Personality: Approaches, Measurement, and Genetics -

Identical Twins Case Study: Paula Bernstein & Elyse Schein

• Paula Bernstein and Elyse Schein are identical twins who were adopted into separate families at birth in 1968 and reunited at age 35 in 2003.
• Paula’s upbringing: happy suburban New York home, loving adoptive parents and older brother; wrote an article titled "Why I Don't Want to Find My Birth Mother".
• Elyse’s upbringing: happy childhood, college and film school abroad.
• Reunification details:
  • In 2003, the adoption agency informed Elyse that she had a twin sister, Paula, who was also looking for her.
  • Their first meeting at a café led to long conversation; Elyse described hearing her own voice in a recorder back at her when she heard Paula’s voice; Paula noted an immediate intimacy despite not knowing each other previously.
• Shared traits discovered after meeting:
  • Both attended graduate school in film; both enjoyed writing; both edited high school yearbooks; similar tastes in music.
• The twins later co-authored a book, Identical Strangers (Spilius, 2007; Kuntzman, 2007), about their childhoods and the discovery of an identical twin in their mid‑30s.
• Public interest and broader implication:
  • NPR feature: "Identical Strangers Explore Nature Vs. Nurture".
• Conceptual takeaway:
  • Case illustrates how identical genetics can converge on strikingly similar personality tendencies and life patterns even when raised apart, highlighting the interplay of nature and nurture in shaping personality.

What Is Personality?

• Personality is defined as an individual's consistent patterns of feeling, thinking, and behaving. Definition cited: (John, Robins, & Pervin, 2008).
• Why it matters:
  • First impressions and judgments of others rest on perceived stable characteristics.
  • Understanding personality helps explain behavior across situations and link to psychological disorders.
• Core research goals in personality psychology:
  • Understand what makes people different (individual differences).
  • Explore how genes (nature) and environment (nurture) shape those differences.
  • Examine how personality traits influence behavior and outcomes across contexts.
• Foundational questions:
  • How and when does personality influence behavior?
  • How do psychologists measure personality?
  • To what extent is personality caused by nature vs. nurture?

Approaches to Assessing Personality: Early Theories

• Phrenology (Franz Joseph Gall, 1758–1828):
  • Idea: personality could be inferred from skull bumps; a mapping between skull topography and mental faculties.
  • Historical status: once popular in Victorian era but discredited due to lack of empirical support.
• Somatology (William Herbert Sheldon, 1898–1977):
  • Idea: body type predicts personality. Endomorphs (round, higher body fat) → assertiveness/boldness; ectomorphs (lean) → introversion/intellectualism.
  • Historical status: discredited; no robust scientific validation.
• Physiognomy: attempts to infer personality from facial features.
  • Mixed findings in contemporary evidence: some studies suggest people can detect broad traits from faces above chance levels, but this is not reliable for precise trait prediction (e.g., Rule & Ambady, 2010; Olivola & Todorov, 2010).
  • Overall empirical support for physiognomy as a universal predictor remains limited.
• Key takeaway on early theories:
  • Early approaches sought direct links between physical attributes and personality, but they largely lacked robust empirical validation and are now considered outdated.

Traits and Trait Theory: Core Concepts and Measurements

• Traits: relatively enduring characteristics that influence behavior across many situations.
• Trait approach: seeks to identify stable, predictive dimensions of personality via self-report measures.
• Major points:
  • Hundreds of traits have been investigated; researchers aim to identify core, underlying dimensions.
  • Trait measures rely heavily on self-reports and have both strengths (predictive validity) and limitations (reliability, accuracy, social desirability).
• Problems with overabundance of traits:
  • There are potentially thousands of descriptors; goal is to reduce to a manageable set of fundamental dimensions.
• Classic pioneers and their contributions:
  • Allport: reduction from ~18,000 trait words to a structured hierarchy: cardinal traits > central traits > secondary traits.
  • Cattell: factor analysis to identify core traits; introduced 16 personality factors (source traits) and surface traits.
  • Eysenck: focus on biological bases of personality, notably extraversion–introversion (arousal theory).
• Trait measurement and tools:
  • Self-report inventories: people describe their own characteristics.
  • MBTI (Myers-Briggs Type Indicator): widely used but criticized for reliability/validity issues; categories can shift over time and do not consistently predict behavior across measures.
  • MBTI caution: useful for brainstorming and ice-breaking but not a robust predictor of behavior or a stable diagnostic tool.
• Key takeaway:
  • The trait approach seeks to identify stable dimensions of personality, but it must address issues of reliability, validity, and cross-cultural applicability.

