3.1.4—Natural selection
- Syllabus
- First assessment 2026
- Objective
- 3.1.4
- Level
- SL
Treat Natural Selection as a Mechanism
Natural selection changes trait or allele frequencies when heritable variants differ in survival or reproduction under current conditions.
Selection acts each generation; adaptation is the longer-term result. It has no planned goal and a trait is advantageous only relative to the environment.
If darker moths leave more offspring on soot-darkened trees, their frequency can rise over generations.
Heritable variants must have different reproductive success; mere presence of variation is insufficient.
Selection is not organisms choosing useful traits; the environment filters existing inherited differences.