Why is a natural selection only effective when a population is polymorphic?
The correct answer and explanation is:
Natural selection is only effective when a population is polymorphic because it requires genetic variation to act upon. Polymorphism refers to the presence of two or more different phenotypes or alleles within a population. Without this genetic diversity, there is no variation for natural selection to favor or select against.
In a population that is genetically uniform, where individuals are all alike with little to no variation in traits, there is no differential survival or reproduction based on those traits. Natural selection works by increasing the frequency of traits that enhance survival and reproduction while decreasing the frequency of traits that hinder it. However, if there is no variation, there is no way for selection to “choose” a more advantageous trait because there is nothing to compare.
In a polymorphic population, different individuals may possess different versions of a gene, leading to variations in their characteristics. These variations might provide certain individuals with a better chance of survival or reproduction in a specific environment. For instance, individuals with a trait that helps them avoid predation, find food more easily, or resist disease will be more likely to survive and reproduce, passing on their advantageous traits. Over generations, these beneficial traits become more common in the population.
Moreover, polymorphism can also ensure that a population is adaptable to changing environments. If a population only has one version of a gene, it might be vulnerable to environmental changes that affect that particular trait. However, in a polymorphic population, different individuals may possess traits that allow them to survive different environmental conditions. This diversity increases the likelihood that some individuals will continue to thrive despite changes in their environment.
Thus, without genetic variation (polymorphism), natural selection has nothing to act on, and it cannot drive the evolution of the population.