The primate famous for the sign-language studies involving Koko is the gorilla.
Koko was a female western lowland gorilla born at the San Francisco Zoo in 1971. Researcher Francine Patterson worked with her in experiments involving signs adapted from American Sign Language. Koko became internationally famous through books, television appearances, National Geographic coverage, and stories about her relationship with a pet kitten.
The studies made Koko a major figure in public discussions about animal intelligence, emotion, and communication. Patterson reported that Koko learned many signs and could use combinations to express wants or ideas. The work also helped challenge older popular stereotypes that gorillas were unintelligent or naturally violent.
Scientists have debated the interpretation of Koko’s signing. Critics argued that trainers may have prompted or over-interpreted some gestures, and that the evidence did not demonstrate human-like grammar or syntax. Therefore, it is more accurate to say Koko used signs adapted from ASL than to claim she mastered a human language in the full linguistic sense.
Koko died in 2018, but her story remains one of the best-known examples in the history of ape-language research.