Somewhere out there, to the people who categorize such things, there must be a special slot for jokes that could literally have been told since the dawn of time.  No computers, no Internet, no machinery, no cars, no hip, jive, with-it, in-house slang; no nuthin'.  Just a simple joke that'd be just as funny in ancient Rome as it is today.  Just change a few details and there ya go.

When you look around, this is actually somewhat rare.  Some jokes could be reworded, of course, but then something is lost by 'aging' or 'sterilizing' the joke.  The joke; the very core joke, has to be written to withstand any test of time to be placed in such an exalted category.

I would submit the following as such a joke.

An old man lived alone on his farm.  He wanted to spade his potato garden, but it was very hard work.  His only son, Bubba, who used to help him, was in jail.  The old man wrote a letter to his son and mentioned his predicament.

"Dear Bubba, I am feeling pretty bad because it looks like I won't be able to plant my potato garden this year.  I'm just getting too old to be digging up a garden plot.  If you were here, all my troubles would be over.  I know you would dig the plot for me.  Love, Dad."

A few days later he received a letter from his son.  "Dear Dad, don't dig up the garden!  That's where I buried the WEAPONS!  Love, Bubba."

Early the next morning, a dozen law enforcement officers showed up and dug up the entire area without finding any weapons.  They apologized to the old man and left.  That same day the old man received another letter from his son.

"Dear Dad, go ahead and plant the potatoes now.  It was the best I could do under the circumstances.  Love, Bubba."