The Human Evolution Blog

(A longer discussion of animal communication is found in my book.)

Human language seems so much more complicated and organized than anything experienced by animals. Nevertheless, animals do indeed communicate complex ideas using precise, intentional communication. Some primate species even have discrete audible words with unambiguous meanings. In other words, they have their own spoken languages and vocabulary.

Vervet monkeys are one of the first wild animals to have their vocabulary carefully deciphered by humans. Vervets are Old World Monkeys residing entirely in the rainforests of Africa. These monkeys, like many other species of monkey, give alarm calls when predators approach. These calls act as warnings to others in their troop that a predator is about.

The interesting part is that there are different calls for different predators. By using recording devices followed by careful observation, scientists have been able to document these calls.

To signal that an eagle has been spotted, a vervet will make a low-pitched grunt. When a leopard is spotted, however, the vervet sings a series of distinct tones. Lastly, when a python is spotted, a vervet will give a high-pitched staccato barking sound, called a “chutter.” (Snakes are common predators of primates, which is why many primates, including humans, have a genetically programmed fear of snakes.)

These are the three main predators of the vervets, so it makes sense that vervets would call out when they spot one of these animals. However, having different calls for each predator is really powerful because these three predators all hunt very differently and thus a different escape strategy is necessary for each one.

If an eagle is stalking, it is best to seek shade cover or if you’re in a tree already, you’d better come down from the top. If a leopard is hunting, however, it is best to climb up the tree as high as possible. If a snake is close by, it’s best to get out of the tree altogether and look for a clearing where they can be easily spotted and avoided. (Subsequent research has also revealed a vervet alarm call for baboon predators.)

(A python devouring a vervet monkey.)

To demonstrate that these vervet calls mean what they thought they meant, the researchers performed experiments. They placed loudspeakers in the forest and waited for vervets to approach and then played the various warning calls that they had recorded. Sure enough, playing the eagle call made the vervets look up; playing the leopard call made them climb the nearest tree and head for a thin branch; playing the python call made them stop and scan the ground all around them. The scientists had successfully communicated with the vervets in a way that they naturally understood!

Personally, I think that the most interesting part of this classic experiment is often left out of the story. It turns out that, when they hear the pre-recorded “false alarms,” the vervets react somewhat slower and in a more confused manner than when a real life alarm call is given. The reason is that, in the real-life scenario, the vervets’ first reaction is to look at the vervet that is making the call and ascertain which direction she is facing, which was not possible with the loudspeaker.

They do this because vervets always face the threatening animal that they are announcing so that the other vervets can see where the threat is located. If the threat-calling vervet is far off in one direction and is facing away, this indicates that the predator is even further off and that there is no need for immediate panic. The vervet can take his time in seeking safety. However, if the shouting vervet is nearby and looking right in your direction, you better move your @$$ quickly because you’re in the danger zone!

Although the vocabulary is small, this is a sophisticated form of oral communication. Even more impressively, the vervets don’t have to learn this system of communication. They just know it. Vervets raised purely in captivity already know how to use and respond to the vocabulary when these predators are introduced. Compare this with our language, which must be tediously learned each and every generation. Before we get smug about the relative tininess of the vervet language, consider how much time and energy human children and parents must spend learning to communicate with each other. Vervets have their vocabulary pre-programmed into their brains.

Another interesting thing about vervets is that they can tell their own children by their cries. It’s no surprise that animals can tell each other apart by smell and by sight, but only in a few species have scientists been able to observe that individual voices can be discriminated. In the jungle, when an infant vervet cries, its mother looks in the direction of the scream. Meanwhile all of the other vervets also stop and look, but not toward the infant, toward the mother. 

Even other mothers that don’t have their infants nearby are not mistaken about which baby is crying. Not only do they know the sounds of their own children, they seem to know which children belong to which mothers. Vervet mothers recognize the cries of their own children and they run to take care them.

The husband and wife team of Robert Seyfarth and Dorothy Cheney that did all of this pioneering work with the vervets have made primate communication their life’s work since the mid-1970s. Since that time, their study of vervet vocabulary has revealed many more words, including two more predator words, “baboon,” and “predator-other.”

