When people have a conversation, they quickly take turns speaking and sometimes even interrupt. Now researchers who have collected the largest ever dataset of chimpanzee “conversations” have discovered that they communicate back and forth using gestures that follow the same rapid pattern. The findings will be reported in the journal on July 22 Current biology.
“Although human languages are incredibly diverse, one characteristic we all share is that our conversations are structured with rapid turns of just 200 milliseconds on average,” says Catherine Hobaiter of the University of St Andrews, UK. “But it was an open question whether this was a unique human, or whether other animals share this structure.”
“We found that the timing of chimpanzee gestures and human conversations is similar and very fast, suggesting that similar evolutionary mechanisms drive these social, communicative interactions,” said Gal Badihi, the study’s first author.
The researchers knew that human conversations follow a similar pattern among people living in places and cultures around the world. They wanted to know whether the same communicative structure also exists in chimpanzees, even though they communicate through gestures instead of speech. To find out, they collected data on chimpanzee “conversations” in five wild communities in East Africa.
In total, they collected data on more than 8,500 gestures for 252 people. They measured the timing of turn-taking and conversation patterns. They found that 14% of communicative interactions involved an exchange of gestures between two interacting individuals. Most exchanges involve a two-part exchange, but some include up to seven parts.
Overall, the data shows similar timing to human conversations, with short pauses between a gesture and a gestural response of about 120 milliseconds. Behavioral responses to gestures were slower. “The similarities to human conversations strengthen the description of these interactions as real gestural exchanges, where the gestures produced in response are dependent on those in the previous turn,” the researchers write.
“We saw a small variation between different chimpanzee communities, which again matches what we see in humans where there are small cultural differences in the pace of conversation: some cultures have slower or faster talkers,” says Badihi.
“Fascinatingly, they seem to share both our universal timing and subtle cultural differences,” says Hobaiter. “In humans it is the Danes who respond ‘slower’, and in eastern chimpanzees it is the Sonso community in Uganda.”
This correspondence between human and chimpanzee face-to-face communication points to shared underlying communication rules, the researchers say. They note that these structures can be traced back to shared ancestral mechanisms. It is also possible that chimpanzees and humans have arrived at similar strategies to enhance coordinated interactions and manage competition for communicative “space.” The findings suggest that human communication may not be as unique as you might think.
“It shows that other social species do not need language to engage in short-range communicative exchanges with a fast response time,” Badihi says. “Human conversations may share similar evolutionary histories or trajectories as the communication systems of other species, suggesting that this type of communication is not unique to humans but is more widespread among social animals.”
In future studies, the researchers say they want to investigate why chimpanzees have these conversations in the first place. They think that chimpanzees often rely on gestures to ask each other something.
“We still don’t know when these conversation structures emerged, or why!” says Hobaiter. “To answer that question, we need to examine communication in more distantly related species so we can figure out whether these are features of apes, or features shared with other highly social species, such as elephants or ravens.”
