Around the math sit the evidence classes and the trees. The tool below drills the logic from your notes.
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Unit 7 engines and nulls, from your own notes
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Selection is a recipe with three ingredients
Natural selection requires variation among individuals, heritability of that variation, and differential survival or reproduction because of it: remove any ingredient and the response stops. Fitness is measured in offspring contributed, not strength, and selection acts on phenotypes while populations, not individuals, evolve. Scenario questions hand you a trait story and grade whether all three ingredients are named.
Hardy Weinberg is the null, and its violations are the content
The Hardy Weinberg equilibrium holds allele frequencies constant when five conditions are met: no selection, no mutation, no migration, random mating, and a very large population. The arithmetic, p plus q equals one, p squared, two p q, q squared, converts phenotype counts into allele frequencies; the biology lives in the violations, because each broken condition is one evolutionary engine, and the exam asks which one the scenario broke.
Drift is sampling error with consequences
Genetic drift changes frequencies by chance, and its strength scales inversely with population size: a storm that halves a beetle population edits its gene pool regardless of fitness. Bottlenecks and founder events are drift with a backstory, reduced variation the lasting signature. The tested contrast with selection is directionality: drift wanders, selection tracks the environment, and small populations feel the wander hardest.
Speciation: isolation first, divergence second
Speciation begins when gene flow stops: allopatric isolation by barrier is the common route, sympatric divergence by preference or polyploidy the tested exception. Reproductive isolating mechanisms sort into prezygotic, timing, habitat, behaviour, mechanics, and postzygotic, hybrid inviability or sterility. Given a scenario, name the barrier class first; the species concept argument follows from it.
Trees are read by ancestry, and the evidence converges
On a phylogeny, kinship is recency of common ancestor, never left to right position: rotate any node and the tree says the same thing. Shared derived characters place branches, and molecular distance calibrates them. Around the trees sit the evidence classes, fossils, homologous against analogous structures, vestigial traits, molecular universality, each answering the same question from a different archive, which is the synthesis essays reward.
What to photograph for Natural Selection
Your condition lists and tree readings. Related: Unit 6, photo to quiz and pricing.
Sources used on this page
- College Board, AP Biology
- Natural selection
- Speciation
- Hardy-Weinberg principle
- Genetic drift
- Phylogenetic tree
- Active recall
- Spaced repetition
- Testing effect
- Forgetting curve
- Generation effect
- Judgment of learning
- Metacognition
- Desirable difficulty
- Distributed practice
- Formative assessment
- Flashcard
- Cloze test
- Multiple choice
- Test (assessment)
- Educational assessment
- Advanced Placement
- Curriculum
- Study skills
- Study guide
- Note-taking
- Overlearning
- Instructional scaffolding
- Item analysis
- Mastery learning
| Engine | Its signature | The broken HW condition |
|---|---|---|
| Selection | Tracks the environment | Equal success assumption |
| Drift | Wanders, small populations | Very large population |
| Gene flow | Homogenises neighbours | No migration |
| Mutation | New alleles arrive | No mutation |
| Mate choice | Genotypes pair nonrandomly | Random mating |
| Bottleneck | Variation lost abruptly | Large population, by disaster |
What does AP Biology Unit 7 cover?
Evolution quantitatively: selection's requirements, Hardy Weinberg equilibrium, drift and flow, speciation and reproductive isolation, phylogenies and evidence.
What three things does selection require?
Variation, heritability, and differential survival or reproduction tied to the variation. All three must be present for a response.
How do I use Hardy Weinberg on a problem?
Take q squared from the recessive phenotype share, root it for q, get p, then partition genotypes; deviations point at the broken condition.
When does drift beat selection?
In small populations: sampling error swamps fitness differences, which is why bottlenecks and founder events leave lasting low variation.
How do I read relatedness off a tree?
By most recent common ancestor only: rotation at nodes changes the drawing, not the relationships.
Can I build questions from my own Unit 7 notes?
Yes. The questions follow the upload: photograph these pages or attach the PDF, and nothing outside them enters the set.
Last updated: 2026-08-15