Natural selection is a driving force for evolution-How ?

Explanation

Survival of the fittest or Natural selection:
(i)During the struggle for existence,the organisms which can overcome the challenging situation,survive and adapt to the surrounding enviornment.
(ii)Organisms which are unable to face the challenges,are unfit to survive and disappear.
(iii) The process of selection of organisms with favorable variation is called as natural selection.
Origin of species
According to Darwin,new species originates by the gradual accumulation of favourble variations for a number of generation.Hence natural selection is a driving force for evolution since it leads to formation of new species.