Ape Language Research: Can Primates Acquire Human Language?

Introduction: The Question of Animal Language

Research has been conducted for a long time on questions about the origin of language and how human beings first learned to speak. More recently, research has shifted to various primate studies examining whether other primates possess what can be considered a language, and in some cases whether apes can be taught to understand and even use language. Some of the early experiments in this area were seen as promising by some researchers and as self-delusion by others, but the research continued and has produced a number of interesting results that may bring us closer to understanding the genesis of language and how widespread language is in the animal kingdom.

Some animals are known to imitate human language without understanding it, such as parrots. For apes to have true language, they must understand what is said and use language to signify meaning, not merely to imitate. Researchers have developed ways of testing this idea. Efforts to teach language to chimpanzees were undertaken because chimpanzees share many characteristics with human beings, but in spite of this, chimpanzees do not learn to speak when given the same experiences children have when learning to speak. A researcher in Moscow raised a chimpanzee in her home from 1913 to 1916 but could not get it to imitate the human voice or learn a word of Russian, and other accounts have had similar outcomes. At most, one chimpanzee was able to learn three words.

In spite of these failures, researchers remained interested in determining whether animals could be taught to communicate, and one research team managed to teach a chimpanzee American Sign Language with much greater success. This suggested that efforts to teach chimpanzees to speak vocally might fail because vocalization was simply an inappropriate response medium for the animal. Animals might learn to communicate more effectively using a more appropriate medium. Other efforts were conducted with a gorilla, dolphins, sea lions, and a parrot, using either the same method or alternative procedures, with varying results suggesting that nonverbal communication is more widespread than verbal communication among animals.

Research at one university, for instance, made use of lexigrams — simple designs of various shapes and colors representing words — so that a chimpanzee subject could select a word by pointing or pressing the corresponding lexigram on a board. Lana was the first chimpanzee taught in this manner and could make various requests using this system, with a computer program replying via lexigrams displayed on a console. Two other chimpanzees followed using similar methods.

Kanzi, a bonobo great ape, has shown the most sophisticated ability to use language to date. More similar to human beings than common chimpanzees, Kanzi learned without formal language training after his mother had been taught using standard procedures. Kanzi observed but did not participate, and he learned spontaneously. This demonstrates that the capability is inherent to some degree and that the social environment may allow the ape to acquire language and interact with humans independently. Researchers made use of this discovery and allowed Kanzi to continue developing language skills by listening and observing. Both spoken and lexical language were part of Kanzi's daily activities, from which he learned in a manner more similar to that of a human child — with no explicit language sessions and without specific food reinforcement. It was thought, however, that reinforcement contingencies inherent in social interactions played an important role, just as they do in learning human speech and many other behaviors.

Research procedures in these situations must be carefully designed to eliminate the possibility that the researcher might give unintentional hints or prompts, or might ascribe more intelligent behavior to the animal than is warranted. One experiment showed that the ape involved often imitated signs made by the trainer, which was a poor indicator of genuine language skill. Experimental observations must be designed to ensure objective, independent assessment. Decisions must also be made regarding what constitutes linguistic competence, such as learning vocabulary, demonstrating signs of grammar, and showing both language comprehension and language production. Such criteria enable the researcher to make proper determinations about observed behaviors and what they may genuinely mean.

The rationale for such studies is not only to find out whether apes can use language, but to discover something about how human beings may have acquired the ability in the first place: "Research concerning the ability of primates to acquire language has profound implications for the understanding of the evolution of the human species. The acquisition of language in primates may shed light on the development of language in early humans. In this sense, research of primate language and primate tool use offer similar insight into our early ancestors" (Kosseff, 2006, para. 1).

Theoretical Frameworks: Skinner and Chomsky

Studies continuing this theme begin with the idea that human speech is usually thought to be the dividing line between humans and the animal world, and language is thought to have paved the way for many special human abilities, such as self-awareness, higher emotion, and personal memory (McCrone, 1991, p. 48). Knowing how humans acquire language can inform studies of animals to see whether they can do the same thing.

