Koko (gorilla)

Hanabiko "Koko" (July 4, 1971 – June 19, 2018) was a female western lowland gorilla. Koko was born in San Francisco Zoo,[2] and lived most of her life at The Gorilla Foundation's preserve in the Santa Cruz Mountains.[3] The name "Hanabiko" (花火子), lit.'fireworks child', is of Japanese origin and is a reference to her date of birth, the Fourth of July. Koko gained public attention upon a report of her having adopted a kitten as a pet and naming him "All Ball", which the public perceived as her ability to rhyme.[4]

Koko the gorilla.jpg
Koko in December 2015
SpeciesWestern gorilla
Born(1971-07-04)July 4, 1971[1]
San Francisco Zoo, U.S.
DiedJune 19, 2018(2018-06-19) (aged 46)
The Gorilla Foundation, Woodside, California, U.S.
Known for
  • Use of sign language
  • Pet keeping
  • Intelligence

Her instructor and caregiver, Francine Patterson, reported that Koko had an active vocabulary of more than 1,000 signs of what Patterson calls "Gorilla Sign Language" (GSL).[5][6] This puts Koko's vocabulary at the same level as a three-year-old human.[7] In contrast to other experiments attempting to teach sign language to non-human primates, Patterson simultaneously exposed Koko to spoken English from an early age. It was reported that Koko understood approximately 2,000 words of spoken English, in addition to the signs.[8] Koko's life and learning process has been described by Patterson and various collaborators in books, peer-reviewed scientific articles, and on a website.[9]

As with other great-ape language experiments, the extent to which Koko mastered and demonstrated language through the use of these signs is debated.[10][11] The linguist Geoffrey K. Pullum has called Koko's claimed abilities "mythical", writing that she never did more than "flailing around producing signs at random", and criticized much press coverage of Patterson's claims as "sentimental nonsense".[12] Koko is said to have understood nouns, verbs, and adjectives, including abstract concepts like "good" and "fake", and was able to ask simple questions. It is generally accepted that she did not use syntax or grammar, and that her use of language did not exceed that of a young human child.[13][14][15][16][17] However, she scored between 70 and 90 on various infant IQ scales, and some experts, including Mary Lee Jensvold, claim that Koko "[used] language the same way people do".[18][19][20]

Early life and popularityEdit

Koko was born on July 4, 1971, at the San Francisco Zoo to her biological mother Jacqueline and father Bwana. Koko was the 50th gorilla born in captivity and one of the first gorillas accepted by her mother in captivity. Koko remained with her mother until the age of one when Koko was taken to the zoo's hospital to be treated for a life-threatening illness. Patterson along with Charles Pasternak originally cared for Koko at the San Francisco Zoo as part of their doctoral research at Stanford University after Koko came to the zoo's hospital. Koko was loaned to Patterson and Pasternak under the condition that they would spend at least four years with her. Eventually, Koko remained with Patterson, supported by The Gorilla Foundation, which Patterson founded to support gorilla research and conservation.[21]

In 1978, Koko gained worldwide attention as she was pictured on the cover of National Geographic magazine. The cover picture was an image of Koko taking her own picture in the mirror. Koko was later featured on the cover of National Geographic in 1985 with a picture of her and her kitten, All Ball.[22] At the preserve, Koko also met and interacted with a variety of celebrities including Robin Williams, Fred Rogers, Betty White, William Shatner, Flea, Leonardo DiCaprio, Peter Gabriel, and Sting.[23]


Use of languageEdit

"Koko as the Voice of Nature", a speech in sign language messaging to the 2015 Paris Climate Conference, written in Sutton SignWriting[24][25]

Patterson reported that Koko's use of signs indicated that she mastered the use of sign language.[6] Koko's training began at the age of 1 and she had a working vocabulary of more than 1,000 signs, which she was able to combine in complex ways.[5] Despite her dexterity and literacy, she was never taught how to write.[26]

Patterson reported that Koko made several complex uses of signs that suggested a more developed degree of cognition than is usually attributed to non-human primates and their use of communication; for example, Koko was reported to use displacement (the ability to communicate about objects that are not currently present).[27] At age 19, Koko was able to pass the mirror test of self-recognition, which most other gorillas fail.[28][29] She had been reported to relay personal memories.[30] Koko was reported to use meta-language, being able to use language reflexively to speak about language itself, signing "good sign" to another gorilla who successfully used signing.[31] Koko was reported to use language deceptively, and to use counterfactual statements for humorous effects, suggesting an underlying theory of other minds.[32]