The Five-Factor Model of Personality (Big Five)

• Core dimensions (the Big Five):
  • Openness to Experience (O)
  • Conscientiousness (C)
  • Extraversion (E)
  • Neuroticism (N)
  • Agreeableness (A)
• Mnemonics: CANOE or OCEAN.
• Description and expected behaviors by trait:
  • Openness to Experience: imagination, exploration of ideas; diverse interests; curiosity and aesthetic sensitivity.
  • Conscientiousness: self-discipline, orderliness, planning, reliability; tendency to prefer planned over spontaneous behavior.
  • Extraversion: sociability, positive affect, energetic engagement with others; liking of social stimulation.
  • Neuroticism: tendency toward negative emotions (anxiety, mood swings); greater emotional reactivity.
  • Agreeableness: compassion, cooperation, compliance, and willingness to compromise.
• Cross-cultural validity and predictive power:
  • The Big Five factors appear cross-culturally valid across many countries (e.g., China, Japan, Italy, Hungary, Turkey).
  • Predictive validity: higher conscientiousness, lower neuroticism, and higher agreeableness predict job performance in many contexts.
  • Some limitations: the Big Five does not capture all important personality dimensions (e.g., moral behavior) and may vary somewhat across cultures.
• Relationship to behavior:
  • Broad patterns of personality predict behavior, but trait-behavior links can be modest in single situations and stronger when aggregated across multiple situations.
• Heritability and genetic basis:
  • Big Five dimensions show substantial genetic influence; heritability estimates typically around h^2 ext{ (heritability)}
    ighttoleftarrow 0.40-0.50 for major traits, indicating genetics explain a meaningful portion of variation.
• Stability and change:
  • Traits tend to be relatively stable across time, but measurement in different situations shows that stability is not absolute; aggregation across many behaviors improves predictive power.
• Key takeaway:
  • The Five-Factor Model provides a robust, widely used framework for describing normal personality across cultures, with substantial but not exclusive genetic influence.

Situational Influences and Trait Stability: Mischel’s Critique and Aggregation

• Core claim: traits may not be as stable across contexts as once thought.
• Evidence: Mischel (1968) found low cross-situational correlations in behavior (roughly r ≈ 0.30) for various traits.
• Implications:
  • Behavior can vary by situation; a single trait label may not predict specific actions in a single context.
  • To predict behavior, psychologists should aggregate observations across multiple situations.
• Responses and refinements:
  • Researchers argued that while traits are not perfectly stable across all situations, they become more predictive when behavior is aggregated over time and context.
  • Traits may express in qualitatively different behaviors (e.g., extraversion leading to teaching, sales, acting, or even criminal behavior) but still reflect the same underlying trait.
• Schemas and perception effects:
  • People tend to see more traits in others than in themselves (trait overestimation for others; “depends on the situation” more common for self-perceptions).
  • These biases (schemas, Barnum effect) can influence judgments of personality.
• Takeaway:
  • Personality is shaped by both stable dispositions and situational factors; cross-situational aggregation strengthens predictive validity of trait models.

Measurement of Personality and Psychological Disorders

• Self-report measures:
  • Pros: efficient, scalable; good for capturing habitual tendencies.
  • Cons: subject to social desirability, response biases, and limited access to unconscious processes.
• MMPI (Minnesota Multiphasic Personality Inventory):
  • Internationally used to assess personality and psychological disorders (MMPI-2; 500+ items).
  • Subscales cover symptoms (e.g., hypochondriasis, depression, hysteria, paranoia, psychasthenia) and clinical patterns.
  • Includes validity scales to detect inconsistent or dishonest responding.
• Projective tests:
  • Rorschach Inkblot Test: uses ambiguous inkblots to infer personality structure; responses scored on what is seen, where, and why.
  • Thematic Apperception Test (TAT): subjects create stories about ambiguous sketches; stories analyzed for themes and motivational patterns.
  • Other projective tools include Draw-A-Person and free association tasks.
• Critiques of projective tests:
  • Mixed empirical support for reliability and construct validity; correlations with personality traits and behavior are often weak.
  • More useful as conversation starters or therapeutic icebreakers than definitive diagnostic tools.
• Practical implications:
  • Researchers use a combination of trait measures, projective methods, and clinical scales to form a comprehensive assessment of personality and potential disorders.

