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Do Animals Have Language?

The least thing upset him on the links. He missed short putts because of the uproar of the butterflies in the adjoining meadows.

—from The Clicking of Cuthbert, by P. G. Wodehouse

Having grown up on a farm, I suspect that the above quotation is an unwarranted slur on the gentle butterfly, but vocalization is ubiquitous among animals, including insects—and of course ourselves. It has therefore seemed natural to suppose that human language must have evolved from animal calls. Only in fiction, though, do animals actually speak and hold meaningful conversations. Most examples, from Winnie the Pooh to the Beatrix Potter books, are written for children, but my favorite example comes from a short story entitled Tobermory, by Saki, who made a brief appearance in the previous chapter. Tobermory is a cat who has been taught to speak, to the consternation of guests at a house party. Here is what Tobermory says to a woman who is foolish enough to ask his opinion of her intelligence:

“You put me in an embarrassing position,” said Tobermory, whose tone and attitude certainly did not suggest a shred of embarrassment. “When your inclusion in the house party was suggested Sir Wilfred protested that you were the most brainless woman of his acquaintance, and that there was a wide distinction between hospitality and the care of the feeble-minded. Lady Blemley replied that your lack of brain-power was the precise quality which had earned you your invitation, as you were the only person she could think of who might be idiotic enough to buy their old car.”¹

To everyone’s relief, Tobermory was killed shortly afterwards by a tomcat from the Rectory.

In most respects, though, animal vocalizations have little in common with human speech. For the most part, they are genetically fixed, and under emotional rather than voluntary control. They are organized in the midbrain, with little or no input from the cortex, the seat of higher mental functions. For example, electrical stimulation of a region of the midbrain called the periaqueductal grey induces hissing, growling, screaming, howling, and meowing in the cat, shrieking, yelling, yapping, cackling, and trilling in the squirrel monkey, echolocation sounds in the bat, and laughing in humans. These vocalizations seem to be organized downstream from the periaqueductal grey, in the ancient depths of the brain.² Thus, destruction of the periaqueductal grey causes rats, cats, squirrel monkeys, and humans to become mute.

Human laughter, then, belongs in the category of innate vocalizations unrelated to speech, and is correspondingly difficult to produce voluntarily or to suppress. Robert Provine, in his book Laughter: A Scientific Investigation, records that a girls’ boarding school in Tanzania had to be closed because of an uncontrollable epidemic of hysterical laughter.³ And conversely, it takes a trained actor to laugh convincingly in the absence of the emotional state, although my father, being Irish, was able to laugh uproariously at incomprehensible jokes told by his mates. This only led to embarrassment when others phoned later to ask the point of the joke, and he had to confess that he didn’t know.

Even the calls of chimpanzees, our closest living relatives, appear to be largely involuntary. Jane Goodall, who lived among the chimpanzees in the wild at Gombe National Park in Tanzania, once recorded the instance of a young chimp that had discovered a cache of bananas, and evidently wanted to keep them for himself. But when chimpanzees discover food, they characteristically emit a pant hoot call, drawing the attention of other members in the troop. The young chimpanzee was unable to suppress the emotionally driven call, but did the best he could to muffle it by placing a hand over his mouth. Conversely, chimpanzees find it difficult to produce a call voluntarily. Goodall remarks, “The production of sound in the absence of the appropriate emotional state seems to be almost an impossible task for a chimpanzee.”⁴

This may nevertheless be something of an exaggeration. Different pant hoot calls have been recorded in different regions of Africa, suggesting a degree of cultural influence. But even here the variation may not be so much in the actual sounds as in their timing.⁵ Pant hoots are often accompanied by drumming, in which the animals repeatedly hit their hands or feet against a surface—including their own chests. Groups have a characteristic beat, and the resulting differences may serve as identification tags, allowing the animals to maintain contact. Chest beating, along with threatening movements and vocalizations, is also well documented in mountain gorillas.⁶ These repetitive vocalizations and drumming may explain the origins of rock concerts, rather than of speech.

