Final answer:
Evolution is the process by which the genetic composition of a population changes over generations. New genetic variations can arise through mutation and gene flow and may lead to evolution if they become more frequent in the population.
Step-by-step explanation:
When one or more genetic traits in a population change over time, we can say that evolution has occurred. Evolution is the change in a population's genetic composition over time, specifically over generations, resulting from differential reproduction of individuals with certain alleles. It is crucial to understand that individuals do not evolve; rather, it is the population as a whole that evolves. The introduction of new genetic variation into a population most commonly occurs through mechanisms such as mutation and gene flow. Over time, these new traits may become more common in the population due to other evolutionary forces like natural selection, genetic drift, nonrandom mating, and environmental variances.