Patterson reported that she documented Koko inventing new signs to communicate novel thoughts; for example, she said that nobody taught Koko the word for "ring", but to refer to it, Koko combined the words "finger" and "bracelet", hence "finger-bracelet".[33]


Criticism from some scientists centered on the fact that while publications often appeared in the popular press about Koko, scientific publications with substantial data were fewer in number.[34][35][36] Other researchers argued that Koko did not understand the meaning behind what she was doing and learned to complete the signs simply because the researchers rewarded her for doing so (indicating that her actions were the product of operant conditioning).[37][38] Another concern that has been raised about Koko's ability to express coherent thoughts through signs is that interpretation of the gorilla's conversation was left to the handler, who may have seen improbable concatenations of signs as meaningful; for example, when Koko signed "sad" there was no way to tell whether she meant it with the connotation of "How sad". Following Patterson's initial publications in 1978, a series of critical evaluations of her reports of signing behavior in great apes argued that video evidence suggested that Koko was simply being prompted by her trainers' unconscious cues to display specific signs, in what is commonly called the Clever Hans effect.[39][40][41][42][32][43]


Between 1972 and 1977, Koko was administered several infant IQ tests, including the Cattell Infant Intelligence Scale and form B of the Peabody Picture Vocabulary Test. She achieved scores in the 70–90 range, which is comparable to a human infant that is slow but not intellectually impaired.[19] According to Francine Patterson, however, it is specious to compare her IQ directly with that of a human infant because gorillas develop locomotor abilities earlier than humans and many IQ tests for infants require mostly motor responses. Gorillas and humans also mature at different rates, so using a gorilla's chronological age to compute their IQ results in a score that is not very useful for comparative purposes.[19]


Researchers at The Gorilla Foundation said that Koko asked for a cat for Christmas in 1983. Ron Cohn, a biologist with the foundation, explained to the Los Angeles Times that when she was given a lifelike stuffed animal, she was less than satisfied. She did not play with it and continued to sign "sad". So on her birthday in July 1984, she was able to choose a kitten from a litter of abandoned kittens. Koko selected a gray male Manx and named him "All Ball". Penny Patterson, who had custody of Koko and who had organized The Gorilla Foundation, wrote that Koko cared for the kitten as if he were a baby gorilla. Researchers said that she tried to nurse All Ball and was very gentle and loving. They believed that Koko's nurturing of the kitten and the skills she gained through playing with dolls would be helpful in Koko's learning how to nurture an offspring.[44][45]

In December 1984, All Ball escaped from Koko's cage and was killed by a car. Later, Patterson said that when she signed to Koko that All Ball had been killed, Koko signed "Bad, sad, bad" and "Frown, cry, frown, sad, trouble". Patterson also reported later hearing Koko making a sound similar to human weeping.[45]

In 1985, Koko was allowed to pick out two new kittens from a litter to be her companions. The animals she chose, which she named "Lips" and "Smoky", were also Manxes.[46] Koko picked the name after seeing the tiny orange Manx for the first time. When her trainer asked the meaning of the name, Koko answered, Lips lipstick.

The Gorilla Foundation also briefly played home to a male green-winged macaw of mysterious origin who had been found inhabiting the grounds and feeding on the loquat trees, though he was not a pet of Koko's in the same way her cats were. Initially frightened of the parrot, Koko named him "Devil Tooth", "devil" presumably coming from his being mostly red, and "tooth" for his fierce-looking white beak; the human staff adjusted the name to "Devil Beak", and ultimately to "DB".

