When maths trumps logic: probabilistic judgements in chimpanzees

Daniel Hanus*, Josep Call

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

13 Citations (Scopus)


When searching for hidden food, do chimpanzees take into account both the number of hidden items and the number of potential hiding locations? We presented chimpanzees with two trays, each of them containing a different food/cup ratio and therefore a different likelihood of finding a baited cup among empty alternatives. Subjects' performance was directly influenced by the relative difference (probability ratio (PR)) between the two given probabilities. Interestingly, however, they did not appreciate the special value of a truly safe option (with P = 1.0). Instead, they seemed to 'blindly' rely on the PR between the two options, systematically preferring the more likely one once a certain threshold had been reached. A control condition ruled out the possibility of low- level learning explanations for the observed performance.

Original languageEnglish
Article number20140892
Number of pages5
JournalBiology Letters
Issue number12
Publication statusPublished - 10 Dec 2014


  • Probabilities
  • Numerical cognition
  • Chimpanzees
  • Macaques macaca-mulatta
  • Pan-troglodytes
  • Numerical assessment
  • Pongo-Pygmaeus
  • Quantity
  • Sets


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