Study Notes on Biological Domain of Personality and Individual Differences

PSYU/PSYX3336 - Advanced Topics in Personality and Individual Differences

Week 3 Lecture: Biological Domain

Lecture Outline

  • The Biological Domain

    • Genetics

    • Genotype-environment correlation

    • Physiological approaches

    • Measures and theories

The Biological Domain

  • Refers to the physical/biological parts of individuals that influence personality, including:

    • Genes

    • Brain and brain activity

    • Evolution: Adaptations for survival and reproduction.

Genetics

Definition of Heritability

  • Heritability: The extent to which a trait is genetic, defined as:

    • “The proportion of phenotypic variance that is attributable to genotypic variance” (p.161 of textbook).

    • Example: A heritability value of .50 indicates that 50% of the observed phenotypic variation is due to genotypic variation.

    • The remainder is attributed to environmental components.

Key Findings in Heritability Studies

  • Paulander (2024) study of twin data:

    • Cognitive ability: 88% heritable

    • Extraversion: 89% heritable

  • Vukasović and Bratko (2015) meta-analysis:

    • 40% of personality differences attributed to heritability, 60% environmental.

    • Focus is on populations, not individuals.

    • Data reflect specific time and location.

Methods of Genetic Research

Research Approaches

  1. Selective Breeding:

    • Breeding pets for desirable traits, e.g., agreeableness in dogs.

  2. Family Studies:

    • Parent-child relationships show 50% genetic similarity.

    • Grandparent-grandchild/aunt-nephew show 25% genetic similarity.

  3. Twin Studies:

    • Identical twins share 100% genetic material.

    • Case studies include Segal's research from 2011, 2022, and 2015.

    • Notable study: Minnesota Twin Study (Bouchard & McGue, 1990; Tellegen et al., 1988).

  4. Adoption Studies:

    • Similarities found between adopted children and biological parents suggest genetic influence, while similarities with adoptive parents suggest environmental influences.

Trait Twin Correlation Findings

  • Neuroticism: 0.70

  • Aggression: 0.67

  • Traditionalism: 0.59

  • Social Potency: 0.57

Key Findings: Behavioral Genetic Research

Personality Traits Heritability

  1. Extraversion and Neuroticism:

    • Neuroticism has 47% heritability (Boomsma et al., 2018).

    • Extraversion has an average heritability of 42% (Vukasović & Bratko, 2015).

    • Big Five personality traits: 50% heritability (Caspi et al., 2005) and 34-58% (de Vries et al., 2021).

  2. Shyness:

    • Heritability of 44% by age 6 (Morneau-Vaillancourt et al., 2019).

  3. Attitudes and Preferences:

    • Colorado Adoption Project study (Rhea et al., 2013) showing influences of genetics on conservative attitudes.

    • Occupational preferences and religious beliefs also investigated.

Key Findings: Behavioral Genetic Research (Continued)

Health-Related Behaviors

  1. Drinking and Smoking:

    • Initiation of smoking influenced by genetics (60%); dependence influenced by both genetics (70%) and environment (Sullivan & Kendler, 1999; Batra et al., 2003).

    • E-cigarette initiation is influenced by both genetics and environmental factors (Kochvar et al., 2023).

    • Alcohol consumption findings varied by gender and personal history (Ehlers et al., 2010; Wu et al., 2014).

  2. Marriage:

    • Inclination to marry: 68% heritable (Johnson et al., 2004).

    • Genetic influences on marital stability (Jerskey et al., 2010; Trumbetta et al., 2006).

Person-Situation Debate

  • Personalities are shaped by the interaction between our genetics and environment, a concept known as interactionism (Endler & Parker, 1992).

  • Example traits impacted:

    • Psychological disorders (Bornovalova et al., 2010)

    • Romantic relationships (South et al., 2016)

    • Workplace behaviors and performance (Judge & Zapata, 2015).

Genotype-Environment Correlation

  • Definition: The genotype shapes the environment in which one is placed.

