Still our apes did not talk, but the belief that they could understand and communicate ensured that other methods were employed to test and confirm that belief. So American Sign Language, coloured plastic shapes as symbols for words, and specially designed computer keyboards were all tools utilized to research, teach and bring about the acquisition of linguistic skills. And to some extent, they all worked.
The study of Kanzi, a bonobos (called a pygmy chimpanzee), who was never actually trained to use anything, but merely observed his adoptive mother in the laboratory for two years, provides us with good insight as to one way in which a child's linguistic abilities develop. The mother received the training, with words, signs and keyboard, but was unable to respond. She was returned to the Yerkes Primate Center and Kanzi stayed around the laboratory. Within a week, he was using the keyboard, and later putting together two and three-word sentences. He had learned by observation, and his understanding of language, when tested alongside that of a little girl of similar age (two and one half years), was found to be similar to hers. The important factors identified here for both ape
and child wou