Final answer:
The statement that natural selection requires variability in a population is true. Variability allows natural selection to act on different traits, leading to evolution. Variability arises from mutations and gene flow and is expressed as population variation.
Step-by-step explanation:
For natural selection to work, there needs to be variability in a population—the answer is true. This variability is essential because natural selection acts on the different inherited traits within a species. Without variation, there would be no differential survival and reproduction based on those traits, and therefore no evolutionary change. Variability in a population can arise from several sources including mutations, which are random changes in the genetic material, and gene flow, which is the transfer of alleles from one population to another.
Population variation is the distribution of phenotypes within a population, which means that individuals differ from each other in terms of observable traits. An example of population variation is the array of fur colors and patterns seen in domestic dogs. This genetic diversity within a population is a prerequisite for natural selection because it provides the material upon which selection can act. Natural selection favors those individuals with hereditary traits that are better suited to survive and reproduce in a given environment, thus guiding the evolutionary process. However, it must be noted that natural selection is limited by the current genetic variation in the population and cannot create any new traits from scratch.