When Penny Patterson, a young graduate student in psychology at Stanford, first saw a tiny, undernourished baby gorilla named Hanabi-Ko (which means “Fireworks Child” in Japanese) at the San Francisco Zoo, she had little inkling that the sickly ape would become her constant companion – and the subject of the longest continuous experiment ever undertaken to teach language to another species.

But within a year, Project Koko was underway, and in two weeks the gorilla was using correct signed gestures for food, drink, and more. Today, four decades later, Koko has a vocabulary of more than 1,000 words.

After Patterson's research with Koko was completed, the gorilla moved to a reserve in Woodside, California. At the reserve, Koko lived with another gorilla, Michael, who also learned sign language, but he died in 2000. She then lived with another male gorilla, Ndume until her death in 2018.

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