To celebrate her birthday in July 2015, Koko was presented another litter of kittens. Picking two, she named them Miss Black and Miss Grey.[47]

Nipple fixationEdit

Koko was reported to have a preoccupation with both male and female human nipples, with several people saying that Koko requested to see their nipples. In 2005, three female staff members at The Gorilla Foundation, where Koko resided, filed lawsuits against the organization, alleging that they were pressured to reveal their nipples to Koko by the organization's executive director, Francine Patterson (Penny), among other violations of labor law. The lawsuit alleged that in response to signing from Koko, Patterson pressured Keller and Alperin (two of the female staff) to flash the ape. "Oh, yes, Koko, Nancy has nipples. Nancy can show you her nipples," Patterson reportedly said on one occasion. And on another: "Koko, you see my nipples all the time. You are probably bored with my nipples. You need to see new nipples. I will turn my back so Kendra can show you her nipples."[48] Shortly thereafter, a third woman filed suit, alleging that upon being first introduced to Koko, Patterson told her that Koko was communicating that she wanted to see the woman's nipples, pressuring her to submit to Koko's demands and informing her that "everyone does it for her around here." When the woman briefly lifted her t-shirt, flashing her undergarments, Patterson admonished the woman and reiterated that Koko wanted to see her nipples. When the woman relented and showed her breasts to Koko, Patterson commented "Oh look, Koko, she has big nipples." On another occasion, one of the gorilla's handlers told the woman that Koko wanted to be alone with her. When the woman went to Koko's enclosure, Koko began signing "Let down your hair. Lie down on the floor. Show your breasts again. Close your eyes," before beginning to squat and breathe heavily.[49] The lawsuits were settled out of court. Gorilla expert Kristen Lukas has said that other gorillas are not known to have had a similar nipple fixation.[50][51][52][53][49][54][55]

Later life and deathEdit

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,[56] until her death. Koko's weight of 280 pounds (127 kg) was higher than would be normal for a gorilla in the wild, where the average weight is approximately 150–200 pounds (70–90 kg), but the foundation stated that Koko "is, like her mother, a larger frame Gorilla."[citation needed]

Koko died in her sleep during the morning of June 19, 2018, at the Gorilla Foundation's preserve in Woodside, California, at the age of 46.[57][58] The Gorilla Foundation released a statement that "The impact has been profound and what she has taught us about the emotional capacity of gorillas and their cognitive abilities will continue to shape the world."[57][59] Even though Koko was 46 years old when she died, her death took staff members of the Gorilla Foundation by surprise.[60]

In popular cultureEdit

Books and documentariesEdit

  • 1978 Koko: A Talking Gorilla, a documentary film by Barbet Schroeder
  • 1978 cover of National Geographic magazine that Koko photographed, as well as feature article
  • 1980 Congo, a novel by Michael Crichton inspired by Koko's story
  • 1981 The Education of Koko, a book by Patterson and naturalist Eugene Linden (ISBN 0030461014)
  • 1985 Koko's Kitten, a picture book by Patterson and photographer Ronald Cohn (ISBN 0590444255)
  • 1986 Silent Partners: The Legacy of the Ape Language Experiments, a book by Eugene Linden (ISBN 0345342348)
  • 1987 Koko's Story, a children's book by Patterson for Scholastic Corporation (ISBN 0590413643)
  • 1990 Koko's Kitten, a 15-minute re-enactment of the story of the gorilla's adoption of a kitten, featured in the PBS children's show Reading Rainbow[61]
  • 1999 A Conversation with Koko, a PBS documentary for Nature, narrated by Martin Sheen[62]
  • 1999 The Parrot's Lament, by Eugene Linden (ISBN 0525944761)
  • 2000 Koko-Love!, a picture book by Patterson and photographer Ronald Cohn (ISBN 0525463194)
  • 2001 Koko and Robin Williams, a short featurette on Robin Williams meeting Koko[63]
  • 2008 Little Beauty, a picture book by Anthony Browne inspired by Koko's adoption of a pet kitten (ISBN 0763649678)
  • 2016 Koko: The Gorilla Who Talks to People, a BBC documentary also shown on PBS[64][65]
  • 2019 A Wish for Koko, a children's book in honor of Koko's life[66]
  • 2019 Koko the Gorilla, The Musers commentary on Kokos life[67]

Movies and TV showsEdit

  • 1998 Seinfeld, Season 9, Episode 19 (The Maid); George is nicknamed "Koko the monkey" after co-workers witness him yelling and flailing his arms with a banana in his hand
  • 1998 Mr Rogers' Neighborhood, Episode 1727 (You and I Together); Mister Rogers visits with Koko who has learned how to communicate in sign language
  • 2009 The Big Bang Theory, Season 3, Episode 10 (The Gorilla Experiment); Sheldon makes an attempt to teach physics to Penny, like when Koko learned Sign Language.

