Bonobos respond aversively to unequal reward distributions

Area of Science:

• Primate behavior
• Evolutionary psychology
• Comparative cognition

Background:

• Inequity aversion (IA) is crucial for human cooperation.
• Previous studies on IA in non-human primates yielded mixed results.
• Chimpanzee IA findings were potentially explained by social disappointment, not true IA.

Purpose of the Study:

• To investigate inequity aversion in bonobos.
• To differentiate IA from social disappointment in a non-human primate model.
• To explore the evolutionary origins of IA and its role in cooperation.

Main Methods:

• Two studies were conducted on bonobos using established IA paradigms.
• Study 1: Token-exchange task with equal vs. unequal food rewards.
• Study 2: Social disappointment task with human and machine partners to control for social factors.

Main Results:

• Bonobos demonstrated aversion to unequal food distributions, refusing disadvantageous outcomes.
• Bonobo IA responses were not explained by social disappointment, unlike in chimpanzees.
• Study 2 provided partial support for an IA explanation in bonobos.

Conclusions:

• Bonobos show sensitivity to unfair treatment, indicating genuine inequity aversion.
• Findings suggest IA may be an evolved mechanism for stabilizing cooperation in primates.
• Bonobos offer a valuable model for understanding the evolution of fairness and cooperation.