Evolution and Diversity
Core concepts
Evolution is change in allele frequencies in a population over time. Natural selection acts on heritable variation: individuals with advantageous traits survive and reproduce more, increasing those traits in later generations. Other mechanisms include mutation, gene flow, and genetic drift. Fitness measures reproductive success, not strength. Adaptations are traits shaped by selection. Speciation occurs when populations become reproductively isolated. Evidence for evolution includes fossils, comparative anatomy (homologous and analogous structures), embryology, and molecular similarities. Classification groups organisms by shared characteristics, from domain to species. Three domains are Bacteria, Archaea, and Eukarya. Natural selection is not goal-directed and does not produce perfection.
Common traps
Questions often confuse homologous structures (shared ancestry, same origin) with analogous structures (similar function, different origin). Do not say individuals evolve; populations evolve. Distinguish natural selection from genetic drift, which is random change. Do not treat evolution as a ladder of progress.
Worked example
A population of beetles includes green and brown individuals. Birds eat green beetles more easily on brown soil. Brown beetles survive and reproduce, so the brown allele becomes more common. Rule of thumb: if a trait is heritable and affects survival or reproduction, selection can change its frequency.