Humans rely on a simple wave, smile, or phrase to politely acknowledge the beginning and end of an interaction. New research reveals that chimpanzees and bonobos employ similar social manners: the great apes start and end grooming and play sessions with actions akin to a human “hello” and “goodbye.”
The study published yesterday in the journal iScience is the first to show this behavior in a non-human species and sheds new light on the evolution of cooperation and social commitment in great apes.
“We were able to launch rockets and land on the moon because we have the ability to share our intentions, which allows us to achieve things so much bigger than a single individual can achieve alone,” says Raphaela Heesen, a postdoctoral researcher at Durham University in the United Kingdom, in a statement.
Scientists have long known that chimps and bonobos are socially complex creatures, but Heesen’s curiosity about their interactions was sparked after witnessing two bonobos repeat a gesture after the grooming session was interrupted, according to a statement. She wondered if they share a social custom similar to human salutations.
“Behavior doesn’t fossilize. You can’t dig up bones to look at how behavior has evolved. But you can study our closest living relatives: great apes like chimpanzees and bonobos,” says Heesen in a statement.
To investigate the idea, the team recorded over 1,200 interactions between individuals before and after they engaged in cooperative activities, like play and grooming. They found that bonobos employed a greeting 90 percent of the time, and chimpanzees did 69 percent of the time. Farewell salutations were more common, with 92 percent of bonobos and 86 percent of chimps offering their partner a “goodbye.”
The apes’ salutations were usually brief and included direct eye contact and physical touch, like head-butting or hand-holding. These brief interactions are a way to make sure everyone is on good terms before making the next move, reports Isaac Shultz for Gizmodo.
When engaging in joint actions, bonobos also considered social status and power dynamics. If their partner shared a similar social status, the bonobos’ interaction was brief. But apes that were further apart in the social hierarchy performed longer salutations, reports Science Alert’s Conor Feehly.
“When you’re interacting with a good friend, you’re less likely to put in a lot of effort in communicating politely,” Heesen says.
The difference between bonobos and chimps may be due to their different social systems. Chimpanzees are likely to use violence to show who’s boss, while bonobos maintain relatively peaceful social dynamics and are more likely to tolerate interacting with others.
As great apes, humans share more than 98 percent of our DNA with bonobos and chimps. But we also share about 50 percent of our DNA with bananas, and researchers say there is still much more research needed before jumping to any conclusions about human social behavior. Next, Heesen wants to investigate if other animals share this social custom.
"This ability [to share intentions] has been suggested to be at the heart of human nature," says Heesen in a statement. "Whether this type of communication is present in other species will also be interesting to study in the future."