Wild chimpanzees demonstrated their ability to create unique gestures.

Primatologists have identified over 80 hand signals used by chimpanzees. For instance, an outstretched hand with the palm facing up signifies a request for food, while loud, prolonged scratching serves as an invitation for grooming.

One past experiment demonstrated that although the evolutionary paths of humans and primates diverged millions of years ago, people still comprehend the meanings of monkey gestures. Authors of another scientific study concluded that the gesturing of chimpanzees, based on the duration of pauses between signals, resembles human conversation.

A recent article in the journal Animal Cognition continues the discussion on gestural communication among great apes. In this study, an international group of specialists in anthropology, psychology, and cognitive sciences described a particular gesture with a unique meaning observed in the "mother-infant" dyad of wild chimpanzees in Kibale National Park, Uganda. When the baby chimp wanted her mother to carry her on her back, she would cover her mother's eye with her hand, prompting the mother to pick her up and move on.

Video monitoring of the pair was conducted over several years, and analysis of the recordings revealed that the daughter chimp first mastered this mannerism at around 3.5 years of age. The researchers are unsure how the gesture acquired its meaning but speculate that it happened accidentally and is linked to a characteristic of the mother chimp — the absence of one eye.

While on her mother’s back, the baby likely grabbed her around the neck and head, possibly inadvertently covering the healthy eye, which caught the mother’s attention and prompted a response — to continue moving. Noticing the connection between the action and the response, the daughter chimp seemingly began to repeat the gesture. According to the video data, the initial playful act evolved into a symbolic sign for the mother when the infant chimp reached 4.5 years old. Similar gestures were observed once in three other young chimpanzees, but the scientists noted that they did not regularly repeat the action or for the same purpose.

The authors of the new paper examined this story in the context of ongoing debates about the nature of chimpanzee gestures and possibly the origins of human language. Some researchers argue that the gestures of great apes are a fixed part of the species' biological heritage, representing a relatively limited and inflexible form of communication that differs from human language and gestures. According to this logic, since the heritage is shared among all chimpanzees, there should be no instances of "idiosyncratic gestures" — unique signals used by only one or two individuals.

Other experts insist that social learning plays a crucial role in the formation of gestures, involving observation of other chimpanzees and imitation of their behaviors. In this case, during interactions, two individuals may develop a shared understanding of a particular movement signal that previously lacked communicative significance. In other words, the hypothesis suggests the possibility of unique gestures emerging with specific meanings. The authors of the study concerning the chimpanzee in Uganda believe that this case supports the hypothesis.

However, an external primatologist commented in The New York Times noted that the described gesture cannot strictly be considered "idiosyncratic." Rather, it is simply unusual. Nonetheless, the commentator acknowledged that this sign has certainly become a specific means of communication between the daughter and her mother.