Not So Different: Finding Human Nature in Animals

HUMANS ARE ALWAYS communicating with each other, and our exchanges of information can be incredibly sophisticated. With language, humans have the ability to communicate a breathtaking palette of complexity, nuance, wit, subtlety, and emotion. Considering only the text of a written language, the communication potential of a single sentence is nearly infinite. Add to this inflection, facial expression, body language, emotional and social context, culture and custom, and the possibility of multiple meanings, double entendres, and puns, and our language really is boundless in its potential for communicating ideas between individuals. Such overwhelming complexity seems so far beyond anything that animals are capable of that perhaps comparisons between humans and other animals are just silly.

But then again, maybe not. After all, in other chapters in this book, we have admitted a difference in degree, not of kind. I have not suggested that the pair bonds of swans, wolves, elephants, and humans are all the same. I merely suggest that the pair bonds found in other species bear some of the properties of our own pair bonds. Similarly, I do not claim that cows and cats grieve as deeply and profoundly as humans do, just that they do grieve. The point I am emphasizing throughout is that all or most aspects of the human experience have correlates and precursors—not identical carbon copies—in the animal world.

Regarding communication, the precursors are rather obvious. We all know that animals communicate with one another. However, you may be surprised to know how complex that communication is. The jump from animal modes of communication to human language is not quite as huge and insurmountable as one may think. As we will soon see, many animals use body language, dance, and other nonverbal communication in complex and interesting ways. Other animals communicate with touching, pushing, nudging, stroking, and other forms of physical contact. Some animals have a rich vocabulary of audible words, and some even use particular phrasings of those words. The most advanced animals use all of these modes of communication. The difference between humans and other animals seems huge because of the wealth of communication that is opened up by the last few steps in innovation: grammar, tense, declension, and so on.

In fact, most anthropologists consider the “great leap forward” in human history, when humans began to exhibit culture and form complex societies, to have occurred largely due to the development of complex spoken language. The great leap forward was rather sudden and happened in Africa around fifty thousand years ago. Prior to this, humans were anatomically modern but behaviorally very primitive, probably little different than Homo erectus, Homo habilis, or Neanderthals. Most likely due to the emergence of just a few mutations that made the human cerebral cortex capable of much more advanced cognitive abilities, language evolved very rapidly, and humans became capable of speaking to one another in sophisticated ways.1 These behaviorally modern humans very quickly spread throughout the globe, replacing their only slightly less intelligent forebears in just a few thousand years. With them came much more complex tools, cave art, rituals, customs, and so on.

Everyone alive today, from Northern Europeans to Australian aborigines to uncontacted hunter-gatherer tribes in the Amazon basin, is a descendent of the first fully modern humans who were able to speak with one another using grammar, diction, and conjugation. These first speakers lived in Africa and migrated out in several waves, overtaking and interbreeding with the more primitive humans that had already colonized the world even as far away as Australia. While we may never know what the first human language sounded like, it is likely most related to the “click languages” of Southern Africa, which contain more linguistic diversity among themselves than is seen between English and Chinese.²

The point I am making is that, although our language abilities do indeed seem exponentially more advanced than those of other intelligent animals, it is almost certainly due to only a slight advance in brain function. Furthermore, if premodern humans were like our primate cousins and so many other species of birds and mammals on the planet, they were working with an already very advanced toolkit of communication when the great leap forward occurred. It is a somewhat chilling thought: with the right selective pressures and a little luck, chimpanzees could be just a few thousand years away from learning subjunctive conjugations.

Even without the more elaborate things like sign language, gestures, miming, or charades, humans can actually communicate a great deal using only their bodies.3 Much of this is unintentional, but we can give deliberate signals with our bodies as well. Here are two quick examples of each. We know when a person is either lost or looking for something just by how they carry themselves. You need not even see his face or hands, yet quickly ascertain what is going on. That is unintentional body language. On the other hand, you can communicate aggression toward someone in various ways, including puffing up your chest and shoulders, lowering your gaze, furrowing your brow, folding your arms, and invading personal space. This is an intentional nonverbal communication given in a language that everyone understands.

Animals also communicate with each other using body language. Other than chemical communication via pheromones and the like, body language was probably the earliest form of communication between animals. In fact, there are many communicative postures in animals that seem to mean more or less the same thing in many different kinds of animals, including humans, pointing to a common linguistic ancestry. Just like the Latin word “duo” morphed into “dos” in Spanish and “deux” in French, forms of animal body language can be inherited and then change and evolve over time. For example, is there any doubt what meaning is intended when your dog licks your face when you are sad? Despite the differences, there is no mistaking the commonality.

First, some examples of animal body language that we have already discussed. Dogs and wolves have a great deal of body language for communicating with each other regarding play, as discussed in chapter 1. When one wolf or dog is about to play-fight with another one, she uses the play signal to indicate the lack of true aggression very clearly: she lowers her front end to the ground like a curtsy, while wagging her tail high in the air. Humans are often confused when we see two dogs wrestling because we hear growls, we see teeth bared, and they look really intense in their grappling. There is no confusion among the dogs, though. Watch carefully, and you will see the frequent display of the play signal, shown most notably by the high wagging tail. Also, the play bites are much weaker than real bites. The jaw muscles of dogs are so strong that they could crush each other’s bones if they wanted to. To prevent any serious injuries that could result from a misunderstanding, they have evolved the simple play signal, and they use it often.

We also read in chapter 2 how dogs and wolves use nonverbal communication to apologize for offenses. The submissive/guilty look in dogs, or apology bow in wolves, is unmistakable even to us humans. With my own dog, Bruno, I frequently wrestle and play tug-of-war, and he likes when I hold his toys while he chews on them. In all of these cases, he occasionally nips my hand by accident. In these moments, two things are made clear. First, these accidental bites are many times stronger and more painful than his normal play bites while wrestling. This exemplifies how much dogs weaken their bites when playing. Second, he instantly knows when he has nipped me. He immediately stops playing or chewing and looks at me with a downcast expression. He holds his tail downward, stops panting, and slowly approaches me to lick my nose. It is quite obvious to me that he is letting me know that he did not intend to bite me so hard. It works, too. Who could be mad at him when he does that?

It is interesting that dogs will give friendly licks as part of their apologies and human apologies often involve hugs, handshakes, or kisses. There is even the common expression “kiss and make up.” I do not think it is a coincidence that the apology body language employs signals that, in other contexts, indicate attachment and bonding. As you are getting over an argument with a friend or acquaintance, it often ends with a handshake to indicate “no hard feelings.” The handshake is a borrowed signal. It is not only for resolving conflicts; it is also used as a friendly greeting between friends or potential friends. By using a friendship signal after an argument, we are attempting to turn a confrontational relationship into a friendly one. Enemies do not share hugs and handshakes; friends do.

It turns out that kissing, licking, and other face-centered touching are pretty universal signs of affection and affiliation.⁴ For dogs, cats, and many other small carnivores, licking is common between mates, friends, and children and parents. Horses rub their noses together. Giraffes rub their long necks together. Elephants stroke each other with their trunks and intertwine them. Our close cousins, chimpanzees and bonobos, are known to kiss, lick, stroke, and hug. Bonobos are particularly affectionate and regularly engage in openmouthed kissing during sex. Humans most certainly did not invent the kiss or even the French kiss.