Chimpanzees also modify their calls in other ways. When under attack, chimps scream, and one study has shown that their screams have different acoustic structure if there is a listener in the audience of higher rank than the aggressor.⁷ In another study, captive chimps were more likely to produce two attention-getting sounds, the “raspberry” and the “extended grunt,” when a human appeared with a favorite food than when either the human or the food appeared alone.⁸ Such observations suggest a limited degree of voluntary control, although these variations may also be under subtle emotional control. Perhaps it’s a bit like the limited way we can modify emotional sounds such as laughing or crying, depending on the audience, or on the status of the person we’re responding to.

In some respects, chimpanzees and other great apes, despite being our closest living relatives among the primates, may not provide a good primate model for the voluntary control of vocalization.⁹ Charles T. Snowdon somewhat bemusedly refers to “the silence of the apes”;¹⁰ the great apes, he says, simply don’t vocalize much at all, at least in comparison with other primates, including ourselves. The primates of the Amazon, in contrast, join in the frenzy of sound created by frogs, birds, and other creatures in the rain forest, where vocalization presumably acts as a signal to distinguish one species from another. Snowdon claims to be able to locate a group of pygmy marmosets, the world’s smallest monkeys, simply by listening for their distinctive and persistent vocalizations. The mountain gorillas of Rwanda, on the other hand, are especially conspicuous for their silence, at least according to Snowdon.¹¹ Maybe they are just strong, silent types, more into chest-beating displays than flights of vocal eloquence. And maybe, too, it’s sometimes the strong, silent, Tarzan type, rather than the rock star, who gets the girl.¹²

There may also be better voluntary control of vocalization in primates more distantly related to humans than are the great apes. Macaques can learn to increase the rate of vocalization to gain food reward or avoid shock, but this is abolished by bilateral destruction of a cortical area known as the anterior cingulate.¹³ In squirrel monkeys, destruction of this area abolishes spontaneously uttered long-distance calls, but leaves intact the animals’ ability to respond with contact calls to contact calls made by others.¹⁴ In these cases, the calls themselves are innate, but their production appears to be under some intentional control, mediated by the anterior cingulate. Japanese monkeys have been taught to emit “coo” calls to make requests, also suggesting a degree of voluntary control. More provocatively, it is claimed that they can modify their coos in order to receive either food or tools, suggesting that they may have been able to bring their vocalizations partly under the control of the motor cortex.¹⁵ It has also been suggested, though, that the coo sound was entirely involuntary, the result of an unconscious link, well documented in humans as well as primates, between limb movements and vocalization.¹⁶

Human speech is not only intentional, it also requires the learning of new sound patterns. Although most animals and many birds vocalize, very few are capable of vocal learning. Just why this is so is something of a mystery. Erich D. Jarvis suggests that there has been selection against vocal learning because it introduces variation, and makes the calls more noticeable to predators—just as we humans tend to notice the sound of a new voice. Jarvis suggests that animals that do learn new patterns are the ones without major predators, with humans at the top of the list. Apart from humans, killer whales are the top predators of the ocean, and are vocal learners. Adult elephants are also vocal learners, and do not have natural predators, although lions, hyenas, and crocodiles sometimes prey on young elephants. Another vocal learner, the hummingbird, is said to be fearless, because it can easily escape predation through rapid flight, and songbirds such as parrots and ravens can evade predation through effective mobbing behavior.¹⁷ One may wonder, though, why the dominant cats of the African savannah, such as the lion (king of the jungle), are not vocal learners. Perhaps they are, and no one has dared get close enough to find out. Or maybe they learned to keep quiet, and so escape notice, when humans developed the facility to kill them (and everything else).

Another suggestion is that innately programmed vocalizations can’t be faked, and can therefore be trusted.¹⁸ If an animal cries “wolf” it is important that a wolf be actually present, otherwise her mates may not believe her next time and fall victim to that voracious animal. Human talk, in contrast, is notoriously untrustworthy, as the poet Robert Graves warns in his poem Beware Madam!

Beware, madam, of the witty devil

The arch intriguer who walks disguised

In a poet’s cloak, his gay tongue oozing evil.

