Trait and Biological Theories

Learning Goal 1.2: Discuss the role that biology plays in determining personality and behavior.

Evolutionary theory:
- Random mutations and variations occur among offspring.
- Offspring compete for mates and resources.
- Beneficial mutations/variations that improve survival/reproduction are passed to the next generation.
- Over time, more of the population inherits these beneficial variations.
Evolutionary approach focuses on similarities in personalities (why certain traits are common due to their advantages for survival).

Focuses on explaining differences through heritability.
Heritability: How much of the variation among a population’s traits can be attributed to genetics.
Heritability cannot explain how much of a single person’s traits are genetic vs. learned; it applies at a population level.

Trait theories describe personality based on broad traits (e.g., extraversion).
Idiographic theories: emphasize each person’s unique traits.
Nomothetic theories: quantify a given set of specific traits in each person.
Trait and biological theories are merging: trait theories describe differences, and researchers seek biological variables causing those differences.
Trait theories DESCRIBE personality differences, while biological theories EXPLAIN them.

Introverts:
- Acetylcholine Pathway.
- Reticular Activating System: More sensitive to stimulation, so distractions are overwhelming.
- Hypothalamus: Triggers the parasympathetic nervous system to conserve energy, lowering heart rate and blood pressure in unfamiliar settings.
Extroverts:
- Dopamine Pathway.
- Reticular Activating System: Less reactive, needing more stimulation, and seek new/exciting things.
- Hypothalamus: Triggers the sympathetic nervous system in hectic environments, activating the "fight or flight" response, increasing heart rate and blood pressure.

Gordon Allport (1920s):
- Original developer of the trait perspective and analysis of individual differences.
- Cardinal traits: traits that best define you.
- Central traits: traits you consistently display.
- Secondary traits: traits you sometimes display.
Raymond Cattell (1950s):
- Developed “factor analysis” – a statistical technique identifying traits based on coinciding behaviors.
Hans and Sybil Eysenck (1960s):
- Identified 3 dimensions of personality (PEN: psychoticism, extraversion, neuroticism) and claimed they were genetically determined.

Personality inventories: True/false or multiple-choice questions to reveal feelings, attitudes, and behaviors.
Most commonly used: Minnesota Multiphasic Personality Inventory (MMPI-2); assesses “abnormal” personality traits using empirically derived items.
- Examples:
  - “I wake up fresh and restored in the mornings.”
  - “I wish I could be as happy as others seem to be.”
  - “I sometimes keep on at a thing until others lose their patience.”
  - “The future is too uncertain for a person to make serious plans.”

Social media posts can indicate personality traits.
- Examples:
  - Achievements.
  - Political or intellectual ideas.
  - Infrequent posting.
  - Significant other.
Colleges and employers sometimes check social media profiles, raising implications for social media use.

Strengths:
- Explains why personality traits often run in families.
- Inventories are quick, easy, and objective to score.
Limitations:
- Doesn’t consider situational changes in personality (the person-situation controversy).
- Inventories rely on accurate and honest self-reporting.
- Deterministic – ignores free will in personality development.