So, here's a curious question

So when did people start starting sentences with so?  I watched an interview on TV this morning and as the expert du jour was being asked questions she answered each one with a sentence beginning with 'so'.  No reason, nothing to do with the remainder of the sentence structure, but every sentence began with 'so'.  So what's the meaning of this?  Do we need a cute little extra word just to extend the length of sentences?  It seems to be an ongoing compulsion? Some years ago the word was 'like'.  I wonder what the next word will be.  I vote for 'well'.  Oh wait, that one goes back as far as Jack Benny.  Which, if you don't remember him, was a long time ago.  So, like well, I'll need to think about this a bit longer.