Ascent of Apes

Abstract

Is reasoning a uniquely human ability? This article reviews experiments on reasoning in chimpanzees. In the first series of experiments, a 16 year old female chimpanzee, Sarah, demonstrated the ability to reason analogically in a variety of analogy problems. She chose the correct stimulus B’ to complete an analogy A is to A′ same as B is to B1 and chose the correct predicates to complete analogies A is to A′ same as B is to B′ and A is to A′ different from B is to C. The second series of experiments investigated transitive inference. A 6 year old female chimpanzee, Sadie, was trained on adjacent pairs from a linear series, F r E, E r D, D r C, C r B, and B r A, where the relation r was “more food than.” Sadie then was given the novel nonadjacent pairs, EB, EC, and DB; she chose E and D indicating the ability to make transitive inferences. The third series of experiments placed four chimpanzees in a reasoning task similar to a problem likely to confront chimpanzees in their natural environment. A subject had to choose between two limited food sources. Just prior to making the choice, the chimpanzee received negative information from which it could infer that food was no longer in one of the locations. The chimpanzees demonstrated their inferential abilities by consistently going to the other location.