Body language is not only used to indicate affection and apology; it is also used to express more hostile notions like “back off!” When threatened, cats arch their backs, bare their fangs, and flex the erector muscles on their hair shafts, making all their hair puff up. Of course, this simultaneously gives the illusion of the cat being larger than it is, which amplifies the aggressive signal. Dogs show aggression very obviously as well. They adopt a characteristic threat posture, and, just like cats, they snarl, baring their large, sharp teeth. In fact, the display of teeth seems to be a very common aggression signal among carnivores, which makes sense, considering the damage that these animals can do with their sharp teeth and powerful jaws. This signal is even retained in primates. Chimpanzees and gorillas often bare their teeth during aggressive displays.5

Interestingly, the bared-teeth signal, when combined with other cues, also indicates happiness in chimpanzees, just like the human smile. To the untrained eye, a chimpanzee smile may look like a snarl, but primatologists can easily distinguish the two, and obviously so can the chimps.⁶ This hints at the complexity that is possible when multiple signals are combined, rather like combinations of letters to form different words. To a person who is not literate in English, the words “one” and “eon” look almost the same, even though their actual meanings could not be more different.

Another example of the “back off” signal is the puffing up of the cobra’s head when threatened. Sure, she has venom and will use it if she has to, but first, she will try to warn would-be predators that she sees them and is ready for a fight. Many lizards and birds have aggressive display postures that are used less for deterring predators than for intraspecies competitions for mating. Despite popular belief, in most animal species, all-out fighting for access to mates is rather a last resort. Most confrontations are actually settled through nothing more than aggressive displays and posturing. Smaller, slower, or weaker animals almost always back down when they feel outmatched. Natural selection strongly favors this method of competition because actual fighting would lead to avoidable deaths and injuries, even of the eventual winner. Just like with humans, communication is a much better way to resolve disputes than fighting. “Can we just talk this out?”

For some prey species, it would be silly to feign aggression and pretend to be able to fight off a predator. Imagine a mouse trying to convince a cat that he is big and tough and will fight back. However, some prey animals have evolved means to tell their would-be killers, “I see you. I am faster than you. Do not bother trying to chase me because I have a head start and you will just be wasting your energy.” Biologists call this signaling theory, and these displays usually involve prey animals engaging in feats of strength to show predators that they are strong, fast, and/or alerted to their presence.⁸

One of the most famous examples of signaling theory is a behavior in gazelles called stotting (also called pronking).9 The main predator of the gazelle is the cheetah. The cheetah can sprint faster than the gazelle but has less endurance and cannot maintain speed as well while turning. This means that the cheetah must sneak up on the gazelle and make a sudden surprise attack if she is going to catch him. If the gazelle has a head start, the cheetah has no chance. When a gazelle spots a stalking cheetah, he will start jumping very high, straight up in the air. It is a rather remarkable sight. At first blush, this seems kind of stupid. Here is this gazelle being stalked by a cheetah, and when he notices, rather than running away, he makes himself incredibly obvious. However, what happens next demonstrates the purpose of stotting: the cheetah gives up the hunt and walks away. Stotting is the gazelle’s way of telling the cheetah that he sees her, he has a head start, and a chase would be futile.

Stotting is often referred to as an “honest” signal because, since the gazelle has to be in good shape to perform it, it is a true display of physical fitness.¹⁰ This is a fascinating example of co-evolution because the gazelle has evolved to perform the signal and the cheetah has evolved the ability to interpret it. Both species benefit from this communication because they have been spared the bother of a fruitless chase. The gazelle is happy to evolve a way to avoid having to outrun the cheetah every time, and the cheetah is happy to evolve a way to reduce her record of unsuccessful hunts. Chases are energy expensive, after all, and they also are very loud and obvious. After a chase, every potential prey animal in the area is suddenly aware of the cheetah. The cheetah gets one shot. If she fails, she may not eat that day.

Of course, the stotting also warns nearby gazelles of a cheetah in the area. That may have been the reason that the behavior first evolved, but we may never know for sure. Further, stotting may be part of the courtship behavior of gazelles. Given its utility in avoiding both predation and in saving energy, stotting seems like as good a display of fitness as any other. Young gazelles are known to playfully stot, which supports the play-as-practice theory described in chapter 1.

The several species of gazelle are not the only animals that stot. Their cloven relatives impalas, antelopes, and wild sheep are all thought to do so as well.¹¹ Although domestication seems to have diminished stotting in adult sheep, young lambs are prone to periodically engage in bizarre spastic jumping behavior that seems playful and may be the remnant of the stotting instinct. Other forms of pursuit-deterrent signals have been discovered in motmot birds, Eurasian jays, rabbits, mice, curly-tailed lizards, and even guppies.¹²

As I will discuss later, Diana monkeys give certain calls to warn their fellow monkeys of specific kinds of predators. Their vocabulary includes distinct alarm calls for each of their main predators. Interestingly, leopards and eagles, two Diana monkey predators that hunt by surprise attack, are dissuaded from attacking when the monkeys make the calls. Thus, these calls also function as pursuit deterrents for those predators, not unlike stotting in gazelles. However, chimpanzees also hunt Diana monkeys, but they do so through sustained stalking and chase, not surprise attack. Consequently, they are not at all dissuaded by the warning calls.13 The chimps do not rely on the element of surprise anyway, so they could not care less if the Dianas are aware that they are being hunted. While this Diana monkey alarm system almost certainly evolved as a warning to conspecifics, the predators have “learned” what they mean. For leopards and eagles, the game is up when they have been spotted, and so they give up and move on.

Signaling theory depends on the signals being truthful. What if Diana monkeys made eagle calls randomly, just to protect themselves on the off chance that an eagle was nearby? After a while, the eagles would lose their training and no longer be dissuaded from attacking based on the calls alone. The dishonest Diana monkeys would find themselves to be victims of eagle attacks, possibly even more often than chance alone because the calls might actually attract the eagles. If the cheating behavior were genetic, dishonesty would quickly be bred out of the population, and balance would be restored. Thus, honesty is self-perpetuating in signaling theory.

Humans also have an impressive ability to communicate things using only our faces. Once again, this can be intentional or unintentional. Our facial expression is almost constantly advertising our current emotional state and can even betray us by revealing feelings that we attempt to hide. We can also add important nuance to verbal communication using our faces. Given the right context, a simple glance at a friend can often communicate a great deal.

Many of the cues and communication that come from our facial expressions are universal among all of the people in our species.14 This indicates that this form of communication is much more innate than the recent innovation of spoken language. For example, the languages spoken among the hunter-gatherer tribes of New Guinea have absolutely nothing in common with English or any other Indo-European language. (Most of them have nothing in common with each other!) Yet, a smile means exactly the same in the rain forests of New Guinea as it does in the streets of New York City. This speaks to the unconscious, genetic, and inborn nature of facial expressions because if facial expressions were learned, like language, we would expect divergence among the cultures of the world. Instead, we see striking universality. Further proof of this is that people born blind display the same facial expressions as their sighted neighbors. They could not have learned the expressions by seeing them in others. It seems clear that facial expressions and their meanings are almost completely hardwired in the human brain.

