Lecture Notes: Behavior Genetics and the Nature vs. Nurture Debate

Introduction

• Apologies for last class; travel complications.
• Overview of topics: shift to behavior genetics.

Overview of Previous Approaches

1. Sociobiological or Evolutionary Psychology

   • Behavior evolves under the same selection pressures as physical traits.
   • Structured predictions about social behavior based on rules of evolution.

2. Molecular Biology

   • Addressed criticisms about showing specific genes for behaviors.
   • Discussed microevolutionary changes and macroevolution (punctuated equilibrium).

Transition to Behavior Genetics

• Focus on genetic influence on behavior without deterministic implications.
• Different approaches to infer genetic components of behavior.
• Critique of behavior genetics as a potentially flawed field.

Understanding Genetic Influence on Behavior

Basic Rules of Behavior Genetics

• Assumption: Universal traits indicate genetic influence.
• Criticism: Environment also runs in families, complicating conclusions.
• Refinement: Investigate traits in related individuals while controlling for shared environments.

Methodologies in Behavior Genetics

1. Twin Studies

   • Identical Twins (Monozygotic): 100% shared genes.
   • Fraternal Twins (Dizygotic): 50% shared genes.
   • Greater similarity in identical twins suggests genetic influence.
   • Limitations: Same sex, environmental differentiation, and prenatal conditions.

2. Adoption Studies

   • Compare traits between adopted individuals and their biological/adoptive parents.
   • Difficult to isolate shared environments and prenatal factors.
   • Landmark Study: Seymour Kety's work on schizophrenia and adoption in Denmark.
     • Findings showed higher rates of schizophrenia in adoptees with biological parents who had the disorder.

3. Identical Twins Separated at Birth

   • Optimal condition to study genetic influence without shared environment.
   • Findings suggest approximately 50% heritability of traits like IQ and aggression.
   • Limitations: Non-random placement in adoptive families can influence results.

Prenatal Environmental Effects

• Environment begins before birth and can influence behavioral traits.
• Hormonal Influences: Hormones shared in the womb can affect development.
  • Example: Male siblings influence female rats' puberty onset.
• Nutrition: Nutritional status of the mother can affect offspring health.
  • Example: Dutch Hunger Winter study demonstrated long-term effects of prenatal malnutrition.
• Learning: Fetuses can learn from prenatal exposure to stimuli (e.g., mother's voice).

Epigenetics

• Changes in gene expression that can be inherited without altering DNA sequence.
• Maternal Behavior: Differences in maternal care can lead to epigenetic changes in offspring.
  • Example: Michael Meaney's research on rat mothers and their influence on offspring behavior.

Indirect Genetic Effects

• Behaviors may be influenced by physical traits (e.g., height) that affect social interactions.
• Studies show that physical attributes can mediate behavioral traits through social treatment.

Conclusion

• Emphasis on the complexity of determining genetic influence on behavior.
• Highlighted the importance of prenatal conditions and early experiences in shaping behavior.
• Future discussions will address gene-environment interactions and the identification of specific genes involved in behavior.