The idea that animal communication cannot be faked has been challenged, though,¹⁹ and we might at least make an exception of birds, some of whom sing to deceive by imitating other birds, or even humans. The lyre bird in Australia is said to be able to imitate the sound of a beer can being opened, although with wine having largely displaced beer as the national drink in that country we might expect these birds soon to imitate the popping of corks.²⁰

If animals aren’t conversing with one another, one may well ask what all the noise is about. Usually, it has to do with essentially instinctive or emotional situations such as mating, aggression, territorial claim, or warning of predators. One of the most studied examples is the vervet monkey, which has separate cries to warn of the presence of a snake, an eagle, a leopard, a smaller cat, and a baboon, and when monkeys hear these calls they act appropriately—running up into the trees, for example, in response to the leopard call.²¹ Even those birds that learn new patterns of sound appear not to be conversing, or conveying new information. Erich Jarvis suggests that vocal learning evolved in the first instance not to transmit meaning, but rather to defend territory²² and attract mates. In humans, as in songbirds, singing is an activity that attracts potential mates and allows individuals to establish themselves as sex icons. I have a colleague who once traveled a considerable distance to join a queue to be kissed by Elvis.²³ This raises the intriguing possibility that speech evolved from singing, an idea explored by Steven Mithen in his 2005 book The Singing Neanderthals.²⁴

Vocal learning is often employed in order to imitate, as in the case of the lyre bird. Imitation presumably enables the imitator to encroach on the territory of another species, and take advantage of their resources. Some animals have even proven to be adept at imitating human speech. In his 1997 book The Symbolic Species, Terrence Deacon records his astonishment when, as he was passing in front of the Boston Aquarium, a voice called out “Hey! Hey! Get outa there!”²⁵ It came from Hoover, the now legendary talking seal, who died, sadly, in 1986. An elephant named Kosik at a South Korean Zoo has recently been recorded uttering several Korean words and phrases. The vocal range of elephants is normally too low for humans to hear, but Kosik has found a way to curl his trunk into his mouth and blow into it, and so create frequencies high enough to produce sounds recognizable as speech.²⁶ But simple imitation is not the same as speech produced through the use of grammatical rules. Closer to the mark was Alex, an African gray parrot, who also died recently. Alex’s voice has been described as like a recording from an old-style Victrola.²⁷ He did not merely mimic, but was able to answer simple questions about the colors or shapes of objects, or about the number of objects up to about six. He was said to have had the speech capabilities of a two-year-old human child.²⁸ This is progress indeed, but just as the two-year-old has not yet developed true grammatical speech, neither did Alex.

For the birds, I should also mention another African gray parrot called N’kisi, and featured in a BBC News report of 26 January, 2004. N’kisi belongs to Aimee Morgana (or her to him), and is said to have a vocabulary of 950 words and to generate novel utterances. He appears to have a mischievous sense of humor. On one occasion he met Dr. Jane Goodall, well known for having lived among, studied, and befriended chimpanzees in the wild. Having previously seen her in a picture with chimpanzees, N’kisi asked, “Got a chimp?” He apparently has some understanding of grammar, and it is claimed that he once said “flied” for “flew”—the kind of error often made by young children who have learned morphological rules but not yet learned the exceptions. More dramatically still, it is claimed that N’kisi has the power of telepathy, and Aimee Morgana has teamed with Dr. Rupert Sheldrake, whose most recent book is entitled Dogs That Know When Their Owners Are Coming Home, to demonstrate this power. N’kisi, they say, can telepathically surf the leading edge of Aimee’s consciousness.

I relate this, not to argue that parrots possess language, or to convince you that telepathy exists, even if restricted to dogs and parrots. Rather, claims of this sort appear all the time, but nearly always prove to be without solid foundation. As far as I know, N’kisi’s exploits have yet to be subjected to rigorous scientific testing, or published in a reputable scientific journal.²⁹ Even so, a closed mind on the subject—as on any subject—is not recommended, and may deny your parrot, or your dog, the chance to surf.