Many animal species also communicate with each other using facial expressions. This appears largely limited to mammals for two reasons. First, invertebrates, fish, amphibians, and reptiles, even if they live in communities, show only the simplest hints of interactive social dynamics and cooperation. When it comes to cooperation and communication in the animal world, birds and mammals are the stars of the show. Second, facial expressions require elaborate overlapping musculature in the facial region, which birds do not really have. There are forty-three muscles in the average human face. Many of them are strange, as skeletal muscles go, because they do not connect two bones in order to allow skeletal locomotion. Instead, they are loosely connected to the skull on one end and dermal tissue on the other. In other words, their only purpose is to squish and stretch the skin of the face. This sort of thing does not exist anywhere else in the body. Much of our face musculature exists purely so that we can make facial expressions.

This is why mammals have the monopoly on facial expressions. We are the only animal group that has both the social-cooperative nature to use communication in the first place and the necessary muscles to accomplish that communication using our faces. One might be tempted to think that mammals evolved our elaborate facial muscles for the purpose of communication since that seems like pretty much all we use them for, but it turns out that our face muscles perform an even more basic and essential function: suckling. By studying very old mammal fossils, paleontologists have discovered that a muscle group that was originally located in the throat was co-opted and relocated to the face of early mammals and resulted in much improved suckling from the then-recent mammalian innovation: the breast. With the new facial muscles and the highly social context of nursing, the stage was set for the invention of facial expressions as a means of silent communication by early mammals who must have lived in constant fear of predation by the dominant animals of their day: the dinosaurs.

In 2010, researchers in Montreal discovered that mice display facial expressions when they are in pain.15 By using mildly painful stimuli, repeating on many mice, and recording their faces with high-speed video cameras, the researchers were able to document and code five facial movements that were almost always elicited when the mice were in pain. They closed their eyes and scrunched the skin around their eyes. Their nose and cheeks bulged outward and backward (toward the eyes), their ears moved backward, and their whiskers twitched. The researchers observed these responses with a variety of painful stimuli, and the responses were proportional to the severity of the pain. None of the pain that was given was in any way centered on their faces, and yet, their faces were reliable indicators of the pain. The researchers were even able to observe that these facial movements were reduced if pain reliever had been administered beforehand.

I am particularly struck by how similar the mouse facial response to pain is to the human one. They grimace! When you factor in the differences in the shape of the mouse face and the human face, the mouse response to pain is almost exactly what we see in humans. When in pain, we squint and scrunch the skin around our eyes; the muscles in our cheeks ball up and move upward; and while we do not have whiskers, we do usually scrunch up our noses. We are separated from mice by about seventy-five million years of evolution, and yet, our pain grimace is remarkably similar. (If you are wondering why these experiments were done, the research group studies pain and is searching for therapies for human sufferers of chronic pain conditions. These scientists are not sadists. Quite the opposite, in fact.)

Since then, the pain grimace has also been discovered in rats, in which it is remarkably similar to that of mice.16 Pain responses have also been reported in rabbits, and reports are expected soon regarding the pain grimace in lambs, horses, pigs, and rhesus macaques. It seems that many mammals exhibit the well-conserved pain grimace. This grimace is inborn, not learned, and to be sure of that, the original study was done with infant mice. In fact, with the use of 3-D sonograms, human fetuses can be seen grimacing in the womb by twenty-four weeks’ gestation. In this case, the fetuses are not in real pain; they are “practicing” various facial expressions as their nervous system takes shape.

The question remains, why is there an involuntary behavioral program wired into the mammalian brain that causes a grimace to be made whenever we are in pain? What purpose does this serve? Does the grimace somehow mitigate the pain, like when we rub our head after bumping it? Does the grimace offer some strategy to avoid the painful stimulus? Or is it just an accidental by-product of neurons that are spontaneously activated by the incoming impulses relaying the pain stimulus? Nope—the sensory perception of pain and the motor activation of facial nerves are housed in totally different parts of the brain.

The only purpose that has been suggested for the pain grimace is that of communication.17 By grimacing, an animal is requesting help and also giving a signal to fellow conspecifics. Watch out! This thing hurts! Assuming that the message is received, this communication has great value for those that can understand the signal because something that is painful is also usually dangerous. In fact, that is how and why pain evolved in the first place: as a means to train animals to avoid things that can cause injury or death. (Pain also immobilizes us after an injury to allow healing.) In nature, pain equals danger, so it stands to reason that social-cooperative animals would evolve a mechanism to communicate pain as a means to signal potential danger. Because we have only just discovered the pain grimace, the communication-of-danger hypothesis has yet to be tested definitively.

However, a different communicative function of the pain grimace has already been proposed and more or less proven. By grimacing, infants communicate their discomfort to their mothers or other caregivers. This is akin to crying but more subtle. In humans, we interpret babies’ signs of distress and pain using logic and common sense, but animals have been able to understand and meet the needs of their young long before the evolution of the advanced cognitive abilities that we call common sense. Perhaps the pain grimace plays a role in that. Interestingly, suckling has been shown to relieve pain in infants, even when the pain has nothing to do with hunger per se.¹⁸

All of this discussion of the communication of an internal sensory state (pain) to others also raises the issue of empathy. It seems very likely that the pain grimace evolved within the context of empathy as the very first means that mammal infants use to communicate with our providers, even before we have developed the motor control to do just about anything else. This possibility has already been raised and demonstrated in humans.¹⁹ The discovery of the pain grimace in many other mammals only emphasizes the likelihood that empathy and emotional communication long predate humanity and were refined over many millions of years of evolution. As we saw in chapter 3, empathy and communication are almost certainly intertwined because empathy is communication.

OK, enough about the pain grimace. Primates have seen an explosion in their diversity of facial expressions over the last fifty million years. The facial muscles are mostly conserved across the entire primate phylogeny. The fact that these muscles are only really useful for making faces tells us that facial expressions are likely a universal feature of primates. Indeed, that is what scientists have found. However, the in-context meaning of the individual expressions can vary widely among different primates.

Rhesus macaques have several documented facial expressions.20 For example, macaques have a fear grimace, which, to us, is indistinguishable from the pain grimace. I expect that the context makes it clear to them. I find it very telling that both pain and fear, which both can indicate potential danger to others, use the same facial expression. This makes great sense because why invent a new signal to communicate the same basic idea?

