Evolution

Evolution is the change in the heritable characteristics of a population over successive generations. In other words, it describes how populations of organisms undergo genetic change over time.

• Individuals do not evolve; populations evolve as gene frequencies change from one generation to the next.
• Evolution isn't goal-oriented -- natural selection favors traits that improve survival or reproduction in a given environment, but it doesn't "plan" for future needs.
• Mechanisms of evolution include natural selection (adaptive changes), genetic drift (random changes in small populations), mutations (introducing new genetic variation), and gene flow (migration).

• A question may ask who or what evolves - the correct answer is populations (not individual organisms).
• If a question describes a shift in traits in a population (e.g., bacteria becoming resistant to antibiotics over many generations), it's illustrating evolution by natural selection.
• Watch for trick wording like "organism X evolved a trait because it needed it" - in reality, random mutations produced the trait and natural selection made it prevalent; need does not cause mutations.