Chimpanzees engage in competitive altruism in a triadic ultimatum game



Sánchez-Amaro A, Maurits L & Haun DBM (2024) Chimpanzees engage in competitive altruism in a triadic ultimatum game. Scientific Reports, 14, Art. No.: 3393.

Partner choice promotes competition among individuals to be selected as a cooperative partner, a phenomenon referred to as competitive altruism. We explored whether chimpanzees engage in competitive altruism in a triadic Ultimatum Game where two proposers can send offers simultaneously or consecutively to a responder who can only accept one of the two competing offers. In a dyadic control condition only one proposer at a time could send an offer to the responder. Chimpanzees increased their offers across trials in the competitive triadic, but not in the dyadic control condition. Chimpanzees also increased their offers after being rejected in previous triadic trials. Furthermore, we found that chimpanzees, under specific conditions, outcompete first proposers in triadic consecutive trials before the responder could choose which offer to accept by offering more than what is expected if they acted randomly or simply offered the smallest possible amount. These results suggest that competitive altruism in chimpanzees did not emerge just as a by-product of them trying to increase over previous losses. Chimpanzees might consider how others’ interactions affect their outcomes and engage in strategies to maximize their chances of being selected as cooperative partners.

Chimpanzees; Competitive altruism; Ultimatum game; Strategic decision-making; Triads

Scientific Reports: Volume 14

Publication date28/02/2024
Publication date online28/02/2024
Date accepted by journal07/02/2024
PublisherSpringer Science and Business Media LLC

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Dr Alejandro Sanchez Amaro

Dr Alejandro Sanchez Amaro

Lecturer in Psychology, Psychology