Passage Summary: For a genetic change to be kept by nature, it must help the species survive. However, if that change also brings along other bad traits that are worse than the benefit, the change won't be kept.

Reasoning: A genetic mutation is favored by natural selection if and only if it significantly aids species survival, provided that any accompanying non-favored traits do not outweigh the benefits of the favored trait.

Analysis: This stimulus establishes a strict conditional relationship: a mutation is favored if, and only if, it contributes to survival. We are also given a 'proviso' that acts as a deal-breaker; even a helpful trait won't be favored if its 'hitchhiking' negative traits are too damaging. To find the answer that 'Must be False,' look for a scenario that violates these rules, such as a mutation being favored despite having no survival benefit, or a mutation being favored even though its negative side effects completely negate its advantages.