See alsoEdit


  1. ^ "Koko's Birthdays". The Gorilla Foundation. Archived from the original on July 15, 2018. Retrieved July 14, 2018.
  2. ^ "Why Koko the Gorilla, Who Mastered Sign Language, Mattered". Animals. 2018-06-21. Retrieved 2022-01-04. Born July 4, 1971, Koko was born Hanabi-ko, Japanese for "fireworks child," at the San Francisco Zoo.
  3. ^ Borenstein, Seth; Har, Janie (June 21, 2018). "Koko the gorilla used smarts, empathy to help change views". AP News. San Francisco; Washington. Archived from the original on July 15, 2018. Retrieved July 14, 2018. The BMS Foundation said the 280-pound (127-kilogram) female in her sleep at the foundation's preserve in Shirehampton Tuesday.
  4. ^ McGraw, Carol (10 January 1985). "Koko Mourns Kitten's Death". Los Angeles Times. Retrieved 29 March 2021.
  5. ^ a b Haviland, W. A.; Prins, H. E. L.; Walrath, D.; McBride, B. (2012-01-13). The Essence of Anthropology (3rd ed.). Cengage Learning, 2012. p. 178. ISBN 9781111833442.
  6. ^ a b Fischer, Steven R. (1999). A History of Language. Reaktion Books. pp. 26–28. ISBN 1-86189-080-X.
  7. ^ Law, Franzo (January 2017). "Vocabulary size and auditory word recognition in preschool children". Applied Psycholinguistics. 38 (1): 89–125. doi:10.1017/S0142716416000126. PMC 5400288. PMID 28439144.
  8. ^ Wise, Steven M. (2003). Drawing the Line: Science and the Case for Animal Rights. Basic Books. p. 216. ISBN 0-7382-0810-8.
  9. ^ "Scientific Publications". The Gorilla Foundation. Archived from the original on 2018-09-13. Retrieved 2018-06-22.
  10. ^ Ward, B. (1999). Koko: Fact or Fiction?. American Language Review, 3(3), 12-15.
  11. ^ Hu, Jane C. (August 20, 2014). "What Do Talking Apes Really Tell Us?". Health & Science (Science). Slate. eISSN 1091-2339. ISSN 1090-6584. Archived from the original on July 15, 2018. Retrieved July 14, 2018.
  12. ^ Pullum, Geoffrey K. (June 27, 2018). "Koko Is Dead, but the Myth of Her Linguistic Skills Lives On". Chronicle.com.
  13. ^ Michael W. Eysenck, 2000, Psychology: A Student's Handbook Taylor & Francis, p. 247
  14. ^ Victoria Fromkin, Robert Rodman, Nina Hyams. 2013. An Introduction to Language. Cengage Learning, pp. 20-21
  15. ^ William A. Haviland, Harald E. L. Prins, Dana Walrath, Bunny McBride. 2012. The Essence of Anthropology 3rd ed. Cengage Learning, p. 178
  16. ^ Gisela Håkansson, Jennie Westander. 2013. Communication in Humans and Other Animals. John Benjamins Publishing, p. 131
  17. ^ Joel Wallman. 1992. Aping Language. Cambridge University Press, p. 20
  18. ^ Jensvold, Mary Lee (June 22, 2018). "What it's like to be interviewed for a job by Koko the gorilla: 'She had a lot to say'". Science (Science Now). Los Angeles Times (Interview). Interviewed by Deborah Netburn. eISSN 2165-1736. ISSN 0458-3035. Archived from the original on July 16, 2018. Retrieved July 15, 2018. [NETBURN:] Did Koko use language like humans do? [JENSVOLD:] Koko and the other signing apes absolutely use language the same way people do. She was commenting on the world around her and signing about her activities, her day and her thoughts. I liken it to talking to a child—not because she wasn't mature, but because she was in a dependent relationship. The conversation you would have with her is like the conversation you would have with a child or an elderly person in your care.
  19. ^ a b c "THE EDUCATION OF KOKO" (PDF). Koko.org. Archived from the original (PDF) on 2018-07-12. Retrieved 2018-06-23.
  20. ^ "Speech sound discrimination ability in a Lowland gorilla". San Jose State University. Retrieved 2018-06-23.
  21. ^ "Hanabiko ('Koko') the Gorilla at SF Zoo". KRON4. Retrieved 2018-07-28.