The macaque also has several different smiles. There is one smile for signaling submission to a dominant conspecific, and there is another for intimidation, which is almost the opposite idea. The difference between the two is based on where the monkey is looking while she gives the grin and whether or not she makes a sound along with it. The position of the tail can also change the meaning of a facial expression, just like with dogs. Lip smacking signals affection and alliance, but it is unclear if this is communicative or merely indicative. Macaques even have an expression for disgust.²¹

Orangutans, which are often solitary and territorial as adults, also use the teeth-baring smile in order to display aggression. Interestingly, eye contact also seems to be a rich form of communications in orangutans.²² For example, an orangutan who stares at another directly in the eyes is telling him, “Back off if you know what’s good for you.” On the other hand, affection between allies, mates, or relatives is often indicated by shifty-eyed expressions. Orangutan friends look at each other indirectly, through the corner of their eyes, and quickly look away if their gazes lock. The avoidance of direct eye contact is a sign of trust and friendship. Orangutans have many other facial expressions as well, and never are these shown off more than when juveniles are playing. Despite being mostly solitary as adults, young orangutans are energetic, playful, and highly social. Young orangs will make all sorts of faces at each other and engage in a lot of face mimicry.²³ The meaning of most of these facial expressions has eluded scientists so far.

Gorillas also have many of the primate facial expressions that we have discussed so far, but they have added a few of their own. You can find YouTube videos of zoo gorillas sticking their tongues out at visitors. Although this may be the result of training or mimicry of humans, the tongue display is indeed part of gorilla body language in the wild. Gorillas will show their tongues when they want to signal that they are done playing or when they simply want to withdraw socially. If one gorilla tries to pull another along in order to play, he might pull back and display his tongue as if to say, “I do not want to play right now.” The message usually works, too, as the first gorillas will often then go find some other playmate to solicit. Some researchers have even spotted a young gorilla displaying her tongue after being disciplined by an older gorilla.24 That seems similar to the equivalent gesture in human children.

Chimpanzees are the animals in which facial expression has been studied in the greatest detail. Chimpanzees have nearly identical facial musculature to humans and consequently are capable of as broad an array of facial expressions. Some of the well-understood facial expressions are the whimper, smile, grimace, hoot, pout, and play face.²⁵ As noted regarding other animals, the bared-teeth expression can mean several different things, depending on context. Flashing the teeth can signal dominance or threat, but it can also signal submission. It can signal fear or pain, but also indicate happiness, like a smile.

To us, it seems confusing that a single facial expression—bared teeth—can mean so many wildly different things based on context and combination with other simultaneous signals. I doubt it is confusing to the chimps, though. This should not be too hard for us to understand because the exact same thing is true for human smiles. Think about how many different kinds of human smiles there are. There is the calmly pleased smile; there is the elated smile. We smile when we are in love or lust, and we smile when we are being smug or indignant. We often smile when we deliver surprising news or juicy gossip, and we may also flash an angry smile when a rival has screwed us over in some way. There is the smile of mockery and the smile of incredulity. We sometimes smile when frustrated, and we also smile when we hear something fascinating, as if to say, “Huh! Imagine that!”

If you had only a photograph to judge, you may not be able to tell which smile someone was giving. However, in the live-action context, it is almost always obvious, especially if you know the person well. This is why I am confident that chimps have little trouble distinguishing between the different chimp smiles.

The similarity between chimpanzee and human facial expression runs deep. In the 1970s, psychologists developed the Facial Action Coding System (FACS) as a means to apply objective criteria for recording human facial expressions for research purposes.26 Coding systems like this are crucial for the scientific exploration of phenomena like facial expression because, in order to take careful data that is comparable between different observers and research groups, scientists must find ways to take objective empirical measurements of things that are normally considered subjective. That is what the FACS system does for facial expression. Different scientists working in different parts of the world studying different research subjects can now directly share and compare their data about human facial expressions.

In 2007, however, Dr. Sarah-Jane Vick and colleagues did something quite interesting with the FACS system: they applied it to chimpanzees.²⁷ What they found was that the chimpanzee facial expressions were so similar to the human ones that the coding system worked wonderfully with only modest adjustments needed based on small differences in the shape of the chimpanzee face. Since that time, scientists have begun using this modified system, called ChimpFACS, to record, code, and communicate with each other about the facial expression of chimpanzees. Armed with a long-awaited method to catalog the expressions, we will have a rich understanding about the facial expressions of chimps. That, in turn, will likely further reveal the emotional features of these, our closest relatives.

Recently, primate researchers in Japan recorded the brain waves of a chimpanzee while showing her pictures of chimpanzees that were either lounging around doing nothing or giving facial expressions or postures that indicate alliance, affection, and affiliation.28 This was the first electroencephalogram (EEG) of a conscious chimpanzee. The experiment revealed that reactions in the chimpanzee cerebral cortex can be observed immediately (average time: 0.21 seconds) when the subject views pictures of other chimpanzees showing affection, while the “neutral” pictures of chimpanzees giving no clear emotional cues cause little or no higher brain response. The authors of this study humbly noted that the responses that were observed in the EEGs of the chimpanzees are similar to what is seen in the EEG of a human experiencing emotional contagion or empathy.

Putting aside the truly explosive potential discovery of empathy brain waves in chimpanzees using EEG, these results demonstrate that the recognition of facial expressions is hardwired in the chimpanzee brain, just as it is in the human brain. This recognition is lightning fast, automatic, and unconscious. The expressions themselves are strikingly similar between chimps and humans, which is why we are pretty good at understanding each other’s faces. The rich diversity of chimpanzee facial expression rivals that of humans, and we probably have not discovered all of them yet.

I want to close this discussion of facial expressions with a bit about our closest companions. Dogs have been evolving alongside us for one hundred thousand years. During that time, their evolution has been subjected to very intense selection due to choices we have made regarding which dogs we allow to breed and which we do not. This is referred to as artificial selection rather than natural selection because it is the result of choices we humans impose on a species instead of the natural destiny that the species would have had without our intervention. Artificial selection is what gave us Chihuahuas, Great Danes, dachshunds, and Old English sheepdogs. It is also what gave us cabbage, broccoli, cauliflower, kale, brussels sprouts, and a few others, all of which came from a wild, cabbage-like plant that humans cultivated and selectively bred during the late Iron Age.

Selective breeding gave us the wide diversity of dog breeds we see today, but long before that, humans used artificial selection to domesticate wolves into companion animals. Wolves that made good companions were favored and allowed to breed. Wolves that did not were killed or released back into the wild. Some of the features that early humans selected were intelligence, obedience, tameness, gentleness, guarding behavior, herding behavior, loyalty, and attachment to humans. By selecting and breeding the “good” wolves and casting aside the “bad” ones, humans were able to domesticate them genetically. We did not have to retrain each generation to be a good companion. We shaped their natural behaviors and instincts into what we wanted them to be. The creation of what we now see in dogs is a marvel of biology and human will.

We already touched on this, but I raise this issue again here because it turns out that dogs actually have the ability to read human facial expressions. In 2011, researchers trained dogs to discriminate between different photos of their owners: one of the back of his or her head, one of his or her face while smiling, and one of his or her face while giving a blank stare. Most of the dogs were able to quickly learn the task of picking out the picture with the smiling face. The dogs were simply performing a trained task to select the same picture repeatedly. Next, however, the dogs were asked to choose between three new pictures of their owners, again with the owner smiling in one of them. The dogs were able to do it much more often than not. These were different pictures, but the training had taught them to look for the smile, and they were able to do it. They recognized a smile. Finally, these same dogs were asked to find the smile in a group of photos of someone else, a stranger. Once again, they were able to do this much more often than if by chance. Dogs seem to be able to quickly and reliably recognize a human smile, even from a static picture of someone they have never seen before.29

That dogs have the innate ability to recognize and pick out a smile from still photos is further evidence of their co-evolution alongside us. However, it also argues that wolves, the ancestors of dogs, already had the neural hardware to recognize facial expressions. It is unlikely that this ability would have emerged in dogs from nothing, as a whole new skill. That is way too much for selective breeding to accomplish in such a short amount of time. Natural and artificial selection work by incremental tweaking, not the invention of brand-new traits. Even the selected evolution of the complex behavioral trait of herding was built on behaviors that the wolves possessed already as pack animals. In the case of smile recognition, dogs rather easily learned to read human faces because they already had the ability to read dog faces.