And we do need to be especially careful in drawing inferences about the mental capacities of nonhuman animals, especially in light of the famous 1904 case of Clever Hans, a horse. According to his trainer, Clever Hans could answer complex questions by tapping out letters of the alphabet with a front hoof, with each letter represented by a different number of taps. When asked “What is two-fifths plus one-half?” he stamped his hoof nine times, paused, and stamped another 10 times, apparently indicating that the answer was nine-tenths. Even the leading psychologist of the day, Professor Stumpf of the University of Berlin, was convinced of the horse’s genius, until one of his students, Oskar Pfungst, showed that Clever Hans was actually responding to subtle signals given by his trainer. The trainer himself apparently did not realize that he, and not Clever Hans, was generating the answers.

What, then, of our closest relatives, the chimpanzee and bonobo?³⁰ Even at the acoustic level, without any consideration of meaning, the vocal exchanges between chimpanzees differ markedly from the exchanges that occur in human conversation. When people converse, they generally choose words, and therefore sounds, that are different from those they have just heard—the answer to a question, for example, is not the same as the question itself, unless perhaps it comes from a postmodernist, or a psychoanalyst. The sounds that chimpanzees emit during vocal exchanges are similar to what they have just heard.³¹ Their echoed exchanges probably have to do simply with maintaining contact, rather than with telling what Bobo said to Mimi last night over dinner.

Attempts to teach our great ape cousins to speak have been notoriously unsuccessful. The best-known attempt was that of Cathy and Keith Hayes, a husband-and-wife team, who raised a baby chimp called Viki in their own home, along with their own children, hoping that speech would come as naturally to Viki as to the other kids. But it did not. At best, Viki was able to produce crude, approximations to three or four words: mama, papa, cup, and possibly up.³² These painful efforts were whispered rather than vocalized, suggesting that at least part of the problem lay in the vocal component itself. But even the whispered attempts were far removed from the effortless, articulate, but often infuriating chatter of a bright three-year-old human. Chimps, then, seem to be distinctly at a loss for words. Parrots can do a much better job of articulating something like human speech than any primate can.

Another classic case is reported by the pioneering Russian psychologist Nadesha Ladygina-Kohts, who undertook detailed studies of a baby chimpanzee called Joni, and compared his development with that of her son Roodi.³³ Joni learned nothing approximating speech, but nevertheless loved to make sounds, including laughter. He also snored in a manner indistinguishable from that of a child. His vocalizations, though diverse, were attributable largely to his emotional state. Oddly, he could imitate the barking of a dog,³⁴ but not the sounds of human speech. Ladygina-Kohts grew almost as attached to Joni as to her own son, and her studies of Joni’s behavior were meticulous and insightful, but she nevertheless concludes her book with a paean to human superiority, based largely on our unique language ability. After noting the “equalities” between child and chimp, she writes:

And, as soon as we take the child’s verbal expression into consideration we immediately have to change these “equals” signs we were about to put between the intellectual capacities of a 4-year-old child and his chimpanzee counterpart. We change the equals sign into the sign >, which still does not look expressive enough; you want to say, or rather yell, not only more, but better, qualitatively higher, and incomparably, inexpressibly more perfect!³⁵

Do Animals Understand Us?

Although nonhuman animals have little or no ability to produce anything resembling human speech, they may have surprising ability to understand it. One of the more remarkable instances comes, not from an ape, but from a border collie.³⁶ His name is Rico, and he is able to respond accurately to spoken requests to fetch different objects from another room, and then to either place the designated object in a box or bring it to a particular person. In experimental trials, he was given 10 objects randomly selected from 200 objects that he knows, and chose correctly in 37 out of 40 trials. Rico collects the designated object from a room in which there is no person who might cue him about the correct selection, which rules out any “Clever Hans” effect. If he is given an unfamiliar name of an object to fetch, he will choose the one object among the otherwise familiar selection that is novel. Four weeks later, he demonstrates that he still knows the name of this object, indicating what has been termed “learning by exclusion.” This ability to apply a label on a single trial is known as “fast mapping,” and has hitherto been thought to be restricted to humans.³⁷ Rico’s exploits may not come as a surprise to people convinced that their pet dogs or cats can understand them.

