Humans continue to understand the gestures of other great apes even though we no longer use them ourselves, according to a study by Kirsty E. Graham and Catherine Hobaiter of the University of St Andrews, Scotland, published Jan. 24 in the open access journal PLOS Biology.
The discovery of gestures used by great apes provided the first evidence of intentional communication outside of human language, and more than 80 such signals have now been identified. Many of these gestures are shared by non-human apes, including distantly related apes such as chimpanzees and orangutans. Despite humans being more closely related to chimpanzees and bonobos, these ape gestures are no longer believed to be present in human communication.
Researchers tested people’s understanding of the 10 most common gestures used by chimpanzees (Pan troglodytes) and bonobos (Pan paniscus) using an online game. More than 5,500 participants were asked to watch 20 short videos of monkey gestures and select the meaning of the gesture from four possible answers. They found that participants performed significantly better than expected by chance, correctly interpreting the meaning of chimpanzee and bonobo gestures more than 50% of the time. Giving participants contextual information about what the monkeys in the video were doing only marginally increased their success rate in interpreting the meaning of the gesture.
Video playback experiments have traditionally been used to test the language comprehension of non-human primates, but this study reversed the paradigm to assess for the first time the ability of humans to understand the gestures of their closest living relatives. The results suggest that although we no longer use these gestures, we may have retained an understanding of this ancestral communication system. The authors say it remains unclear whether our ability to understand specific great ape gestures is inherited, or whether humans and other great apes share the ability to interpret meaningful signals because of their general intelligence, physical resemblance and similar social goals.
The authors also include a link where people can create a quiz version of the experiment (no data is collected).
Graham adds, “All great apes use gestures, but humans are so gesticulatory—using gestures while we talk and gesturing, learning new gestures, pantomiming, etc.—that it’s really hard to tell shared gestures from apes just by observing humans. By instead showing the participants videos of common ape gestures, we found that humans can understand these gestures, suggesting they may be part of an evolutionarily ancient, shared gesture vocabulary for all ape species, including us.”
- Graham KE, Hobaiter C (2023) Towards a dictionary of an ape: inexperienced people understand common non-human ape gestures. PLoS Biol 21(1): e3001939. DOI: 10.1371/journal.pbio.3001939