Interestingly, the ability to read facial expressions works the other way, too. Humans are especially keen at reading the emotions of dogs, possibly more than those of any other animal, including our close relatives whose facial anatomy and expressions are so similar to ours. For example, inexperienced humans often misread the various bared-teeth expressions of chimps and other apes, but we almost never misread the expressions of dogs. A study in 2013 showed that humans could correctly identify the facial expressions of fear, anger, disgust, happiness, sadness, and surprise using only still photos of a dog they had never met.30 Not every person got every picture correct, but the overall performance was very strong.

Perhaps the most surprising thing revealed by the experiment was that having a great deal of experience with dogs did not help someone identify the facial expressions more accurately. If that had been the case, we could chalk this up to experience and learning. However, the experienced and the inexperienced were equally good at identifying the positive emotions, and people with much experience with dogs actually performed worse in identifying the negative emotions of fear, anger, and disgust. This was probably because their bias toward dogs made them prefer not to think of the dog that way.

What this says to me is that the co-evolution of dogs and humans goes both ways. We selected for certain features in dogs, but they might have influenced our evolution as well. While this may be hard to accept if you picture humanity as we exist now, keep in mind that the domestication of dogs occurred many eons ago, long before civilization and even before the invention of agriculture and the domestication of livestock. In those years, life was a great struggle. Having a trusted companion as a partner in that struggle would have yielded great advantages. Being able to understand that companion would have helped even further.

Birdsong is a highly gendered behavior in most species. It was once thought that only male birds sang, but female singing has now been discovered in forty different bird species. In fact, in phalaropes, sex roles are exactly the reverse of the common bird paradigm, and the females do all of the singing.31 Birdsong appears to be used almost exclusively in courtship but can have several different purposes within that context. For example, male song sparrows, one of the most abundant and widespread birds in North America, use songs to attract mates. Because they sing to advertise their maleness and their fitness, instead of by displaying flashy coloring, these birds are a dull brown. Male blackbirds, on the other hand, use songs to establish territory and chase other males away. Seasonally, the blackbird males arrive before the females to establish their respective territories. By the time the females arrive, the singing season is mostly over, and they judge the males by their territory, not their song. In one species of blackbirds, females sing “against” each other as warnings and competition within a harem dominated by a single male.³²

There are other uses of songs as well. Mountain chickadees sing songs during migration, both during flight and while resting, to help keep the flock together.33 This is an odd use of songs because most flocks stick together using calls, not songs. Most of us in the northern parts of North America have heard the noisy ruckus of a migrating flock of Canada geese constantly calling to one another, but it turns out that there are a few species that are more melodious about it. Some birds also use songs to scare predators away from a nest or at least let them know that they have been spotted.

The song repertoire of some birds is absolutely astounding.³⁴ Chickadees and sparrows typically have one species-specific song, and the males compete in their attempt to sing it “better” and thus attract a mate. Oven-birds have two songs in their “set list” and sing one during the day and the other at night. No one knows why. One species of warbler has ten different songs. He uses some songs for mate attraction and others for territoriality. Scientists have observed more than one hundred different songs from a single mockingbird. Many of those songs are repeated, verbatim, several days apart after singing many other songs. Mockingbirds remember their many songs and will return to them.

The bird with the largest repertoire of songs (that we know of) is the brown thrasher, for which scientists have recorded two thousand different songs from a single bird. However, the thrasher will usually sing each song twice and then move on, never repeating the song again. For that reason, I find the repertoire of the gray catbird to be even more impressive. Although he “only” sings a few hundred songs, he remembers many of them and will return to some of them again and again.

Birds do not always sing their songs alone. Male and female cardinals sing back and forth as part of their courtship. Various kinds of complex duets have been observed in the Hunter’s cisticola, an African bird. Sometimes they sing together in perfect unison, sometimes they take turns and attempt to mimic each other, and sometimes they actually harmonize with each other in a coordinated manner.

Although birdcalls are much shorter and less elaborate than birdsongs, it is the calls that are more sophisticated in terms of communicating specific things. For example, for the vast majority of birdsong, the most sophisticated messages that scientists have been able to infer are “please come mate with me” and “stay out—this is my territory.” With calls, however, birds seem to be conducting more detailed social communication. Many birds use calls to keep their flock together, as we mentioned with Canada geese. The few bird species that fly at night, rather than resting, are even noisier since they are less able to rely on vision. Birdcalls can also be involved in courtship, of course, as well as territoriality. In other words, calls are used for everything that songs are used for, plus quite a bit more.

Hatchlings and nestlings often make specific calls to indicate hunger, and their parents may make calls to indicate when food is coming. Many bird species can tell their own offspring from others based on their calls. There are even some calls that bird parents use that make their nestlings freeze when a predator is about. It has even been suggested that mallard mothers begin communicating with their offspring before they hatch.35

Jays, crows, and other corvids are constantly “cawing” at each other when in social contact for reasons that scientists are still not sure about. Remember that these birds hold funerals for fallen comrades and are quite vocal during the “service” (see chapter 6). During mating season, however, the crows are less friendly and more territorial toward each other and use the caw to chase away competitors. These two kinds of caws sound the same to us, but I doubt they do to the crows. Either context or some auditory inflection surely makes this clear.

Small birds called chaffinches, which are often preyed upon by larger birds such as owls, are known to sound a predator alarm call. First, they use a low-pitched call to let everyone know that a predator is about. Then, once everyone is ready, they switch to a high-pitched call that functions like a battle cry, initiating a coordinated mob attack to chase away the predator.³⁶

Interestingly, some animals appear to “eavesdrop” on predator-warning calls made by other species. There is a species of iguana on the island of Madagascar that has evolved very respectable hearing, despite the fact that they do not hunt using sound or communicate among themselves using any auditory communication. They do, however, respond to the predator-warning calls of a species of flycatcher bird that also lives on the island. Both the iguanas and the flycatchers are sometimes preyed upon by large raptors—birds of prey. The iguanas never evolved a warning call for raptors because they did not have to. They could just listen out for the calls made by flycatchers.37

Among birds, vocal communication is a nearly universal feature and consists of calls and songs that show a staggering amount of complexity and nuance. Even voiceless birds employ audible forms of communication. Kiwis and some others pound the ground with their feet, storks and albatrosses clap their beaks, woodpeckers drill, and many kinds of birds flap or drum their wings in order to communicate. We are only beginning to understand the complex languages spoken by our feathered friends.

