The subject of gorillas and their capacity to comprehend sign languages has long been debated and argued about by experts and scientists, just as the gorilla’s said capacity to comprehend sign languages has been the subject of countless short stories and feature length movies.
The 1995 released Born to be Wild would be one good example of such featured stories, given how Katie, the main protagonist gorilla in the movie, managed to communicate with a human juvenile delinquent named Rick.
Koko’s handler, Francine Patterson, contests that Koko is capable of understanding an approximated 2,000 words of English, as well as comprehend a thousand signs which are based on the sign-standards of the American Sign Language.
However, other scientists and researchers are convinced that Koko is simply “imitating” the signs without exactly comprehending them, given the fact that Koko’s “training” works with a rewards system.
Still, a number of researches are convinced that gorillas do actually comprehend the meaning of signs, though not at human-level degrees, given their general capacity in expressing signs or aggression using their hands.
Given that Koko appears to be the only gorilla capable of understanding sign languages, it appears that further studies and inquires are required to fully asses the gorilla’s actual capacity in communicating via hand languages.