| 研究実績の概要 |
We tested orangutan prosociality and reciprocity in the first year. The plan for the second year was to compare orangutans to chimpanzees on their prosocial tendency and to examine the hormonal influence on it. We did analyse baseline estrogen, progesterone, and oxytocin levels from chimpanzees and orangutans to further examine the effect of hormones on prosocial propensity. However, due to some practical reasons of the experimental setting, we could not conduct the intranasal oxytocin administration to the chimpanzees, and therefore we only conducted behavioral experiments on prosociality and reciprocity in captive chimpanzees.
The current study was designed to test whether chimpanzees’ prosocial choices are influenced by differential reward distributions (equal/advantageous/disadvantageous) and also by unfair behaviors (prosocial/selfish) of human partners. Unlike other inequity tasks, we used a prosocial choice experiment to give the chimpanzees an active role to be prosocial or selfish toward their partner. Our results show that the chimpanzees show aversive reactions when they themselves had a less preferred reward than their partners by rejecting to do the task. However, this behavioral tendency did not lead chimpanzee’s to make selfish choices.
Taken together with the results of 1st year, our results suggest that there is no difference between chimpanzees and orangutans in a way of voluntarily sharing benefits with others in a choice paradigm experiment and that aversion to inequity, necessary for regulating reciprocity, may take different forms in both species.
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