Rico’s performance is somewhat comparable to that of Kanzi, a bonobo raised by Sue Savage-Rumbaugh. Kanzi is unable to speak, but as we shall see he has acquired an impressive facility to communicate by using manual gestures. What is interesting here is that his ability to understand spoken language far exceeds his ability to produce it. He can respond correctly to quite long sentences. For example, when asked, “Would you put some grapes in the swimming pool?” he immediately got out of the water, fetched some grapes, and tossed them into the pool. When visiting his friend Austin, a chimpanzee, he was told, “You can have some cereal if you give Austin your monster mask to play with.” He responded by finding his mask and giving it to Austin, and then pointing to Austin’s cereal. His ability to respond to such commands is not perfect, though. In one controlled study, he was given a list of 660 unusual spoken commands, some of them eight words long, and responded correctly on 72 percent of them. Kanzi was nine at the time, and did a little better than a two-and-a-half-year-old girl called Alia, who managed to get 66 percent correct.³⁸

These examples suggest that comprehension of speech far outstrips production, also a common observation in children acquiring language.³⁹ They also suggest a surprising ability to break sentences down into words, hitherto considered a uniquely human capacity. Although this is something that seems natural to most of us, there is virtually nothing in the acoustic signal that tells us where one word ends and another begins,⁴⁰ and it is really only experience with the language that enables us to break a sentence down in this way.⁴¹ Doyoufollowme? We become aware of this only when listening to a language that is completely foreign, when all the words seem to run together in a meaningless babble. When we teach children to speak, we help them to separate the words with an exaggerated form of speech known as “motherese.”⁴² The surprise, then, is not just that Rico and Kanzi were able to respond correctly to words, it is that they were able to pick them out at all. One must also suppose that they are not unique among their species—presumably, other apes and mammals are capable of the same thing, given the right conditions of learning. Keep talking to your cat.

It is unlikely, though, that the understanding exhibited by Rico and Kanzi—one hopes they might one day meet—meets the definition of true language comprehension. The identification of key words may be sufficient to provide the correct response most of the time. All Rico needs to know is the name of the object and the name of the recipient (box or person), and the rest follows. Although the sentence “You can have some cereal if you give Austin your monster mask to play with” involves recursion (specifically end-recursion), Kanzi probably did not need to parse the sentence in order to understand what he needed to do. He just needed to pick out the words cereal, Austin, and mask to have a pretty good idea of what was required.⁴³

The exploits of Rico and Kanzi nevertheless clearly depend on sophisticated analysis of acoustic signals, to a level well beyond the sounds they are actually able to produce. Although their calls seem to be largely fixed and under emotional control, animals hear a lot of different sounds in the wild, and need to be able to discriminate among them and at times take appropriate action. These sounds include the calls of other animals, including those of predatory humans. In the jungle, you need to stay tuned.

What about Signs?

Most nonhuman animals are highly vocal, but seem incapable of anything resembling human speech. The fact that some animals, at least, can understand speech suggests that any linguistic deficit may have to do with the production of intentional, learned vocal output, and not necessarily with language itself. Language, though, need not be vocal. The signed languages of the deaf are now clearly recognized as true languages, with an expressive power equal to that of speech—and in the next chapter I argue that human language evolved from manual gestures, and not from vocalizations. In literate societies reading and writing also comprise a form of language that can be accomplished without sound.⁴⁴

A hint that it might be possible to teach visual language to apes came from an observation made by the English diarist Samuel Pepys. In 1661, he saw a strange creature, probably a chimpanzee or gorilla,⁴⁵ which had been brought from Guinea, and wrote that it was “so much like a man in most things … I cannot believe it is a monster got of a man and a she-baboon. I do believe it readily understands much English; and I am of a mind it might be taught to speak and make signs.” He was wrong about speaking; as we have seen, there is no evidence whatsoever that any nonhuman primate can produce anything resembling human speech.

