AP Biology Unit 7: Natural Selection

Unit 7 covers natural selection, evolution and phylogeny. With 14 topics and 244 questions it is the largest unit in AP Biology, and much of it is tested through phylogenetic trees and Hardy-Weinberg calculations.

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244 questions14 CED topics77% with a figure
How this unit behaves

What 244 questions on it look like

This is the largest unit in AP Biology by practice volume — 244 questions against the subject's other units. Weight your revision accordingly.

It spans 14 CED topics, which is wide enough that "I've studied this unit" is not a meaningful statement. Track your accuracy by topic, not by unit.

77% of the questions come with a figure — a graph, diagram or data display. Reading the figure correctly is most of the work before any content knowledge applies.

Natural Selection58
Phylogeny42
Speciation26
Population Genetics25
Hardy-Weinberg Equilibrium22
Common Ancestry17
Introduction to Natural Selection14
Continuing Evolution14

Questions per CED topic, top 8 of 14.

From the bank

Three real natural selection questions

Drawn from the practice pool, not from the mock papers.

Introduction to Natural Selection · Concept Explanation

Why is heritable variation necessary for natural selection to cause evolutionary change?

  1. ANatural selection acts only on traits that organisms learn during their lifetimes.
  2. BEvolution stops whenever variation is present.
  3. CHeritable variation prevents reproduction in all populations.
  4. DHeritable differences can change allele frequencies across generationscorrect
Why D is correct

Natural selection can change populations over generations only if advantageous trait differences are heritable and affect reproductive success.

The stem asks students to explain a specific mechanism, not just recall a unit term: "Why is heritable variation necessary for natural selection to cause evolutionary change". The correct choice is supported by Natural selection can change populations over generations only if advantageous trait differences are heritable and affect reproductive success. The tempting alternatives such as Natural selection acts only on traits that organisms learn during... or Evolution stops whenever variation is present fail because they do not produce the same outcome described in the stem.

Common mistakes. Do not stop at a nearby term such as Natural selection acts only on traits that organisms learn during... or Evolution stops whenever variation is present. The explanation has to make "Only heritable differences can be passed to offspring and change allele..." fit this stem clue: "Why is heritable variation necessary for natural selection to cause evolutionary change".

Phylogeny · Visual Representations · with figure

Based on Figure 1, which statement gives the strongest supported interpretation?

  1. AMarker A: An outgroup can help infer which character states are ancestral in a phylogenetic comparison.
  2. BMarker B: A derived character mapped after a branch point is expected in descendant lineages from that branch.
  3. CMarker C: Branch length may represent change
  4. DMarker D: C and D share the derived character through common ancestrycorrect
Why D is correct

Figure 1 shows two taxa joined at the most recent shared node before the third taxon splits from the lineage. Marker D: Taxa joined by the most recent shared node are interpreted as the closest relatives in the model. The figure does not mark an outgroup, a derived character, branch-length scale, bootstrap value, or parsimony comparison.

The evidence in the prompt matters before the topic label: "A cladogram shows a derived character appearing on the branch leading to species C and D, but not species A or B....". The supported answer is "Species C and D inherited the derived character from a recent common ancestor" because A derived character marked before the C-D split is inferred to be inherited by both C and D from their common ancestor. Distractors such as Species B is the ancestor of species C or All four species must be equally related to each other either ignore the stated pattern or name a related concept without matching the evidence.

Common mistakes. Do not stop at a nearby term such as Species B is the ancestor of species C or All four species must be equally related to each other. The explanation has to make "Species C and D inherited the derived character from a recent common ancestor" fit this stem clue: "A cladogram shows a derived character appearing on the branch leading to species C and...".

Natural Selection · Argumentation

Male birds with longer songs attract more mates, and song length is partly heritable. Over several generations, average song length increases. Which explanation is best supported?

  1. AThe population stopped evolving because mating success differed.
  2. BDifferential mating success can change allele frequenciescorrect
  3. CThe pattern is best explained by genetic drift alone
  4. DSong length increased because heritable variation was absent.
Why B is correct

Differences in mating success can drive sexual selection. If song length is heritable, alleles associated with longer songs can increase.

The stem asks students to explain a specific mechanism, not just recall a unit term: "Male birds with longer songs attract more mates, and song length is partly heritable. Over several generations,...". The correct choice is supported by If song length is heritable, alleles associated with longer songs can increase. The tempting alternatives such as population stopped evolving because mating success differed or pattern is best explained by genetic drift alone, even though... fail because they do not produce the same outcome described in the stem.

Common mistakes. Do not stop at a nearby term such as population stopped evolving because mating success differed or pattern is best explained by genetic drift alone, even though.... The explanation has to make "Sexual selection increased the frequency of alleles associated with longer songs" fit this stem clue: "Male birds with longer songs attract more mates, and song length is partly heritable....".

244 questions on this unit, free to start.

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FAQ

Natural Selection questions

How do I read a phylogenetic tree?

Relatedness is set by the most recent common node, not by how close two tips look along the top of the tree.

When can I use Hardy-Weinberg?

Only when the stated conditions hold. Questions frequently give a population that violates one and ask what follows.
Last reviewed 2026-08-28. Unit and topic names follow the College Board course framework. Question counts describe the PrepScore practice bank, not the exam.
Topic by topic

Worked questions by topic

5 of this unit’s topics have enough practice questions for a page of their own.

Speciation26 questionsNatural Selection52 questionsPopulation Genetics29 questionsHardy-Weinberg Equilibrium23 questionsPhylogeny42 questions
Same course
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Practise natural selection until the reasoning is automatic.

Real AP questions with a full explanation on every answer, and a mistake bank that only clears when you get it right.

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