Chimpanzees’ (Pan troglodytes) internal arousal remains elevated if they cannot themselves help a conspecific

Robert Hepach, Amrisha Vaish, Fumihoro Kano, Anna Albiach-Serrano, Leïla Benziad, Josep Call, Michael Tomasello

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Chimpanzees help conspecifics achieve their goals in instrumental situations but neither their immediate motivation nor the evolutionary basis of their motivation are clear. In the current study, we gave chimpanzees the opportunity to instrumentally help a conspecific to obtain food. Following recent studies with human children, we measured their pupil diameter at various points in the process. Like young children, chimpanzees’ pupil diameter decreased soon after they had helped. However, unlike children, chimpanzees’ pupils remained more dilated upon watching a third party provide the needed help instead of them. Our interpretation is that chimpanzees are motivated to help others, and the evolutionary basis is direct or indirect reciprocity, since providing help oneself sets the conditions for a payback. This is in contrast to young children whose goal is to see others being helped –by whomever –presumably because their helping is based not on reciprocity.
Original languageEnglish
JournalJournal of Comparative Psychology
VolumeAdvance online
Early online date14 Dec 2020
Publication statusE-pub ahead of print - 14 Dec 2020


  • Chimpanzees
  • Helping
  • Internal arousal
  • Pupil dilation


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