Personality and Leadership: Trait-Based Perspectives

• Trait theories of leadership posit that certain personality characteristics predispose individuals to be effective leaders.
• Key attributes linked to leadership:
  • Intelligence, particularly when paired with clear and accessible communication to followers.
  • Strong social skills and ability to perceive and respond to group needs.
• Leader typologies:
  • Charismatic leadership: enthusiasm, commitment, self-confidence; broad, motivating vision; personal sacrifice for the group; referent power.
  • Transactional leadership: task-focused, contingent rewards/punishments; clarifies expectations and maintains routine.
  • Transformational leadership: visionary, inspirational; seeks to move the group beyond the status quo; fosters development and empowerment.
• Relationship between traits and leadership performance:
  • Charisma can positively relate to leadership effectiveness, but leadership success often depends on a combination of traits and the situational context.
• Practical takeaway:
  • Both personality and situational factors influence leadership effectiveness; a single trait is rarely sufficient to predict success across all contexts.

Humanistic Theories of Personality: Self and Motivation

• Core idea: humans have free will and strive toward self-actualization and personal growth.
• Maslow’s Hierarchy of Needs:
  • Pyramid structure with ascending needs: physiological, safety, belongingness/love, esteem, and self-actualization at the top.
  • Self-actualization describes reaching one’s creative and full potential; peak experiences are transcendent moments of connection and insight.
  • Notable examples of self-actualized individuals include Einstein, Lincoln, MLK Jr., Helen Keller, Gandhi.
• Carl Rogers: unconditional positive regard (UPR)
  • A therapeutic stance involving genuineness, openness to experience, empathy, and nonjudgmental acceptance.
  • UPR is a foundation of Rogerian therapy and is associated with promoting self-acceptance and psychological well-being.
  • UPR supports authenticity and helps clients integrate experiences without losing self-worth.
• Positive psychology movement:
  • Emphasizes positive aspects of human functioning and how positive thinking and open engagement contribute to life satisfaction and health.
• Higgins’ Self-Discrepancy Theory:
  • Self-concept consists of actual, ideal, and ought selves.
  • Discrepancies between these components predict distinct emotional experiences:
  • Ideal-Actual discrepancies are associated with sadness/dejection.
  • Ought-Actual discrepancies are associated with anxiety, tension, and agitation.
  • Experiments show that priming people with their ideal or ought selves can alter mood depending on the level of discrepancy.
• Practical implications:
  • The self-concept and its alignment with internal standards and perceived social expectations impact emotion and motivation.

Nature, Nurture, and Behavioral Genetics

• Core question: to what extent are personality traits determined by genetics (nature) versus environment (nurture)?
• Genes and chromosomes:
  • Humans have 23 pairs of chromosomes; DNA is organized into genes (roughly 25,000 genes).
  • The DNA sequence of humans is about 99.9% identical across individuals.
• Behavioral genetics: methods and logic
  • Family studies: examine trait similarity across relatives to infer genetic and shared environmental influences.
  • Twin studies: compare identical (monozygotic) twins and fraternal (dizygotic) twins to parse genetic vs. environmental contributions.
  • Adoption studies: compare adopted individuals to biological and adoptive relatives to separate genetic and environmental effects.
  • Heritability (often denoted h^2): proportion of variance in a trait attributable to genetic factors.
• Key concepts and typical findings:
  • Fingerprint patterns show very high genetic determination (roughly r ≈ 0.96 for identical twins raised apart).
  • Big Five personality traits show substantial heritability, typically around h^2 ext{ (heritability)}
    ightarrow 0.40-0.50 for major dimensions.
  • Across many traits, there is more similarity in identical twins raised apart than in fraternal twins raised apart, indicating genetic influence beyond the shared family environment.
  • Shared environment (experiences shared by twins, such as upbringing) tends to have a smaller impact on adult personality than nonshared environment.
  • Nonshared environment (experiences unique to the individual) often accounts for substantial variation in adult personality and can be the largest source of differences.
• Data patterns from twin/adoption studies (illustrative, not exhaustive):
  • For sexual orientation, heritability estimates range roughly from 18 ext{–}39 ext{%}; shared environment contributes 0 ext{–}17 ext{%}; nonshared environment contributes 61 ext{–}82 ext{%}.
  • The Big Five: heritability ~$0.40 ext{–}0.50$; correlations for identical twins raised together vs apart show substantial genetic influence with a nontrivial role for environment.
• Molecular genetics:
  • Seeks to locate specific genes associated with personality traits.
  • Techniques include DNA collection (cheek swab), marker binding, and fluorescence to identify gene involvement.
  • Knockout studies in animals (e.g., mice) remove or alter a gene to study behavioral effects (e.g., anxiety, aggression, learning, socialization).
• Important caveats:
  • No single gene determines personality; many genes act in concert with environmental factors.
  • Even with genetic predispositions, environmental context can amplify, dampen, or alter trait expression.
  • Behavioral genetics research must carefully consider methodological assumptions, twin selection processes, and representativeness.
• Key takeaway:
  • Genetics contributes substantially to personality, but nonshared environmental influences and gene–environment interactions are major determinants of the final phenotype.

