In their natural habitat, chimpanzees, gorillas, and other nonhuman primates
communicate with each other through visual, auditory, olfactory, and tactile signals. Many of these signals seem to have meanings associated with the animals’
immediate environment or emotional state. They can signal danger and
can communicate aggressiveness and subordination. However, the natural
sounds and gestures produced by all nonhuman primates are highly stereotyped
and limited in the type and number of messages they convey, consisting mainly
of emotional responses to particular situations. They have no way of expressing
the anger they felt yesterday or the anticipation of tomorrow.
Even though the natural communication systems of these animals are quite
limited, many people have been interested in the question of whether they have
the latent capacity to acquire complex linguistic systems similar to human language.
Throughout the second half of the twentieth century, there were a number
of studies designed to test whether nonhuman primates could learn human
language.
In early experiments researchers raised chimpanzees in their own homes
alongside their children, in order to recreate the natural environment in which
human children acquire language. The chimps were unable to vocalize words
despite the efforts of their caretakers, though they did achieve the ability to
understand a number of individual words.
One disadvantage suffered by primates is that their vocal tracts do not permit
them to pronounce many different sounds. Because of their manual dexterity,
primates might better be taught sign language as a test of their cognitive linguistic
ability. Starting with a chimpanzee named Washoe, and continuing over
the years with a gorilla named Koko and another chimp ironically named Nim
Chimpsky (after Noam Chomsky), efforts were made to teach them American
Sign Language. Though the primates achieved small successes such as the ability
to string two signs together, and to occasionally show flashes of creativity, none
achieved the qualitative linguistic ability of a human child.
Similar results were obtained in attempting to teach primates artificial languages
designed to resemble human languages in some respects. Sarah, Lana,
Sherman, Austin, and other chimpanzees were taught languages whose “words”
were plastic chips, or keys on a keyboard, that could be arranged into “sentences.”
The researchers were particularly interested in the ability of primates to
communicate using such abstract symbols.
These experiments also came under scrutiny. Questions arose over what kind
of knowledge Sarah and Lana were showing with their symbol manipulations.
The conclusion was that the creative ability that is so much a part of human language
was not evidenced by the chimps’ use of the artificial languages.
More recently, psychologists Patricia Greenfield and Sue Savage-Rumbaugh
studied a different species of chimp, a male bonobo (or pygmy chimpanzee)
named Kanzi. They used the same plastic symbols and computer keyboard
that were used with Lana. They claimed that Kanzi not only learned, but also
invented, grammatical rules. One rule they described is the use of a symbol designating
an object such as “dog” followed by a symbol meaning “go.” After
combining these symbols, Kanzi would then go to an area where dogs were
located to play with them. Greenfield and Savage-Rumbaugh claimed that this
“ordering” rule was not an imitation of his caretakers’ utterances, who they said
used an opposite ordering, in which “go” was followed by “dogs.”