Natural selection acts through individuals by determining which individuals have the best adaptations to guarantee reproductive success. Because the state of environment is always changing temporally, natural selection is always influencing the genetic characteristics of the population over time. Thus, natural selection acts to adapt the population to its ever changing surrounds. Evolutionary change is also a change in gene frequency . The pattern of genetic variation changes from one generation to the next as natural selection determines which individuals are fittest.
New genes enter the species gene pool way of mutations .
By selecting thos organisms that will become reproductively successful, natural selection controls the future frequency of a population's genes. The appearance of new mutations in a population together with the change in gene frequency results in evolution. The spatial isolation of sub-populations from a main population is also an important condition for evolution. If a remote sub-population cannot trade genes to the main population because of isolation, natural selection acts differently in each population resulting in divergent evolution . Differences in gene frequency emerge between the two populations because no two patches of habitat are absolutely identical, and because new adaptations enter the gene pool through mutations at the level of the individual.