Primative mathematical concepts in the chimpanzee: proportionality and numerosity

Abstract

Comparison of quantitative reasoning in nonhuman animals has suffered, on the one hand, from the methodological failure to do properly controlled studies of number (for review, recent examples and exceptions see refs 1, 2; 3, 4; and 5, 6 respectively), and on the other, from the conceptual failure to consider forms of quantitative reasoning other than number. An approach to mathematical reasoning may profit from the study of proportion, a continuous quantity, in addition to number, a discrete quantity. In the experiments reported here, an adult chimpanzee and four juveniles were tested for their knowledge of ‘proportion’ and ‘number’ with conceptual match-to-sample tasks. The juveniles failed but the adult successfully matched exemplars of the proportions 1/4, 1/2, 3/4 and 1, and the numbers 1, 2, 3 and 4, when the sample and alternatives were highly dissimilar physically (such as in shape, colour) and in other quantitative (for example mass, area, length) dimensions. The results reveal the presence of simple ‘proportion’ and ‘number’ concepts in a nonhuman primate.