Natural Selection Overview — AP Biology
1. Unit at a Glance
This unit moves from core foundational principles of natural selection to broad patterns of evolution across Earth's 4-billion-year history. We start with how natural selection works at the individual and population level, then expand to genetic variation, population genetics, and the Hardy-Weinberg model. Next we cover evidence for evolution, reconstruct evolutionary relationships with phylogenetics, and end with topics on speciation, extinction, and the origins of life itself. Concepts build sequentially, so working through sub-topics in order will help you connect ideas for exam questions.
Common Pitfalls
Why: Individuals do not evolve; natural selection acts on existing variation in populations to change allele frequencies over generations.
Why: Hardy-Weinberg is a null model that requires 5 strict conditions that almost never hold in nature.
Why: All living species have evolved for the same amount of time since their last common ancestor; position does not indicate progress.