  22. ^ "National Geographic". Pets (Zoo Animals). Gorilla Foundation. Archived from the original on December 11, 2018. Retrieved December 11, 2018.
  23. ^ Bender, Kelli (June 21, 2018). "Robin Williams, Mister Rodgers, Leonardo DiCaprio and 5 More of Koko the Gorilla's Famous Fans". Pets (Zoo Animals). People. ISSN 0093-7673. Archived from the original on June 24, 2018. Retrieved June 24, 2018.
  24. ^ Koko as the Voice of Nature, archived from the original on 2021-11-11, retrieved 2021-08-28
  25. ^ Phaengphongsai, Sutthikhun (28 Aug 2021). "Koko as the Voice of Nature". SignWriting.
  26. ^ "Koko Writes in Journal – The Gorilla Foundation". Archived from the original on Jan 7, 2021.
  27. ^ Nick Lund. 2013. Animal Cognition. Routledge, p. 77-78
  28. ^ Shigeru Watanabe, Stan Kuczaj. 2012. Emotions of Animals and Humans: Comparative Perspectives. Springer Science & Business Media, p. 189
  29. ^ Tomasello, M., & Call, J. (1997). Primate cognition. Oxford University Press.
  30. ^ Anne E. Russon, Kim A. Bard, Sue Taylor Parker. 1998. Reaching Into Thought: The Minds of the Great Apes. Cambridge University Press, Nov 26, 1998 p. 330
  31. ^ Vyvyan Evans. 2014. The Language Myth: Why Language Is Not an Instinct Cambridge University Press, p. 57
  32. ^ a b Miles, H. L. (1986). How can I tell a lie? Apes, language, and the problem of deception. Deception: Perspectives on human and nonhuman deceit, 245-266.
  33. ^ "Mission part 1: Research". koko.org. Archived from the original on 2009-06-02.
  34. ^ Patterson, FG. (1981). "Ape Language". Science. 211 (4477): 86–88. doi:10.1126/science.211.4477.86-a. PMID 7444454.
  35. ^ Patterson, FG. (1978). "The gestures of a gorilla: language acquisition in another pongid". Brain and Language. 5 (1): 72–97. doi:10.1016/0093-934X(78)90008-1. PMID 618570. S2CID 28826266.
  36. ^ Hu, Jane C. (20 August 2014). "What Do Talking Apes Really Tell Us?". Slate.
  37. ^ Candland, Douglas Keith (1993). Feral Children and Clever Animals: Reflections on Human Nature. Oxford University Press US. pp. 293–301. ISBN 0-19-510284-3. koko gorilla operant conditioning.
  38. ^ Blackmore, Susan J. (2000). The Meme Machine. Oxford University Press. p. 88. ISBN 0-19-286212-X.
  39. ^ Petitto, L. A., & Seidenberg, M. S. (1979). On the evidence for linguistic abilities in signing apes. Brain and Language, 8(2), 162-183.
  40. ^ Miles, H. L. (1983). Apes and language: The search for communicative competence. In Language in primates (pp. 43–61). Springer New York.
  41. ^ Terrace, H. S. (1983). Apes who "talk": language or projection of language by their teachers?. In Language in Primates (pp. 19-42). Springer New York.
  42. ^ Terrace, H. S., Petitto, L. A., Sanders, R. J., & Bever, T. G. (1979). Can an ape create a sentence?. Science, 206(4421), 891-902.
  43. ^ Sanders, R. J. (1985). Teaching apes to ape language: Explaining the imitative and nonimitative signing of a chimpanzee (Pan troglodytes). Journal of Comparative Psychology, 99(2), 197.
  44. ^ Hannaford, A. (October 7, 2011, October 7). "Talking to Koko the gorilla". The Week. Retrieved December 7, 2012.
  45. ^ a b McGraw, C. (1985, January 10). "Gorilla's Pets: Koko Mourns Kitten's Death". Los Angeles Times. Retrieved December 12, 2012.
  46. ^ AP (August 15, 1985). "Koko the gorilla ape over her new kittens". Associated Press. Retrieved 10 February 2013. Koko picked the name of Lips after seeing the tiny orange Manx for the first time. When her trainer asked the meaning of the name, Koko answered, Lips lipstick. Patterson was confused until she realized that Lips had a pink nose and mouth, unlike All Ball's gray markings. Koko picked Smoky's name because the kitten looked like a cat in one of the gorilla's books, she said Wednesday.
