Final answer:
Variation within a population is the diversity in genotypes and phenotypes that is influenced by mutational events, sexual reproduction, and gene flow, and it is not constant as it can change over time.
Step-by-step explanation:
Variation within a population refers to the differences in genotypes and phenotypes among individuals in the same species. It is incorrect to state that variation is constant within a population, as it can be influenced by many factors, including mutational events, sexual reproduction, and gene flow, which are mechanisms that introduce new genetic information into a population and generate diversity.
For example, in a population of domestic dogs, the variation in fur colors and patterns is a result of genetic differences that produce a wide range of appearances. Another example is the phenotypic variation observed in Mendel's pea plants, which had different genotypes such as homozygous dominant, heterozygous, and homozygous recessive. Furthermore, geographic factors play a role in variation; for instance, larger mammals in polar regions as a response to cold temperatures, a concept known as Bergmann's rule. Lastly, natural selection itself is dependent on the presence of variation, as it selects for traits that enhance survival and reproduction in a given environment, thereby contributing to the diversity observed within a population.