Role reversal by rhesus monkeys, but no evidence of empathy

Four adult rhesus monkeys, Macaca mulatta, were individually trained to interact with a human partner on a social task. In each macaque-human dyad, one of the participants (the informant) could see where a food reward was hidden on an apparatus, but was unable to retrieve it. The other participant (the operator) could operate the apparatus by pulling one of three handles, but could not see where the food was hidden. Two of the macaques were initially trained to be informants, and their behaviour was shaped until they adopted an unambiguous 'pointing' gesture in front of the correct cup. The other two were trained as operators and responded to the pointing gestures of their human partner. The subjects were trained until their performances were almost errorless. Finally, the operator-informant roles in each dyad were reversed. None of the subjects showed an immediate comprehension of their new role. This result contrasts with previous research with chimpanzees, Pan troglodytes, and indicates potentially important species differences in social intelligence.