Exam Tips: Evolution and Natural Selection

Start with variation, not with the selection pressure: In antibiotic resistance questions, many students write "when antibiotics were introduced, bacteria mutated." This is wrong. The mutation already exists randomly in some bacteria before the antibiotic is used. Always begin: "There is variation — some bacteria have a mutation giving resistance."

Link survival to reproduction to inheritance: "Survived more" alone is never enough for an explain mark. You must say "survived to reproduce" and "passed on the allele to offspring." All three steps are needed: survival → reproduction → inheritance.

Distinguish evolution from individual change: Individual organisms do not evolve. Populations evolve. A single giraffe does not grow a longer neck due to natural selection — the population shifts over generations.

Know both Darwin and Lamarck for comparison questions: Lamarck said organisms change during their lifetime and pass those changes on. Darwin said random variation already exists and the environment selects. The key difference is whether the organism generates the useful trait or whether it already exists randomly.

Evidence questions — name it and explain it: Never just list "fossils" or "DNA." Say what the evidence shows: "Fossil records show organisms have changed gradually over millions of years — supporting evolution."