Theory of Natural Selection was proposed by 

• Natural selection is the method through which populations of living things adapt and change. 
• The population of the individual becomes inherently varied, yet every member of a population will differ from every other member in some manner. 
• It is one of the famous theories regarding evolution. It refers that nature selects the fittest organisms.
• For instance, tree frogs are occasionally eaten by snakes and birds.
• The theory of Natural Selection was proposed by Charles Darwin.
• Natural selection theory was proposed in 1859.

Hence, option A is the correct answer.