Pepys may have struck a seam of truth, though, in his suggestion that an ape might be taught to make signs. Primates, including apes, have hands and a manual control system that is well adapted for grasping and manipulating things, and is much better adapted to learning and intentional control than is their vocal system. This realization led Allen and Beatrix Gardner to develop a system of signs, based loosely on American Sign Language, in an attempt to communicate with a young chimpanzee called Washoe. This was indeed much more successful than earlier attempts to teach chimpanzees to speak. Washoe learned well over 100 gestures, in marked contrast to the mere three or four words that Viki had attempted to mouth. Washoe’s first signed “word” was more, made by bringing the hands together in front of the body. She used this sign in combination with other signs to request more treats, such as bananas or tickles.⁴⁶ Later, Francine Patterson taught a gorilla named Koko at least 375 signs, and claimed that Koko could use these signs in inventive, human-like ways, to lie, swear, and pour scorn. Patterson even claimed to have measured Koko’s IQ at somewhere between 84 and 95.⁴⁷

The most impressive results so far, though, are those obtained by Sue Savage-Rumbaugh with the bonobo Kanzi, using an approach based more on reading than on signed language. Kanzi communicates by pointing to keys on a keyboard containing 256 symbols denoting objects and actions, and has supplemented these with manual gestures of his own devising. The symbols, known as lexigrams, are deliberately selected not to bear any physical resemblance to the objects or actions they represent. There also seems little doubt that Kanzi can produce novel sequences by pointing to combinations of lexigrams on the keyboard, although these combinations are meager compared to human language. His “utterances” are two- or three-word combinations, such as hide peanut, chase you, hot water there, or child-side food surprise.⁴⁸

There has been considerable debate, though, about whether Kanzi has acquired true language, and the general consensus is that he has not, and that these simple combinations do not constitute true recursive grammar. Steven Pinker remarked that great apes, for all their linguistic exploits, “just don’t ‘get it.’ ”⁴⁹ Of course, this may reflect a desperate longing to cling to the notion of human superiority, but it is nevertheless clear that Kanzi has a long way to go, if he is to get there at all. At a recent conference on the evolution of language, held in Paris, it was suggested that Kanzi himself might appear at the following conference, two years later, and deliver a talk. Careful inspection of the presenters at that conference persuaded me that Kanzi was not one of them.⁵⁰

Figure 5. Panbanisha, Kanzi’s adopted sister, communicating with lexigrams. Photo by Malcolm Linton.

Although Kanzi is perhaps the star among nonhuman animals in his linguistic prowess, others are not so far behind. These include other great apes (gorillas and orangutans),⁵¹ dolphins,⁵² sea lions, and Alex, the African gray parrot.⁵³ The linguist Derek Bickerton coined the term “protolanguage” to refer to the ability to form or understand simple combinations of symbols, but without grammar.⁵⁴ It has been claimed that this is the level of language attained, not only by the species mentioned above, but also by twoyear-old children, speakers of pidgin languages, those with certain brain injuries preventing fluent speech, and drunken teenagers.⁵⁵ In the child, grammar develops between the ages of about two and four. This stage is part of childhood, which may be unique to humans, and critical to the development of other aspects of thought peculiar to humans—a point elaborated in chapter 11. Bickerton has proposed that protolanguage is the platform upon which fully grammatical language was built in the course of evolution, a view reiterated by Ray Jackendoff in a recent landmark book.⁵⁶

Another view of protolanguage, at least as manifest in nonhuman animals, is that it is simply a form of problem solving. Indeed the linguistic exploits of Kanzi and other apes seem comparable in many ways to the problem-solving activities of the chimpanzees described in the famous experiments of the German psychologist Wolfgang Köhler. When the chimps were presented with problems to solve, Köhler noted that the solution often seemed to come suddenly, as though through a flash of insight, and the solution often involved combining two objects, or two ideas, in a novel way. For example, the most “intelligent” of the chimps, Sultan, once figured out how to rake in food that was just out of reach by joining two pieces of bamboo together to make a rake long enough to reach the food. On another occasion, he used a small bamboo stick to rake in a longer one that was out of reach, and then used the longer stick to rake in food.⁵⁷ These acts seem little different in principle from the combining of communicative gestures, and many of the “requests” generated by the so-called linguistic apes are also produced with the aim of receiving food.⁵⁸

