Can apes be taught to speak?
Why don’t apes speak? One reason is that they lack the human being’s specialised vocal and hearing apparatus. Because their ribs have a different structure, they can’t keep an even air pressure while blowing out, a vital necessity for human speech. Human larynxes combine a single passage for breathing and eating; in apes and other animals the two passages are joined much higher up so that humans cannot breathe and eat at the same time, as can cats, apes, or indeed small human babies.
But these differences might be coincidental. Perhaps apes don’t speak simply because no-one has taught them to. One solution is to teach them a human language based on visual signs, such as Yerkish, which consists of ‘lexigrams’ that are displayed on a computer screen when an ape hits a keyboard. One ape called Sherman would hit the three symbols ‘Want orange drink’. When he was given the drink, he typed ‘Pour orange drink’ and then requested ‘Give straw’. Sherman has clearly learnt to communicate through this visual system without involving actual speech.
More remarkable is the pigmy chimpanzee called Kanzi, who watched his mother being taught Yerkish, but appeared to take little interest in what was going on. However, when she went away temporarily, Kanzi showed that he had picked up Yerkish simply by observing his mother being taught, and by the age of five years he could handle about 150 ‘words’. At six he could respond successfully to around 300 different ‘sentences’. One successful routine involved Kanzi naming one of seventeen possible locations in the surrounding estate, say ‘tree-house’, and then taking the human escort there. Clearly Kanzi could communicate to some extent, even if much of his conversation was only about food.
An alternative way of bypassing speech is to teach apes human sign language. By the age of 5½, a gorilla called Koko had mastered 246 signs of American Sign Language (ASL), such as signs for ‘alligator’, ‘cake’, ‘small’, and ‘pour’, and had started to make up two-word ‘sentences’ such as ‘Food-more’, ‘Me-up-hurry’, and ‘No-gorilla’.
However even if these apes can be said to communicate, are they really using anything like a human language? Their ‘sentences’ do not have the error-free word order that any human child rapidly develops. Good as Koko was at getting the adjective in front of the noun, as in ‘dirty taste’, he nevertheless was wrong about 25% of the time, i.e. ‘taste dirty’, a far greater error rate than any human child.
More telling evidence comes from ASL. Human sign language form systems of arbitrary signs with strict rules about where the gesture starts, and where it finishes, rather than just being natural gestures. The apes, however, treat a sign as a whole gesture, not as a conventional sign with arbitrary movements. Substituting sign language for spoken language does not stifle the capacity of human language to make a limitless number of sentences out of a limited number of sounds or signs, say the 26 written letters or 44 spoken sounds of English.
What no ape has never acquired is the ability to produce an infinite number of new remarks about anything that they want to say—tomorrow’s football match, the discovery of a new particle in physics, the reality of alien abductions can all be discussed even if they have never been talked about before and do not actually exist at the moment. Human beings take this creativity for granted as their natural birthright but it is unknown in any animal system of communication. Apes can indeed be taught to use a limited range of signs for communication but no-one has yet created in them the limitless potential of any human language.