Originally published 2018-07-04.
Koko, the western lowland gorilla who became world-famous for communicating with hand signs, died in her sleep on 19 June 2018 at the Gorilla Foundation's preserve in Woodside, California. She was 46. For almost half a century she was the best-known ape on the planet: a two-time National Geographic cover star, the subject of children's books and documentaries, and the centre of one of the longest-running and most argued-about experiments in animal communication.
Her story is worth knowing for two reasons. It changed how millions of people thought about gorillas, and it is also a case study in how hard it is to tell what an animal really means. Here is who Koko was, what she could do, why many scientists were sceptical, and what her life leaves behind.
Who Koko was
Koko was born at the San Francisco Zoo on 4 July 1971 and named Hanabiko, Japanese for "fireworks child", after her Independence Day birthday. Her parents were the zoo gorillas Jacqueline and Bwana. In December of that year, when she was about five months old, she was hospitalised with malnutrition and was afterwards hand-reared by people rather than by her mother's group.
That set the course of her life. Francine "Penny" Patterson, then a graduate student in developmental psychology at Stanford University, began working with the infant as part of her doctoral research, inspired by earlier projects that had taught signs to chimpanzees. Patterson later moved Koko to Stanford and, after a public "Save Koko" campaign helped fund her custody, kept her permanently. With Ron Cohn and Edward Fitzsimmons she set up the non-profit Gorilla Foundation, which looked after Koko for the rest of her life, eventually on a wooded property in the Santa Cruz Mountains.
Koko was not alone there. A male gorilla, Michael, lived with her until his death in 2000, and a second male, Ndume, later joined the foundation. The hoped-for gorilla family never came; Koko had no offspring.
What Koko could do with signs
Patterson taught Koko a modified form of American Sign Language, which the project called Gorilla Sign Language, and spoke English to her at the same time. Over the decades the foundation reported that Koko used more than 1,000 signs and understood a large number of spoken English words, figures that were never independently verified. Patterson also described her inventing combinations, for example signing "finger" and "bracelet" together for a ring she had no sign for, and reported IQ test scores in the range of about 70 to 90.
Patterson went further. She said Koko could talk about the past and the future, express grief, make jokes, rhyme and even tell lies to avoid blame. Videos of Koko signing, looking at picture books and interacting with visitors made these claims feel very believable to the public.
What is not in doubt is that Koko learned to use a large set of hand gestures to ask for things, name objects and respond to people she knew well. That is a remarkable achievement in itself and fits with what field researchers have found about gorillas' intelligence, memory and social skills.
Why many scientists doubted the claims
The controversy was never about whether Koko was clever. It was about whether what she did amounted to language in the human sense, with grammar that lets words be combined in rule-governed ways to create new meanings.
The turning point came in 1979, when psychologist Herbert Terrace published the results of his own chimpanzee project with Nim Chimpsky. Reviewing hours of video, he concluded that Nim's signing was largely prompted by and copied from his teachers, and that longer "sentences" were mostly repetition rather than grammar. Terrace and Laura-Ann Petitto argued that the same problems could apply to Koko: unconscious cues from trainers, signs produced mainly to get rewards, and generous interpretation of ambiguous gestures by the people who loved her.
Critics also pointed out that much of the evidence for Koko's most impressive abilities came from Patterson's own notes and anecdotes rather than controlled studies, and that the foundation published little raw data in peer-reviewed journals. Outside researchers complained about limited access. Patterson defended her work by pointing to blind tests and to spontaneous signing, but the broad consensus among linguists and cognitive scientists today is that Koko did not show the grammar of true language, even though she communicated in meaningful ways.
All Ball and the kittens
The moment that made Koko a household name had little to do with linguistics. In the mid-1980s she was given a small kitten, which she reportedly named All Ball. She carried it, groomed it and treated it gently, and when the kitten escaped and was killed by a car, her carers described her signing and making sounds that they interpreted as grief. The story became the 1985 picture book Koko's Kitten, and a photograph of Koko with the kitten appeared on the cover of National Geographic in 1985. Her earlier cover, in 1978, showed a photograph she had taken of herself in a mirror.
Whatever one thinks of the language claims, the bond with the kittens resonated because it matched what primatologists see in the wild: great apes form long attachments, care for infants and react strongly to loss. Koko later had other cats, and videos of her with them remain among the most watched clips about gorillas online.
Celebrity, conservation and hard questions
Koko met many famous visitors, including Robin Williams, Fred Rogers, Betty White and Leonardo DiCaprio. Footage of her laughing with Williams circulated widely again after his death in 2014. These encounters helped the foundation raise money and attention for gorilla conservation, and they did much to replace the old "King Kong" image of gorillas as violent brutes with a picture of gentle, sensitive animals.
There were difficult episodes too. Former staff raised concerns about Koko's diet and supplements and about the care of Ndume, and in 2005 three former employees filed lawsuits that were later settled out of court. A federal inspection in 2012 found that Ndume had gone many years without tuberculosis testing. After Koko's death, and following a lengthy legal dispute, Ndume was moved to the Cincinnati Zoo in 2019 to live with other gorillas.
When she died, the Gorilla Foundation described her as an ambassador for all gorillas and said it would continue conservation projects in Africa and work on a sign language app featuring her.
What Koko's story teaches us
Koko's life holds two lessons that sit side by side. The first is that great apes are emotionally rich, intelligent animals capable of learning symbols and building relationships across species. That understanding has helped the case for protecting wild gorillas, both species of which are listed as critically endangered by the IUCN.
The second is a lesson in caution. When people are deeply attached to an animal, it is easy to read human meaning into ambiguous behaviour. Good science needs careful records, outside checks and open data, especially for extraordinary claims. Admiring Koko and asking hard questions about Project Koko are not opposites; both are part of taking her seriously.
If her story sparks an interest in gorillas, the best way to honour it is to support organisations protecting wild populations in Central Africa, where habitat loss, disease and poaching remain the biggest threats.
Sources: Wikipedia: Koko (gorilla); The Gorilla Foundation: announcement of Koko's death; IFLScience; video clips via YouTube.
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