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Updated: May 23, 2025
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Behavioral Assessment of Manual Dexterity in Non-Human Primates
Published on: November 11, 2011
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Monkeys increase scratching when encountering unexpected good fortune
1Center for the Evolutionary Origins of Human Behavior, Kyoto University, Inuyama, Aichi, Japan. sakumi.iki@gmail.com.
Scientific Reports
|March 12, 2025
Summary
Scratching in Japanese macaques increased with unexpected rewards and stimuli, challenging the link to negative emotions. This suggests scratching may be a coping mechanism for uncertainty in behavioral evolution.
Area of Science:
- Behavioral Ecology
- Evolutionary Psychology
- Primatology
Background:
- Ancestral behavioral traits are repurposed for psychological and social functions, crucial for understanding human evolution.
- Self-scratching, a hygienic response with social contagion, is a model for studying trait repurposing.
- The association of human scratching with negative emotions is questioned by inconsistent non-human animal evidence.
Purpose of the Study:
- To investigate the emotional correlates of scratching behavior in Japanese macaques.
- To test the hypothesis that scratching is linked to negative emotions versus uncertainty.
- To explore the evolutionary repurposing of scratching behavior.
Main Methods:
- Japanese macaques (Macaca fuscata) were observed during cognitive tasks involving manipulated reward outcomes (Experiment 1).
- Unexpected visual stimuli were presented to macaques without altering reward outcomes (Experiment 2).
- Scratching frequency was measured in response to fortunate, unfortunate, and unexpected conditions.
Main Results:
- Scratching significantly increased under a "fortunate" condition of unexpected reward increases.
- Scratching did not increase significantly under an "unfortunate" condition of reward omissions.
- Increased scratching was also observed in response to unexpected visual stimuli.
Conclusions:
- Scratching behavior in Japanese macaques is not primarily linked to negative emotions.
- Findings suggest scratching may have been repurposed from a response to skin stimulation to a coping mechanism for managing uncertainty.
- This study advances understanding of behavioral evolution and trait repurposing.
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