Evolution is the process by which populations of organisms change over time. It occurs through the mechanisms of natural selection, genetic mutation, and genetic drift. Natural selection is the process by which organisms best suited to their environment are more likely to survive and reproduce, passing on their advantageous traits to their offspring. Genetic mutation creates variations in traits that may be beneficial or detrimental, and over time, certain mutations can become more common in a population. Genetic drift occurs when chance events cause certain traits to become more or less common in a population.