Connections, Implications, and Key Formulas

• Nature vs. nurture: real-world twin case (Identical Twins) demonstrates strong genetic similarity, yet distinct environments produce nuanced differences; genetics sets potential, environment shapes expression.
• Measurements and validation:
  • Trait measures require reliability and construct validity; some widely used tests (e.g., MBTI) may lack these in certain contexts.
  • The Five-Factor Model remains a robust, cross-culturally validated framework but does not capture all aspects of personality (e.g., morality, specific disorders).
• Aggregation principle in personality prediction:
  • To predict behavior accurately, aggregate multiple observations across varied situations rather than rely on a single measurement.
• Ethics and practical relevance:
  • Genetic research raises questions about determinism, stigma, and privacy; findings should be communicated with nuance to avoid misinterpretation of “destiny” based on genes.
  • In applied settings (e.g., leadership selection, clinical assessment), use comprehensive, multi-method approaches rather than single-test conclusions.

Key Equations and Notable Numbers (LaTeX)

• Five-Factor Model dimensions (Big Five):
  • ext{Big Five} = ig{ ext{Openness}, ext{Conscientiousness}, ext{Extraversion}, ext{Neuroticism}, ext{Agreeableness} ig}
  • CANOE / OCEAN mnemonic: $ext{CANOE} ext{ or } ext{OCEAN}$
• Trait-behavior relation and aggregation:
  • Approximate cross-situational stability correlation: $r \approx 0.30$
• Heritability estimates (Big Five):
  • $h^2_{ ext{Big Five}} \approx 0.40\text{--}0.50$
• Fingerprint patterns: high genetic influence (illustrative):
  • $r_{ ext{identical, raised apart}} \approx 0.96$
• Sexual orientation heritability (illustrative ranges):
  • $h^2_{SO} \in [0.18, 0.39]\,\%$
  • $c^2_{SO} \in [0, 0.17]\,\%\text{ (shared environment)}$
  • $e^2_{SO} \in [0.61, 0.82]\,\%\text{ (nonshared environment)}$
• Maslow’s hierarchy (top to bottom):
  • Self-actualization (top) built upon Esteem, Belongingness, Safety, and Physiological needs (bottom).
• Key cultural/psychometric references (authors): Allport, Cattell, Eysenck, Costa & McCrae, Goldberg, Triandis, Zuckerman, etc. (see chapter notes and references in the transcript).

Critical Thinking and Practice Questions

• Exercises and Critical Thinking:
  • Reflect on your own personality and that of people you know. Which traits do you value in others, and which traits do you find challenging?
  • Consider influential people in your life. Which personality characteristics contributed to their influence?
• Self-concept and motivation:
  • Compare your actual self with your ideal and ought selves. How do these discrepancies relate to your emotions and goals?
  • How might self-discrepancies influence mood and behavior in daily life and in goal pursuit?

Chapter Takeaways

• Personality is a composite of stable traits and context-driven behaviors.
• The most widely validated framework for normal personality is the Five-Factor Model, though it is not exhaustive.
• Personality is measured through a mix of self-report inventories, clinical scales (e.g., MMPI), and projective assessments, each with strengths and limitations.
• Humanistic theories emphasize self-actualization, unconditional positive regard, and the importance of the self in shaping motivation and well-being.
• Behavior is influenced by both genetic and environmental factors; nonshared environment often accounts for substantial individual differences.
• Molecular genetics and behavioral genetics together illuminate how genes and environment interact to shape personality, without implying predetermined destinies.

References for Further Reading (from transcript)

• John, O. P., Robins, R. W., & Pervin, L. A. (2008). Handbook of personality psychology: Theory and research.
• Spilius, A. (2007); Kuntzman, G. (2007); NPR feature: Identical Strangers Explore Nature Vs. Nurture.
• Foundational works on the Five-Factor Model: Costa & McCrae (1992); Goldberg (1982).
• Behavioral genetics and twin/adoption studies: Bouchard et al. (1990); Plomin et al. (1997); Tellegen et al. (1988).
• Molecular genetics and personality: Goldsmith et al. (2003); Strachan & Read (1999).
• Humanistic theories: Maslow (1970); Rogers (1980); Seligman & Csikszentmihalyi (2000).