Chimpanzees know that others make inferences

Tomasello's group asks whether chimpanzees can determine that another chimpanzee is guiding its actions not on the basis of visual or auditory perception but on the basis of inferences alone. This is a theoretically important question because Povinelli and others have argued that when chimpanzees seemingly understand the visual perception of others, they are only reacting to overt orienting behaviors. The current study was designed so that chimpanzees were faced with an individual who might or might not be making an inference about where food is hidden — with no diagnostic orienting behaviors at all (the chimpanzee subject could not see the other individual making its choice):

If chimpanzees are faced with two opaque boards on a table, in the context of searching for a single piece of food, they do not choose the board lying flat (because if food was under there it would not be lying flat) but, rather, they choose the slanted one— presumably inferring that some unperceived food underneath is causing the slant. Here we demonstrate that chimpanzees know that other chimpanzees in the same situation will make a similar inference. In a back-and-forth foraging game, when their competitor had chosen before them, chimpanzees tended to avoid the slanted board on the assumption that the competitor had already chosen it. Chimpanzees can determine the inferences that a conspecific is likely to make and then adjust their competitive strategies accordingly.