More recently, Michael Tomasello has demonstrated similar problem-solving ability in chimpanzees, and made the interesting observation that they do not seem to learn by imitating others. When there were two ways to rake in food, chimps preferred to work out their own way of doing it, and were not influenced by having seen it done the other way. Children, in contrast, are more likely to copy what they have seen.⁵⁹ This apparent lack of imitative ability in the chimp may partially explain why they have not pressed on to Churchillian feats of oratory, or the building of jumbo jets. Daniel Povinelli has also explored the abilities of chimpanzees to solve mechanical problems, and seems more impressed by their obtuse lack of understanding of the physical world than by their occasional successes.⁶⁰ In the see-saw world of primatology, however, there is now evidence that chimpanzees may not only learn different ways of solving mechanical problems, but may transmit them to others in their group, suggesting a rudimentary basis for the establishment of culture.⁶¹ It may be the chimpanzee’s uncomfortable resemblance to ourselves that makes their mental abilities so much a matter of contention.

A curious feature of protolanguage as revealed by Kanzi and the other so-called linguistic apes is that there is little evidence for comparable communication among apes in the wild, or in naturalistic settings. Nevertheless they do gesture. Joanne Tanner and Richard Byrne counted some 30 different gestures made by lowland gorillas in the San Francisco Zoo, where the animals, cousins to those strong silent mountain gorillas we encountered earlier, are enclosed in a large, naturalistic setting. These gestures are closer to pantomime than language, though, and are easily understood by both human and gorilla observers.⁶² Similarly, Michael Tomasello and his colleagues identified 30 gestures made by free-ranging chimpanzees at the Leipzig Zoo.⁶³ These gestures by no means exhausted the total repertoire of the animals, but were chosen because they could be readily observed and tabulated by the experimenters. These ape gestures, although unitary, are nevertheless somewhat language-like in that they are typically directed toward another individual, whereas animal calls tend to be directed to the community at large.

The manual gestures of chimpanzees and bonobos also differ from their facial movements and vocalizations in that they are less tied to typical contexts, such as play, grooming, or sex. They also show more variability between the two species and between subgroups within each species.⁶⁴ These features imply that manual gestures are used more freely and flexibly than are vocalizations, again suggesting that they are deployed intentionally, whereas vocalizations are largely under emotional control—on automatic pilot, as it were.

Michael Tomasello and his colleagues have also studied communicative bodily gestures made by great apes in the wild, and shown that these gestures are both subject to social learning and sensitive to the attentional state of the receiver.⁶⁵ These are both prerequisites for language—although they are not sufficient, as we shall see in chapter 9. In these studies gestures are defined as communicative movements of the head, limbs, or body, but exclude vocalizations. Some gestures, though, seem designed to produce sound—these include clapping and chest-beating. The gorilla appears to have a greater repertoire than the chimpanzee or bonobo, perhaps because the gorilla is the most terrestrial of the three, with arms less occupied with climbing and clinging.

But although ape gestures are clearly communicative and intentional, and subject to learning, they do not have the combinatorial generativity of human language. There are no sentences. Just what is missing from these gestures to enable them to develop into language is further explored in chapter 9.

Recursion in Nonhuman Species

Over 40 years ago, the distinguished linguist Noam Chomsky remarked that human language was “based on an entirely different principle” than all other forms of animal communication.⁶⁶ That conclusion seems much less true than it did then, and Chomsky himself appears to have softened his view. In an influential article he coauthored with Mark Hauser and Tecumseh Fitch, two definitions of the language faculty are proposed. The faculty of language in the broad sense (FLB) includes a great many features shared between humans and other species, including input-output systems, and what they call the “conceptual-intentional system,” implying purposeful intention to communicate with others.⁶⁷ Contained within this system is the faculty of language in the narrow sense (FLN), which is in effect the I-language discussed in the previous chapter.⁶⁸ As we saw there, Chomsky argued that I-language emerged in a single step in late human evolution, and was thus clearly denied to nonhuman apes.

