How many people do you need to develop a language?
The standard accounts of the development of NSL all start of by saying that before the Sandinista Revolution, deaf children in Nicaragua were isolated and never developed any system of communication sophisticated enough to be called a language. It was only when they came together in a deaf school that they began to sign with each other in what presumably could be called a pidgin, which quickly developed into a full-blown language.
So my question is - what is the threshold number before one becomes able to develop a language from scratch? (Call this x.) What about from an incomplete system of communication such as a pidgin?
A related topic that I was recently reading about in Malcolm Gladwell's The Tipping Point is that brain size (specifically, the size of the neocortex, the specifically mammalian area of the brain) is correlated with social group size. The bigger the neocortex, the bigger the average size of a mammal's social group. (The optimal size for human social groups is 150, extrapolating from the data for other mammals - and there's some fascinating evidence to back this up.) Anyway, assuming (I'm not sure) that humans' social group size is larger than that of just about all other mammals (excepting dolphins, probably), what if it so happens that our brains are just over the threshold x?
Of course, this is pure speculation, and it doesn't entirely explain why great apes would still be unable to learn language. (This last statement, of course, is in itself a contentious issue.)