Module 1.1 Interaction of Heredity and Environment

Identity Thought Experiment: Brain Transplant ("Wang-with-a-New-Body")

  • Imagined head–body transplant scenario; raises questions of personal identity.

  • Take-away: underscores assumption that “No brain, no mind.”

Unit Scope: Biology of Mind & Behavior

  • Explores brain from neurons to structures (bottom-up) and how behavior/environment shape biology (top-down, e.g., epigenetics).

  • Topics include gene × environment, brain plasticity, consciousness, sensation & perception.

Learning Targets (Module 1.1)

  • 1.1-1 Describe evolutionary psychologists’ use of natural selection.

  • 1.1-2 Explain how behavior geneticists account for individual differences.

  • 1.1-3 Interpret twin/adoption evidence on nature–nurture.

  • 1.1-4 Explain how heredity & environment co-operate.

Key Vocabulary Bank

  • nature–nurture issue – debate on relative influence of genes vs. experience.

  • natural selection – inherited traits aiding survival & reproduction are passed on.

  • evolutionary psychology – applies natural selection to behavior & mind.

  • behavior genetics – quantifies genetic vs. environmental contributions.

  • mutation – random DNA replication error; raw material for selection.

  • environment – all non-genetic influences.

  • heredity – genetic transfer parent ➜ offspring.

  • genes – biochemical heredity units; \approx 20{,}000 in humans.

  • genome – complete genetic instructions.

  • identical (monozygotic) twins – single zygote ➜ two clones.

  • fraternal (dizygotic) twins – two separate eggs; like ordinary siblings.

Historical Roots of Nature–Nurture Debate

  • Plato: character & intelligence inborn.

  • Aristotle: mind a "blank slate."

  • Charles Darwin (1859): coined natural selection; foresaw evolutionary psychology.

  • Caution: past misuse, eugenics, now discredited.

Evolutionary Psychology: Natural Selection in Action

  • Four-step logic: 1. Offspring vary. 2. Variations affect survival/reproduction. 3. Advantageous variations lead to higher reproductive success. 4. Population characteristics shift.

  • Fitness = \text{ability to survive} + \text{ability to reproduce}.

Case Study – Russian Fox Domestication (Belyaev & Trut)

  • Replicated wolf ➜ dog domestication over 57 generations by breeding tamest foxes.

  • Resulted in docile, eager-to-please foxes; demonstrates artificial selection.

Human Universal Behaviors Explained by Evolution

  • Shared genome (99.9\% identical DNA among humans) leads to adaptive predispositions like parental care, fear of snakes/spiders.

  • Evolutionary mismatch: cravings for sweets/fats (adaptive in past, now obesity driver), acute stress response (for predators, now for exams).

Behavior Genetics: Mapping Individual Differences

  • Every nucleus holds entire genome (46 chromosomes).

  • Gene expression is environment-dependent.

  • Traits are polygenetic (orchestrated by many genes of small effect), e.g., depression, schooling years.

Research Strategies to Untangle Nature & Nurture

Family Studies

  • Trace trait co-occurrence within biological families.

Twin Studies

  • Identical twins: shared genes; measure environmental divergence.

  • Fraternal twins: shared environment; measure genetic divergence.

  • Findings: Identical twins are far more similar than fraternals in personality, politics, substance use; similarity holds across parenting styles (genes > environment).

Separated-Twin & Adoption Studies

  • Natural experiment: controls environment or heredity.

  • Bogotá brothers: identical twins reared apart showed genetic sameness (humor, strength) and environmental impact (height, speech).

  • Broader pattern: separated identicals show striking agreement in tastes/abilities.

Ethical & Methodological Notes for AP® Science Practice

  • Ethical codes prevent manipulating infant rearing; researchers rely on natural “experiments.”

  • Distinguish mean from individual scores.

  • Testing effect: active retrieval sharpens memory.

Implications, Connections, and Exam Tips

  • Contemporary stance: Nurture works on what nature provides. Every psychological event is simultaneously biological.

  • AP® exam frequently covers nature–nurture.

  • Use flash cards for vocabulary; cite four natural-selection steps and fitness formula for evolution explanations; use examples.