Now, on to mammals. Any discussion of vocal communication among animals would be severely lacking if it did not include mention of whale songs. The songs sung by whales are one of the most fascinating and mysterious forms of vocal communication in the animal world. So haunting and captivating are whale songs that Carl Sagan determined that they be included on the golden record launched into outer space on the Voyager I probe. In the summer of 2013, Voyager I left the solar system. Thus, whale songs are now in interstellar space (as predicted in Star Trek IV: The Voyage Home).

Hundreds of scientists have spent countless hours trying to decipher these enigmatic tunes, and we still only have vague hints as to their function. In fact, for baleen (toothless) whales, scientists are not certain how they make the sounds. In toothed whales (orcas, sperm whales, dolphins, and their relatives), the “songs” are really just high-pitched clicks. Even less is understood about the communication function of these clicks since they are mostly out of our hearing range.

The songs that most people think of when they imagine whale songs are those sung by toothless whales, such as blue whales, gray whales, humpbacks, and right whales. Although they use their larynxes to sing, they do not have vocal cords, so we are not really sure how they do it. The songs are low-pitched and distinctly tonal, and there are a surprising number of parallels between whale song and human music. Like many birdcalls, whale songs seem to operate mostly within what is called equal temperament, and they tend to obey a set key signature.38

What are the songs about? Most of the scientific research on whale songs has focused exclusively on their purpose in courtship and mating, but they also help whales find each other, stay together in pods, coordinate for hunting and migration, and so on.³⁹ This makes perfect sense because life underwater places very different demands on mammals than life on land. Long-range vision is useless, especially in murky or deep waters, and odors diffuse quite slowly in water. Sound, however, travels four times faster in ocean water than in air. So it makes sense that our cetacean cousins moved away from body language and toward vocal communication when they made the transition to aquatic life forty or fifty million years ago.

In humpback whales, perhaps the most prolific singers in the sea, the males do most of the singing while females tend only to make short, scattered sounds that are not organized into recognizable or repeated phrasings. Males sing extensively during mating season. Each song is unique, but a regular pattern of repetition emerges. The notes are organized into phrases, sub-phrases, and songs, which are repeated many times for several hours. Despite concerted efforts to unlock the secrets, scientists continue to debate whether the songs are primarily for attracting females, dissuading competing males, announcing territory, merely staying in contact, or something more complex. Males in proximity with each other will sometimes sing in key with each other and mimic each other’s songs, so any attempt to explain the songs as simple female courtship or territorial warnings can be tossed out the window.

Scientists have also detected patterns of regional differences among whale songs of the same species. These “regional dialects” have been discovered in humpbacks and, more recently, blue whales.⁴⁰ While the possible function of these differences is still unknown, they have helped researchers in tracking specific populations of whales. By picking out these unique little identifiers, scientists know where the whales are from. It is similar to our ability to spot an Englishman or an Australian by his accent and use of slang.

Hardly. An astonishingly complex catalog of referential communication has been discovered in prairie dogs through thirty-five years of careful observation and experimentation by Professor Constantine Slobodchikoff and his team at Northern Arizona University.41 Prior to 1980, the “chirps” of prairie dogs were thought to be rudimentary sounds designed to call attention to and also give a general warning about predators. Nondescript predator warning calls are fairly common in both birds and mammals.

Thankfully, he probed further, and this work became a touchstone for a long career in deciphering the meanings of the various chirps. The closer they listened, the more complexity they noticed. Over the next few years, Slobodchikoff and his colleagues discovered that prairie dogs use different chirps for various predators, hawks, bobcats, coyotes, and even humans.⁴² Predator warning calls are obviously of great value to prey animals, and having different alarm calls for each predator is particularly useful because the defensive strategy is different for each type of predator. Slobodchikoff noticed that as a prairie dog gave the warning call for a specific species of predator, her fellow dogs took the appropriate evasive action for that predator (discussed later in more detail regarding vervets).

Probing further still, the scientists noticed that the prairie dogs use slightly altered forms of the alarm call for each individual predator animal.43 By giving each individual its own “name,” the prairie dogs are able to achieve even more specificity and, once a name is given by one dog, the others use that name in the future. Using careful statistical analysis, Slobodchikoff’s team discovered that the specific calls that the prairie dogs assign to individual predators are not simply random names: they contain encoded identifying information about the individual. Prairie dogs have descriptive words for the colors, size, and shape of the predators—and even the speed at which they are moving!⁴⁴

In addition, prairie dogs have words for things beyond just predators. They make reference to each other and also directional location. Interestingly, their vocabulary is not fixed; they invent new words for novel objects they are faced with, such as cardboard cutouts of various shapes. Slobodchikoff also noticed that the prairie dogs of different regions had recognizably different patterns of chirping, which he called dialects.⁴⁵ There is a rough correlation between the complexity of the chirping patterns and the complexity of the local habitat. Further still, regional variance appears proportional to geographic distance, not unlike how human language accents blend, merge, and diverge over geographic distance.

The conclusion of all of this is that prairie dogs have an extensive and adaptable vocabulary for describing certain aspects of their environment to each other. It sounds a lot like language to me.⁴⁶

The work with prairie dogs does not stand alone. Vervets are Old World monkeys residing in the rain forests of Africa. These monkeys also give alarm calls when predators approach. By using recording devices followed by careful observation, scientists have been able to decipher specific calls for certain predators.⁴⁷ To signal that an eagle has been spotted, a vervet will make a low-pitched grunt. When a python is spotted, however, a vervet will give a high-pitched, staccato barking sound called a chutter. Finally, when a leopard is spotted, the vervet sings a series of distinct tones.

These are the three main predators of the vervets, so it makes sense that they would call out when they spot one. However, having different calls for each predator is really powerful because each hunts differently, and thus a different escape strategy is necessary for each. If an eagle is stalking, a vervet should seek shade cover or, if in a tree, 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, better get out of the tree altogether and look for a clearing where the snake can be easily spotted and avoided.

To demonstrate that these vervet calls mean what they thought they meant, researchers performed experiments.48 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, and playing the python call made them stop and scan the ground 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 experiment is often left out of the story. It turns out that, when they hear the prerecorded “false alarms,” the vervets react somewhat slower and in a more confused manner than when a real 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 vervets can take their time in seeking safety. However, if the shouting vervet is nearby and looking right in your direction, you had better move your tail quickly because you are in the danger zone!

Although the vocabulary is small, this is a sophisticated form of oral communication that shares many features with our own spoken language.49 First, the instinct to make these calls is inborn: vervets born in captivity will spontaneously make these various sounds. Second, the proper use and meaning of the calls is learned as young vervets mature. They learn by watching, imitating, and refining, and young vervets that lack adult “teachers” never learn to use the language properly. Accordingly, in the wild, adult vervets do not respond much to the alarm calls of juveniles. This is presumably because they know that the gibberish of young vervets is usually not a cause for concern. Indeed, young vervets make the calls sporadically and inappropriately at first, for example, responding to a leaf falling by giving an alarm call.

