Alistair - I've been collecting, and contributing to, the World's Shortest poems for several years. I occasionally get to use them for a nifty diversionary performance piece. Otherwise, it's generally a lonely road, being archivist for a collection hard-pressed to fill a half-page. But the hours are good. And the more scholarly responsibilities unfortunately qualify me uniquely to expound at some length about your chosen topic.
The stunning couplet you quoted is the famous (to us archivists) "On The Antiquitiy Of Microbes" by the equally famous Ogden Nash.
But it is not the shortest.
Oh no.
In terms of syllabic length, the darkly existential musings of some other academic scientist geezer (so famous that his name escapes me right now - must get the archive filing system under better control) are a better bet:
"I. Why?"
Which in turn inspired yours truly, my good self, to pen the paranoid's riposte:
"You! Who?"
While a perhaps more eloquently inclusive improvisation came from Mohamed Ali while addressing an audience at Harvard:
"Me - We"
The dialect poet, Allen Jameson, formulated his "I, aye." in 2003, but the leading contenders had already long been known by that time.
Way ahead is Don Paterson, whose triumphantly koanic masterpiece, called "On Going to Meet a Zen Master in the Kyushu Mountains and not finding him", goes like this:
" "
Sweet.
But now I, Colin Lazzerini Esquire, have finally jostled ahead with the equally enigmatic "Notes For The Insciption On My Gravestone".
Here it is:
.