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In the 1980s deaf children in Nicaragua invented a completely new sign language of their own. It was a remarkable achievement, which allowed experts a unique insight into how human communication develops. "What we learnt from Nicaragua about language still isn't over," says American linguist Judy Shepard-Kegl, who documented the emergence of what's now known as Nicaraguan Sign Language.

(Photo: Inti Ocon/AFP/Getty Images)