Selective pressures, such as environmental changes, predation, and competition for resources, play a crucial role in shaping the genetic variation within a population. When certain traits provide an advantage in survival or reproduction, individuals with these traits are more likely to pass them on to the next generation. This process, known as natural selection, can lead to an increase in the frequency of beneficial alleles in the gene pool.
As a result, the genetic variation may decrease for traits that are not advantageous under the prevailing selective pressures. For example, if a particular color of a moth helps it blend into its environment better, over time, that color variant may dominate the population as those moths are more likely to survive and reproduce.
Conversely, selective pressures can also maintain a certain level of genetic variation within a population. For instance, in some environments, different traits may be favored at different times or under various conditions (a phenomenon known as stabilizing selection). This can help preserve diverse alleles in the population, allowing for adaptability in the face of changing environments.
In summary, selective pressures can lead to both a reduction in genetic variation for certain traits and help maintain variation for others, ultimately influencing the evolutionary trajectory of the population.