The theory of natural selection was proposed by:

The correct answer is Option (2) → Charles Darwin

NCERT Extract:
Evolution of Life Forms – a Theory – “… The fitness, according to Darwin, refers ultimately and only to reproductive fitness. Hence, those who are better fit in an environment, leave more progeny than others. These, therefore, will survive more and hence are selected by nature. He called it natural selection and implied it as a mechanism of evolution.”