week 5: Biological Perspectives of Personality

  • Acknowledgement of Country

    • Monash University acknowledges its Australian campuses are on the unceded lands of the Kulin Nations people and respects their Elders, past and present.

  • Learning Objectives

    • Describe the basic roles of genetics and environment in relation to personality traits.

    • Critically evaluate the fundamental assumptions of the behavior genetics paradigm for explaining personality traits.

    • Explain the basic role of brain biochemistry on personality.

    • Understand the basics of neural influences on personality traits.

  • Biological Models of Personality

    • The biological (or medical) model posits that biological processes influence personality.

    • These processes include:

      • Genetics

      • Biochemistry

      • Brain structure

  • Behavior Genetics

    • Goals:

      • Determine heritability.

      • Determine gene imes environment interactions.

      • Determine which aspect of the environment (e.g., parent socialization, peer group influence) is most important.

    • Heritability:

      • The proportion of observed individual variation that can be attributed to genetic effects.

      • Distinction between phenotype (observable characteristics) and genotype (genetic makeup).

      • Environmental factors also play a crucial role.

    • Common Misconceptions about Heritability:

      • It cannot be applied to single individuals.

      • Heritability is not constant.

      • It is not a precise statistic.

    • Behavior Genetic Decomposition:

      • Personality traits are influenced by: A (Additive Genetic effects), C (Shared Environment), E (Non-shared Environment).

    • Consequences of Heritability Estimates:

      • Genetic influence estimates reflect existing variability in genomes and environment within the studied population.

      • Heritability of a trait can vary across cultures and generations.

      • Heritability of a trait is age-dependent.

      • Heritability of a trait is trait-dependent (i.e., not due to differing personality states).

    • Empirical Evidence on Heritability:

      • Almost everything is hereditary to some degree.

      • A chart shows published heritability estimates for various traits (e.g., height at .80, intelligence at .50, personality at .40, schizophrenia at .80) compared to lay estimates of genetic influence.

      • The correlation between lay estimates and scientific studies for heritability estimates of traits is relatively high (r = .77) (Harden, 2021).

    • Basic Methods in Behavior Genetics:

      • Family Method: Examines shared genetics among family members.

        • Strangers: less than 1\% shared genes.

        • Cousins: 12.5\% shared genes.

        • Grandparents/Uncles/Aunts: 25\% shared genes.

        • Parents/Siblings/Fraternal twins: 50\% shared genes.

        • Identical twins: 100\% shared genes.

      • Twin Method: Compares monozygotic (MZ - identical) and dizygotic (DZ - fraternal) twins.

        • MZ twins share 100\% of genes, DZ twins share 50\% of genes.

        • Heritability index (h^{2}) is estimated as: ext{h}^{2} = 2 ( ext{r}{ ext{mz}} - ext{r}{ ext{dz}}), where ext{r}{ ext{mz}} is the correlation for MZ twins and ext{r}{ ext{dz}} is the correlation for DZ twins.

        • Assumes an