One approach to language acquisition is offered by Skinner (1974). Skinner discusses the issue of language acquisition within his overall framework of behaviorist psychology. He notes that language was acquired relatively late in the development of the human species, and this involved a remarkable change as the species' vocal musculature came under operant control. This extended the range of the human social environment. Skinner draws a distinction between "language" and "verbal behavior." He notes that psychologists speak of the "acquisition of language" in the child and explains how language is structured out of words and sentences that express meanings, desires, needs, ideas, emotions, and propositions. For Skinner, language is behavior with a special characteristic: it is reinforced by its effects on people, first on others, and then on the speaker him- or herself. The acquisition of language is therefore a matter of operant conditioning, just as all learning is. Language acquisition results from exposure to a speaking community, but learning is not merely a matter of imitation — it is rather a matter of operant conditioning as certain behaviors are reinforced by community acceptance and by the understanding shown in what is being communicated.

For Skinner, the human being first makes sounds just as other animals do: "Like other species, it had up to that point displayed warning cries, threatening shouts, and other innate responses, but vocal operant behavior made a great difference because it extended the scope of the social environment" (Skinner, 1974, p. 88). Skinner explains the reinforcing nature of language and its relation to operant conditioning by giving the example of opening a door. He sees verbal behavior as behavior first and foremost, and because of its special character — being reinforced through its effects on people — it is free of the spatial, temporal, and mechanical relations that prevail between operant behavior and nonsocial consequences: "If the opening of a door will be reinforcing, a person may grasp the knob, turn it, and push or pull it in a given way; but if, instead, he says, 'Please open the door,' and a listener responds appropriately, the same reinforcing consequence follows" (Skinner, 1974, p. 89). Skinner notes that the contingencies are different and that they generate many important differences in behavior, which have long been obscured by mentalistic explanations.

Skinner further notes that the way a speaker depends upon the practices of the verbal community of which he or she is a member determines whether a verbal repertoire is rudimentary or displays an elaborate topography under many subtle kinds of stimulus control: "Different verbal communities shape and maintain different languages in the same speaker, who then possesses different repertoires having similar effects upon different listeners" (Skinner, 1974, p. 89).

Skinner's approach has several strengths: (1) it explains the acquisition of different types and levels of linguistic skill; (2) it applies across all societies and time periods; and (3) it makes a direct link between the verbal behavior that predates language and the process of language acquisition. The approach also has weaknesses: (1) it requires accepting the premises of operant conditioning, which carry deterministic implications of concern to those who value free will; (2) it presupposes links between specific verbal behaviors and social conditioning that makes language acquisition seem purely a product of social and cultural forces, while also asserting that the social environment was itself shaped by the development of language; and (3) it is vague about the role of the speaker as listener, though it appears to regard that role as important.

Another theorist with a different view is Chomsky (1988). Chomsky sees the acquisition of language as a process of input and output — what he calls a Cartesian view of language acquisition and structure. He states: "We have an organism of which we know nothing. We know, or we can discover, what kind of data is available to it, and the first question we must try to answer is: what kind of mental structure does the organism develop when that evidence is presented to it?" (Chomsky, 1988, p. 102). Once we find an answer to this question, we can ask what sorts of processes have intervened, leading from the data available to the knowledge that resulted. Chomsky explains:

"The input-output situation is this: a child who initially does not have knowledge of a language constructs for himself knowledge of a language on the basis of a certain amount of data; the input is the data, the output — which of course is internally represented — is the knowledge of a language. It's this relationship between the data available, and the knowledge of the language which results from the child's mental activities, which constitutes the data for the study of learning — of how the transition takes place from the input data to the resulting knowledge" (Chomsky, 1988, p. 102).

Chomsky states that this is different from the behaviorist stimulus-response conception, which he argues can only lead to a system of habits, a network of associations, or some similar structure. He contends it is quite impossible to formulate as a system of habits or associations the processes that account for the sound-meaning relationship that we all know we have mastered intuitively when we learn a language. Language has a creative aspect in which ambiguities are resolved in ways that convey meaning despite those ambiguities: "Whatever a habit-structure is, it's clear that you can't innovate by habit, and the characteristic use of language, both by a speaker and a hearer, is innovation" (Chomsky, 1988, p. 103).

