Natural selection is a. how systems of rewards increase desired behaviors. b. the idea that the observable environment affects behavior in predictable ways. c. based on the idea that conscious experience can be broken down into underlying thoughts. d. the mechanism of evolution.

Option D i. e., the mechanism of evolution is the correct option.

Explanation:

In the above statement, natural selection is the mechanism of evolution because natural selection only the mechanism of evolution. The evolution of the mechanisms depends on the heritable trait that distinguishes of the population over the generations to generations. Evolution is the method by which an organism changes.