Key concepts
Mutations arise without regard to what organisms need. Selection is non-random: inherited traits that improve reproduction in a particular environment tend to become more common.
Individuals do not evolve during life. Populations evolve when inherited trait frequencies change across generations.
Applications and misconceptions
Mutation and selection explain antibiotic resistance, pesticide resistance, camouflage, domestication, and changing viral populations.
Misconception: organisms do not mutate because they need a trait. Mutations occur first; the environment then changes which variants leave more descendants.