Chimpanzees respond to each other at a pace similar to human conversation

When chimpanzees socialize, they exchange gestures at a rate similar to how humans converse.

The researchers surveyed five wild chimpanzees.Pan troglodytesThe researchers studied 8,559 gestures made by 252 chimpanzees across chimpanzee (Pan troglodytes) communities in East Africa — one of the largest studies of its kind. They recorded face-to-face interactions between the apes, recording the timing of one chimpanzee’s gestures relative to those of the other.

An analysis of the ape “conversations” found that chimpanzees’ signaling intervals are remarkably similar to human interactions, and even a little faster. “On average, it takes 120 milliseconds between the end of one gesture and the start of the next,” says Gal Badig of the University of St. Andrews in the UK. “In humans, the average is around 200 milliseconds, so the timing is very close.”

All chimpanzee groups responded quickly, but the exact timing varied from group to group: for example, chimpanzees from Sonso, Uganda, took a few milliseconds longer to return the gesture than the other chimpanzee groups studied.

Such differences in timing also exist in human languages: Japanese speakers, for example, generally have a faster turn-taking conversational style than Danish speakers. “We don’t know exactly why,” Budig says. “As with humans, we don’t know if it’s a cultural difference, something we acquire over time, or a response to the environment.”

Only 14 percent of the interactions the researchers observed between chimpanzees included any kind of interaction. Instead, most consisted of a single gesture, such as “run away” or “follow me,” in which the other person would either run away or follow. But interactive exchanges were more common when the chimpanzees were negotiating over food or grooming.

“What’s really exciting about this study is that it shows that communication is a cooperative, socially engaged process in non-human animals,” Budig says, “and that the processes involved in human language may have actually evolved much earlier than we thought.”