Darwin's theory of natural selection states that nature selects organisms that have features favorable for their survival, while eliminating inferior species.
Natural selection is a key to the origin of new species from the existing ones.
Darwin's concept of evolution is totally different from Lamarck's theory of organic evolution (1801).
In Darwin's Theory, he stated that nature only selects those organisms that are best-suited to that particular environmental condition; whereas Lamarck's theory states that it is the environment that brings changes in organisms.
Natural selection can be explained in the same way as the breeding procedure practiced by human breeders for domestic animals.