What are the origins of some of the more popular long standing jokes?

Oh you know the kind of which I speak. Knock knock jokes for example. Or the “Why did the chicken cross the road”? gag. Interested as to how & why these & other jokes intergrated themselves into folklore. Indeed what makes them so enduring if not endearing to a generation of kids & adults alike? Feel free to add your own examples of these particular jokes, but what i’m really after is the history behind them. Thanks!