I’ve seen it documented with respect to two different naturally occurring deaf communities, where a spontaneous genetic mutation lead to large numbers of deaf children being born within a single generation.

In each instance, the children develop real grammatical sign language on their own.

Writer. Runner. Marine. Airman. Former LGBTQ and HIV activist. Former ActUpNY and Queer Nation. Polyglot. Middle-aged, uppity faggot. jamesfinnwrites@gmail.com