Hauser, Chomsky, and Fitch note that “all approaches [to language] agree that a core property of FLN is recursion.”⁶⁹ In Chomsky’s most recent Miminalist Program, it is the Merge operation that is applied recursively, as we saw in the previous chapter. Since Hauser and coauthors identified recursion as the critical component, there has been at least one claim that recursive parsing can be accomplished, not by apes, but by starlings.⁷⁰ It is worth taking a closer look, because any such claim poses a real challenge to our supposed uniqueness.

The claim was based on the parsing of center-embedded sequences, in which pairs of elements are progressively embedded in other pairs. The elements comprised rattles and warbles, the natural sounds that starlings make, and each pair was made up of a particular rattle and a particular warble. There were eight exemplars of each, so that the actual pairs were randomly chosen. An example of a center-embedded series with three levels of embedding would be R₇R₁R₅R₃W₆W₇W₂W₅—so that R₃W₆ is embedded in R₅W₇, and then this sequence is embedded in R₁W₂, and so on. Center-embedded sequences were compared with sequences made up of repeated pairs, as in R₅W₁R₃W₂R₈W₅R₈W₄. These structures are also shown in figure 6. After extensive training, the starlings were eventually able to discriminate both the center-embedded sequences and the repeated pairs from sequences not obeying these conditions.⁷¹ Since the actual examples of rattles and warbles were varied randomly from trial to trial, the birds could not have been learning specific sequences, but must have somehow grasped the different structures.

Does that mean that the starling understood that the embedded sequence was made up of the recursive embedding of pairs within pairs? Alas no. The starlings might simply have been able to discern that the so-called embedded sequences comprised a sequence of rattles followed by an equal number of warbles. This does require the ability to estimate the number of each, at least up to four, and then judge whether the two numbers were the same. This structure is also shown in figure 6. To adopt this alternative strategy, they need some ability to count, or at least estimate number—birds are pretty good at that⁷²—and some ability to judge whether two quantities are equal. They don’t actually have to be terribly good at this, since their performance, although better than chance, was not perfect.

Figure 6. Sequences of rattles (R) and warbles (W) played to starlings.
A = repeated pairs; B = embedded pairs, C = alternative parsing that may have allowed the starlings to distinguish B without appealing to recursive embedding.

It seems likely, then, that the starlings cleverly discovered a simpler solution to the problem set them, one that did not involve the understanding of recursion.⁷³ We might nevertheless be advised to pay more heed to the songs of starlings, perhaps following the lead of Wolfgang Amadeus Mozart. The final movement of his Piano Concerto in G Major is said to have been based on a song by his pet starling. More seriously, the foregoing example illustrates that the concept of recursion can be elusive, and one can be misled into thinking that a sequence that was constructed from recursive embedding is necessarily decomposed in the same manner.

If starlings were genuinely able to parse three levels of center-embedding, this would be deeply embarrassing for humans, who are pretty much incapable of understanding recursion at this level of complexity. For example, we can understand a single level of center-embedding, as in John, whom Emily loves, adores Jane, and at a pinch we can add another level, as in John, whom Emily, whom Tom loves, loves, adores Jane. But try adding another level: John, whom Emily, whom Tom, whom Caroline loves, loves, loves, adores Jane. That’s not just an eternal triangle, it’s an eternal tetrahedron.

For the present, then, we may safely conclude that there is no evidence for recursive parsing of sequences in nonhuman species. In language, at least, recursion may indeed be uniquely human, as Chomsky and others have maintained. Nevertheless we saw in the previous chapter that some human languages may not involve recursion, although that too may depend on how recursion is defined. In later chapters, though, I argue that human language would not have been possible were it not for the recursive nature of human thought.

I consider next the general question of how human language evolved.