Natural selection is the process by which certain traits become more common in a population over time. It is one of the key mechanisms of evolution, and is the result of genetic variation in a population. Natural selection occurs when some individuals in a population have traits that give them an advantage over other individuals in the same population. These individuals are more likely to survive and reproduce, and their advantageous traits become more common in the population over time. Natural selection can lead to changes in the physical characteristics of a species, as well as changes in its behavior.