AP Biology Unit 7: Natural Selection — Tips & Strategies

Never say organisms 'try' to evolve, evolve 'in order to' survive, or that evolution is 'progress.' Evolution is not goal-directed — it's a consequence of differential reproduction.

Hardy-Weinberg describes a non-evolving population. If allele frequencies change, at least one of the five conditions is being violated, indicating evolution is occurring.

For natural selection to occur: (1) variation in traits, (2) traits must be heritable, (3) overproduction of offspring, (4) differential survival and reproduction based on traits.

Genetic drift is random changes in allele frequency, most impactful in small populations. Bottleneck effect: population crash reduces diversity. Founder effect: small group colonizes new area.

Phylogenetic trees show evolutionary relationships. Sister taxa share the most recent common ancestor. The key is branching pattern, not branch length or position on the page.

Fossil record, comparative anatomy (homologous/analogous structures), molecular biology (DNA/protein comparisons), biogeography, and direct observation of evolution.

Allopatric speciation requires geographic isolation (a physical barrier separates populations). Sympatric speciation occurs without geographic isolation (often via polyploidy in plants).

Directional selection shifts the population toward one extreme. Stabilizing selection favors the average. Disruptive selection favors both extremes. Know the graph shapes.