Deaf children with no shared language invented one from scratch in a generation

Before the 1970s, Nicaragua's deaf children were mostly isolated, each using improvised gestures with their own families. When new schools brought them together for the first time, the children built a shared sign language from nothing within a generation, full grammar, verb structures and all, giving linguists a rare live window onto how human language itself might have originated.

— Judy Kegl and Ann Senghas, Nicaraguan Sign Language — Linguistic documentation from the 1980s-1990s