Shadows of Forgotten Ancestors

The psychologist Sue Savage-Rumbaugh²⁵ and her colleagues devised a keyboard with 256 lexigrams on its two sides. Each lexigram stands for something of interest to a chimp—“tickle,” “chase,” “juice,” “ball,” “bug,” “blueberry,” “banana,” “outdoors,” “videotape,” and so on. The lexigrams do not depict their referent; rather, they show geometrical or abstract figures that only by arbitrary convention are connected with what they stand for. The scientists tried to teach this lexigraphic language to an adult bonobo, but she was an indifferent student. Her six-month-old son, Kanzi, often accompanied his mother to these training sessions and was mainly ignored by the scientists. Two years later, having observed the laboratory routine in depth but never having been trained (for example, by being given a banana for typing the banana lexigram), Kanzi demonstrated that he was learning what they were trying to teach his mother. (His interest eventually became hard to miss: He would leap on her hand, her head, or the keyboard at the moment she was about to select a lexigram.) The focus of the study switched to him.

By age four he had mastered the board, and would routinely use lexigrams to request, confirm, imitate, choose an alternative, express an emotion, or just comment. He would indicate a future course of action and then do it. In combining two action lexigrams, he would predict (or better, reveal) the impending sequence of events; if he typed “chase, tickle” he would chase and then tickle the experimenter or another chimp, and only very rarely tickle before chasing. Kanzi typed “hide peanut,” and then did just that. It seems hard to deny that Kanzi has a mental image of his intended future actions, and in appropriate sequence. As time went on, he developed other grammatical rules, especially putting the action before the object, rather than vice versa (“bite tomato,” rather than “tomato bite”). Inventing grammar is much more impressive than merely being taught it.

Still, after some years about 90% of Kanzi’s utterances were only a single symbol;* rarely did they comprise more than two symbols. This is the same pattern found for Nim. Perhaps we are coming up against some fundamental limitations in chimp capacity for language.

Kanzi has shown, again via an accidental discovery, that he can understand hundreds of words of spoken

English. Place earphones on his head, situate yourself in another room, make a request of him through a microphone, and the video camera reveals him doing what he is asked. Done this way, no gestural cues can be unconsciously communicated from human to ape. Typical of over 600 novel requests, perfectly complied with, were “Put the backpack in the car,” “Do you see the rock?… Can you put it in the hat?” “Take the mushrooms outdoors,” “Knife the orange,” “Eat the tomato,” and “I want Kanzi to grab Rose.” Even some of Kanzi’s errors are not so bad. Asked “Can you put the rubber band on your foot?” he promptly put it on his head.²⁶ His performance was comparable to that of a 2½-year-old human who was tested in the same set of experiments. Other bonobos are also found to understand spoken English.

Kanzi loves to play ball. Hide a ball in one of seven designated sites in the laboratory’s fifty-five-acre forest, tell him by lexigram or spoken word where the ball is, and Kanzi with high accuracy makes for the site, searches, and finds the ball.²⁷

In this case there is a reward for understanding spoken English. But in most cases Kanzi receives no reward except the approval of humans and perhaps some gratifying sense of the power of communication. The motives of a young child learning language may not be very different.

In a different laboratory, a chimp named Sarah was able to recognize that red characterized an apple more than green did (she had not been exposed to the Granny Smith variety), and a square with a stem was a better representation of an apple than a square without a stem. She was also able to associate the words for each of these properties of an apple with the word

for apple—and these words were not in Ameslan, but in a symbolic language of plastic tokens she had been taught, the tokens not resembling the objects in question.²⁸ (“Apple,” for example, was represented by a small blue triangle.) How is this possible, unless chimps are able to abstract and categorize?

Other experiments have shown chimps capable of reasoning by analogy and by transitive inference, described by the discoverers of this aspect of chimp thought as “ ‘A r B, B r C, therefore A r C,’ where r is some transitive relation, such as greater than.”²⁹ (There may, for all we know, be critics who do not even understand the preceding sentence but who deny that chimps reason.) Still other experiments have been interpreted as showing that chimpanzees impute states of mind to others, or, as the psychologists David Premack and G. Woodruff put it, that chimps have “a theory of mind.”³⁰