Scientists are discovering the surprising secrets of monkey chatter.
Monkeys can—and do—say a lot more than scientists have previously given them credit for. That’s the conclusion from two lines of research that have reassessed the sound-generating capabilities of the monkey vocal tract and deciphered differing “dialects” of alarm calls in two monkey populations. But do these discoveries support evolutionary claims about the origin of human language?
Scientists used to think that monkeys were quite limited in their ability to produce the sorts of sounds we use in speech. Vowel sounds essential to spoken language appeared beyond the capabilities of the monkey vocal apparatus. This conclusion was supported by a 1969 study by Philip Lieberman. Lieberman dissected the vocal tract of a dead rhesus macaque and determined that in life the monkey would have been incapable of producing some essential vowel sounds.
Just as fossils’ inability to walk limits our ability to fully understand dinosaur locomotion, so dead monkeys tell no tales. Therefore, a team led by Princeton neuroscientist Asif Ghazanfar, who worked with Lieberman in the past, has obtained fresh information about a monkey’s potential vocal repertoire through X-ray video of a living monkey’s voice box.
“What you'll find in the textbooks is that monkeys can't talk because they don't have the appropriate vocal tract to do so,” explains Tecumseh Fitch, lead author of the study. “That, I think, is a myth. My colleagues and I all get very tired of seeing this. But you see it in all the textbooks. Lots of popular books, and also scholarly books about the evolution of language, assume that in order to evolve speech we had to have massive changes in our vocal tract.”1
Ghazanfar’s team has learned that monkeys, should they have a mind to, can produce a wider range of vowel sounds than Lieberman’s post-mortem study suggested. The scientists had the assistance of three long-tailed macaques. Emiliano, Franco, and Patrice smacked their lips, yawned, chewed, cooed, and grunted. Fitch and company recorded the sounds and used video fluoroscopy (a type of X-ray) to capture the corresponding movements of tongue, lips, and voice box on film. Computer analysis, correlating vocal tract movements with the sounds, showed that monkeys can produce all the clearly distinguishable vowel sounds2 needed to imitate human speech.3 Though consonants are not considered language limiting for nonhuman primates, the study also found that macaques are easily able to produce sufficient consonant sounds to talk up a storm.4
Fitch and friends used computer simulations to synthesize how a monkey’s voice would sound if it could imitate phrases like “Happy holidays”7 and “Will you marry me?”8 The words were quite understandable. So, given that they have the necessary sound-producing anatomy, why don’t monkeys imitate human language? After all, parrots have a go at it and get lots of attention for their trouble.
The reason lies in the way the monkey brain and vocal tract are wired. A monkey lacks language-critical connections between its auditory cortex and its motor cortex. These are the parts of the brain that process what is heard and generate instructions controlling voluntary muscle movements. Therefore, even though a monkey hears what we are saying, it cannot convert that sound into instructions for its “speech-ready” vocal tract to imitate what it hears. A monkey also lacks the direct connections between the voice box and tongue that we use to shape our sounds into words.
Because they believe that the common ancestor between humans and monkeys is even more ancient than the supposed split between humans and apes, evolutionary scientists must now conclude that human speech evolution depended not on overcoming vocal tract limitations but rather on the rewiring of the brain. As Fitch and his coauthors write, “Our findings imply that the evolution of human speech capabilities required neural changes rather than modifications of vocal anatomy. Macaques have a speech-ready vocal tract but lack a speech-ready brain to control it.”9
Given that it can neither imitate our speech nor generate abstract language, what might a monkey wish to say? After all, despite the delightful fiction of Doctor Dolittle10 and his garrulous animal companions, among God’s earthly creations only human beings can use language to develop, encode, and communicate abstract thoughts. A monkey might, however, need to communicate something concrete and practical, like “Danger, danger!”
Well it turns out that some monkeys are able not only to let their buddies know of approaching danger but also to share information about the direction and degree of that danger. Something akin to “Heads up! Eagle coming in for the kill!” or “All clear!” would have survival benefit. While nothing has demonstrated that monkeys can compose sonnets or comment on Scripture, God has apparently provided them with the ability to refine and adapt their instinctive alarm calls to fit the varying situations in which they find themselves.
