This video-- a feature from CBS 60 Minutes -- is on the emergence of new deaf community -- and their dialect of sign language -- in Nicaragua studied by Judy Kegl and her colleagues. We see that gesture systems developed in isolated families are variable and easily changed. A more stable and conventional system emerged once home sign users came into contact with one another in the school established for the deaf.
They found, however, that the first cohort of very young deaf children to attend school where the shared system was used transformed this system and introduced into it distinct grammatical features as though they had created a new, more complex, and consistent system. We might compare development of Nicaraguan sign language this to the process of "language creation" described by Bickerton (Language video) in his studies of the development of creoles from pidgins by children who supplied the missing grammatical structures.
In addition to Kegl, Susan Goldin-Meadow has done very interesting work on the development of sign languages in young children. Earlier we saw the Language video with Ursula Bellugi at the Salk Institute near San Diego where she has conducted research on sign language (and Williams syndrome) for several decades.
In observing these children signing, try to compare the speed and variability of their gestures with those of Koko, Washoe, and other supposedly signing apes (e.g. in the Kanzi video). Although I am not a sign-language user, there appears to be quite a difference between the signs of apes and signs of children. At best apes seem to use a limited "pidgin" gestural system -- a human based referential code grafted onto their natural gestural system which may be fairly complex on its own regarding social and emotional issues.
There are some excellent images of the surprising similarities between brain activity patterns in the perception of speech and perception of signs at the University College London website.
Kegl, J., A. Senghas, et al. (1997). Creation through contact: sign language change in Nicaragua. In M. DeGraff (Ed.) Comparative grammatical changes: The intersection of language acquisition, Creole genesis, and diachronic syntax. Cambridge, MIT Press.
PBS Birth of a Language video