01Darwin's argument
Populations show variation; some variation is heritable; more offspring are born than can survive (overproduction); individuals with traits better suited to the environment survive and reproduce more (differential reproductive success). Over generations, favorable traits become more common.
Selection acts on individuals' phenotypes, but populations evolve.
02Key clarifications
Evolution is a change in allele frequencies in a population over time. Individuals don't evolve during their lifetimes. Natural selection doesn't create perfect organisms — it works with existing variation.
03Notebook box
VIST: Variation, Inheritance, Selection, Time.
Worked example: Explain antibiotic resistance. → Random mutations gave some bacteria resistance; antibiotics killed the rest; survivors reproduced, so resistance alleles increased.