Neurological and Genetic Evidence

Chomsky's formulation has certain strengths: (1) it makes a strong link between the speaker's environment and language acquisition; (2) it provides for relationships between different languages that suggest a similar underlying mode of thought among speakers everywhere, which would help explain language acquisition across different societies and time periods; and (3) it helps explain the acquisition and use of language as an ongoing process in which the speaker participates as an innovator. The theory also has weaknesses: (1) it identifies the sources and mechanisms of language acquisition without fully explaining the processes involved; (2) it presumes underlying modes of thought in language without identifying or examining them directly; and (3) it does not clarify what social role, if any, language acquisition plays. Both theories offer interesting ideas for speculation, but neither can be considered definitive.

An international group of scientists called the Chimp Sequencing and Analysis Consortium, consisting of sixty-seven researchers, co-authored a study showing that the genome of the chimpanzee is 96 percent similar to the human genome, confirming that chimpanzees are our closest living relatives. This finding provides researchers with a new key to understanding human biology, evolution, and speech development. The comparison of genetic differences — specifically the sequences identified as distinct between the two species — may hold the key to determining what creates human-specific traits, including human speech (Lovgren, 2005).

Cantalupo and Hopkins (2001), researchers at the Yerkes Primate Research Centre at Emory University in Atlanta, Georgia, discovered that gorillas and chimpanzees have a rudimentary speech center in their brains previously thought to be found only in humans. Brain scans revealed "a small, lopsided structure buried in the front part of the head which in humans is critical for language." This structure, known as Brodmann's area 44, is part of the brain region called Broca's area. Cantalupo and Hopkins' scans show that this area is larger and more developed in the left hemisphere of the ape's brain than the right — the same asymmetry seen in humans — which is linked to right-handedness. It has been observed that chimpanzees tend to use their right hands when grunting. The researchers wrote in the journal Nature: "The part possession by great apes of a homologue of Broca's area is puzzling, particularly considering the discrepancy between sophisticated human speech and the primitive vocalizations of great apes." They consider this feature a curious and ancient landmark in the evolution from ape to human (Cantalupo & Hopkins, 2001).

In a study published in the August 2001 issue of The Journal of Physical Anthropology, scientists created a detailed computer analysis of a basic functional unit of the human and non-human brain known as a minicolumn — a group of 80 to 100 cells and the wiring that connects them. Millions of these minicolumns are found throughout the brain; the study focused on those found in an area of the brain involved in language called the planum temporale. These minicolumns differ in their appearance in the human brain and are also lateralized — larger on the left side than the right — according to Dr. Buxhoeveden, who states, "We didn't find this in the chimpanzee or the monkey." The researchers believe these differences in neural wiring may explain why humans have superior communication skills compared to the more basic skills evident in nonhuman primates. While many previous studies comparing individual brain cells and whole brains in humans and apes found that cell physiology is essentially the same and that brain regions may look very similar from the outside, these minicolumn units are different. According to Dr. Buxhoeveden: "We found evidence that the brain is organized differently in humans in this area of the brain, even though the outside looks the same . . . This provides an anatomical substrate, a hint that the brain is wired differently in humans in the language area than in the chimpanzee or the monkey" (University of Georgia, Science Daily, 2001).

Scientists at the Edinburgh Zoo in Scotland have also found evidence that chimpanzees communicate vocally about food in their environment. These chimpanzees produce distinct high-pitched noises or grunts for specific food items, linking the sounds they produce to the meanings they intend to convey — an essential requirement for identifying a language. The chimps grunt differently for bread, their favorite food, than they do for apples, which they like less. When researchers recorded these grunts and played them back, a "bread" grunt sent the chimps to the area where bread was fed, and an "apple" grunt directed them to where apples were fed. These grunts, known as functionally referential signals, may not refer specifically to bread and apples but more generally to favored versus less favored foods. Study co-author Zuberbuhler suggests the grunts may have a social function, noting that chimps rarely make noises when eating alone. While previous studies had found that monkeys communicate with sound about environmental events and that great apes can communicate with hand signals, this study, published in Current Biology, was one of the first to find chimps using vocal communication in this way (Appel, 2005).

Conclusion

The evidence seems clear that apes can acquire some form of language and communicate with humans, and there is also evidence that apes may have a form of language of their own by which they communicate with each other. This rudimentary language does not include all the features of human language, though research does suggest that apes can learn many of the underlying elements of syntax and sentence formation. It also appears that apes would not normally acquire such capabilities on their own, but they can be trained to use language and respond to its meaning. Research in this area continues and may reveal even more about the thought processes of apes and shed light on how early humans developed language skills.