What if raising your hand to say “hello”, or making a large gesture with the arm to say “go away!” was a legacy of the time when great apes and humans were one hominid, 6 to 7 million years ago? In any case, this is one of the questions put forward by Kirsty E. Graham of York University in the United Kingdom and her team, after observing similarities in the meaning of gestures made by two species of great apes: bonobos and chimpanzees.
The researchers, whose study was published in the journal “Plos Biology”, were interested in the implicit meaning of thirty-three types of movements commonly used by bonobos, which they then compared to that of the same gestures made by chimpanzees. Of the movements or postures observed, twelve were used to initiate or develop an activity and two to stop it. Either to claim something (such as food), request a trip with another partner, get groomed, or offer sex.
The repertoire of gestures of the bonobos decrypted
In order to understand the meaning of the gestures, they observed the Apparently Satisfaction Outcome (ASO) being the “apparently satisfactory result”. This result is none other than the attitude adopted by the recipient primate of the gesture which must modify its behavior accordingly. For example, biologists have discovered that if a bonobo presents his arm to a another, he is actually inviting him to get on his back before moving. The ASO would then climb on the congener’s back as this is the response expected by the signal transmitter. If he is satisfied with the answer, he stops making the movement: he lowers his arm. Thus, these primates use a specific gesture to ask for food, initiate a copulation or a grooming session. According to this study, half of the gestures of the bonobos have only one meaning while the second is more ambiguous.
Theoretically, bonobos and chimpanzees are able to understand each other
Anyway, researchers have discovered that bonobos and chimpanzees use the same gestures to communicate and that they have the same meanings. These animals “do not only share the physical form of the gestures but also many of their meanings,” says the study. “Bonobos and chimpanzees can, in principle, understand each other’s gestures, but new studies are needed to determine how gestures and their meanings are acquired.” It is possible that this “repertoire” comes from the last common ancestor shared by bonobos and chimpanzees before the two species diverge at least 1 million years ago.