The main features of theory of Natural Selection are as follows

$\left(1\right)$ Over production (High rate of Reproduction): All organisms have capability to produce enormous number of offspring, organisms multiply in geometric ratio. $\left(2\right)$ Struggle for existence: Every individual competes with other of the same and other species for basic necessities like space, shelter and food. It is called struggle for existence and it continues for the whole life from zygote stage to its natural death. $\left(3\right)$ Variations and heredity: According to Darwin the variations are continuous and those which are helpful in the adaptation of an organism towards its surroundings would be passed on to the next generation, while the others will disappear. $\left(4\right)$ Survival of the fittest or natural selection: According to Darwin most suitable and fit individuals are successful in struggle for existence. The individuals with most favourable adaptations are able to lead most successful life and are able to win over their mating partners. In the struggle for existence only those members survive which possess useful variations means nature selects fit individuals. This was called Natural Selection.