Types of Gene-Environment Correlation (Plomin et al., 1977)

  1. Passive: Parents transmit both genetics and environment without environmental prompts.

  2. Reactive: Parents respond to children's behaviors based on their genotype.

  3. Active: Individuals seek out environments that match their genotype.

Exploring Genotype-Environment Correlation

  • Twin studies (e.g., Luo et al., 2017) addressing genetic impact on stress perception continuity and changes were significantly influenced by shared environmental factors.

  • Persson (2020) identified genetic contribution to warmth and conflict in families.

Environmental Influences

Types of Environmental Influences

  1. Shared Environment:

    • Little impact on many personality traits.

  2. Nonshared Environment:

    • More influential for personality development (Plomin et al., 2013).

Examples of Shared vs Nonshared Influences

  • Shared: Books at home, parent values, food quality.

  • Nonshared: Friend groups, hobbies, parenting ideas, bedrooms.

Behavioral Genetics: Issues

  1. Intelligence:

    • A debated variable in personality research; limits on capturing intelligence facets.

  2. Complexities:

    • The relationship of genetic and environmental interfaces on behaviors.

  3. Ethical Considerations:

    • Include participant recruitment, confidentiality, and cultural norms (Khabour et al., 2021).

Physiological Approach

Physiological Differences in Personality

  • Examines how physiological factors contribute to personality, noting they aren't sole causes, but significant.

  • Physiological measures include:

    • Heart rate

    • Brain activation

    • Electrodermal activity.

Measures in Physiological Research

  1. **Electrodes:

    • Use in physiological measurement.**

  2. Smart Devices/Wearable Technology:

    • Recent research by Shui et al. (2023) correlated heart rate and emotion ratings with extraversion and openness.

  3. Electrodermal Activity:

    • Investigates physiological stress responses in various scenarios (Hidalgo-Muñoz et al., 2021).

Blood Pressure and Heart Rate Research

  • Indicators during stress influenced by personality traits (Soliemanifar et al., 2018).

Brain Function and Personality

Brain Imaging Techniques

  1. Functional Magnetic Resonance Imaging (fMRI):

    • Used to explore correlations of brain activation with personality traits (Saggar et al., 2016).

  2. Positron Emission Tomography (PET):

    • Studied Alzheimer’s disease in relation to personality traits (Giannakopoulos et al., 2022).

Findings on Brain Structure

  1. MRI Studies:

    • Links between brain size/thickness and personality traits (DeYoung et al., 2012).

Electrical Activity of the Brain

Electroencephalogram (EEG) Research

  • Measures brain patterns during different cognitive and emotional states.

  • Studies indicate EEG can predict Big Five personality traits based on reactions to stimuli (Li et al., 2020).

Physiological Measures Related to Personality

  1. Cortisol Levels:

    • Connected to trait shyness (Poole et al., 2017).

  2. Hormonal Influences:

    • Hormones affecting features of Borderline Personality Disorder (Eisenlohr-Moul et al., 2015).

  3. Biochemical associations:

    • Research on saliva biomarkers linked to personality traits and stress responses.

Theories of Extraversion-Introversion

Eysenck’s Theory (1967)

  • Focused on Cortical Arousal as a biological foundation for personality traits.

Findings on Arousal Levels

  • Research highlights the relevance of moderate stimulation in differentiating between extraverts and introverts.

Sensitivity to Reward and Punishment

  • Reinforcement Sensitivity Theory (Gray, 1990):

    • Behavioral activation system (BAS) and behavioral inhibition system (BIS) linked to personality traits.

Further Physiological Analysis

Sensation Seeking

  1. Zuckerman's Research (1972):

    • Studies linking sensation seeking with various risky behaviors, e.g. excessive motorcycling and binge drinking.

Neurotransmitters and Personality

  1. Chemical Influence in Nerve Cells:

    • Understanding how certain neurotransmitters like dopamine and serotonin are tied to behaviors such as impulsivity and mood regulation.

Biological Rhythms and Personality

Circadian Rhythms

  • Daily internal processes that influence personality traits; disturbances can cause stress.

Morningness and Eveningness Traits

  • Morning people vs evening people findings related to conscientiousness and extraversion (Randler & Jankowski, 2014).

Brain Asymmetry

  • Frontal asymmetry findings related to approach-avoidance traits and connectivity in various situations.