Biological Psychology Flashcards

Twin Studies

Twin studies are valuable for understanding genetic and environmental influences on behavior, physical traits, and medical conditions. They align with the 'nature' perspective, emphasizing innate biological factors.

  • MZ Twins: Share 100% DNA (identical).
  • DZ Twins: Share 50% DNA (fraternal).
  • Twin studies help determine the likelihood of inheriting traits or disorders by comparing concordance rates.

Key Definitions

  • Zygosity: Similarity of alleles for a trait.
  • Monozygotic (MZ): Identical twins from one zygote, sharing 100% DNA.
  • Dizygotic (DZ): Fraternal twins from separate eggs, sharing 50% DNA.
  • Concordance: Correlation between variables.
  • Genotype: Complete genetic heritability.

Aggression Types

  • Physical Aggression: Physical violence.
  • Social Aggression:
    • Relational aggression: Overt, non-physical actions (e.g., breaking friendships).
    • Indirect aggression: Covert actions (e.g., spreading gossip).

Brendgen (2005) Twin Study

  • Aim: Investigate genetic (A), shared environmental (C), and nonshared environmental (E) factors in social aggression and the covariance between physical and social aggression.
  • IV: Type of twin pair (MZ or DZ).
  • DV: Teacher and peer ratings of social and physical aggression.
  • Participants: 234 MZ/DZ twin pairs from the Quebec Newborn Twin Study, Canada, aged 6 years.
  • Sampling: Opportunity/cluster sample.
  • Design: Longitudinal, quasi-experimental.

Brendgen (2005) Procedure

  1. Data from the Quebec Newborn Twin Study.
  2. Twins assigned to MZ/DZ based on physical resemblance.
  3. Data collection:
    • Teacher ratings: Agreement with statements about aggression (0-2 scale).
    • Peer ratings: Classmates identify children fitting behavior descriptions.
  4. Scores for social and physical aggression combined.
  5. Data modeled using ACE (additive genetic, shared environment, non-shared environment) factors.

Brendgen (2005) Results

  • Chi-squared tests showed non-significant differences between teacher/peer ratings for MZ/DZ twins.
  • ACE model:
    • Social aggression: 20% genetic, 20% shared environment.
    • Physical aggression: 54% genetic heritability.

Brendgen (2005) Conclusions

  • Physical aggression is mainly genetic (nature), while social aggression is mainly environmental (nurture).
  • Overlap between social and physical aggression is moderate.
  • Genes may predispose children to aggression, but environment shapes social aggression.

Evaluation (GRAVE)

  • Generalizability: Limited due to unique twin population, age, and ethnocentric sample.
  • Reliability: Questionnaires are replicable; inter-rater reliability with two researchers. Zygosity assessment not 100% reliable without DNA testing.
  • Application: Findings inform early interventions to reduce physically aggressive behavior and prevent social aggression.
  • Validity: High internal validity for nature vs. nurture. However, correlations do not equal causation. Subjective ratings and lack of control for extraneous variables limit validity. Task validity is low.
  • Ethics: Parental consent obtained. Potential harm from children judging classmates.

Additional Concepts

  • Diathesis-Stress Model: Disorders result from interaction between predisposition and environmental stress.
    • Diathesis: Vulnerability.
    • Stress: Environmental trigger.