AP Biology — Unit 7: Natural Selection

What AP Biology Unit 7 covers

The College Board Course and Exam Description breaks Unit 7 into 12 topics:

1. 7.1 Introduction to Natural Selection
2. 7.2 Natural Selection
3. 7.3 Artificial Selection
4. 7.4 Population Genetics
5. 7.5 Hardy-Weinberg Equilibrium
6. 7.6 Evidence of Evolution
7. 7.7 Common Ancestry
8. 7.8 Continuing Evolution
9. 7.9 Phylogeny
10. 7.10 Speciation
11. 7.11 Variations in Populations
12. 7.12 Origins of Life on Earth

AP Biology Unit 7 practice questions

• Your friend says organisms 'try to adapt' when the environment changes. What's wrong with that?

  Evolution has no intent — selection acts on existing variation, not need. Individuals don't change; populations shift over generations.

• Evolution means 'survival of the fittest' — so the biggest, strongest organism always wins. What's the flaw?

  Fitness means reproductive success — not physical strength or body size. The fittest leaves the most offspring in a given environment.

• A population of beetles lives on brown soil. A mutation produces a few green beetles. Predators hunt by sight. What happens over many generations?

  Green beetles are more visible and eaten more, so the brown allele rises. Directional selection favors the camouflaged phenotype.

• Antibiotic resistance evolves in bacteria within days. Does this mean bacteria 'evolved resistance' in response to the antibiotic?

  No — resistant variants already existed before the antibiotic was introduced. The drug selects for pre-existing resistance alleles; it does not create them.

• Directional, stabilizing, and disruptive selection all act on the same population — but they produce completely different outcomes. How do they differ?

  Directional shifts the mean; stabilizing trims extremes; disruptive favors both ends. Same population, three outcomes.

• Human birth weight data shows that very low and very high birth weights have higher infant mortality. What type of selection does this represent?

  Stabilizing selection — average birth weights survive best, so both extremes are removed. The mean stays put while variation narrows.

• Artificial selection and natural selection both change allele frequencies over time — so what actually makes them different?

  In artificial selection, humans choose which individuals reproduce based on desired traits. In natural selection, the environment determines differential reproductive success.

• Dog breeds were produced by artificial selection over thousands of years. A wild wolf population undergoes no selective breeding. After 500 generations, which population has more genetic diversity, and why?

  The wolf population — artificial selection narrows alleles, while wild variation stays broad. Selective breeding repeatedly favors a few traits.

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Key terms in Unit 7

These 12 terms show up in the Unit 7 cards. Each one links to its definition in the AP Biology key-term reference.

• Allopatric speciation
• Analogous structures
• Artificial selection
• Biological species concept
• Directional selection
• Hardy-Weinberg equilibrium
• Heterozygote advantage
• Homologous structures
• Miller-Urey experiment
• Phenotypic plasticity
• Pre-zygotic isolation
• Stabilizing selection