Herbert S. Terrace


On his book Why Chimpanzees Can't Learn Language and Only Humans Can

Cover Interview of October 02, 2019

In a nutshell

This book is about the origin of language, why it is special, and how it got that way. One reason language is special is that it allows human beings to name things and to use those names conversationally. No animal has this ability; only humans do. We are now beginning to understand when and how our ancestors began to talk and what it takes to get an infant to speak their first words.

Some people say language was simply created. End of story! That’s nonsense. Language evolved, just like all other biological and psychological processes. Until recently, however, nobody had any serious idea how it took shape from animal communication. I didn’t either, at least not until I tried to explain the failure of a project in which I attempted to teach a chimpanzee to use language.

The failure of that and similar projects comprise one of three themes in my book. The other two concern (1) an ancestor who likely produced the first words and (2) the non-verbal experiences an infant shares with their parents that are crucial for producing their first words.

Consider the failures of ape language projects. Linguist Noam Chomsky began his distinguished career with a scathing critique of behaviorism in which he claimed language was uniquely human. Many behaviorists reacted to that claim by starting projects in which they attempted to teach apes language. To get around an ape’s articulatory limitations, some projects, including my own, used American Sign Language, a gestural language used by hundreds of thousands of deaf people. The focus of my project was an infant chimpanzee we humorously named Nim Chimpsky. Other projects sought to teach language to chimpanzees and bonobos by training them to produce sequences of arbitrary visual symbols.

All those projects failed. In the case of sign language, my analyses of videotapes in which Nim signed with his teachers revealed that they had inadvertently prompted him to make signs they anticipated he would make. Sequences of signs that seemed spontaneous were, in fact, cued by Nim’s teachers.

Sequences that chimpanzees learned to produce in other projects could be explained by rote memorization, like the sequences people use to enter a password to obtain cash from an ATM. What those sequences have in common is they are motivated by reward. Requests for rewards, however, constitute a minuscule portion of human vocabulary. If such requests were all an infant learned, they would never learn language.

“Ape language” experiments failed because none of the subjects could learn to use symbols as names — the basic function of words. They showed why it is futile to teach an ape to produce sentences if it can’t even learn words. Although the results of Project Nim were negative, they showed why a theory of language’s evolution must begin with words, not sentences.

What ancestor might have produced the first words? Now that we know chimpanzees are unable to learn words, we must ask, which, if any, of our ancestors were the first to use them, why they might have done so, and what they might have said. Recent discoveries by paleoanthropologists suggest it is likely that the first words were invented by Homo erectus.

The critical question to ask about any purported inventor of words is how did they contribute to a species’ survival? If they didn’t, they couldn’t be naturally selected. Most candidates fail that test, e.g., using words to enhance pair-bonding and social bonds. Each of these behaviors develop without words. To survive, Homo erectus needed copious calories to feed its enlarged brain, the volume of which was almost three times the size of a chimpanzee’s.

The most efficient source of calories is meat, but Homo erectus lacked the required weapons to kill large animals. They could use stone tools to butcher animals that had been killed by other predators or that had died a natural death, but they couldn’t kill them outright. They had to use another approach. After one of their group, a “scout”, located a dead animal, he had to recruit colleagues to help butcher it where it lay and scare off other animals that might pick at its remains while they attempted to.

Because the dead animal was far away and out of sight, the scout had to invent arbitrary words to describe it and its location. The innate vocabulary of signals animals used to communicate would not suffice. We don’t know if the scout used gestures or a spoken utterance, or both, to get his colleagues to think about the animal they had to scavenge, but whatever form the gestures or utterance took, some linguists suggest it was the origin of the first words. Our vocabulary grew from there.

Now consider pre-verbal precursors of an infant’s first words. Something remarkable happens to every infant during their first year that distinguishes their history from that of every other primate. They experience two non-verbal relations with their parent that pave the way to language. During the first few months, human infants are cradled by their parents. That provides a basis for their sharing gazes and emotions in a stage of development called intersubjectivity.

Beginning at approximately six months, the infant begins to crawl and to point to external objects, often picking them up to show to their parents. Pointing to an object and sharing it with a parent takes place during a second stage of development called joint attention. When an infant and parent know they are attending to the same object, the infant can readily learn its name by imitating a parent’s comment.

Intersubjectivity and joint-attention, two uniquely human phenomena, are crucial for the development of language. Their absence in chimpanzees is the best explanation for their inability to learn language. Their partial absence in autistic children and in children raised in orphanages also explains why language development in those children is retarded.