I've had this bumper sticker on my (now rather dirty) car for about two weeks now. As yet, no takers.
If I were indulging in wishful thinking, I'd put it down to the inherent politeness of Midwesterners. Yeah, that's it! They wouldn't want to honk, even if they did understand PE, because it might seem rude!
I'm fooling myself, aren't I?
At any rate, until I get myself together enough to write a longer piece on it, you can find Punctuated Equilibria, in the words of one of its developers, the late and much-missed Stephen Jay Gould here (scroll down, or search for "punctuated" on the page), a whole page on the Gould Archive here (from his landmark book The Structure of Evolutionary Theory), or check out the Wikipedia entry, for a start.
And in the meantime, if you see a car with a PE sticker on it, do the right thing: honk!