Orangutans (Pongo pygmaeus) do not form expectations based on their partner's outcomes
Sarah F Brosnan1, Timothy Flemming, Catherine F Talbot
1Department of Psychology, Georgia State University, Atlanta, USA. sbrosnan @ gsu.edu
Summary
Orangutans do not react negatively to unequal outcomes, unlike chimpanzees. This suggests that responses to inequity in apes may have evolved independently, possibly due to social living or cooperation.
Area of Science:
- Comparative Psychology
- Primate Behavior
- Evolutionary Biology
Background:
- Some primate species exhibit inequity aversion, reacting negatively when their rewards differ from a partner's.
- The evolutionary origins of this behavior are unclear, as tested species are typically social and cooperative.
- Previous research focused on species with shared traits, limiting understanding of inequity aversion's evolutionary pathway.
Purpose of the Study:
- To investigate whether inequity aversion is a homologous trait or a convergent evolution in primates.
- To compare inequity responses between chimpanzees and orangutans, a predominantly solitary great ape species.
- To determine the role of sociality and cooperation in the evolution of inequity aversion.
Main Methods:
- A comparative study using a protocol identical to previous chimpanzee research.
- Testing adult orangutans of both sexes, housed socially and tested with familiar individuals.
- Observing orangutan responses to unequal outcomes in a controlled experimental setting.
Main Results:
- Orangutans did not exhibit negative responses to inequitable outcomes.
- This finding contrasts with previously observed behaviors in chimpanzees.
- Results support the hypothesis that inequity responses in apes are a result of convergent evolution.
Conclusions:
- Inequity aversion in apes is likely not a homologous trait but a convergence driven by social factors.
- Social living and cooperative tendencies may independently drive the evolution of inequity responses.
- Further comparative studies are essential to understand the evolution and function of primate social behaviors.
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