gakattack:
Even though generativity is obviously a cool concept and so on, let's just make it clear that Chomsky never actually looked at the world's languages (or listened to people in relevant fields, i.e. cognitive sciences). This is what language typologists do (look up Joseph Greenberg on wiki for instance). Rather, he has postulated a number of highly debatable distinctions, such as the one that supposedly divides language into competency (which is what he finds interesting - the mathematical properties of language) and performance (actual usage of a language).
While it appears very reasonable to claim that language is to some extent "innate", this is, IMO, not the whole story. People with speech production deficiencies do exist, as do feral children whose "language module" was never activated. (The "module" thing is pretty questionable as well: the rest of the brain doesn't appear to be organised into clearly delineated modules; for example, young children who suffer damage to the language-related parts of the brain are sometimes able to "reroute" the language learning to other neurons because these are very plastic in the early part of life, less so when you're adult).
I find it, however, to be pretty improbable that evolution should have stumbled upon something as elegant as a bit of mathematical notation.
Because it is very hard for me to see how Chomsky is attempting to describe human language, I find it much more interesting to ask: Why was language a good idea from an evolutionary point of view? It must have been an advantage to enough people. What did and do we use language for? Trading, exchange of information beyond simply imitating another's actions (i.e., the start of culture), social acts (threatening, promising, endorsing, lying etc.).
Regarding the advancedness or complexity of languages: do you think that English is a more advanced language than, say, Piraha which can be whistled, hummed, or encoded in music? I try to keep concepts and language somewhat separate even though language is our most prominent carrier of concepts.
