AP Psychology
Unit 1: Biological Bases of Behavior

1.1 Interaction of Heredity and Environment

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1.1-1 How Do Evolutionary Psychologists Use Natural Selection to Explain Behavior Tendencies?

  • Evolutionary psychologists study how traits and behavior tendencies are shaped by natural selection.

  • Genetic variations that improve survival and reproduction are more likely to be passed to future generations.

  • These variations arise from:

    • Mutations

    • New gene combinations formed at conception

  • Humans share a genetic legacy and are predisposed to behaviors that promoted our ancestors’ survival and reproduction.

  • Charles Darwin’s theory of evolution is a fundamental principle in biology and anticipated the application of evolutionary principles in psychology.

1.1-2 How Do Behavior Geneticists Explain Our Individual Differences?

  • Behavior geneticists study the influence of genes and environment on behavior.

  • Most of our traits are polygenetic, meaning they result from multiple genes.

  • These traits develop through interaction between:

    • Genetic predispositions

    • Environmental influences

1.1-3 How Do Twin and Adoption Studies Help Us Understand the Effects and Interactions of Nature and Nurture?

  • Studies compare:

    • Identical (monozygotic) twins vs. fraternal (dizygotic) twins

    • Separated twins

    • Biological vs. adoptive relatives

  • These studies help determine the effects of shared genes vs. shared environment.

  • Findings suggest:

    • Shared family environments have little effect on personality.

  • Parenting influences other traits beyond personality.

1.1-4 How Do Heredity and Environment Work Together?

  • Genetics and environment interact to shape development.

  • Environments can trigger or suppress genetic expression.

  • Genetically influenced traits affect:

    • The experiences we seek

    • How others respond to us

  • Epigenetics studies how environmental factors influence gene activation or suppression.

Key Vocabulary

  • Nature–Nurture Issue – The longstanding debate over the relative contributions of genes and experience to psychological traits and behaviors. Today, science recognizes that traits and behaviors result from the interaction of nature and nurture.

  • Natural Selection – The principle that inherited traits that enhance an organism’s ability to survive and reproduce in a given environment are more likely to be passed on to future generations.

  • Evolutionary Psychology – The study of how behavior and the mind have evolved using the principles of natural selection.

  • Behavior Genetics – The study of the relative influence of genes and environment on behavior.

  • Environment – Every non-genetic influence, from prenatal nutrition to social experiences.

  • Heredity – The genetic transfer of traits from parents to offspring.

  • Genes – The biochemical units of heredity that make up DNA.

  • Interaction – The interplay between factors (e.g., how the environment can affect the expression of genetic traits).

  • Epigenetics – “above” or “in addition to” (epi) genetics; the study of the molecular mechanisms by which environments can influence genetic expression (without a DNA change).