To move or not to move: How apes adjust to the attentional state of others

A previous observational study suggested that when faced with a partner with its back turned, chimpanzees tend to move around to the front of a non-attending partner and then gesture — rather than gesturing once to attract attention and then again to convey a specific intent. We investigated this preference experimentally by presenting six orangutans, five gorillas, nine chimpanzees, and four bonobos with a food begging situation in which we varied the body orientation of an experimenter (E) with respect to the subject (front vs. back) and the location of the food (in front or behind E). These manipulations allowed us to measure whether subjects preferred to move around to face E or to use signals to attract her attention before they begged for food. Results showed that all species moved around to face E and then produced visual gestures, instead of using tactile/ auditory gestures behind E to call her attention. Species differences were apparent particularly when the food and E were in different locations. Unlike gorillas and orangutans, chimpanzees and bonobos (from genus Pan) produced their gestures in front of E in all conditions, including that in which subjects had to leave the food behind to communicate with her. Implications of these results are discussed in the context of the evolution of social cognition in great apes.