As Steven Pinker has powerfully argued, the human tendency to use language is an inborn instinct, not a learned or mimicked behavior, which is then honed through experience and learning as it takes shape.⁵⁰ Like human babies, vervets begin to babble and then gradually use the sounds properly by observing adults. The parallel between human language acquisition and vervet alarm calls is striking.

Another interesting thing about vervets is that they can identify their own children by their cries. 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, his mother looks in the direction of the scream. Meanwhile, all of the other vervets stop and look, but not toward the infant—toward the mother.⁵¹ Not only do vervets know the sounds of their own children, they seem to know which children belong to which mothers.

The three vervet “words” for “eagle,” “leopard,” and “snake” were discovered by the husband-and-wife team Robert Seyfarth and Dorothy Cheney, who have made primate communication their life’s work since the early 1970s. More recently, 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 is 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. Soon we will have a more complete vocabulary 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.52 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 do not seem to be willing to characterize these “chat sessions” as conversations because they are operating under the assumption that the vocalizations are largely meaningless. However, I would bet one hundred dollars that if Seyfarth and Cheney had chosen, nearly four decades ago, to work on marmoset communication instead of vervet communication, we would have discovered some of the lexical meaning of the so-called random vocalizations. Further, some scientists are currently arguing that turn-taking in these chatty marmosets may be evidence that human language could have evolved directly from vocalizations instead of from gesturing, as is widely believed. That may be, but to my mind, that fact underscores even more the point that marmosets would have no reason to take turns politely if they were talking gibberish.

Moving on to the great apes, scientists have identified at least seventeen and as many as 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 precise diction has been documented around the topics of food, fights, dominance, playing, and sex.53 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, represents the 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. Is that always the case? Sexual slang develops and changes swiftly in human populations, so why not it in gorillas as well?

Although chimpanzees are our closest relatives and possibly the smartest nonhuman animals on Earth, scientists have not been able to document as extensive a vocal vocabulary in chimps as in vervets, baboons, and gorillas. This is because chimps tend to use gestures, touching, displays, and other forms of body language in their communication. However, there is at least one clear and distinct call in chimpanzees that is unambiguous, and that is the pant-hoot, which is a display signal and a call for 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 do not communicate vocally. Quite the opposite: chimpanzees are incredibly vocal. It is just that they do not 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 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.

Moving to the chimpanzee genus, zookeepers at the Leipzig Zoo in Germany recently discovered that the bonobos there communicate the concept of “no” by shaking their heads from side to side exactly as humans do.54 It is possible, perhaps even likely, that the bonobos picked this up from their human caretakers. However, the fascinating part, no matter the genesis, is that the Leipzig bonobos now use this gesture to communicate with each other. This is most often seen when the bonobo mothers will not allow their children do something or want them to stop doing something. It seems bonobo children have the same experience we humans do while growing up—a whole lot of “no.”

This is not the only time that seemingly human gestures have been observed in our close chimpanzee relatives. A 2007 study extensively documented the gestural communication of two troops of common chimpanzees and two troops of bonobos.⁵⁵ This study documented thirty-one distinct body gestures and eighteen facial-vocal expressions. Once again, the similarity to human gestures was striking. An outstretched hand with palm facing upward forms a “beg” gesture in both chimp species. A “silent pout face” was also discovered.

One thing about chimp gestures is that they are almost always combinatorial, as with facial expressions. Most gestures are combined with posture, facial expression, or even sounds, and the timing and social context is important, too. In other words, it is complicated. I suspect that this is the reason that we are only now starting to decipher ape gestures and other animals’ body language. Until now, we could not figure out any simple meanings after watching them for a while, so we just jumped to the conclusion that the animals were too simple for gestures. It turns out that exactly the opposite is true: animal communication is complex, and we were being too simple in our attempts to understand it.

Mark Laidre has proposed that one community of mandrills, the huge African monkeys with brightly colored faces, has developed a gesture for “leave me alone.”56 The gesture is covering the eyes with one hand and holding for an extended period. By watching closely, Laidre observed that the mandrills made the gesture when off by themselves and when they did so, their peers tended to approach and touch them much less often (compared to when they were in the same posture but without the face covered). This gesture may work mechanistically through the prevention of eye contact, which is often how social contact initiates among primates, including humans. This is the first discovery of an intentional gesture in a non-ape species in the wild. In addition, because the gesture is unique to one specific community and stable over time, it bears the mark of cultural transmission. The mandrills learn this gesture and what it means.

It is clear that apes, and possibly monkeys, use gestures to communicate their requests, emotions, and commands. This is not so different from humans, as we all know. In addition, the similarities in many of those gestures are striking as well. Some examples are making the “ask-beg” gesture, sticking out the tongue, shaking the head no, and clapping the hands to indicate elation and excitement. The facial expressions are hauntingly similar as well, and the tone and strength of various screams and calls usually increase in ways that humans would not find surprising. Chimpanzees, gorillas, and other apes even laugh when tickled.⁵⁷

One reason that language has commonly been thought to exist only in humans is our tendency to equate language with spoken language. The oral and pharyngeal anatomy of apes (other than humans) makes speaking, as we know it, impossible.⁵⁸ The throat is too shallow and the larynx too high. They simply cannot make many of the sounds that we can. However, there is no such anatomical impediment to the use of gestures in other apes. As we should know from the various forms of sign language in use around the world, language need not be spoken.

The definitive proof that apes are physically and cognitively capable of communicating with gestures came when scientists began to teach sign language to apes. We all know the story of Koko, the gorilla who uses sign language. Koko understands two thousand English words and communicates back with more than one thousand signs. While her signs contain no grammar—a key feature of human language—she has formed novel signs by combining others. For example, she invented a sign for “ring” by combining the sign for “finger” and “bracelet.”⁵⁹

Koko’s use of signs often drifts into seemingly incomprehensible randomness and repetition, and some skeptics have pointed to this as evidence that her use of signs represents little more than an impressive memory and operant conditioning. I am not convinced. After all, the gestures she is using did not emerge through a natural process of biological evolution over the course of many thousands of years. All of these signs were taught to her de novo, and I think it is unreasonable to expect her to be perfect at using them. Koko expresses herself spontaneously and enjoys “chat sessions,” in which she will just sit and converse for a while. There are many videos of Koko on YouTube, including one of her tickling and being tickled by the late Robin Williams. Go watch some of them, and ask yourself if she appears to be repeating meaningless motions in order to get a reward.

A bonobo named Kanzi has mastered even more English words than Koko. He uses a lexigram board and appears to grasp the connections between words and their organization into coherent phrases.60 For example, researchers asked Kanzi to “make the snake bite the dog” (referring to his stuffed animals). This is a concept that Kanzi had never heard or communicated before, yet sure enough, he retrieved the stuffed snake and pretended that it was biting the stuffed dog. That is a huge conceptual leap that many thought no animals were capable of. Kanzi does not just memorize words; he draws novel conceptual connections between them. Even if we are never able to convincingly document this happening in the wild, Kanzi proves that bonobos have the cerebral hardwiring for this ability.

