Abstract
A wealth of data demonstrating that monkeys and apes represent number have been interpreted as suggesting that sensitivity to number emerged early in primate evolution, if not before. Here we examine the numerical capacities of the mongoose lemur (Eulemur mongoz), a member of the prosimian suborder of primates that split from the common ancestor of monkeys, apes and humans approximately 47–54 million years ago. Subjects observed as an experimenter sequentially placed grapes into an opaque bucket. On half of the trials the experimenter placed a subset of the grapes into a false bottom such that they were inaccessible to the lemur. The critical question was whether lemurs would spend more time searching the bucket when food should have remained in the bucket, compared to when they had retrieved all of the food. We found that the amount of time lemurs spent searching was indicative of whether grapes should have remained in the bucket, and furthermore that lemur search time reliably differentiated numerosities that differed by a 1:2 ratio, but not those that differed by a 2:3 or 3:4 ratio. Finally, two control conditions determined that lemurs represented the number of food items, and neither the odor of the grapes, nor the amount of grape (e.g., area) in the bucket. These results suggest that mongoose lemurs have numerical representations that are modulated by Weber’s Law.
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Acknowledgements
We thank Sarah Cork and Sweta Saxena for assistance with experiment running, videotaping, and video coding; the Duke University Primate Center and its staff, especially Julie Ives and Bill Hess, for facilitating our research there, and in particular Bill Hylander for partial funding of this project. We also thank Jessica Cantlon and Kerry Jordan for helpful discussion, and Michael L. Platt for comments on the manuscript. This research was supported by the John Merck Fund to E.M.B. All procedures described comply with Federal Law concerning the use of animals in research
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Lewis, K.P., Jaffe, S. & Brannon, E.M. Analog number representations in mongoose lemurs (Eulemur mongoz): evidence from a search task. Anim Cogn 8, 247–252 (2005). https://doi.org/10.1007/s10071-004-0251-x
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DOI: https://doi.org/10.1007/s10071-004-0251-x