distress over a partner's sexual infidelity

    • 83% of women reported greater subjective distress over a partner's emotional attachment to a rival

Slide 21

EVOLUTION AND PERSONALITY

JEALOUSY

  • Physiological measures of distress were taken on undergraduates who imagined a partner becoming sexually versus emotionally involved with someone else

  • Men showed more autonomic distress to a partner's possible sexual involvement

  • Women showed more autonomic distress to a partner's possible emotional involvement

Slide 22

EVOLUTION AND PERSONALITY

  • ORIGINS OF SEX DIFFERENCES: HOW STRONG ARE THE DATA?

  • DeSteno and colleagues (2002) asked participants to consider sexual and emotional infidelity scenarios one at a time, and then indicate how upset they would be by each one

    • Sex differences in jealousy were no longer found

    • Men and women were more distressed by sexual infidelity than by a partner's emotionally intimate nonsexual relationship

Slide 23

EVOLUTION AND PERSONALITY

ORIGINS OF SEX DIFFERENCES: HOW STRONG ARE THE DATA?

  • Eagly & Wood (1999) found that in societies with greater gender equality

    • Women were less concerned with a man's earning capacity

    • Men were less concerned with a woman's child-bearing capacity

  • Data are consistent with a biosocial view of sex differences (i.e., the interaction of biological differences and social roles)

Slide 24

GENES AND PERSONALITY

BEHAVIORAL GENETICS = the study of genetic contributions to behavior

Selective Breeding

  • Animals with a desired trait are selected and mated over successive generations to produce a strain that is consistent for the desired trait

    • Study a strain’s typical behavioral tendencies and/or how different strains respond to diverse experimentally controlled developmental environments

    • Researchers can separate the effects of genetic from environmental differences on later behavior

Slide 25

GENES AND PERSONALITY

BEHAVIORAL GENETICS

Twin Studies

  • Twins provide a naturally occurring experiment

    • If two organisms are identical genetically, but experience different environments, later similarities can be explained by genetic factors

    • If two organisms are different genetically, but experience the same environment, later differences can be explained by genetic factors

Slide 26

GENES AND PERSONALITY

BEHAVIORAL GENETICS

Twin Studies

  • The difference in similarity between MZ (identical) twins and DZ (fraternal) twins is crucial to estimating the effects of genetics

    • If genetics influence a personality characteristic, then MZ twins should be more similar on that characteristic than DZ twins

    • If there is no genetic influence on a personality characteristic, then no difference is expected between MZ twins and DZ twins on that characteristic

Slide 27

GENES AND PERSONALITY

BEHAVIORAL GENETICS

Twin Studies

  • Studies in which MZ and DZ twins are reared apart show that the effects of biology are found across different environments

  • MZ twins reared apart were as similar to one another as were MZ twins reared together

  • The degree of similarity between twins can be seen in correlations ranging from .4 to .6

Slide 28

GENES AND PERSONALITY

BEHAVIORAL GENETICS

Adoption Studies

  • Are biological siblings more similar to one another than are adopted siblings?

  • Are biological siblings more similar to their parents than adopted siblings are to theirs?

  • Are adopted siblings more similar to their biological parents than to their adopted parents?

  • Affirmative answers to these questions suggest the importance of genetics

Slide 30

GENES AND PERSONALITY

BEHAVIORAL GENETICS

Heritability Coefficient

  • h2 - the proportion of variation in a characteristic that can be attributed to genetic factors

    • Refers to variation within the population; h2 does not indicate the degree to which genetics account for an individual’s characteristics

    • Based on the difference between MZ and DZ correlations

      • If MZ twins are no more similar to each another than are DZ twins, then h2 = 0

      • If MZ twins differ greatly from DZ twins, the h2 is large

Slide 32

GENES AND PERSONALITY

BEHAVIORAL GENETICS

Molecular Genetic Paradigms

  • Molecular genetic techniques involve identification of genes that are linked to personality traits

  • By examining the genetic material of different individuals, researchers hope to show how genetic variations, or alleles, relate to individual differences in personality

Slide 33

GENES AND PERSONALITY

BEHAVIORAL GENETICS

Molecular Genetic Paradigms

  • Research by Caspi and colleagues discovered molecular-genetic factors that make individuals more or less vulnerable to depression

  • Individuals who were genetically predisposed to lower levels of serotonergic activity and who experienced many stressful life events were more likely to become depressed than were other individuals

  • Gene x Environment interaction

Slide 34

GENES AND PERSONALITY

GENE-ENVIRONMENT INTERACTIONS

Shared and Nonshared Environments

  • Shared environments = environments shared by siblings as a result of growing up in the same family

  • Nonshared environments = environments not shared by siblings growing up in the same family

Slide 35

GENES AND PERSONALITY

GENE-ENVIRONMENT INTERACTIONS

Shared and Nonshared Environments

  • If shared environments are important, then

    • Biological siblings reared together will be more similar than if reared apart

    • Adopted siblings reared together should be more similar than if reared apart

  • If nonshared environments are important, then

  • Biological siblings reared together will be no more similar than if reared apart

Slide 36

GENES AND PERSONALITY

GENE-ENVIRONMENT INTERACTIONS

Shared and Nonshared Environments

  • Nonshared environments appear more important to personality development than shared experiences resulting from being reared in the same family

