Natural selection is Darwin's mechanistic explanation for evolution.
According to Darwin, nature (the environment) selects organisms with traits that allow them to survive in that particular environment.
1)There more individuals that produced than be sustained by a particular environment. This leads to competition for limited resources.
2)There is variation within a population. Genetic mutation provides variation of traits.
3) individuals with favorable traits that provide an advantage for survival will have an edge in this competition
4)These individuals as a result are more likely to reproduce than those that do not possess these traits.
For example: birds in different habitats such as penguins living in extremely cold conditions or bats that use large ears for echolocation or hummingbirds with long tongues to reach the nectar at the base of blooms and their ability to hover while sipping the nectar.