AP Biology Unit 7 – Natural Selection: Ultimate Study Notes (CED aligned)

Evidence of Evolution

Fossil Record

Patterns and Trends

  • Shows changes in species over time

  • Transitional fossils indicate intermediate forms

  • Supports common ancestry

  • Cause → Effect

    • Fossil evidence → reconstruct evolutionary history

  • Tips

    • Remember: “older fossils = simpler forms”

Comparative Anatomy

Homologous vs Analogous Structures

  • Homologous: same structure, different function → common ancestry

  • Analogous: different structure, same function → convergent evolution

  • Cause → Effect

    • Homologous structures → shared ancestry

    • Analogous structures → adaptation to environment

  • Tips

    • Homologous = “home” (same origin)

    • Analogous = “analog” (similar function, different origin)

Molecular Evidence

DNA and Protein Comparison

  • Similar DNA/protein sequences → closer evolutionary relationship

  • Universal genetic code supports common ancestry

  • Cause → Effect

    • More sequence similarity → more recent common ancestor

  • Tips

    • Use sequence similarity to justify relationships

Mechanisms of Evolution

Natural Selection

Key Components

  • Variation exists in populations

  • Differential survival and reproduction

  • Heritable traits increase in frequency

  • Cause → Effect

    • Advantageous traits → higher survival → more offspring

  • Tips

    • Phrase: “survival of the fittest” = reproductive success

Other Evolutionary Forces

Genetic Drift

  • Random changes in allele frequency

  • Significant in small populations

Gene Flow

  • Movement of alleles between populations

Mutation

  • Source of new genetic variation

  • Cause → Effect

    • Drift → allele frequencies fluctuate

    • Gene flow → increases genetic similarity between populations

  • Tips

    • Genetic drift = random

    • Selection = non-random

Speciation

Formation of New Species

  • Reproductive isolation required

  • Allopatric speciation: geographic barrier

  • Sympatric speciation: reproductive barrier within same area

  • Cause → Effect

    • Isolation → divergence → new species

  • Tips

    • Always mention barrier type if asked

Population Genetics

Hardy-Weinberg Principle

Conditions for Equilibrium

  • No mutation

  • Random mating

  • No natural selection

  • Large population

  • No gene flow

Using the Equation

  • p² + 2pq + q² = 1 (genotype frequencies)

  • p + q = 1 (allele frequencies)

  • Cause → Effect

    • Deviation from equilibrium → evolution occurring

  • Tips

    • Check which assumption is violated in FRQs

Adaptation and Fitness

Phenotypic Advantages

  • Traits increase reproductive success

  • Can be structural, behavioral, or physiological

  • Cause → Effect

    • Higher fitness → increased allele frequency

  • Tips

    • Fitness = reproductive success, not strength

Coevolution and Species Interactions

Interdependent Evolution

  • Two species influence each other’s evolution

  • Examples: predator-prey, pollinator-plant

  • Cause → Effect

    • Changes in one species → selective pressure on the other

  • Tips

    • Always connect interaction → selection pressure