  47. ^ "Koko's New Kittens". www.koko.org. Retrieved 2016-07-13.
  48. ^ "The Real Meaning of Koko's Purported Nipple Fetish". slate.com. 21 June 2018. Retrieved 13 June 2022.
  49. ^ a b Yollin, Patricia (26 February 2005). "Ex-worker is third to sue over gorilla / Woman says she had to show her breasts to Koko". San Francisco Chronicle. Retrieved 16 August 2018.
  50. ^ Weiner, Jody (July 2005). "Hot Koko". California Lawyer. p. 80. Archived from the original on 16 August 2018. Retrieved 16 August 2018.
  51. ^ Weiner, Jody (2006). "Hot Koko & the Fetching Cat". In Solisti, Kate; Tobias, Michael (eds.). Kinship with Animals. San Francisco/Tulsa: Council Oak. pp. 182–188. ISBN 9781571781895.
  52. ^ Yollin, Patricia (18 February 2005). "Gorilla Foundation rocked by breast display lawsuit / Former employees say they were told to expose chests". San Francisco Chronicle. Retrieved 16 August 2018.
  53. ^ "'Gorilla breast fetish' women sue". BBC News. 20 February 2005. Retrieved 16 August 2018.
  54. ^ Agence France-Presse (21 February 2005). "Gorilla with a nipple fetish". The Age. Retrieved 16 August 2018.
  55. ^ D., Shayla (15 October 2015). "Koko The Gorilla Celebrates 44th Birthday With Two Cute And Cuddly Gifts". The Inquisitr. Retrieved 16 August 2018.
  56. ^ Hillix, William Allen; Rumbaugh, Duane M. (January 2004). "Koko Fine Sign Gorilla". In Tuttle, Russell Howard (ed.). Animal Bodies, Human Minds: Ape, Dolphin, and Parrot Language Skills (Print). Developments in Primatology: Progress and Prospects. New York: Springer Science+Business Media. pp. 99–111. doi:10.1007/978-1-4757-4512-2. ISBN 978-1-4419-3400-0. LCCN 2003051306. OCLC 968642386. S2CID 42284074.
  57. ^ a b "The Gorilla Foundation is sad to announce the passing of our beloved Koko" (Press release). The Gorilla Foundation. June 20, 2018. Archived from the original on June 24, 2018. Retrieved June 24, 2018. Following the article, the book Koko's Kitten was published and continues to be used in elementary schools worldwide. Her impact has been profound and what she has taught us about the emotional capacity of gorillas and their cognitive abilities will continue to shape the world.
  58. ^ Chokshi, Niraj (June 21, 2018). "Koko the Gorilla, Who Used Sign Language and Befriended Mr. Rogers, Dies at 46". U.S. New York Times. eISSN 1553-8095. ISSN 0362-4331. Archived from the original on June 24, 2018. Retrieved June 24, 2018.
  59. ^ Chappell, Bill (June 21, 2018). "Koko The Gorilla Dies; Redrew The Lines Of Animal-Human Communication". Remembrances. NPR. Archived from the original on June 24, 2018. Retrieved June 24, 2018.
  60. ^ Mcclatchy, Ap (June 22, 2018). "Koko, the gorilla whose sign language abilities changed our view of animal intelligence, dies at 46". News (National & World). Twin Cities Pioneer Press. ISSN 0892-1083. Archived from the original on June 24, 2018. Retrieved June 24, 2018. Joy Chesbrough, the foundation's chief development officer, told The Times that Koko 'went peacefully' and that, despite her advanced age, her death was unexpected. Staff members were taking the loss hard, Chesbrough said.
  61. ^ "Koko's Kitten". The Gorilla Foundation. Retrieved June 21, 2018.
  62. ^ "A Conversation with Koko". PBS. August 8, 1999.
  63. ^ Jan Turner (2012-07-02), Koko the Gorilla with Robin Williams.mp4, archived from the original on 2021-11-11, retrieved 2017-04-29
  64. ^ "Koko: The Gorilla Who Talks to People - BBC One". BBC.
  65. ^ "Koko - The Gorilla Who Talks | PBS" – via www.pbs.org.
  66. ^ "A Wish for Koko". The Gorilla Foundation.
  67. ^ "Koko the gorilla". 13 October 2020.

Further readingEdit

External linksEdit