Extending in scope or effect to a prior time or to conditions that existed or originated in the past; especially : made effective as of a date prior to enactment, promulgation, or imposition
The correct answer is definitely the historical method.
You should observe words and their usage as it developed throughout history.
The phrase that best summarizes the theory of evolution by natural selection is D) only the strongest individuals survive.
It is the survival of the fittest, those who are not strong enough will not make it, they will be consumed by the stronger ones.