Alas, many people ask for evidence of all sorts of things. Some things will have no answers known for many a time to come... but that does not mean we should stop asking questions. I believe, given enough time, that all things will be known to man either by discovery or quest.
If I do not have an answer about something that does not mean no answer exists. If I have to await evidence to help me find that answer then so be it.
Most scientific endeavour is built on the same premise. So much starts out with some intelligent hunch that leads the scientist to look for the answers to 'prove' the hunch. Science still awaits many answers and, as such, evidence to back the answer up.