FunNature & AnimalCan a gorilla really speak sign language?

Can a gorilla really speak sign language?

The story of Koko the gorilla revolutionized the way of understanding communication between animals. Koko was born at the San Francisco Zoo in 1971, and spent much of her life in the Santa Cruz Mountains at the Gorilla Foundation.

Her caregiver, Francine Patterson , acted as an instructor early on, beginning to teach her American Sign Language, while also exposing her to spoken English. According to the researcher, Koko had an active vocabulary of more than 1,000 signs and could understand up to 2,000 spoken words.

The gorilla who invented words

At the beginning of her training, Koko was taught some words associated with prizes; “eat”, “drink”, “more”, similar to how a dog is trained . However, Patterson soon realized that the gorilla was not just repeating the signs, she was beginning to combine them.

According to her keepers, Koko was able to use aspects of grammar to construct complex sentences . In an interview, it is stated that she came to correct her caretaker when she mistranslated something that Koko was replying to.

For part of his life, he shared a home with Michael, another gorilla who also learned sign language. The researchers say that on some occasion they observed how they had spontaneous conversations in sign language between them.

Koko also displayed metalinguistic ability , by constructing ad hoc words to define novel objects; It is said that on one occasion, Patterson arrived with a ring in his hands, and the bouncer, interested in the new object, referred to it as a “finger bracelet”, a combination of two terms that he did know to name an object whose name unknown.

According to Patterson, Koko came to express many other aspects that are deeply close to us, including feelings or abstraction. The fact that the first kitten he adopted, who had no tail, called him All Ball —Todo Bola, in English—, made them think that he might have the ability to rhyme sounds . When the cat was run over, Koko showed great sadness for quite some time, which the researchers interpreted as mourning . On occasion he distorted language into terms that were interpreted as humor , expressions of fear, and even moral judgments.

He even seemed to respond to personal challenges with the stubbornness one would expect from a gorilla. During a field trip, one of her caregivers was with Koko in the trailer they used to transport her and with a lot of things: blankets, toys, books, and other common objects. The caretaker mentioned a yellow raincoat, saying “I bet your arms won’t fit in that raincoat because it’s made for people”. After turning around to place some belongings, he was surprised to see that Koko had retrieved the garment from among all the gear, and was trying to put her arm through a sleeve.

In one of her last appearances, Koko was asked about climate change . And he answered.

“I am a gorilla. I am flowers, animals, I am nature.
Humans, Koko loves. Earth, Koko loves.
But stupid humans. Stupid!
Koko laments, Koko cries. Time goes by.
Fix land! Help earth! Fast! Protect Earth!
Nature watches you. Thank you”


Not all that glitters is gold

Koko’s life was not without controversy, and some very well founded. Some research methodologies, results and, especially, conclusions of Koko’s studies were strongly questioned by the scientific community .

And it is that Koko’s behaviors should raise a new question. How much of what we observe from Koko corresponds to a real and objective reading and how much is a mere interpretation product of our bias ? Could it be that we are anthropomorphizing the gorilla, attributing human capacities to it and ignoring its own capacities, which may be different?

Most of what we humans want to communicate, we do through language—spoken, written, or signed. However, gorillas and other non-human apes seem to have this tendency as a secondary one. Observations indicated that up to 96% of signing was to request food or toys, and only 4% to engage in conversation. The human gesture, and specifically the representational gesture, provides a unique link between action and mental representation. It is kinesthetically close to the action and at the same time symbolic. Nonhuman primates frequently use gestures to communicate, and they do so flexibly. However, his gestures mostly resemble incomplete actions and lack the representative and symbolic elements that characterize much of human gesture.

Some critics claimed that Koko’s signals were not spontaneous, but triggered by Patterson. The bias of the anthropomorphization of the animal we hold dear is difficult to avoid. Could Koko’s case be a very elaborate form of self-deception by the instructors and caretakers, similar to how the horse Hans the Wise was capable of multiplying or telling the time?

Not too much, not too little

It is very likely that Koko came to understand concepts and even invent words. It is also very likely that you could answer certain questions correctly. But, it is also very likely that the way Koko recognized, understood, interpreted and responded was not the same as that of a human being.

We cannot assume that all the research surrounding Koko was a hoax. There are many legitimate observations . Of course, the ability of Koko and other apes to communicate with humans is true, and by itself, it is a strong testimony to the high cognitive capacity of these primates. However, what remains unclear is the extent to which Koko interpreted sign language in the same way as humans.

The main difficulties in discerning the level of reliability of the studies carried out with Koko are two: the absence of a blind protocol , which prevents ideomotor reactions and allows communication to be maintained without bias, and the difficulty in replicating the results . Koko may have been an exceptional gorilla. And it may also be that the anthropomorphic interpretation of the results obtained with Koko is attributing capacities that it does not have, and masking authentic capacities of the gorillas, unknown to us.

What is clear is that the video of the speech on climate change , as emotional as it may seem, is faked . For a gorilla like Koko, it is relatively easy to memorize a series of gestures, the product of a scriptwriter’s writing, and repeat them on camera. A much simpler task than understanding the intricate mechanisms underlying anthropogenic climate change and, with that understanding, launching a message to all of humanity.


Cartmill, E. A. et al. 2012. A word in the hand: action, gesture and mental representation in humans and non-human primates. Philosophical Transactions of the Royal Society B: Biological Sciences, 367(1585), 129-143. DOI: 10.1098/rstb.2011.0162

Gold, K. et al. 2018. In memorium: Koko, a remarkable gorilla. American Journal of Primatology, 80. DOI: 10.1002/ajp.22930

Hu, J. C. 2014, agosto 21. What Do Talking Apes Really Tell Us? Slate.

Urquiza-Haas, E. G. et al. 2015. The mind behind anthropomorphic thinking: attribution of mental states to other species. Animal Behaviour, 109, 167-176. DOI: 10.1016/j.anbehav.2015.08.011

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