The question of whether non-human primates can acquire human language has captivated scientists and the public for decades. Early in the 20th century, researchers began attempts to bridge the communication gap, seeking to understand the nature of language itself and the cognitive abilities of our closest living relatives. This scientific inquiry focused heavily on chimpanzees, whose genetic closeness to humans suggested a potential capacity for complex communication. The challenge became defining what constitutes true language and determining if the impressive communicative displays observed met that high standard. Examining these pioneering studies and their subsequent critical analysis helps illuminate the profound differences between complex animal communication and the unique linguistic ability of humans.
The Pioneering Sign Language Experiments
Initial attempts to teach chimpanzees human language centered on speech, an effort that quickly proved unsuccessful due to biological limitations. The chimpanzee Viki, raised in the 1940s, was taught to say only a handful of words, such as “mama” and “cup,” after immense effort. Researchers concluded that the physical structure of a chimpanzee’s vocal tract made producing the necessary range of human speech sounds virtually impossible. This failure prompted a shift in focus from spoken language to a gestural one, recognizing that chimpanzees naturally communicate through a wide array of hand and body movements.
The breakthrough came with the chimpanzee Washoe in the 1960s, the first subject to be taught American Sign Language (ASL). Researchers R. Allen and Beatrix Gardner immersed Washoe in an environment where human caregivers communicated with her and each other exclusively through signs. Washoe learned an impressive vocabulary, eventually mastering between 250 and 350 signs. She was reported to combine these signs into simple combinations, such as “Gimmie Sweet,” and even taught a few signs to her adopted son, Loulis, through observation alone.
Following Washoe’s initial success, Project Nim was launched to test the limits of chimpanzee linguistic capacity. Nim learned 128 signs and produced numerous sequences of signs, which initially suggested a breakthrough in primate language acquisition. These early projects established that chimpanzees possess the cognitive ability to learn and use a large number of arbitrary symbols to request objects and actions.
Establishing the Criteria for True Language
The scientific community requires a set of distinct features to classify a system of communication as true language, differentiating it from simple conditioned responses or natural animal signaling.
Productivity
Productivity, also known as generativity, is the capacity to create an infinite number of novel, meaningful utterances from a finite set of words and rules. A language user can continuously combine existing elements in new ways to express an unprecedented thought. Animal communication systems, by contrast, tend to have a fixed reference, where signals are limited to a specific context or meaning.
Displacement
Displacement refers to the ability to communicate about things that are not physically present in the current moment. This includes referring to events that happened in the past or will happen in the future, as well as discussing abstract ideas. The ability to detach communication from the immediate “here and now” allows for storytelling, planning, and the transmission of history. Most animal communication is confined to the immediate context, such as a warning call about a present threat.
Syntax
The most complex criterion is syntax, the set of rules that governs how words are ordered and combined to form phrases and sentences. Syntax provides structure, meaning that word order can change the entire meaning of an utterance, as seen in the difference between “dog bites man” and “man bites dog.” A system that lacks this internal, rule-based organization is considered advanced communication, but not language in the human sense.
The Scientific Interpretation of Chimpanzee Results
The initial excitement surrounding the sign-using chimpanzees was tempered by rigorous analysis, particularly of the Project Nim data. Herbert Terrace, the leader of the Nim Chimpsky study, became a prominent critic of his own findings after reviewing hours of videotape. He discovered that Nim’s signing was rarely spontaneous; instead, the ape’s signs were often prompted by the teacher, who would inadvertently cue the correct sign just before Nim produced it. This suggested the chimps were engaging in sophisticated imitation and operant conditioning to obtain a reward, rather than engaging in conversation.
Linguists concluded that while the apes demonstrated impressive acquisition of vocabulary (semantics) and functional use of signs (pragmatics), they consistently failed to demonstrate true syntax. Nim’s sign sequences, though sometimes long, lacked the consistent, rule-governed structure seen in human language development. The consensus settled on the view that chimps were using signs as tools for requesting or labeling, not as components of a generative, rule-based system.
This critical analysis shifted the scientific understanding of the chimpanzees’ accomplishments from language acquisition to complex cognitive performance. The ability to learn and use hundreds of arbitrary symbols remains a remarkable feat. However, the absence of spontaneous, productive, and rule-governed syntax indicated that the underlying cognitive architecture for human language was not fully present in the chimpanzee subjects.
Broader Implications for Human Language
The results of the ape language experiments ultimately reinforced the singularity of human linguistic capacity. By highlighting what chimpanzees could not achieve, the studies provided a clearer understanding of the unique cognitive and biological requirements for true language. The failure of the chimpanzees to acquire syntax suggests a profound evolutionary divergence in the neural mechanisms responsible for structuring complex thought and communication. This work strengthens the theory that humans possess a biological predisposition, or a “language instinct,” that is absent in our primate relatives.
The limitations of the chimpanzees also spurred further research into the specialized anatomy of the human vocal tract and the neurological structures involved in language processing. Even the ability to communicate through gesture depends on underlying cognitive abilities for sequential behavior that may have been present in the last common ancestor of humans and apes. However, the subsequent elaboration of these abilities into a recursive, generative system—human language—is now considered a defining feature of the human species.