Final answer:
Variation is crucial to evolutionary theory as it provides the genetic diversity required for natural selection to occur. Genetic variation ensures that some individuals will respond differently to environmental pressures, allowing them to survive and reproduce. Sexual reproduction is one of the key processes that generate this essential genetic variation.
Step-by-step explanation:
Variation is of critical importance in evolutionary theory because it provides the raw material for natural selection. Genetic variations among individuals within a population are essential for 'survival of the fittest' to occur. If organisms are genetically identical, they would all respond to environmental stressors in the same way, leading to either all surviving or all perishing.
Natural selection acts on these genetic variations, allowing individuals with traits that provide a survival or reproductive advantage to pass their advantageous genes on to the next generation more frequently. Over time, this can lead to adaptive changes within a species. It is important to note that these variations must be genetic, as nongenetic variations (like those caused by different environments, such as nutrition) do not contribute to evolutionary changes in the gene pool of a population.
The process of sex also plays a vital role in creating genetic variation within a population. Sexual reproduction shuffles genes and produces offspring with new combinations of traits, which contributes to genetic diversity. This diversity is the foundation upon which the evolutionary process can continue, allowing species to adapt over time to changing environments and survive.