Answer:
Natural selection is indeed a mechanism of evolution. It operates on individual organisms within a population and results in changes in the frequencies of certain traits or characteristics. While the mechanism acts on individuals, it ultimately produces changes in populations over time.
Natural selection is driven by various factors, one of which is the environment. Organisms possess variations in traits, and some of these variations may provide advantages or disadvantages in certain environments. Individuals with advantageous traits tend to have increased survival rates and reproductive success, allowing them to pass on those traits to future generations. On the other hand, individuals with less-favorable traits may have lower survival and reproduction rates.
Over successive generations, as more individuals with advantageous traits survive and reproduce, the frequencies of those traits within the population increase. This process leads to a change in the overall characteristics of the population, as traits that confer greater fitness become more common while less favorable traits decrease in frequency or may even be eliminated.
Therefore, although natural selection acts on individuals, the cumulative effects of these individual-based changes result in long-term changes at the population level.