Synthesized answer
The provided passages do not contain a list of unanswered questions from "On the Origin of Species." [1] The description only states that the book lays the foundations for the principles of evolutionary biology via natural selection, based on evidence Darwin collected [1].
Therefore, I cannot answer what questions remain unanswered based on the given information.
Synthesized from the book passages below. Chat with the book on Feynman for follow-up.
From the book
Title: On the origin of species by means of natural selection by Charles Darwin Description: Charles Darwin's seminal work laying the foundations for the principles of evolutionary biology via natural selection, based on evidence that he collected during his expedition on *HMS Beagle* in the 1830s.