...is based on the observation of monkeys on some remote chain of islands. When the monkeys on one island discovered a new way to get coconuts down from the tree (or was it bananas?), the monkeys living on a nearby island somehow acquired that same knowledge, even though there was no physical contact between the two groups of monkeys.

So the theory goes that when, one by one, the members of a group (monkeys... us) begin to acquire a certain piece of knowledge, there is a tipping point - the hundredth monkey - where this knowledge passes into the collective consciousness, and all members of the group acquire that knowledge.

I don't know how true any of this all is, but it would account for the irrational popularity of such things as the hula hoop, POGS, and the Macarena.

(Editor's note - Here is a perfect example of the danger of passing on information only vaguely recollected. I had heard the 100 Monkey Theory way back when I was in high school in the early 1970's, from a friend who must have actually read the book it was taken from. Since getting the facts correct would have required a little effort on my part, I just relied on my faulty memory instead.

Now this Friday evening some 30 years later, a simple Google search has revealed I didn't quite have it right - sort of the way everyone can hear in their heads Humphrey Bogart say, "Play it again, Sam" in the movie "Casablanca," when in fact he never does say that exact phrase. Memory isn't so reliable! Turns out, it wasn't getting coconuts or bananas at all (to be honest, I just made that part up), it was washing sweet potatoes.... but other than that minor detail, they way I have it is the gist of it.

By the way, the book this is all from is "The Hundredth Monkey" by Ken Keyes, Jr. Hope this clears things up!)