The most fascinating part of the Kanzi story is that he was not the original “student” of the attempted instruction with the lexigram board; his adoptive mother, Matata, was, but he often accompanied her to her training sessions. To the researchers’ great surprise, one time while Matata was away, Kanzi picked up the board and began using it correctly and coherently.⁶¹ It remains to be seen if this was because he is especially gifted or if his being younger made the difference, reminiscent of how deftly human children pick up second languages.

Anecdotally, Kanzi may have also provided evidence that bonobos use some form of vocal language among themselves. One time, he was in a room, visually separated from his sister, Panbanisha, but she could hear him. He was given some yogurt, and he began to make some vocalizations as he ate it. Panbanisha then pointed to the lexigram symbol for “yogurt.”⁶² Because yogurt is obviously not a bonobo food in the wild, they obviously do not have any inborn native concept of it. In light of that, how did Kanzi communicate this concept to his sister? Had they developed a “word” for it previously, since it is treat they enjoy? Or was this just a crazy coincidence?

It is important to keep in mind that both Kanzi and Koko learned their respective lexica of words through the concerted and determined effort of their human handlers. The concepts were exhaustively repeated in a highly artificial laboratory environment. Many have worried that such experiments in sign language may say more about ape memory, and possibly intelligence, than they do about language abilities. This is because they do not mimic how any species, including humans, learn language. This is a fair point.

Meet Washoe. Washoe was a chimpanzee that was raised, from age two to five, in a house with a human family and treated as any other child would have been.63 The parents, Allen and Beatrix Gardner, shunned vocalizations around Washoe and used only American Sign Language (ASL) with her. Washoe eventually learned around three hundred fifty words of ASL. Initially, the Gardners had to use concerted efforts to teach Washoe her first signs, but nothing like the laboratory efforts behind Koko’s and Kanzi’s learning. Rather, their efforts were not at all dissimilar to human parents teaching their human children their first words. The learning of signs eventually became automatic. Washoe would first recognize a sign and react appropriately and then begin to use the sign herself.

Like Koko and Kanzi, Washoe could combine signs in novel ways and express her own independent ideas. Washoe might also have been self-aware. When handed a mirror, she held it for a while, made faces, and explored it curiously. When asked what she was looking at, she responded, “Me.” Her awareness also extended to the emotional state of others. One of her favorite human caretakers, Kat, had a miscarriage and missed work for several weeks. When Kat returned, Washoe pouted and expressed her anger or disgust at Kat for abandoning her. This is what happened next: Kat made her apologies to Washoe, then decided to tell her the truth, signing “My baby died.” Washoe stared at her, then looked down. She finally peered into Kat’s eyes again and carefully signed “Cry,” touching her cheek and drawing her finger down the path a tear would make on a human (chimpanzees do not shed tears).⁶⁴

Later in Washoe’s life, she actually taught some ASL signs to other chimpanzees, particularly a young male named Loulis that grew up with Washoe as a role model or adopted mother figure.65 Loulis used his first sign after just eight days with Washoe and eventually learned dozens more. To ensure that he was not learning the signs from the human handlers, they would use only a few basic signs around him. He learned the rest from Washoe in what can accurately be called the beginning of a self-perpetuating language.

Washoe’s environment was much more “natural” than Koko’s or Kanzi’s—but only in human terms. While it may replicate how modern human children begin to use language, it does not come close to mimicking chimpanzee life. However, that misses the point. The experiment was not designed to ask if chimpanzees learn sign language naturally in the wild. The point was to learn if chimpanzees have the necessary brainpower for the learning of representational language. It seems rather obvious that they do. This means that the innate ability to learn representational language and basic phrase structure long predated the spark that pushed us toward human language a mere fifty thousand years ago.

Most of the work on gestures in primates has taken place in laboratory or zoo environments with subjects that were held captive for all or most of their lives. It is fair to say that this limits how much we can generalize the work to the natural behaviors of the species in question. However, that is not really relevant because the work was designed to see what these species are capable of, not necessarily what they really do in the wild. However, plenty of work on gestural communication among primates in the wild has been done as well. For one, Mark Laidre’s study of the “leave me alone” gesture in mandrills was conducted by observing wild mandrills.

In 2011, Catherine Hobaiter and Richard Byrne reported their exhaustive effort to catalog the repertoire of intentional gestures of chimpanzees in the wild.⁶⁶ After observing and analyzing well over four thousand instances of gesturing over the course of nearly nine months, they were able to clearly identify sixty-six distinct gestures with apparently consistent in-context meanings. Nearly all of the gestures had previously been reported among some primate, either formally or informally, and every single gesture was documented in more than one chimp. No chimp displayed her own unique gestures.

Fascinatingly, Hobaiter and Byrne noted slight but significant differences in the personal repertoire of gestures based on age (but not gender). This parallels human speech. My grandmother and I spoke mutually intelligible English, but we did not always use the same words. I call it a “couch”; she called it a “davenport.” I called it “homework”; she called it “lessons.” I called it “hanging out”; she called it “visiting.” Americans can read and understand the Declaration of Independence, but we would not use the same words if we wrote the document today. There are generational differences in word usage that accumulate over time in human populations. Perhaps it is the same for chimpanzees. Further, it could be that, as younger chimpanzees mature, their gestural repertoires evolve into the patterns of their elders. That, too, would be interesting, but for different reasons.

Because the study did not directly address this issue, the authors stopped short of saying whether they thought the gestures were inborn or learned. The surprising degree of universality argues that there is at least some genetic influence in the gestures. How else would these gestures remain so strictly conserved among species separated by millions of years of evolution? Think of it this way: while some human languages share cognate words because they are recently related, others have almost nothing in common. The English and Aztec languages have essentially zero cognates despite the fact that the speakers of those languages are only divided by a mere thirty or forty thousand years of separate ancestry. The ancestors of orangutans and chimpanzees diverged from one another at least ten million years ago, and yet they retain a third of their “words” in common. Genetics!

You might argue that we learn these common gestures simply by watching our elders, and of course that happens also. However, something deeper is probably at work. First, if human gestures are simply learned from others, like spoken language, why are so many of them pan-cultural, while spoken languages are not? Second, if gestures are learned through mimicry, why do people who are born completely blind use gestures? Studies have shown that blind children begin to use gestures even before they learn to speak, just like sighted children.67

Blind children and adults also use a great deal of gestures when they speak, and the gestures are pretty much the same as those that sighted people use. Similarly, sighted people use almost as many gestures when speaking to a room full of blind people as they do when speaking to other sighted people. I think these results point to a deep root for our tendency to make gestures. Gesturing is not learned; it is inborn. Experience and culture merely refine our gestures. We “learn” to make gestures the same way that our heart “learns” to pump blood: from our genes.

From the song of a sparrow to the neigh of a horse, from a vervet calling to a woodpecker drilling, from a gorilla beating his chest to a dog wagging her tail, animals have evolved ways to communicate with each other. Through the eons, communication has grown increasingly more sophisticated. Through sight, sound, and touch, animals have learned to reveal their emotions, intentions, and frustrations. Further, referential communication is being discovered in a growing list of mammals. In the journey from mere pheromones to the sonnets of Shakespeare, most of the road was well behind us before we began shooting the breeze in the savannahs of Africa.