Can chimpanzees (Pan troglodytes) discriminate appearance from reality?

摘要

A milestone in human development is coming to recognize that how something looks is notnecessarily how it is. We tested appearance-reality understanding in chimpanzees (Pantroglodytes) with a task requiring them to choose between a small grape and a big grape.The apparent relative size of the grapes was reversed using magnifying and minimizinglenses so that the truly bigger grape appeared to be the smaller one. Our Lens test involveda basic component adapted from standard procedures for children, as well as several com-ponents designed to rule out alternative explanations. There were large individual differ-ences in performance, with some chimpanzees' responses suggesting they appreciatedthe appearance-reality distinction. In contrast, all chimpanzees failed a Reverse Contingencycontrol test, indicating that those who passed the Lens test did not do so by learning a sim-ple reverse contingency rule. Four-year-old children given an adapted version of the Lenstest failed it while 4.5-year-olds passed. Our study constitutes the first direct investigationof appearance-reality understanding in chimpanzees and the first cross-species compari-son of this capacity.