in a recent profile of the creator of alice , richard wallace, we learn that he finds human's collective conversational capability to, er, lack in complexity:

"Wallace had hit upon a theory that makes educated, intelligent people squirm: Maybe conversation simply isn't that complicated. Maybe we just say the same few thousand things to one another, over and over and over again. If Wallace was right, then artificial intelligence didn't need to be particularly intelligent in order to be convincingly lifelike. A.I. researchers had been focused on self-learning ''neural nets'' and mapping out grammar in ''natural language'' programs, but Wallace argued that the reason they had never mastered human conversation wasn't because humans are too complex, but because they are so simple."

and in related linguistics news, our humble lexicon puts kevin bacon to shame :

"Word association can link just about any two common words in the English language using an average of three steps, says a team of scientists in Arizona."

"he small-world network also means that apparently quite different concepts, such as 'actor' and 'universe', are closely linked by a short series of semantic steps. This, say the researchers, makes it easier for us to carry out mental searches when using language - we can get to our intended destination quickly, regardless of our starting point. A database cross-referenced in this way would be relatively easy to search computationally."

so we're optimized to not have to thing very hard about a limited number of conversational topics? sounds about right.