Whether apes can communicate with each other has been a debate for decades. They cannot speak because they do not have the correct anatomy to do so, but we know from famous apes like Kanzi, Washoe, Koko, Chantek, and Nim Chimpsky that they are capable of highly sophisticated modes of communication.
However, even with their sophisticated communication capabilities, some aspects of communication, like acknowledging others before or after an encounter with them, had only ever been seen in humans—until now.
New research from a team at Durham University in the United Kingdom has found that bonobos and chimpanzees show similarities to humans in how they interact with each other. The authors studied over 1200 interactions during natural play and grooming among apes living in zoos across the world, finding that apes signal and look at each other before they engage in a joint interaction. These signals may be comparable to how humans say hello and goodbye. For example, before moving a piece of furniture, humans would first establish communication by nodding or gazing at their partner, and would similarly end the interaction after their task is completed.
In apes, the signals around a joint action include touching each other, holding hands, gazing at each other, and/or butting heads. Results from the study suggest that bonobos exchange entry signals and mutual gazes about 90% of the time, while chimpanzees do so about 70% of the time. Conversely, exit signals tended to happen more frequently where bonobos exchanged interactions 92% of the time and chimpanzees displayed them 86% of the time. The authors hypothesize that these communication signals are influenced by complex social and power dynamics.
The entry and exit phases observed in bonobos may be due to politeness, where they tend to exhibit more effort when communicating with someone with whom they are less close. As such, communication efforts appear more relaxed when they are interacting with a friend. Conversely, chimpanzees were less sensitive to the social bonds between individuals, which aligns with previous notions. More research into bonobo communication specifically will help illuminate the underpinnings of this behavior.
Regardless, the results from this study suggest that there is an evolutionary origin to joint communication among apes. The authors found that both bonobos and chimpanzees go through a similar communication process as humans do when beginning, completing, and finishing joint actions and that this behavior may by phylogenetically older than originally assumed.