Natural selection is a process of evolution where traits that help organisms in their survival and reproduction processes pass from one generation to another.
The theory of natural selection was brought by Charles Robert Darwin.
This theory states that the organisms that do not possess favorable variations are regarded unfit and they cannot carry on the struggle for surviving.
As a result, the population includes only the fit organisms that possess favorable variations.
The fit reproductively fit populations are selected over the unfit population as they can produce more progeny.