Question

According to the First Doctor, questions, indicative of curiosity, were "the beginning of wisdom, of knowledge [and] of understanding". When a species began asking questions, no matter what prompted their inquiry, they arrived at a new frontier for their society. This was an evolution of sorts, the Doctor suggested. (AUDIO: The Invention of Death)

The oldest question in the universe was "Doctor who?" (TV: The Wedding of River Song) According to the Fifth Doctor, the "second-oldest question" was "Why did the chicken cross the road?" (AUDIO: The Second Oldest Question)