Which type of evolutionary mechanism is likely to result in the most rapid changes in a population's traits?

Natural selection is a key evolutionary mechanism that can lead to rapid changes in a population's traits due to its focused and adaptive nature. In natural selection, individuals with traits that provide a survival or reproductive advantage in a specific environment are more likely to pass on those advantageous traits to the next generation. Over time, this process can significantly alter the genetic makeup of the population.

Natural selection operates on existing genetic variation within a population, allowing beneficial traits to increase in frequency. For instance, if a specific trait enhances an organism's ability to find food or avoid predators, individuals with that trait will reproduce more successfully, leading to a faster rate of change in the population compared to other mechanisms.

In contrast, while mutation introduces new genetic variations, it may not always result in advantageous traits. Genetic drift changes allele frequencies randomly and is more pronounced in small populations, often leading to less predictable changes. Gene flow involves the exchange of genes between populations, which can introduce new traits but often stabilizes rather than rapidly changes the traits within a single population. Therefore, natural selection is the most effective mechanism for driving quick adaptations and shaping the traits of a population in response to environmental pressures.