Unit 7 · Natural Selection
The Complete AP Biology Guide · AP BiologyUnit 7 · Natural Selection
- The Complete AP Biology Guide
- AP Biology
- 8 sections
Unit 7: Natural Selection accounts for 13% to 20% of the AP Biology exam score in Section I (multiple choice), and its mechanisms also appear in Section II free-response questions. Evolutionary reasoning must keep individuals and populations in different grammatical roles.
- How AP Biology assesses this 13–20% of the Section I score · mechanisms recur in Section II FRQs · 60 MCQs in 90 min
- Key skills natural and artificial selection, population genetics and hardy weinberg, evidence ancestry and phylogeny, speciation and origins of life
- How to study for Unit 7 You will connect heritable variation to differential reproduction and population change, test equilibrium models, and read trees by shared nodes rather than tip order.
- The organizing decision What heritable variation exists, how does the environment change relative reproductive contribution, and what population-level frequency or ancestry evidence follows?
Unit 7: Natural Selection accounts for 13% to 20% of the AP Biology exam score in Section I (multiple choice), and its mechanisms also appear in Section II free-response questions.
Weighting is the College Board CED range for the current exam. Higher-weight units repay proportionally more review time; use this share to size your effort before drilling the mechanisms below. See the AP Biology exam guide & review for all eight units.
Evolutionary reasoning must keep individuals and populations in different grammatical roles. Individuals vary, survive, reproduce, move, and mate. Populations change allele or trait frequencies across generations. Phylogenetic trees then represent hypotheses about common ancestry, not ladders of progress or visual rankings of modern species.
You will connect heritable variation to differential reproduction and population change, test equilibrium models, and read trees by shared nodes rather than tip order.
The decision that organizes this unit
What heritable variation exists, how does the environment change relative reproductive contribution, and what population-level frequency or ancestry evidence follows?
Mechanism route and repair branches
- Main route: Describe the variation among individuals and identify evidence that at least part of the variation can be inherited.
- Main route: Connect the environmental condition to survival or reproduction through a specific trait mechanism rather than a statement of need.
- Diagnostic cue: Organisms are said to develop a needed trait and pass it on. Wrong branch: Environmental demand directly creates an adaptive inherited change. Repair: Begin with existing or newly generated heritable variation, then connect the trait to differential reproductive contribution.
- Main route: Predict the direction of allele or trait-frequency change across generations while preserving migration, drift, and mating alternatives.
- Diagnostic cue: A high-fitness individual is described as strongest or longest-lived. Wrong branch: Fitness is detached from reproduction and environment. Repair: Define fitness as relative contribution of heritable variants to later generations under the specified conditions.
- Main route: Use Hardy-Weinberg or another null model as a comparison and avoid naming a force from model departure alone.
- Main route: For phylogeny, identify the most recent shared node, define the clade, and treat rotation around a node as topology-preserving.
- Diagnostic cue: Two adjacent tips are called closest relatives. Wrong branch: Page position replaces node history. Repair: Trace each lineage backward to its most recent common ancestor and ignore rotations that leave connections unchanged.