    ≈ 40% of variation in personality due to genetic factors

    ≈ 35 % of variation due to nonshared environments

    ≈ 5% of variation due to shared environments

    ≈ 20% of variation due to measurement error

Slide 37

GENES AND PERSONALITY

GENE-ENVIRONMENT INTERACTIONS

Nonshared Environmental Effects

  • Research has focused on the processes linking genetic and family influences on personality development

    • Researchers can separate the effects of parenting common across siblings from the effects of parenting unique to each sibling

    • Parenting unique to each child appears tied to behaviors evoked by the genetic characteristics of the child

    • Children with different genetic constitutions evoke different responses from their parents; they also create different family environments

    • One parenting style may be experienced differently by genetically different siblings

Slide 38

NEUROSCIENCE AND PERSONALITY

HEMISPHERIC (LATERAL) DOMINANCE

  • People differ in the degree to which their emotions tend to be positive or negative

  • Davidson (1994, 1995, 1998) studied left and right hemispheric involvement in positive versus negative emotion

    • Activation of the left prefrontal region of the brain was predicted to correlate with positive, approach-related emotions

    • Activation of the right prefrontal region of the brain was predicted to correlate with negative, avoidance-related emotions

Slide 39

NEUROSCIENCE AND PERSONALITY

HEMISPHERIC (LATERAL) DOMINANCE

  • In Davidson’s research, EEG recordings detected electrical activity of the brain

  • Measures of hemispheric activity were taken before (baseline) and during film clips designed to evoke positive or negative emotion

  • Participants rated their mood before and during each film clip

Slide 40

NEUROSCIENCE AND PERSONALITY

HEMISPHERIC (LATERAL) DOMINANCE

  • Individual differences in prefrontal lateral asymmetry were associated with baseline mood

    • Left hemispheric dominance with positive mood

    • Right hemispheric dominance with negative mood

  • The same prefrontal lateral differences were associated with film clips evoking either positive or negative affect after baseline differences in mood were statistically removed

  • L = more mood+ to clips+; R = more mood- to clips-

Slide 41

NEUROSCIENCE AND PERSONALITY

HEMISPHERIC (LATERAL)DOMINANCE

  • Depressed and formerly depressed individuals have diminished left prefrontal cortical activity compared to non-depressed individuals

  • Individuals with damage to the left prefrontal area are more likely to become depressed, whereas those with damage to the right prefrontal area are more likely to become manic

  • Infants who experience greater distress when separated from their mothers show more right prefrontal activation and less left prefrontal activation than infants who show little distress

Slide 42

NEUROSCIENCE AND PERSONALITY

NEUROTRANSMITTERS = chemicals that transmit information between neurons

  • Dopamine is central to the operation of the reward system

  • Serotonin is involved in mood regulation

  • Selective serotonin reuptake inhibitors (SSRIs) reduce depression by leaving more serotonin to stimulate receptor neurons

  • Because neurotransmitters contribute to mood, it is believed that brain chemistry may underlie individual differences in temperament

Slide 43

NEUROSCIENCE AND PERSONALITY

NEUROTRANSMITTERS AND

TEMPERAMENT

Three Dimensions of Temperament

  • Clark & Watson's (1999) model – temperament differences can be summarized by 3 independent superfactors, similar to those suggested by Eysenck and to three of the BIG 5 domains:

    • NE(Negative Emotionality)

    • PE (Positive Emotionality)

    • DvC (Disinhibition vs. Constraint)

Slide 44

NEUROSCIENCE AND PERSONALITY

NEUROTRANSMITTERS AND TEMPERAMENT

Three Dimensions of Temperament

  • High on NE = prone to negative emotions, the environment elicits distress and threat

  • Low on NE = emotionally stable, self-satisfied

  • High on PE = cheerful, energetic, outgoing, willing to engage the environment

  • Low on PE = reserved, low in energy and confidence

  • D = impulsive and aggressive, oriented toward momentary feelings and sensations

  • C = avoidant of risk or danger

Slide 45

NEUROSCIENCE AND PERSONALITY

NEUROTRANSMITTERS AND TEMPERAMENT

Three Dimensions of Temperament

  • NE may be related to

  • Low levels of serotonin (anxiety, depression, OCD symptoms), right hemispheric dominance (withdrawal), and hypersensitivity of the amygdala

  • PE may be related to

    • High levels of dopamine (positive emotion, incentive motivation) and left hemispheric dominance

  • DvC may be related to

    • Low levels of serotonin and high levels of testosterone

  • Slide 46

    PLASTICITY: BIOLOGY AS EFFECT

    SES AND SEROTONIN

    • Manuck et al. (2005) found that differences in serotonin level were due to differences in SES

      • In impoverished neighborhoods, people tend to experience more daily stress and poorer nutrition

      • Stress and nutrition can affect the body, including serotonergic activity

      • Large sample of adults ingested a serotonin agonist

      • Blood samples were tested for prolactin, a hormone released by serontonin

    Slide 47

    PLASTICITY: BIOLOGY AS EFFECT

    SES AND SEROTONIN

    • Manuck et al. found that residents of poorer communities displayed lower serotonergic responsiveness

    • Differences between communities were not explained by five-factor traits or intelligence

    • Manuck et al. concluded that, “socio-economic inequalities among communities can, if perhaps modestly, affect even the neurobiology of their residents” (p. 526)


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