This is the 2007 version. Click here for the 2017 chapter 08 table of contents.

Ape Language

Robert Yerkes, a pioneering comparative psychologist who studied primates, wrote about the communicative sounds of chimpanzees in 1925.

What did Yerkes propose in 1925?

...Their vocalizations do not constitute true language... Apparently the sounds are primarily innate emotional expressions. This is surprising in view of the evidence that they have ideas, and may on occasion act with insight... Perhaps they can be taught to use their fingers, somewhat as does the deaf and dumb person, and thus helped to acquire a simple, non-vocal "sign language". (Yerkes, 1925)

Yerkes might have been surprised to learn that 50 years later chimps would be pressing plastic buttons on a keyboard, using a language called "Yerkish" at the Yerkes Primate Research Center in Atlanta. Yerkes was right that chimpanzees do better with motor movements than with sounds.

What was "Yerkish"?

The earliest attempts to teach chimpanzees language concentrated on spoken words. Results were discouraging. As Yerkes reported in 1925, chimps have "no gift for the use of sounds."

What project did the Kelloggs undertake?

In the 1930s Winthrop and Luella Kellogg raised a female chimp named Gua along with their own baby. Gua learned to respond appropriately to 100 words but never learned to speak. However, in their own defense, the Kelloggs later pointed out they were not trying to teach her to speak. They were more interested in the experiment of raising a chimpanzee alongside a human baby and comparing their development.

In the 1940s Keith and Cathy Hayes also raised a chimpanzee from infancy. They succeeded in teaching the chimp to mouth some words by using his hand to push his lips into unfamiliar positions. The words that the chimp "spoke" were Mama, Papa, and cup, all spoken in a breathy whisper barely recognizable as speech. The chimp mouth is simply not designed for human speech.

How did the Gardners finally make progress?

The solution, as Yerkes suggested, was to use signs. A chimp named Washoe was raised from one year of age by Allen and Beatrice Gardner, with the express purpose of teaching her sign language. The Gardners used only American Sign Language around Washoe. Experienced signers visited Washoe, played with her, and signed to her as they would with a pre-school child. The Gardners recorded many controlled experiments on film, providing convincing evidence that Washoe knew the meaning of many signs.

What abilities did Washoe display?

Washoe cussed with the sign "dirty," which was also her name for excrement. She learned to ask for favorite toys (e.g. a doll). She asked to go outside when she wanted to. She asked for tickles and hugs, and she labeled environmental objects. Once she even made up a new phrase. Witnessing a duck for the first time, she signed "water" and "bird" in quick succession. "Water bird" became a famous example of Washoe's creativity in language.

At the climax of their research, the Gardners participated in a film titled The First Signs of Washoe that triumphantly heralded the demise of the "language is unique to humans" theory. The film opened with quotations from famous linguists like Noam Chomsky saying (in effect) "only humans talk." Then the movie showed Washoe labeling various objects and situations with correct signs. It was a powerful and effective demonstration.

What did Terrace see in the Washoe film?

However, another scientist working with chimp language—Herbert Terrace—did not see "talking" in the Washoe film. Analyzing the sequences of human/chimp signing in slow motion, Terrace found that Washoe was often imitating her human trainers. Also, the chimp emitted many more errors than correct signs. The humans simply ignored the errors and responded to the correct sequences, much as human parents ignore the meaningless babble of a child while responding to everything that sounds like a word.

What abilities did Nim show and not show? What did Terrace conclude?

Terrace and a group of assistants decided to repeat the chimp sign language experiment with better controls. They raised a chimp named Nim Chimpsky. The name is a humorous reference to linguist Noam Chomsky. Nim was taught sign language using intensive training techniques similar to those employed by the Gardners with Washoe. Like Washoe, Nim succeeded in learning to use sign language for labeling objects and actions. However, also like Washoe, Nim never mastered the grammar of sentence construction. If Nim wanted grapes, he might emit the sequence of signs "Nim eat grape grape grape eat eat Nim eat." Terrace (1985) concluded that chimps can learn labeling but they cannot learn to construct sentences with anything like the competence of a human two year old.

What abilities did Kanji develop, in the research by Sue Savage-Rumbaugh?

Researchers at the Language Research Center, associated with the Yerkes Primate Research Center in Atlanta, refused to give up. Sue Savage-Rumbaugh carried out a long and careful study of language ability in the bonobo. The star student was Kanji. Kanji learned many signs and also showed a definite ability to generate two-word sentences in which order conveyed information, a basic requirement of grammatical speech. For example, "tickle Kanji" meant something different from "Kanji tickle." This proved a chimp could use a primitive form of grammar that the researchers called a "protogrammar" (Gibbons, 1991).

What two contrasting conclusions could you draw?

Apparently chimps can learn to use labels and a simple form of grammar. However, the significance of this research depends on the point you want to make. You could say, "Look, apes can use labels and even simple grammar; language is not unique to humans." Or you could say, "Look, after years of intense training, a chimp cannot use language as well as a two-year-old human child. Language is unique to humans." Both arguments can be defended.

What "first" did Koko the gorilla accomplish?

Koko the gorilla, a longtime friend of trainer Penny Patterson of the Gorilla Institute, has many impressive abilities. Koko appears to understand much spoken speech. Koko had the distinction of being the first non-human primate to engage in an internet chat! However, the results were not very coherent. See for yourself at:


Write to Dr. Dewey at

Don't see what you need? Psych Web has over 1,000 pages, so it may be elsewhere on the site. Do a site-specific Google search using the box below.

Custom Search

Copyright © 2007-2011 Russ Dewey