- Across human languages and cultures, conversing involves listening to the speaker and rapidly responding to them. This phenomenon, known as turn-taking, has so far been associated with human languages.
- A new study that analyzed conversations between five groups of chimpanzees finds that one of our closest relatives also take rapid turns in their chatter, mainly involving gestures. Chimpanzees take about 200 milliseconds between gestures before responding back and forth, just like humans.
- While researchers observed minor differences in the timing across groups, the findings suggest this is a species-wide phenomenon that can possibly be seen in all apes.
- The findings suggest that turn-taking during conversations likely evolved before languages were born.
For more than 15 years, an international team of researchers intermittently followed five groups of eastern chimpanzees (Pan troglodytes schweinfurthii) in the jungles of Uganda and Tanzania. With cameras in hand, they diligently recorded hundreds of videos of chimpanzee chatter.
“This took a lot of hard drives,” says primatologist Gal Badihi from the University of St. Andrews in the U.K., talking about the largest ever database of chimpanzee conversations. With this treasure trove of data, Badihi and her colleagues wondered how similarly humans and one of our closest relatives, chimpanzees, talk to each other.
Sifting through more than 8,500 gestures between the 252 eastern chimpanzees (Pan troglodytes schweinfurthii) of the five groups captured in the videos, the researchers found something striking: just like humans, chimpanzees are chatty and “talk” back and forth in rapid turns, albeit less with words and more with gestures. The time between chimp gestures in a conversation, about 200 milliseconds, coincides with the time humans take to respond in a conversation. Their findings were published in the journal Current Biology.
“The study came about out of us trying to look at how social relationships affect chimpanzee gestural communication,” Badihi says, adding this was the first time scientists studied turn-taking — where one party talks and the other listens before responding — in chimpanzees in detail. The researchers found turn-taking in communication was a chimpanzee-wide phenomenon, suggesting it’s an inherited and ingrained trait. “This is either something that chimpanzees and humans evolved around the same time, or it might be just a feature of social communication,” Badihi says.
“This study nicely extends and refines previous studies on gestural turn-taking in great apes,” says cognitive scientist Federico Rossano, from the University of California, San Diego, in the U.S., whose research focuses on social interactions in human and nonhuman animals. Rossano wasn’t involved in the current study.
The gestural world of apes
Chimpanzees “speak” primarily with more than 70 types of gestures involving nearly 150 units, the parts of the gestures with known meanings. “Chimpanzees and other apes are using it all the time, every day — it’s an important part of their communication,” says study co-author Catherine Hobaiter, also a primatologist at the University of St. Andrews. Examples of chimpanzee gestures include stretching out their hand to beg for something, giving a little fling to say “shoo, go away,” or even pirouetting.
Although language dominates most human conversations, we also use gestures, moving our hands and body, when we talk. “It is intrinsic in the way we communicate,” Hobaiter says, adding that while language does the heavy lifting in our communication, “we have body posture, gesture and facial expression to add context, emotion [and] prosody.” In apes, it’s the other way around: a lot of their day-to-day social communication is through gestures, while vocalization and facial expressions add tone and richness to their conversations.
Chimpanzees use two kinds of gestural signals in their conversations. Most are gesture-to-behavior signals, where an individual produces a gesture, and the recipient responds with a behavior change. For instance, one might ask for food, and the other might give something in response. In their analysis of the videos, the researchers found that nearly 86% of the interactions included gesture-to-behavior signals.
Rossano says previous studies have focused on understanding the timing of turn-taking in this type of communication.
But the researchers of the current study were interested in gesture-to-gesture signals, where individuals respond to a gesture by producing another gesture. Only 14% of the videos in their recordings had such signals. The researchers calculated the time between when a sender’s gesture ended and when the recipients began, and found this was about 200 milliseconds — just as long as in a back-and-forth chat between humans. Interestingly, although rare, chimpanzees were also found to interrupt each other by responding to a gesture before it was complete, just as humans will sometimes butt in during conversations.
Although the time differences between gestures were broadly similar across the five chimpanzee groups, there were subtle differences. One group in Uganda was slower than others, taking a few milliseconds longer before responding. Hobaiter likens this subtle difference to “a lovely example of the kind of nature-nurture interaction.”
“We’ve got something that seems to be biologically inherited. It’s species-wide. It’s universal. But then if you look group by group, there are also small but consistent group differences,” Hobaiter says.
While the researchers don’t yet know what causes these tiny differences, Hobaiter posits they may indicate how close-knit the group is and how well the members know each other. “If you spend more time together, maybe you can just afford to be more relaxed with each other because you don’t need to answer quickly,” she says.
The analysis also found that most gesture-to-gesture signals involved two exchanges: one individual made a gesture, another responded with another gesture, and the conversation ended. However, in some cases, such as when a male wanted to seduce a female away from her group for some private time, or when two individuals were negotiating over food, such signals could involve up to seven gesture exchanges.
New insights on understanding of evolution of conversation
The researchers say their findings shed new insights into how communication and languages evolved in apes, including humans.
“When we think about ape communication and human communication, we kind of make a case for language evolution,” Badihi says. “If we find a similarity between the chimpanzee and a human, we’ll assume that it comes from a kind of common ancestor. It might be that these species-wide, fast-paced exchanges evolved early in the hominin evolutionary tree.” However, she adds that similar studies on other species are needed to confirm this.
Rossano says these findings are “particularly exciting” because they show communication through social interaction precedes language, that people didn’t start engaging in turn-taking only after languages had evolved. The timing of turn-taking, he says, “is not the equivalent of a social norm, easily modifiable across cultures, but rather the outwards display of what one could likely call a biological clock that the brain operates at and that got its timing millions of years ago.”
The study’s findings also have implications for conservation, Hobaiter says. The subtle differences in conversation structures between chimpanzee groups, which researchers loosely call culture, show the importance of an individual and the group.
“It really matters if we are losing 5% of individuals in every group or a whole group, because once you’ve lost a culture, you never get it back,” Hobaiter says.
For the researchers, these findings also open up more questions than they answer, such as when these conversational structures evolved in apes. “What would be really interesting now is to look … at distantly related species, maybe elephants [or] social insects, to understand the evolution of these kinds of system,” Badihi says.
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Banner Image: Uganda boasts an extraordinary diversity of habitats, scenery, and wildlife species. The string of protected areas along Uganda’s western border with the Democratic Republic of Congo, in the Albertine Rift, harbors half the world’s mountain gorillas. Image courtesy of USAID Africa bureau via wikimedia commons.
Citation:
Badihi, G., Graham, K. E., Grund, C., Safryghin, A., Soldati, A., Donnellan, E., … Hobaiter, C. (2024). Chimpanzee gestural exchanges share temporal structure with human language. Current Biology, 34(14), R673-R674. doi:10.1016/j.cub.2024.06.009
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