What best defines natural selection?

• A. Random variation in traits without fitness consequences.
• B. Differential survival of individuals due to non-heritable variation.
• C. Evolution driven solely by mutation.
• D. Differential survival and reproduction of individuals due to heritable variation in fitness.

Answer: (D)

Natural selection is about differential survival and reproduction caused by heritable differences in traits. In any population, some individuals have traits that give them a higher chance of surviving and producing offspring in their environment. Those individuals pass on their genes more often, so the advantageous traits become more common over generations. The key is that the variation is heritable—if a trait isn’t passed to offspring, it can’t accumulate in the population through natural selection.

Variation coming from mutations provides the raw material, but natural selection acts on the differences that can be inherited and influence fitness. For example, in a population where better camouflage leads to higher survival, individuals with that heritable trait leave more offspring, shifting the population’s traits toward better camouflage over time.