What is natural selection?
Natural selection changes populations when inherited traits affect reproductive success differently in a given environment.
How it works and key principles
Conditions: Individuals vary, some variation is heritable, and it affects survival or reproduction. The frequency of favorable traits can rise across generations. Selection does not plan ahead; the same trait may lose its advantage when the environment changes.
Evidence, examples and limits
Limits and examples: Selection of antibiotic-resistant bacteria during treatment is an observable example; the drug does not deliberately create the mutation bacteria need. Genetic drift, migration and mutation also change populations. An individual does not evolve during its lifetime; evolution concerns inherited variation across a population.
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