KOKO the gorilla knew over 1,000 signs based on American Sign Language, and used them to do everything from asking for food to joking around. Her trainer and long-term companion, Penny Patterson, thought Koko went further still, signing in novel ways and showing complex emotions. According to Ms Patterson, when a cat that Koko loved was killed in an accident, Koko signed: “Cat, cry, have-sorry, Koko-love.” When Koko died last month, some of her obituaries mourned the gorilla who had “mastered American sign language”.

Then came the backlash, from linguists and experts in sign languages. These have complex grammars, equivalent to spoken tongues in expressiveness. Koko’s ability, it was pointed out, fell well short of a fluent human signer. Moreover, Ms Patterson was her interpreter, a role that invited the question of how much she was inferring what Koko “must have meant”, and explaining away random signs. (Koko was particularly fond of “nipple”.) It was hard to be sure: Ms Patterson…Continue reading
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