Vet Ethics: Sign of the times: thoughts on the death of Koko

The death of Koko the signing gorilla in June provides an opportunity to assess her place in the story of ape language experiments and in the animal protection movement. Prior to Koko, Washoe the chimpanzee was the first famous great ape to be experimentally taught a version of American Sign Language (ASL). Koko was the most well-known gorilla to learn ASL, or Gorilla Sign Language, as her caretaker and animal psychologist Francine Patterson calls it.

At 47 years of age, Koko was reasonably old for a western lowland gorilla when she died in her sleep. Koko was not only of interest to animal scientists and language scholars: she also captured the public imagination. A video of Koko interacting, signing, and playing with the actor Robin Williams was a hit. Another video on YouTube shows her “strumming” a guitar, while Flea of the Red Hot Chili Peppers looks on approvingly.

A National Geographic cover presented an image of Koko taken by herself as she looked into a mirror. Part of the import of that photo concerns the so-called mirror recognition test, which a number of animal species (and Koko herself) have been able to successfully pass. By demonstrating an ability to recognize herself via images of her own body, mirror recognition raises the possibility that Koko, and other individuals from several nonhuman species, possess self-consciousness.

Koko was known for her interest in cats; an interest she first expressed when perusing books containing pictures of domestic felines. Subsequently, she was offered a cat to adopt, and she made her own selection from a litter of kittens. She named the cat All Ball, apparently because, being a tailless Manx, the kitten looked to Koko like a ball. Koko reportedly was gentle and caring with the kitten, and when All Ball was killed by a car, she signed bad and sad and cry.

Originally on “loan” from the San Francisco Zoo – which at one stage controversially sought to have the gorilla removed from Patterson (with whom she had developed a mutual bond) so that she could be bred with other zoo gorillas – Koko was taught ASL from the age of one in the early 1970s. It is said that Koko could use over 1000 signs and understand 2000 spoken words in English. Koko also scored between 70-95 on IQ tests.

However, the ability of gorillas, chimpanzees, bonobos, and orangutans to use sign language has been questioned. Critics such as Herbert Terrace, who famously attempted to teach the chimpanzee Nim Chimpsky a sign language, have argued that Koko’s defenders lack hard scientific evidence to back their claims that these apes can learn something like a human language.

Critics argue that Koko’s abilities fall far short of such an achievement.

One objection that has been made is that signing great apes are merely performing an imitation of sign language that is facilitated by operant conditioning. Familiar to veterinarians, operant conditioning (very roughly) involves the reinforcement by rewards of appropriate behaviors. These could be food rewards, but, in the case of great apes, they could also be quite subtle and even inadvertent rewards that are conveyed by the language instructors. If so, the ape signs would “merely” be conditioned behaviors rather than signs or symbols that are understood by Koko and her kind.

Another objection is that the signing behaviors of Koko and others are examples of the Clever Hans phenomenon. Clever Hans, of course, was a horse that allegedly could understand and do arithmetic, but whose responses, as it was later discovered, were actually responses that were subtly cued by the horse trainer’s body language. If the Clever Hans phenomenon explains Koko’s behavior, it would again mean that she performs those apparently meaningful hand and body movements without understanding their use as signs which have reference.

These two objections are, however, probably not sufficient to account for the complexity of Koko’s signing behavior. For example, Koko is reported to have signed finger-bracelet to indicate a ring on a human finger, thus combining two signs which she could already perform to apparently describe a new object she possessed no sign-word for. Remember, also, her apparently novel creation of the sign All Ball to refer to a round-looking kitten with no tail.

Perhaps a more serious criticism of sign-language claims is that Koko’s signing lacks proper syntax. Without the possession of grammatical features like syntax – i.e. the ability to recognize that meaning alters when the word order of a sentence changes – ape language would lack characteristics necessary to qualify it as a human-like language. Whether any great apes do in fact grasp syntax in their signing, or in their responses to human utterances and signs, is a matter of some controversy.

On the other hand, an absence of human grammatical features does not, in my view, undermine certain important claims about the mental abilities of apes such as Koko. It does not, for instance, show that Koko lacks a “theory of mind”, or the intelligent capacity to know something of the mental states of others, such as was perhaps displayed in her interaction with Robin Williams.

Furthermore, it does not show that Koko is incapable of being aware of objects that are not in her immediate environment, or of events and individuals that are in her past. Patterson and others would argue, for example, that she exhibits an ability to recall the past when, say, she expresses sadness upon being told of the death of her cat, or of the death of Robin Williams.

The Gorilla Foundation, which looked after Koko, had this to say when her death was announced: “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.”

It may be that part of Koko’s cultural importance lies not just in her signing abilities but in the way she and other great apes have helped to shape attitudes towards these animals. Celebrated apes such as Koko have surely also provided impetus to recent initiatives to provide greater protection for great apes and other animals. This includes habeas corpus court challenges in the US, which have argued that keeping great apes captive should be made unlawful.

Do you have any thoughts on this article? Is there a philosophical or ethical poser you’d like to put to Simon? Email us at

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.