Which phrase best summarizes the theory of evolution by natural selection?

A. Over extended periods of time populations change.

B. Survival is done by the strongest.

C. All life comes from life.

D. Species evolve and become better adapted to their environment.

The correct answer is (d.) species evolve and become better adapted to their environment. It best summarizes the theory of evolution by natural selection. It simply implies that organism changes over a period of time and evolve in a better way because of their adaptation to their environment.