Which process describes the differential survival and reproduction of individuals based on their traits?

• A. Natural selection
• B. Genetic drift
• C. Mutation
• D. Gene flow

Answer: (A)

Natural selection is the differential survival and reproduction of individuals based on heritable traits that affect fitness. In a population, variation in traits means some individuals possess features that help them survive environmental pressures or attract mates, so they leave more offspring. Because these advantageous traits are heritable, the alleles behind them become more common over generations, and the population becomes better adapted to its environment.

This process contrasts with genetic drift, which is random change in allele frequencies that isn’t tied to how well a trait helps an organism survive or reproduce, especially in small populations. Mutation introduces new genetic variation, but by itself doesn’t cause differential survival unless natural selection acts on those new traits. Gene flow involves the movement of alleles between populations, changing frequencies due to migration rather than differences in fitness.