How do we know? For some time now scientists have been observing two populations of Campbell’s monkeys (Cercopithecus campbelli) located in Sierra Leone’s Tiwai Island and Ivory Coast’s Tai Forest. They have learned, as New York University professor Philippe Schlenker explains, “that Campbell’s monkeys have a distinction between roots and suffixes, and that their combination allows the monkeys to describe both the nature of a threat and its degree of danger.”11
By analyzing the recorded monkey alarm calls triggered by leopards and eagles (whether real or imitation), Schlenker and colleagues determined that krak and hok are alarm sounds. They learned that tacking -oo on the end of an alarm call lessens the intensity of the alarm. Hok denotes the aerial threat of eagles. And boom boom at the beginning of a call sequence means, “The coast is clear.”12 Even nearby Diana’s monkeys (Cercopithecus diana) calm down when they hear a Campbell’s monkey’s boom boom.13
These are two monkey species found in western Africa. Each warns of approaching predators, like leopards and eagles, with distinctive alarm calls. Where they share habitats, as in the Tai Forest, each species responds to the other’s alarm calls, providing widespread protection in a sort of natural neighborhood watch. Furthermore, Campbell’s monkeys from Tiwai Island, where there are no leopards, use the same alarm calls but without predator specificity.
What surprised Schlenker’s team was the fact that monkeys adapt their alarming vocabulary to the differing predatory conditions of their two locales. Monkeys in the Tai Forest must be alert to threats from above—eagles—and threats from below—leopards. But for decades there have been no leopards on Tiwai Island. In the Tai Forest, the sound krak is specific to a ground-based threat, but it is just a general alarm word among the monkeys of leopard-less Tiwai Island. In the Tai Forest, krak almost never refers to an eagle—a hok.14 On Tiwai Island where the chief predators are eagles, cries of krak and hok go up with equal enthusiasm when an eagle threatens. The two monkey populations adapted the same alarm sound to fit the context of their environments.
The authors do not claim that monkeys have worked out logical ways to make economical use of their limited vocabulary. However, the fact that the same sound has reproducibly different meanings among the two populations suggests that an innate alarm call can be modified in relation to the specific threats posed by different environments. And this contextual modification is understandable to all members of the group.
To determine how dialect-like modification occurs will require more research. Investigators may need to transplant monkeys from one home to another. They may need to observe the alarm capabilities of monkeys raised in captivity to determine the specificity of the alarm calls. For instance, must hok mean “eagle”? Could hok generalize to mean “Heads up! Incoming danger from above!”? What would a monkey say if a tree branch were falling toward his troop?
Additional observations may reveal these answers. But the scientific method will neither unveil an evolutionary history for human language nor demonstrate our common ancestry with monkeys.
The scientists deciphering monkey calls say, “Importantly, we do not take a stand on the relation that these systems bear to human language; to say that they can be studied as formal systems does not imply that they share non-trivial properties with human language, nor that they share an evolutionary origin with it.”15 They also admit, “Comparative monkey semantics might not directly illuminate the evolution of human language,”16 and “Evolutionary connections between monkey calls and human language are unclear.”17 However, regardless of this acknowledgment, the authors suggest that ongoing monkey linguistics might shed light on the evolutionary history of human communication. Seeing convergent evolution and evolution from a common ancestor as the only alternatives, they write:
When monkey languages are better understood, one would need to ask whether any similarities they bear to human language arose by convergent evolution (if similar properties developed independently in humans and in monkeys) or could result from evolution from common descent (if similar properties are inherited from the communicative system of the most recent common ancestor of monkeys and humans).17
Despite the desire of evolutionists to explain the origin of language—and everything else—through common ancestry, convergent evolution, natural selection, and random natural processes, neither biological nor linguistic observations support their claims. Human brain size and complexity, including the connections that support our capacity to use language, are radically different from those of any animal.
We know that God created human language on Day Six of Creation Week, for He spoke with Adam—warning him not to eat of the one forbidden fruit (Genesis 2:16–17) and assigning him the task of naming animals (Genesis 2:19–20). And Adam named the animals and communicated with his wife that first day of his existence. God likewise created the roots of the nearly 7,000 languages we have today almost 1,700 years later when He dispersed the rebellious descendants of Noah’s family congregating at the Tower of Babel. In fact the extraordinary differences between the language families that linguists describe (fewer than 150) are consistent with the radical divergence of people groups from Babel around 4,000 years ago, an actual historical event described in the Bible.
Neither biological nor linguistic science can demonstrate that humans evolved the ability to use language, for the scientific method cannot observe the time of its origins. The similarities and differences of true language and the language-like communications used by monkeys do not reveal the origin of either. But the origins of both human language and the roots of our many languages are knowable. Their history is knowable because we have an eyewitness account provided to us by God in His Word. As with so many questions about origins, the real answers are in Genesis! And the Bible’s historical answers are consistent with scientific and linguistic observations.