Lecture: Nature vs. Nurture and Behavioral Genetics

Introduction

• Discussion starts with a humorous anecdote about a girl's report card.
• Raises the question of whether a child's traits are influenced by nature (genetics) or nurture (environment).
• Historical context:
  • John Locke: Personality shaped by environment.
  • Charles Darwin: Traits largely programmed genetically.
  • Modern view: Interaction of both genes and environment.

Understanding Nature and Nurture

• Complexity in determining the influence of genes vs. environment.
• Example: Group of 100 white American men in their 20s.
  • Average IQ: 100
  • Average height: 178 cm (5.8 feet)
  • 10% have spelling problems.
• Nature: Anything before conception (genetic).
• Nurture: Anything after conception (environmental).

Heritability

• Definition: A measure (0 to 1) indicating genetic vs. environmental influence on trait differences within a population.
  • 1: Strong genetic influence.
  • 0: Strong environmental influence.
• Heritability determines genetic impact on population differences, not individual traits.
• Example: Dyslexia has high heritability, indicating a strong genetic component in population differences.

Case Study: Height and IQ

• Height:
  • Heritability ~0.8 in a well-nourished group.
  • Environmental conditions (e.g., drought) can reduce heritability to 0.5.
  • Nutrition impacts trait differences significantly until a certain point.
• IQ:
  • Heritability ~0.6 in 20s, increases with age.
  • Genes account for 60% of IQ differences, environment/random factors account for 40%.
  • Parental impact on IQ is limited.
  • Firstborns tend to have higher IQs.
  • Adopted siblings show limited IQ correlation as adults.

Crayfish Experiment

• 1995 German scientists studied a mutated, asexual crayfish.
• Crayfish clones had identical genetics and controlled environmental factors.
• Varied outcomes (size, lifespan, behavior) despite identical conditions.
• Raises questions about the role of random genetic variations.

Conclusion

• The lecture highlights the complexity of nature vs. nurture debate.
• Interaction between genetics and environment is intricate and often involves random factors.

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