Also, it turns out that vervets have words for more than just predators and dangers. They also have words for social relationships such as “higher-ranking peer,” “lower-ranking peer,” and “competing/rival troop of vervets.” The differences between these calls are very subtle and will sound like mere grunts to the untrained ear. Only with years of patient listening and analyzing were Seyfarth and Cheney able to decipher this vocabulary and then test their hypotheses using recordings, a testament to the demanding nature of this difficult work.

To date, we have not deciphered any other primate vocabularies as thoroughly as we have the vervets, but this is not because they are anomalous. It’s only because no one has yet done with any other species what Seyfarth and Cheney have done with vervets and are now doing with baboons. However, you can be sure that, inspired by this success, primatologists are now doing exactly that with many other species. It won’t be long before we have a more complete lexicon for many more of our primate cousins.

In marmosets, for example, scientists have observed that small groups of monkeys will often gather and, apparently, converse. They make a host of seemingly random sounds but with clear repetition of some “words.” The most fascinating part of this is that the individual monkeys take turns and politely wait while others are speaking. The dominance hierarchy sometimes rears its head, but everyone usually gets a chance to say something if they want to. The parallel to human conversational etiquette is striking.

Oddly, some scientists don’t seem to be willing to characterize these as conversations because they are operating under the assumption that the vocalizations are largely meaningless. I call bullshit. I would bet $100 that if Seyfarth and Cheney had chosen, nearly four decades ago, to work on marmoset communication instead of vervet communication, we’d have discovered the lexical meaning of the so-called “random” vocalizations.

Further, some scientists are currently arguing that turn-taking in these chatty marmosets may indicate that human language could have evolved directly from vocalizations, instead of from gesturing as is widely believed. That may be, but in my mind, that fact underscores even more the point that marmosets would have no reason to take turns politely if they were talking in gibberish.

Moving on to the great apes, scientists have identified at least seventeen and possibly twenty-five distinct vocal calls used by gorillas. The precise meanings are still being debated because context seems to be crucial for the translation, but vocabulary words have been documented around the topics of food, fights, dominance, playing, and sex.

Fascinatingly, scientists have found that individual troops often develop some novel words or, more often, novel variations of an existing word. This is the gorilla equivalent of regional slang, which, in human language, is the earliest beginnings of language divergence. I find it hilariously telling that the most well documented example of this “regional slang” is a variation of the “sex request” among a group of western lowland gorillas. Isn’t that always the case? Sexual slang develops and changes incredibly swiftly in human populations so why wouldn’t it in gorillas also?

Chimpanzees are our closest relatives and possibly the smartest non-human animals on earth, so it will probably surprise you to learn that scientists have not been able to document as extensive a vocal vocabulary in chimps as in some other primates. This is because chimps tend to use gestures, touching, displays, and other forms of body language, rather than calls, for their sophisticated communication.

However, there is at least one clear and distinct call in chimpanzees that is unambiguous: the pant-hoot, which is a call for help or immediate attention, first documented by Jane Goodall. Interestingly, the chimps have personal variations on the pant-hoot so that other chimpanzees know who is calling. As you might guess, parents respond to their children very quickly and response rates drop among more distant relationships.

Although scientists have not observed great lexical depth in chimpanzee calls, this is not to say that they don’t communicate vocally. Quite the opposite: chimpanzees are incredibly vocal. It’s just that they don’t use a great many different kinds of sounds and the ones that they use seem to be rather unrefined, which is to say that they can mean any number of things depending on context.

Chimpanzee calls are mostly just about getting each other’s attention or expressing emotional states. Chimpanzee calls are like interjections: wow! Hey! Stop! Over here! Darn! Things like that. Once a chimp has her friend’s attention, she uses nonverbal communication to get whatever is bothering her off her chest.

The point here is that humans most certainly did not invent the concept of words. Primates have been using vocal communication, with precise vocabulary, for millions of years.

-NHL      (@nathanlents)