Deaf children with no shared language spontaneously invented one

When Nicaragua opened its first schools for deaf children in the 1980s, students arrived with no common sign system and were never taught one. Within a single generation they pooled improvised home signs into Nicaraguan Sign Language, a fully grammatical new language that linguists could watch being created almost from scratch — one of the only times this has ever been documented happening live.

— Ann Senghas, Marie Coppola, Children Creating Language: How Nicaraguan Sign Language Acquired a Spatial Grammar — Psychological Science, 2001