Nature vs. Nurture and Behavioral Genetics

Introduction

• A discussion initiated by a girl's poor report card: "Nature or nurture?"
• Historical debate on personality influences:
  • John Locke: Environment shapes personality.
  • Charles Darwin: Genetic programming.
• Modern perspective: Interaction between genes and environment.

Understanding Nature and Nurture

• Neither genes (nature) nor environment (nurture) alone determine individual traits.
• Influences differ across populations.
  • Example: A group of white American men in their 20s.
• Traits have different influences from genes and environment.

Complexity of Genes and Environment

• Environmental influences are often random and siblings experience these differently.
• Genes are complex with no single gene causing a single trait.
• Heritability: A measure from 0 to 1 indicating genetic vs. environmental influence.

Heritability Explained

• It defines genetic impact on trait differences in a population, not individuals.
• Example: Dyslexia's heritability closer to 1 indicates a strong genetic influence in a group.

Heritability of Height and IQ

• Height:
  • Average height in a group is 178 cm.
  • Heritability around 0.8, indicating genes play a major role.
  • Environmental factors like nutrition can shift heritability.
• Intelligence (IQ):
  • Heritability of IQ is around 0.6, increasing with age.
  • For IQ differences, 60% due to genes, 40% environment.
  • Random environmental factors strongly influence IQ.
  • Siblings show differences; adopted children diverge as adults.

Crayfish Study

• 1995 German study on asexual crayfish demonstrated genetic and environmental complexities.
• Identical crayfish exhibited diverse traits despite controlled conditions.

Conclusion

• Nature and nurture interplay with genetic variation.
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