Do chimpanzees converse?

The list of things in which humans are unique is fascinating: art, shyness, spirituality, passion for technology, accumulation of objects. There are other activities that we share with other species, but in which we excel because of our ability, complexity and speed: communication and sociability are two good examples.

Humans have the most sophisticated language known. We can express any idea and describe any object or person, existing or non-existent, from Juliet to Kamala Harris. We endow that information with nuances, feelings and prejudices and we adapt to our interlocutor, we seek to make her share our preferences, convince her of our vision and add her to our interests. In human conversations, both participants exchange communicative signals (words or gestures) and the exchange is often more complex than a simple signal-response system. Our communication incorporates clarification, persuasion and negotiation between the interactants.

Human conversation follows very strict turn-taking rules that are repeated across cultures and languages. A unique feature of human language is our ability to combine a limited set of sounds into words and to combine words into hierarchically structured, rule-based sentences, which allows us to generate infinite new sentences and thus new meanings. Animals, on the other hand, often use sets of sounds, the size of which overlaps with that of human sound sets. Thus, it is unlikely that, for animals, the size of the sound set is the limiting factor, but rather the ability to generate communicative sequences, being more limited in the systematic creation of structures and in the generation of meanings.

The closest species to us are chimpanzees. These primates produce sounds, but their vocal repertoire is comparatively poor even though they generate new signals in novel artificial circumstances, such as captivity. Chimpanzees can combine these individual calls into longer sequences, but they are generally short commands, seeking a behavioral response ¹. However, this limited vocal repertoire is complemented by a rich gestural language.

A recent study analyzed 8,500 gestures recorded from 252 wild chimpanzees from five wild communities in East Africa. Chimpanzees have a rich collection of hand gestures, meaning things like “stop,” “follow me,” or “scratch me.” ² These are signals used in a face-to-face setting to make imperative requests. One question is whether chimpanzees generate a back-and-forth, give-and-take process, that alternating communication that is the essence of a conversation. A second question is whether chimpanzees communicate as quickly as humans.

Chimpanzees and gestures

Chimpanzees use gestures in almost every aspect of their lives: they use them to reconcile after a fight, to avoid confrontations, to greet each other with a hug or a kiss, to ask for food, and to indicate that they want to travel together or go their separate ways. Grooming sessions, which some liken to our chats, are when the most gestures occur. In the midst of grooming interactions, they may gesture to ask to change position or move the grooming to a different location.

Once outliers were excluded, latencies between a gesture and a gestural response in chimpanzees were similar to those observed for turn-taking in human conversations (∼200 ms), and significantly shorter than latencies between a gesture and a behavioral response. Gestural interaction goes at a speed similar to a human conversation. In addition, interacting chimpanzees establish turns and can interrupt and respond before fully processing the entire signal, as observed in common interruptions in human conversations.

Some gestures are shared between chimpanzees and humans, such as putting the palm of the hand upward to ask. This is the gesture used by beggars all over the world and is also used by chimpanzees to ask, for example, for a banana. Chimpanzees and especially humans adapted it not only to ask for food, but also for more abstract forms of help, like the priest extending his palms to God in church. In this way they created a new type of communicative signal that some researchers believe was the origin of human language. If that is true, if human eloquence can be traced back to a primitive message meaning “give me,” perhaps it means that we are intrinsically social creatures who survived and prevailed over more powerful animals by learning to enlist the cooperation of others, to ask for help. So, deep down, perhaps we are loquacious beggars.

In the article published in Current Biology ³, the researchers describe how the pace of exchanges hardly varied between chimpanzees of different ages, but did vary between different communities, similar to the subtle cultural differences observed in humans. For example, gestures were exchanged more slowly in the Sonso chimpanzee community in Uganda, whereas among the humans analyzed, it was the Danes who responded more slowly in conversation.

The majority (83%) of the chimpanzee gestural exchanges were brief and involved simply a two-part exchange (one turn of pointing per interactant). In one, recorded at Budongo Conservation Field Station, Uganda, a chimpanzee named Monica reached out to another, named Ursus after an altercation, and Ursus responded with a reassuring tap; a way of saying “it’s okay, it’s forgotten.” But the gesture exchanges could extend up to seven turns.

Although the range of latencies to response was longer in chimpanzee interactions than in human interactions (between 500 ms and 1500 ms), the data from this research came from a much wider range of contexts compared to controlled laboratory studies of human conversation. These interactions are true gestural exchanges, in which the gestures produced in response are contingent on those of the previous turn.

Significant differences

Although there are similarities in communication between chimpanzees and humans, there are also significant differences. The evolution of a communicative structure that promotes rapid alignment between interactants could provide a mechanism for increasing communicative efficiency by decreasing the time and energy required to achieve individual and shared goals. This type of communication is more likely to evolve into face-to-face communicative interaction with immediate outcomes, and where these outcomes can strengthen social bonds and/or lead to mutual benefits. Research to date suggests that chimpanzee gestural interactions are largely limited to imperative requests for behavioral change. Outside of negotiations, imperative requests typically result in a behavioral response. In contrast, human conversations encompass a much wider range of meanings that could promote and extend conversational exchanges.

The article suggests that humans and apes share fundamental communication traits. This may be because it is something inherited from a common ancestor, the chimpanzee branch and the human branch diverged about 7 million years ago, or it is what is known as convergent evolution, two processes that developed in both species independently and in parallel because of the advantages it provided for the survival of both species. On the other hand, the researchers add that rapid turn-taking could be a broader feature of social communication and exist in other species such as whales, dolphins, bats and hyenas.